Cherenkov polaritonic radiation in a natural hyperbolic material

The existence of the forward and the reverse Cherenkov radiation for phonon polaritons (PhPs) in a natural hyperbolic material is theoretically demonstrated. It is shown that the forward and reverse Cherenkov polaritonic radiation can be simultaneously excited by an electron at a low velocity moving above a hexagonal boron nitride (hBN) layer within its upper and lower bands, respectively. The results show that the wavelength of polaritons radiation can be tuned by changing the thickness of the hBN layer and the radiation angles can be controlled by velocity of the moving electron. The proposed approach avoids the high velocity threshold of charged particle in conventional materials and complex fabrication of artificial metamaterials, opening a possibility of applications for polariton source, infrared spectroscopy and photonic integrated circuits, and offering a platform to investigate the light-matter interactions in nanoscale. (C) 2019 Elsevier Ltd. All rights reserved.