Plasmon Damping in Electronically Open Systems.

Rapid progress in electrically controlled plasmonics in solids poses a question about possible effects of electronic reservoirs on the properties of plasmons. We find that plasmons in electronically open systems [i.e., in (semi)conductors connected to leads] are prone to an additional damping due to charge carrier penetration into contacts and subsequent thermalization. We develop a theory of such lead-induced damping based on the kinetic equation with microscopic boundary conditions at the interfaces, followed by perturbation theory with respect to transport nonlocality. The lifetime of the plasmon in an electronically open ballistic system appears to be finite, of the order of conductor length divided by carrier Fermi velocity. The reflection loss of the plasmon incident on the contact of the semiconductor and perfectly conducting metal also appears to be finite, of the order of Fermi velocity divided by wave phase velocity. Recent experiments on plasmon-assisted photodetection [Nat. Commun. 9, 5392 (2018)NCAOBW2041-172310.1038/s41467-018-07848-w] are discussed in light of the proposed lead-induced damping phenomenon.

Feasibility of surface plasmon lasing in HgTe quantum wells with population inversion.

Surface plasmon lasing in semiconductor gain media at far-infrared frequencies requires simultaneously long non-radiative recombination times and large plasmon propagation length. In this paper, we show that these conditions are realized in mercury-telluride quantum wells (HgTe QWs) near the topological transition. We derive the conditions of surface plasmon amplification in HgTe QWs with interband population inversion. To this end, we calculate the spatially-dispersive high-frequency conductivity of pumped HgTe QWs taking into account their realistic band structure, and compare the interband gain with Drude absorption and collisionless Landau damping. An extra necessary condition of plasmon lasing is revealed, namely, the non-equilibrium carrier density should be high enough to make the plasmon spectrum overlap with the frequency domain of interband excitations. The latter condition limits the processes of both stimulated and spontaneous plasmon emission at low temperatures, and should have a strong impact on the recombination kinetics of HgTe QWs at low temperatures.