Quantum limit of the triplet proximity effect in half-metal - superconductor junctions

TL;DR

This paper investigates the quantum mechanical limits of the triplet proximity effect in superconductor-half metal junctions using a scattering matrix approach, revealing conditions where zero bias conductance vanishes but Josephson current persists.

Contribution

It introduces a scattering matrix method to analyze the triplet proximity effect in quantum limit systems, surpassing previous quasiclassical approaches.

Findings

Zero bias Andreev conductance vanishes in certain junctions.

Nonzero zero bias Josephson current exists despite vanishing conductance.

Method applicable to single-channel and quantum dot systems.

Abstract

We apply the scattering matrix approach to the triplet proximity effect in superconductor-half metal structures. We find that for junctions that do not mix different orbital modes, the zero bias Andreev conductance vanishes, while the zero bias Josephson current is nonzero. We illustrate this finding on a ballistic half-metal--superconductor (HS) and superconductor -- half-metal -- superconductor (SHS) junction with translation invariance along the interfaces, and on HS and SHS systems where transport through the half-metallic region takes place through a single conducting channel. Our calculations for these physically single mode setups -- single mode point contacts and chaotic quantum dots with single mode contacts -- illustrate the main strength of the scattering matrix approach: it allows for studying systems in the quantum mechanical limit, which is inaccessible for quasiclassical Green's function methods, the main theoretical tool in previous works on the triplet proximity effect.