Superconducting gap anisotropy in monolayer FeSe thin film

TL;DR

This study uses high-resolution ARPES to analyze the Fermi surface and superconducting gap anisotropy in monolayer FeSe, revealing complex pairing symmetry constraints and potential sign-changing or orbital-dependent pairing mechanisms.

Contribution

It provides detailed measurements of the Fermi surface and superconducting gaps in monolayer FeSe, offering new insights into its pairing symmetry and superconducting properties.

Findings

Superconducting gap is nodeless but moderately anisotropic.

Gap maxima are along the major axis of elliptical electron pockets.

Presence of four gap minima suggests sign change or orbital dependence.

Abstract

Fermi surface topology and pairing symmetry are two pivotal characteristics of a superconductor. Superconductivity in one monolayer (1ML) FeSe thin film has attracted great interest recently due to its intriguing interfacial properties and possibly high superconducting transition temperature (Tc) over 77 K. Here, we report high-resolution measurements of the Fermi surface and superconducting gaps in 1ML FeSe using angle-resolved photoemission spectroscopy (ARPES). Two ellipse-like electron pockets are clearly resolved overlapping with each other at the Brillouin zone corner. The superconducting gap is nodeless but moderately anisotropic, which put strong constraints on determining the pairing symmetry. The gap maxima locate along the major axis of ellipse, which cannot be explained by a single d-wave, extended s-wave, or s$\pm$ gap function. Four gap minima are observed at the intersection of electron pockets suggesting the existence of either a sign change or orbital-dependent pairing in 1ML FeSe.