Microwave fluctuational conductivity in YBa$_{2}$Cu$_{3}$O$_{7-\delta}$

TL;DR

This study measures microwave fluctuational conductivity in YBa2Cu3O7−δ films above Tc, revealing faster decay than traditional theories and confirming a modified gaussian model with renormalization and spectral cutoff.

Contribution

The paper introduces a modified gaussian theory incorporating renormalization and spectral cutoff to accurately describe finite-frequency fluctuational conductivity in anisotropic 3D superconductors.

Findings

Fluctuational excess conductivity decreases faster than traditional models predict.

Slowing down of fluctuations observed near Tc.

Modified theory matches experimental data across frequencies and temperature range.

Abstract

We present measurements of the microwave complex conductivity at 23.9 and 48.2 GHz in YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ films, in the fluctuational region above $T_{c}$. With increasing temperature, the fluctuational excess conductivity drops much faster than the well-known calculations within the time-dependent Ginzburg-Landau theory [H. Schmidt {\em Z. Phys.} {\bf 216}, 336]. Approaching the transition temperature, slowing down of the fluctuations is observed. We discuss the results in terms of a modified gaussian theory for finite-frequency fluctuational conductivity, where renormalization is introduced in order to account for the $T\to T_{c}$ regime, and a spectral cutoff is inserted in order to discard high-momentum modes. The data are in excellent agreement with the modified theory, when formulated for three-dimensional, anisotropic superconductors, in the whole experimentally accessible temperature range, and for both frequencies.