Electronic structure of electron-doped superconducting curpates studied by photoelectron spectroscopy

Photoemission data of n-type superconducting $RE_{2−x}Ce_xCuO_{4−δ}$ (RE = Pr, Nd and Sm) and $Nd_2CuO_{4−y}F_y$ are presented. An XPJ and an XPS resonant photoemission study reveals that the RE elements are trivalent with decreasing 4f-O 2p-hybridization from RE = Pr to Sm, whereas Ce has a valence of 3.6. The partial Cu$_3$d emission shows valence band satellites indicating the existence of strong electron-electron correlation. These results can be well reproduced by cluster calculations. An decrease of the on-site Coulomb repulsion energy U from RE = Pr to Sm is found in $RE_{2−x}Ce_xCuO_{4−δ}$