Three-dimensional higher-order topological acoustic system with multidimensional topological states

TL;DR

This paper reports the experimental realization of a 3D topological acoustic system with multidimensional states, including surface, hinge, and corner modes, promising advanced applications in acoustic devices and signal processing.

Contribution

The work demonstrates a 3D topological acoustic system with experimentally confirmed multidimensional topological states, expanding the understanding of topological phases in acoustic materials.

Findings

Confirmed 2D surface propagations on all six surfaces

Observed 1D hinge propagations as robust acoustic fibers

Identified 0D corner modes as localized resonances

Abstract

Topologically protected gapless edge/surface states are phases of quantum matter which behave as massless Dirac fermions, immunizing against disorders and continuous perturbations. Recently, a new class of topological insulators (TIs) with gapped edge states and in-gap corner states have been theoretically predicted in electric systems 1,2, and experimentally realized in two-dimensional (2D) mechanical and electromagnetic systems 3,4, electrical circuits 5, optical and sonic crystals 6-11, and elastic phononic plates 12. Here, we elaborately design a strong three-dimensional (3D) topological acoustic system, by arranging acoustic meta-atoms in a simple cubic lattice. Under the direct field measurements, besides of the 2D surface propagations on all of the six surfaces, the 1D hinge propagations behaving as robust acoustic fibers along the twelve hinges and the 0D corner modes working as robust localized resonances at the eight corners are experimentally confirmed. As these multidimensional topological states are activated in different frequencies and independent spaces, our works pave feasible ways for applications in the topological acoustic cavities, communications and signal-processing.