Creep motions of flux lines in type II superconductors with point-like defects

TL;DR

This study uses simulations to analyze flux line creep in type II superconductors with point defects, confirming theoretical predictions and revealing a new phase transition related to replica-symmetry breaking.

Contribution

It provides the first simulation-based estimate of the creep exponent for the vortex glass and explores a new phase transition in the Bragg glass phase.

Findings

Pinning barrier increases as force decreases, following a power law.

The creep exponent for vortex glass is approximately 0.28.

The creep exponent for Bragg glass is approximately 0.5, matching theoretical predictions.

Abstract

We simulated the creep motions of flux lines subject to randomly distributed point-like pinning centers. It is found that at low temperatures, the pinning barrier $U$ defined in the Arrhenius-type $v-F$ characteristics increases with decreasing force $U(F) \propto F^{-\mu}$, as predicted by previous theories. The exponent $\mu$ is evaluated as $0.28\pm 0.02 $ for the vortex glass and $\mu\simeq 0.5\pm 0.02$ for the Bragg glass (BrG). The latter is in good agreement with the prediction by the scaling theory and the functional-renormalization-group theory on creep, while the former is a new estimate. Within BrG, we find that the pinning barrier is suppressed when temperature is lifted to approximately half of the melting temperature. Characterizations of this new transition at equilibrium are also presented, indicative of a phase transition associated with the replica-symmetry breaking.