Pseudospin-dependent topological refraction in acoustic topological heterostructure

The topological refractions created by valley sonic crystals have attracted great attention owing to their reflection-free characteristic. However, the refraction angles of valley-locked topological refractions are dependent on the placement of valley SCs. To address this limitation, we experimentally demonstrate an acoustic topological heterostructure composed of three SCs with the same regular triangular rods, which enables the pseudospin-dependent topological refraction. By rotating triangular rods in SCs, we achieve an acoustic topological phase transition to obtain topological trivial and nontrivial SCs. The designed heterostructure is constructed by two SCs with distinct topological phases and a third SC with a double Dirac cone. This configuration significantly reduces the gap size inside the zigzag edge states, thereby broadening the operational frequency range. The measured transmittance spectra indicate that the pseudospin-dependent edge states are robust against various defects. Moreover, the measurement of the outcoupling of the edge states into the ambient space at a zigzag termination confirms the pseudospin-dependent topological refraction phenomenon. Furthermore, we validate that the pseudospin-dependent topological refraction is independent of the placement between the topological trivial and nontrivial SCs. Our work provides a scalable framework for designing robust directional sound transmission and communication devices.