Dynamics of coupled gap solitons in diatomic lattices with cubic and quartic nonlinearities

The dynamics of coupled gap solitons in diatomic lattices with cubic and quartic nonlinearities is considered analytically based on an extended quasidiscreteness approach. For various mass differences (and thus different gap widths of the phonon spectrum), the coupled gap solitons are shown to display very rich dynamical behavior and their properties are strongly dependent on the force-constant ratio [Formula Presented] where [Formula Presented] are the force constants for the quadratic, cubic, and quartic parts of the intersite interaction potential, respectively. Several previous theoretical approaches for studying gap soliton dynamics in diatomic lattices are recovered in our scheme, and the relations between these methods are elucidated in a systematic way.