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physicsworld.com Volume 24 No 4 April 2011

SUPERCONDUCTIVITYTHE

FIRST

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Frontiers 4Doppler shift reversed ● NIFty breakthrough for fusion ● Periodic table shapes up● ¿Habla Español o Galego? ● Quantum-dot TV

News & Analysis 7Nations weigh up nuclear options ● Funding uncertain in US budget stalemate● MESSENGER arrives in orbit ● Researchers plan experiments on SpaceShipTwo● NASA’s Glory missions fails ● Mission to Mars takes top priority ● Concerns raisedover antenna-site decision ● China revokes top science prize ● Brazil slashes sciencebudget ● India plans to join LIGO-Australia ● Simon van der Meer: 1925–2011● Middle East unrest affects SESAME project ● Kathleen Amm: magnet pioneer● Superconducting cables coming of age?

Feedback 16More on physicists and finance, plus comments from physicsworld.com on Soviet scientists

SuperconductivityDown the path of least resistance 18Paul Michael Grant describes the key milestones in superconductivity over the lastcentury from its discovery in April 1911

Fantastic five 23Check out our top five applications of superconductivity with the biggest impact onsociety today

The forgotten brothers 26Stephen Blundell highlights the achievements of Fritz and Heinz London inpioneering our understanding of how superconductors behave

Superconductivity timeline 30Relive the discoveries, breakthroughs and Nobel prizes

Resistance is futile 33Ted Forgan examines where we are now with high-temperature superconductivity,25 years after its discovery

Taming serendipity 41Laura H Greene calls for a worldwide collaboration in the search for a new class of superconductors

Reviews 44The unseen universe ● Stephen Hawking’s views on M-theory ● Web life: STAR-LITE

Careers 50A super(conducting) career Joe Brown ● Once a physicist: Rob Cook

Recruitment 53

Lateral Thoughts 60Superconductor memories Cormac O’Raifeartaigh

On the up – high-Tc materials 33–38

Physics World is published monthly as 12 issues per annualvolume by IOP Publishing Ltd, Dirac House, Temple Back, Bristol BS1 6BE, UK

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Physics World (ISSN 0953-8585) is published monthly by IOP Publishing Ltd, Dirac House, Temple Back, Bristol BS1 6BE,UK. Annual subscription price is US $610. Air freight and mailingin the USA by Publications Expediting, Inc., 200 Meacham Ave,Elmont NY 11003. Periodicals postage at Jamaica NY 11431.US Postmaster: send address changes to Physics World,American Institute of Physics, Suite 1NO1, 2 Huntington Quadrangle, Melville, NY 11747-4502

On the cover

Superconductivity (David Parker/IMI/University of Birmingham High Tc Consortium/Science Photo Library) 17–43

Mystery men – the London brothers 26–29

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.physicsworld.com Contents: April 2011

1Physics World Apri l 2011

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The true scope of the tragedy stillremains beyond comprehension andis a shocking reminder of the reality ofthe nuclear threatMikhail Gorbachev, former president of the SovietUnion, writing in the Bulletin of the Atomic ScientistsMarking 25 years since the accident at theChernobyl nuclear power station, Gorbachev warnsof the importance in keeping weapons-gradenuclear material out of the hands of terrorists.

We do have room-temperaturesuperconductivity. It just depends onwhere you have your roomJörg Schmalian, from Iowa State University,speaking at the 2011 American Association forthe Advancement of Science conference inWashington, DCAs materials have been found that superconductat about 140 K, we do have room-temperaturesuperconductivity – on the Moon that is.

I speak as a citizen not as a scientist,but I think I know a rip-off when I see onePhysicist Freeman Dyson quoted in Princeton MagazineDyson thinks a lot of people have made aprofession out of global warming and decries the“tremendously dogmatic” predictions aboutworldwide temperature trends.

We are bringing the spirit of scienceback to a subject that has become tooargumentative and too contentiousRichard Muller from the University of California,Berkeley, quoted in the GuardianMuller is leading the Berkeley Earth project – what claims to be a completely independentassessment of global warming.

Greenland is destined to beremembered as a classic example ofhow not to put science on the stagePhysicist and science writer Graham Farmelo

quoted in the Times Higher EducationFarmelo was commenting on a play at the National Theatre looking into our society’s currentposition on climate change.

Any woman who collects Star Warstoys is fine with mePhysicist Brian Cox quoted in the Daily MailCox, star of BBC TV series Wonders of the Universe,explains what made him fall in love with his wife.

For the record

Quanta

No pan intendedQuiz question. What object is shown in theabove image? No, it’s not Mars or Mercury– or indeed any other planet in our solarsystem for that matter. The picture is in factof the underside of that common kitchenutensil – the frying pan. The images weretaken by Norwegian-based artistChristopher Jonassen for his new bookDevour, which showcases the wear and tearof one frying pan after another. Jonassentook the pictures after exposing hiscollection of worn-out pans to cooking oils,using various lighting techniques to bringout different textures in the images. ButJonassen does not appear to be aware ofthe pan–planet similarities. “In thebeginning, I was mainly interested in theabstract splatter of the cooking oil, but itwas really interesting to discover howeveryday life was wearing out the surfaceand metal of the frying pans one tinyscratch at the time,” Jonassen told Physics World. “It became a really powerfulmetaphor for how we are exhausting theplanet we inhabit.” Right…

Place your bidsGot some spare change lying around?Then get down to Sotheby’s in New Yorkon 12 April. The auction house is invitingbids for the Soviet Union’s legendaryVostok 3KA-2 capsule, which is expected tofetch $2–10m. The craft, which took off inMarch 1961, is famous for being the lasttest flight for the Soviet 3KA-3 capsule thatblasted Yuri Gagarin into space 50 yearsago on 12 April 1961 and made him the firstperson to leave the Earth’s bounds. But ifyour piggy bank doesn’t quite stretch thatfar, then you might instead fancy somespacesuits worn by cosmonauts Alexei Leonov and Gennadi Strekalov,which Bonhams are auctioning in New York on 5 May. Estimated to fetchabout $100 000 each, Leonov’s suit wasworn during the 1975 Apollo–Soyuzmission – the first joint US/Soviet Unionspaceflight – while Gennadi’s outfit was

worn during a trip to the Mir space stationin 1990. Also getting in on the goldenjubilee of Gagarin’s flight is Australian firmFour Pines Brewing Company, which hasdeveloped “Vostok” – the first beerdesigned to be drunk in space. Vostok isless carbonated than normal beer and has astronger flavour to counteract the fact thatin zero-g the tongue swells and the sensesdull. “Wherever humans have journeyed inthe last 1000 years, we first worry aboutwater, food, shelter and clothing,” Jaron Mitchell, founder of Four Pines toldnews.com.au. “In many cases, beer is thenext consideration.” We’ll drink to that.

Not so elementaryAfter crushing former Jeopardy! TV game-show champions Ken Jennings andBrad Rutter, scientists at IBM must have been pleased with their latestsupercomputer “Watson” – until it came upagainst physicist and US CongressmanRush Holt that is. In Jeopardy! contestantsare presented with clues in the form ofanswers, and must phrase their responsesin question form. For example, if told “It isthe only state lying south of the Tropic ofCancer”, the correct answer would be“What is Hawaii?”. Watson, which wasespecially designed for Jeopardy!, uses aseries of algorithms and some heavy-dutyprocessing – including nine servers – todetermine the answer with the highestprobability of being correct. Watson finallymet its match with Holt, former assistantdirector of the Princeton Plasma PhysicsLaboratory, who amassed $8600 toWatson’s $6200. Sadly, the two only camemonitor-to-head in a first-round game andnever played a full Jeopardy! match.

In it to win itSpeaking of quizzes, whatelement in the periodictable has the atomicnumber 36? And whichNobel laureate’s real name

was Gábor Dénes? These were some of thetaxing questions faced by a Physics Worldteam at last month’s Big Science Pub Quizheld at Imperial College London. A totalof 16 teams entered – from the Guardian tothe BBC – with each group of journalistsjoining forces with select academics fromImperial. The Physics World team, aided byphysicist John Tisch and four members ofhis quantum-optics research group, came arespectable eighth, with 52.5 out of 95.Maybe we could have done with Watson(see above) on our side.

Seen and heard

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Doppler shift is a well-known feature ofphysics, apparent in many processes fromthe redshifted light emitted by acceleratingdistant galaxies to the fading pitch of anambulance siren as it races off into the dis-tance. However, physicists have now seenthe more exotic inverse Doppler shift at op-tical frequencies for the first time. The effect,which was first observed with radio waves,involves the frequency of waves emitted by,or bouncing off, an object increasing (ratherthan decreasing) as the object moves awayfrom an observer.

The inverse Doppler shift was seen by agroup led by Songlin Zhuang of the Shang-hai University of Science and Technology inChina and Min Gu of the Swinburne Uni-versity of Technology in Australia. They firedan infrared laser through a photonic crystalcomprising a lattice of 2 µm diameter siliconrods attached to a moving platform and thenrecorded the frequency shift of the light leav-ing the lattice. As with other photonic crys-

tals, the lattice has characteristic band gapsthat prevent light over a narrow range ofwavelengths from passing through it.

By tuning their laser so that its wavelengthmatched the edge of the band gap, the re-searchers were able to “negatively” refractthe laser light, thus causing the light to beinverse Doppler-shifted. But because thesource and detector cannot be positioned in-side the crystal, the team devised a clever wayof confirming that the effect had indeedoccurred. This involved splitting the beamfrom the laser into two and adjusting the pathlength of the part not passing through thecrystal so that it underwent the same con-ventional Doppler shift as the light that didgo through. The beat frequency when the twobeams interfere revealed the frequency shiftcaused by only the inverse Doppler effect.

According to Gu, the trick is to arrange thesilicon rods in such a way as to ensure thatthe laser beam follows the simplest paththrough the photonic crystal. Otherwise, hesays, it would be too difficult to calculate theexpected inverse Doppler shift and imposs-ible to compare theory with experiment. Theteam also carried out the same experimentusing a normal glass prism instead of thephotonic crystal, and saw the conventionalDoppler shift as expected.

The result is important as it provides fur-ther proof of the still-contested phenom-enon of negative refraction. It could alsolead to practical applications, such as meas-uring the speed of complicated blood flows.

Physicists at the $3.5bn National IgnitionFacility (NIF) at the Lawrence LivermoreNational Laboratory in California say theyhave taken an important step in the bid togenerate fusion energy using ultra-powerfullasers. Although they have not yet generatedenough energy to ensure that the fusionprocess is self-sustaining, what the NIF re-searchers have done is to achieve the tem-perature and compression conditions thatwould be needed for a fusion reaction to con-tinue without any external energy source.NIF director Ed Moses expects the lab topass this process of “ignition” next year.

NIF consists of 192 giant lasers focused ona hollow gold cylinder a few centimetres longknown as a hohlraum. When fully up andrunning, this hohlraum will house pepper-corn-sized spheres of beryllium containingdeuterium and tritium fuel. Using the lasers,researchers hope to generate enough heat

and X-rays to make the beryllium spheresexplode, which will force the deuterium andtritium to rapidly compress. A shockwavefrom the explosion would then heat thecompressed matter enough to let the nucleiovercome their mutual repulsion and fuse.Researchers hope that by burning some20–30% of the fuel inside each sphere, thereactions will yield between 10 and 20 timesas much energy as supplied by the lasers.

In the new experiment, two independentgroups at NIF used plastic spheres contain-ing helium, rather than actual fuel pellets, asthese are easier to analyse. By combiningtheir experimental measurements with com-puter simulations, the researchers found thatthe hohlraum converted nearly 90% of thelaser energy into X-rays and that its tempera-ture increased to 3.6 × 106 K (Phys. Rev. Lett.106 085004 and Phys. Rev. Lett. 106 085003).The next step will be to use beryllium sphereswith unequal quantities of deuterium andtritium to study how hydrodynamic stabil-ities might lead to asymmetrical implosions.

Antarctic meteorite may have seeded lifeResearchers in the US say they have found strongevidence to support the theory that life on Earthwas seeded by meteorites from outer space. Theystudied the CR2 Grave Nunataks (GRA) 95229meteorite, discovered in Antarctica in 1995, andfound that it released abundant amounts ofammonia when treated with water at hightemperature (300 °C) and pressure (100 MPa).They speculate that similar meteorites could haveprovided the Earth’s early atmosphere with a supplyof nitrogen – a precursor to complex biologicalmolecules such as amino acids and DNA. What ismore, many of the nitrogen-based compoundsfound in the meteorite are water-soluble, which isalso essential because biologists agree that lifeemerged from watery environments (Proc. NatlAcad. Sci. USA 10.1073/pnas.1014961108).

To thicken, just add waterChefs have known for a long time that meltedchocolate can be solidified again with the simpleaddition of water. Researchers in Germany nowsay that this counterintuitive transition is a generalphenomenon and they have been able to pin downthe mechanism responsible. In an experiment,they dispersed water-repelling glass beads into anorganic solvent to form a viscous solution. Then,when they stirred water to this mixture, until itmade up just 1% of the suspension by mass, thefluid transformed into a gel-like material. Theresearchers argue that this effect is caused by thefact that the water does not wet as well as thesolvent. So instead of coating the particles, thewater flows to minimize the total area of contactbetween the particles and the bulk fluid, thusbinding the beads together into a more rigidnetwork (Science 331 897).

Cold atoms coupled with spinSpin–orbit coupling has been simulated inultracold neutral atoms for the first time.Conventionally, this coupling describes theinteraction between the intrinsic spin of an electronin a solid and the magnetic field induced by themotion of the electron relative to the surroundingions. Physicists in the US have now simulated theeffect in a Bose–Einstein condensate (BEC) withabout 180 000 rubidium atoms at a temperatureof less than 100 nK. A laser beam applied to theBEC along the x-direction causes rubidium atomsin a certain spin state to absorb a photon. Theseatoms can then be stimulated to emit a photon inthe y-direction by a second laser beam appliedperpendicular to the first. This alters themomentum of the atom, thereby coupling its spinand momentum (Nature 471 83).

Doppler shift is seen in reverse

Forward to fusion

In brief

Read these articles in full and sign up for freee-mail news alerts at physicsworld.com

Inverse Doppler effect Researchers have turned awell-known physics phenomenon on its head.

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TV screens that combine a vast colour range withan incredibly small pixel size could be producedusing red, green and blue quantum dots – tiny nanometre-sized regions of compound-semiconductor crystal containing just a fewthousand atoms. That is the claim of a group ofresearchers led by Tae-Ho Kim at the SamsungAdvanced Institute of Technology in South Koreaalong with colleagues in the UK. The quantum dotsemit a narrow band of light when electrons insidethem recombine with positively charged holes.

Making a colour display with quantum dotsinvolves depositing them onto a substrate in a well-controlled manner, which can be tricky.Monochrome quantum-dot displays have beenmade before by dropping a dot-containing solutiononto a substrate and spinning this around to yielda thin film of the material. But this “spin-coating”approach is not suitable for making a full-colourdisplay because it would cross-contaminate thered, green and blue pixels.

In the new work, Kim’s team overcame this issueby spin-coating red, green and blue dots ontoseparate “donor” substrates, before transferringthem one colour at a time to the display with apatterned rubber stamp. To make a four-inchdiameter display with 320 × 240 pixels, a pair ofelectron-transporting polymers was deposited ontoa piece of glass coated in indium tin oxide. Red,green and blue dots were stamped onto thisstructure, which was then coated with titaniumdioxide – a material that transports holes well.

Adding a thin-film transistor array allowed adifferent voltage to be applied to each of thepixels, which were 46 μm by 96 μm in size.Increasing this voltage makes the pixels shinemore brightly because more electrons and holesare driven into the dots, where they recombine toemit light. The researchers say they have alsodemonstrated an array of narrow quantum-dotstripes 400 nm wide, which indicates that it shouldbe possible to do nano-printing of quantum dotswith extremely high resolution (Nature Photonics10.1038/nphoton.2011.12). This, the Koreanteam says, proves that the technology can producedisplays with the highest practical resolution forviewing with the naked eye, which can only resolvepixel sizes down to 40 μm.

One downside of the display it that it currentlyhas a relatively low efficiency – just a few lumens per watt, which is about half that of anincandescent bulb. But Byoung Lyong Choi, one ofthe Samsung researchers, told Physics World thatfar higher efficiencies should be possible bymodifying the quantum dots.

Watch this space forquantum-dot TV

These colourful figures are part of a new project to create a periodic table of shapes that could do forgeometry what Dmitri Mendeleev did for chemistry in the 19th century. The three-year project, led byresearchers at Imperial College London, could result in a useful resource for mathematicians andtheoretical physicists seeking all the shapes across three, four and five dimensions that cannot be brokendown into simpler shapes, of which there are likely to be thousands. They find these basic building blocksof the universe, known as “Fano varieties”, by looking for solutions to string theory, which assumes that inaddition to space and time, there are other hidden dimensions. According to the researchers, physicistscan study these shapes to visualize features such as space–time or interactions inside subatomicparticles. For the shapes to actually represent practical solutions to physical problems, however, physicistswill need to look at slices of the Fano varieties known as Calabi–Yau 3-folds, which give possible shapes ofthe curled-up extra dimensions. The periodic table could also help in the field of robotics, where engineersneed to develop algorithms that operate in high dimensions to make movements more lifelike.

Innovation

Physicists in Spain are challenging the ideathat two languages cannot continue to existside by side within a society. Jorge MiraPérez, who led the research, became inter-ested in the issue of language survival be-cause of the situation in his own region ofGalicia in north-west Spain, where peoplespeak both Spanish and the local language,Galician. Teaming up with his colleagues atthe University of Santiago de Compostela,Mira Pérez built on an earlier mathematicalmodel developed at Cornell University inthe US, in which speakers in a society canswitch between two distinct language groups.

In the Cornell model, the weaker languagealways dies out in the end. Mira Pérez’s teamrealized, however, that the model did nottake into account bilingualism and the im-pact this can have on the stability of eachlanguage. The researchers have thereforedeveloped a more advanced model that in-cludes three distinct groups – the two mono-

linguists and the bilingual – where peoplecan shift between all three groups.

To test their model against a real-worldsituation, the researchers compared it withhistorical data for the preponderance ofSpanish and Galician from the 19th centuryto 1975, and found that the fit was quitegood. They find that both languages can co-exist indefinitely as long as each is initiallyspoken by enough people and both are suf-ficiently similar. Survival is also related tothe “status” of each language, a parameterthat takes into account the social and eco-nomic advantages of that language (New J.Phys. 13 033007).

The findings are good news for languagessuch as Galician and Catalan, spoken inautonomous communities in Spain, whichhave relatively steady numbers of speakersand share many similarities with Spanish,the dominant national language. The re-search could, however, be ominous for moredistinctive languages such as Quechua inSouth America, which is very different fromSpanish and is already being marginalized.

Talking bilingualism

Towards a periodic table for geometry

Tom

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Governments around the world areplanning to review their nuclear pro-grammes following last month’searthquake that badly damaged theFukushima Daiichi nuclear powerplant in Japan. As Physics World wentto press, officials had raised the se-curity alert level at the plant from four to five on the seven-point Inter-national Nuclear and RadiologicalEvent Scale, placing it just two pointsbelow 1986’s Chernobyl disaster. Therating indicates “an accident withwider consequences” and limited re-lease of radioactive material.

The UK government has alreadycommissioned its chief nuclear in-spector, Mike Weightman, to conducta review into the implications ofevents at the Japanese nuclear reac-tors on existing and new plants in theUK. An interim report is expected bymid-May and a final report within sixmonths. “Safety is and will continueto be the number-one priority for ex-isting nuclear sites and for any newpower stations,” says Chris Huhne,the UK energy secretary. “I want toensure that any lessons learned fromWeightman’s report are applied to theUK’s new build programme.”

Germany has taken its seven oldestreactors offline until at least June andput on hold plans to extend their lives.France, the number-two producer ofnuclear power behind the US, has

meanwhile announced that it willconduct tests on security systems at the country’s 58 nuclear reactors. USPresident Barack Obama has also re-quested a comprehensive review ofAmerican nuclear facilities to be car-ried out by the US nuclear regulatorycommission. India, China and Pakis-tan are among other nations that willreview their nuclear safety too.

Early reports suggest the emer-gency at Fukushima stemmed from afailure of cooling systems associatedwith the plant’s six reactors. When theearthquake struck, damage to powersupplies meant that cooling watercould no longer be circulated withinthe reactor core, causing fuel rods tooverheat and their metal casings to

partially melt. This released chem-icals that reacted with water vapour to produce hydrogen, which escapedand exploded, damaging the reactorbuildings. As an emergency response,Japanese authorities drenched thereactor compound with seawater latelast month, and there have alreadybeen signs of elevated levels of radi-ation in agricultural products such asmilk and spinach.

The earthquake and tsunami havealso affected some of Japan’s majorscientific facilities, although the coun-try’s strict building codes managed toprevent major damage. A preliminaryinspection of the massive new $1.5bnJapan Proton Accelerator ResearchComplex (J-PARC), which lies about200 km south of the region worst hitby the quake, revealed it had come offrelatively unscathed, although it is ex-pected to take more than six monthsfor its neutron spallation source toreturn to normal. Not so fortunate,however, is the Photon Factory, a na-tional synchrotron-radiation facilitybased at the KEK particle-physics labin Tsukuba, some 50 km north-east ofTokyo. The lab’s director, Soichi Wa-katsuki, has reported that the facility’slinear accelerator has suffered “sub-stantial damage”, including the dis-placement of three radio-frequencymodules by about 10 cm.James Dacey

News & Analysis

Japan quake triggers nuclear rethink

No smoke

without fire

The 9.0 magnitudeearthquake andsubsequent tsunamithat struck Japan last month badlydamaged theFukushima Daiichinuclear power plantcausing explosionsand fires.

Uncertainty is spreading through the US

science community as a divided Congress

appears unable to agree the details of the

country’s 2011 budget, which began in

October last year. The Republican-led

House of Representatives is proposing

cuts to discretionary spending, which

includes support for science, by a massive

$61bn. Those proposals, which were

passed by the House in February, have led

to a deadlock in Congress as the

Democratic-majority Senate opposes

such swingeing cuts.

Since December, Congress has been

operating the national budget on a

“continuing resolution” bill, which has

frozen the 2011 budget at 2010 levels.

That resolution was extended to 18 March

together with $4bn in cuts, and just

before that deadline, the Senate

approved another continuing resolution

that would cut another $6bn and last until

8 April. Although the reductions have so

far had little impact on science funding,

researchers fear that the House will aim

for more reductions in the final 2011

budget, which may not emerge until May.

If the $61bn cuts pass the Senate,

it would mean an 18% reduction in

funding for the Office of Science in the

Department of Energy (DOE). However,

because government departments have

been spending at 2010 levels, the actual

cut would amount to 31% for the rest of

this financial year. The National Science

Foundation (NSF) would lose 8.9% of its

funding, while the Environmental

Protection Agency would be faced with a

massive 30% fall.

The Task Force on American Innovation

– representing hi-tech firms, research

universities and scientific societies –

has warned that the cuts would have a

“devastating impact” on the US’s

scientific infrastructure. It warns that

“virtually all DOE national laboratory user

facilities…would cease operations…and

10 000 fewer university researchers

would receive support [from the NSF]”.

Peter Gwynne

Boston, MA

The Task Forceon AmericanInnovation haswarned thatthe cuts would have a“devastatingimpact” on the country’sscientificinfrastructure

Funding

Physicists face anxious wait for outcome of US budget

REU

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The first spacecraft to orbit Mercurybegan circling the solar system’ssmallest and least-understood planetlast month in what mission scientistshailed as the “historic” conclusion to asix-and-a-half year, 7.9 billion kilo-metre journey. At 12.45 a.m. GMT onFriday 18 March, the main thrusterson NASA’s MESSENGER craft be-gan firing, slowing it down by0.862 km s–1 so that it could be “cap-tured” by Mercury, which has anescape velocity of 4.25 km s–1. After a15 min “burn” was completed, staff atJohns Hopkins University’s AppliedPhysics Lab (APL) briefly analysedanticipated radio signals from thecraft before announcing success.

“This accomplishment is the fruit ofa tremendous amount of labour onthe part of the navigation, guidanceand control, and mission operationsteams, who shepherded the spacecraftthrough its journey,” says the APL’sPeter Bedini, MESSENGER’s projectmanager. By 1.45 a.m. GMT the crafthad rotated back towards the Earthand started transmitting its first data.Later that morning MESSENGERbegan its first full orbit around theplanet, tracing out an elliptical paththat brings it within 200 km of Mer-cury’s scorched and cratered surfacebefore swooping out to 15 193 km,

where the reflected heat from the sur-face is less intense.

Over the next year, the craft willcomplete one revolution every 12Earth-hours, racking up 730 laps be-fore the mission is scheduled to end.During this time, instruments on thehalf-tonne, $446m craft will collect un-precedented amounts of data aboutMercury’s surface features and com-position, as well as its magnetic fieldand tenuous atmosphere, or “exo-sphere”. According to MESSENGERprincipal investigator Sean Solomonfrom the Carnegie Institution for Sci-ence in Washington, DC, these datawill yield new information on some ofMercury’s biggest mysteries – inclu-

ding the intriguing possibility that itmay harbour small amounts of waterice at its poles, even though surfacetemperatures can exceed 700 K.

MESSENGER is the first space-craft to visit Mercury since the 1970s,when the Mariner 10 probe flew pastthree times. Although that missiondiscovered Mercury’s magnetic fieldand exosphere, it only managed tomap 45% of the planet’s surface andleft many questions unanswered.MESSENGER has already addednew insights, having flown past theplanet three times in 2008 and 2009,imaging most of what Mariner 10 mis-sed, collecting data on the planet’scomposition, and sketching out thegeometry of its magnetic field.

The craft’s orbit around Mercury,however, marks the real start ofMESSENGER’s mission. One keypuzzle is why Mercury has a weakmagnetic field, whereas larger planetssuch as Mars and Venus have no in-trinsic dipolar field at all. Anothermystery is Mercury’s huge density,which at 5.3 g cm–3 is the biggest of anyplanet in the solar system, after gravi-tational compression is factored out.Margaret Harris

● Listen to an audio interview withSean Solomon at physicsworld.com/cws/article/news/45415

MESSENGER spacecraft enters orbit around MercuryAstronomy

Mercury rising

NASA’s MESSENGERcraft is due to starttransmitting its firstscientific data on4 April.

NAS

A

Virgin Galactic has announced thefirst ever commercial contracts thatwill enable researchers to carry out ex-periments in zero-g environments. Thedeal between Virgin Galactic and theprivate Southwest Research Institute(SwRI), based in San Antonio, Texas,will pave the way for scientists to per-form microgravity, biology, climateand astronomy research on VirginGalactic’s SpaceShipTwo spacecraft.It can travel about 100 000 m aboveEarth, allowing passengers to experi-ence about 6 min of weightlessness.

The SwRI has made full deposits ofabout $400 000 for two researchers tofly on SpaceShipTwo and intends tobook six more seats at a total cost of$1.6m. The SwRI will also aim to helpUS researchers who do not have di-rect spaceflight experience to develop

their payloads on such missions. Theexperiments will be performed inSpaceShipTwo’s cabin, which is about2.5 m in diameter and 18 m long.

