Phase-change in topological chiral phononic crystal for directional coupling switch

Recently, acoustic valley Hall topological insulators have become a cutting-edge area of acoustic physics, where the topological phase transition in phononic crystals shows the presence of band inversion through the Dirac point in the momentum space. We developed a 2D hexagonal lattice chiral phononic crystal using reconfigurable construction by extending one side of the original rectangular rods. When the variation of the side length was from left to right, the topological phase transition is triggered by reopening the Dirac degeneracies beyond high-symmetry points in the first Brillouin zone. We numerically showed valley edge state’s propagation through the interface bent toward distinct chiral topological phononic crystals. Moreover, we assembled 2 × 2 cross-waveguides with a defect cavity based on double heterostructure interfaces. The simulated results verify that the phase change is achieved by the directional coupling switching. This research possibly paves the way for exploiting valley edge states to design the complex acoustic waveguide.