Wang Hanyu, Xu Wei, Zhu Zhihong, Yang Biao
College of Advanced Interdisciplinary Studies, National University of Defense Technology, Changsha 410073, China.
Hunan Provincial Key Laboratory of Novel Nano-Optoelectronic Information Materials and Devices, National University of Defense Technology, Changsha 410073, China.
Nanomaterials (Basel). 2024 Apr 1;14(7):620. doi: 10.3390/nano14070620.
Topological Weyl semimetals are characterized by open Fermi arcs on their terminal surfaces, these materials not only changed accepted concepts of the Fermi loop but also enabled many exotic phenomena, such as one-way propagation. The key prerequisite is that the two terminal surfaces have to be well separated, i.e., the Fermi arcs are not allowed to couple with each other. Thus, their interaction was overlooked before. Here, we consider coupled Fermi arcs and propose a Weyl planar waveguide, wherein we found a saddle-chips-like hybridized guiding mode. The hybridized modes consist of three components: surface waves from the top and bottom surfaces and bulk modes inside the Weyl semimetal. The contribution of these three components to the hybridized mode appears to be z-position-dependent rather than uniform. Beyond the conventional waveguide framework, those non-trivial surface states, with their arc-type band structures, exhibit strong selectivity in propagation direction, providing an excellent platform for waveguides. Compared with the conventional waveguide, the propagation direction of hybridized modes exhibits high z-position-dependency. For example, when the probe plane shifts from the top interface to the bottom interface, the component propagating horizontally becomes dimmer, while the component propagating vertically becomes brighter. Experimentally, we drilled periodic holes in metal plates to sandwich an ideal Weyl meta-crystal and characterize the topological guiding mode. Our study shows the intriguing behaviors of topological photonic waveguides, which could lead to beam manipulation, position sensing, and even 3D information processing on photonic chip. The Weyl waveguide also provides a platform for studying the coupling and the interaction between surface and bulk states.
拓扑外尔半金属的特征是其端面上存在开放的费米弧，这些材料不仅改变了人们对费米环的传统概念，还催生了许多奇异现象，比如单向传播。关键前提是两个端面必须充分分离，即费米弧彼此不允许耦合。因此，此前它们的相互作用被忽视了。在此，我们考虑耦合的费米弧并提出一种外尔平面波导，在其中我们发现了一种类似鞍形芯片的杂化导模。杂化模由三个分量组成：来自顶面和底面的表面波以及外尔半金属内部的体模。这三个分量对杂化模的贡献似乎与z位置有关，而非均匀分布。超越传统波导框架，那些具有弧型能带结构的非平凡表面态在传播方向上表现出很强的选择性，为波导提供了一个绝佳平台。与传统波导相比，杂化模的传播方向表现出高度的z位置依赖性。例如，当探测平面从顶部界面移动到底部界面时，水平传播的分量会变暗，而垂直传播的分量会变亮。在实验中，我们在金属板上钻出周期性孔洞，以夹入理想的外尔超晶体并表征拓扑导模。我们的研究展示了拓扑光子波导的有趣行为，这可能会导致光束操控、位置传感，甚至在光子芯片上进行三维信息处理。外尔波导还为研究表面态与体态之间的耦合和相互作用提供了一个平台。
