Orbital Josephson Interference in a Nanowire Proximity Effect Junction

TL;DR

This paper models a nanowire SNS junction under axial magnetic field, revealing a novel orbital Josephson interference effect caused by subband coupling, with flux-aperiodic oscillations in the critical current.

Contribution

It introduces a theoretical model showing how orbital angular momentum coupling in nanowire junctions leads to unique Josephson interference patterns.

Findings

Flux-aperiodic oscillations in critical current due to orbital effects

Phase shifts in Andreev bound states caused by magnetic field

Reduction to semi-classical model under Andreev approximation

Abstract

A semiconductor nanowire based superconductor-normal-superconductor (SNS) junction is modeled theoretically. A magnetic field is applied along the nanowire axis, parallel to the current. The Bogoliubov-de Gennes equations for Andreev bound states are solved while considering the electronic subbands due to radial confinement in the N-section. The energy-versus-phase curves of the Andreev bound states shift in phase as the N-section quasiparticles with orbital angular momentum couple to the axial field. A similar phase shift is observed in the continuum current of the junction. The quantum mechanical result is shown to reduce to an intuitive, semi-classical model when the Andreev approximation holds. Numerical calculations of the critical current versus axial field reveal flux-aperiodic oscillations that we identify as a novel form of Josephson interference due to this orbital subband effect. This behavior is studied as a function of junction length and chemical potential. Finally, we discuss extensions to the model that may be useful for describing realistic devices.