Correlations, Fluctuations and Elementary Excitations in Insulating and Doped Quantum Magnets

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9616574 Singh This mid-career PI has been successful in rejuvenating the technique of high temperature series expansion in statistical mechanics and has applied it to a wide variety of problems in quantum magnetism. The new magnetic materials in this study include, apart from the technologically important high-temperature superconductors and colossal magnetoresistance Perovskites; the inorganic spin-Peierls CuGeO3 and quasi two dimensional spin gap materials CaV4O9. In this grant the high temperature series expansion is supplemented by zero temperature high order perturbation expansion and exact diagonalization (especially the Kernel Polynomial method) for finite lattices. The focus will be to calculate the temperature dependent spectral properties of the various quantum spin models, e.g. Heisenberg-Ising, and their parent models of strongly correlated electrons such as, Hubbard, t-J, Kondo-lattice and double exchange models. %%% This mid-career PI has been applauded for revitalizing the technique of high temperature series expansion in statistical mechanics. He has successfully applied this technique to gather critical insight in the properties of several novel magnets. This grant is to support a continuing growth of his research program which includes consideration of additional, more complex techniques. The results will be compared to a variety of experiments.