Minimal model to describe the magnetism of $CuGe{O}_3$

Abstract

We show that to describe properly the low energy excitations of $CuGe{O}_3$ one must include the effects of a transverse antiferromagnetic coupling, which is estimated to be $J_{\perp }=0.15J$. Owing to this coupling the frustration in the chains is significantly lower than recent 1D estimates based on purely one-dimensional arguments, we find $J_2=0.2J$. Furthermore we have found a strong modulation of the nearest neighbour coupling due to the static distortion $\delta =0.065$, which is 5 times higher than that previously deduced from a 1D chain approach. Our set of parameters gives, i) a value of the distorsion which agreeswell with some recent estimate for a lower bound, we are able to perfectly reproduce ii)the dispersions, iii) the experimental susceptibility at both high and low temperatures. By performing DMRG calculations for 2 coupled chains we have analysed the effect of the transverse coupling on the ratio of singlet to triplet gaps. The ratio is very sensitive to the parameters and the universality reported in the strict one dimensional case is lost. As an additional point, we provide a simple picture to explain the interesting new feature observed in recent inelastic neutron scattering experiments: the existence of a second branch of excitations.

7 pages latex, figure included, accepted in PRB (issue dec.99)

References in corpus (4)

• Elementary Excitations in Dimerized and Frustrated Heisenberg Chains
• Peierls Dimerization with Non-Adiabatic Spin-Phonon Coupling
• Dynamical effects of phonons on soliton binding in spin-Peierls systems
• Stability of the Haldane phase in anisotropic magnetic ladders

Cited by in corpus (5)

• An Electron Spin Resonance Selection Rule for Spin-Gapped Systems
• High-field spectroscopy of singlet-triplet transitions in the spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8
• Modeling the spin-Peierls transition of spin-$1/2$ chains with correlated states: $J_1-J_2$ model, CuGeO${}_3$ and TTF-CuS${}_4$C${}_4$(CF${}_3$)${}_4$
• Triplet Dispersion in CuGeO_3: Perturbative Analysis
• Spin-Peierls transition in an anisotropic two-dimensional XY model