Non-resonant inelastic x-ray scattering involving excitonic excitations
Abstract
In a recent publication Larson et al. reported remarkably clear d-d excitations for NiO and CoO measured with x-ray energies well below the transition metal K edge. In this letter we demonstrate that we can obtain an accurate quantitative description based on a local many body approach. We find that the magnitude of q can be tuned for maximum sensitivity for dipole, quadrupole, etc. excitations. We also find that the direction of q with respect to the crystal axes can be used as an equivalent to polarization similar to electron energy loss spectroscopy, allowing for a determination of the local symmetry of the initial and final state based on selection rules. This method is more generally applicable and combined with the high resolution available, could be a powerful tool for the study of local distortions and symmetries in transition metal compounds including also buried interfaces.