Dynamics of Magnetic Vortices with Twofold Anisotropic Interaction Potential*

The dynamics of vortices in type-II superconductors has been studied extensively in systems with an isotropic vortex-vortex interaction potential; however, much less is known about systems in which the potential is anisotropic. We use molecular dynamics simulations to study the dynamics of vortices with twofold anisotropic interactions, for driving forces applied along the two principal symmetry directions of the interaction potential. The simulations are performed with varying numbers of randomly placed pinning sites to represent the defects which are always present in real materials. We find that as the anisotropy of the potential is increased, the vortex lattice defect density becomes less sensitive to the magnitude of the applied drive. Furthermore, the system exhibits a hysteresis effect in which, for a decreasing drive, an ordered state persists down to currents below the threshold current at which the ordered state first forms for an increasing drive. We discuss these results and their possible underlying mechanisms.