High-energy magnetic excitation in CuGeO3

The high-energy magnetic excitation continuum in CuGeO3 has been studied by inelastic neutron scattering. At low temperatures, the upper part of the continuum expected for an ideal Heisenberg chain is replaced by a well-defined magnonlike excitation. This branch exhibits a sinusoidal dispersion with frequencies below the positions where the upper boundary of the continuum would be expected. In contrast to the triplet excitation, this high-energy magnonlike branch is not affected by the spin-Peierls transition, but disappears near 150 K. The high-energy feature seems to be a signature of a strong frustration induced by spin phonon coupling.