Evidence for spin-polarized bound states in semiconductor-superconductor-ferromagnetic insulator islands

TL;DR

This study provides experimental evidence for spin-polarized bound states in semiconductor-superconductor-ferromagnetic insulator nanowires, revealing tunable subgap states and spin splitting effects exceeding the superconducting gap.

Contribution

It introduces a combined experimental and theoretical analysis demonstrating spin-polarized Andreev levels in hybrid nanowires with ferromagnetic insulators, a novel insight into spin-dependent subgap states.

Findings

Cotunneling features linked to spin-polarized Andreev levels.

Zero-field spin splitting exceeds the induced superconducting gap.

Subgap states are tunable via electrostatic gating.

Abstract

We report Coulomb blockade transport studies of semiconducting InAs nanowires grown with epitaxial superconducting Al and ferromagnetic insulator EuS on overlapping facets. Comparing experiment to a theoretical model, we associate cotunneling features in even-odd bias spectra with spin-polarized Andreev levels. Results are consistent with zero-field spin splitting exceeding the induced superconducting gap. Energies of subgap states are tunable on either side of zero via electrostatic gates.