THz response of nonequilibrium electrons of highly doped graphene on a polar substrate

Abstract

High-frequency response of a system with drifting electrons in a highly doped graphene and surface polar optical phonons of a polar substrate is considered. For this interacting system, we obtained a dielectric function, frequencies and decrement/increment of cooperative plasmon-optical phonon oscillations. We found, that the response is significantly depends on the degree of nonequilibrium of the electrons. In particular, interaction between drifting plasmons and surface polar optical phonons leads to an instability of the electron subsystem due to Vavilov-Cherenkov effect. We suggest that the hybrid system - graphene on a polar substrate - is capable to be used in amplifiers or generators of THz electromagnetic radiation.