扭曲双曲范德华晶体中的增强切伦科夫辐射
Enhanced Cherenkov radiation in twisted hyperbolic Van der Waals crystals
AI总结：
研究快电子与扭曲双曲范德华晶体相互作用，在平带共振频率实现宽动量范围增强切伦科夫辐射，为定向自由电子辐射提供新途径。
摘要：
在经历强烈辐射增强的人造结构中，切伦科夫辐射在自由电子量子发射器、宽带光源、微型化粒子探测器等方面具有重要应用前景。然而，快电子与发射光子之间的动量匹配条件通常将辐射增强限制在特定动量上。许多应用迫切需要在宽动量范围内实现高效切伦科夫辐射，但这仍是一项艰巨的任务。为此，我们探索了快电子与扭曲双曲范德华晶体之间的相互作用，并在平带共振频率处观察到增强的切伦科夫辐射。我们表明，在扭曲晶体的光子魔角处，电子动量一旦与平带光子动量匹配，就会产生最大能量损失（对应于表面声子产生），比传统双曲材料高一个数量级。这种显著增强归因于在宽动量范围内平带表面声子极化激元的激发。我们的发现为高度定向的自由电子辐射和辐射整形提供了一条可行途径。
英文摘要：
Cherenkov radiation in artificial structures experiencing strong radiation enhancements promises important applications in free-electron quantum emitters, broadband light sources, miniaturized particle detectors, etc. However, the momentum matching condition between the swift electron and emitted photons generally restricts the radiation enhancement to a particular momentum. Efficient Cherenkov radiation over a wide range of momenta is highly demanded for many applications but has still remained a challenging task. To this end, we explore the interaction between a swift electron and twisted hyperbolic Van der Waals crystals, and observe enhanced Cherenkov radiation at the flatband resonance frequency. We show that, at the photonic magic angle of the twisted crystals, the electron momentum, once matching with that of the flatband photon, gives rise to a maximum energy loss (corresponding to the surface phonon generation), one-order of magnitude higher than that in conventional hyperbolic materials. Such a significant enhancement is attributed to the excitation of flatband surface phonon polaritons over a broad momentum range. Our findings provide a feasible route to highly directional free-electron radiation and radiation shaping.
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