Dirac points and the transition towards Weyl points in three-dimensional sonic crystals

Abstract

Acoustic metamaterials: Exotic sonic surface states and their transition The realization of exotic surface states in an acoustic metamaterial opens the door to new ways of manipulating sound waves. Some acoustic metamaterials behave like the sonic equivalents of topological insulators, which are insulators in their bulk but conduct electricity on their surfaces. Now, Shuqi Chen at Nankai University in Tianjin and co-workers have shown that the surfaces of a sonic crystal can conduct sound by supporting three-dimensional (3D) Dirac points – four-fold degenerate band crossings that possess topological charge. The researchers used 3D printing to build a sonic crystal from hexagonal unit cells, linked by tube structures that enable hopping between acoustic ‘atoms’. When chiral hopping is introduced, it allowed Dirac points to split into so-called Weyl points, enabling the transition of exotic surface states and interface states.