Electronic structure of CeFeAsO_1-xF_x (x=0, 0.11, and 0.12)

We report an extensive study on the intrinsic bulk electronic structure of the high-temperature superconductor CeFeAsO0.89 F0.11 and its parent compound CeFeAsO by soft and hard x-ray photoemissions, x-ray absorption, and soft x-ray emission spectroscopies. The complementary surface/bulk probing depth, and the elemental and chemical sensitivity of these techniques allow resolving the intrinsic electronic structure of each element and correlating it with the local structure, which has been probed by extended x-ray absorption fine-structure spectroscopy. The measurements indicate a predominant 4 f1 (i.e., Ce3 ⁺) initial-state configuration for cerium and an effective valence-band-to- 4f charge-transfer screening of the core hole. The spectra also reveal the presence of a small Ce f0 initial-state configuration, which we assign to the occurrence of an intermediate-valence state. The data reveal a reasonably good agreement with the partial density of states as obtained in standard density-functional calculations over a large energy range. Implications for the electronic structure of these materials are discussed.