Electronic structure of the electron-doped superconductor ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{-}\mathit{y}}$ studied by photoemission spectroscopy

The electronic structure of the electron-doped superconductor ${\mathrm{Nd}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_{4\mathrm{-}\mathit{y}}$ has been studied by photoemission spectroscopy. The results indicate that the system is indeed doped with electrons supplied by the ${\mathrm{Ce}}^{4+}$ ions substituting ${\mathrm{Nd}}^{3+}$ sites. From the Cu core-level and the valence-band results, however, we find no evidence for the occupation of Cu 3d orbitals by the doped electrons at least for low doping concentrations x≤0.15.