Anisotropic Vortex Squeezing in Synthetic Rashba Superconductors: A Manifestation of Lifshitz Invariants

Abstract

Epitaxial superconductor-semiconductor heterostructures combine superconductivity with strong spin-orbit interaction resulting in synthetic Rashba superconductors. The theoretical description of such superconductors involves Lifshitz invariants that are predicted to feature numerous exotic effects with so far sparse experimental evidence. Using a new observable—vortex inductance—we investigate the pinning properties of epitaxial Al/InAs-based heterostructures. We find a pronounced decrease of the vortex inductance with increasing in-plane field which corresponds to a counterintuitive increase of the pinning force. When rotating the in-plane component of the field with respect to the current direction, the pinning interaction turns out to be highly anisotropic. We analytically demonstrate that both the pinning enhancement and its anisotropy are consequences of the presence of Lifshitz invariant terms in the Ginzburg-Landau free energy. Hence, our experiment provides access to a fundamental property of Rashba superconductors and offers an entirely new approach to vortex manipulation.