Collective Modes of Massive Dirac Fermions in Armchair Graphene Nanoribbons

TL;DR

This paper investigates the plasmon dispersion in armchair graphene nanoribbons with a band gap, revealing how extrinsic and intrinsic plasmons behave differently and providing an analytical model for their velocities.

Contribution

It introduces a detailed tight-binding model with third-nearest-neighbor coupling for armchair graphene nanoribbons and analyzes plasmon dispersion for both intrinsic and extrinsic cases.

Findings

Extrinsic plasmon dispersion approaches a common curve with increasing chemical potential.

Intrinsic plasmon dispersion exhibits energy and momentum thresholds.

An analytical model for extrinsic plasmon group velocity is developed.

Abstract

We report the plasmon dispersion characteristics of intrinsic and extrinsic armchair graphene nanoribbons of atomic width N = 5 using a p_z-orbital tight binding model with third-nearest-neighbor (3nn) coupling. The coupling parameters are obtained by fitting the 3nn dispersions to that of an extended Huckel theory. The resultant massive Dirac Fermion system has a band gap E_g \approx 64 meV. The extrinsic plasmon dispersion relation is found to approach a common dispersion curve as the chemical potential $\mu$ increases, whereas the intrinsic plasmon dispersion relation is found to have both energy and momentum thresholds. We also report an analytical model for the extrinsic plasmon group velocity in the q \rightarrow 0 limit.