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Quasiclassical Hamiltonians for large-spin systems

D. A. Garanin·K. Kladko·P. Fulde
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Abstract

We propose a method for obtaining effective classical Hamiltonians \cal H for many-body quantum spin systems with large spins. This method uses the coherent-state representation of the partition function Z and the cumulant expansion in powers of 1/S. For the quantum Hamiltonian \hat H of a Heisenberg form, the 1/S corrections in \cal H have a non-Heisenberg many-spin form. The effective Hamiltonian \cal H can be treated by methods familiar for classical systems. The non-Heisenberg terms in \cal H may be responsible for such effects as spin-Peierls transition and uplifting of the classical degeneracy by quantum fluctuations.

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D. A. Garanin, K. Kladko, P. Fulde. 2002-03-01. Quasiclassical Hamiltonians for large-spin systems. https://doi.org/10.1007/s100510050132

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