Liu Gui-Geng, Mandal Subhaskar, Xi Xiang, Wang Qiang, Devescovi Chiara, Morales-Pérez Antonio, Wang Ziyao, Yang Linyun, Banerjee Rimi, Long Yang, Meng Yan, Zhou Peiheng, Gao Zhen, Chong Yidong, García-Etxarri Aitzol, Vergniory Maia G, Zhang Baile
Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, Singapore.
Research Center for Industries of the Future, Department of Electronic and Information Engineering, School of Engineering, Westlake University, Hangzhou, China.
Science. 2025 Jan 10;387(6730):162-166. doi: 10.1126/science.adr5234. Epub 2025 Jan 9.
Axions, hypothetical elementary particles that remain undetectable in nature, can arise as quasiparticles in three-dimensional crystals known as axion insulators. Previous implementations of axion insulators have largely been limited to two-dimensional systems, leaving their topological properties in three dimensions unexplored in experiment. Here, we realize an axion insulator in a three-dimensional photonic crystal and probe its topological properties. Demonstrated features include half-quantized Chern numbers on each surface that resembles a fractional Chern insulator, unidirectional chiral hinge states forming topological transport in three dimensions, and arithmetic operations between fractional and integer Chern numbers. Our work experimentally establishes the axion insulator as a three-dimensional topological phase of matter and enables chiral states to form complex, unidirectional three-dimensional networks through braiding.
轴子是自然界中仍无法探测到的假设基本粒子，可作为三维晶体（即轴子绝缘体）中的准粒子出现。此前轴子绝缘体的实现主要局限于二维系统，其三维拓扑性质在实验中尚未得到探索。在此，我们在三维光子晶体中实现了轴子绝缘体并探测其拓扑性质。展示的特性包括每个表面上类似分数陈绝缘体的半量子化陈数、在三维中形成拓扑输运的单向手性棱边态，以及分数陈数和整数陈数之间的算术运算。我们的工作通过实验确立了轴子绝缘体作为一种三维拓扑物相，并使手性态能够通过编织形成复杂的单向三维网络。
