Observation of Yu-Shiba-Rusinov-like states at the edge of CrBr3/NbSe2 heterostructure

TL;DR

This study uses high-resolution scanning tunneling microscopy to investigate CrBr3/NbSe2 heterostructures, revealing Yu-Shiba-Rusinov-like states at the edges, which clarifies the nature of in-gap states and their relation to atomic edge reconstruction.

Contribution

The paper provides detailed experimental evidence that the in-gap edge states are Yu-Shiba-Rusinov states, not Majorana modes, refining understanding of interfacial phenomena in ferromagnet-superconductor heterostructures.

Findings

In-gap states observed at CrBr3 edges include zero-energy peaks and particle-hole symmetric bound states.

Edge states' behavior under tunneling transmissivity changes aligns with Yu-Shiba-Rusinov states.

CrBr3 acts as an insulating barrier with superconducting properties similar to NbSe2 underneath.

Abstract

The hybrid ferromagnet-superconductor heterostructures have attracted extensive attention as they potentially host topological superconductivity. Relevant experimental signatures have recently been reported in CrBr3/NbSe2 ferromagnet-superconductor heterostructure, but controversies remain. Here, we reinvestigate CrBr3/NbSe2 by an ultralow temperature scanning tunneling microscope with higher spatial and energy resolutions. We find that the single-layer CrBr3 film is insulating and acts likely as a vacuum barrier, the measured superconducting gap and vortex state on it are nearly the same as those of NbSe2 substrate. Meanwhile, in-gap features are observed at the edges of CrBr3 island, which display either a zero-energy conductance peak or a pair of particle-hole symmetric bound states. They are discretely distributed at the edges of CrBr3 film, and their appearance is found closely related to the atomic lattice reconstruction near the edges. By increasing tunneling transmissivity, the zero-energy conductance peak quickly splits, while the pair of nonzero in-gap bound states first approach each other, merge, and then split again. These behaviors are unexpected for Majorana edge modes, but in consistent with the conventional Yu-Shiba-Rusinov states. Our results provide critical information for further understanding the interfacial coupling in CrBr3/NbSe2 heterostructure.