We numerically investigate the dynamical properties of a nonlinear quantum-mechanical model system of local electronic two-level centers coupled to acoustic phonons. Nonadiabatic processes are included. No rotating-wave approximation has been used. In spite of the discreteness of the lattice, ‘‘ultrashort’’ solitons are found with half-widths down to one wavelength of the phonons which are in resonance with the energy splitting of the two-level centers. In homogeneous systems solitons are created in pairs, while in heterosystems they may appear isolated. The solitons of a pair have different velocities, but the same half-width. We investigate the threshold behavior of the soliton formation and the stability of solitons against fluctuations. We perform numerical simulations of soliton-soliton and soliton-phonon interactions and discuss reflection processes at the end of the chain.

• Received 24 August 1989

DOI:https://doi.org/10.1103/PhysRevB.41.3627