Magnetic field tuning of terahertz Dirac plasmons in graphene

TL;DR

This study investigates how strong magnetic fields influence graphene plasmons, revealing edge and bulk mode splitting, increased edge plasmon lifetimes, and doping-dependent behaviors, highlighting potential for tunable terahertz devices.

Contribution

First analysis of graphene plasmon behavior under strong magnetic fields, showing mode splitting, lifetime enhancement, and doping effects unique to graphene.

Findings

Edge and bulk plasmon modes split with magnetic field.

Edge plasmon lifetimes increase with magnetic field.

Doping influences mode splitting uniquely in graphene.

Abstract

Boundaries and edges of a two dimensional system lower its symmetry and are usually regarded, from the point of view of charge transport, as imperfections. Here we present a first study of the behavior of graphene plasmons in a strong magnetic field that provides a different perspective. We show that the plasmon resonance in micron size graphene disks in a strong magnetic field splits into edge and bulk plasmon modes with opposite dispersion relations, and that the edge plasmons at terahertz frequencies develop increasingly longer lifetimes with increasing magnetic field, in spite of potentially more defects close to the graphene edges. This unintuitive behavior is attributed to increasing quasi-one dimensional field-induced confinement and the resulting suppression of the back-scattering. Due to the linear band structure of graphene, the splitting rate of the edge and bulk modes develops a strong doping dependence, which differs from the behavior of traditional semiconductor two-dimensional electron gas (2DEG) systems. We also observe the appearance of a higher order mode indicating an anharmonic confinement potential even in these well-defined circular disks. Our work not only opens an avenue for studying the physics of graphene edges, but also supports the great potential of graphene for tunable terahertz magneto-optical devices.