Vortex Dynamics and Defects in Simulated Flux Flow

TL;DR

This paper uses molecular dynamics simulations to study vortex flow in disordered superconductors, revealing a transition from correlated to plastic flow characterized by distinct velocity distributions.

Contribution

It identifies two flow regimes in vortex arrays driven through random pinning, introducing velocity distribution bimodality as a signature of plastic flow.

Findings

Weak disorder leads to crinkle flow with single-peaked velocity distribution.

Strong disorder causes plastic flow with bimodal velocity distribution.

Velocity distribution shifts and bifurcates depending on disorder strength.

Abstract

We present the results of molecular dynamic simulations of a two-dimensional vortex array driven by a uniform current through random pinning centers at zero temperature. We identify two types of flow of the driven array near the depinning threshold. For weak disorder the flux array contains few dislocation and moves via correlated displacements of patches of vortices in a {\it crinkle} motion. As the disorder strength increases, we observe a crossover to a spatially inhomogeneous regime of {\it plastic} flow, with a very defective vortex array and a channel-like structure of the flowing regions. The two regimes are characterized by qualitatively different spatial distribution of vortex velocities. In the crinkle regime the distribution of vortex velocities near threshold has a single maximum that shifts to larger velocities as the driving force is increased. In the plastic regime the distribution of vortex velocities near threshold has a clear bimodal structure that persists upon time-averaging the individual velocities. The bimodal structure of the velocity distribution reflects the coexistence of pinned and flowing regions and is proposed as a quantitative signature of plastic flow.