Unoccupied electronic structure and core-hole effects in the x-ray-absorption spectra of ${\mathrm{Cu}}_2$O

X-ray-absorption measurements at the Cu ${\mathit{L}}_{2,3}$ and O K edges of ${\mathrm{Cu}}_2$O reveal the presence of unoccupied states of predominantly Cu d and O p character at the bottom of the conduction band. We find that spectral features up to 25 eV from threshold can be assigned to structures in the calculated unoccupied density of states, projected on the Cu and O sites. However, for a satisfactory description of the anomalous line shape and threshold intensity of the Cu edges, the core hole created in the absorption process must be included in the calculation. We have investigated this effect by a modified Clogston-Wolff impurity model, based on the calculated band structure. We conclude that, possibly because of the peculiar Cu-O coordination, the Cu 2p core-hole potential is stronger in ${\mathrm{Cu}}_2$O than in other Cu(I) materials, and that the Cu ${\mathit{L}}_{2,3}$ spectra present both band features, typical of monovalent Cu materials and of copper metal, and a resonant contribution, typical of divalent compounds such as CuO.