SPATIALLY LOCALIZED, TEMPORALLY QUASI-PERIODIC, DISCRETE NONLINEAR EXCITATIONS

In contrast to the commonly discussed discrete breather, which is a sp atially localized, time-periodic solution, we present an exact solutio n of a discrete nonlinear Schrodinger breather which is a spatially lo calized, temporally quasiperiodic nonlinear coherent excitation. This breather is a multiple-soliton solution in the sense of the inverse sc attering transform. A discrete breather of multiple frequencies is con ceptually important in studies of nonlinear lattice systems. We point out that, for this breather, the incommensurability of its frequencies is a discrete lattice effect and these frequencies become commensurat e in the continuum limit. To understand the dynamical properties of th e breather, we also discuss its stability and its behavior in the pres ence of an external potential. Finally, we indicate how to obtain an e xact N-soliton breather as a discrete generalization of the continuum multiple-soliton solution.