Simple Coupling Method for Topological Acoustic Metamaterial Measurement

Topological notions were heavily explored in condensed matter physics.

Recent years, acoustic waves have emerged as an excellent platform that exemplify the universality and diversity of topological phases.

Since the properties of topological insulators and their surface states highly depend on the dimension of the material and its symmetries, and can be categorized using the periodic table of topological insulators, it means that some combinations of dimension and symmetries would prevent topological insulation. From the experimental perspective, it is crucial to satisfy certain structures and to display the symmetry, preserving the symmetry is equivalent to preserving the topological properties. Therefore, to preserve symmetry, coupling method has to be carefully chosen. The question then arises: In discrete acoustic resonant models, how to efficiently couple the resonators to form a desired structure and to preserve the symmetry in the mean time, so it complies with the idea of topological meta-material?

Here, we propose an experimentally ingenious implementation to couple the acoustic crystals in topological acoustic system, and demonstrate that our implementation supports topologically protected edge and interface states. The setup is easy to assemble and dissemble as Lego bricks, and is proven to be effective to preserve the topological symmetry.