Anisotropic gap structure and sign reversal symmetry in monolayer Fe(Se,Te)

TL;DR

This study investigates the superconducting gap structure in monolayer Fe(Se,Te)/SrTiO3, revealing anisotropic gaps and sign reversal consistent with s+- wave pairing, advancing understanding of unconventional and topological superconductivity.

Contribution

It provides the first quasiparticle interference evidence of anisotropic gap structure and sign change in monolayer Fe(Se,Te), supporting a spin fluctuation-driven s+- pairing mechanism.

Findings

Observation of anisotropic superconducting gap

Detection of sign reversal on electron pockets

Consistency with s+- wave pairing symmetry

Abstract

The iron-based superconductors are an ideal platform to reveal the enigma of the unconventional superconductivity and potential topological superconductivity. Among them, the monolayer Fe(Se,Te)/SrTiO3(001), which is proposed to be topological nontrivial, shows interface-enhanced high-temperature superconductivity in the two dimensional limit. However, the experimental studies on the superconducting pairing mechanism of monolayer Fe(Se,Te) films are still limited. Here, by measuring quasiparticle interference in monolayer Fe(Se,Te)/SrTiO3(001), we report the observation of the anisotropic structure of the large superconducting gap and the sign change of the superconducting gap on different electron pockets. The results are well consistent with the 'bonding-antibonding' s+- wave pairing symmetry driven by spin fluctuations in conjunction with spin-orbit coupling. Our work is of basic significance not only for a unified superconducting formalism in the iron-based superconductors, but also for understanding of topological superconductivity in high-temperature superconductors.