Cherenkov radiation generated in hexagonal boron nitride using extremely low-energy electrons

Tuo Qu,Yuechai Lin,Yidong Huang,Kaiyu Cui,Wei Zhang,Fang Liu,Xue Feng

doi:10.1515/nanoph-2020-0090

Abstract

Abstract Cherenkov radiation (CR) is the electromagnetic shockwaves generated by the uniform motion of charged particles at a velocity exceeding the phase velocity of light in a given medium. In the Reststrahlen bands of hexagonal boron nitride (hBN), hyperbolic phonon polaritons (HPPs) are generated owing to the coupling between mid-infrared electromagnetic waves and strong anisotropic lattice vibrations. This study theoretically and numerically investigates the generation of volume CR based on HPPs in hBN with super-large wavevectors. Results reveal that CR can be generated using free electrons with an extremely low kinetic energy of 1 eV—two orders of magnitude lower than that reported in extant studies. The findings of this investigation provide new insights into significantly reducing the electron energy required for CR generation and potentially open new research avenues in the fields of CR and HPP.

Highlights

Cherenkov radiation (CR) refers to the electromagnetic shockwaves generated by charged particles moving with a uniform velocity exceeding the phase velocity of light in a given medium [1, 2]
Since hexagonal boron nitride (hBN) is a naturally occurring hyperbolic material that supports hyperbolic phonon polaritons (HPPs) [30], CR could be excited by free electrons with extremely low energy due to the coupling from evanescent waves surrounding the electron bunch to the propagating HPP waves in hBN
Results obtained in this study reveal that when employing a Cherenkov launching approach in hBN thin films, the wavevectors can be continuously tuned with the largest value of kz/k0 = 500

Summary

Introduction

Cherenkov radiation (CR) refers to the electromagnetic shockwaves generated by charged particles moving with a uniform velocity exceeding the phase velocity of light in a given medium [1, 2]. In 1958, for the discovery and explanation of CR, Pavel A. Tamm were jointly awarded the Nobel Prize in physics [3,4,5]. CR has since been employed in several applications, including particle detection [6], free-electron lasers [7], medical imaging [8], and phototherapy [9]

Results

Discussion

Conclusion