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

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.

5 pages, 4 figures

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