Elastic Valley Spin Controlled Chiral Coupling in Topological Valley Phononic Crystals

TL;DR

This paper demonstrates how local elastic spin controls chiral coupling and directional routing of valley phonons in topological valley phononic crystals, revealing a new mechanism for topological wave manipulation.

Contribution

It introduces the concept of local elastic valley spin and its role in controlling chiral phonon coupling and directionality in topological phononic crystals.

Findings

Observation of local elastic valley spin and spin-valley locking.

Reversible one-way phonon routing via elastic spin meta-source.

Experimental and theoretical validation of spin-controlled chiral coupling.

Abstract

Distinct from the phononic valley pseudo-spin, the real physical spin of elastic waves adds a novel tool-kit capable of envisaging the valley-spin physics of topological valley phononic crystals from a local viewpoint. Here, we report the observation of local elastic valley spin as well as the hidden elastic spin-valley locking mechanism overlooked before. We demonstrate that the selective one-way routing of valley phonon states along the topological interface can be reversed by imposing the elastic spin meta-source at different interface locations with opposite valley-spin correspondence. We unveil the physical mechanism of selective directionality as the elastic spin controlled chiral coupling of valley phonon states, through both analytical theory and experimental measurement of the opposite local elastic spin density at different interface locations for different transport directions. The elastic spin of valley topological edge phonons can be extended to other topological states and offers new tool to explore topological metamaterials.