Frequency-dependent fluctuational conductivity above Tc in anisotropic superconductors: effects of a short wavelength cutoff

TL;DR

This paper investigates how a short wavelength cutoff affects the fluctuational conductivity above T_c in anisotropic superconductors, revealing significant suppression of paraconductivity at high temperatures compared to Gaussian predictions.

Contribution

It introduces a phenomenological short wavelength cutoff in the fluctuational spectrum within a TDGL framework for various anisotropic superconductor geometries, providing explicit formulas for finite frequency conductivity.

Findings

Strong suppression of paraconductivity above T_c at high epsilon values.

Cutoff effects are negligible close to T_c, recovering Gaussian results.

Results align with experimental data on high-T_c superconductors.

Abstract

We discuss the excess conductivity at nonzero frequencies in a superconductor above T_c within the gaussian approximation. We focus the attention on the temperature range not too close to T_c: 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 T_c the cutoff has no effect, and the known results for Gaussian fluctuations are recovered. Above T_c, and already for epsilon = ln(T/T_c) > 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-T_c superconductors.