Observation of Andreev bound states at spin-active interfaces

TL;DR

This study demonstrates the detection of Andreev bound states at superconductor/ferromagnet interfaces, revealing spin-dependent phase shifts and advancing understanding of triplet proximity effects through high-resolution conductance measurements.

Contribution

It provides direct experimental evidence of Andreev bound states at spin-active interfaces and quantifies spin-dependent phase shifts, offering new microscopic insights into the triplet proximity effect.

Findings

Observation of symmetric subgap conductance features shifting with magnetic field

Determination of spin-dependent interfacial phase shifts from bound state energies

Enhanced understanding of triplet superconductivity at spin-active interfaces

Abstract

We report on high-resolution differential conductance experiments on nanoscale superconductor/ferromagnet tunnel junctions with ultra-thin oxide tunnel barriers. We observe subgap conductance features which are symmetric with respect to bias, and shift according to the Zeeman energy with an applied magnetic field. These features can be explained by resonant transport via Andreev bound states induced by spin-active scattering at the interface. From the energy and the Zeeman shift of the bound states, both the magnitude and sign of the spin-dependent interfacial phase shifts between spin-up and spin-down electrons can be determined. These results contribute to the microscopic insight into the triplet proximity effect at spin-active interfaces.