Depairing currents in superconducting films of Nb and amorphous MoGe

TL;DR

This study measures the depairing current in thin superconducting films of Nb and amorphous MoGe using pulsed currents, successfully comparing experimental results with theoretical predictions across various temperatures.

Contribution

It introduces a pulsed current method to accurately measure depairing currents in superconducting films, overcoming heating and vortex flow challenges.

Findings

Good agreement between experimental and theoretical depairing currents for small samples.

Demonstrates effectiveness of pulsed current technique in superconducting measurements.

Provides data across a range of temperatures below critical temperature.

Abstract

We report on measuring the depairing current J_{dp} in thin superconducting films as a function of temperature. The main difficulties in such measurements are that heating has to be avoided, either due to contacts, or to vortex flow. The latter is almost unavoidable since the sample cross-section is usually larger than the superconducting coherence length \xi_s and the magnetic field penetration depth \lambda_s. On the other hand, vortex flow is helpful since it homogenizes the distribution of the current across the sample. We used a pulsed current method, which allows to overcome the difficulties caused by dissipation and measured the depairing current in films of thin polycrystalline Nb (low \lambda_s, low specific resistance \rho) and amorphous Mo_{0.7}Ge_{0.3} (high \lambda_s, high \rho), structured in the shape of bridges of various width. The experimental values of J_{dp} for different bridge dimensions are compared with theoretical predictions by Kupriyanov and Lukichev for dirty limit superconductors. For the smallest samples we find a very good agreement with theory, over essentially the whole temperature interval below the superconducting critical temperature.