Disordered vortex matter out of equilibrium: a Langevin molecular dynamics study

Abstract

We discuss the use of Langevin molecular dynamics in the investigation of the non-equilibrium properties of disordered vortex matter. Our special focus is set on values of system parameters that are realistic for disordered high-Tc superconductors such as YBCO. Using a discretized elastic line model, we study different aspects of vortices far from thermal equilibrium. On the one hand we investigate steady-state properties of driven magnetic flux lines in a disordered environment, namely the current-voltage characteristics, the gyration radius, and the pinning time statistics. On the other hand we study the complex relaxation processes and glassy-like dynamics that emerge in type-II superconductors due to the intricate competition between the long-range vortex-vortex repulsion and flux pinning due to randomly placed point defects. To this end we consider different types of sudden perturbations: temperature, magnetic field, and external current quenches.

Enhanced flux pinning in YBCO multilayer films with BCO nanodots and segmented BZO nanorods

“…The simulation takes into account vortex-vortex interaction 22,32 , vortex-pinning site interaction 33 and line tension 34 due to vortex line energy. Furthermore, the magnetic energy of the vortex in magnetic field was also included and vortices were also subject to Lorentz force due to current in the superconductor.…”

“…Calculations are usually based on solving Ginzburg-Landau equations 19,20 where all the interactions come into the model intrinsically but these models are computationally expensive. Another way to study vortices is to use molecular dynamics (MD) simulations 21,22 to describe effective vortex dynamics. However, such models have previously been used only as toy models for studying the critical dynamics of vortex flow.…”

Pinning time statistics for vortex lines in disordered environments

“…We set the layer spacing equal to the pinning center radius γ = b 0 . In previous work [13,14], we have extensively tested this discretized elastic line model and verified that it correctly reproduces the expected thermodynamic phases (for F = 0) as well as the established nonequilibrium steady-state properties at finite drive current.…”

Structural relaxation and aging scaling in the Coulomb and Bose glass models

“…This study is significant because it analyzes the effects of abrupt changes in the external magnetic field on the spatial rearrangements of magnetic vortex lines in type-II superconductors, while our earlier work in Ref. [25,26] focused on the flux lines height fluctuations and the structural relaxation time regime remained inaccessible.…”

“…Thereafter, Refs. [25,26] utilized these Langevin molecular dynamics simulations to investigate the effects of flux line density quenches on the lines' transverse fluctuations and found that the aging scaling exponents for these transverse fluctuations depended on the choice of initial conditions [24,25,26]. The structural rearrangements of these vortex lines could not be probed in the computationally accessible time scales.…”