Breakdown of the escape dynamics in Josephson junctions

TL;DR

This paper investigates the anomalous escape behavior in high critical current density Josephson junctions, revealing local nonequilibrium dynamics that challenge the realization of macroscopic quantum phenomena in such systems.

Contribution

It demonstrates that high Jc Josephson junctions exhibit local nonequilibrium escape dynamics, diverging from standard stochastic models, impacting quantum applications.

Findings

High Jc junctions do not follow expected stochastic switching distributions.

Switching current distributions indicate local rather than global dynamics.

Macroscopic quantum phenomena are unlikely in high Jc junctions.

Abstract

We have identified anomalous behavior of the escape rate out of the zero-voltage state in Josephson junctions with a high critical current density Jc. For this study we have employed YBa2Cu3O7-x grain boundary junctions, which span a wide range of Jc and have appropriate electrodynamical parameters. Such high Jc junctions, when hysteretic, do not switch from the superconducting to the normal state following the expected stochastic Josephson distribution, despite having standard Josephson properties such as a Fraunhofer magnetic field pattern. The switching current distributions (SCDs) are consistent with nonequilibrium dynamics taking place on a local rather than a global scale. This means that macroscopic quantum phenomena seem to be practically unattainable for high Jc junctions. We argue that SCDs are an accurate means to measure nonequilibrium effects. This transition from global to local dynamics is of relevance for all kinds of weak links, including the emergent family of nanohybrid Josephson junctions. Therefore caution should be applied in the use of such junctions in, for instance, the search for Majorana fermions.