Acoustic Pseudospin Transport in Dual-Layer Topological Insulators with Multiple Topological Phases

Pseudospin-dependent acoustic topological insulators (ATIs) with high-robustness edge states have recently attracted as surge of interest owing to their potential applications, such as one-way sound transport and acoustic communications. Despite the rapid development of pseudospin-dependent ATIs, most existing efforts are limited to monolayer, restricting degree of freedoms to achieve novel physical phenomena and device applications. Here, a series of pseudospin-dependent ATIs composed of dual-layer honeycomb-lattice sonic crystals is experimentally proposed. By introducing the layer degree of freedom, the dual-layer ATIs have four distinct topological phases and can be used to construct six types of domain walls, exhibiting different transport behavior, such as layer-mixed, layer-polarized, and single-layer propagation characteristics. This further enables to experimentally realize interlayer converters for functional sound devices that are otherwise impossible for single-layer ATIs. This work may find various acoustic applications in layer-selective emitters and splitters, multi-path topological sorting, and multifunctional information processing.