Superconductivity Two Decades On
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NEWS NATURE|Vol 446|8 March 2007 Superconductivity two decades on DENVER, COLORADO They were lionized in the press, celebrated by the US government, and even given exclusive access to New York City nightclubs — that was PHYS. AM. INST. 20 years ago. This week, the physicists who made key early breakthroughs in the field of high-temperature superconductivity recalled their fame and expressed hopes that the field would once again dramatically move forward. Back then, in a marathon session on the evening of 18 March 1987, at a meeting of the American Physical Society, researchers dis- cussed a new-found class of ‘superconducting’ material that carried electrical current with- out resistance at dramatically higher tempera- tures than its predecessors. The impromptu lectures at the New York City Hilton ran until after 3 a.m. and were later dubbed the “Woodstock” of physics. “The euphoria was really unbelievable,” says Paul Grant, a physi- The “Woodstock” of physics: 18 March 1987, when physicists met to discuss a stunning class of material. cist at Stanford University, California, who was there that night. yttrium–barium–copper oxide material that cuprate materials have been discovered, the By contrast, the mood was nostalgic at this could superconduct at 93 K, above the temper- record for superconductivity remains at 164 K, year’s American Physical Society meeting, held ature of liquid nitrogen. The discovery meant about halfway between absolute zero and room this week in Denver, Colorado, when many of that superconductors would be cheaper to cool temperature. The theoretical understanding of those at the original 1987 session gathered for and easier to use. “It created the feeling in many the material is incomplete as well, says physicist a reunion and to discuss the future. people that nothing is impossible,” says Bed- Douglas Scalapino of the University of Califor- Superconducting materials differ markedly norz, who won the 1987 Nobel physics prize nia, Santa Barbara. Although many researchers from other conductors. Normally, the atomic with Müller for their discovery. believe that electrons pairs underlie supercon- lattice in a metal causes electrons to scatter, cre- Condensed-matter physicists found them- ductivity even in these new materials, no one ating heat. But in superconductors, the elec- selves turned into overnight celebrities. “New knows how the electrons bind together. “We trons pair together in a way that allows them to Superconductors Offer Chance to Do the don’t understand what causes it,” he says. travel effortlessly through the material. Super- Impossible,” trumpeted The New York Times. A low point came last September when conductivity was first discov- Physicists were invited to the two German researchers predicted that, given ered in 1911, and described in “It created the feeling White House for a demonstra- current trends, publications of papers in theoretical calculations in 1957 in many people tion to then-President Ronald high-temperature superconductivity would by John Bardeen, Leon Cooper Reagan and given free passes to end between 2010 and 2015. The researchers and John Robert Schrieffer. that nothing a New York City discothèque. later revised their estimates, but not before The materials offer the tan- is impossible.” “It was a heady, heady experi- angering many scientists (see Nature 443, talizing possibility of allowing ence,” says Grant. Buoyed by 376–377; 2006). energy to be transmitted with virtually no loss, the promises, Congress passed the Supercon- But despite the frustrating lack of progress, promising powerful motors and better genera- ductivity Competitiveness Act of 1988, which many remain hopeful. Room-temperature tors. But the low temperatures at which super- boosted funding for the field. superconductors may yet be found, says Chu: conductors originally worked prevented them But there remained a problem. Nobody “At this moment, there’s no evidence, either from being practical. For most of the 1970s and knew exactly how the new materials worked. theoretical or experimental, that tells us it’s 1980s, the record for a high-temperature super- After their initial discovery, little progress was impossible.” conductor remained at a miserable 23 kelvin, made in increasing their operating tempera- And high-temperature cuprates may soon or 23 degrees above absolute zero. tures. And, because the materials were ceramic, find some applications in defence, says Grant. Then in 1986, Georg Bednorz and Alex they proved difficult to manufacture and incor- The materials’ electrical efficiency may make Müller of IBM’s Zurich Research Laboratory porate into existing infrastructures. them useful for high-power microwave beams in Rüschlikon discovered a new class of super- Today, says Grant, little has come of those that can be used to disable small ships. conductor that worked at 30 K. These cuprates, early claims. “No high-temperature supercon- Optimists say the field could be reinvigor- as they are known, consisted of layers of copper ducting technology is turning a profit,” he says. ated at any time by a new discovery, whether oxide with small amounts of other materials “If you reflect back on 1987 there were a lot of through serendipity or otherwise. “If some- added. The IBM work was soon confirmed futures promised, I think irresponsibly.” thing happens, there will be another Wood- by others, including Paul Chu of the Univer- And the scientific field has also slowed. stock and another explosion,” Grant says. ■ sity of Houston, Texas, who discovered an Although more than 100 superconducting Geoff Brumfiel 120.