Percolative supercurrent in superconductor-ferromagnetic insulator bilayers

Abstract

We report tunneling spectroscopy and transport measurements in superconducting Al and ferromagnetic-insulator EuS bilayers. The samples display remanent spin-splitting, roughly half the superconducting gap, and supercurrent transport above the average paramagnetic limit. We interpret this behavior as arising from the interplay between two characteristic length scales: the superconducting coherence length, $\hat{I}¾$, and the magnetic domain size, $d$. By comparing experimental results to a theoretical model, we find $\hat{I}¾/d\approx 10$. In this regime, spin-averaging across the micromagnetic configuration can locally suppress superconductivity, resulting in percolative supercurrent flow.

14 pages, 11 figures