Resonant inelastic x-ray scattering from strongly correlated copper oxides

We report resonant inelastic x-ray scattering from Nd2CuO4 and two other copper oxides, YBa2Cu3O7-delta and CuGeO3. In each case an excitation of similar to 6 eV is observed when the incident photon energy is tuned through the Cu K-edge. Calculations for Nd2CuO4, based on the Anderson impurity model identify this as a charge transfer excitation to the antibonding state. For Nd2CuO4, the incident energy dependence of the inelastic intensity exhibits a single resonance at 8990 eV, corresponding to a <(1s)under bar>3d(0)4(kappa), intermediate state. The absence of a resonance associated with the <(1s)under bar>3d(0)(L) under bar 4p(kappa) intermediate state is attributed to non-local effects. Preliminary results from CuCeO3, which exhibit two resonances support this conclusion.