Observation of topologically protected helical edge modes in Kagome elastic plates

TL;DR

This paper reports the experimental discovery of topologically protected helical edge modes in elastic Kagome plates, demonstrating one-way wave propagation and robustness against imperfections in elastic media.

Contribution

It presents the first experimental observation of topologically protected elastic edge waves in a Kagome-structured plate, emulating quantum spin Hall effects.

Findings

Observation of helical edge modes in elastic plates.

Protection from backscattering demonstrated.

Potential for robust elastic waveguides established.

Abstract

The investigation of topologically protected waves in classical media has opened unique opportunities to achieve exotic properties like one-way phonon transport, protection from backscattering and immunity to imperfections. Contrary to acoustic and electromagnetic domains, their observation in elastic solids has so far been elusive due to the presence of both shear and longitudinal modes and their modal conversion at interfaces and free surfaces. Here we report the experimental observation of topologically protected helical edge waves in elastic media. The considered structure consists of an elastic plate patterned according to a Kagome architecture with an accidental degeneracy of two Dirac cones induced by drilling through holes. The careful breaking of symmetries couples the corresponding elastic modes which effectively emulates spin orbital coupling in the quantum spin Hall effect. The results shed light on the topological properties of the proposed plate waveguide and opens avenues for the practical realization of compact, passive and cost-effective elastic topological waveguides.