Triplet dispersion in CuGeO3:: Perturbative analysis -: art. no. 094401

We reconsider the two-dimensional model for CuGeO3 introduced previously [Phys. Rev. Lett. 79, 163 (1997)]. Using a computer aided perturbation method based on how equations we expand the 1-triplet dispersion up to 10th order. The expansion is provided as a polynom in the model parameters. The latter are fixed by fitting the theoretical result to experimental data obtained by inelastic neutron scattering. For a dimerization delta approximate to0.08(1) we find an excellent agreement with experiment. This value is at least 2 to 3 times higher than values deduced previously from one-dimensional chain approaches. For the intrachain frustration alpha (0) we find a smaller value of 0.25(3). The existence of interchain frustration conjectured previously is confirmed by the analysis of temperature-dependent susceptibility.