State Key Laboratory of Optoelectronic Materials and Technologies &School of Physics, Sun Yat-Sen University, Guangzhou 510275, China.
NSF Nanoscale Science and Engineering Center (NSEC), University of California, Berkeley, California 94720, USA.
Nat Mater. 2017 Mar;16(3):298-302. doi: 10.1038/nmat4807. Epub 2016 Nov 28.
Photonic crystals offer unprecedented opportunity for light manipulation and applications in optical communication and sensing. Exploration of topology in photonic crystals and metamaterials with non-zero gauge field has inspired a number of intriguing optical phenomena such as one-way transport and Weyl points. Recently, a new degree of freedom, valley, has been demonstrated in two-dimensional materials. Here, we propose a concept of valley photonic crystals with electromagnetic duality symmetry but broken inversion symmetry. We observe photonic valley Hall effect originating from valley-dependent spin-split bulk bands, even in topologically trivial photonic crystals. Valley-spin locking behaviour results in selective net spin flow inside bulk valley photonic crystals. We also show the independent control of valley and topology in a single system that has been long pursued in electronic systems, resulting in topologically-protected flat edge states. Valley photonic crystals not only offer a route towards the observation of non-trivial states, but also open the way for device applications in integrated photonics and information processing using spin-dependent transportation.
光子晶体为光的操控以及在光通信和传感领域的应用提供了前所未有的机会。在具有非零规范场的光子晶体和超材料中探索拓扑结构激发了许多有趣的光学现象，例如单向传输和外尔点。最近，在二维材料中出现了一个新的自由度，即谷。在这里，我们提出了具有电磁对偶对称性但没有反转对称性的谷光子晶体的概念。我们观察到了源自谷依赖的自旋劈裂体带的光子谷霍尔效应，即使在拓扑平凡的光子晶体中也是如此。谷-自旋锁定行为导致在体谷光子晶体内部产生选择性的净自旋流。我们还展示了在单个系统中对谷和拓扑的独立控制，这在电子系统中一直是长期追求的目标，从而产生了拓扑保护的平坦边缘态。谷光子晶体不仅为观察非平凡态提供了途径，而且为使用自旋相关输运的集成光子学和信息处理中的器件应用开辟了道路。
