Acoustic spin Hall-like effect in hyperbolic metamaterials controlled by the helical wave

Because of the spin-less nature of sound, acoustic helical wave with different helical directions can be taken as a “spin-like” degree of freedom. In this Letter, we examine the pseudospin-orbit coupling effect in acoustics when an acoustic helical wave emitter interacts with the acoustic hyperbolic metamaterial (AHMM). The acoustic helical wave emitter is situated at the boundary of the AHMM, which gives rise to the unidirectional excitation with the trajectory controlled by the helical directions, and hence the acoustic spin Hall-like effect (ASHE) is observed. The ASHE is further demonstrated for the string-type and the membrane-type AHMM based on the hyperbolic dispersion. The reported ASHE paves a new way to exploiting signal routing and unidirectional excitation controlled by the helical directions of the acoustic helical wave.