According to SwRI researcher AlanStern, who will be one of the scientistsaboard the spacecraft, all scientistswill have to pass pre-flight medicaltests. Stern and his co-investigators

Daniel Durda and Cathy Olkin havealready been practising with the US’sNational AeroSpace Training and Re-search (NASTAR) centrifuges andtaking test flights aboard the US AirForce Starfighter F-104 jets to helpthem get used to the conditions.

One experiment the SwRI research-ers will perform will be to measureheart rates and blood pressure of thescientists throughout the flight. SwRIresearchers also intend to test theperformance of an ultraviolet imagerthat could be used to study planets at wavelengths that are blocked byEarth’s atmosphere. “There are agreat deal of risks, but the knowledgeto be gained and inspiration to newgenerations of researchers makes it allwell worth it,” says Durda.Gemma Lavender

Need a lab in space? Yours for just $200 000 per headSpace

Flying high

The SouthwestResearch Instituteplans to book seatson Virgin Galactic’sSpaceShipTwo craftto carry out researchin a microgravityenvironment.

Virg

in G

alac

tic

physicsworld.comNews & Analysis



http://physicsworld.com/cws/article/news/45415

http://physicsworld.com/cws/article/news/45415

NASA has launched an investigationinto last month’s dramatic failure ofthe $424m Glory satellite, althoughthe agency says it has no plans to re-build the craft. The probe was meantto study how the Sun and aerosols inour atmosphere affect the Earth’s cli-mate but it crashed shortly after take-off, landing in the South Pacific. Theseven-member investigation panel,led by Bradley Flick, a director atNASA’s Dryden Flight ResearchCenter in Edwards, California, is ex-pected to make recommendations toNASA boss Charles Bolden on how to avoid a similar accident happeningagain. According to NASA spokes-person Stephen Cole, the investiga-tion could take “six months or more”and that “the priority is to do athrough investigation, not meet apreset deadline”.

The 545 kg craft took off on aTaurus rocket early last month fromthe Vandenberg Air Force Base inCalifornia after technical issues de-layed the original 23 February launchdate. However, six minutes into themission NASA declared that theTaurus XL rocket had malfunctioned

and the “fairing” – the part of therocket that covers the satellite on topof the rocket – had failed to separateproperly so the satellite could not driftaway in orbit.

This is not the first time a NASAsatellite has failed in this manner. In2009 NASA’s $270m Orbiting CarbonObservatory (OCO) did not properly

separate from its Taurus XL rocketafter launch. The probe later landedin the Pacific Ocean near Antarctica.

Glory was meant to operate at analtitude of 700 km carrying two maininstruments: the Aerosol PolarimetrySensor (APS) and the Total Irradi-ance Monitor (TIM). The APS, oper-ating from the visible to short-waveinfrared, would have studied the dis-tribution of small particles in theatmosphere – including their size,quantity, refractive index and shape – and how they can influence theEarth’s climate by reflecting and ab-sorbing solar radiation.

The APS would have been the firstspace-based instrument to be able toidentify different aerosol types, whichwould have helped researchers to dis-tinguish the effect that natural andman-made aerosols have on the cli-mate. The TIM instrument wouldhave extended the three-decades-long record of the amount of solarenergy striking the top of the Earth’satmosphere. The accuracy of Glory’sTIM instrument was expected to bebetter than that of any other solar irra-diance instruments currently in space.

Glory was to be the fifth instalmentof NASA’s “A-Train”, which when it is complete will be a set of eight sat-ellites that study changes in Earth’sclimate system.Michael Banks

NASA’s Glory mission fails on take-offEarth observation

A sample-return mission to Mars hascome top of a wish list drawn up byplanetary scientists in the US lastmonth. NASA’s $3.5bn Mars Astro-biology Explorer Cacher (MAX-C)was chosen ahead of missions toJupiter and Uranus in the surveyfrom the National Research Council(NRC), which picks key missions andchallenges in planetary science forthe period 2013 to 2022. However,the report, written by a 17-strongpanel led by Steven Squyres from theCenter for Radiophysics and SpaceResearch at Cornell University,warns that any of the priority missionsshould be cancelled if costs balloon.

The top pick, MAX-C, is a roverthat would collect and store samplesfrom the Martian surface for returnto Earth. The second-choice missionis the $4.7bn Jupiter Europa Orbiter(JEO), which would map the Jovianmoon Europa to gain a better under-standing of the environment beneath

the body’s icy surface, where it isthought there is an ocean of waterthat could harbour life. The third pri-ority is the Uranus Orbiter and Probemission, which would investigate theplanet’s interior structure, atmo-sphere and composition.

However, the report, entitled “Vi-sion and Voyages for Planetary Sci-ence in the Decade 2013–2022”, says

that NASA should only fund MAX-Cif the cost is kept to $2.5bn. Missionsto Jupiter and Uranus are also in thefiring line. The authors say that NASAshould only build JEO if costs can be reduced, and that if the Uranusprobe’s budget rises above $2.7bn,then it should be reduced in scope oreven cancelled.

The report does not prioritize“medium-class” missions, which arecapped at a cost of about $500m, butsays NASA should select two suchmissions to fly between 2013 and2023. “Our recommendations are sci-ence driven that have the potential togreatly expand our knowledge of thesolar system,” says Squyres. “How-ever, in these tough economic times,some difficult choices may have to be made. Our priority missions werecarefully selected based on theirpotential to yield the most scientificbenefit per dollar spent.”Michael Banks

US picks Mars sample-return mission as top priorityAstronomy

Mourning Glory

NASA says it currentlyhas no plans torebuild the $424mGlory satellite after it failed just six minutes after take-off last month.

NAS

A

First in line

NASA’s $3.5bn MarsAstrobiology ExplorerCacher has beenselected as the highest priorityplanetary mission forlaunch between2013 and 2022.

NAS

A

physicsworld.com News & Analysis



A decision to give away a prototypeUS telescope to a consortium of Tai-wanese and US astronomers has beenput on hold following accusations thatthe bidding process could have in-volved “a perception of cronyism”.The National Science Foundation(NSF) announced last year that itwould donate the $6.3m Vertex Pro-totype Antenna (VPA) – a high pre-cision 12 m diameter millimetre/submillimetre antenna – to any insti-tution or group willing to refurbish thetelescope and move it from New Mexi-co, where it is currently based. Butwhen the NSF announced that theUS–Taiwan collaboration had won thebid, a rival complained the choice wasbased on an old-boy network, ratherthan scientific merit.

The VPA served as the prototypefor the Atacama Large MillimeterArray (ALMA) – a set of 66 antennaslocated in Chile that will study blackholes as well as planetary and star for-mation when it begins observationslater this year. Improvements to thedesign of the ALMA antennas, basedon research performed by the VPA,made the prototype redundant and sothe NSF called on US institutions as

well as countries that “form the NorthAmerican ALMA region” to submitproposals for hosting the antenna.

In January the NSF announced the VPA would go to a collaborationbetween the Harvard-SmithsonianCenter for Astrophysics (CfA) inCambridge, Massachusetts, and theAcademia Sinica Institute of Astron-omy and Astrophysics (ASIAA) inTaiwan. The collaboration had indi-cated that it might relocate the tele-scope to Greenland. However, RobertShelton, president of the University ofArizona, expressed his objections in a letter to Edward Seidel, NSF’s as-sistant director of mathematical and

physical sciences. Shelton complainedof “a perception of cronyism” fromNational Radio Astronomy Obser-vatory (NRAO) director Fred Lo, whoheads ASIAA’s scientific advisoryboard, and Vernon Pankonin, the NSFofficial who made the decision. Shel-ton asserts the CfA–ASIAA proposalhas less scientific merit than that of hisuniversity, which planned to place theantenna on nearby Kitt Peak. “Theantenna was built with US taxpayers’money. It cannot be in the nationalinterest to transfer ownership of anasset such as the VPA to a foreign-ledgroup that proposes to locate theantenna in Greenland – yet anotherforeign country,” he writes.

The NSF has acknowledged Shel-ton’s letter and plans to review itsoriginal decision. The University ofArizona expects a response thismonth, although the NSF has pro-vided no schedule. Charles Alcock,director of the CfA, says that a CfA–ASIAA collaboration has good ex-perience, having built the world’s onlyexisting submillimetre array, whichhas operated since 2003 at an altitudeof 4 080 m on Mauna Kea in Hawaii.He adds that moving the telescope to Greenland, should that happen,would benefit performing submilli-metre observations, as it is substan-tially dryer than any possible US site.Peter Gwynne

Boston, MA

Dispute arises over antenna giveawayAstronomy

Uncertain future

The National ScienceFoundation isreviewing its decisionto let the 12 mdiameter VertexPrototype Antenna bemoved to Greenland.

Kelly

Gat

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/AU

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The Chinese government has – for thefirst time – revoked a top national sci-ence and technology award because of research fraud. An investigation byChina’s National Office for Scienceand Technology Awards and the coun-try’s science ministry announced inFebruary that Liansheng Li, a me-chanical engineer formerly from theXi’an Jiaotong University (XJTU) inShan’xi province, was guilty of pla-giarism in the work that won him thecountry’s 2005 Scientific and Tech-nological Progress Award. Li will nowbe stripped of the award and forced toreturn the $15 000 prize money.

A problem first came to light in2007 when Yongjiang Chen, a retiredXJTU mechanical engineer, togetherwith five other XJTU colleagues,found that Li had copied their workfor designing reciprocating compres-sors – a device for compressing air –that are used in air-conditioners and

vacuum pumps. Li claimed to havedevised new analytical methods thathe then incorporated into a softwareprogram used to improve the designof compressors.

However, Chen found that Li hadcopied both the software and themethod from work done by Zhong-chang Qu, also from the XJTU. Chenthen wrote about the plagiarism in2009 on ScienceNet.cn – a website runby the Chinese Academy of Sciences

(CAS). Li was later fired by the XJTUin March 2010 after an investigativenews TV programme in China cov-ered the controversy.

“The fraud is only the tip of the ice-berg,” says Daguang Li from theCAS’s graduate school in Beijing,who was a member of the panel thatstripped Li of his prize. “I haveworked in academic circles for morethan 20 years, helplessly watchingacademic misconduct.”

Others, however, are calling for re-forms into how awards and researchgrants are handed out. “It is essentialto have more openness and trans-parency in handling prizes, awardsand grants, to ensure fair competitionand selection of the best, and to deterand expose frauds,” says Xuelei Chen,a cosmologist at the CAS’s NationalAstronomical Observatories.Jiao Li

Beijing

China withdraws top science award after fraud claimsResearch misconduct

Fighting fraud

Daguang Li, from theChinese Academy ofScience’s graduateschool in Beijing, waspart of a panel thatfound mechanicalengineer Liansheng Liguilty of fraud.

JiFu

Du



PWApr11news 21/3/11 17:30 Page 10

http://sciencenet.cn

Brazil’s 2011 science budget will becut by almost a fifth to help reducepublic expenditure and control raginginflation. The budget, which wasannounced in February by Brazil’s re-cently elected President Dilma Rous-seff, will now stand at $3.84bn – some18% less than last year. The savagecut was announced after Rousseffvetoed a $4.4bn package that had al-ready been approved by the country’scongress, which would have amoun-ted to a rise of 7%.

The cuts have shocked researchers,who had benefited from the strongsupport for science from former presi-dent Luiz Inácio Lula da Silva. During2003 and 2010 Lula doubled the coun-try’s science budget, the number ofstudent in public universities and thenumber of grants for researchers. AsRousseff’s government was presentedduring the general-election campaignas a continuation of that of Lula,

scientists trusted she would go onsupporting science, especially as shehad promised to turn Brazil into a“scientific powerhouse”.

It is not clear yet where the cuts willbe made but research projects in uni-versities and institutes are likely to bethe first to be hit. However, large sci-entific projects, such as the BrazilianSynchrotron Light Laboratory, arelikely to remain unscathed.

Brazilian scientists are hopeful thatthe cuts will only be temporary. In2009, for example, an 18% cut in thescience budget was reconsidered fol-lowing protests from the country’sscientific community. “Despite previ-ous cuts, Brazil has kept a consistentrhythm of development during thepast decade,” says Ronald CintraShellard, deputy director of the Bra-zilian Center for Research in Physics(CBPF), in Rio de Janeiro.Gabriela Frías Villegas

Brazil’s researchers dismayed as science budget is cutFunding

Australia’s chief scientist quitsPenny Sackett, Australia’s first full-timechief scientist, has resigned only half waythrough her five-year term, citing both“professional and personal reasons”.Sackett took up the post in September2008 after the Labor government, led byformer Prime Minister Kevin Rudd, madethe position full-time. Sackett obtained a PhD in theoretical physics at theUniversity of Pittsburgh before switching toastronomy. Since 2002 she has been aprofessor at the Australian NationalUniversity, a position that she retainedduring her time as chief scientist. “She hasbeen a terrific communicator at home andabroad, and has helped conveycomplicated messages about the issuesconfronting Australia,” science ministerKim Carr said in a statement. TheAustralian government is now seeking a replacement.

Carbon-capture plant picks siteThe US Department of Energy (DOE) hasannounced that the $1.3bn FutureGencarbon-capture demonstration plant,which will involve adapting a 200 MW coalplant that closed last year at Meredosia inIllinois, is to inject its sequesteredgreenhouse gases into underground rocksat a site some 5 km away in MorganCounty. The DOE chose Morgan County asit is relatively close to the Meredosia powerplant, thereby simplifying pipeline routingand reducing the project’s overall cost. The DOE also highlighted the area’s “high-quality geology”, which makes it wellsuited for the long-term storage of carbondioxide. However, the site still needs anenvironmental review and permits beforecarbon can be buried.

Fear over emissions voteUS climate scientists have raisedconcerns after the energy and commercecommittee of the House ofRepresentatives voted last month toremove the Environmental ProtectionAgency’s regulatory control overgreenhouse-gas emissions. MostRepublicans on the committee say theagency’s control is unnecessary anddamages commercial competitiveness.“We can have a good-faith debate abouthow to deal with the challenges andthreats of human-caused climate change,but we cannot have a good-faith debateabout its existence,” says climate scientistMichael Mann from Pennsylvania StateUniversity. “Those who deny the veryreality of the problem are poisoning thediscourse and potentially causing greatharm to us all.”

Sidebands

Cutting costs

Brazil’s recentlyelected PresidentDilma Rousseff hasannounced an 18%cut to the country’sscience budget much to the shock of physicists.

Seven Indian institutions have proposed

joining the Advanced Laser Interferometer

Gravitational Observatory – a

US–Australian effort to build an advanced

gravitational-wave detector. The Indian

scientists would help to commission the

facility during 2011–2017 and contribute

equipment for LIGO-Australia’s

sub-systems such as ultrahigh-vacuum

components for the detectors. The

proposal is currently being evaluated by

both the Department of Science and

Technology and the Department of Atomic

Energy for approval.

Last October the US announced that it

would build one of its advanced

gravitational-wave detectors at Gingin –

about 80 km from Perth – to help

determine the origin of such waves, which

have never before been detected (see

Physics World November p10). In early

March the LIGO-Australia proposal was

submitted to the Australian science

minister Kim Carr for a decision. The

five-university Australian Consortium for

Interferometric Gravitational Astronomy

has since been seeking to include other

countries, such as India and China, to

cover some of the $140m costs of

LIGO-Australia.

“We are certain that Australia would

not fund unless there are international

partners,” says David Blair, director of the

Australian International Gravitational

Research Centre. “There are so many

mutual benefits for our major regional

partners India and China to be involved

that I believe that the proposal is much

more compelling with their inclusion.”

The seven collaborating institutions in

the Indian Initiative in Gravitational-wave

Observations (IndIGO) consortium

include the Tata Institute of

Fundamental Research (TIFR), the

Inter-University Centre for Astronomy and

Astrophysics in Pune, and the Indian

Institute of Science Education and

Research in Thiruvananthapuram.

If India joins LIGO-Australia,

researchers hope their resulting

experience might enable a gravitational-

wave detector to be built in India. First

mooted in 2007, the TIFR even approved a

3 m interferometer prototype at the

institute in 2009 at a cost of $450 000.

The project is part of a roadmap for a 4 km

baseline instrument. “LIGO-Australia is

the best pathway and opportunity for

Indian participation in the global

programme of gravitational-wave

research and astronomy,” says Bala Iyer,

a gravitation theorist at the Raman

Research Institute in Bangalore and chair

of IndIGO’s council.

Ramaseshan Ramachandran

New Delhi

Gravitational waves

India considers joining Australian bidThere are somany mutualbenefits forIndia andChina to beinvolved

Agên

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PWApr11news 21/3/11 17:31 Page 11

Simon van der Meer, who shared the1984 Nobel Prize for Physics withCarlo Rubbia, died on 4 March at the age of 85. The pair were awardedthe prize for their roles in discoveringthe W and Z bosons – the particlesthat carry the weak force – at theSuper Proton Synchrotron (SPS) atthe CERN particle-physics lab nearGeneva. Van der Meer pioneered thetechnique of “stochastic cooling”,which helped to ensure that sufficientantiprotons entered the collider.

Van der Meer was born on 24 No-vember 1925 in the Hague, the Neth-erlands, before studying technicalphysics at the University of Technol-ogy in Delft. Graduating in 1952, heworked for the Philips Research La-boratory in Eindhoven, developinghigh-voltage equipment and elec-tronics for electron microscopes. Hejoined CERN in 1956, where he wasto remain until he retired in 1990.

Under the leadership of futureCERN boss John Adams, Van derMeer made his name in the early1960s developing the “neutrino horn”– a device that can increase the in-tensity of neutrino beams. These de-vices are still used as they allowfocused beams of neutrinos to be sent

through the Earth to huge, ultrasen-sitive underground detectors. Van derMeer then worked on an experimentat CERN measuring the anomalousmagnetic moment of the muon.

It was while developing magnetpower supplies for CERN’s acceler-ators, including the Intersecting Stor-age Rings (ISR), that Van der Meerdevised the idea of stochastic cooling.Although the technique was not usedon the ISR, it was trialled on theInitial Cooling Experiment, persuad-ing Rubbia and others in 1976 todeploy it on the SPS. Van der Meersubsequently joined the SPS, helping

to lead the Antiproton Accumulatorproject, which used stochastic coolingto accumulate enough antiprotons forthe collider.

The technique uses sensitive elec-trodes to pick up small “stochastic”electromagnetic signals that registerthe average condition of a particlebeam, such as its density. These sto-chastic signals – and hence the prop-erties of the beam itself – can then becontrolled using a high-frequency“kicker” that sends out rapidly varyingelectric and magnetic fields. The tech-nique can therefore shrink the size of abeam, thereby boosting its intensity.The beam has been “cooled” becausethe particles occupy a smaller volume.

Researchers at the SPS eventuallydiscovered the W and Z bosons inexperiments between October 1982and January 1983. Speaking toPhysics World, Rubbia said Van derMeer was “one of the most extraor-dinary people” he had ever met. “Hewas able to make everybody feel atease by the clarity of his thinking and his enormous kindness,” Rubbiaadded. “His ideas were extremely ori-ginal and he was able to make every-one understand them.”Matin Durrani

Simon van der Meer: 1925–2011

A major scientific project designed to

foster collaboration between countries in

the Middle East is facing difficulties

following growing political unrest in the

region. The Synchrotron-light for

Experimental Science and Applications in

the Middle East (SESAME) is currently

being built in Jordan and due to start up in

2015. But the toppling of the Egyptian

government – and turmoil elsewhere –

is putting a strain on the ability to

guarantee the funding needed to

complete the facility.

SESAME is designed to produce X-rays

to study materials in a range of

disciplines from biology to condensed-

matter physics. Its members are currently

Bahrain, Cyprus, Egypt, Iran, Israel,

Jordan, Pakistan, the Palestinian

Authority (PA) and Turkey. But the

revolution in Egypt and growing

anti-government protests in Iran and

Bahrain have put the project on an

uncertain footing. “In the short term it is

very worrying,” Chris Llewellyn Smith,

president of the SESAME council, told

Physics World.

Although Llewellyn Smith says the

unrest has yet to have a direct impact on

the project, the former director-general of

CERN is working with the SESAME

members to put together a financial

package that would guarantee the

roughly $35m that is needed to open the

facility by 2015. “[The package] is now in

jeopardy as ministers of member

countries are changing,” says

Llewellyn Smith. “It is a moment of great

uncertainty for the project.”

Back in February, Llewellyn Smith had

been in discussions with the then

Egyptian science minister Hany Helal

about SESAME, but days later Helal was

removed from office by the military-led

government. Egypt had been expected to

contribute about $5m to the $35m

required, but it is not clear what

importance any new government will

attach to SESAME. Despite the problems,

Llewellyn Smith remains “optimistic”

about the project, with the new package

due to be announced as Physics World

went to press. “With more democratic

governments, maybe we can get renewed

and greater support for SESAME,”

he says.

Michael Banks

Obituary

Political unrest puts SESAME project in jeopardyMiddle East

Happy days

Simon van der Meer(right) with Carlo Rubbia at CERNin October 1984celebrating the awardof that year’s NobelPrize for Physics.

CERN

Troubled times

A new financialpackage of $35m isbeing negotiated toenable SESAME toopen by 2015.

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PWApr11news 21/3/11 17:31 Page 12

How long have you been involved

superconductivity?

For more than 16 years, now. I did myPhD at the National High MagneticField Laboratory in Florida, where Iworked on the thermal properties ofhigh-temperature superconductors,particularly HgBa2Ca2Cu3Ox, whichat 133 K had the highest transitiontemperature of any other material.

What attracted you to work for a

company attempting to commercialize

superconductivity, instead of pursuing

an academic career?

My father had a long career as a geo-physicist in the oil industry, and I al-ways wanted to go into industry ratherthan staying in academia. GE wasworking on products utilizing super-conductors – particularly magnets formagnetic resonance imaging (MRI) –and driving new innovations in thearea, so it seemed like a good firm tojoin. When I joined, I was initiallyworking on the properties of super-conductors, which was similar to myPhD work.

How are superconductors used in MRI?

An MRI machine uses a magnet toalign the magnetization of particularatoms in the body, which causes thenuclei to produce a rotating magneticfield that is detectable by a scanner.Strong magnetic-field gradients causenuclei at different locations to rotateat different speeds, so MRI providesgood contrast between different tis-sues of the body, making it especiallyuseful for imaging the brain, muscles,the heart and tumours. Supercon-ducting magnets – made from coils ofsuperconducting wires – can producegreater magnetic fields than standardelectromagnets and are also cheaperto operate because no energy is dis-sipated as heat in the windings.

What superconducting material does GE

use for its MRI magnets and why?

We use niobium titanium (NbTi), asit is a good workhorse material. It hasa superconducting transition tem-perature of about 9.2 K, so it needs tobe cooled by liquid helium to around4.2 K. The advantage of this material

is that it has many years of researchbehind it and it is easy to wind the ma-terial for magnets. But we are cer-tainly looking at the potential of usingmagnesium diboride in our magnets,which is cheaper and has a highertransition temperature of about 40 K.

What about other materials such as

copper oxides or the recently discovered

iron-based superconductors. Could they

be useful?

We are always looking at other ma-terials and YBCO [yttrium–barium–copper-oxide] is one of them. But thechallenge there is building robuststructures that can be manufacturedinto magnets. YBCO is very brittleand although the material has thepotential to be cheaper, current ma-nufacturing processes make the con-ductors expensive at this time. But ifthe costs come down, then we couldsee an advantage in using it. As for theiron-based superconductors, we arefollowing the research; it is all veryinteresting but we will have to seewhere it leads.

In the 1970s GE decided not to pursue

applications of superconductivity

thinking there was not enough demand

in the market. In hindsight, was that a

good decision?

I wouldn’t say that GE dropped theidea of developing applications in su-perconductivity. GE has a long historyin superconductivity and a number ofNobel laureates have worked at GElabs, such as Ivar Giaever, who shared

the 1973 Nobel Prize for Physics withLeo Esaki and Brian Josephson. GEdid initially spin-off a company calledIntermagnetics General (IG) in 1971,which GE had a vested interested in.The company later became indepen-dent and is now part of Philips.

In 1984, after smelling huge market

opportunities in MRI, GE returned to the

superconducting market with force,

rolling out its first machine that year.

Would you say MRI is now the only real

market for superconductivity?

Yes. There is no doubt that MRI is thelargest opportunity. It is now a $4bnglobal market. But there is also a well-established industry for supplyingmagnets for use in nuclear-magnetic-resonance imaging.

Can you see any other application of

superconductors that may lead to a

market as big as that for MRI?

There is potential in power generationand in renewable energy, although Ithink it is not entirely clear yet wherethat demand will come from. As it didin the case of MRI, superconductivitymust provide a unique value to be suc-cessful. For example, the high powerdensity that superconductivity canbring to power generation can lead toapplications where weight reductionis critical. For example, GE partneredwith the Air Force Research Lab todevelop lightweight generators forairborne applications. This aids indeveloping the power infrastructureneeded for the ever increasing electri-cal demand on aircraft.

If a room-temperature superconductor

was found, how would that change the

MRI business?

Well, the dream is to have room-tem-perature superconductivity. But, ofcourse, whatever material that mightbe, it would have to be reliable andeasily manufactured into wires. Ifthis were the case, then I think youwould see it implemented every-where, as there would be no need forcryogenic equipment.

What currently excites you about

superconductivity?

I can remember back when high-tem-perature superconductors were firstdiscovered in 1986, and it captured myimagination. There was a lot of excite-ment in the field and it was somethingI wanted to be part of. Superconduc-tors also play a critical role in impro-ving healthcare through the use ofMRI. It is exciting to be involved indeveloping a technology that can en-hance and save lives.

Looking ahead

Kathleen Amm seesopportunities forsuperconductors inpower generation andrenewable energy,but is uncertainwhere the demandwill come from.

Superconductivitymust provide aunique value tobe successful

Industry giant General Electric has a long history of making superconductingmagnets for magnetic resonance imaging. Michael Banks talks to Kathleen Amm, GE’s head of MRI technology, about the challenges ahead

Q&A

A life in magnets

News & Analysisphysicsworld.com


PWApr11news 21/3/11 17:31 Page 13

“This will change the world,” was thefirst thought of Gregory Yurek, a me-tallurgist working at the Massachu-setts Institute of Technology (MIT),when he heard about a major dis-covery in condensed-matter physics.It was 1986 and Georg Bednorz andAlex Müller, both working at the IBMResearch Laboratory in Zurich, hadjust discovered that the electrical re-sistance of a material made from lan-thanum, barium, copper and oxygen(LaBaCuO) fell abruptly to zero whencooled below a temperature of 35 K.The appearance of superconductivity– where a material can conduct elec-trons with zero resistance below thesuperconducting transition tempera-ture – was only 12 K higher than theprevious record of 23 K in Nb3Ge,which was discovered in 1973. How-ever, physicists knew that LaBaCuOwas a major breakthrough becausedifferent elements in the materialcould be substituted for others, open-ing the door to potentially highersuperconducting temperatures.

Within a year of Bednorz andMüller’s discovery, a new materialbased on yttrium, barium, copper andoxygen (YBa2Cu3O, also known asYBCO) became the first material tosuperconduct above the boiling pointof liquid nitrogen at 77K, with a super-conducting transition temperature of93 K. That was quickly followed in1988 by a material containing bismuth,strontium, calcium, copper and oxy-gen (BSCCO) that superconducts atabout 105 K. Results and new com-pounds were appearing thick and fast– there seemed no limit to what trans-ition temperatures might be possible.With the dream of room-temperaturesuperconductors alive, Bednorz andMüller’s discovery earned them the1987 Nobel Prize for Physics.

