Topological non-reciprocal robust waveguide transport

Devices that surpass the restriction of reciprocity of classical physical waves have brought intriguing possibilities for wave modulation. Non-reciprocal acoustic devices that rely on the viscosity of the medium or nonlinear effect have low efficiency and distortion problems respectively, and poor immunity to defects. The appearance of acoustic topological insulators achieves non-reciprocal transport with high robustness. However, the local nature of topological states means that their appearance depends on a system with a larger dimension. That is, most of the area of a topological device is occupied by useless lattices that do not directly contribute to non-reciprocal transport. The extra cost of topology protection severely limits the application scenarios of topology states, decreases the cost-effectiveness of topology devices, and is not conducive to device miniaturization and integration. In this work, we construct an acoustic three-layer heterojunction by introducing two types of domain walls into a conventional quantum Hall effect acoustic topological insulator, and successfully construct a non-reciprocal scattering network that forms topological modes spanning the interlayer domain. These extended states are still protected by bulk-band topology, making their non-reciprocity robust against disorder. This structure flawlessly realizes the path broadening in a two-dimensional topological system and can accomplish functions such as non-reciprocal acoustic splitting and multichannel transmission. Our work opens up opportunities for developing topological-insulator-based non-reciprocal devices in acoustics.