Valleylike Edge States in Chiral Phononic Crystals with Dirac Degeneracies beyond High-Symmetry Points and Boundaries of Brillouin Zones

Recently, the field of topological acoustics has rapidly developed, where the topological phase transition in phononic crystals is unveiled to occur through band inversion via the Dirac degeneracy in momentum space. Here, we focus on a class of low-symmetry acoustic valleylike topological insulators (VTIs), with honeycomb-lattice scatterers being chiral with ${C}_{1}$ symmetry. The valley Hall transition can be generated by simply rotating the chiral scatterers, where the topological phase transition is triggered by reopening the Dirac degeneracies beyond high-symmetry points and boundaries in the Brillouin zones. We numerically and experimentally demonstrate robust transport against different defects in chiral VTIs. For applications, we construct a topological beam splitter to verify the valley-selective one-way transport in chiral VTIs. Based on valleylike edge states, we design a topological acoustic switch with one input and two outputs, where the switching functionality at outputs with the on-off, off-off, and off-on states is confirmed by simulations and experimental tests. We also provide a more complex four-port acoustic switch based on chiral VTIs. The chiral VTI-based splitter and switches may have potential applications in constructing intelligent acoustic devices.