Frequency-dependent fluctuational conductivity above Tc in anisotropic superconductors: effects of a short wavelength cutoff
Abstract
We discuss the excess conductivity at nonzero frequencies in a superconductor above Tc within the gaussian approximation. We focus the attention on the temperature range not too close to Tc: within a time-dependent Ginzburg-Landau formulation, we phenomenologically introduce a short wavelength cutoff (of the order of the inverse coherence length) in the fluctuational spectrum to suppress high momentum modes. We treat the general cases of thin wires, anisotropic thin films and anisotropic bulk samples. We obtain in all cases explicit expressions for the finite frequency fluctuational conductivity. The dc case directly follows. Close to Tc the cutoff has no effect, and the known results for Gaussian fluctuations are recovered. Above Tc, and already for epsilon = ln(T/Tc) > 10-2, we find strong suppression of the paraconductivity as compared to the gaussian prediction, in particular in the real part of the paraconductivity. At high epsilon the cutoff effects are dominant. We discuss our results in comparison with data on high-Tc superconductors.
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