Anomalous Fraunhofer Interference in Epitaxial Superconductor-Semiconductor Josephson Junctions

TL;DR

This study explores unusual interference patterns in superconductor-semiconductor Josephson junctions, revealing edge current flow and asymmetries influenced by magnetic fields, with a model explaining the interplay of flux focusing, Zeeman, and spin-orbit effects.

Contribution

It demonstrates anomalous Fraunhofer interference patterns in epitaxial superconductor-semiconductor junctions and provides a comprehensive model explaining these effects.

Findings

Higher order nodes are strengthened indicating edge current flow.

Asymmetries in interference patterns depend on magnetic field direction.

Model shows flux focusing, Zeeman, and spin-orbit effects produce observed anomalies.

Abstract

We investigate patterns of critical current as a function of perpendicular and in-plane magnetic fields in superconductor-semiconductor-superconductor (SNS) junctions based on InAs/InGaAs heterostructures with an epitaxial Al layer. This material system is of interest due to its exceptionally good superconductor-semiconductor coupling, as well as large spin-orbit interaction and g-factor in the semiconductor. Thin epitaxial Al allows the application of large in-plane field without destroying superconductivity. For fields perpendicular to the junction, flux focusing results in aperiodic node spacings in the pattern of critical currents known as Fraunhofer patterns by analogy to the related interference effect in optics. Adding an in-plane field yields two further anomalies in the pattern. First, higher order nodes are systematically strengthened, indicating current flow along the edges of the device, as a result of confinement of Andreev states driven by an induced flux dipole; second, asymmetries in the interference appear that depend on the field direction and magnitude. A model is presented, showing good agreement with experiment, elucidating the roles of flux focusing, Zeeman and spin-orbit coupling, and disorder in producing these effects.