Enhanced Cherenkov radiation in twisted hyperbolic Van der Waals crystals

Abstract

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 swift electrons 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 still remains a challenging task. To this end, we explored the interaction between swift electrons and twisted hyperbolic Van der Waals crystals and observed 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 for highly directional free-electron radiation and radiation shaping.

Keywords

free electron radiation / metamaterials / nanophotonics / Van der Waals crystals

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Funding

Distinguished Professor Fund of Jiangsu Province(1004-YQR23064); Distinguished Professor Fund of Jiangsu Province(1004-YQR24010); Selected Chinese Government Talent-Recruitment Programs of Nanjing(1004-YQR23122); Startup Grant of Nanjing University of Aeronautics and Astronautics(1004-YQR23031); National Natural Science Fund for Excellent Young Scientists Fund Program of China; National Natural Science Foundation of China(62175212); Zhejiang Provincial Natural Science Fund Key Project(LZ23F050003); Fundamental Research Funds for the Central Universities(226-2024-00022); Fundamental Research Funds for the Central Universities(NS2024022)