Acoustic topological insulator and robust one-way sound transport

Topological design of materials enables topological symmetries and facilitates unique backscattering-immune wave transport(1-26). In airborne acoustics, however, the intrinsic longitudinal nature of sound polarization makes the use of the conventional spin-orbital interaction mechanism impossible for achieving band inversion. The topological gauge flux is then typically introduced with a moving background in theoretical models(19-22). Its practical implementation is a serious challenge, though, due to inherent dynamic instabilities and noise. Here we realize the inversion of acoustic energy bands at a double Dirac cone(15,27,28) and provide an experimental demonstration of an acoustic topological insulator. By manipulating the hopping interaction of neighbouring 'atoms' in this new topological material, we successfully demonstrate the acoustic quantum spin Hall effect, characterized by robust pseudospin-dependent one-way edge sound transport. Our results are promising for the exploration of new routes for experimentally studying topological phenomena and related applications, for example, sound-noise reduction.