Browsing by Author "Khaliullin, G"

Now showing 1 - 5 of 5
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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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    Competing exchange interactions on the verge of a metal-insulator transition in the two-dimensional spiral magnet Sr3Fe2O7
    (Americal Physical Society, 2014-10-03) Kim, JH; Jain, A; Reehuis, M; Khaliullin, G; Peets, DC; Ulrich, C; Park, JT; Faulhaber, E; Hoser, A; Walker, HC; Adroja, DT; Walters, AC; Inosov, DS; Maljuk, A; Keimer, B
    We report a neutron scattering study of the magnetic order and dynamics of the bilayer perovskite Sr 3 Fe 2 O 7 , which exhibits a temperature-driven metal-insulator transition at 340 K. We show that the Fe 4+ moments adopt incommensurate spiral order below T N =115  K and provide a comprehensive description of the corresponding spin-wave excitations. The observed magnetic order and excitation spectra can be well understood in terms of an effective spin Hamiltonian with interactions ranging up to third-nearest-neighbor pairs. The results indicate that the helical magnetism in Sr 3 Fe 2 O 7 results from competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions whose strengths become comparable near the metal-insulator transition. They thus confirm a decades-old theoretical prediction and provide a firm experimental basis for models of magnetic correlations in strongly correlated metals. © 2014, American Physical Society.
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    Long-range transfer of electron-phonon coupling in oxide superlattices
    (Australian Institute of Physics, 2013-02-06) Ulrich, C; Driza, AN; Blanco-Canosa, SA; Bakr, M; Soltan, S; Khalid, S; Mustafa, L; Kawashima, K; Christiani, G; Habermeier, HU; Khaliullin, G; Le Tacon, M; Keimer, B
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    Long-range transfer of electron-phonon coupling in oxide superlattices
    (Nature Publishing Group, 2012-08-01) Driza, N; Blanco-Canosa, S; Bakr, M; Soltan, S; Khalid, M; Mustafa, L; Kawashima, K; Christiani, G; Habermeier, HU; Khaliullin, G; Ulrich, C; Le Tacon, M; Keimer, B
    The electron-phonon interaction is of central importance for the electrical and thermal properties of solids, and its influence on superconductivity, colossal magnetoresistance and other many-body phenomena in correlated-electron materials is the subject of intense research at present. However, the non-local nature of the interactions between valence electrons and lattice ions, often compounded by a plethora of vibrational modes, presents formidable challenges for attempts to experimentally control and theoretically describe the physical properties of complex materials. Here we report a Raman scattering study of the lattice dynamics in superlattices of the high-temperature superconductor YBa2Cu3O7 (YBCO) and the colossal-magnetoresistance compound La2/3Ca1/3MnO3 that suggests a new approach to this problem. We find that a rotational mode of the MnO6 octahedra in La2/3Ca1/3MnO3 experiences pronounced superconductivity-induced line-shape anomalies, which scale linearly with the thickness of the YBCO layers over a remarkably long range of several tens of nanometres. The transfer of the electron-phonon coupling between superlattice layers can be understood as a consequence of long-range Coulomb forces in conjunction with an orbital reconstruction at the interface. The superlattice geometry thus provides new opportunities for controlled modification of the electron-phonon interaction in complex materials. © 2012, Nature Publishing Group.
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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.