Thermodynamic Fluctuation of the Order Parameter in the Vortex State of Type II Superconductors

Abstract

Restricting ourselves to dirty type II superconductors, we study the effect of the thermodynamic fluctuation of the order parameter in the vortex state. The fluctuation propagator for the order parameter in the vicinity of the upper critical field is determined for all temperatures. The space average of the fluctuation diverges logarithmically in an infinite system, which may imply the instability of the Abrikosov lattice. The excess electrical conductivity in the vortex state due to the thermodynamical fluctuation of the order parameter is then calculated, which diverges like (H_c²-B)^-1/2 as the induction B approaches the upper critical field. Since the coefficient of this diverging term is reasonably large, we believe that this effect is experimentally accessible. We discuss also briefly the excess conductivity above the upper critical field, where the anomalous term (or the Maki term) is rather important.