It was all a revelation to Yurek, whoimmediately started to work on thechemical and physical properties ofthese materials. It was not just theunderstanding of these systems or the hunt for higher superconductingtemperatures that fascinated him, butalso how society could reap the re-wards of the discovery for applica-tions. Indeed, TIME magazine ran awhole issue in May 1987 devoted tothe breakthrough: “Wiring the future:

the superconductivity revolution”.The dream then was of maglev “levi-tating” trains speeding through thecountryside with the help of high-tem-perature superconducting magnets,as well as the promise of power distri-bution being revolutionized throughthe lossless transmission of electricity.

Keen to get in on the commercialpossibilities, Yurek, together with hiswife Carol and fellow MIT researcherJohn Vander Sande, formed Ameri-can Superconductor (AMSC) in April1987. They were buoyed by the factthat a new market for magnets inmagnetic resonance imaging (MRI)was then slowly emerging that usedsuperconducting wires from materialswith lower transition temperatures,such as niobium tin (Nb3Sn), whichsuperconducts at 18.3 K.

Based in Devens, Massachusetts,the company now employs about 900people. Yet in the 25 years since thediscovery of high-temperature super-conductors, the widespread applica-tion of them has somewhat failed tolive up to its promise. Indeed, insteadof producing hundreds of kilometresof cable for power grids all over theworld as it had envisaged, AMSC hasbeen steadily diversifying its businessto other areas such as renewable en-ergy. In the third quarter of 2010 – thelatest available figures – barely $2.1mof AMSC’s $114.2m revenue camefrom its superconducting-wire busi-ness. The rest comes from AMSC’s“power systems” division, which pro-vides wind-turbine designs and powerelectronics for wind turbines and the

power grid.Yurek is, however, confident that

the company’s fortunes and demandfor superconducting cables is startingto take shape, or as he puts it “super-conductors are now coming of age”.Indeed, there is some evidence to backup his claims. Last year South Koreanpower-cable manufacturer LS Cableplaced the world’s largest order forsome three million metres of wirefrom AMSC. LS Cable plans to usethis wire to deploy approximately25km of superconductor power cablesfor the South Korean and globalpower-grid markets over the nextseveral years.

However, other industry insidersare less sure that the time has comefor high-temperature superconduct-ing cables. “Utility companies are stillto be convinced,” says Pradeep Hal-dar, who co-founded the US-basedsuperconductor-wire manufacturerSuperPower, which was bought up byelectronics giant Philips in 2006, andwho now works at the University atAlbany, State University of New York.“The promise is still there, but it is stilla huge challenge to get it widespreadin the industry.”

The optical fibre of wireThe first high-temperature super-conductor material to be utilized incommercial wires was BSCCO-2223(Bi2Sr2Ca2Cu3O10 + x) – known as afirst-generation (1G) wire – thatAMSC brought out in 1995. Thesesuperconductor wires are made bypacking ceramic powders of BSCCOinto silver tubes. The packed powderis extracted and rolled into a flat tape,which is heated to make it suitable forwinding cables or coils for transfor-mers, magnets, motors and generators.

Typical BSCCO tapes are 4 mmwide and 0.2 mm thick, and can sup-port a current at 77 K of 200 A, givinga critical current density of about104 A cm–2. To make a superconduct-ing cable, the tapes are typicallywrapped around a copper core, sur-rounding which are various levels ofelectrical shielding. The cables alsohave thermal insulation for the liquidnitrogen, which is used to cool thetape down to 77 K.

One big success of this 1G wirecame in 2008, when it was used in atransmission-voltage superconductingpower cable that operated at industrystandards for the first time in a gridsetting. Funded by the US Depart-ment of Energy, the Holbrook Super-conductor project involved about600 m of underground cable contain-ing about 160 km of AMSC’s BSCCO

Laying the

ground work

The HolbrookSuperconductorproject at a substationin Long Island, New York, has beenoperating with some 160 km ofsuperconductingcables since 2008.

AMSC

Wiring the marketFirms have spent the last 25 years trying to create a market for high-temperature superconducting wires, but their widespreadapplication may still be some years away. Michael Banks reports



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wire, installed at a Long Island sub-station in New York. The supercon-ducting wire has been successfullyoperating in the grid since April 2008.Although the demonstration suc-ceeded, the problem with BSCCOwire is that making it requires a lot ofsilver, which is expensive, and means1G wires are unlikely to ever be cost-effective when compared with copper.

While other wire manufacturers,such as Japan’s Sumitomo, are stillusing BSCCO wires, AMSC andSuperPower have already broughtout a second-generation (2G) wire,which is based on YBCO. AlthoughYBCO has a lower superconductingtransition temperature than BSCCO,it could potentially deliver muchhigher current densities of about106 A cm–2 – more than 100 times thecurrent density of copper wires – andoutperforms BSCCO in high mag-netic fields. “We think that it may bepossible for YBCO wires to have amuch higher current density, reach-ing about 107 A cm–2,” says VenkatSelvamanickam, SuperPower’s chieftechnology advisor who is based atthe University of Houston, Texas.

Making YBCO involves depositinglayers of the superconductor onto asubstrate consisting mostly of nickelrather than silver. YBCO wires areabout 4–12 mm wide and 0.1mmthick, and are 1% YBCO with the restbeing the nickel, copper and a little sil-ver. Selvamanickam says that Super-power’s technique can produce wiremore than 1 km in length.

As for AMSC’s 2G wire, which goesunder the name “Amperium”, it canconduct more than 100 times the elec-trical current of copper wire of thesame dimensions. It now accounts for85% of all wires sold to industry, andthe company has more than 150 pa-

tents on the wire. Yurek calls Am-perium the “optical fibre of wire” be-cause just as high-capacity opticalfibres have revolutionized the tele-coms industry, so superconductingwires, he thinks, will revolutionize theelectric power industry.

That may sound optimistic, butwires based on YBCO are starting tobe used. AMSC, for example, is in-volved in the $1bn Tres AmigasSuperStation, which is located inClovis, New Mexico, and is expectedto be in operation by 2014. The stationwill connect the US’s three powergrids – the Western, Eastern andTexas interconnections – to increasethe reliability of the grid and to enablea faster adoption of renewable en-ergy. The grids will be linked togethervia three superconducting high-volt-age direct-current power transmis-sion lines, which allow for much bettercontrol of energy and are much moreefficient than conventional cables.

There is also a $39m project called“Hydra”. Initially proposed in 2007, itwas put on hold following the globaleconomic downturn, but is now, ac-cording to Yurek, “back on the table”.Partially funded by the US Depart-ment of Homeland Security, it willdeploy 2G wire into the grid in lowerManhattan to protect substationsfrom fault currents – power surgesthat could damage grid connections.“I think what you are likely to see overthe next 10 or 20 years is utilities in-stalling more demonstration cableshere and there, but not on a hugescale,” says Haldar.

A superconductivity revolution?So why have utility companies aroundthe world not been falling over them-selves to install superconductingwires? “The issue with Long Island

and the like is that, although theyshow that superconducting wires canwork, it is not at all a market demon-stration,” says Haldar. “Utility com-panies need something to be tested to work on the scale of many years,maybe up to 30 years, to show that thecables can survive.”

Yurek also blames the “notoriouslyslow” power industry – sentimentsthat are reiterated by Trudy Lehner,director of marketing and govern-ment affairs at SuperPower. “We havea saying in the industry that the utilitycompanies like to be first to be sec-ond,” he says. Another barrier is theprice of uprooting parts of a grid toinstall new cable. Moreover, the cur-rent global economic downturn hasdissuaded many firms from investingin new infrastructure. “Utility com-panies have basically told us that theycannot invest at this time, so they haveput it back on the shelf,” says Yurek.

Although the cost of YBCO wiresis coming down all the time, Selva-manickam says that superconductingcables are still about a “factor of five”times more expensive than standardcopper cable, mostly because of theneed for coolant systems. However,Haldar thinks that the cost of coolantis a red herring. “In addition to cost,training a whole new set of engineersto work with it, entering an alreadymature industry and turning it on itshead is very hard to do,” he says.

Yet Yurek is expecting a number of“meaningful orders” from China inthe coming months and is confidentthat the US and Europe will eventu-ally begin to catch up with Asia. “As anAmerican who has put a lot of blood,sweat and tears into this, it is a pity[the US is not leading],” says Yurek.“But I am confident that will changeat some point.”

I think what youare likely to seeover the next10 or 20 yearsis utilitiesinstalling moredemonstrationcables hereand there, but not on ahuge scale

While wire manufacturers wait for utility companiesto show more interest in high-temperaturesuperconducting cables, second-generation (2G)wires are finding some applications in generatorsand motors. A generator’s weight can be reducedsignificantly – by a half or so – with superconductorwires as there is no need for a heavy iron core in thegenerator. “But when designing a motor orgenerator with superconducting wires, you have tothrow away the book and basically start fromscratch,” says Gregory Yurek of AmericanSuperconductor (AMSC). “People in the industrysay ‘wow that’s fantastic, but I don’t know how tochange my business’.”

Yurek says this is why AMSC has decided to startbuilding and selling its own generator and motorsthat take advantage of superconducting wires.“Sometimes you can’t depend on other companies

and have to take it forward yourself,” he says. One example is in wind turbines, wheresuperconducting cables can be used in thegenerator to make it more efficient thanconventional generators. There is also someinterest from the US Navy in using generators madewith superconducting wires so that the size andweight of vessels can be reduced. In fact, AMSC

has successfully tested the world’s first 36.5 MWhigh-temperature superconducting ship-propulsionmotor, which has been built at the US Navy’sIntegrated Power System Land-Based Test Site in Philadelphia.

Although the industry that AMSC was created topioneer has yet to fully take off, optimism abounds.“If you look back in history, you would have saidthat in the1950s superconductivity looked like afailure, but then magnetic resonance imaging camealong and created a billion-dollar industry,” saysPradeep Haldar, who co-founded the US-basedsuperconductor-wire manufacturer SuperPowerand now works at the University of Albany, State University of New York. “In my view, we willfind a silver-bullet application for high-temperaturesuperconductors, the question we do not know atthe moment is what it will be.”

Superconductors head into the niche

AMSC



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Physicists and financeIn his letter (February p20), Jim Groziersurmised that not many readers wouldagree with using physics PhD studentshipsto train people for a career in commerce.On the contrary, I think most readers wouldreadily accept that not only do physics PhDstudentships offer the ideal environmentfor commercial training, but that it is rightthat such studentships should be used forproducing well-trained personnel for thebanking, finance and services sector.

Far from insisting that those who leavephysics for jobs in finance and bankingshould pay back their studentship money,as Grozier suggests, we should recognizethat trained physicists have an immenselypositive impact on the economy and thatthe tax revenues they generate compensatemany times over for the costs of their PhDs.Many of these physicists are key people inthe financial sector in and around the City of London, which is one of the mostsuccessful financial centres in the world.Indeed, the sector contributed £53bn in

taxes to the UK exchequer during the2009/10 tax year – more than any other areaof the economy.

Without such revenues, not only would itbe impossible to fund physics PhD places,but also academic positions, such as theone presumably occupied by Grozier,would not be viable. Surely it is clear thatwe should positively and wholeheartedlyencourage physics PhD students to followtheir chosen path, especially if they wish toenter the world of commerce and finance,because there they will thrive, and that willbe to the benefit of all of us.William Quinton

Reading, [email protected]

Still contributingI much appreciated the article “Retired, but still a physicist” (February pp42–43),which provided both practical advice and abalanced assessment of “career” prospectsafter retirement. On a personal level, I havebeen extremely fortunate. Now 76, I havebeen allowed to retain my office at the university and, as a retired professor, I continue to receive an annual grant fortravel and research. I also teach an electiveundergraduate course once a year that hasbeen approved for credit (27 students completed the course this year). I attendfaculty meetings as an observer and I amoccasionally consulted by both faculty andgraduate students. I go to the occasionalconference, though my presentations tendto focus on “historical” perspectives andassessments, not original work, and I try to

make sure that anything I have to say meetsthe expectations of the organizers.

There are, of course, problems. Mymetabolism has slowed and I do not havethe concentration to keep up with the literature – a problem exacerbated byfailing eyesight. There is no way that I canwork in the laboratory or even participatein all the seminars and seminar discussionsthat I would like to. I have to remind myselfthat some of my one-time students are nowsenior staff members with serious responsibilities and at least as much knowledge as I possess, so I try to keep alow profile. I hope that I will retain thegood sense to know when I am no longerable to make a contribution.David Brandon

Technion – Israel Institute of [email protected]

Impériale unitsI was reminded of the recent Physics Worlddiscussion about unusual units when, on16 February, an Ariane 5 rocket blasted offfrom French Guiana. It was carryingEurope’s second space freighter, theJohannes Kepler, loaded with supplies forthe International Space Station. On Frenchtelevision news this payload was described,in French, as being “as big as a Londonbus”. The French for a double-decker is l’autobus à impériale. Thus it would appearthat the French, of all people, haveinvented the ultimate imperial unit!Peter Gill

Riscle, [email protected]

Letters to the Editor can be sent to Physics World, Dirac House, Temple Back, Bristol BS1 6BE, UK, or to [email protected]. Please include your address and a telephone number. Letters should be no more than500 words and may be edited. Comments on articlesfrom physicsworld.com can be posted on the website;an edited selection appears here

Feedback

Zhores Alferov makes an interesting – and

controversial – subject for a biography.

Renowned in the physics community for his work

on heterotransistors, which won him a share of

the Nobel prize in 2000, Alferov is also an

outspoken communist and a prominent member

of Russia’s parliamentary opposition. Which

aspect should a biographer emphasize?

In his review of Lenin’s Laureate: Zhores Alferov’s

Life in Communist Science (March pp46–47),

Alexei Kojevnikov criticized author

Paul R Josephson for softening Alferov’s

communist views, arguing that if we want to

understand Russia’s current political situation,

“we need to start hearing, rather than turning a

deaf ear to, the political voices of Alferov and

his comrades”. For a few physicsworld.com

readers, Kojevnikov’s words touched a nerve.

Why not listen also to other Soviet Nobel winnerssuch as Vitaly Ginzburg, Lev Landau and AndreiSakharov, who used to be quite pro-Soviet and pro-Communist but came to see how wrong theyhad been? Landau said in 1957 that “Our regime is

definitely a fascist regime, and it could not changeby itself in any simple way. If our regime is unable tocollapse in a peaceful way, then a Third World Warwith all its attendant horrors is inevitable.” AndSakharov, a foremost opponent of the Sovietregime, explained that “Because I had alreadygiven so much to the cause and accomplished somuch, I was unwittingly creating an illusory world tojustify myself.” Why these illusory worlds are sodurable is another question.gorelik, US

I think these “illusory worlds” are durable becausepeople need ideals to live and work for – somethingbetter than stealing as much as possible from yourfellow humans, killing competition as the cheapestway to success, and so on. This is especially true inscience. What happens to “science” when it is runas a private business is, in my opinion, nothinggood at all. It simply disappears when it is run by“businessmen”, because the only purpose of abusiness is not to make scientific advances (or, forthat matter, even to produce anything useful), but simply to make money, as the economist

Milton Friedman said. How [the money is made] isnot important – whichever way is cheaper.Alex244

I came from the Soviet Union to the US more than15 years ago. Although I was very thrilled at first,now I see that both opposites (radical socialismand extreme capitalism) are equally bad, and insome senses are very similar – equally oppressive,but with different tools. Also, people (intellectuals,scientists, writers, etc) who were at the top of thedissident movement in the Soviet Union now are notso excited about what happened in Russia. Most ofthem have become poor and neglected. Is it possible to combine good characteristics of socialism and capitalism? In Russia they combinednegative sides of both systems, as I see it.postfuture

Read these comments in full and add your own atphysicsworld.com

Comments from physicsworld.com

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Superconductivity

Physics World celebrates the centenary of the discovery of superconductivity

Kwik nagenoeg nul. Scrawled in a lab notebook by the Dutch low-temperature physi-cist Heike Kamerlingh Onnes on 8 April 1911, these words are what signalled thatsuperconductivity – that mysterious and bizarre phenomenon of condensed-matterphysics – had been discovered. Onnes, together with his colleague Gilles Holst, hadfound that the resistance of mercury, when chilled to a temperature of below 4.2 K,fell to practically zero – the hallmark of superconductivity. Interestingly, it was onlylast year that the precise date of the discovery and this phrase – which means“Quick[silver] near-enough null” – came to light, thanks to some clever detectivework by Peter Kes from Leiden University, who trawled through Onnes’s manynotebooks, which had been filled (often illegibly) in pencil (Physics Today September2010 pp36–43).

Researchers soon began to dream of what superconductivity could do (p18),with talk of power cables that could carry current without any losses, and later evenlevitating trains. Sadly, with a few honourable exceptions such as superconduct-ing magnets (p23), there have been far fewer applications of superconductivitythan from that other product of fundamental physics – the laser. Over the years,superconductivity has also baffled theorists: it was not until the mid-1930s thatbrothers Fritz and Heinz London made a big breakthrough in understanding howthese materials work (p26). As for high-temperature superconductors (p33 andp41), theorists are still scratching their heads.

Fortunately, today’s theorists are in good company. A true understanding ofsuperconductivity foxed some of the giants of physics, including Dirac, Feynmanand Einstein himself, who in 1922 noted that “with our wide-ranging ignorance ofthe quantum mechanics of composite systems, we are far from able to compose atheory out of these vague ideas”. Einstein felt that progress in superconductivitycould only be made by relying on experiment. A century on from its discovery,those words continue to ring true.Matin Durrani, Editor of Physics World● Check out physicsworld.com during April for our series of superconductivity-related videos

The contents of this magazine, including the views expressed above, are the responsibility of the Editor. They do not represent the views or policies of the Institute of Physics, except where explicitly stated.

Physics World

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The first 100 years

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Of all the discoveries in condensed-matter physics dur-ing the 20th century, some might call superconduc-tivity the “crown jewel”. Others might say that honourmore properly belongs to semiconductors or the elu-cidation of the structure of DNA, given the benefitsthat both have brought to humanity. Yet no-one woulddeny that when a team led by Heike KamerlinghOnnes stumbled across superconductivity – the ab-solute absence of electrical resistance – at a laboratoryin Leiden, the Netherlands, 100 years ago, the scien-tific community was caught by complete surprise.Given that electrons usually conduct imperfectly bycontinually colliding with the atomic lattice throughwhich they pass, the fact that conduction can also beperfect under the right conditions was – and is – surelyno less than miraculous.

The discovery of superconductivity was the culmin-ation of a race between Onnes and the British physicistJames Dewar as they competed to reach a temperatureof absolute zero using ever more complex devices toliquefy gases. Onnes won after he successfully lique-fied helium by cooling it to 4.2 K, for which he wasawarded the 1913 Nobel Prize for Physics. (The cur-rent low-temperature record stands at about 10–15 K,although it is of course thermodynamically impossibleto ever get to absolute zero.) But researchers did notonly want to reach low temperatures just for the sakeof it. What also interested them was finding out howthe properties of materials, particularly their electricalconductance, change under cryogenic conditions. In1900 the German physicist Paul Drude – building onthe conjectures and experiments of J J Thomson andLord Kelvin that electricity involves the flow of tiny,discreet, charged particles – had speculated that the re-sistance of conductors arises from these entities boun-cing inelastically off vibrating atoms.

So what would happen to the resistance of a metalimmersed in the newly available liquid helium? Phy-sicists had three main suspicions. The first was that theresistance would keep decreasing continuously towardszero. The second was that the conductivity would in-stead saturate at some given low value because therewould always be some impurities off which electronswould scatter. Perhaps the most popular idea, however– predicted by the emerging picture of discrete, lo-

calized atomic orbitals – was that the electrons wouldeventually be captured, leading to an infinite resistance.But before anyone could find out for sure, researchersneeded a very pure metal sample.

Gilles Holst, a research associate in Onnes’s instituteat Leiden University, thought it might be possible toobtain such a sample by repeatedly distilling liquidmercury to remove the impurities that were found todominate scattering below 10 K. The Leiden lab hadlots of experience in fabricating mercury resistors foruse as thermometers, and Holst suggested enclosingthe mercury in a capillary tube to keep it as pure aspossible before finally submersing it in a sample ofliquid helium. And so it was in April 1911 (the precisedate is not known for sure due to Onnes’s unclear anduncertain notebook entries) that Holst and his lab tech-nician Gerrit Flim discovered that the resistance of li-quid mercury, when cooled to 4.2 K, reached a value sosmall that it is impossible to measure. This phenomen-on – the complete absence of electrical resistance – isthe hallmark of superconductivity. Ironically, had theLeiden team simply wired up a piece of lead or solderlying around the lab – rather than using mercury – theirtask would have been far easier, because lead becomessuperconducting at the much higher temperature of7.2K. In fact, three years later, acting on a suggestion byPaul Ehrenfest, researchers at the Leiden lab were ableto produce and measure “persistent” currents (whichwould last a billion years) in a simple lead-ring sample.

Since its discovery 100 years ago, our understanding ofsuperconductivity has developed in a far from smoothfashion. Paul Michael Grant explains why this beautiful,elegant and profound phenomenon continues toconfound and baffle condensed-matter physicists today

Paul Michael Grant

is at W2AGZTechnologies,San Jose, California,US, e-mail [email protected], Web www.w2agz.com

Down the path of least resistance

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History credits – erroneously in my opinion – Onnesas the sole discoverer of what he, writing in English,called “supra-conduction”. (Where the work was firstpublished is hard to decipher, although the first reportin English was in the Dutch journal Communicationsfrom the Physical Laboratory at the University of Leiden(120b 1911).) Clearly, the discovery would not havehappened without Onnes, but to publish the work with-out his colleagues as co-authors would be unthinkabletoday. At the very least, the announcement should havebeen made under the names of Onnes and Holst. As ithappens, life panned out well for Holst, who becamethe founding director of the Philips Research Labor-atory in Eindhoven and a distinguished professor atLeiden. But that does not mean that he and othersshould be forgotten as we celebrate the centenary ofthe discovery of superconductivity.

Conforming to type

After the 1911 discovery, research into superconduc-tivity languished for several decades, mainly becauseduplicating the Leiden facility was difficult and ex-pensive. However, research also stalled because thezero-resistance state disappeared so easily when a sam-ple was exposed to even quite modest magnetic fields.The problem was that most early superconductors weresimple elemental metals – or “type I” as they are nowknown – in which the superconducting state exists onlywithin a micron or so of their surface. The ease with

which they became “normal” conductors dashed earlydreams, voiced almost immediately by Onnes andothers, that superconductivity could revolutionize theelectricity grid by allowing currents to be carried with-out any loss of power

However, other labs in Europe – and later in NorthAmerica too – did eventually start to develop their ownliquid-helium cryogenic facilities, and as the monopolyheld at Leiden slowly broke, interest and progress insuperconductivity resumed. In 1933 Walther Meissnerand Robert Ochsenfeld observed that any magneticfield near a superconducting material was totally ex-pelled from the sample once it had been cooled belowthe “transition temperature”, Tc, at which it loses allresistance. The magnetic field lines, which undernormal circumstances would pass straight through thematerial, now have to flow around the superconductor(figure 1). This finding, which came as a total surprise,was soon followed by the observation by Willem Kee-som and J Kok that the derivative of the specific heatof a superconductor jumps suddenly as the material is cooled below Tc. Nowadays observing both thesebizarre effects – “flux expulsion” and the “second-orderspecific-heat anomaly” – is the gold standard for prov-ing the existence of superconductivity. (Legend has it infact that the latter measurements were actually per-formed by Keesom’s wife, who was also a physicist yetdid not get any credit at the time.)

The mid-1930s also saw the discovery by Lev Shub-nikov of superconductivity in metallic alloys – mater-ials in which the critical magnetic field (above whichsuperconductivity disappears) is much higher than insimple elemental metals. The experimental and theor-etical study of these alloys – dubbed “type II” – quicklydominated research on superconductivity, especially inthe Soviet Union under the leadership of Pyotr Kapitsa,Lev Landau and Shubnikov himself. (The latter, whowas Jewish, was imprisoned in 1937 by the secret policeduring the Stalinist purges and later executed, in 1945.)Soviet theoretical efforts on the statistical mechanicsof superconductivity – and the related phenomenon ofsuperfluidity – continued throughout the Second WorldWar and the Cold War, led primarily by the late VitalyGinzburg, Alexei Abrikosov and Lev Gor’kov. Alhoughmuch of it was unknown to the West at the time, theGinzburg–Landau–Abrikosov–Gor’kov, or “GLAG”,model underlies all practical applications of supercon-ductivity. The model is so useful because it is empiricaland thermodynamic in nature, and does not thereforedepend on the microscopic physics underlying a par-ticular second-order phase transition, be it magnetism,superfluidity or superconductivity.

Towards BCS theory

Progress in unravelling the fundamental theory under-pinning superconductivity advanced more slowly. In1935 Fritz and Heinz London proposed a phenom-

For Onnes to publish the discoverywithout his colleagues as co-authorswould be unthinkable today

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enological “adjustment” to Maxwell’s constituentequations to accommodate the notion of a “penet-ration depth” of an externally applied magnetic fieldbeyond the surface of a superconductor (see “The for-gotten brothers” by Stephen Blundell on page 26).However, it was not until the mid-1950s that the the-oretical web surrounding superconductivity was finallyunravelled, having frustrated attempts by some of the20th century’s brightest and best physicists, includingDirac, Einstein, Feynman and Pauli. This feat waseventually accomplished by John Bardeen, LeonCooper and Robert Schrieffer, leading to what is nowcalled BCS theory, for which the trio shared the 1972Nobel Prize for Physics (see box on page 35 for moreon BCS theory). A key development was the deter-mination by Cooper that a gas of electrons is unstablein the presence of any infinitesimal attractive interac-tion, leading to pairs of electrons binding together.Bardeen and his student Schrieffer then realized thatthe resulting quantum state had to be macroscopic andstatistical in nature.

But where did the attractive interaction come from?In 1950 Emanuel Maxwell of the US National Bureauof Standards noticed that the transition temperatureof mercury shifted depending on which of its isotopeswas used in the particular sample, strongly suggestingthat somehow lattice vibrations, or “phonons”, are in-volved in superconductivity. BCS theory proved, giventhe right conditions, that these vibrations – which areusually the source of a metal’s intrinsic resistance –could yield the attractive interaction that allows a ma-terial to conduct without resistance.

Quite simply, BCS theory ranks among the most ele-gant accomplishments of condensed-matter physics.Generally stated, it describes the pairing of two fer-mions mediated by a boson field: any fermions, by anyboson. All known superconductors follow the generalrecipe dictated by BCS, the basic form of which is an

extraordinarily simple expression: Tc∝Θ/e1/λ, where Tcis the transition, or critical, temperature below whicha material superconducts, Θ is the characteristic tem-perature of the boson field (the Debye temperature ifit is comprised of phonons), and λ is the coupling con-stant of that field to fermions (electrons and/or holesin solids). A material with a large value of λ is generallya good candidate for a superconductor even if it is,counterintuitively, a “poor” metal under normal con-ditions with electrons continually bouncing off thevibrating crystal lattice. This explains why sodium, gold,silver and copper, despite being good metals, are notsuperconductors, yet lead is (figure 2).

However, BCS is descriptive and qualitative, notquantitative. Unlike Newton’s or Maxwell’s equationsor the framework of semiconductor band theory, withwhich researchers can design bridges, circuits andchips, and be reasonably assured they will work, BCStheory is very poor at pointing out what materials to useor develop to create new superconductors. For all thatits discovery was an intellectual tour de force, it is theGerman-born physicist Berndt Matthias who perhapssummed the theory up best when he said (in effect) that“BCS tells us everything but finds us nothing”.

