Behavior of solitary waves of coupled nonlinear Schr\"odinger equations subjected to complex external periodic potentials with anti-$\mathcal{PT}$ symmetry

TL;DR

This paper investigates the behavior and stability of solitary waves in a two-component nonlinear Schrödinger system subjected to complex, anti-PT symmetric periodic potentials, using numerical simulations and a collective coordinate approach.

Contribution

It introduces a collective coordinate approximation for coupled solitary waves in anti-PT symmetric potentials and compares its predictions with numerical simulations, revealing stability criteria.

Findings

Qualitative agreement between collective coordinate approximation and numerical simulations.

Instability often occurs due to opposite height changes in components.

Stability criteria from one-component cases are effective for the coupled system.

Abstract

We discuss the response of both moving and trapped solitary wave solutions of a nonlinear two-component nonlinear Schr\"odinger system in 1+1 dimensions to an anti-$\mathcal{PT}$ external periodic complex potential. The dynamical behavior of perturbed solitary waves is explored by conducting numerical simulations of the nonlinear system and using a collective coordinate variational approximation. We present case examples corresponding to choices of the parameters and initial conditions involved therein. The results of the collective coordinate approximation are compared against numerical simulations where we observe qualitatively good agreement between the two. Unlike the case for a single-component solitary wave in a complex periodic $\mathcal{PT}$-symmetric potential, the collective coordinate equations do not have a small oscillation regime, and initially the height of the two components changes in opposite directions often causing instability. We find that the dynamic stability criteria we have used in the one-component case is proven to be a good indicator for the onset of dynamic instabilities in the present setup.