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 qu artic nonlinearities is considered analytically based on an extended quasid iscreteness approach. For various mass differences (and thus different gap widths of the phonon spectrum), the coupled gap solitons are shown to displ ay very rich dynamical behavior and their properties are strongly dependent on the force-constant ratio K-3(2)/(K2K4), where K-j (j=1,2,3) are the for ce constants for the quadratic, cubic, and quartic parts of the intersite i nteraction potential, respectively. Several previous theoretical approaches for studying gap soliton dynamics in diatomic lattices are recovered in ou r scheme, and the relations between these methods are elucidated in a syste matic way.