Abstract:
The flow equation method (Wegner, 1994) is used as continuous unitary transformation to construct perturbatively effective Hamiltonians. The method is illustrated in detail for dimerized and frustrated antiferromagnetic S =1/2 chains. The effective Hamiltonians conserve the number of elementary excitations which are S =1 magnons for the dimerized chains. The sectors of different number of excitations are clearly separated. Easy-to-use results for the gap, the dispersion and the ground state energies of the chains are provided.
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Knetter, C., Uhrig, G. Perturbation theory by flow equations: dimerized and frustrated S = 1/2 chain. Eur. Phys. J. B 13, 209–225 (2000). https://doi.org/10.1007/s100510050026
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DOI: https://doi.org/10.1007/s100510050026