Resonance states near a quantum magnetic impurity in single-layer FeSe superconductors with $d$-wave symmetry

Abstract

In this work, we investigate the local density of states (LDOS) near a magnetic impurity in single-layer FeSe superconductors. The two-orbital model with spin-orbit coupling proposed in Ref. [{\emph{Phys. Rev. Lett.} \textbf{119}, 267001 (2017)}] is used to describe the FeSe superconductor. In the strong coupling regime, two impurity resonance peaks appear with opposite resonance energies in the LDOS spectral function. For a strong spin-orbit coupling, the superconducting gap in this model is $d$-wave symmetric with nodes, the spatial distributions of the LDOS at the two resonance energies are fourfold symmetric, which reveals typical characteristic of $d$-wave pairing. When the spin-orbit coupling is not strong enough to close the superconducting gap, we find that the spatial distribution of the LDOS at one of the resonance energies manifests $s$-wave symmetry, while the pairing potential preserves $d$-wave symmetry. This result is consistent with previous experimental investigations.