Non-Hermitian topological whispering gallery
Non-Hermitian topological whispering gallery
复制标题
非厄米拓扑回音壁
DOI：
10.1038/s41586-021-03833-4
复制
发表时间：
2021-09-30
期刊：
影响因子：
64.8
通讯作者：
Christensen, Johan
中科院分区：
文献类型：
--
作者：
Hu, Bolun;Zhang, Zhiwang;Christensen, Johan
1878 年，雷利勋爵观察到了备受赞誉的声波现象，这种现象在伦敦圣保罗大教堂的弧形画廊周围蔓延(1,2)。这些回音壁波在外壳周围有效地散射，几乎没有衍射，并且已在超声波疲劳和裂纹测试以及使用二氧化硅微米级环形线圈的纳米颗粒或分子的光学传感中得到应用。最近，大量的研究工作集中在探索具有巧妙匹配增益和损耗的非厄米系统，促进单向不可见性和异常点的奇异特征(3,4)。同样，使用由非平凡的对称保护相组成的拓扑绝缘体的物理学浪潮为重塑高度非常规的途径奠定了基础，以实现声音和光的稳健且无反射的引导和转向(5,6)。在这里，我们使用由热塑性棒制成的声波晶体构造了一个拓扑画廊绝缘体，该声波晶体装饰有碳纳米管薄膜，通过电热声耦合充当声波增益介质。通过为激活的棒设计特定的非厄米性纹理，我们能够打破回音壁模式的手性对称性，从而实现拓扑“音频激光”模式与所需旋向性的外耦合。我们预计这些发现将刺激无损测试和声学传感方面的进步。声学拓扑画廊绝缘体由声波晶体构成，该声波晶体由装饰有碳纳米管薄膜的热塑性棒制成，能够在可听频率下耦合放大和聚焦的声音。
In 1878, Lord Rayleigh observed the highly celebrated phenomenon of sound waves that creep around the curved gallery of St Paul's Cathedral in London(1,2). These whispering-gallery waves scatter efficiently with little diffraction around an enclosure and have since found applications in ultrasonic fatigue and crack testing, and in the optical sensing of nanoparticles or molecules using silica microscale toroids. Recently, intense research efforts have focused on exploring non-Hermitian systems with cleverly matched gain and loss, facilitating unidirectional invisibility and exotic characteristics of exceptional points(3,4). Likewise, the surge in physics using topological insulators comprising non-trivial symmetry-protected phases has laid the groundwork in reshaping highly unconventional avenues for robust and reflection-free guiding and steering of both sound and light(5,6). Here we construct a topological gallery insulator using sonic crystals made of thermoplastic rods that are decorated with carbon nanotube films, which act as a sonic gain medium by virtue of electro-thermoacoustic coupling. By engineering specific non-Hermiticity textures to the activated rods, we are able to break the chiral symmetry of the whispering-gallery modes, which enables the out-coupling of topological 'audio lasing' modes with the desired handedness. We foresee that these findings will stimulate progress in non-destructive testing and acoustic sensing.An acoustic topological gallery insulator constructed from sonic crystals made of thermoplastic rods decorated with carbon nanotube films enables the out-coupling of amplified and focused sound at audible frequencies.