A new discovery has the superconductivity community abuzz: A boron-containing metal compound that superconducts at 39 K, nearly twice the temperature of the previous metallic record holder. Although some ceramics can superconduct at temperatures up to 96 degrees higher, most metallic compounds make better wires for magnetic resonance imaging (MRI) machines and other applications.
Researchers have spent decades looking at boron-containing compounds for hints of superconductivity, because theory suggests they should have a relatively high superconducting temperature. Some do. But magnesium diboride (MgB2) beats them hands down, as physicist Jun Akimitsu of Aoyama Gakuin University in Tokyo reported at the Symposium on Transition Metal Oxides, held in Sendai, Japan, on 10 January. The result has already been replicated by other teams, and now physicists are racing to make sense of MgB2's abnormally high superconducting temperature.
Materials superconduct when electrons inside overcome their usual repulsion and pair up; that allows them to surf through a material's crystalline lattice without banging into atoms that would slow their progress. But in most metallic superconductors these pairs break apart when the temperature rises much above 20 K. So figuring out what is keeping electron pairs together at nearly 40 K in MgB2 has become the latest contest in the most competitive area of materials physics. "I can't sleep," says Jorge Hirsch, a superconductivity theorist at the University of California, San Diego. "It's extremely exciting." Hirsch's insomnia may be short lived. A series of papers posted to the Los Alamos physics preprint server this month report that MgB2's behavior strongly resembles that of its closest metallic cousins.
No matter what the mechanism, MgB2 could generate an even greater buzz in the real world. Despite the hype that accompanied the earlier high-temperature superconductors, low-temperature metallic superconductors continue to dominate the applications arena, because these materials can be fashioned into wires that carry large currents. Yesterday, a team led by Iowa State University physicist Paul Canfield reported on the Los Alamos site that they've already made superconducting MgB2 wires. Because magnesium and boron are cheap compared to other metallic superconductors, MgB2 could be in store for a powerful future.
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