Negative Temperatures in Type-II Superconductors

Abstract

The possibility of attaining negative temperatures demonstrated by Onsager for ensembles of vortices in a two-dimensional fluid, is investigated for current vortices in a two-dimensional Type-II superconductor. As in the fluid, their phase space is finite, corresponding to classical equations of motion which are of first order in the time. Clustering of vortices of the same sign, which might be indicative of negative temperature has been reported for various materials but explained differently. No observation is known of the characteristic precession of nearby pairs. It is not yet clear how a negative-temperature instability, if one exists, could be exploited as a negative resistance.