Andreev reflection from non-centrosymmetric superconductors and Majorana bound state generation in half-metallic ferromagnets

TL;DR

This paper investigates how spin-orbit interaction enables triplet Andreev reflection in half-metal/superconductor interfaces, leading to Majorana bound states in disorder-free systems, with potential implications for topological quantum computing.

Contribution

It demonstrates that spin-orbit interaction induces triplet Andreev reflection and Majorana states in half-metal/superconductor systems, a novel mechanism for topological superconductivity.

Findings

Triplet Andreev reflection occurs due to spin-orbit interaction.

An excitation gap proportional to spin-orbit strength is opened in disorder-free systems.

Majorana bound states are supported at the ends of the half-metal wire.

Abstract

We study Andreev reflection at an interface between a half metal and a superconductor with spin-orbit interaction. While the absence of minority carriers in the half metal makes singlet Andreev reflection impossible, the spin-orbit interaction gives rise to triplet Andreev reflection, i.e., the reflection of a majority electron into a majority hole or vice versa. As an application of our calculation, we consider a thin half metal film or wire laterally attached to a superconducting contact. If the half metal is disorder free, an excitation gap is opened that is proportional to the spin-orbit interaction strength in the superconductor. For electrons with energy below this gap a lateral half-metal--superconductor contact becomes a perfect triplet Andreev reflector. We show that the system supports localized Majorana end states in this limit.