We demonstrate that unidirectional and backscattering immune propagation of terahertz optical waves can be achieved in a topological valley-Hall waveguide made of graphene nanohole plasmonic crystals. In order to gain deeper physical insights into these phenomena, the band diagram of graphene nanohole plamsonic crystals has been investigated and optimized. We found that a graphene plasmonic crystal with nanohole arrays belonging to the $C_{6v}$ symmetry group possesses gapless Dirac cones, which can be gapped out by introducing extra nanoholes such that the symmetry point group of the system is reduced from $C_{6v}$ to $C_{3v}$. Taking advantage of this feature, we design a mirror symmetric domain-wall interface by placing together two optimized graphene plasmonic crystals so as to construct valley-polarized topological interface modes inside the opened bandgap. Our computational analysis shows that the valley-Hall topological domain-wall interface modes can be achieved at an extremely deep subwavelength scale, and do not rely on the application of external static magnetic fields. This work may pave a new way to develop highly-integrated and robust terahertz plasmonic waveguides at deep-subwavelength scale.

中文翻译：

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石墨烯纳米孔等离子体晶体波导中的 Valley-Hall 拓扑等离子体

我们证明了在由石墨烯纳米孔等离子体晶体制成的拓扑谷霍尔波导中可以实现太赫兹光波的单向和反向散射免疫传播。为了更深入地了解这些现象，对石墨烯纳米孔等离子晶体的能带图进行了研究和优化。我们发现具有纳米孔阵列的石墨烯等离子体晶体属于$C_{6v}$ 对称群具有无间隙的狄拉克锥体，可以通过引入额外的纳米孔使系统的对称点群从 $C_{6v}$ 至 $C_{3v}$. 利用这一特点，我们通过将两个优化的石墨烯等离子体晶体放置在一起来设计镜像对称畴壁界面，以便在开放带隙内构建谷极化拓扑界面模式。我们的计算分析表明，谷-霍尔拓扑畴壁界面模式可以在极深的亚波长尺度上实现，并且不依赖于外部静磁场的应用。这项工作可能为在深亚波长范围内开发高度集成和鲁棒的太赫兹等离子体波导铺平了道路。