Wei Qiang, Zhang Xuewei, Deng Weiyin, Lu Jiuyang, Huang Xueqin, Yan Mou, Chen Gang, Liu Zhengyou, Jia Suotang
State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan, China.
Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, China.
Nat Mater. 2021 Jun;20(6):812-817. doi: 10.1038/s41563-021-00933-4. Epub 2021 Feb 15.
The notion of higher-order topological insulators has endowed materials with topological states beyond the first order. Particularly, a three-dimensional (3D) higher-order topological insulator can host topologically protected 1D hinge states, referred to as the second-order topological insulator, or 0D corner states, referred to as the third-order topological insulator. Similarly, a 3D higher-order topological semimetal can be envisaged if it hosts states on the 1D hinges. Here we report the realization of a second-order topological Weyl semimetal in a 3D-printed acoustic crystal, which possesses Weyl points in 3D momentum space, 2D Fermi arc states on surfaces and 1D gapless states on hinges. Like the arc surface states, the hinge states also connect the projections of the Weyl points. Our experimental results evidence the existence of the higher-order topological semimetal, which may pave the way towards innovative acoustic devices.
高阶拓扑绝缘体的概念赋予了材料超越一阶的拓扑态。特别地，三维（3D）高阶拓扑绝缘体可以拥有拓扑保护的一维棱态，称为二阶拓扑绝缘体，或者零维角态，称为三阶拓扑绝缘体。类似地，如果三维高阶拓扑半金属在一维棱上存在态，那么它也是可以设想的。在此，我们报道了在一种3D打印声学晶体中实现了二阶拓扑外尔半金属，该晶体在三维动量空间中拥有外尔点，在表面上有二维费米弧态，在棱上有一维无隙态。与弧面态一样，棱态也连接外尔点的投影。我们的实验结果证明了高阶拓扑半金属的存在，这可能为创新声学器件铺平道路。
