Diamagnetic mechanism of critical current non-reciprocity in multilayered superconductors

TL;DR

This paper demonstrates that critical current non-reciprocity in multilayered superconductors arises from diamagnetic currents and Josephson vortex formation under magnetic fields, rather than intrinsic material properties, enabling new device designs.

Contribution

It reveals a diamagnetic mechanism for NRC in multilayered superconductors, independent of crystallographic orientation, and reports experimental observation in InAs/Al nanowires.

Findings

NRC is caused by diamagnetic currents in multilayered structures.

Josephson vortices form at high fields and currents.

NRC evolution with magnetic field is non-monotonic.

Abstract

Recent excitement in observation of non-reciprocal critical current (NRC) is motivated by a suggestion that "superconducting diode effect" may be an intrinsic property of non-centrosymmetric superconductors with strong spin-orbit interactions[1]. Theoretically it has been understood that linear in the Cooper pair momentum terms, caused by the Rashba spin-orbit and Zeeman interactions or, more generally, any symmetry-allowed Lifshitz invariants[2] in uniform singlet superconductors, do not contribute to the supercurrent, although the role of higher-order terms remains unclear[3, 4]. In this work we show that critical current non-reciprocity is a generic property of multilayered superconductor structures in the presence of magnetic field-generated diamagnetic currents. In the regime of an intermediate coupling between the layers, the Josephson vortices are predicted to form at high fields and currents. We report the observation of NRC in nanowires fabricated from InAs/Al heterostructures. The effect is independent of the crystallographic orientation of the wire, ruling out an intrinsic origin of NRC. Non-monotonic NRC evolution with magnetic field is consistent with the generation of diamagnetic currents and formation of the Josephson vortices. This extrinsic NRC mechanism can be used to design novel devices for superconducting circuits.