https://doi.org/10.1007/s100510050026
Perturbation theory by flow equations: dimerized and frustrated S=1/2 chain
Institut für Theoretische Physik, Universität zu Köln,
Zülpicher Straße 77, Köln 50937, Germany
Received:
5
May
1999
Revised:
7
June
1999
Published online: 15 January 2000
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.
PACS: 75.10.Jm – Quantized spin models / 02.30.Mv – Approximations and expansions / 03.65.-w – Quantum mechanics
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2000
