Breather dynamics in diatomic FPU chains

Discrete breathers dynamics in the alternate mass FPU chain (quartic potential) is analysed. The conditions for the existence of such periodic, spatially localized solutions with frequency above the optical band and inside the gap separating it from the acoustic one are discussed. Stability analysis of breathers is also reported: the main issue concerns the identification of a bifurcation mechanism that connects the symmetric stable solution of the alternate mass chain with the antisymmetric stable one of the equal mass chain. Multi-breather excitations have also been investigated: The main outcomes concern the analysis of the dynamical mechanism yielding the "merging" of two breather states into a single breather solution and the robustness of long living breather-like states emerging from spatially extended coherent excitations. (C) 1998 Elsevier Science B.V.