Topologically protected interface phonons in two-dimensional nanomaterials: hexagonal boron nitride and silicon carbide

TL;DR

This paper demonstrates the existence of topologically protected phonon modes in a 2D hexagonal boron nitride sheet, which are localized at interfaces and exhibit robustness against defects, opening new avenues in nanomaterial mechanics.

Contribution

The study provides the first demonstration of topologically protected phonon modes in 2D nanomaterials using lattice dynamics and molecular dynamics simulations.

Findings

Topological phonon modes are localized at interfaces with distinct valley Chern numbers.

These modes cross the frequency gap [1123, 1278] cm^{-1} and are robust against defects.

Vibrational energy within this gap is topologically protected, enabling defect-robust wave propagation.

Abstract

We perform both lattice dynamics analysis and molecular dynamics simulations to demonstrate the existence of topologically protected phonon modes in a two-dimensional, monolayer hexagonal boron nitride sheet. The topological phonon modes are found to be localized at an in-plane interface that divides the system into two regions of distinct valley Chern numbers. The dispersion of this topological phonon mode crosses over the frequency gap [1123, 1278] cm^{-1}, which is opened through analogy with the quantum valley Hall effect by breaking inversion symmetry of the boron and nitride atoms in the primitive unit cell. Consequently, vibrational energy with frequency within this gap is topologically protected, resulting in wave propagation that exhibits minimal backscattering, is robust with regards to structural defects such as sharp corners, and exhibits excellent temporal stability. Our findings open up the possibility of realizing topological phonons and mechanics in two-dimensional nanomaterials.