Effect of current quenches on the dynamics of magnetic flux lines in type-II superconductors*

The mixed phase in type-II superconductors is characterized by the presence of mutually repulsive magnetic flux lines with normal cores. While external currents drive these vortices via the Lorentz force, material defects (point-like or extended) in the superconducting material act as pinning centers for them. We describe the disordered vortex system with an elastic line model, whose dynamics we investigate numerically by means of Langevin Molecular Dynamics. We specifically study the effects of sudden changes of the driving current on the time evolution of the mean flux line gyration radius and the associated transverse displacement correlation functions. Within the moving phase, we obtain fast exponential relaxation to a new non-equilibrium stationary state. Upon quenching from the moving into the pinned glassy phase, we observe algebraically slow relaxation kinetics, with the associated breaking of time translation invariance and indications of aging scaling behavior.