Acoustic multichannel transports of valley edge states in bilayer sonic crystals

Backscattering immunity of valley edge states for a monolayer sonic crystal provides a basis for designing devices with unconventional functions. Recently, the valley edge state of a bilayer sonic crystal, regarded as a new degree of freedom, gives a powerful platform for manipulating acoustic waves. In this Letter, we realize valley spin insulators in a bilayer sonic crystal and find that the layer-mixed, layer-polarized, and layer-locked edge states exist on both zigzag and armchair interfaces. There are significant differences between the armchair edge states and the zigzag edge states at the interfaces formed by two domains of distinct acoustic layer-valley Hall phases. Based on the projected dispersion relations for a bilayer sonic crystal, we achieve theoretically and experimentally bilayer multichannel transmission with different layers locking. This paper provides a design approach for applications of bilayer acoustic multichannel communication devices.