Anisotropic renormalized fluctuations in the microwave resistivity in YBCO

TL;DR

This paper investigates the impact of uniaxial anisotropy on renormalized order-parameter fluctuations in YBCO, explaining microwave resistivity behavior above Tc through an extended theoretical model and experimental data.

Contribution

It extends the isotropic fluctuation theory to account for anisotropy effects in YBCO, aligning theoretical predictions with microwave and dc resistivity measurements.

Findings

The extended theory accurately describes the onset of superconductivity.

Departure from Gaussian fluctuations toward renormalized fluctuations is observed.

Consistent superconducting parameters are obtained from theory and experiments.

Abstract

We discuss the excess conductivity above Tc due to renormalized order-parameter fluctuations in YBCO at microwave frequencies. We calculate the effects of the uniaxial anisotropy on the renormalized fluctuations in the Hartree approximation, extending the isotropic theory developed by Dorsey [Phys. Rev. B 43, 7575 (1991)]. Measurements of the real part of the microwave resistivity at 24 and 48 GHz and of the dc resistivity are performed on different YBCO films. The onset of the superconducting transition and the deviation from the linear temperature behavior above Tc can be fully accounted for by the extended theory. According to the theoretical calculation here presented, a departure from gaussian toward renormalized fluctuations is observed. Very consistent values of the fundamental parameters (critical temperature, coherence lenghts, penetration depth) of the superconducting state are obtained.