Plasmon-phonon coupling in graphene

TL;DR

This paper investigates how collective electron-phonon excitations interact in monolayer and bilayer graphene, revealing strong coupling in monolayer and density-dependent coupling in bilayer, explaining experimental plasmon dispersion.

Contribution

It provides a non-perturbative calculation of plasmon-phonon coupling in graphene, highlighting differences between monolayer and bilayer systems due to screening effects.

Findings

Strong plasmon-phonon coupling in monolayer graphene at all densities.

Significant coupling in bilayer graphene only at high densities.

Plasmon-phonon interaction explains the observed linear plasmon dispersion.

Abstract

Collective excitations of coupled electron-phonon systems are calculated for both monolayer and bilayer graphene, taking into account the non-perturbative Coulomb coupling between electronic excitations in graphene and the substrate longitudinal optical phonon modes. We find that the plasmon-phonon coupling in monolayer graphene is strong at all densities, but in bilayer graphene the coupling is significant only at high densities satisfying the resonant condition $\omega_{pl} \approx \omega_{ph}$. The difference arises from the peculiar screening properties associated with chirality of graphene. Plasmon-phonon coupling explains the measured quasi-linear plasmon dispersion in the long wavelength limit, thus resolving a puzzle in the experimental observations.