Topological superconductivity in semiconductor-superconductor-magnetic insulator heterostructures

TL;DR

This paper explores how magnetic insulators can induce topological superconductivity in semiconductor heterostructures without external magnetic fields, proposing spin-filter barriers as a key mechanism for topological phase transitions.

Contribution

It introduces a novel approach using spin-filter tunnel barriers to achieve topological phases, reducing the need for external magnetic fields in superconductor-semiconductor heterostructures.

Findings

Spin splitting in superconductors alone cannot induce topological transition.

Spin-filter barriers enhance magnetic exchange and enable topological phases.

Band alignment critically affects the topological transition in quantum-confined systems.

Abstract

Hybrid superconductor-semiconductor heterostructures are promising platforms for realizing topological superconductors and exploring Majorana bound states physics. Motivated by recent experimental progress, we theoretically study how magnetic insulators offer an alternative to the use of external magnetic fields for reaching the topological regime. We consider different setups, where: (1) the magnetic insulator induces an exchange field in the superconductor, which leads to a splitting in the semiconductor by proximity effect, and (2) the magnetic insulator acts as a spin-filter tunnel barrier between the superconductor and the semiconductor. We show that the spin splitting in the superconductor alone cannot induce a topological transition in the semiconductor. To overcome this limitation, we propose to use a spin-filter barrier that enhances the magnetic exchange and provides a mechanism for a topological phase transition. Moreover, the spin-dependent tunneling introduces a strong dependence on the band alignment, which can be crucial in quantum-confined systems. This mechanism opens up a route towards networks of topological wires with fewer constraints on device geometry compared to previous devices that require external magnetic fields.