Realization of an acoustic third-order topological insulator

Abstract

The recent discovery of higher-order topological insulators (TIs) has opened new possibilities in the search for novel topological materials and metamaterials. Second-order TIs have been implemented in two-dimensional (2D) systems exhibiting topological 'corner states', as well as three-dimensional (3D) systems having one-dimensional (1D) topological 'hinge states'. Third-order TIs, which have topological states three dimensions lower than the bulk (which must thus be 3D or higher), have not yet been reported. Here, we describe the realization of a third-order TI in an anisotropic diamond-lattice acoustic metamaterial. The bulk acoustic bandstructure has nontrivial topology characterized by quantized Wannier centers. By direct acoustic measurement, we observe corner states at two corners of a rhombohedron-like structure, as predicted by the quantized Wannier centers. This work extends topological corner states from 2D to 3D, and may find applications in novel acoustic devices.

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• Third-order topological insulator in three-dimensional lattice of magnetic vortices
• Floquet higher-order topological phases in momentum space
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• Nonlinear topological phase diagram in dimerized sine-Gordon model
• Higher-order topological corner states induced solely by onsite potentials with mirror symmetry
• Microwave hinge states in a simple-cubic-lattice photonic crystal insulator
• Hierarchical Topological States in Thermal Diffusive Networks
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• Fragile topological phase on the triangular kagome lattice and its bulk-boundary correspondence
• Family of third-order topological insulators from Su-Schrieffer-Heeger stacking
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