Stochastic and deterministic domino processes in photoinduced structural changes

The photoinduced structural change is discussed theoretically using a one-dimensional model, which is composed of localized electrons and lattices. We clarify the condition for the adiabatic and/or diabatic approximations. The global structural change by one-site excitation is possible in both cases. Under the adiabatic picture, the domain wall between the two phases moves at constant velocity, and the structural change in each site occurs nonradiatively within the time order of the lattice vibration. On the contrary, under the diabatic picture, the motion of the domain wall becomes a stochastic process because the structural change in each site occurs via the radiative transition, which takes a longer time than the lattice vibration. (C) 1999 Elsevier Science Ltd. All rights reserved.