Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China.
Institute for Advanced Studies, Wuhan University, Wuhan 430072, China.
Phys Rev Lett. 2023 Mar 17;130(11):116103. doi: 10.1103/PhysRevLett.130.116103.
Higher-order topological phases have raised widespread interest in recent years with the occurrence of the topological boundary states of dimension two or more less than that of the system bulk. The higher-order topological states have been verified in gapped phases, in a wide variety of systems, such as photonic and acoustic systems, and recently also observed in gapless semimetal phase, such as Weyl and Dirac phases, in systems alike. The higher-order topology is signaled by the hinge states emerging in the common band gaps of the bulk states and the surface states. In this Letter, we report our first prediction and observation of a new type of hinge states, the bound hinge states in the continuum (BHICs) bulk band, in a higher-order Weyl semimetal implemented in phononic crystal. In contrast to the hinge state in gap, which is characterized by the bulk polarization, the BHIC is identified by the nontrivial surface polarization. The finding of the topological BHICs broadens our insight to the topological states, and may stimulate similar researches in other systems such as electronic, photonic, and cold atoms systems. Our Letter may pave the way toward high-Q acoustic devices in application.
近年来，高阶拓扑相引起了广泛的关注，其特征是系统体相维度小于二维或更低的拓扑边界态。高阶拓扑相已经在各种系统中得到了验证，如光子和声子系统，最近也在无能隙半金属相中观察到，如 Weyl 和 Dirac 相，在类似的系统中。高阶拓扑通过在体相和表面相公共带隙中出现的铰链态来指示。在这封信件中，我们报告了在高阶 Weyl 半金属声子晶体中首次预测和观察到的一种新型铰链态，即连续体中的束缚铰链态（BHIC）。与具有体极化的能隙中的铰链态不同，BHIC 由非平凡的表面极化来确定。拓扑 BHIC 的发现拓宽了我们对拓扑态的认识，并可能激发其他系统（如电子、光子和冷原子系统）的类似研究。我们的信件为应用中的高 Q 值声波器件铺平了道路。
