Multi-dimensional wave steering with higher-order topological phononic crystal

TL;DR

This paper demonstrates multi-dimensional wave steering in a 3D phononic crystal by exploiting topological boundary states of different orders, enabling advanced sound manipulation and novel acoustic devices.

Contribution

It introduces a 3D phononic crystal with nontrivial topology supporting boundary states at multiple orders, enabling diverse wave steering functionalities across different dimensions.

Findings

Experimental demonstration of 2D negative refraction of sound.

Implementation of a 3D acoustic interferometer using hinge states.

Topological boundary states enable versatile wave manipulation.

Abstract

The recent discovery and realizations of higher-order topological insulators enrich the fundamental studies on topological phases. Here, we report three-dimensional (3D) wave-steering capabilities enabled by topological boundary states at three different orders in a 3D phononic crystal with nontrivial bulk topology originated from the synergy of mirror symmetry of the unit cell and a non-symmorphic glide symmetry of the lattice. The multitude of topological states brings diverse possibility of wave manipulations. Through judicious engineering of the boundary modes, we experimentally demonstrate two functionalities at different dimensions: 2D negative refraction of sound wave enabled by a first-order topological surface state with negative dispersion, and a 3D acoustic interferometer leveraging on second-order topological hinge states. Our work showcases that topological modes at different orders promise diverse wave steering applications across different dimensions.