Bilayer

Quantum mechanics

Phase (matter)

Biology

Materials science

Layer (electronics)

Telecommunications

Computer science

Hexagonal crystal system

Genetics

Physics

Nanotechnology

Membrane

Mathematics

Topological insulator

Enhanced Data Rates for GSM Evolution

Condensed matter physics

Phase diagram

Combinatorics

Crystallography

Chemistry

Topology (electrical circuits)

Physical Review Letters

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.

Valley Topological Phases in Bilayer Sonic Crystals