Plasmonics in graphene at infrared frequencies

Abstract

We point out that plasmons in doped graphene simultaneously enable low-losses and significant wave localization for frequencies below that of the optical phonon branch ω Oph ≈ 0.2 eV. Large plasmon losses occur in the interband regime (via excitation of electron-hole pairs), which can be pushed towards higher frequencies for higher doping values. For sufficiently large dopings, there is a bandwidth of frequencies from ω Oph up to the interband threshold, where a plasmon decay channel via emission of an optical phonon together with an electron-hole pair is nonegligible. The calculation of losses is performed within the framework of a random-phase approximation and number conserving relaxation-time approximation. The measured DC relaxation-time serves as an input parameter characterizing collisions with impurities, whereas the contribution from optical phonons is estimated from the influence of the electron-phonon coupling on the optical conductivity. Optical properties of plasmons in graphene are in many relevant aspects similar to optical properties of surface plasmons propagating on dielectric-metal interface, which have been drawing a lot of interest lately because of their importance for nanophotonics. Therefore, the fact that plasmons in graphene could have low losses for certain frequencies makes them potentially interesting for nanophotonic applications.

Electronic modulation of infrared radiation in graphene plasmonic resonators

“…For the case of the 1,360 cm À 1 feature we observe here, the plasmonic loss (and corresponding plasmon generating) processes are attributed to the factors that limit the electron mobility of the graphene, such as defect scattering, impurity scattering, and inelastic electron-electron and electron-phonon interactions 15,22,25,30,33 . In addition, plasmons have been shown to decay via loss channels associated with the edges of graphene nanostructures and by coupling to substrate phonons 22,25 .…”

“…The optical absorptivity/emissivity of graphene depends on two carrier density-dependent terms: an intraband contribution that is characterized by a large Drude-like peak in the DC to far-IR range, and an interband contribution that manifests as a step-like feature in the absorption in the far to near-IR [8][9][10][11][12][13] . In addition, the linear bandstructure and two-dimensional nature of graphene allow for it to support plasmonic modes that have a unique dispersion relation [14][15][16][17] . These plasmonic modes have been proposed as a means of efficiently coupling to THz radiation [18][19][20] , and they have been shown to create strong absorption pathways in the THz to mid-IR when the graphene is patterned to form plasmonic Fabry-Perot resonances [21][22][23][24] .…”

Highly Confined Tunable Mid-Infrared Plasmonics in Graphene Nanoresonators

“…One explanation of this trend is that the graphene plasmons should be damped as the plasmon energy moves above the in-plane optical phonon energy of at 0.2eV. 3 Although this effect may play a role in increasing ∆߱ as the resonant frequencies (߱ ሻ increase, it is important to note that the peak widths that we experimentally measure are due to multiple effects, many of which are expected to show an energy dependence.…”

Hybrid Surface-Phonon-Plasmon Polariton Modes in Graphene/Monolayer h-BN Heterostructures

“…The carrier scattering rate Γ takes into account scattering by impurities with the carrier mobility of 500cm 2 /Vs, and by optical phonons estimated from theoretically obtained self-energy. 2,3 The in-plane and out-of-plane relative permittivity of graphene are then separately assigned as ε=1+iσ/ωδ and 1, respectively. The thickness of graphene(δ) and h-BN are both set as 0.34nm from the interlayer spacing of bulk hBN and…”