Plasmonic response of graphene nanostructures

Abstract

Graphene is a planar monolayer of carbon atoms tightly packed into a 2D honeycomb lattice. Since the first experimental isolation in 2004, graphene has attracted an enormous interest due to its extraordinary optoelectronic properties for nanophotonics. The unique band structure of graphene consists of a lower or valence band and an upper or conduction band, which at low energies resemble the shape of two inverted cones touching at one point (the so-called Dirac point) that marks the Fermi level in the neutral state. In this state, the valence band is completely filled with electrons, while the conduction band is empty. Interestingly, when extra electrons are added to graphene (doping), they start filling unoccupied states in the conduction band up to a certain level that corresponds to the new Fermi level EF=ħvF(n)½, where n is the electronic density per unit area, and vFc/300 their velocity. The collective oscillations of these extra electrons are known as Dirac plasmons, and they are subdivided into two different subgroups: surface plasmon polaritons (SPPs) and localized surface plasmons (LSPs). In the second chapter of this thesis, we classically study Dirac plasmons assuming an inhomogeneous distribution of n in different graphene nanostructures (ribbons and disks), and also a periodic distribution in extended graphene layers. When the characteristic length of the nanostructure is of the order of the Fermi wavelength, classical electromagnetism is no longer valid, and a quantum-mechanical approach is necessary. In the third chapter of this thesis, we provide extensive quantum calculations of the response of LSPs sustained on narrow nanoribbons.The fourth chapter of this thesis is devoted to the study of the strong nonlinear plasmonic response of doped graphene. Finally, in the fifth chapter, we show the outstanding potential of graphene LSPs to resolve the chemical identity of molecules.