Polarization x-ray-absorption near-edge structure study of Pr2−xCexCuO4 single crystals: The nature of Ce doping

Abstract

A polarization Cu K-edge x-ray-absorption near-edge structure (XANES) study has been carried out on ${\mathrm{Pr}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Ce}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ single crystals. The spectra for x-ray polarization vector E nearly parallel to the crystal c axis suggest that electrons contributed by Ce doping are initially localized at the Cu site. The spectra for E perpendicular to the c axis exhibit an almost rigid edge shift to lower energies upon Ce doping. This suggests that the unoccupied in-plane Cu 4p states shift to lower energies. Therefore, the Ce doping donates electrons to the Cu site and also shifts the unoccupied 4p band. We propose that the upper unoccupied band consisting of predominantly Cu 3d states shifts downward and eventually joins the initially localized states near the Fermi level and thus, forms the conduction band in the n-type superconductor.