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Register a new userDynamical properties of the one-dimensional spin-1/2 Bose-Hubbard model near Mott-insulator to ferromagnetic liquid transition
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We investigate the dynamics of the one-dimensional strongly repulsive spin-1/2 Bose-Hubbard model for filling $ ule1.$ While at $ u=1$ the system is a Hubbard-Mott insulator exhibiting dynamical properties of the Heisenberg ferromagnet, at $ u<1$ it is a ferromagnetic liquid with complex spin dynamics. We find that close to the insulator-liquid transition the system admits for a complete separation of spin and density degrees of freedom valid at {it all} energy and momentum scales within the $t-J$ approximation. This allows us to derive the propagator of transverse spin waves and the shape of the magnon peak in the dynamic spin structure factor.
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We report structural, magnetization, electrical resistivity and nuclear- and electron spin resonance data of the complex transition metal oxide In_2VO_5 in which structurally well-defined V-O chains are realized. An itinerant character of the vanadium d-electrons and ferromagnetic correlations, revealed at high temperatures, are contrasted with the insulating behavior and predominantly antiferromagnetic exchange between the localized V^{4+} S = 1/2-magnetic moments which develop below a certain characteristic temperature T* ~ 120 K. Eventually the compound exhibits short-range magnetic order at $T_SRO ~ 20 K. We attribute this crossover occurring around T* to the unusual anisotropic thermal contraction of the lattice which changes significantly the overlap integrals and the character of magnetic intra- and interchain interactions.
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