Hot Prize for Cold Physics

Peeking through. Magnetic field lines (white dots) seen penetrating a type-II superconductor, bearing out Abrikosov's theoretical predictions.

Three theorists have gotten a warm reception for their work on the very cold. Vitaly Ginzburg, Alexei Abrikosov, and Anthony Leggett have been awarded this year's Nobel Prize in Physics and will split the $1.3 million award.

The prize honors Ginzburg and Abrikosov's work on superconductors, materials that lose all electrical resistance at very low temperatures. Superconductivity, which was discovered early in the 20th century, was a baffling phenomenon that seemed to defy conventional wisdom about how materials should behave. In 1950, Ginzburg, of the P. N. Lebedev Physical Institute in Moscow, and colleague Lev Landau formulated a theory that describes how superconductors behave when subjected to a magnetic field. The Ginzburg-Landau theory implied that superconductors can behave in two different ways when exposed to ever-stronger magnetic fields. Type-I superconductors are completely impermeable to magnetism; magnetic "field lines" can't pass through the superconducting material at all. Type-II superconductors, though, have a limited capacity to allow field lines to penetrate. Abrikosov, who's now at Argonne National Laboratory in Argonne, Illinois, built upon the Ginzburg-Landau theory to characterize the behavior of type-II superconductors; he predicted, for example, that penetrating field lines would create a regular lattice pattern in the superconductor, a phenomenon observed directly in 1967.

Although a fuller description of superconductivity would have to await BCS theory, which was formulated by three physicists (Bardeen, Cooper, and Schrieffer) in the late 1950s, "Ginzburg and Abrikosov did extremely important phenomenological work before BCS theory," says Leggett, who hails from the University of Illinois, Urbana-Champaign. Leggett's own contribution, however, has to do not with superconductivity, but superfluidity, a phenomenon wherein very cold liquid helium acquires strange properties, such as flowing without friction. BCS theory explained helium-4's superfluidity nicely, but it didn't seem to work for helium-3. The atoms in helium-3 pair up, making it a more complex beast than the solitary atoms in superfluid helium-4. By taking this complexity into account, Leggett explained how helium-3 superfluidity fits into the existing theory.

"I was absolutely floored," says Robert Schrieffer, a physicist at Florida State University (and the S of BCS theory), of his reaction to Leggett's analysis. "We thought that the reach of the theory would be for ordinary metal superconductors," but not for helium-3. Schrieffer says he repeatedly nominated all three of today's winners for the prize. The Nobel committee certainly agreed--and given that four of the last eight physics Nobels have had to do with the physics of low temperatures, it's clear that cold research doesn't mean a cold shoulder from the Swedish Academy.

Related site
More information about the 2003 Nobel in Physics
Abrikosov's site
Leggett's site

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