Effective spin models for spin-phonon chains by flow equations

Issue		Eur. Phys. J. B Volume 21, Number 3, June I 2001


Page(s)		369 - 374
Section		Solid and Condensed State Physics
DOI		10.1007/s100520100712

Eur. Phys. J. B 21, 369-374

Effective spin models for spin-phonon chains by flow equations

C. Raas, A. Bühler and G.S. Uhrig

Institut für Theoretische Physik, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany

(Received 21 February 2001 and Received in final form 4 April 2001)

Abstract
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

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