Dynamics of a bond-disordered Peierls chain and mixed gap states

We numerically apply a femtosecond electric pump pulse to a bond-disordered Su-Schrieffer-Heeger model and observe the formation of excitations like bound and separate soliton pairs as well as neutral localized breathers. Bound soliton pairs though overall charge neutral show an electric dipole moment oscillating with the transition frequency between the partially occupied gap states. Furthermore, the dipole moment amplitude pulsates while the solitons are interacting with the localized breathers. We investigate the ground slate and dynamics of the bound soliton pairs as mixed gap states. In their ground state a discontinuous phase transition from bound to separate soliton pairs is found. The dynamics of these states is very similar to the dynamics under the pump-pulse excitation. We discuss their ground state and the dynamics in terms of the soliton-pair solution of the continuum model. [S0163-1829(98)08045-X].