Activated vortex lattice transition in a superconductor with combined sixfold and twelvefold anisotropic interactions

TL;DR

This study uses numerical simulations to explore how vortex lattice phases in a superconductor transition from metastable to ground states under combined anisotropic interactions and external drives, revealing complex decay dynamics.

Contribution

It introduces a simulation approach to analyze vortex lattice transitions with combined sixfold and twelvefold anisotropic interactions, highlighting the decay process under oscillating drives.

Findings

Metastable twelvefold vortex state decays to sixfold under drive.

Decay involves a two-step process with avalanches and dislocation annihilation.

Results align with neutron scattering observations in MgB2.

Abstract

Numerical simulations are used to examine the transition dynamics between metastable and ground state vortex lattice phases in a system with combined sixfold and twelvefold contributions to the vortex-vortex interactions. The system is initially annealed using a twelvefold anisotropy, yielding domains of two different orientations and separated by grain boundaries. The vortex-vortex interaction is then suddenly changed to a sixfold anisotropy, rendering the twelvefold state metastable. Applying a drive that mimics an oscillating magnetic field causes the metastable state to decay, indicated by the structure factor that evolves from twelve to six peaks. The results fit the behavior seen in recent small-angle neutron scattering studies of the vortex lattice in MgB2. At higher drive amplitudes, the decay exhibits a two step process in which the initial fast decrease is followed by a slower regime where avalanches or bursts are correlated with dislocation annihilation events. The results are compared to other types of metastable systems with quenched disorder that decay under a periodic external drive.