Topological materials for full-vector elastic waves

TL;DR

This paper introduces a 3D printed bilayer elastic metamaterial with topologically protected edge states on its boundary, enabling novel control of elastic waves for potential device applications.

Contribution

It demonstrates a new elastic topological metamaterial with boundary-only edge modes and tunable edge transport, advancing elastic wave manipulation technology.

Findings

Realized topological elastic edge states on the boundary of a single phase

Introduced chiral interlayer couplings to induce spin-orbit effects in elastic waves

Demonstrated tunable edge transport in a heterostructure of the metamaterial

Abstract

Elastic wave manipulation is important in a wide variety of scales in applications including information processing in tiny elastic devices and noise control in big solid structures. The recent emergence of topological materials opens a new avenue toward modulating elastic waves in solids. However, because of the full-vector feature, and the complicated couplings of the longitudinal and transverse components of elastic waves, manipulating elastic waves is generally difficult, compared with manipulating acoustic waves (scalar waves) and electromagnetic waves (vectorial waves but transverse only). Up to date, topological materials, including insulators and semimetals, have been realized for acoustic and electromagnetic waves. Although topological materials of elastic waves have also been reported, the topological edge modes observed all lie on the domain wall. A natural question can be asked: whether there exists an elastic metamaterial with the topological edge modes on its own boundary only? Here, we report a 3D metal-printed bilayer metamaterial, insulating topologically the elastic waves. By introducing the chiral interlayer couplings, the spin-orbit couplings for elastic waves are induced, which give rise to nontrivial topological properties. The helical edge states with the vortex feature are demonstrated on the boundary of the single topological phase. We further show a heterostructure of the metamaterial, which exhibits tunable edge transport. Our work may have potential in devices based on elastic waves in solids.