Theoretical studies on the high-energy excitation spectra of multinary compounds

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The present research clarified the capability of high-energy spectroscopies as tools to investigate the electronic states of multinary compounds. Particular attention was paid to the theoretical studies on the oxygen 1s resonant x-ray emission spectroscopy (O 1s RXES) of transition-metal oxides. The present theoretical calculations showed that the O 1s RXES provides us with information on the itinerant valence electrons as well as the localized ones. In the case of insulating cuprates for instance, it observes the inelastic x-ray scattering due the electronic transition from the Zhang-Rice singlet band to the upper Hubbard band (UHB). The present research also predicted that the polarization correlation between incident and scatted x-rays is very strong in the O 1s RXES.The present research clarified the electronic state of one-dimensional Y_2BaNiO_5-type nickel compounds. The theoretical calculations on the O 1s RXES and O 1s X-ray absorption spectrum (O 1s XAS) showed that the Hund's … More coupling is very important in understanding the valence electron states. For divalent Ni compounds, the present theory predicted a new type of excitation. It consists of simultaneous double excitations at distant Ni ions, where the Ni 3d spin state of each Ni is changed from triplet to singlet. We also succeeded in observing the excitation in NiO.In order to emphasize the importance of comprehensive analysis of various high-energy spectra, we extended the study to the calculations of Cu 2p x-ray photoemission spectroscopy (Cu 2p XPS), angle-resolved photoemission (ARPES) and Cu 1s resonant inelastic x-ray scattering (Cu 1s RIXS). We also showed a close relationship between the Cu 2p XPS and ARPES through the theoretical calculations on the carrier doping dependence of those spectra Moreover, we studied the effects of Cu 3d orbital degeneracy on the Cu 1s RIXS to show the dd excitation mechanism in the Cu 1s RIXS. The result showed that the excitation selection rules of the Cu 1s RIXS differ from those of the O 1s RXES in many respects. It indicates that the Cu 1s RIXS and O 1s RXES are complementary to each other. Less