Later landmarks

Following the development of BCS theory, one of thenext landmarks in superconductivity was the predic-tion in 1962 by Brian Josephson at Cambridge Uni-versity in the UK that a current could electrically tunnelacross two superconductors separated by a thin insu-lating or normal metal barrier. This phenomenon, nowknown as the Josephson effect, was first observed thefollowing year by John Rowell and Philip Anderson ofBell Laboratories, and resulted in the development ofthe superconducting quantum interference device, orSQUID, which can measure minute levels of magneticfield and also provide an easily replicated voltage stan-

One of the most unusual properties of superconducting materials is what happens when they are placed near a magnetic field. At hightemperatures and field strengths (blue region), the magnetic field lines pass straight through the material as expected. But as Walther Meissnerand Robert Ochsenfeld discovered in 1933, when a superconducting material is cooled below the transition temperature, Tc, at which currentcan flow without resistance, the field lines are expelled from the material and have to pass around the sample – what is known as the “Meissnereffect” (yellow region). Certain superconductors, known as “type II”, can also exist in a “vortex state” (green region), where resistive andsuperconducting sub-regions co-exist. Practical demonstrations of magnetic levitation always use type II superconductors because the magneticvortices are pinned in place, making the magnet laterally stable as it hovers.

mag

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normal state

vortex state

Meissner state Tc

temperature

1 Get out, stay out

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UnlikeNewton’s orMaxwell’sequations, with whichresearcherscan designbridges,circuits andchips, BCStheory is very poor atpointing outwhat materialsto use ordevelop




dard for metrology labs worldwide.For the next landmark in superconductivity, however,

we had to wait more than two decades for Georg Bed-norz and Alex Müller’s serendipitous observation ofzero resistance at temperatures above 30 K in layeredcopper-oxide perovskites. Their discovery of “high-temperature superconductors” at IBM’s Zurich lab in1986 not only led to the pair sharing the 1987 NobelPrize for Physics but also triggered a boom in researchinto the field (see “Resistance is futile” by Ted Forganon page 33). Within a year M K Wu, Paul Chu and their collaborators at the universities of Houston andAlabama had discovered that an yttrium–barium–copper-oxide compound – YBa2Cu3O6.97, also knownas YBCO, although the precise stoichiometry was notknown at the time – could superconduct at an astound-ing 93 K. As this is 16 K above the boiling point of liquidnitrogen, the discovery of these materials allowed re-searchers to explore for the first time applications ofsuperconductivity using a very common and cheap cryo-gen. The record substantiated transition temperaturerests at 138K in fluorinated HgBa2Ca2Cu3O8+d at ambi-ent pressure (or 166 K under a pressure of 23 GPa).

With Bednorz and Müller about to pack their bagsfor Stockholm as the latest researchers to win a Nobelprize for their work on superconductivity, it was ahappy time for those in the field. Literally thousands ofpapers on superconductivity were published that year,accompanied by a now legendary, all-night celebratorysession at the March 1987 meeting of the AmericanPhysical Society in New York City now dubbed “theWoodstock of physics” at which those involved, meincluded, had one hell of a good time.

Technology ahead of its time

Alongside these advances in the science of supercon-ductivity have been numerous attempts to apply thephenomenon to advance old and create new technol-ogies – ranging from the very small (for ultrafast com-puters) to the very large (for generating electricity).Indeed, the period from the 1970s to the mid-1980switnessed a number of technically quite successful de-monstrations of applied superconductivity in the US,Europe and Japan. In the energy sector, perhaps themost dramatic was the development between 1975 and1985 of an AC superconducting electricity cable at theBrookhaven National Laboratory in the US, funded by the Department of Energy and the PhiladelphiaElectric Company. Motivated by the prospect of large-scale clusters of nuclear power plants requiring massivetransmission capacity to deliver their output, the cableattracted a good deal of attention. Although the cableworked, it unfortunately turned out not to be needed asthe US continued to burn coal and began to turn to na-tural gas. Similarly, in Japan, various firms carried outdemonstrations of superconducting cables, generatorsand transformers, all of which proved successful froma technical point of view. These projects were generallysupported by the Japanese government, which at thetime was anticipating a huge surge in demand for elec-tricity because of the country’s growing population.That demand failed to materialize, however, and I knowof no major superconductivity demonstration projectsin Japan today apart from the Yamanashi magnetic-levitation test track, which opened in the mid-1970susing niobium–titanium superconductors.

In 1996 I published a paper “Superconductivity and

Over the last 100 years, an ever bigger range of elements in the periodic table has been found to superconduct. Shown here are those elements that superconduct atambient pressure, shaded according to when this ability was first unearthed (yellow/orange), and those elements that superconduct only at high pressure (purple). Adapted from Superconductivity: A Very Short Introduction by Stephen Blundell (2009, Oxford University Press)

K Ca Sc Ti V

Rb Sr Y Zr Nb

Na Mg

Li Be

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Cs Ba Hf Ta W

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Ce Pr Nd

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Al Si P S Cl Ar

B C N O F Ne

He

Pb Bi Po At Rn

Mn Fe Co Ni Cu

Sg Bh Hs Mt

*

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superconductors at ambient pressure up to 19201921–19301931–19501951–2011

superconductors at high pressure

2 Spreading its wings

physicsworld.com Superconductivity: 100 years of history



electric power: promises, promises…past, present andfuture” (IEEE Trans. Appl. Supercond. 7 1053), in whichI foresaw a bright future for high-temperature super-conductivity. A large number of successful power-equipment demonstrations once more followed, withvarious firms developing superconducting cables, gen-erators, conditioners (transformers and fault-currentlimiters), all of which proved successful. Although few– if any – of these demonstrations have been turnedinto working products, there is nevertheless a lot ofgood, advanced superconductor technology now sit-ting on the shelf for the future, if needed. Unfor-tunately, it has so far not had much of an impact on theenergy industry, which is driven as much by politics andpublic perception as it is by technological elegance.When it comes to the electronics industry, in contrast,price and performance – say of the latest laptop orsmartphone – are everything.

A somewhat similar story accompanies the appli-cation of superconductivity to electronics, a primeexample being computers based on “Josephson junc-tions”, which promised to bring faster CPU speeds dis-sipating less heat than the bipolar silicon technologythat dominated from the 1960s to the early 1980s. IBMand the Japanese government bet heavily on its suc-ceeding, as it did from a technical point of view, butwere blind-sided by the emergence of metal-oxide–silicon field-effect transistors (MOSFETs), which de-livered both goals without requiring cryogenic pack-aging. (Other applications, including my personal topfive, are given in “Fantastic five” on page 23.)

Cool that sample

In January 2001, exactly a year after the dawn of thenew millennium, Jun Akimitsu of Aoyama-GakuinUniversity in Japan announced at a conference ontransition-metal oxides the discovery of superconduc-tivity in magnesium diboride (MgB2) – a material that

had first been successfully synthesized almost 50 yearsearlier at the California Institute of Technology. Aki-mitsu and colleagues had actually been looking forsomething else – antiferromagnetism – in this mater-ial but were surprised to find that MgB2, which has ahexagonal layered structure and can be fabricated withexcellent microcrystalline detail, became supercon-ducting at the astonishingly high temperature of 39 K.The discovery prompted many other researchers tostudy this simple material and, over the past decade,high-performance MgB2 wires have been fabricated.Indeed, MgB2 has the highest upper critical field (abovewhich type II superconductivity disappears) of any ma-terial apart from YBCO, with calculations suggestingthat it remains a superconductor at 4.2 K even whensubjected to massive fields of 200 T.

However, there is an interesting twist to the story. In1957 the chemists Robinson Swift and David White atSyracuse University in New York measured the latticespecific heat of MgB2 between 18 K and 305 K to see if it depended on the square of temperature, just as otherlayered structures do. Their results, which showed no T2 dependence, were published in the Journal of theAmerican Chemical Society not as a graph but as a table.When their data were re-analysed after Akimitsu’s 2001announcement and plotted in graphical form, PaulCanfield and Sergei Bud’ko at Iowa State University (as well as the present author, working independently),were surprised to find a small specific-heat anomaly near38–39 K, indicating the onset of superconductivity.

The question is this: if the Syracuse chemists hadplotted their data and shown it to their physicist col-leagues, would the history of superconductivity fromthe mid-20th century have taken a different course? Tome it is likely that all the niobium intermetallics, such asthe niobium–titanium alloys used in the supercon-ducting magnets in CERN’s Large Hadron Collider,would never have been needed, or even fully developed(figure 3). High-field magnets would have been fabri-cated from MgB2 and perhaps even superconductingpower cables and rotating machinery made from thisordinary material would be in use today.

The lesson is clear: if you think you have a new (orold) metal with unusual structural or chemical proper-ties, do what Holst, Bednorz and Akimitsu did – coolit down. Indeed, Claude Michel and Bernard Raveauat the University of Caen in France had made 123 sto-ichiometric copper-oxide perovskites four years beforeChu, but having no cryogenic facilities at their lab – and,finding it awkward to obtain access to others elsewherein the French national research council system – missedmaking the discovery themselves.

Superconductivity arguably ranks among the ulti-mate in beauty, elegance and profundity, both experi-mentally and theoretically, of all the advances incondensed-matter physics during the 20th century,even if it has to date yielded only a few applications thathave permeated society. Nonetheless, the BCS frame-work that underlies superconductivity appears to reachdeep into the interior of neutron stars as well, with thepairing of fermionic quarks in a gluon bosonic field ex-periencing a transition temperature in the range 109 K.A century after Leiden, in the words of Ella Fitzgerald,“Could you ask for anything more?” ■

3 Round the bend

Superconductors can be found in all sorts of applications, one of the most famous of which isin the dipole magnets at the Large Hadron Collider at CERN. The collider has 1232 suchmagnets, each 15 m long, consisting of coils of superconducting niobium–titanium wire cooledto 1.9 K using liquid helium. Carrying currents of 13 000 A, the magnets generate extremelyhigh fields of 8.3 T, which help to steer the protons around the 27 km circumference collider.

CERN




Perhaps no other potential application ofsuperconductivity has captured the pub-lic’s imagination more than magneticallylevitated (maglev) trains; you can even buytoy models of them. There have also beenscience-fiction-like maglev concepts thatin principle would work, featuring curvedtunnels through the Earth’s mantle,whereby the train first falls on a levitatedtrack, generating electricity as it does sofor the trip back up. Indeed, the first pa-tents on the basic concept date back to1907 – four years before superconductiv-ity was even discovered.

However, every maglev system everbuilt, apart from the Yamanashi test line inJapan, has used conventional technologyinvolving ordinary (albeit powerful) iron-

core electromagnets. Moreover, the topspeed of the Yamanashi superconductingprototype is 581 km h–1, which, despitebeing a world record for mass surfacetransportation, is only 6 km h–1 faster thanthe ordinary wheel-on-rail French TGVtrains. The message is clear: faster surfacetransportation may be important, butsuperconductivity has not – and is unlikelyto – play much of a role in that quest.

So if not maglev, then what have beenthe most significant applications of super-conductivity in terms of their impact onsociety? This article lists a top five selectedby Paul Michael Grant from W2AGZTechnologies in San Jose, California. Su-perconducting wires top the list, followedby magnets for medical imaging and for

particle colliders in second and third, re-spectively, with superconducting motorsin fourth and a unique dark-matter experi-ment in fifth. One other application ofsuperconductors that has not quite madethe cut involves using them in electro-magnets or flywheels to store energy. Suchsuperconducting magnetic-energy storagedevices store energy in the magnetic fieldcreated by an electric current flowing in asuperconducting coil. As almost all theenergy can be recovered instantly, thesedevices are incredibly efficient and wouldbe ideal for storing electricity in the homeshould we be forced to rely much more onrenewable sources of power that are notalways on tap.

But let’s start with those wires…

Superconductivity may be a beautiful phenomenon, but materials that can conduct with zero resistancehave not quite transformed the world in the way that many might have imagined. Presented here are thetop five applications, ranked in terms of their impact on society today

Fantastic five

1 Wires and films

One thing is for sure: there would be no applications of superconductivity ifphysicists and materials scientists had not managed to develop – as theydid in the 1970s – superconducting wires and films made from niobium–titanium and niobium–tin. These materials can carry high currents, even inthe presence of strong magnetic fields, when cooled with liquid helium to atemperature below 4.2 K. They are generally packaged as bundles of wiresin a matrix, allowing them to be sold both as wire filaments and as solidcores encased in copper. They can carry currents of up to 50 A whilewithstanding magnetic fields of 10 T.

Firms such as American Superconductor, SuperPower and Zenergy Power now also make high-temperature superconducting tapefrom yttrium–barium–copper-oxide (YBCO). It is just as robust as low-temperature niobium alloys and can be used for transmission powercables but using liquid nitrogen – not helium – as the cryogen. What isremarkable is that YBCO is a hard and brittle ceramic (like a teacup), yet itcan be made in batches thousands of metres long. This is done bydepositing a continuous film of it onto a specially prepared “texturedsubstrate” base – typically a stainless-steel-like alloy coated with anotherlayer of magnesium oxide or yttrium zirconia.

The resulting technology is truly a tour de force. Indeed, the “uppercritical field” – the maximum field that YBCO tape can be subjected to andstill superconduct – is so high at 4.2 K that it has never been, and probablycannot be, measured. These materials are ideal for use assuperconducting power cables, which could carry electricity without any ofthe power losses that afflict conventional copper cables. (Note thatsuperconductivity is only “perfect” for direct-current transmission; foralternating current there are always losses.)

The US in particular has ploughed much money into this field, largelythrough a 20-year research and development effort funded by theDepartment of Energy that ended in 2010. Its fruits are now on the shelf,

waiting to be harvested by the utility industry and its suppliers. However, itis likely that upgrading and replacing conventional cables will not happenas fast as was once envisaged. Instead, it is likely to occur graduallythrough mega-projects, such as the “SuperGrid” concept, which envisageselectricity from nuclear power stations carried along superconductingcables cooled by hydrogen that is produced by the power plant and thatcould also be used as a fuel (Physics World October 2009 pp37–39).

And the winner is...

Slice of magic Cross-section through a niobium–tin cable.

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physicsworld.com Superconductivity: Top five applications



2 Medical imaging

A peace-time offshoot of the development ofradar in the Second World War was the inventionof nuclear magnetic resonance (NMR), whichcan determine the structure and composition ofmaterials by studying how nuclei, such ashydrogen, with a non-zero spin absorb photonswhen bathed in a magnetic field. By the late1960s, with the development of “tomographic”techniques that can build up 3D X-ray images ofthe human body from a series of individual 2D“slices”, medical physicists realized that NMRcould also be used to study the distribution ofhydrogen nuclei in living tissue. By the late1970s the first full-body magnetic resonanceimaging (MRI) scanners had been developed,which required a constant and uniform magneticfield surrounding the body of about 1 T –something that is only easily practical usingsuperconducting magnets.

MRI has since become perhaps the mostwidespread medical diagnostic tool and there isat least one such scanner in every majorhospital around the world. An MRI solenoidtypically has up to 100 km of niobium–titaniumor niobium–tin wire made from individual wires,each several kilometres long, connected byspecial joints that let the current continue toflow without any losses. Most of these magnetsuse mechanical cryocoolers in place of liquidhelium and thus operate continuously. Onevariant of MRI that is also becoming popular is“functional MRI” (fMRI) – a technique thatneeds twice the magnetic field of “standard”MRI machines (sometimes as high as 4 T). It is used to monitor motion in the human bodyin real time, such as how the flow of blood in the brain changes in response to particularneural activity.

A similar medical scanning technique usessuperconducting quantum interference devices,or SQUIDs, held at liquid-helium temperature, todetect the tiny magnetic fields generated by theexceedingly small currents in the heart or brain.Known as magnetocardiography (when studyingthe heart) or magnetoencepholography (whenstudying the brain), it is non-invasive and doesnot require any equipment to be wired directlyonto the body. Magnetocardiography, which candetect cardiac anomalies that escape routineelectrocardiography, has already undergonenumerous successful clinical trials in the US,Europe and China, although it is not yet widelyused in hospitals.

We should not forget that MRI-scalesuperconducting magnets have also had a bigimpact on condensed-matter physics andmaterials science. Most universities andindustrial laboratories have at least one“physical properties measurement system” thatcan make a variety of transport, magnetic,

optical and microscopy measurements fromroom temperature to 1.2 K (and below) in fieldsof up to 16 T.

3 High-energy physics

Although it might be considered esoteric andunrelated to general human welfare, it could beargued that no human endeavour surpasses thesearch for our origins. Every civilization on ourplanet has devoted a portion of its wealth to that quest – take the pyramids of Giza orTeotihuacan, for example – and today’s largeparticle-physics labs are continuing thattradition. However, particle colliders would benothing without the superconducting magnetsthat bend accelerate particles around in a circle.The Tevatron collider at Fermilab in the US, forexample, has huge bending magnets carryingcurrents of 4000 A that produce magnetic fieldsof about 4.2 T when cooled with liquid helium,while those at the Large Hadron Collider (LHC) atCERN produce fields of roughly twice thatstrength at 1.9 K.

The Tevatron, which is due to close later thisyear, can generate centre-of-mass collisionenergies of 2 TeV, while the LHC can currentlyproduce 7 TeV collisions, with 14 TeV as a longer-term target. Either facility could, in principle,spot the Higgs boson and thus complete the finalpiece of the Standard Model of particle physics,although the LHC, operating at higher energy andstill so new, is more likely to do so.

But what lies beyond the Standard Model?Many high-energy theorists suspect there may be a large energy gap before something“interesting” appears again, which might requirecollision energies of 100–200 TeV or more (i.e. 50–100 TeV per beam). Unfortunately, amachine that could generate these energies andthat is no bigger than a conventional collider

such as the LHC (i.e. with a circumference ofabout 27 km) would lose most of its beamenergy in the form of synchrotron X-rays. (Such X-rays can, though, be extremely useful tocharacterize materials, which is why there arenow 50 or so dedicated synchrotron radiationfacilities around the world, most of which havesuperconducting magnets.)

Interestingly, however, Fermilab physicistBill Foster, now a member of the US House ofRepresentatives, and his colleagues haveproposed revisiting an old idea by Robert Wilson,Fermilab’s first director. It would involve simplysaturating a 2 T iron magnet with a high-temperature superconducting cable cooled withliquid nitrogen and carrying a current of75 000 A. The snag is that reaching energies of50 TeV would require a ring with a circumferenceof about 500 km. Such a large project would bedifficult to carry out in areas of significantpopulation, but in principle would be possible todeploy in more remote areas. As ever, all it wouldtake is money.

4 Rotating machinery

Superconducting materials have long beentouted as having a bright future in motors andgenerators. The problem is that conventionalmotors are currently quite good at convertingelectrical power into rotational power – being upto 95% efficient for large 100 kW–1000 MWindustrial devices. Replacing the rotatingelectromagnet (i.e. the rotor) in a motor with asuperconducting material might increase theconversion by 2%, but this will hardly makemuch difference.

Nevertheless, in 1983 the Electric PowerResearch Institute (EPRI) in the US, working withWestinghouse Electric Company, successfullydemonstrated a 300 MW electric generator using

Best of the rest

Take a picture A magnetic-resonance-imaging scanner uses small superconducting magnet coils toproduce detailed images of any part of the body.

Interconnected A welder works on the junctionbetween two of the Large Hadron Collider’ssuperconducting-magnet systems.

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physicsworld.comSuperconductivity: Top five applications



niobium–titanium wire kept at 5 K. Similar effortswere carried out at the Massachusetts Instituteof Technology, while in 1988 the Japanesegovernment inaugurated the “Super-GM” project,which sought to provide superconductinggenerators to meet Japan’s growing electricityneeds. However, when the country’s powerdemands failed to materialize, the project,despite having succeeded from a technical pointof view, never got off the ground and was neverdeployed by Japan’s electricity utilities.

The tangible advantage of usingsuperconducting wires – whether of the low- orhigh-temperature variety – in rotating machinesis that they significantly reduce the amount ofiron required, which normally forms the core ofconventional electromagnets. Removing the ironin this way makes the generator lighter, smallerand so more efficient. These advantages havebeen fully recognized for many years by the US military, which has a culture in which theeffectiveness of a given technology outweighsthe cost. However, despite several successfuldemonstrations of propulsion motors by the US Navy using low-temperature materials, itultimately did not adopt them.

The winds are now shifting. The US Navy is on the verge of using high-temperaturesuperconducting “degaussing” cables on all ofits light, high-speed destroyer-class ships toshield them from being detected by enemysubmarines. (These cables are simply loops thatcreate a magnetic field, which cancels that fromthe iron components of the ship.) Moreover,high-temperature superconducting motors arealso likely to be deployed as “outboard” units onUS submarines and surface attack resources. Ifso, we are likely to see such devices “trickledown” to holiday cruise ships and commercialvessels. Finally, superconducting generators are

also likely to find themselves used in windturbines, greatly reducing the ecological impactof wind farms. In the far future, we might evensee superconducting motors – and possiblymagnetohydrodynamic pumps – used totransport water from wet to dry areas to adapt tothe effects of global warming.

5 Dark matter

As Physics World readers will surely know, muchof the mass in our galaxy, and others too, ismissing, or at least we cannot “see” it. That is,astronomers have observed deviations in therotational motion of galaxies that cannot beaccounted for by ordinary matter that we canobserve simply by using electromagneticradiation. It turns out that about four-fifths of thematter in the universe is invisible “dark matter”.(All matter, dark or otherwise, makes up about27% of the mass–energy density of the universe,with the other 73% being “dark energy”, but thatis another story…) The exact nature of darkmatter is, of course, still not clear, which meansthat finding out is one of the big challenges ofphysics and indeed a central questionunderlying our existence.

Dark matter is a field wrought by, or fraughtwith, considerable confusion and debate. Eventhe names of the particles that could form darkmatter are bizarre – from MACHOs, RAMBOs andWIMPs to chameleons and axions, to name but afew. Where superconductivity fits in is in thesearch for axions, which are postulated to resultfrom the assumed violation of charge–paritysymmetry under strong coupling within theStandard Model. The idea is that when axions ofa given mass–energy (in the μeV to meV range)enter a microwave cavity sited in a 5–7 Tmagnetic field from a liquid-helium-cooledsuperconducting solenoid, they will interact withthe field and decay into photons. These photonscan then be amplified and detected usingSQUIDs operating at 2 K. The rationale for usingSQUIDs is that they lower the noise level, andthus sensitivity, to as close to the ultimate limitset by Planck’s constant as possible.

Such experiments are not science fiction butare already under way as part of the Axion DarkMatter Experiment (ADMX) collaboration,previously located at the Lawrence LivermoreNational Laboratory and now at the University ofWashington in the US. The superconductingmagnet at the heart of the device consists ofniobium–titanium wire wrapped 37 700 timesaround the core, which has a bore of 60 cm.Although ADMX has not yet managed to detectany axions, we do know that, if they exist, theycannot have masses in the 3.3–3.53 × 10–6 eVrange. Detection of axions at any energyanywhere will surely earn someone a Nobel prizeand tickets to Stockholm. Stay tuned.

.

A peek inside The cavity at the centre of the Axion DarkMatter Experiment contains a niobium–titaniumsuperconducting magnet.

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physicsworld.com Superconductivity: Top five applications



http://www.cryocon.com


In 1934 two brothers Fritz and Heinz London, bothrefugees from Nazi Germany, were working in an up-stairs room in a rented house in Oxford. There theysolved what was then one of the biggest problems insuperconductivity, a phenomenon discovered 23 yearsearlier. The moment of discovery seems to have beensudden: Fritz shouted down to his wife “Edith, Edithcome, we have it! Come up, we have it!” She later re-called, “I left everything, ran up and then the door wasopened into my face. On my forehead I had a bruise fora week.” As Edith recovered from her knock, Fritz toldher with delight “The equations are established – wehave the solution. We can explain it.”

Though the discovery of what are now known as “theLondon equations” came in a dramatic flash of inspi-ration, the brothers’ ideas had been gestating for sometime and their new intellectual framework would latermature through subsequent work by older brother Fritz.John Bardeen, who won his second Nobel prize in 1972for co-developing the Bardeen–Cooper–Schrieffer(BCS) theory that provided a coherent framework for understanding superconductivity, regarded theachievement of the London brothers as pivotal. “By farthe most important step towards understanding thephenomena”, Bardeen once wrote, “was the recogni-

tion by Fritz London that both superconductors andsuperfluid helium are macroscopic quantum systems.”Before then, quantum theory had only been thought toaccount for the properties of atoms and molecules atthe microscopic level. As Bardeen explained, “It wasFritz London who first recognized that superconduc-tivity and superfluidity result from manifestations ofquantum phenomena on the scale of large objects.”

But despite Fritz’s leading role in the breakthroughthat solved one of the knottiest conundrums of theearly 20th century, he did not secure a permanent jobat the University of Oxford once his temporary con-tract was up. Only two years later he was forced to upsticks and continue his postdoctoral wanderings. Itmight seem strange that such a bright spark was notsnapped up, but even more surprising, perhaps, is thelack of recognition that the London brothers receivetoday. Like most institutions, Oxford has a culture ofcelebrating famous physicists of the past who haveworked there, some of whom it has to be admittedhave only had a rather tenuous connection with theplace. But among the rows of photographs lining thewalls of the Clarendon Laboratory, the London bro-thers are nowhere to be seen. How has this omissionof recognition happened?

Stephen Blundell tells of how Fritz London and his younger brother Heinz cracked the decades-longmystery of superconductivity, but wonders why their achievement is still overlooked today

Stephen Blundell isa professor of physicsat the University ofOxford and the authorof Superconductivity:A Very ShortIntroduction, [email protected]

The forgotten brothers

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physicsworld.comSuperconductivity: Fritz and Heinz London


PWApr11blundell 15/3/11 16:55 Page 26


From Breslau to Oxford

Fritz London was born in 1900 in the German city ofBreslau (now Wroclaw, Poland) and nearly became aphilosopher. However, he switched to physics and be-came immersed in the heady intellectual atmosphereof the 1920s that surrounded the new quantum theory.London’s early career saw him travelling around Ger-many, taking positions with some of the great quantumpioneers of the time: Max Born in Göttingen; ArnoldSommerfeld in Munich; and Paul Ewald in Stuttgart.London worked on matrix mechanics and studied howthe newly discovered operators of quantum mechan-ics behave under certain mathematical transforma-tions, but he really made his name after moving again to Zurich in 1927. The lure of Zurich had been to workwith Erwin Schrödinger, but almost immediatelySchrödinger moved to Berlin and London teamed upwith Walter Heitler instead. Together they producedthe Heitler–London theory of molecular hydrogen – abold and innovative step that essentially founded thediscipline of quantum chemistry.

The following year London moved to Berlin, wherehe worked on intermolecular attraction and originatedthe concept of what are now known as London disper-sion forces. He also succumbed to the interpersonalattraction of Edith Caspary, whom he married in 1929.By now the name “Fritz London” was becoming wellknown – he was fast gaining a reputation as a creativeand productive theorist. However, with Hitler becom-ing German chancellor in 1933, the Nazis began aprocess of eliminating the many Jewish intellectualsfrom the country’s academic system, putting both Lon-don and his younger brother Heinz at risk. Born inBonn in 1907, Heinz had followed in his older brother’sfootsteps, studying physics, but became an experimen-talist instead, obtaining his PhD under the famous low-temperature physicist Franz Simon.

