Impact of spin-orbit coupling and Zeeman interaction on the subharmonic gap structure due to multiple Andreev reflections in nanoscopic Josephson junctions

TL;DR

This paper theoretically studies how spin-orbit coupling and magnetic fields influence the subharmonic gap structure caused by multiple Andreev reflections in nanoscopic Josephson junctions, revealing new features in conductance.

Contribution

It introduces a theoretical analysis of the impact of spin-orbit coupling and Zeeman interaction on Andreev reflection features in Josephson junctions, highlighting the role of spin polarization.

Findings

Spin-orbit coupling causes avoided crossings in the lead dispersion relation.

These avoided crossings lead to pronounced multiple Andreev reflection features.

External magnetic fields modify the visibility of these features based on band spin polarization.

Abstract

Multiple Andreev reflections in voltage-biased Josephson junctions give rise to the subharmonic gap structure in the conductance, which is widely used to characterize transport properties and estimate the induced gap in the junctions. Here we theoretically investigate the evolution of the subharmonic gap structure in spinful Josephson junctions. Spin mixing introduced by the spin-orbit coupling opens avoided crossings in the dispersion relation of the leads, which, as we demonstrate, subsequently results in pronounced multiple Andreev reflection features in the conductance traces. We analyze how these features evolve under an external magnetic field and explain that their visibility in conductance is governed by the spin polarization of the bands.