期刊
NATURE COMMUNICATIONS
卷 11, 期 1, 页码 -出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/s41467-020-15705-y
关键词
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资金
- National Science Foundation [DMR1809915, EFRI-1641069]
- Defense Advanced Research Project Agency
- Mina Rees Dissertation Fellowship at Graduate Center of CUNY
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.
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