A possible way out from the Nazi threat was providedby an unlikely source. Frederick Lindemann, later tobecome Winston Churchill’s wartime chief scientificadviser and to finish his days as Viscount Cherwell, wasthen the head of the Clarendon Laboratory. Linde-mann was half-German and had received his PhD inBerlin, so was well aware of the political situation inGermany. He decided to do what he could to provide asafe haven in Oxford for refugee scientists. His motiveswere not entirely altruistic, however: Oxford’s physicsdepartment was then a bit of an intellectual backwaterand this strategy would effect an instantaneous invig-oration of its academic firepower in both theoreticaland experimental terms. Later that year Lindemannpersuaded the chemical company ICI to come up withfunds to support his endeavour.

Lindemann initially lured both Schrödinger andAlbert Einstein to Oxford, although Einstein quicklymoved on to Princeton University in the US. Simonalso came, bringing with him Heinz London as his as-sistant as well as Nicholas Kurti (later to be a pioneer ofboth microkelvin cryogenics and the application ofphysics to gastronomy). But Lindemann also wanted atheorist and admired Fritz London as a no-nonsense,practical sort of person who was able to work on down-to-earth problems. Thus both London brothers endedup in Oxford, Heinz sharing a rented house with his

brother and sister-in-law. Fritz was the superior the-orist but Heinz had deep insight into, and a great lovefor, thermodynamics, something that he had picked upfrom Simon. He frequently quipped “For the secondlaw, I will burn at the stake.” With Simon’s arrival inOxford, and the installation there of the first heliumliquefier in Britain, experimental research began onlow-temperature physics, leading Fritz London to workon superconductivity.

The quest to understand superconductivity

The discovery of superconductivity in April 1911 byHeike Kamerlingh Onnes and Gilles Holst was the in-evitable consequence of Onnes devoting many years tothe development of the cryogenic technology neededto achieve low temperatures. With Onnes’s laboratoryin Leiden being the first to liquefy helium came the firstchance to explore how materials behave in such extremelow-temperature conditions. The disappearance ofelectrical resistance in a sample of mercury was an un-expected shock, but in retrospect it was an inevitableconsequence of having developed a far-reaching newtechnology that opened up an unexplored world.

But nobody knew how this new effect worked. Fordecades theorists tried and failed to come up with an

Some 23 years after the discovery of superconductivity, Fritz and Heinz Londondescribed how superconductors interact with electromagnetic fields. In doing so theyintroduced two equations that now bear their name. Their first equation is E∝ d J/dtand relates electric field, E, to current density, J, where t is time, and supersedesOhm’s law (E =ρJ, where ρ is the resistivity). Using Maxwell’s equations it can beshown that this leads to ∇2(dB/dt) = (dB/dt)/λ2, which predicts blocking out or“screening” of time-varying magnetic fields on a length scale λ. This is enough toexplain the Meissner effect, which shows that the magnetic field, B, itself is screened.

In 1935 the London brothers argued that a more fundamental relation is given bytheir second equation, ∇× J∝– B, which, using Maxwell’s equations, gives ∇2B = B/λ2. This predicts screening of the magnetic field itself, so that an externalmagnetic field can only penetrate into the surface of a superconductor over a lengthscale λ, which is now called the London penetration depth. Fritz London later realizedthat the locking of all carriers into a single momentum state yields the relationJ = –(nq2/m)A, where there are n carriers per unit volume, each with mass m andcharge q. This equation linking current density and the magnetic vector potential, A,is probably the best summary of the London theory.

The London legacy begins

Family affair Left, Fritz London (1900–1954) and, right, his brother Heinz (1907–1970).

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Physics World Apri l 2011 27


explanation. Felix Bloch is remembered for his epony-mous theorem about waves in periodic potentials, buthis failure to make progress with understanding super-conductivity reduced him to formulate a tongue-in-cheek statement that also became known at the time as Bloch’s theorem: “the only theorem about super-conductivity that can be proved is that any theory of su-perconductivity is refutable” or, more succinctly,“superconductivity is impossible”.

The crucial clue came from the famous 1933 experi-ment of Walther Meissner and Robert Ochsenfeld.They showed that a superconductor cooled to below itstransition temperature in an applied magnetic fieldsuddenly expels that magnetic field. In this “Meissnereffect”, surface superconducting electrical currents(supercurrents) flow around the superconductor insuch a way as to shield the interior from the appliedmagnetic field. These circulating supercurrents opposethe applied magnetic field, so that deep within thesuperconductor the magnetic field is close to zero – aneffect known as perfect diamagnetism. Fritz Londonrealized that this perfect diamagnetism is even morecentral to the behaviour of a superconductor than per-fect conductivity. Until then perfect conductivity hadbeen thought of as the superconductor’s defining qual-ity – hence the name – but London realized that it ismore of a by-product. While others had been trying to figure out how to formulate a new Ohm’s law for asuperconductor, in other words to find a relationshipbetween electric current and electric field, London sawthat what was needed was a new relation between elec-tric current and magnetic field.

Existing theories had postulated some sort of accel-eration equation: an electric field might not drive a cur-rent (as it does in a conventional metal) but it mightcause one to accelerate. The perfect conductivity in asuperconductor meant that there could be no electricfield, but this absence of an electric field could be con-

sistent with an already accelerated current of carriers.However, the equations that described this situationonly led to a screening of time-varying magnetic fieldsand not time-independent ones, as evidently screenedin the Meissner–Ochsenfeld experiment, and so did notaccount for the observations.

The London brothers instead insisted that the fun-damental principle of superconductivity is the expul-sion of magnetic fields. It was their conviction in thisline of thought that led to their 1934 eureka moment –the one that caused Edith London’s bruised forehead.They postulated an equation that links the magneticfield to the electric current density and produces therequired screening of static magnetic fields and hencethe Meissner effect (see box on page 27). This equationand the brothers’ modified version of an accelerationequation became known as the London equations,which they published in 1935 (Proc. R. Soc. A 149 71).Their theory also predicted a length scale over which amagnetic field can penetrate through the surface of asuperconductor, which became known as the Londonpenetration depth (figure 1).

When the money runs out

In formulating their theory, the London brothers madethe most significant progress in our understanding ofsuperconductors in the first half of the 20th century.However, their situation at Oxford was precarious.Their 1935 paper contains a fulsome acknowledgmentto “Professor F A Lindemann, FRS, for his kind hos-pitality at the Clarendon Laboratory” and also to “Im-perial Chemical Industries whose generous assistanceto one of us has enabled us to undertake this work”.However, the hospitality and generosity were comingto an end.

By 1936 the ICI money that had funded the refugeescientists had dried up and Lindemann could not findfunds to offer positions to all of them: he had to make

The London penetration depth, which is the distance a magnetic field can penetrate into a superconductor, can be inferred using various experimental techniques. Sincethe 1990s, Elvezio Morenzoni and co-workers at the Paul Scherrer Institute in Switzerland have developed a method of measuring it directly. They use spin-polarizedpositive muons as a probe. These particles are slowed or “moderated” to a low energy and then reaccelerated into the surface of a superconductor by applying a voltageto it. By varying this voltage, the muons can be implanted at different depths. A magnetic field is then applied and the spin of the muon precesses at a rate that dependson the field it experiences. Measuring this rotational speed of the spin of the muon yields the magnetic field inside the superconductor at different depths, and hence theLondon penetration depth can be extracted.

moderator

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physicsworld.comSuperconductivity: Fritz and Heinz London



a choice. Heinz was in a junior position without anyexpectation of remaining at Oxford, and so took anappointment at the University of Bristol, but Fritzentertained hopes of staying on. Schrödinger was a bigname and was clearly a high priority for Lindemann tokeep, though Schrödinger subsequently left anywayand settled in Dublin. Lindemann also wanted to retainthe famous Simon. Fritz London, who had apparentlyonly produced some obscure theoretical work with hisbrother, which few at Oxford really understood, wastold that his contract was at an end.

Fritz therefore accepted an offer of another tempor-ary research position in Paris, where he stayed for threeyears, eventually leaving for a permanent academicposition at Duke University in North Carolina. Fritzand his wife departed from France in September 1939,though because of their German passports they werenot permitted to sail on the ship they had planned toboard and they were forced to take a later one. This wasjust as well, as German U-boats torpedoed the earliership, with great loss of life.

Macroscopic quantum coherence

Through work begun in Oxford and furthered in Paris,Fritz London grasped that superconductivity is anexample of quantum coherence writ large – not on thescale of a single atom a fraction of a nanometre across,but on the scale of a piece of superconducting wirecentimetres across. He coined the phrase macroscopicquantum phenomenon to categorize superconductiv-ity: a macroscopic sample of superconductor behaveslike a giant atom.

In a normal metal, electrons have the freedom tooccupy many different quantum states, but Londonrealized that the carriers in a superconductor are farmore constrained. As London put it: “If the various su-percurrents really were to correspond to a continuumof different quantum states, it would seem extremely

hard to understand how a supercurrent could resist somany temptations to dissipate into other states.” Bylocking all the carriers into a single quantum state thesupercurrent is fixed to a single value and has no free-dom to do anything else. This means that a supercur-rent flowing around a loop of wire keeps going on andon, endlessly circulating without dissipation.

London noticed that this behaviour is reminiscent ofthe orbits of electrons around an atom: the energy andangular momentum of an electron in an atom are re-stricted to certain quantized values, because the elec-tronic wavefunction is coherent around the atom. In1948, still at Duke, he deduced that because the wave-function in a superconductor is coherent, somethingsimilar must occur. If one takes a loop of supercon-ducting wire with a current flowing endlessly round it,London showed that the magnetic flux penetrating theloop should be quantized to certain fixed values (figure2). A supercurrent travelling in a loop produces a mag-netic field that is a precise signature of that supercur-rent, and the quantization of magnetic flux is intimatelyrelated to the nailing down of that supercurrent to a single quantum state. London calculated that thequantum of magnetic flux would be exceedingly tinyand thus impossible to observe with techniques avail-able at the time. In fact, it was not until 1961, four yearsafter London’s death in 1957, that magnetic flux quan-tization was experimentally observed by Robert Dolland Martin Näbauer, and, independently, by Bascom SDeaver Jr and William Fairbank.

By that time, the remarkable achievement of Bar-deen, Robert Cooper and Leon Schrieffer had pro-vided the world with a wonderfully complete theory ofsuperconductivity that explained most of the proper-ties that had been measured so far. The edifice of BCStheory was built squarely on the foundations providedby Fritz London and his concept of a coherent andrigid wavefunction. London’s vision of macroscopicquantum coherence, where the subtle absurdities ofquantum mechanics are writ large, is now a firmlyestablished part of physics, but is no less wonderful orsurprising for that.

Bardeen demonstrated his respect for Fritz London’swork by using his cut of the 1972 Nobel prize (he alsoshared the 1956 prize for discovering the transistor) tofund the Fritz London memorial prize, which recog-nizes outstanding contributions to low-temperaturephysics. Duke University has a chair named in hishonour, and Fritz London’s life has been recorded inKostas Gavroglu’s superb 1995 biography. But what isstriking is how little known the London brothers are,and in particular the lack of recognition they receivetoday at the very institution where they came up withthose paradigm-changing equations. Perhaps the rea-son is that Lindemann, who was inordinately proud ofhis achievement in getting various Jewish scientists outof Germany in the 1930s, did not want to be remindedof the one he was forced to get rid of. In this centenaryyear of superconductivity I am ensuring that photo-graphs of the London brothers will be hung in theClarendon Laboratory, and am enthusiastic about pub-licizing their remarkable contribution to making quan-tum mechanics move out of the microscopic world ofatoms and into our own. ■

The magnetic flux through a hole in a superconductor is related to thesupercurrent around the inside of the hole. Because the supercurrent(light blue) is phase coherent, the phase of the wavefunction mustwind an integer number of times around the loop (shown schematicallyby yellow and purple rods), which leads to the magnetic flux (red)being quantized. The number of times the wavefunction winds roundthe loop – here three – is equal to the number of magnetic flux quantathrough the loop.

2 Magnetic flux quanta In formulatingtheir theory, theLondon brothersmade the most significantprogress in ourunderstanding ofsuperconductorsin the first half ofthe 20th century

physicsworld.com Superconductivity: Fritz and Heinz London



Superconductivity at 100

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1908 and 1911

Heike Kamerlingh Onnes wins the race against James Dewar to liquefy helium (1908), then discovers zero resistance in mercury with Gilles Holst (1911)

1933

Walther Meissner and Robert Ochsenfeld discover that magnetic fields are expelled from superconductors. This “Meissner effect” means that superconductors can be levitated above magnets

1935

Brothers Fritz and Heinz London make a long-awaited theory breakthrough, formulating two equations that try to describe how superconductors interact with electromagnetic fields

1931

Wander Johannes de Haas and Willem Keesom discover superconductivity in an alloy

1957

John Bardeen, Leon Cooper and Robert Schrieffer publish their (BCS) theory, which builds on the idea of Cooper pairs proposed the previous year, and describes all the electrons together as one wavefunction. The theory predicts that superconductivity cannot occur much above 20 K

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In the 100 years since the discovery of superconductivity, progress has come in fits and starts. The graphic below shows various types of superconductor sprouting into existence, from the conventional superconductors to the rise of the copper oxides, as well as the organics and the most recently discovered iron oxides. Experimental progress has relied on fortuitous guesses, while it was not until 1957 that theorists were finally able to explain how current can flow indefinitely and a magnetic field can be expelled. The idea that the theory was solved was overturned in 1986 with the discovery of materials that superconduct above the perceived theoretical limit, leaving theorists scratching their heads to this day. In this timeline, Physics World charts the key events, the rise in record transition temperatures and the Nobel Prizes for Physics awarded for progress in superconductivity.

1962

Brian Josephson predicts that a current will pass between two superconductors separated by an insulating barrier. Two of these “Josephson junctions” wired in parallel form a superconducting quantum interference device (SQUID) that can measure very weak magnetic fields

2006

Hideo Hosono and colleagues discover superconductivity in an iron compound. The highest Tc found in these materials to date is 55 K

1987

Paul Chu and his team break the 77 K liquid-nitrogen barrier and discover superconductivity at 93 K in a compound containing yttrium, barium, copper and oxygen, now known as “YBCO”

1986

Georg Bednorz (right) and Alexander Müller (left) find superconductivity at 30 K, over the 20 K limit of BCS theory, and not in a metal, but a ceramic

2001

Jun Akimitsu announces that the cheap and simple chemical magnesium diboride (MgB2) superconducts up to 39 K

1981

Superconductivity is found by Klaus Bechgaard and colleagues in a salt – the first organic material to superconduct at ambient pressure. To date the organic superconductor with the highest Tc is Cs3C60 at 38 K

1957

John Bardeen, Leon Cooper and Robert Schrieffer publish their (BCS) theory, which builds on the idea of Cooper pairs proposed the previous year, and describes all the electrons together as one wavefunction. The theory predicts that superconductivity cannot occur much above 20 K

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My involvement with high-temperature superconduc-tors began in the autumn of 1986, when a student in myfinal-year course on condensed-matter physics at theUniversity of Birmingham asked me what I thoughtabout press reports concerning a new superconductor.According to the reports, two scientists working inZurich, Switzerland – J Georg Bednorz and K AlexMüller – had discovered a material with a transitiontemperature, Tc, of 35 K – 50% higher than the previ-ous highest value of 23 K, which had been achievedmore than a decade earlier in Nb3Ge.

In those days, following this up required a walk to theuniversity library to borrow a paper copy of the ap-propriate issue of the journal Zeitschrift für Physik B. I

reported back to the students that I was not convincedby the data, since the lowest resistivity that Bednorz andMüller (referred to hereafter as “B&M”) had observedmight just be comparable with that of copper, ratherthan zero. In any case, the material only achieved zeroresistivity at ~10 K, even though the drop began at themuch higher temperature of 35 K (figure 1).

In addition, the authors had not, at the time they sub-mitted the paper in April 1986, established the com-position or crystal structure of the compound theybelieved to be superconducting. All they knew was thattheir sample was a mixture of different phases con-taining barium (Ba), lanthanum (La), copper (Cu) andoxygen (O). They also lacked the equipment to test

A quarter of a century ago, they were the hottest thing in physics, with a 1987 conference session aboutthem going down in history as “the Woodstock of physics”. So what happened next for high-temperaturesuperconductors? Ted Forgan recalls those euphoric early days and assesses the remaining challengesin this still-developing field

Ted Forgan is acondensed-matterphysicist at theUniversity ofBirmingham, UK, e-mail [email protected]

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whether the sample expelled a magnetic field, which isa more fundamental property of superconductors thanzero resistance, and is termed the Meissner effect. Nowonder B&M had carefully titled their paper “Possiblehigh Tc superconductivity in the Ba–La–Cu–O system”(my italics).

My doubt, and that of many physicists, was causedby two things. One was a prediction made in 1968 bythe well-respected theorist Bill McMillan, who pro-posed that there was a natural upper limit to the poss-ible Tc for superconductivity – and that we wereprobably close to it. The other was the publication in1969 of Superconductivity, a two-volume compendiumof articles by all the leading experts in the field. As one of them remarked, this book would represent “thelast nail in the coffin of superconductivity”, and so itseemed: many people left the subject after that, feelingthat everything important had already been done inthe 58 years since its discovery.

In defying this conventional wisdom, B&M basedtheir approach on the conviction that superconductivityin conducting oxides had been insufficiently exploited.They hypothesized that such materials might harboura stronger electron–lattice interaction, which wouldraise the Tc according to the theory of superconductivityput forward by John Bardeen, Leon Cooper and Robert

Schrieffer (BCS) in 1957 (see box on page 35). For twoyears B&M worked without success on oxides that con-tained nickel and other elements. Then they turned tooxides containing copper – cuprates – and the resultswere as the Zeitschrift für Physik B paper indicated: atantalizing drop in resistivity.

What soon followed was a worldwide rush to build onB&M’s discovery. As materials with still higher Tc werefound, people began to feel that the sky was the limit.Physicists found a new respect for oxide chemists asevery conceivable technique was used first to measurethe properties of these new compounds, and then toseek applications for them. The result was a blizzard ofpapers. Yet even after an effort measured in many tensof thousands of working years, practical applicationsremain technically demanding, we still do not properlyunderstand high-Tc materials and the mechanism oftheir superconductivity remains controversial.

The ball starts rolling

Although I was initially sceptical, others were moreaccepting of B&M’s results. By late 1986 Paul Chu’sgroup at the University of Houston, US, and ShojiTanaka’s group at Tokyo University in Japan had con-firmed high-Tc superconductivity in their own Ba–La–Cu–O samples, and B&M had observed the Meissnereffect. Things began to move fast: Chu found that bysubjecting samples to about 10 000 atmospheres ofpressure, he could boost the Tc up to ~50 K, so he alsotried “chemical pressure” – replacing the La with thesmaller ion yttrium (Y). In early 1987 he and his col-laborators discovered superconductivity in a mixed-phase Y–Ba–Cu–O sample at an unprecedented 93 K –well above the psychological barrier of 77 K, the boil-ing point of liquid nitrogen. The publication of thisresult at the beginning of March 1987 was preceded bypress announcements, and suddenly a bandwagon wasrolling: no longer did superconductivity need liquidhelium at 4.2 K or liquid hydrogen at 20 K, but insteadcould be achieved with a coolant that costs less thanhalf the price of milk.

Chu’s new superconducting compound had a rather different structure and composition than the onethat B&M had discovered, and the race was on tounderstand it. Several laboratories in the US, theNetherlands, China and Japan established almostsimultaneously that it had the chemical formulaYBa2Cu3O7–d, where the subscript 7–d indicates a vary-ing content of oxygen. Very soon afterwards, its exactcrystal structure was determined, and physicists rapidlylearned the word “perovskite” to describe it (see boxon page 37). They also adopted two widely used abbre-viations, YBCO and 123 (a reference to the ratios of Y,Ba and Cu atoms) for its unwieldy chemical formula.

The competition was intense. When the Dutch re-searchers learned from a press announcement thatChu’s new material was green, they deduced that thenew element he had introduced was yttrium, which cangive rise to an insulating green impurity with the chem-ical formula Y2BaCuO5. They managed to isolate thepure 123 material, which is black in colour, and theEuropean journal Physica got their results into printfirst. However, a group from Bell Labs was the first tosubmit a paper, which was published soon afterwards

Adapted from J Georg Bednorz and K Alex Müller’s landmark paper, thisgraph heralded the beginning of high-temperature superconductivity. It shows that the resistivity of their barium–lanthanum–copper-oxidecompound rises as its temperature is reduced, reaching a value about5000 times that of copper before it begins to fall at ~35 K. Suchbehaviour is quite different from that of simple metals, for which theresistivity generally falls smoothly as the temperature is reduced, with a sharp drop to zero if they become superconducting. The circlesand crosses represent measurements at low and high currentdensities, respectively.

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Superconductivityno longer neededliquid helium orliquid hydrogen,but instead couldbe achieved witha coolant thatcosts less thanhalf the price of milk

physicsworld.comSuperconductivity: High-temperature materials



in the US journal Physical Review Letters. This raceillustrates an important point: although scientists mayhigh-mindedly and correctly state that their aim anddelight is to discover the workings of nature, the desireto be first is often a very strong additional motivation.This is not necessarily for self-advancement, but for thebuzz of feeling (perhaps incorrectly in this case) “I’mthe only person in the world who knows this!”.

“The Woodstock of physics”

For high-Tc superconductivity, the buzz reached feverpitch at the American Physical Society’s annual“March Meeting”, which in 1987 was held in New York.The week of the March Meeting features about 30 gru-elling parallel sessions from dawn till after dusk, wherea great many condensed-matter physicists present theirlatest results, fill postdoc positions, gossip and net-work. The programme is normally fixed months inadvance, but an exception had to be made that year anda “post-deadline” session was rapidly organized for theWednesday evening in the ballroom of the HiltonHotel. This space was designed to hold 1100 people,but in the event it was packed with nearly twice thatnumber, and many others observed the proceedingson video monitors outside.

Müller and four other leading researchers gave talksgreeted with huge enthusiasm, followed by more than50 five-minute contributions, going on into the smallhours. This meeting gained the full attention of thepress and was dubbed “the Woodstock of physics” in

recognition of the euphoria it generated – an echo ofthe famous rock concert held in upstate New York in1969. The fact that so many research groups were ableto produce results in such a short time indicated thatthe B&M and Chu discoveries were “democratic”,meaning that anyone with access to a small furnace (oreven a pottery kiln) and a reasonable understanding ofsolid-state chemistry could confirm them.

With so many people contributing, the number ofpapers on superconductivity shot up to nearly 10 000 in1987 alone. Much information was transmitted infor-mally: it was not unusual to see a scientific paper with“New York Times, 16 February 1987” among the refer-ences cited. The B&M paper that began it all has beencited more than 8000 times and is among the top 10most cited papers of the last 30 years. It is noteworthythat nearly 10% of these citations include misprints,which may be because of the widespread circulation offaxed photocopies of faxes. One particular misprint, anincorrect page number, occurs more than 250 times,continuing to the present century. We can trace thisparticular “mutant” back to its source: a very early andmuch-cited paper by a prominent high-Tc theorist.Many authors have clearly copied some of their cita-tions from the list at the end of this paper, rather thangoing back to the originals. There have also been nu-merous sightings of “unidentified superconductingobjects” (USOs), or claims of extremely high transitiontemperatures that could not be reproduced. One sus-pects that some of these may have arisen when a voltage

Although superconductivity was observed for thefirst time in 1911, there was no microscopictheory of the phenomenon until 1957, when John Bardeen, Leon Cooper and Robert Schrieffermade a breakthrough. Their “BCS” theory – whichdescribes low-temperature superconductivity,though it requires modification to describe high-Tc – has several components. One is theidea that electrons can be paired up by a weakinteraction, a phenomenon now known asCooper pairing. Another is that the “glue” thatholds electron pairs together, despite theirCoulomb repulsion, stems from the interaction of electrons with the crystal lattice – as describedby Bardeen and another physicist, David Pines, in 1955. A simple way to think of this interactionis that an electron attracts the positively chargedlattice and slightly deforms it, thus making apotential well for another electron. This is ratherlike two sleepers on a soft mattress, who each roll into the depression created by the other. It is this deforming response that caused Bill McMillan to propose in 1968 that thereshould be a maximum possible Tc: if theelectron–lattice interaction is too strong, thecrystal may deform to a new structure instead ofbecoming superconducting.

The third component of BCS theory is the ideathat all the pairs of electrons are condensed intothe same quantum state as each other – like the

photons in a coherent laser beam, or the atomsin a Bose–Einstein condensate. This is possibleeven though individual electrons are fermionsand cannot exist in the same state as each other,as described by the Pauli exclusion principle.This is because pairs of electrons behavesomewhat like bosons, to which the exclusionprinciple does not apply. The wavefunctionincorporating this idea was worked out bySchrieffer (then a graduate student) while hewas sitting in a New York subway car.

Breaking up one of these electron pairsrequires a minimum amount of energy, Δ, perelectron. At non-zero temperatures, pairs areconstantly being broken up by thermalexcitations. The pairs then re-form, but when they

do so they can only rejoin the state occupied bythe unbroken pairs. Unless the temperature isvery close to Tc (or, of course, above it) there isalways a macroscopic number of unbrokenpairs, and so thermal excitations do not changethe quantum state of the condensate. It is thisstability that leads to non-decayingsupercurrents and to superconductivity. BelowTc, the chances of all pairs getting broken at thesame time are about as low as the chances thata lump of solid will jump in the air because allthe atoms inside it are, coincidentally, vibratingin the same direction. In this way, the BCS theorysuccessfully accounted for the behaviour of“conventional” low-temperaturesuperconductors such as mercury and tin.

It was soon realized that BCS theory can begeneralized. For instance, the pairs may be heldtogether by a different interaction than thatbetween electrons and a lattice, and twofermions in a pair may have a mutual angularmomentum, so that their wavefunction varieswith direction – unlike the spherically symmetric,zero-angular-momentum pairs considered byBCS. Materials with such pairings would bedescribed as “unconventional superconductors”.However, there is one aspect of superconductivitytheory that has remained unchanged since BCS:we do not know of any fermion superconductorwithout pairs of some kind.

The BCS theory of superconductivity

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B, C and S John Bardeen (left), Leon Cooper (centre)and Robert Schrieffer.




lead became badly connected as a sample was cooled;of course, this would cause the voltage measured acrossa current-carrying sample to drop to zero.

Meanwhile, back in Birmingham, Chu’s paper wasenough to persuade us that high-Tc superconductivitywas real. Within the next few weeks, we made our ownsuperconducting sample at the second attempt, andthen hurried to measure the flux quantum – the basicunit of magnetic field that can thread a superconduct-ing ring. According to the BCS theory of superconduc-tivity, this flux quantum should have the value h/2e, withthe factor 2 representing the pairing of conductionelectrons in the superconductor. This was indeed thevalue we found (figure 2). We were amused that theaccompanying picture of our apparatus on the frontcover of Nature included the piece of Blu-Tack we usedto hold parts of it together – and pleased that whenB&M were awarded the 1987 Nobel Prize for Physics(the shortest gap ever between discovery and award),our results were reproduced in Müller’s Nobel lecture.

