Song Daohong, Leykam Daniel, Su Jing, Liu Xiuying, Tang Liqin, Liu Sheng, Zhao Jianlin, Efremidis Nikolaos K, Xu Jingjun, Chen Zhigang
The MOE Key Laboratory of Weak-Light Nonlinear Photonics, and TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin 300457, China.
Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi 030006, China.
Phys Rev Lett. 2019 Mar 29;122(12):123903. doi: 10.1103/PhysRevLett.122.123903.
We demonstrate valley-dependent vortex generation in photonic graphene. Without breaking inversion symmetry, the excitation of two valleys leads to the formation of an optical vortex upon Bragg reflection to the third equivalent valley, with its chirality determined by the valley degree of freedom. Vortex-antivortex pairs with valley-dependent topological charge flipping are also observed and corroborated by numerical simulations. Furthermore, we develop a three-band effective Hamiltonian model to describe the dynamics of the coupled valleys and find that the commonly used two-band model is not sufficient to explain the observed vortex degeneracy lifting. Such valley-polarized vortex states arise from high-band excitation without a synthetic-field-induced gap opening. Our results from a photonic setting may provide insight for the study of valley contrasting and Berry-phase-mediated topological phenomena in other systems.
我们展示了光子石墨烯中依赖能谷的涡旋产生。在不破坏空间反演对称性的情况下，两个能谷的激发会在布拉格反射到第三个等效能谷时导致光学涡旋的形成，其手性由能谷自由度决定。还观察到了具有依赖能谷的拓扑电荷翻转的涡旋-反涡旋对，并通过数值模拟得到了证实。此外，我们开发了一个三能带有效哈密顿模型来描述耦合能谷的动力学，发现常用的两能带模型不足以解释所观察到的涡旋简并解除。这种能谷极化的涡旋态源于高能带激发，而无需合成场诱导的能隙打开。我们在光子环境下的结果可能为研究其他系统中的能谷对比和贝里相介导的拓扑现象提供见解。
