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要旨:
We analyze the high-temperature spin dynamics of quantum compass models by a moment expansion method. We point out that the evaluation of moments maps to the enumeration of paths in a branching process on the lattice. This mapping to a statistical mechanics combinatorics problem provides an elegant visualization of this analysis. We present results for the time-dependent spin autocorrelation function (which is of relevance to NMR experiments) for two compass models: the honeycomb (Kitaev) and two-dimensional compass lattice model. Furthermore, following this approach, we argue that in quantum compass models the spin correlations are generically strongly anisotropic and short ranged.
