Universal Voltage Fluctuations in Disordered Superconductors

TL;DR

This paper demonstrates that disordered superconductors exhibit reproducible, antisymmetric voltage fluctuations linked to vortex behavior, revealing quantum vortex effects analogous to universal conductance fluctuations in mesoscopic systems.

Contribution

It provides experimental evidence of universal voltage fluctuations in disordered superconductors and interprets them through the Aronov-Casher effect and random matrix theory.

Findings

Reproducible voltage fluctuations antisymmetric to magnetic field.

Fluctuation behavior matches predictions of Aronov-Casher physics.

Quantum vortex effects observed above and below $T_c$.

Abstract

The Aharonov-Casher effect is the analogue of the Aharonov-Bohm effect that applies to neutral particles carrying a magnetic moment. This can be manifested by vortices or fluxons flowing in trajectories that encompass an electric charge. These have been predicted to result in a persistent voltage which fluctuates for different sample realizations. Here we show that disordered superconductors exhibit reproducible voltage fluctuation, antisymmetrical with respect to magnetic field, as a function of various parameters such as magnetic field amplitude, field orientations and gate voltage. These results are interpreted as the vortex equivalent of the universal conductance fluctuations typical of mesoscopic disordered metallic systems. We analyze the data in the framework of random matrix theory and show that the fluctuation correlation functions and curvature distributions exhibit behavior which is the fingerprint of Aronov-Casher physics. The results demonstrate the quantum nature of the vortices in highly disordered superconductors both above and below $T_c$.