We report a study on the temperature dependence of the charge-neutral crystal field (dd) excitations in cupric oxide, using nonresonant inelastic x-ray scattering (IXS) spectroscopy. Thanks to a very high energy resolution (60 meV), we observe therma
l effects on the dd excitation spectrum fine structure between temperatures of 10-320 K. With an increasing temperature, the spectra broaden considerably. We assign the temperature dependence of the dd excitations to the relatively large electron-phonon coupling.
We report on strong dipole transitions to 3d orbitals of neighboring Co atoms in the Co 1s x-ray absorption pre-edge. They are revealed by applying high-resolution resonant x-ray emission spectroscopy (RXES) to compounds containing CoO6 clusters. Whe
n contrasted to quadrupole local 1s3d excitations, these non-local 1s3d transitions are identified by their energy dispersion and angular dependence, their sensitivity to second-shell effects (i.e. the connection mode of the CoO6 octahedra and the bond lengths), and an upwards energy shift of 2.5 eV due to the poorer screening of the core hole. The experiment reveals that the intensity of the non-local transitions gauges the oxygen-mediated 4p-O-3d intersite hybridization. We propose a revised interpretation of the pre-edges of transition metal compounds. Detailed analysis of these new features in the pre-edge offers a unique insight in the oxygen mediated metal-metal interactions in transition metal-based systems, which is a crucial aspect in orbital ordering and related electronic and magnetic properties. In addition, the exceptional resolving power of the present 1s2p RXES experiment allows us to demonstrate the coherent second-order nature of the underlying scattering process.
