On-site interband excitations in resonant inelastic x-ray scattering from Cu2O

The electronic structure of cuprite (Cu2O) has been studied by high-resolution x-ray photoemission (XPS), x-ray absorption (XAS), and resonant x-ray emission spectroscopies (XES) supported by band structure calculations using a hybrid exchange approximation to density functional theory. A pronounced loss feature at about 4.5 eV due to on-site interband excitation has been identified in resonant inelastic x-ray scattering from Cu2O close to the L-3 (Cu 2p(3/2)) core threshold. Although Cu2O nominally has a filled upper valence band of Cu 3d states and an empty conduction band of Cu 4s states, the band structure calculations show that there is substantial 3d character in the conduction band and that the inelastic loss is dominated by on-site 3d to 3d excitation conforming to the selection rule Delta l=0 rather than 3d to 4s transitions with Delta l=-2. However, unlike in previous work, these transitions do not arise from ligand field splitting of the Cu 3d states but rather from on-site 3d-4s hybridization which introduces 3d character into the conduction band. Comparison between XPS, XES, and XAS data shows that Cu L-3 XAS is dominated by a core exciton lying 0.65 eV below the bottom of the conduction band and that inelastic scattering is only observed for photon energies below that required to excite the core electron into the conduction band.