Electronic structure of Nd2-xCexCuO4-δ studied by photoelectron spectroscopy

Photoelectron spectroscopy at the electron-doped superconducting cuprate Nd2-xCexCuO4-δ gives evidence to strong electronic correlations by valence band data as well as by Cu core level spectra which reveal that doping by electrons gives rise to an admixture of Cu 3d10 to the 3d9-state which is pure in Nd2CuO4-δ. An enhanced on-site Coulomb repulsion energy Udd and augmented Cu 3d-ligand hybridization is found for Nd2-xCexCuO4-δ in comparison with the p-type cuprate superconductors. A XPS study of the valence of the constituents reveals that Nd is trivalent with strong Nd 4f-O 2p hybridization, which is confirmed by resonant photoemission, whereas Ce has a 4f occupation number nf≅ 0.45 as in CeO2