Effective spin models for spin-phonon chains by flow equations\n

Abstract

\n \nWe investigate the anti-adiabatic limit of an anti-ferromagnetic S=1/2\nHeisenberg chain coupled to Einstein phonons. The flow equation method is used\nto decouple the spin and the phonon part of the Hamiltonian. \nIn the effective spin model long range spin-spin interactions are generated.\nWe determine the phase transition from a gapless state to a gapped (dimerized)\nphase, which occurs at a non-zero value of the spin-phonon coupling.\nIn the effective phonon sector a phonon hardening is observed.\n\n\n