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Author: Rosner, H. × DDC: 620 ×

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    Magnon spectrum of the helimagnetic insulator Cu2OSeO3
    (London : Nature Publishing Group, 2016) Portnichenko, P.Y.; Romhányi, J.; Onykiienko, Y.A.; Henschel, A.; Schmidt, M.; Cameron, A.S.; Surmach, M.A.; Lim, J.A.; Park, J.T.; Schneidewind, A.; Abernathy, D.L.; Rosner, H.; van den Brink, Jeroen; Inosov, D.S.
    Complex low-temperature-ordered states in chiral magnets are typically governed by a competition between multiple magnetic interactions. The chiral-lattice multiferroic Cu2OSeO3 became the first insulating helimagnetic material in which a long-range order of topologically stable spin vortices known as skyrmions was established. Here we employ state-of-the-art inelastic neutron scattering to comprehend the full three-dimensional spin-excitation spectrum of Cu2OSeO3 over a broad range of energies. Distinct types of high- and low-energy dispersive magnon modes separated by an extensive energy gap are observed in excellent agreement with the previously suggested microscopic theory based on a model of entangled Cu4 tetrahedra. The comparison of our neutron spectroscopy data with model spin-dynamical calculations based on these theoretical proposals enables an accurate quantitative verification of the fundamental magnetic interactions in Cu2OSeO3 that are essential for understanding its abundant low-temperature magnetically ordered phases.
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    Electronic structure and aspects of unconventional superconductivity in NaxCoO2.yH2O
    (São Carlos : Universidade Federal de São Carlos, 2003) Rosner, H.; Drechsler, S.-L.; Fuchs, G.; Handstein, A.; Wälte, A.; Müller, K.-H.
    We examine the electronic structure of NaxCoO2.yH2O within the local density approximation. The parametrization of the band which forms the largest hole-Fermi surface centered at G shows significant deviations from what is frequently assumed in recent sophisticated theoretical studies. In particular, the commonly used nearest neighbor approaches in the framework of single band pictures are found to be unrealistic. The special role of H2O in screening the disorder in the charge reservoir is briefly discussed and compared with the case of Y1–xCaxCu3O6+d.
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    Signatures of a magnetic field-induced unconventional nematic liquid in the frustrated and anisotropic spin-chain cuprate LiCuSbO4
    (London : Nature Publishing Group, 2017) Grafe, H.-J.; Nishimoto, S.; Iakovleva, M.; Vavilova, E.; Spillecke, L.; Alfonsov, A.; Sturza, M.-I.; Wurmehl, S.; Nojiri, H.; Rosner, H.; Richter, J.; Rößler, U.K.; Drechsler, S.-L.; Kataev, V.; Büchner, B.
    Modern theories of quantum magnetism predict exotic multipolar states in weakly interacting strongly frustrated spin-1/2 Heisenberg chains with ferromagnetic nearest neighbor (NN) inchain exchange in high magnetic fields. Experimentally these states remained elusive so far. Here we report strong indications of a magnetic field-induced nematic liquid arising above a field of ~13 T in the edge-sharing chain cuprate LiSbCuO4 ≡ LiCuSbO4. This interpretation is based on the observation of a field induced spin-gap in the measurements of the 7Li NMR spin relaxation rate T1−1 as well as a contrasting field-dependent power-law behavior of T1−1 vs. T and is further supported by static magnetization and ESR data. An underlying theoretical microscopic approach favoring a nematic scenario is based essentially on the NN XYZ exchange anisotropy within a model for frustrated spin-1/2 chains and is investigated by the DMRG technique. The employed exchange parameters are justified qualitatively by electronic structure calculations for LiCuSbO4.