  The role of dynamical magneto-elastic coupling in spin-Peierls chains is
investigated by numerical and analytical techniques. We show that a Heisenberg
spin chain coupled to dynamical optical phonons exhibits a transition towards a
spontaneously dimerized state in a wide range of parameter space. The low
energy excitations are characterized as solitons. No binding between solitons
occurs in the isolated spin-phonon chain and the dynamical spin structure
factor shows a broad magnon dispersion. However, elastic interchain coupling
can lead to the formation of bound states.
