Linear model of surface terahertz plasmons amplification in two parallel graphene sheets

Amplification of terahertz plasmons in a pair of parallel active graphene monolayers is studied theoretically. It is shown that the antisymmetric mode increment of plasmons in the two parallel graphene monolayers may be several times greater than that in a single graphene layer due to deceleration of the antisymmetric plasmon mode as compared to the plasmon mode in a single graphene monolayer. The symmetric mode increment of plasmons in the two parallel graphene monolayers can be two times greater in magnitude than that in a single graphene layer due to constructive interference of the plasmon fields in the structure with two parallel graphene monolayers. Background and Objectives: Graphene, being a natural two-dimensional material with zero band-gap, appears to be a perfect platform for terahertz (THz) radiation amplification. Justification of the possibility of possessing the negative conductivity of graphene at THz frequencies resulted in the proposals of THz graphene lasers and plasmonic amplifiers which may be used for signal processing in THz integrated nanocircuits in the subwavelength regime. The double-layer graphene structure consists of two parallel graphene monolayers with a narrow dielectric gap (barrier layer) between them. Electromagnetic fields of plasmons propagating in these layers interact with each other giving rise to a single unified plasmon in the pair of parallel graphene monolayers surrounded by dielectric claddings. In this paper, we study the gain 32 of THz plasmons in the double-layer graphene. Materials and Methods: The plasmon gain is calculated from the dispersion relation obtained in the strict electrodynamic approach. Results: It is shown that the antisymmetric mode increment of plasmons in the double-layer graphene may be several times greater than that in a single graphene layer, the symmetric mode increment of plasmons in the double-layer graphene may be two times greater in magnitude than that in a single graphene layer. Conclusion: In conclusion, we have studied the gain of the symmetric and antisymmetric plasmon modes in the double-layer graphene heterostructure. It is shown that the antisymmetric mode increment of plasmons in the doublelayer graphene may be several times greater than that in a single graphene layer, the symmetric mode increment of plasmons in the double-layer graphene may be two times greater in magnitude than that in a single graphene layer. Amplified plasmons can be used in low-loss interconnects and active elements in THz plasmonic graphene nanocircuits.