Evidence for Induced Magnetization in Superconductor-Ferromagnet Hetero-structures: a Scanning Tunnelling Spectroscopy Study

TL;DR

This study uses scanning tunneling spectroscopy to observe evidence of induced magnetization in superconductors near ferromagnetic islands, revealing effects larger than theoretical predictions.

Contribution

It provides experimental evidence of induced magnetization in superconductors, showing a longer penetration depth than predicted by existing theories.

Findings

Detected small gap-like features on ferromagnetic islands

Observed anomalous split-gap structures near ferromagnetic islands

Found the effect's length scale exceeds theoretical expectations

Abstract

We performed scanning tunneling spectroscopy of c-axis oriented YBCO films on top of which ferromagnetic SRO islands were grown epitaxially in-situ. When measured on the ferromagnetic islands, the density of states exhibits small gap-like features consistent with the expected short range penetration of the order parameter into the ferromagnet. However, anomalous split-gap structures are measured on the superconductor in the vicinity of ferromagnetic islands. This observation may provide evidence for the recently predicted induced magnetization in the superconductor side of a superconductor/ ferromagnet junction. The length scale of the effect inside the superconductor was found to be an order of magnitude larger than the superconducting coherence length. This is inconsistent with the theoretical prediction of a penetration depth of only a few superconducting coherence lengths. We discuss a possible origin for this discrepancy.