Key Laboratory of Artificial Micro- and Nano-Structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China.
Phys Rev Lett. 2023 Jan 6;130(1):017201. doi: 10.1103/PhysRevLett.130.017201.
Topological features embedded in ancient braiding and knotting arts endow significant impacts on our daily life and even cutting-edge science. Recently, fast growing efforts are invested to the braiding topology of complex Bloch bands in non-Hermitian systems. This new classification of band topology goes far beyond those established in Hermitian counterparts. Here, we present the first acoustic realization of the topological non-Hermitian Bloch braids, based on a two-band model easily accessible for realizing any desired knot structure. The non-Hermitian bands are synthesized by a simple binary cavity-tube system, where the long-range, complex-valued, and momentum-resolved couplings are accomplished by a well-controlled unidirectional coupler. In addition to directly visualizing various two-band braiding patterns, we unambiguously observe the highly elusive topological phase transitions between them. Not only do our results provide a direct demonstration for the non-Hermitian band topology, but also the experimental techniques open new avenues for designing unconventional acoustic metamaterials.
拓扑特征嵌入在古代编织和打结艺术中，对我们的日常生活甚至前沿科学都产生了重大影响。最近，人们投入了大量的精力来研究非厄米系统中复杂布洛赫带的编织拓扑结构。这种新的能带拓扑分类远远超出了在厄米系统中建立的那些分类。在这里，我们提出了基于一个双带模型的第一个声学实现的拓扑非厄米布洛赫编织，这个模型很容易实现任何所需的结结构。非厄米带是由一个简单的二元腔管系统合成的，其中远程、复数值和动量分辨的耦合是通过一个很好控制的单向耦合器来实现的。除了直接可视化各种双带编织模式外，我们还明确地观察到它们之间高度难以捉摸的拓扑相变。我们的结果不仅为非厄米带拓扑提供了直接的证明，而且实验技术也为设计非常规声超材料开辟了新的途径。
