Dynamical properties of low dimensional CuGeO3 and NaV2O5 systems

TL;DR

This study investigates the dynamical properties of low-dimensional spin-Peierls systems CuGeO3 and NaV2O5 using exact diagonalization, revealing differences in spin-phonon coupling and predicting spectral features consistent with experimental observations.

Contribution

It provides a comparative analysis of CuGeO3 and NaV2O5, determining model parameters from experimental data and highlighting the stronger spin-phonon coupling in NaV2O5.

Findings

NaV2O5 has 2-3 times larger spin-phonon coupling than CuGeO3.

Magnon excitations are separated from triplet continuum by a finite gap.

Model reproduces inelastic neutron scattering spectra with static dimerization approximation.

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 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. 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.