Realization of an acoustic third-order topological insulator

• Main Authors: Xue, Haoran, Yang, Yahui, Liu, Guigeng, Gao, Fei, Chong, Yidong, Zhang, Baile
• Other Authors: School of Physical and Mathematical Sciences
• Format: Article
• Language: English
• Published: 2019
• Subjects: Topological Materials; Science::Physics; Mechanical and Acoustical Properties
• Online Access: https://hdl.handle.net/10356/106320; http://hdl.handle.net/10220/49638
• Institution: Nanyang Technological University

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 band structure has nontrivial topology characterized by quantized Wannier centers. By direct acoustic measurement, we observe corner states at two corners of a rhombohedronlike 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.