Electronic Structure of Nd 2- x Ce x CuO 4-δ Studied by Photoelectron Spectroscopy

Photoelectron spectroscopy at the electron-doped superconducting cuprate Nd 2- x Ce x CuO 4-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 3 d 10 to the 3 d 9 -state which is pure in Nd 2 CuO 4-δ . An enhanced on-site Coulomb repulsion energy U dd and augmented Cu 3 d -ligand hybridization is found for Nd 2- x Ce x CuO 4-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 4 f -O 2 p hybridization, which is confirmed by resonant photoemission, whereas Ce has a 4 f occupation number n f ≈ 0.45 as in CeO 2 .