Topological Node-Lines in Mechanical Metacrystals

TL;DR

This paper demonstrates three-dimensional mechanical metacrystals with topological node-lines that support robust, subwavelength elastic wave surface states, advancing the design of topological mechanical metamaterials.

Contribution

It introduces an elastic-wave analogue of topological node-lines in 3D mechanical metacrystals and uncovers design principles linking material symmetry and topological properties.

Findings

Identification of topological node-lines in 3D mechanical metacrystals

Robust subwavelength elastic surface states observed

Design principles connecting symmetry and topological features

Abstract

Topological acoustic and elastic waves have recently emerged as an exciting interdisciplinary field which is still mainly focused on low-dimensional structures and model systems. Here we demonstrate numerically an elastic-wave analogue of topological node-lines in three-dimensional mechanical metacrystals with ribbon- or drumhead-like surface states. These two-dimensional topological surface states offer unprecedented, robust subwavelength confinement of elastic waves. Design principles for topological mechanical metamaterials, from both material and symmetry aspects, are unveiled and connected to fundamental conservation laws and nonsymmorphic space group. Our study paves the way toward the synergy between three-dimensional mechanical metamaterials and topological wave dynamics.