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Surface impedance and generalized chiral symmetry in acoustic higher-order topological insulators
Physical Review B ( IF 3.7 ) Pub Date : 2021-06-22 , DOI: 10.1103/physrevb.103.214112
Zhang-Zhao Yang , An-Yang Guan , Wen-Jie Yang , Xin-Ye Zou , Jian-Chun Cheng

The emergence of higher-order topological states is always considered to be determined by nontrivial topology of the bulk bands, and such the topological invariants strongly depend on specific symmetry of the bulk lattice. However, for real-physical systems, the intrinsic chiral-symmetry breaking can hinder the measurement of these states, and a spectrally isolated topological state always requires compensation to the on-site energy on the boundary sites. In this work, we reveal that in acoustic systems, the compensation is intensively determined by the surface impedance. Based on a regular Su-Schrieffer-Heeger (SSH) topological chain, we derive the analytical solutions of the topological states in acoustic systems and show that generalized chiral symmetry requires acoustic soft-wall boundary condition. Further, we propose a SSH-like chain and show that the surface impedance also crucially impacts the bulk topology. Finally, we extend our results to two-dimensional condition and demonstrate the consistency of the results. Our results provide new insights into the origin of the acoustic topological phenomena, which in turn offers a platform to design topological materials with desired topological properties.

中文翻译:

声学高阶拓扑绝缘体的表面阻抗和广义手征对称性

高阶拓扑状态的出现总是被认为是由体带的非平凡拓扑决定的,这种拓扑不变量强烈依赖于体晶格的特定对称性。然而,对于真实的物理系统,内在的手征对称性破坏会阻碍这些状态的测量,并且光谱隔离的拓扑状态总是需要对边界站点上的现场能量进行补偿。在这项工作中,我们揭示了在声学系统中,补偿主要由表面阻抗决定。基于常规的 Su-Schrieffer-Heeger (SSH) 拓扑链,我们推导出声学系统中拓扑状态的解析解,并表明广义手征对称需要声学软壁边界条件。更多,我们提出了一个类似 SSH 的链,并表明表面阻抗也对体拓扑结构产生了至关重要的影响。最后,我们将结果扩展到二维条件并证明结果的一致性。我们的结果为声学拓扑现象的起源提供了新的见解,这反过来又为设计具有所需拓扑特性的拓扑材料提供了一个平台。
更新日期:2021-06-22
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