Cu core-level spectroscopy of ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_4$

We have measured the Cu 1s and 2p near-edge x-ray-absorption, electron-energy-loss, and resonant-photoemission spectra of superconducting n-type doped ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$. The 1s x-ray-absorption spectra appear consistent with two possibilities: (1) that Ce causes a decrease in the Cu valence; and (2) that Ce causes a shift in the Cu 1s position. However, the Cu 2p absorption and energy-loss spectra, and the photoemission results, are more easily reconciled with (2), and we conclude that Ce doping probably does not create local ${\mathrm{Cu}}^{1+}$ ions, but rather increases the occupancy of less localized states.