Browsing by Author "Lorenz, T"

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    Anomalous spin dynamics and orbital excitations in Mott-insulating titanates
    (Australian Institute of Physics, 2010-02-03) Ulrich, C; Khaliullin, G; Ament, LJP; Ghiringhelli, G; Braicovich, L; Lorenz, T; Tokura, Y; van den Brink, J; Keimer, B
    Spin and orbital degrees of freedom play an important role in the various phenomena of strongly correlated electron systems like unconventional high-temperature superconductivity in cuprates or colossal magnetoresistance in manganates. Our extensive neutron scattering experiments on the cubic perovskite titanates LaTiO3 and YTiO3 lead to the discovery of a highly unusual magnetic ground state which is in contradiction to the standard Goodenough-Kanamori rules, but indicates the presence of strong orbital fluctuations [1-4]. Raman light scattering spectra of LaTiO3 and YTiO3 exhibit unexpected features in the high energy range well above the phonon spectrum [5]. Using momentum dependent resonant inelastic x-ray scattering (RIXS) experiments in combination with theoretical calculations, we were able to identify these excitations as collective orbital excitations (orbital waves termed ‘orbitons’) [6-7].
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    Momentum dependence of orbital excitations in Mott-insulating titanates
    (American Physical Society, 2009-09-04) Ulrich, C; Ament, LJP; Ghiringhelli, G; Braicovich, L; Moretti Sala, M; Pezzotta, N; Schmitt, T; Khaliullin, G; van den Brink, J; Roth, H; Lorenz, T; Keimer, B
    High-resolution resonant inelastic x-ray scattering has been used to determine the momentum dependence of orbital excitations in Mott-insulating LaTiO(3) and YTiO(3) over a wide range of the Brillouin zone. The data are compared to calculations in the framework of lattice-driven and superexchange-driven orbital ordering models. A superexchange model in which the experimentally observed modes are attributed to two-orbiton excitations yields the best description of the data. 2008, American Physical Society.