Calculated local density X-ray and photoemission spectra for superconducting La_2-xM_xCuO₄: Localization of Cu-3d

Comparison of UPS (XPS) and XES spectra for the high T_c superconductor La_2-xM_xCuO₄ - calculated using highly precise local density results - with available experimental data reveals a large shift of about 2 eV to lower energies for the Cu-d related features. This shift is interpreted qualitatively in terms of a simple two-level model taking into account the hole-hole repulsion at the Cu sites in the photoemission final state. This simple model explains nicely the magnitude of the shift, the occurence of a Cu related satellite below the valence-bands, and the charge-transfer screening of the Cu-d photo-holes by O-p electrons. The O-states, especially the bonding states at the bottom of the valence band, are less affected and agree reasonably well with the experimental findings.