Breathers in systems with intrinsic and extrinsic nonlinearities

We study the interplay between nonlinearity and localization in a model con sisting of a quantum quasiparticle interacting with a nonlinear extended la ttice. The isolated lattice can support discrete breathers, and the couplin g of the quasiparticle to the lattice leads to localized quasiparticle stat es. Minimum energy states of the full system can have both a breather and a solitonic character. Excited states lead to interesting new phenomena, suc h as full breather states, which arise from the combination of intrinsic an d extrinsic nonlinearity. (C) 2000 Elsevier Science B.V. All rights reserve d.