
Neutron probe yields break in superconductor mystery
Date: Thursday, February 01, 2007 @ 22:33:48 UTC Topic: Science
U.S. and Canadian researchers report a major step toward solving a two-decades-old materials science mystery and progress toward the ultimate goal of engineering materials optimized for magnetic and electric properties.
Call it a break in the case of "hidden order and the unconventional superconductor." Writing in the journal Nature Physics, U.S. and Canadian researchers report a major step toward solving a two-decades-old materials science mystery and progress toward the ultimate goal of engineering materials optimized for magnetic and electric properties.
The advance is the result of investigative work done
at the National Institute of Standards and Technology's Center for
Neutron Research (NCNR), and at the National High Magnetic Field
Laboratory (NHMFL) at Florida State University (FSU).
Stray magnetic fields suppress superconductivity, the
resistance-free passage of electric current. But the object of the
team's scrutiny—a uranium-ruthenium-silicon compound (URu2Si2)—somehow
accommodates the normal adversity between magnetism and
superconductivity. At 17.5 degrees above absolute zero, once-nomadic
electrons that had roamed freely about the compound's lattice-like
atomic structure—and generated their own magnetic fields—behave in a
more orderly and cooperative fashion. This coherence sets the stage for
superconductivity.
URu2Si2 belongs to a class of materials
called heavy fermions, known to be reluctant superconductors. This is
because current-carrying electrons in the intermetallic material
interact with surrounding particles and truly gain from the experience.
The association adds mass—making the electrons behave as though they
were a few hundred times more massive than "normal." The heavy
electrons once were thought to make superconductivity impossible.
However, numerous heavy fermion superconductors now are known, and URu2Si2 ranks among the most curious of the lot.
Unexplained was how a "hidden order" suddenly arose in the wake of
the magnetic instabilities caused by the roving electrons, each one
spinning and producing its own miniature magnetic field. With neutron
probes, researchers managed to track electron movements and determined
that the wandering particles work out an unexpected accommodation in
the spacing of their energy levels.
Citation: C.R. Wiebe, J.A. Janik, G.J. MacDougall, G.M.Luke, J.D.
Garrett, H.D. Zhou, Y.J. Jo, L. Balicas, Y. Qiu, J.R.D. Copley, Z.
Yamani and W.J.L. Buyers, Gapped itinerant spin excitations account for
missing entropy in the hidden order state of URu2Si2, Nature Physics, Feb. 2007
Source: National Institute of Standards and Technology
Article via: http://www.physorg.com/news89573666.html
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