Phan Huyen Thanh, Liu Feng, Wakabayashi Katsunori
Opt Express. 2021 Jun 7;29(12):18277-18290. doi: 10.1364/OE.427222.
We study topological states of honeycomb photonic crystals in the absence of inversion symmetry using plane wave expansion and finite element methods. The breaking of inversion symmetry in honeycomb lattice leads to contrasting topological valley indices, i.e., the valley-dependent Chern numbers in momentum space. We find that the topological corner states appear for 60 degree corners, but absent for other corners, which can be understood as the sign flip of valley Chern number at the corner. Our results provide an experimentally feasible platform for exploring valley-dependent higher-order topology in photonic systems.
我们使用平面波展开法和有限元方法研究了不存在空间反演对称性的蜂窝状光子晶体的拓扑态。蜂窝晶格中空间反演对称性的破缺导致了截然不同的拓扑谷指标，即动量空间中依赖于谷的陈数。我们发现拓扑角态出现在60度角处，而在其他角度不存在，这可以理解为角处谷陈数的符号翻转。我们的结果为探索光子系统中依赖于谷的高阶拓扑提供了一个实验上可行的平台。
