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

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.