Intrinsic plasmons in 2D Dirac materials

TL;DR

This paper theoretically investigates intrinsic plasmons in 2D Dirac materials like graphene at charge neutrality, revealing their dispersion, damping behavior, and conditions for experimental observation using RPA.

Contribution

It provides analytical and numerical analysis of intrinsic Dirac plasmons' properties across temperatures, including damping and dispersion, for both single and double-layer systems.

Findings

Intrinsic plasmons have $q^{1/2}$ dispersion at charge neutrality.

Plasmon energy vanishes as $T^{1/2}$ at low temperatures.

Intrinsic plasmons are well-defined when $q < k_B T/e^2$.

Abstract

We consider theoretically, using the random phase approximation (RPA), low-energy intrinsic plasmons for two-dimensional (2D) systems obeying Dirac-like linear chiral dispersion with the chemical potential set precisely at the charge neutral Dirac point. The "intrinsic Dirac plasmon" energy has the characteristic $q^{1/2}$ dispersion in the 2D wave-vector $q$, but vanishes as $T^{1/2}$ in temperature for both monolayer and bilayer graphene. The intrinsic plasmon becomes overdamped for a fixed $q$ as $T -> 0$ since the level broadening (i.e. the decay of the plasmon into electron-hole pairs due to Landau damping) increases as $T^{-1/2}$ as temperature decreases, however, the plasmon mode remains well-defined at any fixed $T$ (no matter how small) as $q -> 0$. We find the intrinsic plasmon to be well-defined as long as $q < k_B T/e^2$. We give analytical results for low and high temperatures, and numerical RPA results for arbitrary temperatures, and consider both single-layer and double-layer intrinsic Dirac plasmons. We provide extensive comparison and contrast between intrinsic and extrinsic graphene plasmons, and critically discuss the prospects for experimentally observing intrinsic Dirac point graphene plasmons.