Terahertz Amplification Induced by Electron-Phonon Interactions in Gated Graphene Plasmonic System.

Terahertz (THz) amplification presents promising potential for various innovative applications. Here, we achieve an ultra-broadband and high-gain THz amplification from 0.1 to 25 THz with a saturated electric field peaking at 107 V/m by leveraging drift-induced plasmon instability in a single-layer gated graphene system. The plasmon instability arises from the electron concentration modulation due to the nonuniformity of the electron-phonon scattering rate distribution on the Fermi surface. The modulation will introduce increments to compensate for the plasmon loss and even achieve plasmon amplification. Specifically, we derive the nonreciprocal plasmon dispersion using Maxwell's equations in conjunction with the Boltzmann transport equation, incorporating interactions between electrons and phonons. We find that the amplifying plasmon mode propagates against the electron drift velocity, and the amplification efficiency can be tuned by adjusting either the electron concentration or the electron drift velocity. Furthermore, the simulation shows that when the fundamental mode is amplified to saturation, higher harmonics are generated and amplified, forming a THz frequency comb. These results provide a promising avenue for developing tunable on-chip THz light sources, amplifiers, and frequency comb generators within integrated plasmonic systems.