Surface electronic structure and isotropic superconducting gap in (Li$_{0.8}$Fe$_{0.2}$)OHFeSe

TL;DR

This study uses ARPES to analyze the surface electronic structure and isotropic superconducting gap of (Li$_{0.8}$Fe$_{0.2}$)OHFeSe, revealing electron doping, similarities to Rb$_x$Fe$_{2-y}$Se$_2$, and insights into its high $T_c$.

Contribution

First ARPES investigation of (Li$_{0.8}$Fe$_{0.2}$)OHFeSe revealing its surface electronic structure and superconducting gap characteristics.

Findings

Surface FeSe layers are electron-doped by (Li$_{0.8}$Fe$_{0.2}$)OH layers.

Superconducting gap is isotropic around the electron Fermi surface.

Higher $T_c$ compared to similar compounds may be due to layer homogeneity or other effects.

Abstract

Using angle-resolved photoemission spectroscopy (ARPES), we revealed the surface electronic structure and superconducting gap of (Li$_{0.8}$Fe$_{0.2}$)OHFeSe, an intercalated FeSe-derived superconductor without antiferromagnetic phase or Fe-vacancy order in the FeSe layers, and with a superconducting transition temperature ($T_c$) $\sim$ 40 K. We found that (Li$_{0.8}$Fe$_{0.2}$)OH layers dope electrons into FeSe layers. The electronic structure of surface FeSe layers in (Li$_{0.8}$Fe$_{0.2}$)OHFeSe resembles that of Rb$_x$Fe$_{2-y}$Se$_2$ except that it only contains half of the carriers due to the polar surface, suggesting similar quasiparticle dynamics between bulk (Li$_{0.8}$Fe$_{0.2}$)OHFeSe and Rb$_x$Fe$_{2-y}$Se$_2$. Superconducting gap is clearly observed below $T_c$, with an isotropic distribution around the electron Fermi surface. Compared with $A_x$Fe$_{2-y}$Se$_2$ (\textit{A}=K, Rb, Cs, Tl/K), the higher $T_c$ in (Li$_{0.8}$Fe$_{0.2}$)OHFeSe might be attributed to higher homogeneity of FeSe layers or to some unknown roles played by the (Li$_{0.8}$Fe$_{0.2}$)OH layers.