Acoustic Plasmons and Cherenkov Radiation Excited by Low-Energy Electrons in Nonlocal Graphene Hyperbolic Metamaterials

Cherenkov radiation (CR) is no doubt that one of the most important kinds of radiation which is generated in different frequencies, by not only electronic but photonic ways. In this work, we use low-energy electrons to excite CR in graphene hyperbolic metamaterials (GMM). In this situation, the velocity of the electrons can be less than the speed of light in the dielectric. In addition, when we consider the effect of the nonlocal properties of the graphene itself, the electron velocity should within a special range. Specifically, the low-limit is just the Fermi velocity of the graphene, and the high-limit is the original low-limit for conventional CR. Our results show the possibility of novel compact free-electron based terahertz radiation source, which are of great value to the research to not only the physics of CR itself, but the further understanding of light-matter interactions in graphene-based devices.