A dynamical study of phase fluctuations and their critical slowing down in amorphous superconducting films

TL;DR

This study investigates the frequency-dependent complex conductance of amorphous superconducting InO$_x$ films, revealing critical slowing down of fluctuations near the transition, consistent with vortex-like phase fluctuations and phase ordering.

Contribution

It provides the first broadband microwave measurements of phase fluctuations and critical slowing down in amorphous superconducting films, using a novel spectrometer.

Findings

Demonstrates critical slowing down of fluctuation rate near $T_c$

Shows phase fluctuations are vortex-like

Supports phase ordering transition scenario

Abstract

We report a comprehensive study of the complex AC conductance of amorphous superconducting InO$_x$ thin films. Using a novel broadband microwave `Corbino' spectrometer we measure the explicit frequency dependency of the complex conductance and the phase stiffness over a range from 0.21 GHz to 15 GHz at temperatures down to 350 mK. Dynamic AC measurements are sensitive to the temporal correlations of the superconducting order parameter in the fluctuation range above $T_c$. Among other aspects, we explicitly demonstrate the critical slowing down of the characteristic fluctuation rate on the approach to the superconducting state and show that its behavior is consistent with vortex-like phase fluctuations and a phase ordering scenario of the transition.