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Superconductivity

Superconductivity

The magnetism of superconductivity

04 Feb 2003

Plutonium has been added to the list of superconductors and may shed new light on the mechanism responsible for high-temperature superconductivity

There is something magnetic about superconductivity. Those who work in the field may have started out in a rather casual way, thinking “I will just do this one measurement and then go back to what I was doing before”. But superconductivity holds such a strong fascination that it can soon become a lifelong obsession. One attraction might be the appearance of quantum interference on a macroscopic level, but the mechanism of superconductivity itself also appeals to something quite deep within us.

A crystalline metal is composed of a lattice of positively charged ions. These are left behind when their valence electrons “melt” to produce the electron liquid that is responsible for the current-carrying ability of the metal. Electrons in a metal repel each other violently due to their like-charges, but according to the highly successful Bardeen-­Cooper­-Schrieffer (BCS) theory of 1958, a superconductor can overcome this repulsion by the action of a third party. Pairs of electrons attract each other via fluctuating concentrations of positive charge that they induce on the ionic lattice.

Nature also likes superconductors, because we are finding them in increasingly unlikely places. Now John Sarrao and collaborators at the Los Alamos National Laboratory, the University of Florida and the Institute for Transuranium Elements in Karlsruhe, Germany, have announced the discovery of superconductivity in PuCoGa5 or plutonium cobalt gallium-5 (J L Sarrao et al. 2002 Nature 420 297 – see restircted links). The superconductivity survives up to the astonishingly high temperature of 18 K.

In the February issue of Physics World, Stephen Julian describes the superconducting nature of plutonium in more detail.

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