Electronic structure and hybridization of strongly correlated transition metal systems

The purpose of this continuing investigation is explaining the effects of correlation and hybridization within the electronic structure and bonding of both simple transition metal oxides and complex transition metal materials such as superconductors and diluted magnetic semiconductors. The main tools used consist of various forms of soft x-ray emission and absorption spectroscopy which provide that ability to map site- and element-specific electron states in the valence and conduction bands of a compound. Coupling the experimental measurements with the theoretical densities of states (DOS) calculations, a more complete and detailed description of the hybridization between electron states near the Fermi energy is produced. Site-specific resonant x-ray emission spectroscopy (RXES) measurements are shown to provide a description of transitions across the insulating gap as well as the element responsible for states involved in the transitions, producing a refined model for portraying systems as either charge-transfer excitations between elemental atoms (inter-atomic transitions) or transfer between the Hubbard split d-bands of the metal (intra-atomic transitions). Angle-resolved soft x-ray spectroscopy measurements (ARSXS) will not only allow us to measure the site-specific absorbing and emitting states near the Fermi energy, but allow further classification as different bonds of inequivalent atomic lattice position can be targeted.; From different comparisons of these experimental and theoretical techniques, the hybridization of electronic states is displayed in both the valence and conduction bands for the simple transition metal oxide systems NiO and CoO and the diluted magnetic semiconductor Zn0.96Mn0.10S. The character of the insulating energy gap in these systems is shown to depend on the level of hybridization within the system, with each of these systems having properties of both charge-transfer and Mott-Hubbard insulators. Theoretical DFT calculations are shown to provide an excellent model of angle-resolved x-ray absorption and emission measurements of the different p -orbital orientations for the inequivalent O atom sites in the perovskite structure of Sr2RuO4.