Unfinished business

In retrospect, however, our h/2e measurement mayhave made a negative contribution to the subject, sinceit could be taken to imply that high-Tc superconductiv-ity is “conventional” (i.e. explained by standard BCStheory), which it certainly is not. Although B&M’schoice of compounds was influenced by BCS theory,most (but not all) theorists today would say that theinteraction that led them to pick La–Ba–Cu–O is notthe dominant mechanism in high-Tc superconductiv-ity. Some of the evidence supporting this conclusioncame from several important experiments performedin around 1993, which together showed that the pairedsuperconducting electrons have l = 2 units of relativeangular momentum. The resulting wavefunction has afour-leaf-clover shape, like one of the d-electron statesin an atom, so the pairing is said to be “d-wave”. In suchl = 2 pairs, “centrifugal force” tends to keep the con-stituent electrons apart, so this state is favoured if thereis a short-distance repulsion between them (which iscertainly the case in cuprates). This kind of pairing is also favoured by an anisotropic interaction expectedat larger distances, which can take advantage of the clover-leaf wavefunction. In contrast, the original“s-wave” or l = 0 pairing described in BCS theorywould be expected if there is a short-range isotropicattraction arising from the electron–lattice interaction.

These considerations strongly indicate that theelectron–lattice interaction (which in any case appearsto be too weak) is not the cause of the high Tc. As forthe actual cause, opinion tends towards some form ofmagnetic attraction playing a role, but agreement onthe precise mechanism has proved elusive. This ismainly because the drop in electron energy on enter-ing the superconducting state is less than 0.1% of thetotal energy (which is about 1 eV), making it extremelydifficult to isolate this change.

On the experimental side, the maximum Tc has beenobstinately stuck at about halfway to room temperaturesince the early 1990s. There have, however, been a num-ber of interesting technical developments. One is thediscovery of superconductivity at 39 K in magnesiumdiboride (MgB2), which was made by Jun Akimitsu in2001. This compound had been available from chemicalsuppliers for many years, and it is interesting to specu-late how history would have been different if its su-perconductivity had been discovered earlier. It is nowthought that MgB2 is the last of the BCS superconduc-tors, and no attempts to modify it to increase the Tc fur-ther have been successful. Despite possible applicationsof this material, it seems to represent a dead end.

In the same period, other interesting families of su-perconductors have also been discovered, including theorganics and the alkali-metal-doped buckyball series.None, however, have raised as much excitement as thedevelopment in 2008 (by Hideo Hosono’s group atTokyo University) of an iron-based superconductorwith Tc above 40 K. Like the cuprate superconductorsbefore them, these materials also have layered struc-tures, typically with iron atoms sandwiched betweenarsenic layers, and have to be doped to remove anti-ferromagnetism. However, the electrons in these ma-terials are less strongly interacting than they are in thecuprates, and because of this, theorists believe that they

When a ring of YBa2Cu3O7–d is subjected to deliberateelectromagnetic interference, the magnetic flux jumps in and out ofthe ring in integer multiples of the flux quantum (top). In accordancewith BCS theory, the value of this flux quantum was measured to beh/2e. The photograph (bottom) shows the apparatus used tomeasure the flux quantum – complete with Blu-Tack. (Adapted from C E Gough et al. 1987 Nature 326 855)

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On the experimental side, themaximum Tc has been obstinatelystuck at about halfway to roomtemperature since the early 1990s

physicsworld.comSuperconductivity: High-temperature materials



will be an easier nut to crack. A widely accepted modelposits that the electron pairing mainly results from arepulsive interaction between two different groups ofcarriers, rather than attraction between carriers withina group. Even though the Tc in these “iron pnictide”superconductors has so far only reached about 55 K,the discovery of these materials is a most interestingdevelopment because it indicates that we have not yetscraped the bottom of the barrel for new mechanismsand materials for superconductivity, and that researchon high-Tc superconductors is still a developing field.

A frictionless future?

So what are the prospects for room-temperature super-conductivity? One important thing to remember is thateven supposing we discover a material with Tc ~ 300 K,it would still not be possible to make snooker tables withlevitating frictionless balls, never mind the levitatingboulders in the film Avatar. Probably 500 K would beneeded, because we observe and expect that as Tc getshigher, the electron pairs become smaller. This meansthat thermal fluctuations become more important,because they occur in a smaller volume and can moreeasily lead to a loss of the phase coherence essential tosuperconductivity. This effect, particularly in high mag-

netic fields, is already important in current high-Tc ma-terials and has led to a huge improvement in our un-derstanding of how lines of magnetic flux “freeze” inposition or “melt” and move, which they usually do nearto Tc, and give rise to resistive dissipation.

Another limitation, at least for the cuprates, is thedifficulty of passing large supercurrents from one crys-tal to the next in a polycrystalline material. This partlyarises from the fact that in such materials, the super-currents only flow well in the copper-oxide planes. Inaddition, the coupling between the d-wave pairs in twoadjacent crystals is very weak unless the crystals areclosely aligned so that the lobes of their wavefunctionsoverlap. Furthermore, the pairs are small, so that eventhe narrow boundaries between crystal grains presenta barrier to their progress. None of these problemsarise in low-Tc materials, which have relatively largeisotropic pairs.

For high-Tc materials, the solution, developed inrecent years, is to form a multilayered flexible tape inwhich one layer is an essentially continuous single crys-tal of 123 (figure 3). Such tapes are, however, expen-sive because of the multiple hi-tech processes involvedand because, unsurprisingly, ceramic oxides cannot bewound around sharp corners. It seems that even in

Perovskites are crystals that have long beenfamiliar to inorganic chemists and mineralogistsin contexts other than superconductivity.Perovskite materials containing titanium andzirconium, for example, are used as ultrasonictransducers, while others containing manganeseexhibit very strong magnetic-field effects on theirelectrical resistance (“colossalmagnetoresistance”). One of the simplestperovskites, strontium titanate (SrTiO3), isshown in the top image. In this material, Ti4+ ions(blue) are separated by O2– ions (red) at thecorners of an octahedron, with Sr2+ ions (green)filling the gaps and balancing the charge.

Bednorz and Müller (B&M) chose toinvestigate perovskite-type oxides (a few ofwhich are conducting) because of aphenomenon called the Jahn–Teller effect,which they believed might provide an increasedinteraction between the electrons and the crystallattice. In 1937 Hermann Arthur Jahn andEdward Teller predicted that if there is adegenerate partially occupied electron state in asymmetrical environment, then the surroundings(in this case the octahedron of oxygen ionsaround copper) would spontaneously distort toremove the degeneracy and lower the energy.However, most recent work indicates that theelectron–lattice interaction is not the main driverof superconductivity in cuprates – in which casethe Jahn–Teller theory was only useful because itled B&M towards these materials!

The most important structural feature of thecuprate perovskites, as far as superconductivityis concerned, is the existence of copper-oxide

layers, where copper ions in a square array areseparated by oxygen ions. These layers are thelocation of the superconducting carriers, andthey must be created by varying the content ofoxygen or one of the other constituents –“doping” the material. We can see how this worksmost simply in B&M’s original compound, whichwas La2CuO4 doped with Ba to give La2–xBaxCuO4

(x ~0.15 gives the highest Tc). In ioniccompounds, lanthanum forms La3+ ions, so inLa2CuO4 the ionic charges all balance if thecopper and oxygen ions are in their usual Cu2+

(as in the familiar copper sulphate, CuSO4) andO2– states. La2CuO4 is insulating even thougheach Cu2+ ion has an unpaired electron, as theseelectrons do not contribute to electricalconductivity because of their strong mutualrepulsion. Instead, they are localized, one toeach copper site, and their spins line upantiparallel in an antiferromagnetic state. Ifbarium is incorporated, it forms Ba2+ ions, so thatthe copper and oxygen ions can no longer havetheir usual charges, thus the material becomes“hole-doped”, the antiferromagnetic ordering isdestroyed and the material becomes both aconductor and a superconductor. YBa2Cu3O7–d or“YBCO” (bottom) behaves similarly, except thatthere are two types of copper ions, inside andoutside the CuO2 planes, and the doping iscarried out by varying the oxygen content. Thismaterial contains Y3+ (yellow) and Ba2+ (purple)ions, copper (blue) and oxygen (red) ions. Whend ~ 0.03, the hole-doping gives a maximum Tc;when d is increased above ~0.7, YBCO becomesinsulating and antiferromagnetic.

The amazing perovskite family




existing high-Tc materials, nature gave with one hand,but took away with the other, by making the materialsextremely difficult to use in practical applications.

Nevertheless, some high-Tc applications do exist or are close to market. Superconducting power line“demonstrators” are undergoing tests in the US andRussia, and new cables have also been developed thatcan carry lossless AC currents of 2000 A at 77 K. Suchcables also have much higher current densities thanconventional materials when they are used at 4.2 K inhigh-field magnets. Superconducting pick-up coilsalready improve the performance of MRI scanners,and superconducting filters are finding applications inmobile-phone base stations and radio astronomy.

In addition to the applications, there are severalother positive things that have arisen from the dis-covery of high-Tc superconductivity, including hugedevelopments in techniques for the microscopic in-vestigation of materials. For example, angle-resolvedphoto-electron spectroscopy (ARPES) has allowed usto “see” the energies of occupied electron states inever-finer detail, while neutron scattering is the idealtool with which to reveal the magnetic properties ofcopper ions. The advent of high-Tc superconductorshas also revealed that the theoretical model of weaklyinteracting electrons, which works so well in simplemetals, needs to be extended. In cuprates and manyother materials investigated in the last quarter of acentury, we have found that the electrons cannot betreated as a gas of almost independent particles.

The result has been new theoretical approaches andalso new “emergent” phenomena that cannot be pre-dicted from first principles, with unconventional super-conductivity being just one example. Other productsof this research programme include the fractionalquantum Hall effect, in which entities made of elec-trons have a fractional charge; “heavy fermion” metals,where the electrons are effectively 100 times heavierthan normal; and “non-Fermi” liquids in which elec-trons do not behave like independent particles. So issuperconductivity growing old after 100 years? In anumerical sense, perhaps – but quantum mechanics iseven older if we measure from Planck’s first introduc-tion of his famous constant, yet both are continuing tospring new surprises (and are strongly linked together).Long may this continue! ■

The make up of a second-generation superconducting wire, showing the multiplelayers required to achieve good conductivity in the YBCO. Layers of copper (Cu)protect against transient resistive voltages, while layers of lanthanum manganate(LMO) and two types of MgO form substrates for growing single-crystal YBCO films.

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On the money

Stock markets that rise unsustainably can end upplummeting back down – but can physics create lawsdescribing how such crashes occur?

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A subtle yet mind-bending concept about how objects can be the same in literally all their attributes makes thehead spin even faster when applied to the mathematicalstructure of the multiverse

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A century on from the discovery of superconductivity,we still do not know how to design superconductors thatcan be really useful in the everyday world. Despite thisseemingly downbeat statement, I remain enthusiasticabout the search for new superconducting materials.Although my own research in this area has had its shareof null results and knock-backs, in that I am in goodcompany with the true leaders in the field. Optimismabounds, and the past couple of years have seen a re-newed passion, with researchers worldwide wanting towork together to find a way to design new materials thatwe know in advance will function as superconductors.

That would be very different from most of the dis-coveries in superconductivity, which have often beenserendipitous. Indeed, the main quest of Heike Kamer-lingh Onnes was to liquefy gases, and only after man-aging to liquefy helium in 1908 did he set his Leiden labto work on a study of the properties of metals at lowtemperature. The choice of sample was fortunate –mercury was used because it is a liquid at ambient tem-perature and so could easily be purified. The discoveryof its dramatic drop in resistance when cooled to 4 K,which we now know to be the critical temperature, Tc,was an unexpected and fortuitous surprise.

In subsequent years, increasing the critical tempera-ture was achieved by systematic experimental tests ofelements, alloys and compounds, predominantly led by

Bernd Matthias from about 1950, who in doing so be-came the first researcher to discover a new class ofsuperconductors. To begin with, the only known super-conductors were elements, but Matthias found super-conductivity in various combinations of elements thaton their own are non-superconducting. The earliest ofthese was the ferromagnetic element cobalt combinedwith the semiconductor silicon to form CoSi2. Whatchanged the game was the discovery by John Hulm andhis graduate student George Hardy at the Universityof Chicago in 1952 of the vanadium–silicon compoundV3Si, the first of the then-called high-Tc superconduc-tors. This was a completely new class of superconduc-tors – known as the A15s (a particular crystal structureof the chemical formula A3B, where A is a transitionmetal) – and it enabled Matthias to discover more than30 compounds of this type, with values of Tc that rangedup to 18 K in the case of Nb3Ge.

Increasing the critical superconducting temperatureis certainly what most interests the media, but it is notthe only property with which to rank new supercon-ductors. The A15s were the first family of supercon-ductors that maintained a high critical current density,Jc, in the presence of strong magnetic fields, which iscrucial for all current-carrying applications. In 1963Hulm, then with co-workers at the Westinghouse Re-search Laboratories, developed the first commercial

The discovery of high-temperature iron-based superconductors in 2008 thrilled researchers because itindicated that there could be another – more useful – class of superconductors just waiting to be found.Laura H Greene shares that enthusiasm and calls for global collaboration to reveal these new materials

Laura H Greene is aprofessor of physicsat the University ofIllinois at Urbana-Champaign, US, e-mail [email protected]

Taming serendipity

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superconducting wires, based on random alloys ofniobium–titanium, a material discovered at the Ruth-erford Appleton Laboratory in the UK. Althoughniobium–titanium alloys exhibit a lower Tc and Jc thanthe A15s, they were chosen for wires because they aremalleable, reliable and can be used in nearly all prac-tical applications, including the medical technique ofmagnetic resonance imaging (MRI). Despite the im-portance of a high Jc, achievements in this area receivelittle recognition compared with progress in increasingTc. But as my former boss, John Rowell, stated at theretirement party of Jack Wernick, who is noted for thediscovery of several A15s, “High-Tc wins Nobel prizes;high Jc saves lives.” So although the search for new fam-ilies of higher-Tc superconductors is what makes theheadlines, what really matters when it comes to appli-cations is a high value of Jc and mechanical propertiesthat are good for making wires.

In 1979 Frank Steglish and colleagues discoveredsuperconductivity in materials containing rare earths(elements with a 4f electron orbital) or actinides (thosewith a 5f electron orbital). These compounds are calledthe “heavy fermions”, because with antiferromagneticground states, and at low temperatures, the itinerantelectrons behave as if they have masses up to 1000times larger than the free-electron mass. This discoverywas significant because the heavy fermions were the

first truly tunable superconductors, through a compe-tition between superconductivity and magnetic order.But what was even more important was that heavy-fermion superconductors did not follow the rule book:for the first time, the brilliant Bardeen–Cooper–Schrieffer (BCS) theory of superconductivity wasshown to break down. BCS theory explains what ishappening at the microscopic level – it involves pairedelectrons known as “Cooper pairs” travelling aroundthe crystal lattice – and this part of the theory remainsrobust in all the known superconductors. But themicroscopic mechanism for superconductivity in allpreviously found superconductors was attributed inBCS to electron–phonon coupling, which was notsufficient to cause the electron pairing in the newheavy-fermion superconductors (figure 1).

Before the heavy fermions were discovered, it wasaccepted that any kind of magnetism would harm thesuperconducting state. But in this new class of super-conductor the magnetism appeared integral to thestrength of the superconductivity. Another excitingaspect of this class is that higher-Tc heavy-fermion super-conductors – in particular the “115” series beginningwith the discovery of CeCoIn5 – were not discoveredpurely by serendipity, but driven by guidelines learnedfrom many preceding substitution and pressure studies.

New classes

Enter the high-Tc oxides. First was the sensational re-volution of the copper oxides, or “cuprates”: GeorgBednorz and Alex Müller discovered LaBaCuO in 1986with a Tc of 40 K, and subsequently Maw-Kuen Wu andChing-Wu (Paul) Chu discovered YBa2Cu3O7–d, or“YBCO”, with a Tc of more than 90 K. (For more aboutthe high-Tc revolution, see “Resistance is futile” on page33.) These transformative discoveries again relied onguidelines put together by thoughtful and talentedphysicists, but serendipity certainly played a factor. In-deed, I believe the only discovery of a high-Tc systemthat was driven predominantly by theory is Ba1–dKdBiO3,or BKBO (to date at least): Len Mattheiss and Don Ha-mann at Bell Labs used electronic-structure calcu-lations of an earlier low-Tc system, Ba(Pb,Bi)O3, topredict and then make BKBO, for which their colleagueBob Cava drove the Tc to a respectable 30 K.

But what of materials with even higher transitiontemperatures? Through a tremendous amount of hardwork worldwide by many talented physicists, transitiontemperatures in the cuprates have been pushed up to135K at ambient pressure and above 150K at high pres-sure in HgBa2Ca2Cu3O8+d (also known as Hg-1223),which was discovered in 1993. We were then left withthe idea that perhaps there were no other families ofhigh-Tc superconductors. Could it be that the cupratewere the only high-Tc class we would ever find? The fearwas that systematic studies had already found the high-est possible Tc.

But we had guidelines and ideas. Many of these werepublished in a 2006 report for the US Department ofEnergy, Basic Research Needs for Superconductivity.Particularly of note in that report, which outlined theprospects and potential of superconductivity, was ourcanonical phase diagram (figure 2), which hinted thatwe knew where to look: at the boundary between com-

The electrons in all superconductors form Cooper pairs, which carry thesuperconducting current. This was accounted for in the Bardeen–Cooper–Schrieffer (BCS) theory, and in conventional metallicsuperconductors the microscopic mechanism was correctly identifiedas electron–phonon coupling. Phonons are the quantized normal-modevibrations of a lattice, and a strong electron–phonon coupling meansthat the lattice is “squishy” to the electron, like a soft mattress. Asshown in this figure, an electron can distort the lattice, which affects thephonon, leaving something like a positive “wake” that later attracts thesecond member of the Cooper pair. The two negatively chargedelectrons are not bound in real space but are correlated through thevibrational distortions they leave behind. This brilliant idea showed howCoulomb’s law could be repealed. But in many novel superconductingfamilies, electron–phonon coupling alone cannot account for thepairing, the explanation for which remains an unsolved mystery.

1 When a robust theory breaks down

Heavy-fermionsuperconductorsdid not followthe rule book: for the first time,the brilliant BCS theory was shown tobreak down

physicsworld.comSuperconductivity: Another class



peting phases. This personifies the concept of “quan-tum criticality”, where a phase transition occurs notbecause of thermal fluctuations as in a typical thermo-dynamic phase transition, but because of quantum-mechanical fluctuations at zero temperature. The phasediagram shows an antiferromagnetic insulator on theleft and a normal metal on the right. Where they meet atthe centre is the quantum critical point, and as that pointis approached, the quantum fluctuations of the com-peting phases get stronger and a strange “emergent”state of matter appears – in this case, high-temperaturesuperconductivity. The general rule was: the strongerthe competing phases, the stronger the emergent phase.Those ideas remain, but where were these new familiesof superconductors? Had we hit a dead end?

Finally, in 2008, a second class of high-Tc supercon-ductor was discovered. Hideo Hosono at the TokyoInstitute of Technology had discovered iron-basedsuperconductors two years earlier, and in January 2008his first “high-Tc” paper on these materials was pub-lished, which precipitated a renewed excitement and afrenzy of activity. Within four months, ZhongxianZhao’s group at the Institute of Physics in Beijing cre-ated related materials that hold the record with a Tc of58 K. Many of us were awestruck – here finally was anew class of high-temperature superconductors thatbroke the 22-year tyranny of cuprates, and in materialsthat no-one had predicted and were contrary to ourbasic notions of how superconductivity works. Howcould iron – the strongest ferromagnetic element in theperiodic table – be a basis for superconductivity at all,let alone high-temperature superconductivity? Therenow exist whole arrays of iron-based superconductors– pnictides and chalcogenides – all found by clever,hard work, but originally discovered by serendipity.

Laying down the gauntlet

All of these families of superconductors have a greatdeal in common, yet also have unique properties. Thephysics seems to be growing more complex with time,and we continue to build more guidelines and structureinto our search for new superconducting materials.Although the discovery of iron-based superconductorsgave us a lot of research fodder, they will not necessar-ily tell us all we need to know about how to find newclasses of superconductors. But one thing is for sure: thecuprates are not unique and as there is a second class ofhigh-Tc superconductors, I believe there must be a third.

The discovery of iron-based superconductors – thefirst new class of high-Tc superconductors after morethan two decades of only incremental progress –injected a new-found positivity into the field, rivalledonly by the discovery of superconductivity in the cu-prates. The resulting surge of global research, however,has a very different feel from that in 1986. In the earlydays of high-temperature superconductivity the com-petition was fierce – there was a real race to obtainhigher transition temperatures. But now that zealoussense of urgency has been replaced by a more pacedand considered approach.

Many scientists have been working on understand-ing novel superconductors for decades, often in pro-ductive collaborations. Recently, our research fundingand support have been revitalized on a worldwide scale,

in part because of the need to address the global energycrisis by significantly increasing the efficiency of powertransmission. After 25 years of intense and fruitfulwork, the cuprates remain promising, but for variousreasons may still not be the materials of choice to im-pact our power grid. The newly discovered iron-basedhigh-temperature superconductors exhibit many pos-itive aspects, but are likewise not yet in a position toimpact power transmission. Another class of super-conductors is needed.

For any one of us, putting all of our efforts towardsattacking this problem of discovering a new supercon-ductor is highly risky. If we want to find such a thing butdo not manage this after three to five years – the typicallength of most research grants – we seriously risk losingour funding. As a result, we focus most of our effortson understanding the existing novel superconductors.So, I and my colleague Rick Greene (no relation) ofthe University of Maryland, aided by the Institute forComplex Adaptive Matter, have made a call to arms tothe international community, which we are spreadingvia working groups at conferences and workshops: “Itis time for us to join our expertise and resources to-gether, on a worldwide scale, to search for that newclass of superconductors.”

The gauntlet is being taken up with enthusiasm. Withcommunication now flowing between different groups,and across funding and geographical barriers, we hopeto soon reveal at last a clarified vision of high-tempera-ture and novel superconductivity that will set us in thebest possible stead in the quest for a new class.

It is gratifying to see superconductivity, at 100, finallygrowing up. ■

This figure maps out a general phase diagram of the high-temperature cupratesuperconductors. The horizontal axis is nominally the carrier concentration, ρ, which can betuned by pressure or atomic substitution (doping). The vertical axis is temperature. Theantiferromagnetic insulating (AFI) state on the left occurs below the Néel temperature, TN, andthe normal metal (M) state occurs at high ρ. The superconducting (SC) state is bounded by thecritical temperature, Tc, and emerges between competing AFI and M phases as discussed inthe text. The origin of the intriguing pseudogap (PG) state, which appears below the dashedline, T*, and of the other labelled phases – spin-glass (SG), charge-ordered (CO), fluctuatingsuperconductivity (fl-SC) and non-Fermi liquid (NFL) – remains elusive.

TN

TC

M

PG NFL

CO

SC

0 0.05 0.10 0.15 0.20 0.25 0.30

SG

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carrier concentration, ρte

mpe

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2 Competing phases

physicsworld.com Superconductivity: Another class



Reviews

The universe is not like a clock, wherewell-understood parts tick in pre-dictable ways, nor like a balloon ex-panding or contracting. It is in factpushing itself apart with a strangekind of energy, and 96% of it is madeof an unknown kind of matter. Howwe discovered this is the subject of The 4% Universe, which condensesthe complex, messy and startling tale –people, science, instruments, events –into an easily digestible, fast-paced243 pages. That is a startling achieve-ment in itself. To the connoisseur ofpopular science, indeed, the way au-thor Richard Panek tells the tale is asinteresting as the events: half drama,half detective story.

The prologue begins with a one-page “wow!” moment. On 5 Novem-ber 2009 scientists at 16 institutionsaround the world dropped their col-lective jaws as they seemed to catch afirst-ever glimpse of an entirely newstructure of the universe. Two pagesfollow explaining its significance. Re-ferring to the year when Galileo firstused the telescope to reveal entirenew worlds previously unknown tohumankind, Panek writes “It’s 1610all over again.”

What follows in Act One is the

story of how cosmology went fromspeculation to science: how astron-omers discovered that the furnitureof the universe was more than plan-ets and stars, and was on the move toboot. The universe “had a story totell”, Panek writes. “Instead of a stilllife, it was a movie,” he says. We learnhow scientists uncovered this movie’splot by peering over the shoulders of Act One’s two main characters:theoretical physicist Jim Peebles,author of the classic textbook PhysicalCosmology on the physics of the earlyuniverse; and astronomer Vera Ru-bin, whose work on the galaxy-rota-tion problem pointed the way to theidea that the universe contains someamount of “dark” matter, invisible topresent-day instruments.

Act Two introduces more char-acters and “the game”, in which twodifferent teams of scientists vie tounravel the plot by finding distant“Type 1a” supernovae. The game isplayed with telescopes equipped withcharge-coupled devices, which revo-lutionized astronomical photography,and with the Hubble Space Telescope,which peered into hitherto invisiblecorners of the universe, among otherequipment. The first team, the Super-

nova Cosmology Project (SCP), wasled by Saul Perlmutter and Carl Pen-nypacker, particle physicists at theLawrence Berkeley National Labor-atory who applied the tools of theirtrade to astronomy. In doing so, Pa-nek observes, “[T]hey weren’t driftingtowards a new discipline. The disci-pline was drifting towards them.”

The second team was known asHigh-Z, where Z is a term for redshift.Highly redshifted objects are amongthe oldest and most distant in the uni-verse, meaning that they would bearthe clearest traces of any expansion orcontraction. High-Z’s main memberswere Adam Reiss and Brian Schmidt,who hailed from Harvard Universityand viewed supernovae as their areaof expertise. They saw the Berkeleygroup as being out to “beat them attheir own game”. While SCP had asix-year head start, High-Z recruitedthe “old-boy network” to, in effect,beat the Berkeley group at beatingthem at their own game.

In 1997 the two teams converged –simultaneously, yet reluctantly – ontwo wild, tooth-fairy-like ideas: thatthe universe contained “dark matterthey couldn’t see and [a] new forcethey couldn’t imagine”. In Act Three,all the main characters introduced sofar in the drama gather at a meetingwhere the SCP’s results (picked up bydiscerning newspaper reporters) sug-gest that “SCP was beating [High-Z]at beating the SCP at beating [High-Z] at their own game”. Then High-Zoutdid that by securing full credit inthe media. The discovery of this newforce – soon dubbed “dark energy” –became Science magazine’s “break-through of the year” in 1998.

The new idea – that the universe’sexpansion is accelerating – both sim-plifies things, by explaining a lot ofpuzzling data, and makes them morecomplex, by raising a lot of questions.

In Act Four, SCP and High-Z makeplans to hunt for answers to one ques-tion – dark matter – while strugglingover credit for the other, dark energy.The existing picture of the universeturns “preposterous”. But as Perl-mutter remarks on the final page ofthe book, what usually attracts phy-sicists to their field is “not the desireto understand what we already knowbut the desire to catch the universe inthe act of doing really bizarre things”.And so, at the book’s conclusion,while one chapter in astronomy ends,another begins.

Robert P Crease

The dark-energy game

Reviews

The 4% Universe:

Dark Matter, Dark

Energy, and the

Race to Discover the

Rest of Reality

Richard Panek2011 One World/Houghton MifflinHarcourt £12.99pb/$26.00hb 320pp

Puzzling behaviour

Finding the missingpieces of theuniverse.

