Xue Haoran, Yang Yahui, Liu Guigeng, Gao Fei, Chong Yidong, Zhang Baile
Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, Singapore.
State Key Laboratory of Modern Optical Instrumentation, and College of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027, China.
Phys Rev Lett. 2019 Jun 21;122(24):244301. doi: 10.1103/PhysRevLett.122.244301.
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.
高阶拓扑绝缘体（TIs）的最新发现为寻找新型拓扑材料和超材料开辟了新的可能性。二阶TIs已在表现出拓扑“角态”的二维（2D）系统以及具有一维（1D）拓扑“棱态”的三维（3D）系统中得以实现。三阶TIs具有比其本体低三个维度的拓扑态（因此本体必须是3D或更高维度），目前尚未见报道。在此，我们描述了在一种各向异性金刚石晶格声学超材料中实现三阶TI的情况。体声波带结构具有由量子化万尼尔中心表征的非平凡拓扑。通过直接声学测量，我们观察到了如量子化万尼尔中心所预测的在菱面体状结构的两个角处的角态。这项工作将拓扑角态从2D扩展到了3D，并可能在新型声学器件中找到应用。
