Multi-plasmon absorption in graphene

We show that graphene possesses a strong nonlinear optical response in the form of multi-plasmon absorption, with exciting implications in classical and quantum nonlinear optics. Specifically, we predict that graphene nano-ribbons can be used as saturable absorbers with low saturation intensity in the far-infrared and terahertz spectrum. Moreover, we predict that two-plasmon absorption and extreme localization of plasmon fields in graphene nano-disks can lead to a plasmon blockade effect, in which a single quantized plasmon strongly suppresses the possibility of exciting a second plasmon

Plasma echoes in graphene

Plasma echo is a dramatic manifestation of plasma damping process reversibility. In this paper we calculate temporal and spatial plasma echoes in graphene in the acoustic plasmon regime when echoes dominate over plasmon emission. We show an extremely strong spatial echo response and discuss how electron collisions reduce the echo. We also discuss differences between various electron dispersions, and differences between semiclassical and quantum model of echoes

Transverse electric plasmons in bilayer graphene

We predict the existence of transverse electric (TE) plasmons in bilayer graphene. We find that their plasmonic properties are much more pronounced in bilayer than in monolayer graphene, in a sense that they can get more localized at frequencies just below $\hbar\omega=0.4$~eV for adequate doping values. This is a consequence of the perfectly nested bands in bilayer graphene which are separated by $\sim 0.4$~eV

Screening effect on the optical absorption in graphene and metallic monolayers

Screening is one of the fundamental concepts in solid state physics. It has a great impact on the electronic properties of graphene where huge mobilities were observed in spite of the large concentration of charged impurities. While static screening has successfully explained DC mobilities, screening properties can be significantly changed at infrared or optical frequencies. In this paper we discuss the influence of dynamical screening on the optical absorption of graphene and other 2D electron systems like metallic monolayers. This research is motivated by recent experimental results which pointed out that graphene plasmon linewidths and optical scattering rates can be much larger than scattering rates determined by DC mobilities. Specifically we discuss a process where a photon incident on a graphene plane can excite a plasmon by scattering from an impurity, or surface optical phonon of the substrate.Comment: 19 pages, 2 figure

Plasmonics in graphene at infra-red frequencies

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 $\hbar\omega_{Oph}\approx 0.2$ 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 $\omega_{Oph}$ 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.Comment: 5 figure

Elektrodinamička svojstva grafena i primjene u tehnologiji

Graphene is a novel two-dimensional material with fascinating electrodynamic properties like the ability to support collective electron oscillations (plasmons) accompanied by tight confinement of electromagnetic fields. Our goal is to explore light-matter interaction in graphene in the context of plasmonics and other technological applications but also to use graphene as a platform for studying many body physics like the interaction between plasmons, phonons and other elementary excitations. Plasmons and plasmon-phonon interaction are analyzed within the self-consistent linear response approximation. We demonstrate that electron-phonon interaction leads to large plasmon damping when plasmon energy exceeds that of the optical phonon but also a peculiar mixing of plasmon and optical phonon polarizations. Plasmon-phonon coupling is strongest when these two excitations have similar energy and momentum. We also analyze properties of transverse electric plasmons in bilayer graphene. Finally we show that thermally excited plasmons strongly mediate and enhance the near field radiation transfer between two closely separated graphene sheets. We also demonstrate that graphene can be used as a thermal emitter in the near field thermophotovoltaics leading to large efficiencies and power densities. Near field heat transfer is analyzed withing the framework of fluctuational electrodynamics.Grafen je tek nedavno otkriveni dvo-dimenzionalan materijal s vrlo zanimljivim elektrodinamičkim svojstvima poput mogućnosti podržavanja kolektivnih oscilacija elektronskog plina (plazmona) praćenih s jakom loklizacijom elektromagnetskog polja. Cilj ovog doktorata je proučiti interakciju svjetlosti i materije u grafenu u konteksu plazmonike i drugih tehnoloških primjena ali također upotrijebiti grafen kao platformu za istaživanje pojava fizike mnoštva čestica kao što su interakcija između plazmona, fonona i drugih elementarnih pobuđenja. Plazmone i plazmon-fonon interakciju analiziramo u kontekstu aproksimacije samo-konzistentnog linearnog odziva. Pokazujemo da elektronfonon interakcija vodi k jakom gušenju plazmona kada energija plazmona prijeđe energiju optičkog fonona ali također neobično miješanje polarizacija plazmona i optičkog fonona. Plazmon-fonon vezanje je najjače kad ta dva pobuđenja imaju usporedivu energiju i impuls. Također analiziramo svojstva transverzalnog električnog plazmona u dvo-sloju grafena. Konačno pokazujemo da termalno pobuđeni plazmoni kanaliziraju i bitno pospješuju radiativni transfer topline između dvije bliske ravnine grafena. Također pokazujemo da se grafen može koristiti kao termalni emiter u termofotovoltaicima bliskog polja što vodi k velikim efikasnostima i gustoći snage. Prijenos topline u bliskom polju analiziramo u kontekstu fluktuacijske elektrodinamike

Transverse electric plasmons in bilayer graphene

We predict the existence of transverse electric (TE) plasmons in bilayer graphene. We find that their plasmonic properties are much more pronounced in bilayer than in monolayer graphene, in a sense that they can get more localized at frequencies just below $\hbar\omega=0.4$~eV for adequate doping values. This is a consequence of the perfectly nested bands in bilayer graphene which are separated by $\sim 0.4$~eV

Near-field thermal radiation transfer controlled by plasmons in graphene

It is shown that thermally excited plasmon-polariton modes can strongly mediate, enhance and \emph{tune} the near-field radiation transfer between two closely separated graphene sheets. The dependence of near-field heat exchange on doping and electron relaxation time is analyzed in the near infra-red within the framework of fluctuational electrodynamics. The dominant contribution to heat transfer can be controlled to arise from either interband or intraband processes. We predict maximum transfer at low doping and for plasmons in two graphene sheets in resonance, with orders-of-magnitude enhancement (e.g. $10^2$ to $10^3$ for separations between $0.1\mu m$ to $10nm$) over the Stefan-Boltzmann law, known as the far field limit. Strong, tunable, near-field transfer offers the promise of an externally controllable thermal switch as well as a novel hybrid graphene-graphene thermoelectric/thermophotovoltaic energy conversion platform.Comment: 4 pages, 3 figure

Quasiclassical nonlinear plasmon resonance in graphene

Electrons in graphene behave like relativistic Dirac particles which can reduce the velocity of light by two orders of magnitude in the form of plasmon-polaritons. Here we show how these properties lead to a peculiar nonlinear plasmon response in the quasiclassical regime of terahertz frequencies. On the one hand, we show how interband plasmon damping is suppressed by the relativistic Klein tunneling effect. On the other hand, we demonstrate huge enhancement of the nonlinear intraband response when the plasmon velocity approaches the resonance with the electron Fermi velocity. This extreme sensitivity to the plasmon intensity could be used for new terahertz technologies