Polaritons – hybrid light–mater excitations – are very appealing for the confinement of light at the nanoscale. Recently, a particular interest has been focused on thin anisotropic slabs of van der Waals (vdW) materials supporting polaritons with hyperbolic dispersion, which can exhibit ultrahigh momenta and strongly directional in-plane propagation and thus promise novel nano-optical applications in a planar geometry. However, the excitation and manipulation of in-plane hyperbolic polaritons have not yet been well studied and understood. Here, twisted polaritonic crystals (PCs) are introduced – lattices with periods comparable to the polaritons wavelength rotated with respect to the natural vdW crystal axes – to efficiently excite and control in-plane hyperbolic polaritons. A general analytical theory valid for an arbitrary PC made in a thin biaxial slab is developed and the excitation of Bragg resonances tunable by the twisting angle is demonstrated. The findings open novel avenues for both fundamental studies of PCs in vdW crystals and the development of midinfrared sensing and photodetection applications.

中文翻译：

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薄范德华平板中的扭曲极化子晶体

极化子——混合光物质激发——对于纳米尺度的光限制非常有吸引力。最近，人们特别感兴趣的是支持具有双曲线色散的极化子的范德华 (vdW) 材料的各向异性薄板，这种材料可以表现出超高动量和强定向面内传播，因此有望在平面几何中实现新型纳米光学应用. 然而，平面内双曲极化子的激发和操纵尚未得到很好的研究和理解。在这里，引入了扭曲的极化子晶体 (PC)——其周期与相对于自然 vdW 晶轴旋转的极化子波长相当的晶格——以有效地激发和控制面内双曲极化子。开发了适用于在薄双轴板中制成的任意 PC 的一般分析理论，并证明了可通过扭转角调节的布拉格共振的激发。这些发现为 vdW 晶体中 PC 的基础研究以及中红外传感和光电探测应用的开发开辟了新途径。