Role of dynamical phonons in one dimensional spin-Peierls systems
Abstract
We have studied a new model describing magnetic properties of low-dimensional spin-Peierls systems. The model consists of a one dimensional S=1/2 antiferromagnetic frustrated Heisenberg chain linearly coupled to dynamical phonons of wave vector pi whose contribution is expected to be dominant. By exact diagonalizations of small rings with up to 24 sites supplemented by a finite size scaling analysis, static and dynamical properties are investigated. Evidences for a spontaneous discrete symmetry breaking followed by the opening of a spin gap are given. Applications to the cases of the two inorganic spin-Peierls compounds CuGeO3 and NaV2O5 are considered and the parameters of the model are determined from a fit of the experimental spin gaps. Larger dimerizations and larger spin-spin correlation lengths are found compared to the ones obtained in the mean-field static model. Inelastic neutron scattering spectra are calculated and found to be qualitatively similar to the ones obtained with a static dimerization (static model). In particular, the magnon S=1 branch is clearly separated from the continuum of triplet excitations by a finite gap.Keywords
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