Symmetry-controlled edge states in graphene-like topological sonic crystal

Unique topological states emerged in various topological insulators (TI) have been proved with great application value for robust wave regulation. In this work, we demonstrate the parity inversion related to the definition of the primitive cell in one common lattice, and realize a type of symmetry-controlled edge states confined on the zigzag interfaces of the graphene-like sonic topological crystal. By simply sliding the selected 'layer' near the interface, the coupling of the pseudospin states induced by the multiple scattering for the C6v lattice results in the adjustment of the edge states. Based on the physics of the states, we experimentally propose a prototype of acoustic topological filter hosting multiple channels with independent adjustable edge states and realize the selective high transmission. Our work diversifies the prospects for the applications of the gapped edge states in the robust wave regulation, and proposes a frame to design new topological devices.

Various topological phases and their abnormal effects of topological acoustic metamaterials

The last 20 years have witnessed growing impacts of the topological concept on the branches of physics,including materials,electronics,photonics,and acoustics.Topology describes objects with some global invariant property under continuous deformation,which in mathematics could date back to the 17th century and mature in the 20th century.In physics,it successfully underpinned the physics of the Quantum Hall effect in 1984.To date,topology has been extensively applied to describe topological phases in acoustic metamaterials.As artificial structures,acoustic metamaterials could be well theoretically analyzed,on-demand designed,and easily fabricated by modern techniques,such as three-dimensional printing.Some new theoretical topological models were first discovered in acoustic metamaterials analogous to electronic counterparts,associated with novel effects for acoustics closer to applications.In this review,we focused on the concept of topology and its realization in airborne acoustic crystals,solid elastic phononic crystals,and surface acoustic wave systems.We also introduced emerging concepts of non-Hermitian,higher-order,and Floquet topological insulators in acoustics.It has been shown that the topology theory has such a powerful generality that among the disciplines from electron to photon and phonon,from electronic to photonics and acoustics,from acoustic topological theory to acoustic devices,could interact and be analogous to fertilize fantastic new ideas and prototype devices,which might find applications in acoustic engineering and noisevibration control engineering in the near future.