Mixing of magnetic and phononic excitations in incommensurate spin-Peierlssystems - art. no. 144404

We analyze the excitation spectra of a spin-phonon coupled chain in the pre sence of a soliton. This is taken as a microscopic model of a spin-Peierls material placed in a high magnetic held. We show, by using a semiclassical approximation in the bosonized representation of the spins, that a trapped magnetic state obtained in the adiabatic approximation is destroyed by dyna mical phonons. Low energy-states are phonons trapped by the soliton. When t he magnetic gap is smaller than the phonon frequencies, the only low-energy state is a mixed magnetophonon state with the energy of the gap. We emphas ize that our results are relevant for the Raman spectra of the inorganic sp in-Peierls material CuGeO3.