Spin dynamics of the spin-Peierls compound CuGeO3 under a magnetic field

The magnetic field driven transition in the spin-Peierls system CuGeO3 associated with the closing of the spin gap is investigated numerically. The field dependence of the spin dynamical structure factor (seen by inelastic neutron scattering) and of the momentum-dependent static susceptibility are calculated. In the dimerized phase (H<H-c), we suggest that the strong field dependence of the transverse susceptibility could be experimentally seen from the low-temperature spin-echo relaxation rate 1/T-2G or the second moment of the nuclear magnetic resonance spectrum. Above H-c low-energy-spin excitations appear at incommensurate wavevectors where the longitudinal susceptibility chi(zz)(q) peaks.