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High-temp superconductivity study progresses; says researchers

Posted: 10 Jul 2006     Print Version  Bookmark and Share

Keywords:superconductivity  Cooper pair  electron  magnetic resonance  NIST 

Researchers said they have moved a step closer to understanding the mechanism behind high-temperature superconductivity.

The discovery of a high-temperature superconductor (bismuth strontium calcium copper oxide) by IBM in 1986 made lower-cost devices feasible.

Since then, researchers have been trying to understand why these materials superconduct at such a high temperature. Their aim is to design materials that superconduct at even higher temperatures—perhaps even at room temperature.

Earlier this year, IBM confirmed that high-temperature superconduction results from a condensate of Cooper pairs—two electrons bound together with opposing spins. But the mechanism responsible for condensing the Cooper pairs remains a mystery.

"This has been the most important problem in condensed matter physics," said University of Tennessee professor Pengcheng Dai, who collaborated with National Institute of Standards and Technology (NIST) physicist Jeffrey Lynn and University of Tennessee doctoral candidate Stephen Wilson.

Working at NIST's Center for Neutron Research, the team claims to have observed what may be the mechanism that binds Cooper pairs, thereby explaining high-temperature superconductivity.

Materials superconduct at high temperatures, they postulate, because of a magnetic resonance. The effect causes an anti-ferromagnetic lattice to oscillate opposing spin orientations. This occurs in synchronization with the opposing spin orientations of those of a Cooper pair passing through the superconductor's molecular lattice.

"The magnetic resonance we observed is a spin-excitation that is intimately related to superconductivity, [or] when a layer of anti-ferromagnetic molecules begin switching their spins back and forth," Dai said. "This may be the glue that binds the Cooper pairs, since it begins just below the critical [superconducting] temperature and intensifies as superconduction progresses."

Dai stopped short of asserting that magnetic resonance causes high-temperature superconduction. "What we are reporting for the first time is that magnetic resonance is universal in both major classes of high-temperature superconductors. We have observed it in electron-doped superconductors and others had already observed it in hole-doped superconductors."

The researchers are next seeking independent verification of their experimental results. Until then, they will continue characterizing the magnetic resonances of high-temperature superconductors.

- R. Colin Johnson
EE Times




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