Abstract
The electronic structure of the Fe-based superconductorSmFeAsO1−xFx (x = 0 and 0.2) is studied with x-ray photoemission spectroscopy (XPS) through comparing the bandstructures of the nonsuperconducting parent material SmFeAsO and the superconductingSmFeAsO0.8F0.2 (Tc = 52.5 K). A small peak centered at 0.2 eV below the Fermi level,EF, in the valence band is observed in the parent material SmFeAsO, which is due to thelow-spin state of the Fe 3d electrons. With fluorine doping, the peak at 0.2 eV disappearsand a broad plateau forms near the Fermi level; in the meantime, the density of states atEF is slightly suppressed. The O 1s and Sm 3d core levels shift towards high energy by∼0.55 eV with fluorine doping, but in a sharp comparison, the Fe 2p and As 3d core levels do notshift significantly (the binding energy shift is less than 0.01 eV). It is deduced from thecore-level shifts that the Fermi level of the system moves up by 0.55 eV by fluorine doping.
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