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

TL;DR

This study uses simulations to demonstrate that interstitial vortices in superconductors with periodic pinning arrays cause anisotropic transport properties, which vary with magnetic field and array geometry, revealing complex vortex dynamics.

Contribution

The paper introduces a simulation-based analysis of how interstitial vortices induce anisotropic transport in superconductors with various artificial pinning arrays, highlighting the role of vortex ordering and array geometry.

Findings

Transport anisotropy varies with magnetic field and array type.

Anisotropy is most pronounced at matching fields.

Multiple reversals of anisotropy occur in honeycomb and kagome arrays.

Abstract

We show using simulations that when interstitial vortices are present in superconductors with periodic pinning arrays, the transport in two perpendicular directions can be anisotropic. The degree of the anisotropy varies as a function of field due to the fact that the interstitial vortex lattice has distinct orderings at different matching fields. The anisotropy is most 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 in spite of the fact that the perpendicular directions of the square pinning array are identical. We show that the anisotropy results from distinct vortex dynamical states and that although the critical depinning force may be lower in one direction, the vortex velocity above depinning may also be lower in the same direction for ranges of external drives where both directions are depinned. For honeycomb and kagome pinning arrays, the anisotropy can show multiple reversals as a function of field. We argue that when the pinning sites can be multiply occupied such that no interstitial vortices are present, the anisotropy is strongly reduced or absent.