Chirality-assisted three-dimensional acoustic Floquet lattices

Abstract

Artificial topological insulators in classical systems are thriving, especially the meta-atom-based three-dimensional (3D) topological lattices. Here we propose a paradigm based on engineering coupling networks in a generalized spatial Floquet lattice, which gives rise to low-loss and broadband 3D topological systems. A mapping between time and space dimensions is utilized to construct the Floquet system with chirality-assisted coupling patterns periodically modulated in spatial dimensions. The cyclotron orbiting motion of sound in the bulk and reversely orbiting motion on the surface are demonstrated, which provides a direct acoustic analogue of the electronic transport in Chern insulators. Weyl points and Fermi arc-like surface states unveil the topological transport of edge states. Splicing together two Floquet lattices with opposite chirality, we realize low-loss topological negative refraction on the surface, where the mirror reflection at the interface is prohibited. Our findings provide diverse ways to construct 3D devices with topological functionalities in acoustics and beyond.