Cui Xiaohan, Zhang Ruo-Yang, Zhang Zhao-Qing, Chan C T
Department of Physics, The Hong Kong University of Science and Technology, Hong Kong, China.
Phys Rev Lett. 2022 Jul 22;129(4):043902. doi: 10.1103/PhysRevLett.129.043902.
That disorder can induce nontrivial topology is a surprising discovery in topological physics. As a typical example, Chern topological Anderson insulators (TAIs) have been realized in photonic systems, where the topological phases exist without symmetry protection. In this Letter, by taking transverse magnetic and transverse electric polarizations as pseudospin degrees of freedom, we theoretically propose a scheme to realize disorder-induced symmetry-protected topological phase transitions in two-dimensional photonic crystals with a combined time-reversal, mirror, and duality symmetry T_{f}=TM_{z}D. In particular, we demonstrate that the disorder-induced symmetry-protected topological phase persists even without pseudospin conservation, thereby realizing a photonic Z_{2} TAI, in contrast to a Z-classified quantum spin Hall (QSH) TAI with decoupled spins. By formulating a new scattering approach, we show that the topology of both the QSH and Z_{2} TAIs can be manifested by the accumulated spin rotations of the reflected waves from the photonic crystals. Using a transmission structure, we also illustrate the trivialization of a disordered QSH phase with an even integer topological index caused by spin coupling.
无序能够诱导非平凡拓扑结构，这是拓扑物理学中一个令人惊讶的发现。作为一个典型例子，陈拓扑安德森绝缘体（TAIs）已在光子系统中实现，其中拓扑相在没有对称性保护的情况下存在。在本快报中，通过将横向磁极化和横向电极化作为赝自旋自由度，我们从理论上提出了一种方案，以在具有时间反演、镜像和对偶对称性(T_{f}=TM_{z}D)的二维光子晶体中实现无序诱导的对称性保护拓扑相变。特别地，我们证明即使没有赝自旋守恒，无序诱导的对称性保护拓扑相依然存在，从而实现了一个光子(Z_{2})TAI，这与具有解耦自旋的(Z)类量子自旋霍尔（QSH）TAI形成对比。通过制定一种新的散射方法，我们表明QSH和(Z_{2})TAIs的拓扑结构都可以通过光子晶体反射波的累积自旋旋转来体现。使用一种传输结构，我们还说明了由自旋耦合导致的具有偶数整数拓扑指数的无序QSH相的平凡化。
