Solitons on a zigzag-runged ladder lattice

The nonlinear dynamical model on a two-leg ladder lattice with the rungs arranged into a zigzag chain is proposed. The lattice contains two structure elements (molecules) in the unit cell. As a result, the system exhibits the two-branch spectrum in its low-amplitude limit. The similar two branches are shown to be observed in high-amplitude soliton solutions too. The integrability of the model is proved and the one-soliton solutions are explicitly presented and analyzed. The model Hamiltonian, as well as the basic conserved quantities are found.