Encontrados 29 documentos, a visualizar página 1 de 3
Strong light-matter interaction in systems described by a modified Dirac equation
Peres, N. M. R.; Santos, Jaime E.The bulk states of some materials, such as topological insulators, are described by a modified Dirac equation. Such systems may have trivial and non-trivial phases. In this paper, we show that in the non-trivial phase a strong light-matter interaction exists in a two-dimensional system, which leads to an optical conductivity at least one order of magnitude larger than that of graphene.
Observation of intra- and inter-band transitions in the optical response of gra...
Malard, Leandro M.; Mak, Kin Fai; Castro Neto, A. H.; Peres, N. M. R.; Heinz, Tony F.The optical conductivity of freely suspended graphene was examined under non-equilibrium conditions using femtosecond pump-probe spectroscopy. We observed a conductivity transient that varied strongly with the electronic temperature, exhibiting a crossover from enhanced to decreased absorbance with increasing pump fluence. The response arises from a combination of bleaching of the inter-band transitions by Paul...
Scattering by linear defects in graphene : a tight-binding approach
Rodrigues, J. N. B.; Peres, N. M. R.; Santos, J. M. B. Lopes dosWe develop an analytical scattering formalism for computing the transmittance through periodic defect lines within the tight-binding model of graphene. We first illustrate the method with a relatively simple case, the pentagon-only defect line. Afterwards, more complex defect lines are treated, namely the zz(558) and the zz(5757) ones. The formalism developed, only uses simple tight-binding concepts, reducing t...
Enhancing the absorption of graphene in the terahertz range
Peres, N. M. R.; Bludov, Yuliy V.We study graphene on a photonic crystal operating in the terahertz (THz) spectral range. We show that the absorption of graphene becomes a modulated function of frequency and can be enhanced by more than three times at specific frequency values, depending on the parameters of the system. The problem of a semi-infinite photonic crystal is also solved.
A primer on surface plasmon-polaritons in graphene
Bludov, Yuliy V.; Ferreira, Aires; Peres, N. M. R.; Vasilevskiy, MikhailWe discuss the properties of surface plasmons-polaritons in graphene and describe four possible ways of coupling electromagnetic radiation in the terahertz (THz) spectral range to this type of surface waves: (i) the attenuated total reflection (ATR) method us- ing a prism in the Otto configuration, (ii) graphene micro-ribbon arrays or monolayers with modulated conductivity, (iii) a metal stripe on top of the gr...
Unusual reflection of electromagnetic radiation from a stack of graphene layers...
Bludov, Yuliy V.; Peres, N. M. R.; Vasilevskiy, MikhailWe study the interaction of electromagnetic (EM) radiation with single-layer graphene and a stack of parallel graphene sheets at arbitrary angles of incidence. It is found that the behavior is qualitatively different for transverse magnetic (or p-polarized) and transverse electric (or s-polarized) waves. In particular, the absorbance of single-layer graphene attains a minimum (maximum) for the p (s)-polarizatio...
Exact solution for square-wave grating covered with graphene : surface plasmons...
Peres, N. M. R.; Bludov, Yuliy V.; Ferreira, Aires; Vasilevskiy, MikhailWe provide an analytical solution to the problem of scattering of electromagnetic radiation by a square-wave grating with a flat graphene sheet on top.We show that for deep groves there is a strong plasmonic response, with light absorption in the graphene sheet reaching more than 45% due to the excitation of surface plasmon-polaritons. The case of a grating with a graphene sheet presenting an induced periodic m...
Enhanced optical dichroism of graphene nanoribbons
Hipolito, Fábio; Chaves, A. J.; Ribeiro, R. M.; Vasilevskiy, Mikhail; Pereira, Vitor M.; Peres, N. M. R.The optical conductivity of graphene nanoribbons is analytical and exactly derived. It is shown that the absence of translational invariance along the transverse direction allows considerable intraband absorption in a narrow frequency window that varies with the ribbon width, and lies in the THz range domain for ribbons 10–100 nm wide. In this spectral region the absorption anisotropy can be as high as two orde...
Graphene-based polaritonic crystal
Bludov, Yuliy V.; Peres, N. M. R.; Vasilevskiy, MikhailIt is shown that monolayer graphene deposited on a spatially periodic gate behaves as a polaritonic crystal. Its band structure depending on the applied gate voltage is studied. The scattering of electromagnetic radiation from such a crystal is presented calculated and its spectral dependence is analyzed in terms of Fano-type resonances between the reflected continuum and plasmon-polariton modes forming narrow ...
Tunable graphene-based polarizer
Bludov, Yuliy V.; Vasilevskiy, Mikhail; Peres, N. M. R.It is shown that an attenuated total reflection structure containing a graphene layer can operate as a tunable polarizer of the electromagnetic radiation. The polarization of the reflected electromagnetic wave is controlled by adjusting the voltage applied to graphene via external gate, as demonstrated for the cases of linearly and circularly polarized incident radiation. The mechanism is based on the resonant ...
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