Huotari S, Simonelli L, Sahle C J, Sala M Moretti, Verbeni R, Monaco G
Department of Physics, University of Helsinki, PO Box 64, FI-00014, Finland. European Synchrotron Radiation Facility, F-38043 Grenoble cedex, BP 220, France.
J Phys Condens Matter. 2014 Apr 23;26(16):165501. doi: 10.1088/0953-8984/26/16/165501. Epub 2014 Apr 1.
We report a study on the temperature dependence of charge-neutral crystal field (dd) excitations in cupric oxide, using nonresonant inelastic x-ray scattering spectroscopy. Thanks to a very high-energy resolution (ΔE = 60 meV), we observe thermal effects on the dd excitation spectrum fine structure between temperatures of 10-320 K. The spectra broaden considerably with increasing temperature, consistently with an enhancement of the coupling between crystal field excitations and the temperature-dependent continuum of states above the band gap. We discuss this and other mechanisms that may explain this temperature dependence.
