Synthesis of highly confined surface plasmon modes with doped graphene sheets in the mid-infrared and terahertz frequencies

TL;DR

This paper analytically explores highly confined surface plasmon modes in doped graphene sheets, revealing how symmetric and antisymmetric modes behave with varying separation, with implications for mid-infrared and terahertz waveguiding and sensing.

Contribution

It provides an accurate approximate dispersion relation for monolayer graphene plasmons and analyzes the splitting and confinement properties of coupled graphene pairs.

Findings

Symmetric mode confinement improves with reduced absorption at larger gaps.

Antisymmetric mode exhibits lower absorption loss at small gaps or long wavelengths.

Graphene plasmons are promising for mid-infrared and terahertz waveguiding and sensing.

Abstract

We investigate through analytic calculations the surface plasmon dispersion relation for monolayer graphene sheets and a separated parallel pair of graphene monolayers. An approximate form for the dispersion relation for the monolayer case was derived, which was shown to be highly accurate and offers intuition to the properties of the supported plasmon mode. For parallel graphene pairs separated by small gaps, the dispersion relation of the surface plasmon splits into two branches, one with a symmetric and the other with an antisymmetric magnetic field across the gap. For the symmetric (magnetic field) branch, the confinement may be improved at reduced absorption loss over a wide spectrum, unlike conventional SP modes supported on metallic surfaces that are subjected to the trade-off between loss and confinement. This symmetric mode becomes strongly suppressed for very small separations however. On the other hand, its antisymmetric counterpart exhibits reduced absorption loss for very small separations or long wavelengths, serving as a complement to the symmetric branch. Our results suggest that graphene plasmon structures could be promising for waveguiding and sensing applications in the mid-infrared and terahertz frequencies.