Highly anisotropic and two-fold symmetric superconducting gap in nematically ordered FeSe$_{0.93}$S$_{0.07}$

TL;DR

This study reveals a highly anisotropic, two-fold symmetric superconducting gap in FeSe$_{0.93}$S$_{0.07}$, showing nematic effects strongly influence superconductivity without magnetic order complications.

Contribution

It provides detailed angle-resolved photoemission data on the superconducting gap structure in nematic FeSe$_{0.93}$S$_{0.07}$, highlighting the impact of nematicity on superconductivity.

Findings

Superconducting gap exhibits 2-fold anisotropy around the elliptical hole pocket.

No detectable gap at the zone center and zone corner.

Nematicity significantly affects the superconducting gap distribution.

Abstract

FeSe exhibits a novel ground state in which superconductivity coexists with a nematic order in the absence of any long-range magnetic order. Here we report an angle-resolved photoemission study on the superconducting gap structure in the nematic state of FeSe$_{0.93}$S$_{0.07}$, without the complication caused by Fermi surface reconstruction induced by magnetic order. We found that the superconducting gap shows a pronounced 2-fold anisotropy around the elliptical hole pocket near the Z point of the Brillouin zone, with gap minima at the endpoints of its major axis, while no detectable gap was observed around the zone center and zone corner. The large anisotropy and nodal gap distribution demonstrate the substantial effects of the nematicity on the superconductivity, and thus put strong constraints on the current theories.