Encontrados 14 documentos, a visualizar página 1 de 2
Strong light-matter interactions in heterostructures of atomically thin films
Britnell, Líam; Ribeiro, R. M.; Eckmann, A.; Jalil, R.; Belle, B. D.; Mishchenko, A.; Kim, Y.-J.; Gorbachev, R. V.; Georgiou, T.; Morozov, S. V.The isolation of various two-dimensional (2D) materials, and the possibility to combine them in vertical stacks, has created a new paradigm in materials science: heterostructures based on 2D crystals. Such a concept has already proven fruitful for a number of electronic applications in the area of ultrathin and flexible devices. Here we expand the range of such structures to photoactive ones by utilizing semico...
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...
Thermodynamics of a Potts-like model for a reconstructed zigzag edge in graphen...
Rodrigues, J. N. B.; Gonçalves, P. A. D.; Santos, Jaime E.; Castro Neto, A. H.Versão 'draft' ; We construct a three-color Potts-like model for the graphene zigzag edge reconstructed with Stone-Wales carbon rings in order to study its thermal equilibrium properties. We consider two cases which have different ground states: the edge with nonpassivated dangling carbon bonds and the edge fully passivated with hydrogen. We study the concentration of defects perturbing the ground-state config...
Band nesting and the optical response of two-dimensional semiconducting transit...
Carvalho, A.; Ribeiro, R. M.; Castro Neto, A. H.We have studied the optical conductivity of two-dimensional (2D) semiconducting transition metal dichalcogenides using ab initio density functional theory. We find that this class of materials presents large optical response due to the phenomenon of band nesting. The tendency towards band nesting is enhanced by the presence of van Hove singularities in the band structure of these materials. Given that 2D crysta...
Origin of indirect optical transitions in few-layer MoS2, WS2 and WSe2
Zhao, Weijie; Ribeiro, R. M.; Minglin, Toh; Carvalho, A.; Kloc, Christian; Castro Neto, A. H.; Eda, GokiIt has been well established that single layer MX2 (M=Mo,W and X=S,Se) are direct gap semiconductors with band edges coinciding at the K point in contrast to their indirect gap multilayer counterparts. In few-layer MX2, there are two valleys along the Γ-K line with similar energy. There is little understanding on which of the two valleys forms the conduction band minimum (CBM) in this thickness regime. We inve...
Atomically thin boron nitride : a tunnelling barrier for graphene devices
Britnell, Liam; Gorbachev, R. V.; Jalil, R.; Belle, B. D.; Schedin, F.; Katsnelson, M. I.; Eaves, L.; Morozov, S. V.; Mayorov, Alexander S.Documento submetido para revisão pelos pares. a publicar em Nano Letters ; We investigate the electronic properties of heterostructures based on ultrathin hexagonal boron nitride (h-BN) crystalline layers sandwiched between two layers of graphene as well as other conducting materials (graphite, gold). The tunnel conductance depends exponentially on the number of h-BN atomic layers, down to a monolayer thicknes...
Confined magneto-optical waves in graphene
Ferreira, Aires; Peres, N. M. R.; Castro Neto, A. H.The electromagnetic mode spectrum of single-layer graphene subjected to a quantizing magnetic field is computed taking into account intraband and interband contributions to the magneto-optical conductivity. We find that a sequence of weakly decaying quasi-transverse-electric modes, separated by magnetoplasmon polariton modes, emerge due to the quantizing magnetic field. The characteristics of these modes are tu...
Continuum model of the twisted bilayer
Santos, J. M. B. Lopes dos; Peres, N. M. R.; Castro Neto, A. H.The continuum model of the twisted graphene bilayer (Phys. Rev. Lett. 99, 256802, 2007) is extended to include all types of commensurate structures. The essential ingredient of the model, the Fourier components of the spatially modulated hopping amplitudes, can be calculated analytically, for any type of commensurate structures in the low twist angle limit. We show that the Fourier components that could give ri...
Coulomb drag and high resistivity behavior in double layer graphene
Peres, N. M. R.; Santos, J. M. B. Lopes dos; Castro Neto, A. H.We show that Coulomb drag in ultra-clean graphene double layers can be used for controlling the on/o ratio for current ow by tunning the external gate voltage. Hence, although graphene remains semi-metallic, the double layer graphene system can be tuned from conductive to a highly resistive state. We show that our results explain previous data of Coulomb drag in double layer graphene samples in disordered SiO...
Unified description of the DC conductivity of monolayer and bilayer graphene ba...
Ferreira, Aires; Nilsson, Johan; Castro Neto, A. H.; Gomes, J. Viana; Peres, N. M. R.We show that a coherent picture for the DC conductivity of monolayer and bilayer graphene emerges from considering that strong short-range potentials are the main source of scattering in these two systems. The origin of the strong short range potentials may lie in adsorbed hydrocarbons at the surface of graphene. The equivalence between results based on the partial wave description of scattering and the T-matri...
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