Effect of Ce doping on the Cu charge in the electron superconductor ${\mathrm{Nd}}_{2\mathrm{-}\mathrm{x}}$${\mathrm{Ce}}_{\mathrm{x}}$${\mathrm{CuO}}_4$

We have investigated the effect of Ce doping on the net Cu charge via x-ray absorption spectroscopy at the Cu K and the Ce $L_3$ edges. We conclude that Ce ions add electrons to the ${\mathrm{CuO}}_2$ planes. It is most likely that this additional electron is injected into a band rather than being localized on each Cu site leading to ${\mathrm{Cu}}^{1+}$. We observe that the amount of electron doping is larger than Ce concentration.