Modulational Instability and Discrete Localized Modes in Two Coupled Atomic Chains with Next-Nearest-Neighbor Interactions

Abstract

AbstractA pair of one dimensional atomic chains which are coupled via the Klein-Gordon potential is considered in this study, with each chain experiencing both nearest and next-nearest-neighbor interactions. The discrete nonlinear Schrödinger amplitude equation with next-nearest-neighbor interactions is thus derived from the out-phase equation of motion of the coupled chains. This is achieved by using the rotating wave approximations perturbation method, in which both the carrier wave and envelope are explicitly treated in the discrete regime. It is shown that the next-nearest-neighbor interactions greatly modifies the region of observation of modulational instability in the atomic chain. By exploring the discrete Hirota-Bilinear method, we obtain the discrete one-soliton solution which is localized around the origin and structurally stable because it conserves it form as time evolves. However when the atomic chain is purely subjected to a symmetric coupling potential, we observe a structurally unstable discrete excitation that changes into an up-and-down asymmetric localized modes; both in the presence and absence of next-nearest-neighbor interactions. Results of numerical simulations clearly depicts the long term evolution of these discrete nonlinear excitations, that evolve from symmetric to asymmetric localized modes in the atomic chain.