Resonant optical antennas provide unprecedented opportunities to control light on length scales far below the diffraction limit. Recent studies have demonstrated that nanostructures made of multilayer transition metal dichalcogenides (TMDCs) can exhibit well-defined and intense Mie resonances in the visible to the near-infrared spectral range. These resonances are realizable because the TMDC materials exhibit very high in-plane refractive indices, in fact higher than what is found in typical high-index dielectric materials like Si or GaAs. However, their out-of-plane refractive indices are comparatively low. Here we experimentally and theoretically investigate how this unusually large material anisotropy influences the optical response of individual TMDC nanoresonators made of ${\text{MoS}_2}$. We find that anisotropy strongly affects the far-field optical response of the resonators, as well as complex interference effects, such as anapole and resonant Kerker conditions. Moreover, we show that it is possible to utilize the material anisotropy to probe the vectorial nature of the nanoresonator internal near fields. Specifically, we show that Raman spectra originating from individual ${\text{MoS}_2}$ nanoresonators exhibit mode-specific anisotropic enhancement factors that vary with the nanoresonator size and correlate with specific modes supported at resonance. Our study indicates that exploring material anisotropy in novel high-index dielectrics may lead to new nanophotonic effects and applications.

中文翻译：

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高折射率过渡金属二卤化物Mie纳米谐振器中的光学材料各向异性

谐振光学天线提供了前所未有的机会来控制远低于衍射极限的长度尺度的光。最近的研究表明，由多层过渡金属二氢二硫化碳（TMDC）制成的纳米结构可以在可见光到近红外光谱范围内表现出明确的，强烈的Mie共振。这些共振是可以实现的，因为TMDC材料显示出很高的面内折射率，实际上比典型的高折射率介电材料（如Si或GaAs）中的折射率高。但是，它们的面外折射率较低。在这里，我们从实验和理论上研究了这种异常大的材料各向异性如何影响由$ {\ text {MoS} _2} $制成的各个TMDC纳米谐振器的光学响应。我们发现各向异性极大地影响了谐振器的远场光学响应以及复杂的干扰效应，例如偶极子和谐振Kerker条件。此外，我们表明可以利用材料各向异性来探测纳米谐振器内部近场的矢量性质。具体而言，我们显示了源自单个$ {\ text {MoS} _2} $纳米谐振器的拉曼光谱表现出特定于模式的各向异性增强因子，其随纳米谐振器大小的变化而变化，并且与共振支持的特定模式相关。我们的研究表明，探索新型高折射率电介质中的材料各向异性可能会导致新的纳米光子效应和应用。