Universality of Frequency and Field Scaling of the Conductivity Measured by Ac-Susceptibility of a Ybco-Film

TL;DR

This study uses an innovative inversion method to analyze ac-susceptibility data, revealing universal scaling behavior of the complex conductivity in a Ybco film across a broad frequency and field range, indicating a vortex-glass phase transition.

Contribution

It introduces a novel exact inversion scheme to determine complex conductivity from ac-susceptibility measurements over wide frequency and field ranges, confirming vortex-glass universality.

Findings

Evidence for a continuous phase transition at T_g to a vortex-glass state.

Critical exponents ν and z are consistent with isotropic vortex-glass models.

Field dependence of conductivity linked to increasing glass coherence length.

Abstract

Utilizing a novel and exact inversion scheme, we determine the complex linear conductivity $\sigma (\omega )$ from the linear magnetic ac-susceptibility which has been measured from 3\,mHz to 50\,MHz in fields between 0.4\,T and 4\,T applied parallel to the c-axis of a 250\,nm thin disk. The frequency derivative of the phase $\sigma ''/\sigma '$ and the dynamical scaling of $\sigma (\omega)$ above and below $T_g(B)$ provide clear evidence for a continuous phase transition at $T_g$ to a generic superconducting state. Based on the vortex-glass scaling model, the resulting critical exponents $\nu $ and $z$ are close to those frequently obtained on films by other means and associated with an 'isotropic' vortex glass. The field effect on $\sigma(\omega)$ can be related to the increase of the glass coherence length, $\xi_g\sim B$.