Three-dimensional topological disclination in acoustic crystals

TL;DR

This paper presents the first experimental realization of a three-dimensional topological disclination in acoustic crystals, demonstrating fractional charge and localized topological states, thus expanding the understanding of topological defects in 3D systems.

Contribution

It introduces a novel 3D topological disclination in acoustic crystals, combining theoretical design and experimental validation, and reveals new topological phenomena in three dimensions.

Findings

Observation of 0D topological disclination states at the defect core

Confirmation of fractional (1/2) charge in 3D disclinations

Agreement between experimental results, tight-binding model, and simulations

Abstract

Topological disclinations, crystallographic defects that break rotation lattice symmetry, have attracted great interest and exhibited wide applications in cavities, waveguides, and lasers. However, topological disclinations have thus far been predominantly restricted to two-dimensional (2D) systems owing to the substantial challenges in constructing such defects in three-dimensional (3D) systems and characterizing their topological features. Here we report the theoretical proposal and experimental demonstration of a 3D topological disclination that exhibits fractional (1/2) charge and zero-dimensional (0D) topological bound states, realized by cutting-and-gluing a 3D acoustic topological crystalline insulator. Using acoustic pump-probe measurements, we directly observe 0D topological disclination states at the disclination core, consistent with the tight-binding model and full-wave simulation results. Our results extend the research frontier of topological disclinations and open a new paradigm for exploring the interplay between momentum-space band topology and the real-space defect topology in 3D and higher dimensions.