Observation of topological valley transport of sound in sonic crystals

TL;DR

This paper reports the first experimental demonstration of topological valley transport of sound in sonic crystals, showcasing valley-selective edge modes and reflection immunity, which could enable novel acoustic devices.

Contribution

It provides the first experimental evidence of topological valley transport of sound in sonic crystals, demonstrating valley-selective edge modes and reflection immunity.

Findings

Visualization of valley-selective edge modes

Reflection immunity in sharply curved interfaces

Topologically protected sound transport

Abstract

Valley pseudospin, labeling quantum states of energy extrema in momentum space, is attracting tremendous attention1-13 because of its potential in constructing new carrier of information. Compared with the non-topological bulk valley transport realized soon after predictions1-5, the topological valley transport in domain walls6-13 is extremely challenging owing to the inter-valley scattering inevitably induced by atomic scale imperfectness, until the recent electronic signature observed in bilayer graphene12,13. Here we report the first experimental observation of topological valley transport of sound in sonic crystals. The macroscopic nature of sonic crystals permits the flexible and accurate design of domain walls. In addition to a direct visualization of the valley-selective edge modes through spatial scanning of sound field, reflection immunity is observed in sharply curved interfaces. The topologically protected interface transport of sound, strikingly different from that in traditional sound waveguides14,15, may serve as the basis of designing devices with unconventional functions.