Probing long-range correlations in the Berezinskii-Kosterlitz-Thouless fluctuation regime of ultra-thin NbN superconducting films using transport noise measurements

TL;DR

This study uses transport noise measurements to detect long-range correlations and distinguish the nature of superconducting transitions in ultra-thin NbN films, revealing the influence of film inhomogeneity.

Contribution

It introduces a novel fluctuation-based kinetic method to identify BKT versus mean field transitions in disordered low-dimensional superconductors.

Findings

Non-Gaussian resistance fluctuations are sensitive to film thickness.

The non-Gaussian component bounds the transition temperatures.

Film roughness and inhomogeneity significantly affect fluctuation behavior.

Abstract

We probe the presence of long-range correlations in phase fluctuations by analyzing the higher-order spectrum of resistance fluctuations in ultra-thin NbN superconducting films. The non-Gaussian component of resistance fluctuations is found to be sensitive to film thickness close to the transition, which allows us to distinguish between mean field and Berezinskii-Kosterlitz-Thouless (BKT) type superconducting transitions. The extent of non-Gaussianity was found to be bounded by the BKT and mean field transition temperatures and depend strongly on the roughness and structural inhomogeneity of the superconducting films. Our experiment outlines a novel fluctuation-based kinetic probe in detecting the nature of superconductivity in disordered low-dimensional materials.