Metastability and uniqueness of vortex states at depinning

TL;DR

This study uses numerical simulations to explore vortex states in type-II superconductors, revealing metastability, the influence of thermal cycling, and a universal defect density at depinning.

Contribution

It demonstrates the metastability and history dependence of vortex states, and uncovers a universal defect density at the depinning transition.

Findings

FC state has lower defect density than ZFC at zero current

ZFC state becomes stable after cycling current

Defect density at depinning is independent of initial state

Abstract

We present results from numerical simulations of transport of vortices in the zero-field cooled (ZFC) and the field-cooled (FC) state of a type-II superconductor. In the absence of an applied current $I$, we find that the FC state has a lower defect density than the ZFC state, and is stable against thermal cycling. On the other hand, by cycling $I$, surprisingly we find that the ZFC state is the stable state. The FC state is metastable as manifested by increasing $I$ to the depinning current $I_{c}$, in which case the FC state evolves into the ZFC state. We also find that all configurations acquire a unique defect density at the depinning transition independent of the history of the initial states.