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.

1878 年，瑞利勋爵观察到了著名的声波现象，声波在伦敦圣保罗大教堂的弯曲画廊周围蔓延^1,2。这些回音壁波在外壳周围几乎没有衍射的情况下有效地散射，并且已在超声波疲劳和裂纹测试以及使用二氧化硅微尺度环形的纳米颗粒或分子的光学传感中得到应用。最近，密集的研究工作集中在探索具有巧妙匹配的增益和损失的非厄米系统，促进单向不可见性和异常点的奇异特征^3,4. 同样，使用拓扑绝缘体（包括非平凡对称保护相）的物理学激增为重塑高度非常规途径奠定了基础，以实现稳健且无反射的声光引导和转向^5,6. 在这里，我们使用由碳纳米管薄膜装饰的热塑性棒制成的声波晶体构建了一个拓扑廊道绝缘体，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 Hermiticity 纹理，我们能够打破回音壁模式的手征对称性，这使得拓扑“音频激光”模式能够与所需的手性进行外耦合。我们预计这些发现将促进无损检测和声学传感方面的进步。