Resonant inelastic x-ray scattering in electronically quasi-zero-dimensional CuB2O4

We explore the general phenomenology of resonant inelastic scattering (RIXS) using CuB2O4, a network of CuO4 plaquettes electronically isolated by B+3 ions. Spectra show a small number of well-separated features, and we exploit the simple electronic structure to explore RIXS phenomenology by developing a calculation which allows for intermediate-state effects ignored in standard approaches. These effects are found to be non-negligible and good correspondence between our model and experiment leads to a simple picture of such phenomenology as the genesis of d-d excitations at the K edge and intermediate-state interference effects.

Polarization dependence and symmetry analysis in indirect K-edge RIXS

We present a study of the charge-transfer excitations in undoped Nd2CuO4 using resonant inelastic X-ray scattering (RIXS) at the Cu K-edge. At the Brillouin zone center, azimuthal scans that rotate the incident-photon polarization within the CuO2 planes reveal weak fourfold oscillations. A comparison of spectra taken in different Brillouin zones reveals a spectral weight decrease at high energy loss from forward- to back-scattering. We show that these are scattered-photon polarization effects related to the properties of the observed electronic excitations. Each of the two effects constitutes about 10% of the inelastic signal while the 4p-as-spectator approximation describes the remaining 80%. Raman selection rules can accurately model our data, and we conclude that the observed polarization-dependent RIXS features correspond to Eg and B1g charge-transfer excitations to non-bonding oxygen 2p bands, above 2.5 eV energy-loss, and to an Eg d->d excitation at 1.65 eV.