Electronic Structure of $Nd_{2- x}Ce_xCuO_{4-\rho}$ Studied by Photoelectron Spectroscopy

Photoelectron spectroscopy at the electron-doped superconducting cuprate $Nd_{2-x}Ce_xCuO_{4-δ}$ 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 $Nd_2CuO_{4-δ}$. An enhanced on-site Coulomb repulsion energy Udd and augmented Cu 3d-ligand hybridization is found for $Nd_{2-x}Ce_xCuO_{4-δ}$ 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 4f-O 2p hybridization, which is confirmed by resonant photoemission, whereas Ce has a 4f occupation number nf ≈ 0.45 as in CeO$_2$