Abstract
The ground state of the spin-one-half acoustic phonon system is studied in the limitB≪1. The technique is to combine the Brillouin-Wigner variational perturbation theory with a source canonical transformation. With theB=0 source transform the energy is calculated as a function of coupling constant through terms of orderB 2. To this order there is no phase transition. The theory gives the crossover from perturbation theory to an improved classical theory with quantum fluctuations. With a source transform with a nonzero inverse lengthβ the energy estimate is further improved to next order in the coupling constant and for larger values ofB. The soft, infinite-order transition of the modified source theory is removed in the limitB≪1.
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References
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V. J. Emery and A. Luther,Phys. Rev. B 9:215 (1974).
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Gross, E.P. Ground state of a spin-phonon system. III. Small-B limit. J Stat Phys 54, 437–448 (1989). https://doi.org/10.1007/BF01023488
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DOI: https://doi.org/10.1007/BF01023488