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

Abstract

We perform both lattice dynamics analysis and molecular dynamics simulations to demonstrate the existence of topologically protected phonon modes in two-dimensional, monolayer hexagonal boron nitride and silicon carbide sheets. The topological phonon modes are found to be localized at an in-plane interface that divides these systems into two regions of distinct valley Chern numbers. The dispersion of this topological phonon mode crosses over the frequency gap, which is opened through analogy with the quantum valley Hall effect by breaking the inversion symmetry of the primitive unit cells. Consequently, vibrational energy with frequency within this gap is topologically protected, resulting in wave propagation that exhibits minimal backscattering, is robust with regard to structural defects such as sharp corners, and exhibits excellent temporal stability. Our findings open up the possibility of actuating and detecting topological phonons in two-dimensional nanomaterials.