Anomalous interstitial dynamics, Stokes’ drift, and current inversion in AC-driven vortex lattices in superconductors with arrays of asymmetric double-well traps

Using numerical simulations, we study the response, to an AC square-wave Lorentz force, of an assembly of magnetic vortices interacting with a square lattice of double-well asymmetric pinning centers. The collective AC-driven vortex dynamics becomes rectified for drive amplitudes within an optimal rectification window. Here we focus on the dynamics right above the first matching field, where there are slightly more vortices than pinning traps. Remarkably, for low drive amplitudes the excess vortices, i.e., not sitting in the pinning centers, behave either like highly mobile interstitials confined between two adjacent columns of vortices, or like stable discommensurations of single lattice columns. In both cases these excess vortices exhibit a variety of dynamical responses (e.g., current inversion, Stokes’ drift) depending on the amplitude of the applied force.