Surface electronic structure and isotropic superconducting gap in (Li0.8Fe0.2)OHFeSe

Using angle-resolved photoemission spectroscopy (ARPES), we revealed the surface electronic structure and superconducting gap of (Li0.8Fe0.2)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) similar to 40 K. We found that (Li0.8Fe0.2)OH layers dope electrons into FeSe layers. The electronic structure of surface FeSe layers in (Li0.8Fe0.2)OHFeSe resembles that of RbxFe2-ySe2 except that it only contains half of the carriers due to the polar surface, suggesting similar quasiparticle dynamics between bulk (Li0.8Fe0.2)OHFeSe and RbxFe2-ySe2. 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) (A = K, Rb, Cs, Tl/K), the higher T-c in (Li0.8Fe0.2)OHFeSe might be attributed to higher homogeneity of FeSe layers or to some unknown roles played by the (Li0.8Fe0.2) OH layers.