Local magnetism induced by non-magnetic impurities in FeSe in proximity to s-wave superconductivity

Abstract

The response of non-magnetic impurities to superconductivity is useful to characterize the superconducting pairing symmetry. The s-wave superconductivity is not affected by the presence of non-magnetic impurities. However, the unconventional superconductivity responds to the non-magnetic impurities, inducing in-gap states in the superconducting gap. However, this characterization fails if non-magnetic impurities could induce magnetic moments in superconductors. Here, we used scanning tunneling microscopy/spectroscopy to elucidate if non-magnetic impurities are irrelevant to magnetism in FeSe. To study this, we have grown FeSe films on the Pb(111) substrate. We find that the FeSe films are proximity-induced s-wave superconductors. By investigating various non-magnetic impurities and native defects of FeSe, we explicitly show that these impurities and defects can directly induce local magnetism in FeSe.