Qiu Huahui, Xiao Meng, Zhang Fan, Qiu Chunyin
Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China.
Department of Physics, University of Texas at Dallas, Richardson, Texas 75080, USA.
Phys Rev Lett. 2021 Oct 1;127(14):146601. doi: 10.1103/PhysRevLett.127.146601.
Discovering new topological phases of matter is a major theme in fundamental physics and materials science. Dirac semimetal provides an exceptional platform for exploring topological phase transitions under symmetry breaking. Recent theoretical studies have revealed that a three-dimensional Dirac semimetal can harbor fascinating hinge states, a higher-order topological manifestation not known before. However, its realization in experiment is yet to be achieved. In this Letter, we propose a minimum model to construct a spinless higher-order Dirac semimetal protected by C_{6v} symmetry. By breaking different symmetries, this parent phase transitions into a variety of novel topological phases including higher-order topological insulator, higher-order Weyl semimetal, and higher-order nodal-ring semimetal. Furthermore, for the first time, we experimentally realize this unprecedented higher-order topological phase in a sonic crystal and present an unambiguous observation of the desired hinge states via momentum-space spectroscopy and real-space visualization. Our findings may offer new opportunities to manipulate classical waves such as sound and light.
发现物质的新拓扑相是基础物理学和材料科学的一个主要主题。狄拉克半金属为探索对称性破缺下的拓扑相变提供了一个特殊的平台。最近的理论研究表明，三维狄拉克半金属可以存在迷人的棱边态，这是一种前所未知的高阶拓扑表现形式。然而，其实验实现尚未达成。在本信函中，我们提出一个最小模型来构建由C₆ᵥ对称性保护的无自旋高阶狄拉克半金属。通过打破不同的对称性，这个母体相转变为各种新颖的拓扑相，包括高阶拓扑绝缘体、高阶外尔半金属和高阶节线环半金属。此外，我们首次在声子晶体中通过实验实现了这种前所未有的高阶拓扑相，并通过动量空间光谱学和实空间可视化对所需的棱边态进行了明确的观测。我们的发现可能为操控诸如声音和光等经典波提供新的机会。
