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

We reconsider the two-dimensional model for CuGeO3 introduced previously [P hys. 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 latte r 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 leas t 2 to 3 times higher than values deduced previously from one-dimensional c hain approaches. For the intrachain frustration alpha (0) we find a smaller value of 0.25(3). The existence of interchain frustration conjectured prev iously is confirmed by the analysis of temperature-dependent susceptibility .