Dynamical solitons in a one-dimensional nonlinear diatomic chain

Abstract
Solitonlike excitations with frequencies in the gap of a linear spectrum are considered for a diatomic chain with small mass difference. It is shown that these excitations represent themselves as a complicated combination of solitons of the acoustic and quasioptical branches of the spectrum. The evolution of these solutions is studied in the phase plane and analytical expressions are obtained. The situation is general for systems having two interacting fields with the same nonlinearity but with different dispersion signs.