Monolayers of semiconducting transition metal dichalcogenides (TMDs) have long attracted interest for their intriguing optical and electronic properties. Recently, TMDs in their quasi-bulk form have started to show considerable promise for nanophotonics thanks to their high refractive indices, large optical anisotropy, wide transparency windows reaching to the visible, and robust room temperature excitons promising for nonlinear optics. Adherence of TMD layers to any substrate via van der Waals forces is a further key enabler for the nanofabrication of complex photonic structures requiring heterointegration. Here, we use the attractive properties of TMDs and realize topological spin-Hall photonic lattices made of arrays of triangular nanoholes in 50 to 100 nm thick WS₂ flakes exfoliated on SiO₂/Si substrates. High-quality structures are achieved by taking advantage of anisotropic dry etching dictated by the crystal axes of WS₂. Reflectance measurements at room temperature show a photonic gap opening in the near-infrared in trivial and topological phases. Unidirectional propagation along the domain interface is demonstrated in real space via circularly polarized laser excitation in samples with both zigzag and armchair domain boundaries. Finite-difference time-domain simulations are used to interpret optical spectroscopy results. Our work demonstrates the feasibility of more complex nanophotonic devices based on the layered (van der Waals) materials platform.

中文翻译：

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由多层过渡金属二硫化物制成的 Z2 拓扑光子绝缘体的实现


长期以来，半导体过渡金属二硫化物 （TMD） 的单层因其有趣的光学和电子特性而引起了人们的兴趣。最近，准体状 TMD 开始在纳米光子学中显示出相当大的前景，这要归功于它们的高折射率、大的光学各向异性、达到可见光的宽透明窗口以及有望用于非线性光学的坚固室温激子。通过范德华力将 TMD 层粘附到任何衬底上，是需要异质集成的复杂光子结构纳米制造的另一个关键推动因素。在这里，我们利用 TMD 的迷人特性，实现了拓扑自旋霍尔光子晶格，该晶格由 50 至 100 nm 厚的 WS₂ 薄片中的三角形纳米孔阵列制成，这些纳米孔在 SiO₂/Si 衬底上剥离。通过利用 WS₂ 的晶轴决定的各向异性干法蚀刻，可以实现高质量的结构。室温下的反射率测量显示，在微小和拓扑相位中，近红外存在光子间隙开路。在实际空间中，通过圆偏振激光激发，在具有锯齿形和扶手椅畴边界的样品中证明了沿域界面的单向传播。有限差分时域模拟用于解释光谱结果。我们的工作证明了基于多层 （van der Waals） 材料平台的更复杂的纳米光子器件的可行性。