Guided modes in a hexagonal periodic graph like domain

TL;DR

This paper demonstrates the existence and robustness of guided edge modes in a two-dimensional honeycomb-structured medium, using asymptotic analysis and quantum graph approximations, with implications for wave control in engineered materials.

Contribution

It introduces a novel analysis of guided waves and edge states in perturbed honeycomb media, establishing their existence and robustness through asymptotic and quantum graph methods.

Findings

Existence of Dirac points at high frequencies for small thickness elta.

Presence of robust edge modes along zigzag cuts under various boundary conditions.

Almost-non dispersive edge states depend on cut location and frequency.

Abstract

This paper deals with the existence of guided waves and edge states in particular two-dimensional media obtained by perturbing a reference periodic medium with honeycomb symmetry. This reference medium is a thin periodic domain (the thickness is denoted $\delta$ > 0) with an hexagonal structure, which is close to an honeycomb quantum graph. In a first step, we show the existence of Dirac points (conical crossings) at arbitrarily large frequencies if $\delta$ is chosen small enough. We then perturbe the domain by cutting the perfectly periodic medium along the so-called zigzag direction, and we consider either Dirichlet or Neumann boundary conditions on the cut edge. In the two cases, we prove the existence of edges modes as well as their robustness with respect to some perturbations, namely the location of the cut and the thickness of the perturbed edge. In particular, we show that different locations of the cut lead to almost-non dispersive edge states, the number of locations increasing with the frequency. All the results are obtained via asymptotic analysis and semi-explicit computations done on the limit quantum graph. Numerical simulations illustrate the theoretical results.