Elastic Weyl Points and Surface Arc States in Three-Dimensional Mechanical Metamaterials*

We investigate a novel Weyl mechanical metamaterial inspired by the discovery of Weyl semimetal. We propose a three-dimensional mechanical structure in analog to the AA-stacked graphene with chiral intralayer coupling, which carries Weyl points of topological charge ±1. We numerically confirm the existence of the elastic Fermi arc and the associated gapless topologically protected surface states. The full-scale numerical simulation on the hollow 3D mechanical structure demonstrates that the surface elastic waves are robust and directional, which can pass a corner or defect without reflections. The findings from our work can contribute to the novel ways of manipulating elastic energy in 3D structures for potential applications in vibration isolation, advanced sensing, and energy harvesting.