A Monolithic Topologically Protected Phononic Circuit

TL;DR

This paper demonstrates the first elastic analogue of quantum spin Hall effects using a phononic crystal, creating topologically protected, low-loss elastic wave circuits with potential for integrated chip-scale devices.

Contribution

It introduces a monolithic phononic crystal with topological protection, enabling robust elastic waveguiding and devices, a novel application of topological states in elastic media.

Findings

First experimental realization of elastic QSHE analogue

Achieved topologically protected elastic waveguiding with negligible loss

Enabled potential for integrated, robust elastic devices

Abstract

Precise control of elastic waves in modes and coherences is of great use in reinforcing nowadays elastic energy harvesting/storage, nondestructive testing, wave-mater interaction, high sensitivity sensing and information processing, etc. All these implementations are expected to have elastic transmission with lower transmission losses and higher degree of freedom in transmission path. Inspired by topological states of quantum matters, especially quantum spin Hall effects (QSHEs) providing passive solutions of unique disorder-immune surface states protected by underlying nontrivial topological invariants of the bulk, thus solving severe performance trade-offs in experimentally realizable topologically ordered states. Here, we demonstrate experimentally the first elastic analogue of QSHE, by a concise phononic crystal plate with only perforated holes. Strong elastic spin-orbit coupling is realized accompanied by the first topologically-protected phononic circuits with both robustness and negligible propagation loss overcoming many circuit- and system-level performance limits induced by scattering. This elegant approach in a monolithic substrate opens up the possibility of realizing topological materials for phonons in both static and time-dependent regimes, can be immediately applied to multifarious chip-scale devices with both topological protection and massive integration, such as on-chip elastic wave-guiding, elastic splitter, elastic resonator with high quality factor, and even (pseudo-)spin filter.