Pseudospin-layer coupled edge states in an acoustic topological insulator

The acoustic pseudospin edge states characterized by backscattering immunity and unidirectional transport provide a basis for designing devices with unconventional functions. In this Letter, we report pseudospin-layer coupled acoustic topological edge states realized by two layers of coupled honeycomb sonic crystals. With the additional layer degree of freedom, we define two distinctly different topological invariants that collectively determine the direction of the acoustic vortex and the layer polarization. We achieve an interesting phase diagram and explore the edge states between different phases. Additionally, we extend the topological edge states to the heterostructure and experimentally verify its capability to focus acoustic waves and convert layer polarization. Our work may provide a feasible platform for the manipulation of acoustic waves and could have promising applications in various areas, such as acoustic signal transmission and splitting.