Atomic-Site-Dependent Pairing Gap in Monolayer FeSe/SrTiO₃(001)–(√13 × √13)

Abstract

The interfacial FeSe/TiO 2−δ coupling induces hightemperature superconductivity in monolayer FeSe films. Using cryogenic atomically resolved scanning tunneling microscopy/spectroscopy, we obtained atomic-site dependent surface density of states, work function, and the pairing gap in the monolayer FeSe on the SrTiO 3 (001)−(√13 × √13)−R33.7°surface. Our results disclosed the out-of-plane Se−Fe−Se triple layer gradient variation, switched DOS for Fe sites on and off TiO 5□ , and inequivalent Fe sublattices, which gives global spatial modulation of pairing gap contaminants with the (√13 × √13) pattern. Moreover, the coherent lattice coupling induces strong inversion asymmetry and in-plane anisotropy in the monolayer FeSe, which is demonstrated to correlate with the particle−hole asymmetry in coherence peaks. These results disclose delicate atomic-scale correlations between pairing and lattice-electronic coupling in the Bardeen−Cooper−Schrieffer to Bose−Einstein condensation crossover regime, providing insights into understanding the pairing mechanism of multiorbital superconductivity.