Lyne

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Cook

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physicsworld.com


PWApr11reviews 18/3/11 11:42 Page 44

Panek tells the story briskly yetwarmly, capturing personalities andnot overlooking controversies. Hechooses characters carefully. ThroughRubin, for instance, we not only learnabout dark matter, but also what it islike to be a woman in science, literallybalancing child and career: textbookin one hand, pram in the other. Panekalso has a knack for summarizing de-velopments concisely and efficiently,such as in the following passage abouthow astronomy became more spe-cialized over time.

You couldn’t just study theheavens anymore; you studiedplanets, or stars, or galaxies, or theSun. But you didn’t study just starsanymore, either; you studied onlythe stars that explode. And youdidn’t study just supernovae; youstudied only one type. And youdidn’t study just Type 1a; youspecialized in the mechanismleading to the thermonuclearexplosion, or you specialized in whatmetals the explosion creates, or youspecialized in how to use the light

from the explosion to measure thedeceleration of the expansion of theuniverse – how to perform thephotometry or do the spectroscopyor write the code.

Inevitably, Panek makes somecompromises, and the seams of hiscrisp storytelling occasionally show.Galileo is mentioned once too often,and Panek’s apothegmatic style canring precious, as in this remark aboutthe signal from a radio antenna:“[T]his time the source wasn’t a radiobroadcast from the West Coast. It wasthe birth of the universe.” The reader

sometimes feels manipulated, too.That “wow!” moment that kicksthings off so dramatically in the pro-logue? You don’t find out until page197 that it was phoney – not a discov-ery after all.

Another author might have ex-plored why it initially seemed to be adiscovery, why its announcement washyped even after problems were un-covered, and what this says about sci-ence and scientists. But by this time,you are so absorbed in the story thatyou do not care that much. And thebook does convey a good picture ofscientists in the act of catching theuniverse doing really bizarre things –while also showing that this is whythey took the job. Give this book toyour non-scientist friends to showthem what it is all about – and to fel-low scientists as a model of how towrite popular science.

Robert P Crease is chairman of theDepartment of Philosophy, Stony BrookUniversity, and historian at the BrookhavenNational Laboratory, US, e-mail [email protected]

The book conveysa good picture ofscientists catchingthe universe doingbizarre things

URL: www.starlite.nih.gov

So what is the site about?STAR-LITE is a game designed to teach basiclaboratory safety to researchers at the start of theircareers; the name is an acronym of Safe TechniquesAdvance Research – Laboratory Interactive TrainingEnvironment (whew!). To play, you must guide anon-screen avatar through 15 safety-related“quests”, helped (and sometimes hindered) by yourcomputer-controlled lab mates. The game is free todownload and is available for PCs and Macs.

What are some of the quests?After you have designed your avatar (warning: if youtry to wear dangly jewellery or flip-flops, you’ll gettold off), you begin the real game with a tour of thevirtual laboratory environment. This includes an

equipment storage room and a tissue-culture area,as well as a large multipurpose lab, library and staffroom. Once you complete this orientation, youravatar’s next task is a “scavenger hunt”, where youmust find and identify pieces of lab kit such asfume hoods and centrifuges, as well as warningsigns for biohazards, flammable materials and thelike. As the game progresses, you come acrossproblems such as broken equipment and chemicalspills that you have to deal with safely. One helpfulfeature is that before you can begin a particulartask, your avatar needs to be wearing the correctprotective gear. For example, if you try to handleliquid nitrogen with latex gloves instead of insulatedones, your lab mates get annoyed and you lose“health points”.

Who is behind it?The game was developed by the Division ofOccupation Health and Safety within the USNational Institutes of Health (NIH) to make safetytraining fun and engaging. The idea is that byplaying an interactive video game, trainees willretain more information than they would if they justlistened to a safety officer drone on aboutimproperly stored gas cylinders for an hour and ahalf. (Not that we speak from personal experience.)

Who is it aimed at?High-school students and undergraduates are the

game’s main audience, but some quests could alsobe part of a refresher course for postgraduates orother new lab users. Annoyingly, there are nomenus within the game that would allow you tochoose which quests to complete, so you cannotskip irrelevant or too-simple ones once you havestarted playing. However, it is possible to tinker withthe game files to delete quests before you begin;see the site’s FAQs page for details.

How useful is it for physicists?Moderately. As you would expect from an NIHinitiative, the game is primarily designed withmicrobiologists and biochemists in mind.Consequently, a few of the quests – such asoperating a centrifuge and disposing of Petri dishes– will probably only interest the biophysicists inPhysics World’s readership. The game environmentdoes include a laser room and a radiation lab, butunfortunately both are “dummy” areas that youravatar is not trained to access. This is a pity,because both the idea and the execution of STAR-LITE are excellent, and if these specializedrooms were made “live” (perhaps as an advancedgame level), then it would be a great improvement.That said, the game’s designers have obviouslytried to be as inclusive as possible, and questssuch as storing chemicals, looking up informationin material safety data sheets and identifying triphazards are pretty much universal.

Web life: STAR-LITE

physicsworld.com Reviews



http://www.starlite.nih.gov



The Grand Design begins with a seriesof questions: “How can we under-stand the world in which we find our-selves?”, “How does the universebehave?”, “What is the nature of re-ality?”, “Where did all this comefrom?” and “Did the universe need a creator?”. As the book’s authors,Stephen Hawking and Leonard Mlo-dinow, point out, “almost all of usworry about [these questions] someof the time”, and over the millennia,philosophers have worried aboutthem a great deal. Yet after openingtheir book with an entertaining his-tory of philosophers’ takes on thesefundamental questions, Hawking andMlodinow go on to state provocat-ively that philosophy is dead: sincephilosophers have not kept up withthe advances of modern science, it isnow scientists who must addressthese large questions.

Much of the rest of the book istherefore devoted to a description ofthe authors’ own philosophy, an inter-pretation of the world that they call“model-dependent realism”. Theyargue that different models of the uni-verse can be constructed using mathe-matics and tested experimentally, butthat no one model can be claimed asa true description of reality. This ideais not new; indeed, the Irish philo-sopher and bishop George Berkeley

hinted at it in the 18th century. How-ever, Hawking and Mlodinow takeBerkeley’s idea to extremes by claim-ing that since many models of naturecan exist that describe the experi-mental data equally well, such modelsare therefore equally valid.

It is important to the argument ofthe book – which leads eventually tomore exotic models such as M-theoryand the multiverse – that readers ac-cept the premise of model-dependentrealism. However, the history of sci-ence shows that the premise of onemodel being as good and useful asanother is not always correct. Para-digms shift because a new model notonly fits the current observationaldata as well as (or better than) anolder model, but also makes predic-tions that fit new data that cannot beexplained by the older model. Hawk-ing and Mlodinow’s assertion that“there is no picture- or theory-inde-pendent concept of reality” thus fliesin the face of one of the basic tenets ofthe scientific method.

Consider the Ptolemaic model ofthe solar system, in which the planetsmove in circular orbits around theEarth, and the heliocentric model putforward by Copernicus. The authorssuggest that the two models can bemade to fit the astronomical dataequally well, but that the heliocentricmodel is a simpler and more conve-nient one to use. Yet this does notmake them equivalent. New data dif-ferentiated them: Galileo’s observa-tion of the phases of Venus, throughhis telescope, cannot easily be ex-plained in Ptolemy’s Earth-centredsystem. Similarly, Einstein’s theory ofgravity superseded Newton’s laws ofgravitation when its equations cor-rectly described Mercury’s anomalousorbit. One theory, one perception ofreality, is not just as good as another,and this can be shown empirically:Einstein’s gravity is even used to makecorrections to Newton’s in the GlobalPositioning System.

It is true, however, that the situa-tion in quantum mechanics has notyet been resolved. Several differentmodels, such as the “many worlds”interpretation of Hugh Everett III,the Copenhagen interpretation andcertain Bohmian hidden-variable mo-dels, all agree with quantum-mechan-ical experiments, and as yet none of

the interpretations has produced aprediction that would experimentallydifferentiate them. Based on the his-tory of science, however, we have noreason to assume that in the futurethere will not be a decisive experi-ment that will support one modelover the others.

A second premise that the reader isexpected to accept as The GrandDesign moves along is that we can, andshould, apply quantum physics to themacroscopic world. To support thispremise, Hawking and Mlodinow citeFeynman’s probabilistic interpreta-tion of quantum mechanics, which isbased on his “sum over histories” ofparticles. Basic to this interpretationis the idea that a particle can takeevery possible path connecting twopoints. Extrapolating hugely, the au-thors then apply Feynman’s formu-lation of quantum mechanics to thewhole universe: they announce thatthe universe does not have a singlehistory, but every possible history,each one with its own probability.

This statement effectively wipes outthe widely accepted classical model ofthe large-scale structure of the uni-verse, beginning with the Big Bang. Italso leads to the idea that there aremany possible, causally disconnecteduniverses, each with its own differentphysical laws, and we occupy a specialone that is compatible with our ex-istence and our ability to observe it.Thus, in one fell swoop the authorsembrace both the “multiverse” andthe “anthropic principle” – two con-troversial notions that are more philo-sophic than scientific, and likely cannever be verified or falsified.

Another key component of TheGrand Design is the quest for the so-called theory of everything. WhenHawking became Lucasian Professorof Mathematics at Cambridge Univer-sity – the chair held by, among others,Newton and Paul Dirac – he gave aninaugural speech claiming that wewere close to “the end of physics”.Within 20 years, he said, physicistswould succeed in unifying the forcesof nature, and unifying general rela-tivity with quantum mechanics. Heproposed that this would be achievedthrough supergravity and its relation,string theory. Only technical prob-lems, he stated, meant that we werenot yet able to prove that supergravity

John W Moffat

Taking the multiverse on faith

The Grand Design

Stephen Hawking andLeonard Mlodinow2010 Bantam Press£18.99hb 208pp

Dial M for multiverse

Dreaming of a singletheory of everything.

Phot

olib

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physicsworld.comReviews



solved the problem of how to makequantum-gravity calculations finite.

But that was in 1979, and Hawking’svision of that theory of everything isstill in limbo. Underlying his favoured“supergravity” model is the postulatethat, in addition to the known observ-able elementary particles in particlephysics, there exist superpartners,which differ from the known particlesby a one-half unit of quantum spin.None of these particles has been de-tected to date in high-energy accel-erator experiments, including thoserecently carried out at the LargeHadron Collider at CERN. Yet de-spite this, Hawking has not given upon a theory of everything – or has he?

After an entertaining description ofthe Standard Model of particle phys-ics and various attempts at unification,Hawking and his co-author concludethat there is indeed a true theory ofeverything, and its name is “M-the-ory”. Of course, no-one knows whatthe “M” in M-theory stands for, al-though “master”, “miracle” and “mys-tery” have been suggested. Nor cananyone convincingly describe M-the-ory, except that it supposedly exists in11 dimensions and contains string the-ory in 10 dimensions. A problem fromthe outset with this incomplete theoryis that one must hide, or compactify,the extra seven dimensions in order toyield the three spatial dimensions andone time dimension that we inhabit.There is a possibly infinite number ofways to perform this technical feat. Asa result of this, there is a “landscape”of possible solutions to M-theory, 10500

by one count, which for all practicalpurposes also approaches infinity.

That near-infinity of solutions mightbe seen by some as a flaw in M-theory,but Hawking and Mlodinow seizeupon this controversial aspect of it to claim that “the physicist’s tradi-tional expectation of a single theory of nature is untenable, and there existsno single formulation”. Even moredramatically, they state that “the ori-ginal hope of physicists to produce asingle theory explaining the apparentlaws of our universe as the uniquepossible consequence of a few simpleassumptions has to be abandoned”.Still, the old dream persists, albeit in a modified form. The difference, asHawking and Mlodinow assert point-edly, is that M-theory is not one the-ory, but a network of many theories.

Apparently unconcerned that the-orists have not yet succeeded in ex-plaining M-theory, and that it has notbeen possible to test it, the authorsconclude by declaring that they haveformulated a cosmology based on itand on Hawking’s idea that the earlyuniverse is a 4D sphere without abeginning or an end (the “no-bound-ary theory”). This cosmology is the“grand design” of the title, and one ofits predictions is that gravity causesthe universe to create itself sponta-neously from nothing. This somehow

explains why we exist. At this point,Hawking and Mlodinow venture intoreligious controversy, proclaimingthat “it is not necessary to invoke Godto light the blue touch paper and setthe universe going”.

Near the end of the book, the au-thors claim that for a theory of quan-tum gravity to predict finite quantities,it must possess supersymmetry be-tween the forces and matter. They goon to say that since M-theory is themost general supersymmetric theoryof gravity, it is the only candidate for acomplete theory of the universe. Sincethere is no other consistent model,then we must be part of the universedescribed by M-theory. Early in thebook, the authors state that an accept-able model of nature must agree withexperimental data and make predic-tions that can be tested. However,none of the claims about their “granddesign” – or M-theory or the multi-verse – fulfils these demands. Thismakes the final claim of the book – “Ifthe theory is confirmed by observa-tion, it will be the successful conclu-sion of a search going back 3000years”– mere hyperbole. With The GrandDesign, Hawking has again, as in hisinaugural Lucasian Professor speech,made excessive claims for the futureof physics, which as before remain tobe substantiated.

John W Moffat is a member of the PerimeterInstitute for Theoretical Physics in Waterloo,Canada, and professor emeritus at theUniversity of Toronto. He is the author of, mostrecently, Einstein Wrote Back: My Life in Physics (2010, Thomas Allen & Son), e-mail [email protected]

Celebrating 100 years of superconductivityVisit iopscience.org/centenary to browse our collection

of 100 free-to-read articles 100 years of

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A key componentof the book is thequest for a theoryof everything

physicsworld.com Reviews




http://iopscience.org/centenary

Apocalypse eventuallyThe list of disasters that threaten lifeon Earth is long and varied. The listof books that have been writtenabout such disasters, however, iseven longer. With what is, inretrospect, spectacularly bad timing,we picked this month to review a trioof recent books that explores thescience of disasters. Of the three,Armageddon Science: The Science ofMass Destruction is the mostconventional. In it, the science writerBrian Clegg presents a tour of thescience and history behind numerouspossible doomsday scenarios,ranging from the unlikely(antimatter bombs and planet-eatingblack holes) to the all too real(climate change). Not all of them arecovered in the same depth. Forexample, tsunamis, earthquakes,asteroid impacts, supervolcanoeruptions, alien invasions andirradiation by interstellar gamma-raybursts are all crammed into a mere26 pages. In contrast, the chapter onnuclear weapons takes up almost aquarter of the book, and sections onnanotechnology and climate changeare also relatively meaty. One reasonfor this emphasis may be the author’sown background: Clegg is a physicistby training, and he seems more athome with physics-related disastersthan he does with geological ones.However, as the book’s thoughtfulintroduction and conclusion makeclear, Clegg is also primarilyinterested in disasters that are insome sense caused by science, notmerely explained by it. Noting thatMarie Curie died of radiation-induced leukaemia, he observes that“scientists don’t always have a greattrack record in keeping themselvesand others safe”. Apparently callousattitudes such as these – which Clegglinks, tenuously, to the fact that manyscientists exhibit mild symptoms ofautism – have a detrimental effect onthe way outsiders perceive thescientific community.● 2010 St Martins Press£18.99/$25.99hb 304pp

A scientific conspiracy?Large-scale US government supportof scientific research was born in theSecond World War. To keep federaldollars flowing in peacetime,scientists have repeatedly spreadalarms about natural disasters suchas asteroid impacts and climatechange – the solutions to which,inevitably, involve moregovernment-funded research. This,at least, is the argument put forwardby James Bennett in The DoomsdayLobby: Hype and Panic fromSputniks, Martians, and MaraudingMeteors. As this synopsis indicates,Bennett, a political scientist atGeorge Mason University inVirginia, is actively hostile togovernment support of scientificresearch – or, as he terms it, “the federal appropriation dole”.However, readers who are thick-skinned enough to withstandrepeated insults will find a few atomsof truth inside Bennett’s layers ofanti-government ideology. As hepoints out, state-funded science isnot always a benign matter: it hasalso meant despoiling large swathesof the American West with dams,subsidized mining and weaponstesting. Moreover, it is true that informer times, science functionedtolerably well without state support.As Bennett describes in the book’sopening chapters, the rise of USastronomy in the early 20th centurywas funded almost entirely byphilanthropists. Yet his privatelyfunded scientific utopia has afundamental flaw. One of theanecdotes he uses to describe itconcerns a 19th-century “Society forthe Diffusion of Useful Knowledge”,which built itself an observatoryafter selling more than 300memberships at $25 each. That maysound commendably egalitarian, butit is worth noting (as Bennett doesnot) that when the observatoryopened in 1845, $25 was worth asmuch to the average person as$12 300 is today, as measured by percapita GDP. The fact is that before

the late 19th century, scientists were,overwhelmingly, either aristocrats or people who could persuadearistocrats to back them financially.Is that really a better system?● 2010 Springer £22.99/$24.95pb200pp

Things fall apartWhat do the Tay Bridge disaster, a tense family game of Monopolyand the loss of vegetation in theSahara have in common? Accordingto Bristol University physicist Len Fisher, who uses each of them asexamples in his book Crashes, Crisesand Calamities, they all havesomething to tell us about “criticaltransitions”, which occur when asystem “abruptly, without apparentwarning…jump[s] to a very differentstate”. Sometimes, such transitionsare obvious, as in the 1879 collapse ofthe rail bridge across Scotland’s Tay estuary, or a player overturning aMonopoly board in frustration.Others, such as desertification, aremore subtle, and are preceded bycharacteristic signs that can – ifproperly interpreted – alertobservers to impending change. The key point, Fisher writes, is that“to anticipate and deal with suchdisasters, we need to be able topredict the changeover point”. Hisbook outlines three overlappingapproaches for doing this. One ofthem, catastrophe theory, classifiestransition-prone systems into distinctmathematical types – including one,the “cusp catastrophe”, that hasvariously been used to explain love–hate relationships and the behaviourof cornered dogs. The secondapproach, computer modelling, isuseful for predicting the outcome ofcomplex situations, while the thirdfocuses on early-warning signs suchas fluctuations in the population ofan animal species. It is all fascinatingstuff, even if the threads that bindFisher’s examples togethersometimes seem weak.● 2011 Basic Books £13.99/$23.95hb256pp

Between the lines

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Keeping the Earthsafe involves learningfrom past disasters.

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Careers

Shortly after the discovery of supercon-ductivity in 1911, many scientists believedthat it would soon be possible to constructelectromagnets that could generate highfields without the high power requirementsof conventional resistive windings. Thosehopes were, however, quickly dashed whenit was discovered that the presence of mag-netic fields of ~30 mT destroyed a ma-terial’s ability to carry current withoutresistance. It would be another 25 yearsbefore researchers found materials such asPbTl2 that retained some ability to carry cur-rent without resistance in the presence of amagnetic field, and it was not until the late1950s and early 1960s that materials such asNb3Sn and NbTi were developed into formsthat would allow superconducting magnetsto be manufactured commercially.

One of the first firms to take advantage ofthese developments was Oxford Instru-ments, which was formed in 1959 as the firstspin-out company from the University ofOxford. Today, superconducting magnetshave applications that range from the “big physics” of the Large Hadron Colliderthrough to magnetic resonance imaging(MRI) machines used in medical diagnosis,and producing or maintaining them is stillvery much a part of Oxford Instruments’activities. As a consultant magnet engineerin the firm’s nanoscience division, I am in-volved at every step of the process, fromunderstanding customers’ requirements,through design and manufacture, to deliv-ery, installation and technical support.

From welder to magnet engineerMy involvement with superconductivity be-gan almost by accident when, in 1972, I ap-plied for a job as a welder at a company inOxfordshire. I had done my apprenticeshipas a fitter/welder at the UK Atomic EnergyResearch facility in nearby Harwell, and thenspent five years developing advanced weld-ing technologies related to nuclear-fuel andmedical-isotope containment. During thoseyears, I had also studied applied physics part-time at what was then Oxford Polytechnic(now Oxford Brookes University).

Perhaps because of this experience, in-stead of offering me a position as a welder,the company, Thor Cryogenics, asked if I wasinterested in a role as a superconductingmagnet technician – someone responsiblefor winding and assembling superconduct-ing magnets. I had always been interested in science, and the opportunity to work in acompany using superconductivity was veryattractive to me, so I said yes.

My role as a magnet technician developed,and by the time I joined Oxford Instrumentsin 1986 I had moved into project engineer-ing, where I mixed technical activities suchas designing magnets and cryogenic systemswith project-management work like ensur-ing equipment was built on time and withincommercial constraints. In 1999 I progressedto my current role, which is biased towardsthe technical aspects of magnet design.However, most magnet engineers do havesome project-management responsibilities,and I am also involved in mentoring andtraining junior colleagues, visiting customerlaboratories and speaking at conferences.

My career path has not been a typical one:most of my colleagues who have joinedOxford Instruments in recent years havetaken the more academic route of full-timeuniversity education to first degree or evenPhD level. However, there is little formaltraining on the specifics of magnet designavailable, so much of the required knowledgehas to be gained “on the job”. This meansthat a good general education to degree levelin physics or engineering is adequate as a

foundation because it gives you the informa-tion you need to understand the conceptsand processes involved in magnet design and construction.

The design process for a superconductingmagnet is a marriage of mathematical mod-elling and engineering. Today, much of themodelling is done via computer programs,most of which have been developed to pro-vide the specific information needed by themagnet designer. There is, however, a largepart of magnet design that is based on em-pirical data that have built up over the years,related to the processes used to build a work-ing magnet. This is where the engineeringcomes into play, with the need to understandhow to work with the materials and struc-tures used in magnet construction.

A good example of the type of magnet Iam currently working on is one designed foruse in neutron-scattering experiments. Thismagnet has two windings separated by a gapthrough which researchers can fire a neut-ron beam at the sample being studied andobserve the resultant scattered neutrons.This type of magnet is known as a “splitpair” and several factors make it particularlychallenging to design. One is the huge at-tractive forces between the two halves whenthe magnet is energized, which can be ashigh as a few hundred tonnes. Such forcespresent challenges for the mechanical struc-ture and the interfaces between coils andsupporting structure; if the magnet is notdesigned and manufactured correctly, itsperformance can degrade over time. The

A super(conducting) careerJoe Brown explains why he is stillenthusiastic about designing andmanufacturing superconductingmagnets after nearly 40 years inthe industry

Magnetic attraction Joe Brown could not resist the pull of a career in superconductivity.

physicsworld.com


PWApr11careers 17/3/11 17:18 Page 50

usual solution is to separate the two halvesof the magnet with a series of aluminiumalloy rings, which, while sufficiently trans-parent to neutrons, are strong enough tosupport the attractive force.

Another design challenge with this type ofmagnet is that there are trade-offs betweenthe particular geometry of the coils thatwould minimize the superconductor volume(and hence cost), and geometries that pro-duce the required uniformity of magneticfield over the sample volume. Resolving thisproblem normally comes down to a compro-mise depending on the individual circum-stances: financial versus technical.

A third consideration is the need for suffi-cient operating margins in terms of flux den-sity, current density and temperature for thesuperconducting wires used within the mag-net coils. There are also design considera-tions related to dimensional constraints suchas the size of the samples and the neutron-scattering angles. The magnet’s overall size,both mechanically and in terms of “magneticfootprint” (stray flux density), can be a prob-

lem in many applications because of restric-ted access or proximity to other equipment.

When we design magnet structures we doso with the aid of finite-element modelling,where the magnet assembly is computermodelled under its loaded condition to de-termine stress and strain magnitudes anddistributions. This is an iterative process inwhich the structural components are opti-mized to provide the required structuralintegrity. After a magnet has been designed,the next steps are to manufacture and test it.Here, engineers like me are involved at everystage, from defining manufacturing pro-cesses and testing strategies to analysing testresults and presenting them in the form ofoperating instructions and manuals.

Seeing resultsWith my roots firmly in the practical side, Ifind my role very satisfying because it meansthat I get to be involved with the completeprocess – from the customer’s first ideas ofwhat they require to a piece of hardware thatallows the experiment to be performed. I also

get a great sense of pride when I read an ar-ticle or paper detailing the experimental re-sults obtained using a magnet I have designedand helped to manufacture. Most of the mag-nets we manufacture at Oxford Instrumentsare for laboratory-based research and tendto be “one-offs” specially designed to suit aparticular set of experimental requirements.

When it comes to job satisfaction, I thinkthe fact that I have been in the business for almost 40 years says it all. It has not al-ways been easy because, even after 50 yearsof superconducting-magnet manufacture,there are still times when a new behaviourof a magnet will catch you out, leading tosleepless nights when you are trying to workout what is going on. However, it is veryrewarding, and for anyone looking for achallenging role in a hi-tech industry that isstill developing, I cannot think of a betterplace to be.

Joe Brown is a consultant magnet engineer at Oxford Instruments NanoScience, UK, [email protected]

Rob Cook is vice-president ofadvanced technology at PixarAnimation Studios. In 2001 hewon an Oscar for “significantadvancements to the field ofmotion-picture rendering” for co-creating the RenderMan animation software

Why did you decide to study physics?I became interested in it in high school when I reada book on relativity. I thought it was the most fascinating thing around, and I was hooked.

How did you get into computer graphics?After I graduated from Duke University in 1973, Iwas not sure what I wanted to do. However, I hadlearned to program computers as part of a labcourse, so I found a job at the Digital EquipmentCorporation in Massachusetts. There was one person there who was doing computer graphics,but he was actually more interested in medicaldatabases, so I said I would do graphics instead.After I got into it, I thought “This is great, this is whatI want to do”, so I went to Cornell University to get aMaster’s in computer graphics.

How did you get involved in film?At that time, images that were made usingcomputer graphics looked really artificial, like plastic, and nobody knew why. It turned out that themodel they were using for light reflecting offsurfaces was just something someone had madeup – it was not based on physics at all. So for mythesis, I used a different model that included the

physics of how light reflects off surfaces. The resultslooked really good: I was able to simulate particulartypes of materials and really get control over theappearance of the surface. That caught theattention of Lucasfilm, which was just setting up acomputer-graphics division, and it hired me.

What inspired you to develop RenderMan?When you look around, you notice that most thingsare not just made of one material such as bronze orivory. They are more complex than that: they havemultiple materials, they are beaten up, they havescratches. We needed to give artists control overthose surface appearances, so I worked onsomething called programmable shading that usesequations to describe how a surface looks, but alsobuilds a framework over them to allow artists tomake really complex, rich surfaces. That is at theheart of what we do with RenderMan, and over thelast 16 years, every film nominated for visualeffects at the Academy Awards has used it.

How has your training in physics helped you?Aside from my thesis work, it also helped when wewere developing RenderMan. In computer graphics,you have a virtual camera looking at a virtual world,and for special effects you want to match this withlive-action footage. But for it to look convincinglyreal, you have to get the characteristics of your virtual camera to match those of the physical camera. That turns out to be hard for a number ofreasons. One is something called “motion blur”:when a physical camera takes a picture, it opensthe shutter and a certain amount of time goes bybefore it closes. During that time, things move, and

this causes the image to blur. This blur turns out tobe really important for making the motion looksmooth, so you have to simulate it in the renderer.

Another thing you have to simulate is theaperture of the lens – the light is not entering thecamera in one spot, but all over the lens, and thatgives you depth of field. You need to simulate bothblur and lens effects, but that means that not onlyare you integrating the scene around each pixel, youalso have to integrate that pixel over time and overthe lens and over other things. You end up with thisincredibly complex integral, and it turns out thatthere is a technique in physics called Monte Carlointegration that is perfectly suited to dealing with it.

