Thermal escape of fractional vortices in long Josephson junctions

TL;DR

This paper investigates how thermal fluctuations cause fractional vortices in long Josephson junctions to escape at subcritical currents, combining experiments, simulations, and theoretical analysis to understand the influence of junction geometry and topological charge.

Contribution

It provides a comprehensive experimental and theoretical analysis of thermally induced vortex escape in long Josephson junctions, including effects of geometry and topological charge.

Findings

Thermal fluctuations induce vortex escape below critical current.

Junction geometry influences escape probability and dynamics.

Results align with theoretical predictions for infinite junctions.

Abstract

We consider a fractional Josephson vortex in a long 0-kappa Josephson junction. A uniformly applied bias current exerts a Lorentz force on the vortex. If the bias current exceeds the critical current, an integer fluxon is torn off the kappa-vortex and the junction switches to the voltage state. In the presence of thermal fluctuations the escape process takes place with finite probability already at subcritical values of the bias current. We experimentally investigate the thermally induced escape of a fractional vortex by high resolution measurements of the critical current as a function of the topological charge kappa of the vortex and compare the results to numerical simulations for finite junction lengths and to theoretical predictions for infinite junction lengths. To study the effect caused by the junction geometry we compare the vortex escape in annular and linear junctions.