Mismatch of conductivity anisotropy in the mixed and normal states of type-II superconductors

Abstract

We have calculated the Bardeen-Stephen contribution to the vortex viscosity for uniaxial anisotropic superconductors within the time-dependent Ginzburg-Landau (TDGL) theory. We focus our attention on superconductors with a mismatch of anisotropy of normal and superconducting characteristics. Exact asymptotics for the Bardeen-Stephen contribution have been derived in two limits: the cases of small and large electric field penetration depth (as compared to the coherence length). Also we suggest a variational procedure which allows us to calculate the vortex viscosity for superconductors with arbitrary ratio of the coherence lenght to the electric field penetration depth. The approximate analytical result is compared with numerical calculations. Finally, using a generalized TDGL theory, we prove that the viscosity anisotropy and, thus, the flux-flow conductivity anisotropy may depend on temperature.