INTERACTION OF DISCRETE BREATHERS WITH IMPURITY MODES

We study the interaction between a discrete breather and an impurity i n a nonlinear lattice model. Although the existence of the breather is due to nonlinearity while the existence of an impurity mode is due to a mass inhomogeneity, the two modes are very similar and therefore in teract strongly. Their interaction provides some insight on the interp lay between nonlinearity and disorder which localize energy in a latti ce. In particular we show that an impurity can act as a catalyst for t he fusion of two breathers and the generation of a larger excitation.