Plasma wave instabilities in nonequilibrium graphene

Abstract

We study two-stream instabilities in a nonequilibrium system in which a stream of electrons is injected into doped graphene. As with equivalent nonequilibrium parabolic band systems, we find that the graphene systems can support unstable charge-density waves whose amplitudes grow with time. We determine the range of wave vectors q that are unstable, and their growth rates. We find no instability for waves with wave vectors parallel or perpendicular to the direction of the injected carriers. We find that, within the small-wave-vector approximation, the angle between q and the direction of the injected electrons that maximizes the growth rate increases with increasing |q|. We compare the range and strength of the instability in graphene to that of twoand three-dimensional parabolic band systems.

Negative Landau Damping in Bilayer Graphene

“…In fact, under certain conditions, the transfer of energy may occur in the opposite direction, i.e., from the moving charged particles to the plasma waves, leading to the emergence of exponentially growing oscillations [33]. The two-stream instabilities were recently investigated in a nonequilibrium system in which a stream of electrons with a well-defined quasi-momentum is injected into a doped graphene sample [34]. Furthermore, unstable plasma waves can also be generated from the interaction between drifting electrons and the elastic vibrations of the lattice ions (phonons) in high-mobility semiconductors [35][36][37][38].…”

Fate of electron beam in graphene: Coulomb relaxation or plasma instability?

“…On the contrary, reduction of temperature in Maxwell plasma led to an exponential decrease in Landau damping. In this context, we note that neglect of spatial dispersion in the background dielectric function in the first study of beam instability in graphene was not justified and led to quantitatively wrong conclusions [26].…”

“…Before proceeding to calculation, we note a previous attempt to solve the problem of beam instability in graphene in Ref. [26] in the collisionless case. Even in that case, the results of [26] cannot be called satisfactory as the model ignored Landau damping in graphene at frequencies ω < qv 0 .…”

“…[26] in the collisionless case. Even in that case, the results of [26] cannot be called satisfactory as the model ignored Landau damping in graphene at frequencies ω < qv 0 . This presence of such damping changes the character of beam instability from thresholdtype to thresholdless, as it does in textbook case of Maxwell plasma [10].…”