Transport Anisotropy as a Probe of the Interstitial Vortex State in Superconductors with Artificial Pinning Arrays

摘要

We show using simulations that when interstitial vortices are present insuperconductors with periodic pinning arrays, the transport in twoperpendicular directions can be anisotropic. The degree of the anisotropyvaries as a function of field due to the fact that the interstitial vortexlattice has distinct orderings at different matching fields. The anisotropy ismost pronounced at the matching fields but persists at incommensurate fields,and it is most prominent for triangular, honeycomb, and kagome pinning arrays.Square pinning arrays can also show anisotropic transport at certain fields inspite of the fact that the perpendicular directions of the square pinning arrayare identical. We show that the anisotropy results from distinct vortexdynamical states and that although the critical depinning force may be lower inone direction, the vortex velocity above depinning may also be lower in thesame direction for ranges of external drives where both directions aredepinned. For honeycomb and kagome pinning arrays, the anisotropy can showmultiple reversals as a function of field. We argue that when the pinning sitescan be multiply occupied such that no interstitial vortices are present, theanisotropy is strongly reduced or absent.