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

9616574辛格这个职业生涯中期的PI成功地振兴了统计力学中的高温级数展开技术，并将其应用于量子磁学中的各种问题。除了技术上重要的高温超导体和巨磁电阻钙钛矿外，本研究中的新磁性材料还包括无机自旋Peierls CuGeO_3和准二维自旋能隙材料CaV_4O_9。在该方法中，对高温级数展开的补充是对有限晶格的零温高阶微扰展开和精确对角化(特别是核多项式方法)。重点将计算各种量子自旋模型，例如海森堡-伊辛模型，以及它们的强关联电子的母体模型，如Hubbard，t-J，Kondo晶格和双交换模型的随温度变化的光谱性质。%这个职业生涯中期的PI因振兴了统计力学中的高温级数展开技术而受到称赞。他已经成功地将这项技术应用于收集对几种新型磁铁特性的关键见解。这笔拨款是为了支持他的研究计划的持续增长，其中包括考虑更多、更复杂的技术。结果将与各种实验进行比较。

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.