Effect of nonlinearity on the dynamics of a particle in field-induced systems

Dynamics of a particle in a perfect chain with one nonlinear impurity and in a perfect nonlinear chain under the action of dc field is studied numerically. The nonlinearity appears due to the coupling of the electronic motion to optical oscillators that are treated in the adiabatic approximation. We study both the cases of low and high values of field strength. Three different ranges of nonlinearity are obtained each of which has a different dynamics. In the low and intermediate ranges of nonlinearity, the localization effects are reduced. In fact, in the intermediate range case subdiffusive behavior in the perfect nonlinear chain is obtained for a long time. In all cases a critical value of nonlinear strength exists where a self-trapping transition takes place. This critical value depends on the system and the field strength. Beyond the self-trapping transition, nonlinearity enhances the localization.