Valley Topological Phases in Bilayer Sonic Crystals

TL;DR

This paper introduces a bilayer sonic crystal design with tunable topological phases, demonstrating the emergence of valley-projected topological insulators and their edge states, confirmed by theory, simulations, and experiments.

Contribution

It presents a novel bilayer sonic crystal structure enabling tunable topological phases through scatterer rotation, expanding control over acoustic topological insulators.

Findings

Identification of layer-mixed and layer-polarized topological valley Hall phases

Experimental observation of nontrivial edge states propagating along phase interfaces

Numerical confirmation of topological phase diagram and edge state robustness

Abstract

Recently, the topological physics in artificial crystals for classical waves has become an emerging research area. In this Letter, we propose a unique bilayer design of sonic crystals that are constructed by two layers of coupled hexagonal array of triangular scatterers. Assisted by the additional layer degree of freedom, a rich topological phase diagram is achieved by simply rotating scatterers in both layers. Under a unified theoretical framework, two kinds of valley-projected topological acoustic insulators are distinguished analytically, i.e., the layer-mixed and layer-polarized topological valley Hall phases, respectively. The theory is evidently confirmed by our numerical and experimental observations of the nontrivial edge states that propagate along the interfaces separating different topological phases. Various applications such as sound communications in integrated devices, can be anticipated by the intriguing acoustic edge states enriched by the layer information.