Nonlocal conductivity in the vortex-liquid regime of a two-dimensional superconductor

We have simulated the time-dependent Ginzburg-Landau equation with thermal fluctuations, to study the nonlocal dc conductivity of a superconducting film. Having examined points in the phase diagram at a wide range of temperatures and fields below the mean field upper critical field, we find a portion of the vortex-liquid regime in which the nonlocal Ohmic conductivity in real space is negative over a distance several times the spacing between vortices. The effect is suppressed when driven beyond linear response. Earlier work had predicted the existence of such a regime, due to the high viscosity of a strongly correlated vortex liquid. This behavior is clearly distinguishable from the monotonic spatial falloff of the conductivity in the higher-temperature or field regimes approaching the normal state. The possibilities for experimental study of the nonlocal transport properties are discussed.