Tunable Cherenkov Radiation of Phonon Polaritons in Silver Nanowire/Hexagonal Boron Nitride Heterostructures

Abstract

Polaritons in two-dimensional (2D) materials have shown their unique capabilities to concentrate light into deep subwavelength scales. Precise control of the excitation and propagation of 2D polaritons has remained a central challenge for future on-chip nanophotonic devices and circuits. To solve this issue, we exploit Cherenkov radiation, a classic physical phenomenon that occurs when a charged particle moves at a velocity greater than the phase velocity of light in that medium, in low-dimensional material heterostructures. Here, we report an experimental observation of Cherenkov phonon polariton wakes emitted by superluminal one-dimensional plasmon polaritons in a silver nanowire and hexagonal boron nitride heterostructure using near-field infrared nanoscopy. The observed Cherenkov radiation direction and radiation rate exhibit large tunability through varying the excitation frequency. Such tunable Cherenkov phonon polaritons provide opportunities for novel deep subwavelength-scale manipulation of light and nanoscale control of energy flow in low-dimensional material heterostructures.

Free-Electron Radiation Engineering via Structured Environments

“…These striking properties stimulate the recent research on Cherenkov radiation of phonon polaritons in hBN [46][47][48]. The newly revealed Cherenkov radiation opens up an opportunity to realize the tunable free-electron radiation source in the mid-infrared frequency [Figures 1(e), (f)] [49].…”

Polariton panorama

“…The Cherenkov physics is also relevant to the properties of phonon polaritons [76,77]. Infrared nanoimaging experiments reveal Cherenkov phonon polariton wakes emitted by superluminal one-dimensional plasmon polaritons in a silver nanowire on the surface of hexagonal boron nitride [78]. See also Exciton polariton X-waves on superluminal properties in the system of exciton polaritons.…”

Observation of photoacoustic Smith-Purcell radiation

“…Meanwhile, acoustic SPR is not limited to free space, also applicable for bulk conditions, e.g. exciting phonons within layered materials [38]. For example, it has been proposed to generate THz waves using semiconductor superlattices by considering SPR based phonon-photon interactions [39].…”