Relaxation dynamics in type-II superconductors with point-like and correlated disorder

Abstract

We employ an elastic line model to investigate the steady-state properties and non-equilibrium relaxation kinetics of magnetic vortex lines in disordered type-II superconductors using Langevin molecular dynamics (LMD). We extract the dependence of the mean vortex line velocity and gyration radius as well as the mean-square displacement in the steady state on the driving current, and measure the vortex density and height autocorrelations in the aging regime. We study samples with either randomly distributed pointlike or columnar attractive pinning centers, which allows us to distinguish the complex relaxation features of interacting flux lines subject to extended vs. uncorrelated disorder. Additionally, we find that our new LMD findings match earlier Monte Carlo (MC) simulation data well, verifying that these two microscopically quite distinct simulation methods lead to macroscopically very similar results for non-equilibrium vortex matter.

Relaxation dynamics of vortex lines in disordered type-II superconductors following magnetic field and temperature quenches

“…It is worth noting that when comparing the novel results in this paper to our earlier study in Ref. [33] with random initial conditions, we discovered improved dynamical scaling in the vortex mean-square displacement in all situations considered here. Consequently, the currently utilized more realistic initial conditions help the system to equilibrate faster and thus acquire universal features.…”

“…6(d) in Ref. [33]. In contrast, dynamical scaling is not observed for the heightheight autocorrelation function C(Γ, σ).…”

“…Random initial conditions were considered in our earlier work in Refs. [32,33]. In the present study, we focused on the effects of sudden changes in temperature and magnetic field on the ensuing vortex relaxation properties.…”

“…[32] and [33], where Monte Carlo and Langevin molecular dynamics simulations, respectively, were performed to characterize the complex non-equilibrium relaxation of initially straight and randomly placed vortex lines in the presence of point-like disorder. Thermal spatial fluctuations can also be quantified by means of the vortex line radius of gyration…”

“…Pleimling and Täuber then employed an elastic line model and Monte Carlo simulations to investigate the non-equilibrium relaxation properties of magnetic vortices in type-II superconductors starting from somewhat artificial initial configurations where straight flux lines were placed at random positions in the sample [32]. The resulting complex aging features (with identical initial conditions and parameter values) were subsequently confirmed in a very different microscopic representation of the non-equilibrium vortex kinetics through Langevin molecular dynamics [33]. A systematic investigation of the rich non-equilibrium relaxation dynamics and aging features of complex systems such as disordered vortex matter with various competing energy and time scales is of fundamental interest.…”