Tunable Optical Topological Transition of Cherenkov Radiation

Cherenkov radiation is perhaps one of the most famous radiations based on free-electrons. Optical topological transition usually appears in specific metamaterials which possess topological optical properties. In this work, by using the ultrafast photothermal properties of graphene, we indicate the potential of graphene-based hyperbolic metamaterials can be used as a suitable platform for ultrafast tunable Cherenkov radiation sources. On the other hand, the nonlocality of graphene will bring a lower bound of electron velocity for the Cherenkov radiation. It means that the Cherenkov radiation in graphene hyperbolic metamaterials can only be induced by a close range of electron velocity.