SPring-8, the large synchrotron radiation facility

Date: 15:00- , September 29, 2006

Place: HOUKOUKAN in SPring-8

Speaker: Prof. Adolfo G. Eguiluz （Univ. Tennessee, and Oak Ridge National Laboratory)

Title: Charge Excitations in Transition-Metal Oxides

Abstract: The charge-density excitations in prototype transition-metal oxides, including several Mott insulators, are investigated via time-dependent density-functional theory.  The ground state is evaluated within the LDA+U “correlated band-structure” method. The dynamical density response is handled within an adiabatic extension of the local-density approximation.  We argue that the narrow bands typical of Mott insulators embody a natural tendency towards the formation of an electron-hole collective state, with excitation energy on the order of the “Hubbard U.”  Whether the state is actually realized (as we predict for manganites) or not (idem, for monoxides), depends on details of the hybridization between the correlated d orbitals and the oxygen-derived p orbitals. These predictions can be checked directly via inelastic x-ray scattering (IXS) experiments performed at third-generation synchrotron sources. We also discuss the excitations in sodium cobaltates and in another topical material, MgB₂; in the latter case our calculations are in excellent agreement with recent IXS data by Cai et al. performed at SPring-8.  In the case of the monoxides, non-trivial discrepancies with the IXS data, involving excitations in the Mott gap, are discussed.

Organizer: MIZUKI (PHS 3902)