Enhancement of Cherenkov radiation from the topology transition

Cherenkov radiation (CR) is generated when a free electron travels through a dielectric medium at a velocity surpassing the speed of light in that medium. This traditional concept has been extended to semi-infinite scenarios by considering surface waves at interfaces, achieving phase matching between the surface wave and the moving electron, thereby exciting 2D CR. In this work, a universal theoretical model is proposed to describe 2D CR emissions. Assuming the material’s permittivity tensor, we calculate the loss probability across different topological dispersions. It is discovered that perfect alignment between structural and electron dispersions results in a radiation intensity peak at the topological transition. To validate this concept, a terahertz hyperbolic metasurface based on spoof surface plasmons is introduced. Its structural dispersion, dependent on structural parameters, can be modulated in two dimensions to induce anisotropy. A topology transition occurs when wave propagation in one direction is obstructed, leading to the formation of a highly directional surface wave. As the free electron moves above our designed metasurface, 2 D CR is excited, with the loss probability peaking at the topological transition frequency. This enhancement is observed to be up to two orders of magnitude greater than that achieved with conventional uniform gratings. Through this study, we aim to unlock the potential of manipulating dispersion topological transitions to enable more efficient electron-matter interactions and stronger electron-induced radiations.