However, none of this stuff was in theundergraduate curriculum – I had to learn it on myown later. What physics really taught me was howto think about things in a creative and rigorous way.It taught me how to think about hard problems.

Any advice for today’s physics students?I always advise people to do something they reallylove because you are likely to be better at it and youare going to spend a lot of time doing it, so it shouldbe something you genuinely enjoy. I think it is amistake to decide “I’m going to go into this eventhough I don’t really like it that much because I thinkit’s going to be a good career”. It is your life, and youwant to spend it doing something you love.

To make the most of your physics degree, visitwww.brightrecruits.com

Once a physicist: Rob Cook

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Spotlight on: Asoke NandiThe subject of this month’sspotlight is Asoke Nandi, aphysicist and engineer atthe University of Liverpool,UK, who has recently been

awarded a Finland DistinguishedProfessorship (FiDiPro). Such grants areawarded by the Finnish government toresearchers who want to collaborate withcolleagues in Finland on specific projects.

Nandi’s project will combine theoreticalstudies of machine learning withexperimental research on how writtenEnglish is pronounced and how the humanbrain responds to music. The connectionbetween these seemingly unrelated topics,he explains, lies in the ability ofcomputational-intelligence algorithms todiscover or “learn” the relationshipsbetween a set of parameters. “Let’s say youwere looking at a series of pictures ofhuman faces and sorting them into facesyou like or don’t like,” Nandi explains. “Youmight not know why you put a face into aparticular group, but a computational-intelligence algorithm can analyse manydifferent parameters and uncover the

underlying relationship between them.”For example, the algorithm might be able todiscover that less-preferred faces exhibitsubtle asymmetries that humans do notperceive consciously.

The technology needed to support suchresearch has only become available in thepast 10–15 years, and Nandi now wants todevelop new algorithms that will helpcomputers to uncover pronunciation rulesfor spoken English, and others that will“teach” computers how to select andclassify patterns in brain scans taken whilea subject listens to different types of music.

Music is closely linked to humanemotion and this link may date back to anearly period of evolution, since it seems tocross cultures. Figure out a link betweenmusic and brain patterns, Nandi argues,and it might one day be possible to recreatethe experience of listening to a symphonyby stimulating the appropriate areas of thebrain, leaving out the ear entirely.

As for the language-learning side of hisproject, Nandi believes that a list of Englishpronunciation rules might help students –particularly those with learning difficulties– to master a language. Part of the reasonhe was drawn to work in Finland, he says, is

that the country’s education system is “very advanced” in the way that it includesstudents with such difficulties in theclassroom, and how it uses the latestresearch to help teach them.

During his four-year stint as a FiDiPro,Nandi plans to spend his summers inFinland, working with researchers in thedepartments of information technology,music and psychology at the University ofJyväskylä in central Finland, and with brain-imaging scientists at Aalto Universityin Helsinki.

Movers and shakersParticle physicists Douglas Bryman of theUniversity of British Columbia, Canada,Laurence Littenberg of the BrookhavenNational Laboratory, US, and A J StewartSmith of Princeton University, US, havewon the American Physical Society’sW K H Panofsky Prize for their role in the1997 discovery of a rare form of kaondecay. The trio will share a $10 000 prize.

Three physicists are among 11 winners ofthe US Presidential Awards for Excellencein Science, Mathematics and EngineeringMentoring. Richard Cardenas of St Mary’sUniversity, Texas, Isaac Crumbly of Fort Valley State University, Georgia, andDouglass Henderson of the University ofWisconsin-Madison each receive $10 000to advance their mentoring programmes.

The Royal Astronomical Society hasawarded its 2011 Gold Medal forAstronomy to Richard Ellis of theCalifornia Institute of Technology for hiswork on cosmology and astronomicalinstrumentation. Eberhard Grun of theUniversity of Colorado received thesociety’s 2011 Gold Medal for Geophysicsfor research on dust in the solar system.

The American Astronomical Society hasawarded its annual Henry Norris RussellLectureship to Sandra Faber of theUniversity of California, Santa Cruz, inrecognition of “a lifetime of seminal contributions” to our understanding ofgalaxy evolution and the distribution ofdark matter in the universe.

Mogens Høgh Jensen of the Niels BohrInstitute in Copenhagen, Denmark, haswon the Gunnar Randers Research Prizefrom the Norwegian Institute for EnergyTechnology. Jensen, a biophysicist,received the DKK 100 000 (£11 000) awardfor his work on complex systems.

Astrophysicist Saul Perlmutter of theUniversity of California, Berkeley, andastronomer Adam Riess of Johns HopkinsUniversity in Maryland, US, will share theAlbert Einstein Society’s 2011 EinsteinMedal for leading the teams thatdiscovered that the expansion rate of theuniverse is accelerating.

Careers and people

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UCL invites applications for an immediate opening for a detector physicist funded as a core-physicist on the UCL STFC rolling grant who will have responsibility for the development and construction of detectors for the HEP group. The successful candidate will have in-depth knowledge in detector physics and hands-on experience in developing, building and commissioning modern as well as traditional detector systems used in particle physics (scintillator and gaseous detectors, semi-conductor detectors, cryogenic equipment etc.). Familiarity with detector readout technologies is also expected. Apart from his/her own research work the appointee will liaise closely and manage a team of engineers and technicians involved in detector projects.

Salary will be in the range from £31,905 to £38,594 per annum inclusive of London Allowance.

The closing date for applications is 15 April 2011.

Further details about the position and the application procedure can be found at http://www.hep.ucl.ac.uk/positions/detector_physicist_Mar2011.shtml.

Detector Physicist

CCApr11ClUCL_9.2x2_PROOF.indd 1 15/03/2011 14:00

Engineer, Final Test & Installation Thermo Fisher Scientific manufactures surface analysis products for both industry and academia, which includes the “R&D 100 Award” winning K-alpha. We now have an exciting opportunity in East Grinstead for an Engineer, Final Test & Installation.

The role will have responsibility for the factory test and for the on-site commissioning of products internationally. Therefore, extensive international travel is required for this role.

Ideally, you will be a graduate in physical sciences or engineering. You will be a confident self-starter and have a hands-on approach to problem solving. Experience of mechanical, electrical/electronic systems, computer systems or UHV vacuum techniques is beneficial, though not essential, as full training will be provided.

To apply, please send a copy of your CV and a cover letter to [email protected] quoting reference TIE.

Thermofisher_Mar11_9x2.indd 1 18/02/2011 09:46PWApr11_classified.indd 53 22/03/2011 10:42



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The closing date for applications is: Tuesday 17 May 2011

For further information about the Cockcroft Institute, visit http://www.cockcroft.ac.uk orcontact Prof. Swapan Chattopadhyay ([email protected])

Lecturer in Science and Engineering(two posts) (Ref: EPS/11799)

Specializing in any of the following areas: Accelerator, Laser,Material, Microwave, Energy, Photon and Instrumentation Sciences

Salary: £36,862 - £45,336 per annumaccording to relevant experience and qualifications

Particle accelerators serve a wide variety ofpurposes. They are used as innovative tools for“discovery-class” scientific research andinvention at many of the most prestigiousnational and international institutes andlaboratories. Accelerators also serve society incritical areas of need in energy, security, healthand medicine.

The Cockcroft Institute in the UK is a uniqueinternational centre specifically responsible forresearch and development in particleaccelerators, colliders and light sources foradvancing the frontier of particle and nuclearphysics, photon and neutron sciences andvarious applications to society in the areas ofhealth, medicine, energy and security. TheUniversity of Manchester is a major stakeholderand one of the founding members, of TheCockcroft Institute - a partnership of theUniversities of Liverpool, Manchester andLancaster, the Science and Technology FacilitiesCouncil including its Daresbury and RutherfordAppleton Laboratories, UK industry andeconomic development agencies.

As part of this important, internationally-leadingactivity at The Cockcroft Institute, candidateswill also have the opportunity to take advantageof the unique research centres provided at theUniversity of Manchester, including the DaltonNuclear Institute, Photon Science Institute andthe Jodrell Bank Centre for Astrophysics.Applications are invited from Physical andApplied Scientists and Engineers with a PhDdegree at the top of their profession seeking anacademic career specialising in ParticleAccelerator Science and Engineering with afocus on applications to any of the disciplines of

Physics, Energy, Optoelectronics, Photonics,Material, Quantum Electronics, Quantum Opticsand various electrical engineering disciplines ofsensors, instrumentation and ultrafast signalprocessing, and electromagnetic modelling.Significant start-up laboratory equipment andinfrastructure is expected to be made availableto the appointed faculty from the Cockcroft andPhoton Science Institutes. The successfulcandidate will be expected to worksynergistically with existing Cockcroft faculty atthe University of Manchester.

Candidates are sought with interest in areassuch as conception and design of particlecolliders, novel light sources and free electronlasers , for fundamental research as well as fordeveloping cost- and energy-efficient photo-voltaic nano-structures towards solar energy,conception and design of high current protonaccelerators for fundamental research andtowards accelerator-driven subcritical reactorsand various applications of proton and photonbeams for health, medicine and security. Theserepresent exciting and challenging opportunitiesfor someone wishing to excel and lead asignificant contribution to world-widedevelopment of tomorrow’s particle acceleratorsystems for science and society.

The Faculty appointment will provide aprestigious start to an academic career with ademonstrable international research dimension.

The successful candidate will already have anextensive track record in internationally-leadingresearch in any of the areas of theoretical,computational or experimental particleaccelerator, laser and photon beam physics in

any of the following areas: linear and nonlinearcharged particle dynamics; collective dynamicsof beam and plasma instabilities; microwave,radio-frequency, terahertz and optical sciencesand engineering; power engineering; materialsscience including nanostructures and photo-voltaics; charged particle and optical beamdiagnostics and digital electronics, optronics,photonics, sensors and instrumentation. S/hewill have a high-impact publication recordcommensurate with such experience. S/he willalso demonstrate proven ability to lecture atpostgraduate and undergraduate level at thehighest levels of quality and support /encourage taught course and research students.An understanding of current global priorities forparticle accelerator science and relatedapplications will be important, together with theability to contribute to and develop existingtaught provision in related areas of curriculawith an international dimension.

Active involvement and collaboration with theexisting Cockcroft faculty and specialistresearch areas within the University ofManchester, along with relevant activitiesparticularly with the other partners in theCockcroft Institute will be encouraged.

Application forms and further particulars areavailable from our websitehttp://www.manchester.ac.uk/jobs.

If you are unable to go online you canrequest a hard copy of the details from EPSHR Office, The University of Manchester,Sackville Street Building, Manchester, M601QD, Tel: 0161 275 8837; Fax: 0161 306 4037or email: [email protected].

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Mathematical, Physical and Life Sciences Division

Department of Physics

University Lectureship in Accelerator ScienceUniversity of Oxford & STFC Rutherford Appleton Laboratory in association with Wolfson College Oxford

and a

Departmental Lectureship in Accelerator ScienceUniversity of OxfordThe John Adams Institute for Accelerator Science (JAI) in Oxford wants to appoint a University Lecturer in Accelerator Science (permanent academic post) on a joint appointment with STFC’s Rutherford Appleton Laboratory, and a Departmental Lecturer in Accelerator Science (a 5-year fixed term appointment). Current projects include novel compact light sources and FELs based on laser-plasma acceleration, linear collider, neutrino factory, the Muon Ionisation Cooling Experiment (MICE), non-scaling Fixed-Field Alternating Gradient accelerators and plasma accelerator diagnostics. Applications are welcome in any area of accelerator science, especially those aligned with the strategic interests of the JAI, for example the development of compact light sources, areas of synergy between laser and plasma physics and accelerator physics, and areas where accelerator science may prove beneficial in technology, energy and medicine. This work involves close international collaboration. Details about the JAI can be found at http://www.adams-institute.ac.uk.

University Lectureship in Accelerator Science, jointly with the STFC Rutherford Appleton LaboratorySalary on the scale £42,733 - £57,431 The appointee will undertake lecturing, research and administration within the JAI and the Department of Physics in Oxford, and will undertake research at the Rutherford Appleton Laboratory. The successful candidate will be offered a supernumerary Fellowship at Wolfson College Oxford; upon completion of a satisfactory review after an initial period of employment (normally five years), a University Lecturer is eligible for reappointment until retiring age.

Departmental Lectureship in Accelerator ScienceSalary on the scale £29,099 - £39,107 This is a 5-year fixed-term appointment. The Appointee will undertake lecturing, research and administration within the JAI and the Department of Physics in Oxford. Informal enquiries about either post may be made to Professor Andrei Seryi, email: [email protected], and further particulars are available at http://www.physics.ox.ac.uk/pp/jobs/JAI-UL-DL-fp.htm. The deadline for applications is 1st June 2011. Interviews will be held in mid June to early July; candidates should consult the web-site for the exact date and keep this date free in case they are called for interview.Applicants should submit before the deadline a letter of application setting out how they meet the criteria set out in the further particulars, supported by a curriculum vitae, list of publications, a statement of research interests to Mrs. Sue Geddes, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK, email: [email protected], FAX 0044-1865-273417. In addition, candidates should arrange for the three letters of reference to be sent to Mrs. Sue Geddes by the closing date. Applicants should state whether they wish to be considered for the University Lectureship, Departmental Lectureship or both.

Committed to equality and valuing diversity

www.ox.ac.uk/jobs

Faculty of Physics and Applied Sciences

Electronics and Computer Science

Physics and Astronomy

The Optoelectronics Research Centre

The University has invested £120M in a major new 1500m2 clean room

complex that is unique in Europe. It houses a full silicon processing line,

a state-of-the-art optical fibre and integrated circuit fabrication facility

and an advanced suite of nano-processing and instrumentation tools.

The complex is home to the Southampton Nano-Fabrication Centre,

the Southampton Photonics Foundry, the Centre for Photonic

Metamaterials and the EPSRC Centre for Innovative Manufacturing

in Photonics. The three Schools are research-ranked among the top in

the UK and have recently joined forces in a new Faculty to exploit the

huge potential of their fabrication complex. As a result, we are seeking

to make up to six academic appointments to build further

internationally competitive research programmes in the

following areas:

• Nano-electronics and nano-photonics

• Bionanotechnology, biophotonics and planar lightwave technologies

• Quantum optoelectronics and light-matter interactions

• Micro and nano fabrication

• Graphene and other quantum materials and devices

• MEMS/NEMS and spin-based devices

We are particularly seeking persons with an exceptional research track

record and leadership potential at a mid or even an early career stage,

who see this as an extraordinary opportunity to become global leaders

in an exciting topic area. You will work with some of the best-known

names in the field, have all the tools you could hope for and work in a

stimulating research-focused environment. You will contribute to

undergraduate and postgraduate teaching programmes as

appropriate and influence the academic direction of the newly

constituted Faculty. Research fellowship appointments are available

for staff with exceptional research records.

Appointments will be made at senior academic grades, with the

possibility of professorial positions for suitably qualified applicants.

If you are looking to accelerate your research career and think you have

what it takes, please make your formal application to the relevant

academic unit:

• Electronics and Computer Science:

Professor Darren Bagnall, email: [email protected]

• Physics and Astronomy:

Professor Anne Tropper, email: [email protected]

• The Optoelectronics Research Centre:

Professor David Payne, email: [email protected]

Your application must include a full academic CV (including publication

record) and a statement outlining the research you envisage doing in

the next 10 years, together with your vision of how this area at the

University of Southampton will grow under your research leadership.

For more information on the Faculty of Physical and Applied Sciences

please visit www.soton.ac.uk/about/faculties/faculty_physical_applied

_sciences.html

The closing date for this position is 5 May 2011 at 12 noon.

At the University of Southampton we promote equality and

value diversity.

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VICTORIA UNIVERSITY OF WELLINGTONVictoria University delivers internationally-acclaimed results in teaching and research, as well as programmes of national significance and international quality.

As one of Wellington’s largest and most established employers, we’re committed to providing our staff with opportunities for rewards, recognition and development , all within a dynamic and inclusive culture where innovation and diversity are highly valued.

PROFESSOR IN PHYSICS

School of Chemical and Physical SciencesWellington, New Zealand

We are seeking an experimental physicist of professorial standing, with an established record of excellence in research and teaching, who wishes to work in a dynamic multidisciplinary school of physics and chemistry.

The School has a vibrant research programme in experimental and theoretical physics in the fields of astrophysics, condensed matter physics, environmental physics, geomagnetism, and nanotechnology. Candidates will be expected to demonstrate how their research would integrate with and/or synergistically complement the existing strengths of the School (http://www.victoria.ac.nz/scps/research).

The School hosts the MacDiarmid Institute for Advanced Materials and Nanotechnology, a national Centre of Research Excellence. There are strong collaborations with three government research laboratories in the Wellington region, and with other national and international research organizations. The School has modern, well-equipped laboratories, and a research community that includes nearly one hundred postgraduate students and postdoctoral fellows.

The School of Chemical and Physical Sciences offers a full range of undergraduate and postgraduate degrees, with undergraduate majors in Physics and Applied Physics. To be a successful applicant you must demonstrate your ability to teach physics at all levels and have an outstanding record of published research with an established international reputation in a field of relevance to the School. Experience of academic leadership is expected of professorial candidates. Resources required by the successful candidate to establish their research within the School will be negotiable.

For further information visit http://www.victoria.ac.nz/scps/ or contact Professor John L Spencer, [email protected]

Applications close 26 April 2011

Victoria University of Wellington is an EEO employer and actively seeks to meet its obligations under the Treaty of Waitangi.

For more information and to apply online visit http://vacancies.vuw.ac.nz

Reference A065-11E

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University Lectureship in Theoretical High Energy PhysicsDepartment of Physics£36,862 - £46,696 pa

Applications are invited for a University Lectureship in Theoretical High Energy Physics to commence on 1 October 2011 or as soon as possible thereafter. Appointment will be made at an appropriate point on the scale for University Lecturers and will be for a probationary period of five years with appointment to the retiring age thereafter, subject to satisfactory performance.

The lectureship will be based in the Department of Physics as part of the High Energy Physics group in the Cavendish Laboratory. The appointment will consolidate the recent expansion of the group, and is intended to strengthen the group’s existing international reputation in particle physics phenomenology (http://www.hep.phy.cam.ac.uk/theory/). The successful candidate will have a world-class research record in phenomenology and will be expected to work closely with the Cavendish Laboratory’s experimental High Energy Physics group, currently involved in the ATLAS, LHCb and MINOS experiments. The post is part of the Extreme Universe strategic theme of the School of the Physical Sciences, building on existing strengths and collaboration between the Department of Physics, the Institute of Astronomy and DAMTP. The successful candidate will be expected to contribute to teaching and other academic activities in the Cavendish.

Informal enquiries about the post may be addressed to Professor James Stirling ([email protected]) and further information about the Department may be found at http://www.phy.cam.ac.uk.

Further details are available from Ms Leona Hope-Coles ([email protected]) to whom applications should be sent by email consisting of a full curriculum vitae,list of publications, a statement (up to 6 pages) of research interests and future plans, and the names and contact details of three academic referees. Applications should be accompanied by a completed CHRIS/6 cover sheet, Parts 1 and 3 only, (see: http://www.admin.cam.ac.uk/offices/hr/forms/chris6/) and should be received no later than 20 April 2011.

Please quote reference: KA07953. Closing date: 20 April 2011.

The University is committed to Equality of Opportunity.

A world of opportunities

www.cam.ac.uk/jobs/ Lancaster University is currently ranked as a top 10 UK university and in the top 125 universities in the world.

Professor/Reader in ExperimentalCondensed Matter PhysicsSalary will be competitive and subject to negotiation Ref: A083RLancaster University wishes to appoint an outstanding experimentalphysicist at the level of Professor or Reader (equivalent to a FullProfessor or Associate Professor respectively), to lead the creation of a new group specialising in emerging research materials and devices.Activities could encompass low dimensional materials, quantumstructures or cutting edge nano-scale electronic and photonic devices.You will be expected to develop a world-class research programme andwill be supported by substantial university investment in equipment and personnel. This initiative is part of a major investment in a multi-disciplinary Quantum Technology Centre, including new clean roomswith state-of-the-art fabrication and characterisation facilities.Lancaster’s Department of Physics was ranked first and equal-first inthe 2008 and 2001 UK Research Assessment Exercises respectivelyand is seeking to further enhance its scientific standing.The post is permanent and tenable from 1 October 2011. In addition to your research activities, you will also be involved with undergraduateand postgraduate teaching. Salary will be competitive and subject to negotiation.

If you are an ambitious scientist with an international reputation for excellence in research, please contact Professor Peter Ratoff,Head of Department, on tel: +44 1524 593639 or email:[email protected] or Professor Colin Lambert, Director of the Quantum Technology Centre, on tel: +44 1524 593059 or [email protected] for an informal discussion.Closing date: 23rd May 2011.To apply, access further information or register for email job alerts please visit our website.

www.hr-jobs.lancs.ac.uk

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Consortium for Construction, Equipment and Exploitation of the Synchrotron Light Laboratory

Director position at the ALBA light source The Consortium CELLS - jointly owned by the Spanish and Catalan Administrations – is responsible for the operation and future development of ALBA, a 3 GeV third generation synchrotron light facility. At present, the construction is finished and the accelerator complex is being commissioned. Seven state of the art beamlines covering a variety of research fields are already installed and expected to be commissioned with photons by mid 2011 and fully open to external users in 2012. Details may be found at www.cells.es.ALBA is located in Cerdanyola del Vallès, at some 20 km from Barcelona, in a metropolitan region of about 4.5 million people, a zone of improving scientific and technological level, with several international schools, universities and scientific and technological parks and with very good international communications.The Consortium is looking for a new Director of the facility. The Director is responsible for the scientific and technical exploitation of ALBA, for the definition of short and long term development strategies and must report to the Governing Bodies of the Consortium (an Executive Commission and a Rector Council whose delegates are appointed by the Owner Administrations).Candidates must have experience in research institutes or similar facilities, a solid experience with synchrotron light research and have qualifications for Directorship. The working language at Alba is English. Knowledge of Spanish and or Catalan is an asset. The Director will be offered a full time contract according to the Spanish law. Employment conditions and salaries can take into account the needs of professionals and their families. The incorporation date to the position is expected in January 2012.Applications should be sent to the Chairman of the Executive Commission of ALBA; Carretera BP 1413 de Cerdanyola a Sant Cugat, km 3.3; E 08290 Cerdanyola del Vallès; Spain. Candidates should send a letter of motivation and their CV to the Chairman of the Executive Commission of ALBA Prof. Ramon Pascual ([email protected]).Deadline for receiving applications: 15th May 2011.

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I can still remember the first time I heard the word su-perconductor. (A great moniker, by the way, catchy andaccurate). We were told in school that some chap Onnesdiscovered that the electrical resistance of mercury dis-appeared when cooled to 4.2 K (of course, why anyonewould be conducting experiments at this sort of tempera-ture was not explained, but he got a Nobel prize for thissort of thing). The news puzzled me greatly: what aboutOhm’s law? Didn’t I = V/R imply that an infinitely largecurrent could arise under such circumstances? Wasn’t thatdangerous? From that point on, I thought of Ohm’s lawas Ohm’s relation-that-is true-for-some-materials-at-some-temperatures. This was an early lesson in the ap-proximate nature of some physical laws.

Superconductivity showed up again in my first year atuniversity. This time around, it was even more mysterious.Apparently, a material in superconducting state couldrepel an external magnetic field, and even levitate a smallmagnet (another Nobel prize). Clearly, there was some-thing special about these materials; superconductors werenot merely super conductors! However, it was not until Iwas immersed in the horrors of third-year quantum phys-ics that some sort of explanation was forthcoming.

Ah, yes, that business of energy gaps and Cooper pairs;according to the theory of Bardeen, Cooper and Schrieffer(BCS), electrons could get together in pairs and act inconcert. Another Nobel prize, but I must confess I didn’treally understand the theory at the time. (It was years laterthat I realized that the point was that electrons in a super-conducting phase can form a condensate not unlike aBose–Einstein condensate.)

Anyway, the boffins must have got something right;there were plenty of successful applications of supercon-ductor technology already in existence when I was a stu-dent in the mid-1980s, from memory devices based onJosephson junctions to sensitive magnetometers utilizingthe splendidly named SQUIDs (superconducting quan-tum interference devices, if you must). Of course, the killerapplication was the superconducting magnet, a technol-ogy ideal for the intense magnetic fields required by high-energy particle accelerators to bend particles into acircular path. And how could anyone forget the Supercon-ducting Super Collider (SSC)? I was still an undergradu-ate when the SSC was approved; sadly, it was destinednever to be built.

Around this same time, along came superconductivitymark 2. I had just started a PhD in semiconductor physicsat Trinity College Dublin when suddenly everyone wastalking about a brand new phenomenon – the discoveryof high-temperature superconductors by Müller andBednorz (yet another Nobel prize). However, it soontranspired that the correct expression should have beenhigher-temperature superconductors; the new materialshad critical temperatures of 30K, which still called for veryspecialized experimentation. Another snag was that thesematerials were not simple compounds but complex cer-amics with names such as lanthanum–barium–copper-oxide. (Ceramics? I thought ceramics were insulators.)Such materials necessitated skilled chemists and mater-ials scientists on the team, so my supervisor and I decidedto stick with semiconductors.

Still, it was a very exciting time in physics, with research

teams around the world cooking up ceramics of everycombination and reporting superconductors with everhigher critical temperatures. By 1987 materials with crit-ical temperatures above 77 K had been discovered. Sud-denly, superconductivity research was no longer thepreserve of the world’s richest labs; experiments could bedone using liquid nitrogen as a refrigerant. I remembercolleagues in the research group of Mike Coey, an experi-mentalist at Trinity, making several significant advances.

Intriguingly, it emerged at around this time that goodold BCS theory could not account for the new class ofsuperconductors. Indeed, there seemed to be no sign ofan underlying explanation. I have a vivid memory of Coeyremarking acidly at a public seminar that there seemed tobe as many theories as there were theorists. In the absenceof a successful theory, brute empirical work forged aheadin a manner the philosopher Ernst Mach would surelyhave admired.

All in all, it seemed at the time that materials science was truly at the cutting edge of physics. Anything was poss-ible. It was straight into this atmosphere that Pons andFleischmann dropped their announcement of cold fusion.The story of the cold-fusion controversy has been toldmany times, but superconductivity is rarely mentioned. YetI’m convinced it played a role. Physicists had just beenshown how little we knew of the solid lattice and nothingwas off the table. Indeed, quite a few of my contemporarieswere diverted into cold-fusion research for some months.

What is the state of play with superconductivity now?Progress with novel superconducting materials has con-tinued, but the holy grail of this field – a material thatexhibits superconductivity at room temperature – remainsas elusive as ever. There is also still no sign of a successfultheory for the effect, so there is another superconductingNobel out there for someone...

Cormac O’Raifeartaigh lectures in physics at Waterford Institute ofTechnology in Ireland and is currently a research fellow with theScience, Technology and Society Group at the Kennedy School ofGovernment of Harvard University, US, e-mail [email protected]

Superconductor memories

Superconductorswere not merelysuper conductors

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physicsworld.comLateral Thoughts: Cormac O’Raifeartaigh


PWApr11lateral 17/3/11 14:21 Page 60


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SUPERCONDUCTIVITY - University of Warwick

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