van der Waals (vdW) materials supporting phonon polaritons (PhPs) – light coupled to lattice vibrations – have gathered significant interest because of their intrinsic anisotropy and low losses. In particular, α-MoO3 supports PhPs with in-plane anisotropic propagation, which has been exploited to tune the optical response of twisted bilayers and trilayers. Additionally, various studies have explored the realization of polaritonic crystals (PCs) – lattices with periods comparable to the polariton wavelength. PCs consisting of hole arrays etched in α-MoO3 slabs exhibit Bragg resonances dependent on the angle between the crystallographic axes and the lattice vectors. However, such PC concept, with a fixed orientation and size of its geometrical parameters, constrains practical applications and introduces additional scattering losses due to invasive fabrication processes. Here, we demonstrate a novel PC concept that overcomes these limitations, enabling low-loss optical tuning. It comprises a rotatable pristine α-MoO3 layer located on a periodic hole array fabricated in a metallic layer. Our design prevents degradation of the α-MoO3 optical properties caused by fabrication, preserving its intrinsic low-loss and in-plane anisotropic propagation of PhPs. The resulting PC exhibits rotation of the Bloch modes, which is experimentally visualized by scanning near-field microscopy. In addition, we experimentally determine the polaritons momentum and reconstruct their band structure. These results pave the way for mechanically tunable nano-optical components based on polaritons for potential lasing, sensing, or energy harvesting applications.

中文翻译：

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扭转可调面内各向异性偏振偏振晶体


支持声子极化激元 （PhPs） 的范德华 （vdW） 材料（光耦合到晶格振动）因其固有的各向异性和低损耗而引起了人们的极大兴趣。特别是，α-MoO3 支持具有面内各向异性传播的 PhP，这已被用于调节扭曲双层和三层的光学响应。此外，各种研究已经探索了极化激元晶体 （PC） 的实现，即周期与极化激元波长相当的晶格。由蚀刻在 α-MoO3 板中的孔阵列组成的 PC 表现出布拉格共振，具体取决于晶体轴和晶格矢量之间的角度。然而，这种 PC 概念具有固定的几何参数方向和大小，限制了实际应用，并由于侵入性制造工艺引入了额外的散射损失。在这里，我们展示了一种克服这些限制的新型 PC 概念，实现了低损耗光学调谐。它包括一个可旋转的原始原始 α-MoO3 层，该层位于金属层中制造的周期性空穴阵列上。我们的设计防止了制造引起的 α-MoO3 光学特性的退化，保留了 PhP 的固有低损耗和面内各向异性传播。所得 PC 表现出 Bloch 模式的旋转，通过扫描近场显微镜进行实验可视化。此外，我们通过实验确定了极化激元动量并重建了它们的能带结构。这些结果为基于极化激元的机械可调纳米光学元件铺平了道路，用于潜在的激光、传感或能量收集应用。