Flux line relaxation kinetics following current quenches in disordered type-II superconductors

Abstract

We investigate the relaxation dynamics of magnetic vortex lines in type-II superconductors following rapid changes of the external driving current by means of an elastic line model simulated with Langevin molecular dynamics. A system of flux vortices in a sample with randomly distributed point-like defects is subjected to an external current of appropriate strength for a sufficient period of time so as to be in a moving non-equilibrium steady state. The current is then instantaneously lowered to a value that pertains to either the moving or pinned regime. The ensuing relaxation of the flux lines is studied via one-time observables such as their mean velocity and radius of gyration. We have in addition measured the two-time flux line height autocorrelation function to investigate dynamical scaling and aging behavior in the system, which in particular emerge after quenches into the glassy pinned state.

Dynamical regimes of vortex flow in type-II superconductors with parallel twin boundaries

“…We have performed a detailed study of the steady-state behavior of vortex matter subject to two parallel extended planar defects oriented perpendicular to the drive for two orientations of the system and several sample thicknesses (ranging from L = 50b 0 to 250b 0 ). These steady-state curves reveal drive regimes not observed in our previous studies [46,48] with point-like and columnar defects, and underscore the richer kinetics accessible with this defect geometry.…”

“…This particular implementation of the elastic line model was previously used by Dobramysl et al [46] to study relaxation and aging phenomena of flux lines in the presence of point-like and columnar disorder. Since then, it has been employed to investigate relaxation dynamics of vortex lines following magnetic field, temperature and drive quenches [47][48][49], as well as the pinning time statistics for flux lines in disordered environments [50]. We have extended this work to here address the dynamics of vortices driven parallel to the x axis, and perpendicular to two parallel planar defects that are placed either a short distance (16 pinning center radii b 0 ) apart or a large distance (160b 0 ) apart.…”

Optimization of high-temperature superconducting multilayer films using artificial intelligence

“…Thus, this approach is not well suited for extensive sampling required for optimization purposes. To date, molecular dynamics (MDs) based upper-level models, where the vortices are modeled as classical objects that interact with the environment based on formulas originating from the profound GL theory, have turned out to be the most efficient approach to simulate J c,v [26][27][28][29][30][31]. In fact, we have previously addressed the optimization of the layer thicknesses in a simple bilayer structure with fixed APC size and concentration using our own MD based model [20].…”

Critical scaling and aging near the flux-line-depinning transition

“…In this present work, we employ an elastic line model to study critical behavior near the depinning transition for vortices in the presence of weak attractive random quenched disorder (point defects) in a three-dimensional system (d = 3) with a two-dimensional displacement vector (N = 2) [42][43][44][45][46][47] . We perform finite-temperature scaling on both steady-state velocity and radius of gyration data and thereby obtain the stationary critical scaling exponents β, δ, and ν that characterize the depinning process as a continuous second-order phase transition at zero temperature, finding β to be in good agreement with experimental values.…”