Evidence for induced magnetization in superconductor-ferromagnet heterostructures: A scanning tunneling spectroscopy study

This is the authors' abstract. We don't add key points for this paper.

We performed scanning tunneling spectroscopy of c-axis-oriented YBa₂Cu₃O_7-δ films on top of which ferromagnetic SrRuO₃ islands were grown epitaxially in situ. When measured on the ferromagnetic islands, the density of states exhibits small gaplike 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 provides evidence for the recently predicted induced magnetization in the superconductor side of a superconductor/ferromagnet junction and demonstrates its manifestation in the density of states of the superconductor. Surprisingly, 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.