Impurity-state-like nature of Fermi-liquid states in Bi2Sr2CaCu2O8 observed by photoemission and x-ray absorption

Photoemission and X-ray absorption spectroscopy have been performed on Bi₂Sr₂Ca_1−xY_xCu₂O₈ in which the hole concentration is controlled by the ratio between Ca and Y atoms. It was found that the density of electronic states at the Fermi level gradually increases as the hole concentration with almost no rigid shift of the electronic structure with respect to the Fermi level. This suggests that the electronic states at the Fermi level (Fermi-liquid states) would not be simple one-electron states but be a kind of impurity states produced through the strong hybridization between doped O2p hole orbitals and empty Cu3d orbitals.