The recent discovery of natural biaxial hyperbolicity in van der Waals crystals, such as α-MoO3, has opened up new avenues for mid-IR nanophotonics due to their deep subwavelength phonon polaritons. However, a significant challenge is the lack of active tunability of these hyperbolic phonon polaritons. In this work, we investigate heterostructures of graphene and α-MoO3 for actively tunable hybrid plasmon phonon polariton modes via electrostatic gating in the mid-infrared spectral region. We observe a unique propagation direction dependent hybridization of graphene plasmon polaritons with hyperbolic phonon polaritons for experimentally feasible values of graphene chemical potential. We further report an application to tunable valley quantum interference in this system with a broad operational bandwidth due to the formation of these hybrid modes. This work presents a lithography-free alternative for actively tunable, anisotropic spontaneous emission enhancement using a sub-wavelength thick naturally biaxial hyperbolic material.

中文翻译：

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天然双轴双曲范德华异质结构中的门可调谐光-物质相互作用

最近发现的范德华晶体中的天然双轴双曲性，如α-MoO3，由于其深亚波长声子极化子，为中红外纳米光子学开辟了新途径。然而，一个重大挑战是这些双曲声子极化子缺乏主动可调性。在这项工作中，我们研究了石墨烯的异质结构和α-MoO3用于通过中红外光谱区域中的静电门控主动可调混合等离子体声子极化子模式。我们观察到石墨烯等离子体激元与双曲声子激元的独特传播方向依赖性杂交，以获得石墨烯化学势的实验可行值。由于这些混合模式的形成，我们进一步报告了该系统中可调谐谷量子干涉的应用，该系统具有较宽的工作带宽。这项工作提出了一种无需光刻的替代方案，用于使用亚波长厚的自然双轴双曲线材料进行主动可调、各向异性自发发射增强。