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

TL;DR

This paper studies how magnetic impurities affect the local density of states in single-layer FeSe superconductors with d-wave symmetry, revealing resonance peaks and symmetry characteristics linked to spin-orbit coupling strength.

Contribution

It demonstrates the impact of spin-orbit coupling on impurity resonance states and LDOS symmetry in FeSe superconductors, connecting theoretical predictions with experimental observations.

Findings

Two impurity resonance peaks with opposite energies appear in LDOS.

Strong spin-orbit coupling leads to d-wave symmetric gaps with fourfold LDOS distribution.

Weaker spin-orbit coupling results in s-wave symmetry at resonance, despite d-wave pairing potential.

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.