Plasmon-phonon Strongly-Coupled Mode in Epitaxial Graphene

TL;DR

This study investigates the strong coupling between 2D plasmons and surface optical phonons in epitaxial graphene on SiC, revealing dispersion behaviors and damping effects through electron-energy-loss spectroscopy.

Contribution

It provides detailed experimental insights into plasmon-phonon coupling in graphene, highlighting layer-dependent dispersion transitions and damping mechanisms.

Findings

Coupled modes show discrete dispersion in single and bilayer graphene.

Transition from plasmon-like to phonon-like dispersion with more layers.

Plasmon modes are damped by electron-hole pair excitations.

Abstract

We report the dispersion measurements, using angle-resolved reflection electron-energy-loss-spectroscopy (AREELS), on two-dimensional (2D) plasmons in single and multilayer graphene which couple strongly to surface optical phonon (FK phonon) modes of silicon carbide substrate. The coupled modes show discrete dispersion behaviors in the single and bilayer graphene. With increasing graphene layers on SiC(0001), a transition from plasmon-like dispersion to phonon-like dispersion is observed. For plasmon-like modes, the dispersion is strongly damped by electron-hole pair excitations at entering single-particle continuum, while phonon-like mode is undamped. In the region free of coupling, the graphene 2D plasmon exhibits acoustic behavior with linear dispersion with slope and damping determined by the Fermi surface topology.