Observation of Rashba-Surface-Band-Dependent Yu–Shiba–Rusinov States in a Gold-Based Superconductor AuSn4

Abstract

The interplay between the Rashba effect, superconductivity, and magnetism in gold-based superconductors provides a platform for exploring topological superconductivity, yet the interaction between Rashba bands and superconducting bound states remains unexplored. Here, we report Rashba-surface-band-dependent Yu–Shiba–Rusinov (YSR) states around Fe adatoms on the surfaces of AuSn₄, using ultralow temperature (5 mK) scanning tunneling microscope/spectroscopy. On Au-terminated surfaces with Rashba bands, most Fe atoms occupy Au vacancies, while only a few adsorb on the Sn-terminated surfaces with dominant bulk metallic states. Remarkably, YSR states localized on the Fe atom are observed on Sn-terminated surfaces but absent on Au-terminated surfaces. First-principle calculations reveal a significant magnetic moment for Fe adatoms on Sn surfaces compared to a nearly negligible value on Au surfaces, which elucidates the observed surface-dependent YSR states. The termination-dependence local moment arises from the interplay of Rashba surface bands and s-d coupling, as described by the Anderson s-d exchange model.