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arXiv 2405.04879cond-mat.mes-hall
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拓扑边缘能带的非阿贝尔编织

Non-Abelian Braiding of Topological Edge Bands

Yang Long, Zihao Wang, Chen Zhang, Haoran Xue, Yuxin Zhao, Baile Zhang

AI总结:

本研究基于规范富集对称性提出实现多条拓扑边缘能带非阿贝尔编织的方案,构建对应紧束缚模型,并在两种声子晶体中实验观测到3条及4条编织声边缘能带,首次在实际晶体平台实现非阿贝尔编织拓扑。

摘要:

编织是一种几何概念,在从生物学到物理学的诸多科学领域中均有体现,且已被用于对拓扑材料中的体能带拓扑进行分类。拓扑边缘态也可形成编织结构,近期在一类被称为Möbius(莫比乌斯)绝缘体的拓扑绝缘体中得到了证实,这类绝缘体的拓扑边缘态会形成两条带有莫比乌斯扭转的编织能带。尽管莫比乌斯扭转的形成颇具启发性,但它属于简单的阿贝尔编织群$\boldsymbol{\rm B}_2$。拓扑编织最引人入胜的特性依赖于高阶编织群$\boldsymbol{\rm B}_N$($N \boldsymbol{\rm \u2265} 3$)中的非阿贝尔性,这需要多条边缘能带,但迄今为止这一方向尚未被探讨。本文基于规范富集对称性,提出了一种实现多条拓扑边缘能带非阿贝尔编织的方案。我们提出了若干拓扑绝缘体的紧束缚模型,这些模型能够生成形成非阿贝尔编织结构的拓扑边缘态。我们在两种声子晶体中开展了实验验证,这两种晶体分别承载3条和4条编织声边缘能带。观测到的编织结构可对应于投影平移算符复本征值空间中的拓扑缠绕,类似于此前在Hatano-Nelson模型体相中建立的点隙缠绕拓扑。我们的工作还实现了在实际晶体平台上的非阿贝尔编织拓扑,而非基于“虚拟”的合成维度。

英文摘要:

Braiding is a geometric concept that manifests itself in a variety of scientific contexts from biology to physics, and has been employed to classify bulk band topology in topological materials. Topological edge states can also form braiding structures, as demonstrated recently in a type of topological insulators known as Möbius insulators, whose topological edge states form two braided bands exhibiting a Möbius twist. While the formation of Möbius twist is inspiring, it belongs to the simple Abelian braid group $\mathbb{B}_2$. The most fascinating features about topological braids rely on the non-Abelianness in the higher-order braid group $\mathbb{B}_N$ ($N \geq 3$), which necessitates multiple edge bands, but so far it has not been discussed. Here, based on the gauge enriched symmetry, we develop a scheme to realize non-Abelian braiding of multiple topological edge bands. We propose tight-binding models of topological insulators that are able to generate topological edge states forming non-Abelian braiding structures. Experimental demonstrations are conducted in two acoustic crystals, which carry three and four braided acoustic edge bands, respectively. The observed braiding structure can correspond to the topological winding in the complex eigenvalue space of projective translation operator, akin to the previously established point-gap winding topology in the bulk of the Hatano-Nelson model. Our work also constitutes the realization of non-Abelian braiding topology on an actual crystal platform, but not based on the "virtual" synthetic dimensions.

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