Demonstration of a quantized acoustic octupole topological insulator
Demonstration of a quantized acoustic octupole topological insulator
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DOI：
10.1038/s41467-020-15705-y
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发表时间：
2020-04-30
影响因子：
16.6
通讯作者：
Khanikaev, Alexander B.
中科院分区：
文献类型：
--
作者：
Ni, Xiang;Li, Mengyao;Khanikaev, Alexander B.
最近推出的量子化多极拓扑绝缘体（QMTIs）揭示了新类型的带隙边界状态，它们本身代表低维拓扑相位和主机对称性保护的零维角态。受这些预言的启发，人们在量子化四极拓扑相位的实验观测上投入了巨大的努力。然而，由于反交换反射对称性的严格要求，在三维结构中实现更高阶的量化多极矩，例如八极矩，是具有挑战性的。在这里，我们克服了这一挑战，并通过实验实现了声学模拟的量化八极拓扑绝缘体使用负耦合谐振器。我们确认，我们的设计具有量化的八极拓扑相位的第一性原理研究，并通过实验证明了边界模式的层次结构的光谱证据，观察3（第）阶拓扑角状态。此外，我们揭示了从高阶到低阶多极矩的拓扑相变。我们的工作提供了一个途径，探索在3D经典平台的高阶拓扑状态。虽然多极拓扑绝缘体已经在理论上描述和实验上观察到的二维，三阶拓扑绝缘体在三维尚未观察到。在这里，作者实现了第一次在声学超材料的量化八极三维拓扑状态。
Recently introduced quantized multipole topological insulators (QMTIs) reveal new types of gapped boundary states, which themselves represent lower-dimensional topological phases and host symmetry protected zero-dimensional corner states. Inspired by these predictions, tremendous efforts have been devoted to the experimental observation of quantized quadrupole topological phase. However, due to stringent requirements of anti-commuting reflection symmetries, it is challenging to achieve higher-order quantized multipole moments, such as octupole moments, in a three-dimensional structure. Here, we overcome this challenge, and experimentally realize the acoustic analogue of a quantized octupole topological insulator using negatively coupled resonators. We confirm by first-principle studies that our design possesses a quantized octupole topological phase, and experimentally demonstrate spectroscopic evidence of a hierarchy of boundary modes, observing 3(rd) order topological corner states. Furthermore, we reveal topological phase transitions from higher- to lower-order multipole moments. Our work offers a pathway to explore higher-order topological states in 3D classical platforms. Although multipole topological insulators have been theoretically described and experimentally observed in 2D, third-order topological insulators in 3D have not been observed yet. Here, the authors realize for the first time a quantized octupole 3D topological state in an acoustic metamaterial.