近日，香港科技大学Chan, C. T.团队研究了陀螺磁零指数介质中体积-时空涡旋对应。相关论文发表在2025年5月14日出版的《自然》杂志上。

光子双零折射率介质以同时为零值的介电常数和磁导率为特征，表现出自然界中没有的非凡特性。值得注意的是，通过将本构参数从零标量推广到具有非零矩阵元素但行列式为零的非互易张量，可以大大扩展零指数的概念。 

研究组通过实验实现了这类具有双零折射率特征和非互易特征的旋磁双零折射超材料。作为一种内在属性，这种超材料总是出现在拓扑相变的自旋1/2狄拉克点。他们发现并证明了时空反射涡旋奇点总是锚定在超材料的狄拉克点上，涡旋电荷由相变中的拓扑不变跳跃决定。 

这建立了一种独特的体-时空涡旋对应关系，将受保护的边界效应扩展到时域，并表征拓扑相变点，使其与任何预先存在的体-边界对应关系区别开来。基于这种对应关系，研究组提出并实验证明了一种机制，可以确定地产生具有固定中心频率和动量的光学时空涡旋脉冲，从而显示出超鲁棒性。该发现揭示了零折射率光子学、拓扑光子学和奇异光学之间的联系，这可能使人们能够利用极端参数超材料的固有拓扑来操纵时空拓扑光场。

附：英文原文

Title: Bulk–spatiotemporal vortex correspondence in gyromagnetic zero-index media

Author: Zhang, Ruo-Yang, Cui, Xiaohan, Zeng, Yuan-Song, Chen, Jin, Liu, Wenzhe, Wang, Mudi, Wang, Dongyang, Zhang, Zhao-Qing, Wang, Neng, Wu, Geng-Bo, Chan, C. T.

Issue&Volume: 2025-05-14

Abstract: Photonic double-zero-index media, distinguished by concurrently zero-valued permittivity and permeability, exhibit extraordinary properties not found in nature1,2,3,4,5,6,7,8. Notably, the notion of zero index can be substantially expanded by generalizing the constitutive parameters from null scalars to non-reciprocal tensors with non-zero matrix elements but zero determinants9,10. Here we experimentally realize this class of gyromagnetic double-zero-index metamaterials possessing both double-zero-index features and non-reciprocal hallmarks. As an intrinsic property, this metamaterial always emerges at a spin-1/2 Dirac point of a topological phase transition. We discover and demonstrate that a spatiotemporal reflection vortex singularity is always anchored to the Dirac point of the metamaterial, with the vortex charge being determined by the topological invariant leap across the phase transition. This establishes a unique bulk–spatiotemporal vortex correspondence that extends the protected boundary effects into the time domain and characterizes topological phase-transition points, setting it apart from any pre-existing bulk–boundary correspondence. Based on this correspondence, we propose and experimentally demonstrate a mechanism to deterministically generate optical spatiotemporal vortex pulses11,12 with firmly fixed central frequency and momentum, hence showing ultrarobustness. Our findings uncover connections between zero-refractive-index photonics, topological photonics and singular optics, which might enable the manipulation of space-time topological light fields using the inherent topology of extreme-parameter metamaterials.

DOI: 10.1038/s41586-025-08948-6

Source: https://www.nature.com/articles/s41586-025-08948-6