A study of the Fe-based superconductor SmFeAsO1-xFx by x-ray photoelectron spectroscopy

The electronic structure of the Fe-based superconductor SmFeAsO1-xFx (x = 0 and 0.2) is studied with x-ray photoemission spectroscopy (XPS) through comparing the band structures of the nonsuperconducting parent material SmFeAsO and the superconducting SmFeAsO0.8F0.2 (T-c = 52.5 K). A small peak centered at 0.2 eV below the Fermi level, E-F, in the valence band is observed in the parent material SmFeAsO, which is due to the low-spin state of the Fe 3d electrons. With fluorine doping, the peak at 0.2 eV disappears and a broad plateau forms near the Fermi level; in the meantime, the density of states at E-F is slightly suppressed. The O 1s and Sm 3d core levels shift towards high energy by similar to 0.55 eV with fluorine doping, but in a sharp comparison, the Fe 2p and As 3d core levels do not shift significantly (the binding energy shift is less than 0.01 eV). It is deduced from the core-level shifts that the Fermi level of the system moves up by 0.55 eV by fluorine doping.Physics, AppliedPhysics, Condensed MatterSCI(E)EI7ARTICLE1null2