NEUTRON-SCATTERING STUDIES ON SPIN-PEIERLS MATERIAL CUGEO3

Crystal structure and phonon dynamics up to 150 meV of the spin-Peierl s material CuGeO3 have been investigated by neutron scattering experim ents. We found a large lattice anomaly in the a-b plane, vertical to t he one-dimensional antiferromagnetic spin chain, associated with addit ional diffraction peaks in the b-axis at temperatures much higher tha n the spin-Peierls transition temperature. The phonon modes of the cha in oxygens at 100 meV show consistent evolution with diffraction. Ther efore, we conclude that the structural evolution of the chain oxygens in the a-b plane, which mediates the spin-spin interaction along the c -axis, drives the spin-Peierls transition.