Eur. Phys. J. B 1, 19-28 (1998)
https://doi.org/10.1007/s100510050148

Dynamical properties of low-dimensional CuGeO₃ and NaV₂0₅ spin-Peierls systems

Laboratoire de Physique Quantique et Unité Mixte de Recherche CNRS 5626, Université Paul Sabatier, 31062 Toulouse, France

Corresponding author: ^a didier@irsamc2.ups-tlse.fr

Received: 30 July 1997
Revised: 16 September 1997
Accepted: 10 October 1997
Published online: 15 January 1998

Abstract

Properties of low-dimensional spin-Peierls systems are described by using a one-dimensional S={1}/{2} antiferromagnetic Heisenberg chain linearly coupled to a single phonon mode of wave vector π (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. Numerical evidences are given for a spontaneous discrete symmetry breaking towards a spin gapped phase with a frozen lattice dimerization. Special emphasis is put on the comparative study of the two inorganic spin-Peierls compounds CuGeO₃ and NaV₂O₅ and the model parameters are determined from a fit of the experimental spin gaps. We predict that the spin-phonon coupling is 2 or 3 times larger in NaV₂O₅ than in CuGeO₃. Inelastic neutron scattering spectra are calculated and similar results are found in the single phonon mode approximation and in the model including a static dimerization. In particular, the magnon S=1 branch is clearly separated from the continuum of triplet excitations by a finite gap.