Field-induced spin mixing in ultrathin superconducting Al and Be films in high parallel magnetic fields

TL;DR

This study investigates how high parallel magnetic fields induce spin mixing in ultrathin superconducting Al and Be films, revealing a subgap peak in tunneling spectra that suggests a field-induced mixed-spin state rather than spin-orbit effects.

Contribution

It provides experimental evidence of field-induced spin mixing in ultrathin superconducting films, highlighting a new interpretation of subgap features as fluctuations into a mixed-spin state.

Findings

Subgap peak magnitude increases near the critical field

DOS singularities at specific energies indicate spin mixing

Results suggest a field-induced mixed-spin state rather than spin-orbit scattering

Abstract

We report spin-dependent electron density of states (DOS) studies of ultra-thin superconducting Al and Be films in high parallel magnetic fields. Superconductor-insulator-superconductor (SIS) tunneling spectra are presented in which both the film and the counterelectrode are in the paramagnetic limit. This SIS configuration is exquisitely sensitive to spin mixing and/or spin flip processes which are manifest as DOS singularities at eV = 2Delta +- eV_z. Both our Al and Be data show a well defined subgap peak whose magnitude grows dramatically as the parallel critical field is approached. Though this feature has previously been attributed to spin-orbit scattering, it is more consistent with fluctuations into a field induced mixed-spin state.