Effective spin models for spin-phonon chains by flow equations *
Institut für Theoretische Physik, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
Revised: 4 April 2001
Published online: 15 June 2001
We investigate the anti-adiabatic limit of an anti-ferromagnetic S=1/2 Heisenberg chain coupled to Einstein phonons. The flow equation method is used to decouple the spin and the phonon part of the Hamiltonian. In the effective spin model long range spin-spin interactions are generated. We determine the phase transition from a gapless state to a gapped (dimerized) phase, which occurs at a non-zero value of the spin-phonon coupling. In the effective phonon sector a phonon hardening is observed.
PACS: 75.10.Jm – Quantized spin models / 63.20.Kr – Phonon-electron and phonon-phonon interactions / 63.20.Ls – Phonon interactions with other quasiparticles
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2001