Scaling Behaviors and Novel Creep Motion of Flux Lines under AC Driving

TL;DR

This study uses simulations to analyze how flux lines in type II superconductors respond to AC driving, revealing scaling laws, creep behavior, and critical exponents near the depinning transition.

Contribution

It introduces a detailed analysis of flux line dynamics under AC driving, including new scaling laws and creep motion laws, with systematic finite-size scaling validation.

Findings

Scaling laws for flux-line velocity near depinning

Derivation of a creep law with an effective energy barrier

Frequency influences creep motion similarly to temperature

Abstract

We performed Langevin dynamics simulations for the \textit{ac} driven flux lines in a type II superconductor with random point-like pinning centers. Scaling properties of flux-line velocity with respect to instantaneous driving force of small frequency and around the critical \textit{dc} depinning force are revealed successfully, which provides precise estimates on dynamic critical exponents. From the scaling function we derive a creep law associated with the activation by the regular shaking. The effective energy barrier vanishes at the critical dc depinning point in a square-root way when the instantaneous driving force increases. The frequency plays a similar role of temperature in conventional creep motions, but in a nontrivial way governed by the critical exponents. We have also performed systematic finite-size scaling analysis for flux-line velocity in transient processes with \textit{dc} driving, which provide estimates on critical exponents in good agreement with those derived with ac driving. The scaling law is checked successfully.