Press release

Electrons' love-hate relationship breeds superconducting apparition

In a Letter to Nature published this week, scientists in Oxford report that a form of shimmering superconductivity exists at temperatures well above that at which ordinary superconductivity is destroyed. This effect is caused by the tension between the conflicting urges for electrons to pair up (which leads to superconductivity) and to repel each other (which leads to insulating behaviour). The effect has been discovered in a molecular superconductor which is close to the border between superconducting and insulating behaviour so that the tension produced by the electrons' love-hate relationship is most acute: near this border the electrons cannot decide whether to pair up or remain single. If the preference for love very slightly exceeds hate, then it is possible for them to exhibit the shadowy state of fluctuating superconductivity. The discovery was made by Moon-Sun Nam in collaboration with Arzhang Ardavan and Stephen Blundell in Oxford University's Department of Physics, using samples prepared by John Schlueter at Argonne National Laboratory. The team exploited a particularly sensitive probe of superconducting fluctuations called the "vortex-Nernst effect". This effect provides a way of detecting that superconducting vortices are present, even when zero electrical resistance (the characteristic of traditional superconductivity) is not exhibited. Although such shimmering superconductivity above the usual temperature barrier has been observed before in copper-oxide materials, this is the first time it has been seen in an extremely clean and well-controlled system that doesn't have to be chemically doped to produce superconductivity. This means that scientists can be sure that the effect is not associated with impurities. In fact, the team believe that such an effect should be found in all superconductors in which conflicting interactions are finely balanced. This is an important step forward in the quest to understand superconductivity in what are known as "highly correlated" materials: the superconductors of the future.

Fluctuating superconductivity in organic molecular metals close to the Mott transition

Moon-Sun Nam, Arzhang Ardavan, Stephen J. Blundell, and John A. Schlueter,
Nature 449, 584 (2007) Link