Identifying $s$-wave pairing symmetry in single-layer FeSe from topologically trivial edge states

Abstract

Determining the pairing symmetry of single-layer FeSe on SrTiO 3 is the key to understanding the enhanced pairing mechanism; furthermore, it guides exploring new superconductors with high transition temperatures (T c ). Despite significant efforts, it remains controversial whether the symmetry is the sign-preserving sor the sign-changed s ± -wave. Here, we investigate the pairing symmetry of single-layer FeSe from a topological point of view. Using low-temperature scanning tunneling microscopy/spectroscopy, we have systematically characterized the superconducting states at isolated edges and corners of single-layer FeSe. The tunneling spectra collected at edges and corners exhibit full gap and substantial dip, respectively, demonstrating the absence of topologically non-trivial edge/corner modes. According to the theoretical calculation, these spectroscopic features are strong evidence for the sign-preserving s-wave pairing.