Localized states at zigzag edges of bilayer graphene

We report the existence of zero energy surface states localized at zigzag edges of bilayer graphene. Working within the tight-binding approximation we derive the analytic solution for the wavefunctions of these peculiar surface states. It is shown that zero energy edge states in bilayer graphene can be divided into two families: (i) states living only on a single plane, equivalent to surface states in monolayer graphene; (ii) states with finite amplitude over the two layers, with an enhanced penetration into the bulk. The bulk and surface (edge) electronic structure of bilayer graphene nanoribbons is also studied, both in the absence and in the presence of a bias voltage between planes.Comment: 4 pages, 5 figure

Bilayer graphene: gap tunability and edge properties

Bilayer graphene -- two coupled single graphene layers stacked as in graphite -- provides the only known semiconductor with a gap that can be tuned externally through electric field effect. Here we use a tight binding approach to study how the gap changes with the applied electric field. Within a parallel plate capacitor model and taking into account screening of the external field, we describe real back gated and/or chemically doped bilayer devices. We show that a gap between zero and midinfrared energies can be induced and externally tuned in these devices, making bilayer graphene very appealing from the point of view of applications. However, applications to nanotechnology require careful treatment of the effect of sample boundaries. This being particularly true in graphene, where the presence of edge states at zero energy -- the Fermi level of the undoped system -- has been extensively reported. Here we show that also bilayer graphene supports surface states localized at zigzag edges. The presence of two layers, however, allows for a new type of edge state which shows an enhanced penetration into the bulk and gives rise to band crossing phenomenon inside the gap of the biased bilayer system.Comment: 8 pages, 3 fugures, Proceedings of the International Conference on Theoretical Physics: Dubna-Nano200

Disorder Induced Localized States in Graphene

We consider the electronic structure near vacancies in the half-filled honeycomb lattice. It is shown that vacancies induce the formation of localized states. When particle-hole symmetry is broken, localized states become resonances close to the Fermi level. We also study the problem of a finite density of vacancies, obtaining the electronic density of states, and discussing the issue of electronic localization in these systems. Our results also have relevance for the problem of disorder in d-wave superconductors.Comment: Replaced with published version. 4 pages, 4 figures. Fig. 1 was revise

Phenomenological study of the electronic transport coefficients of graphene

Using a semi-classical approach and input from experiments on the conductivity of graphene, we determine the electronic density dependence of the electronic transport coefficients -- conductivity, thermal conductivity and thermopower -- of doped graphene. Also the electronic density dependence of the optical conductivity is obtained. Finally we show that the classical Hall effect (low field) in graphene has the same form as for the independent electron case, characterized by a parabolic dispersion, as long as the relaxation time is proportional to the momentum.Comment: 4 pages, 1 figur

SAMBA: Stochastic Analytical Model with a Bayesian Approach

We develop and estimate a DSGE model for the Brazilian economy, to be used as part of the macroeconomic modeling framework at the Central Bank of Brazil. The model combines the building blocks of standard DSGE models (e.g., price and wage rigidities and adjustment costs) with the following features that better describe the Brazilian economy: (i) a fiscal authority pursuing an explicit target for the primary surplus; (ii) administered or regulated prices as part of consumer prices; (iii) external finance for imports, amplifying the effects of changes in external financial conditions on the economy; and (iv) imported goods used in the production function of differentiated goods. It also includes the presence of financially constrained households. We estimate the model with Bayesian techniques, using data starting in 1999, when inflation targeting was implemented. Model evaluation, based on impulse response functions, moment conditions, variance error decomposition and initial forecasting exercises, suggests that the model can be a useful tool for policy analysis and forecasting.

Perspectivas do uso do ataque sulfúrico (H2SO4 1:1) e da dissolução alcalina (NaOH 0,5 N) para a analise mineralógica expedita de solos com B textural e B latossólico.

Descrição de um.procedimento analitíco para a quantificação dos principais minerais de solos cor B textural e B latossélico (fração argila). O grupo das canditas é determinado por dissolução seletiva com NaOH 0,5 N após a desestabilização térmica a 550 graus Celsius duraante duas horas, mas sem que a amostra sofra nenhum tratamento prévio de natureza química....bitstream/item/62681/1/CNPS-BOL.-PESQ.-34-84.pdfTrabalho apresentado no 19. Congresso Brasileiro de Ciencia do Solo

Double Exchange Model for Magnetic Hexaborides

A microscopic theory for rare-earth ferromagnetic hexaborides, such as Eu(1-x)Ca(x)B6, is proposed on the basis of the double-exchange Hamiltonian. In these systems, the reduced carrier concentrations place the Fermi level near the mobility edge, introduced in the spectral density by the disordered spin background. We show that the transport properties such as Hall effect, magnetoresitance, frequency dependent conductivity, and DC resistivity can be quantitatively described within the model. We also make specific predictions for the behavior of the Curie temperature, Tc, as a function of the plasma frequency, omega_p.Comment: 4 pages, 3 figure

Distribuição radicular da bananeira `prata-anã´ sob diferentes regimes de irrigação no primeiro ciclo.

Objetivou-se com este trabalho avaliar a distribuição do sistema radicular da bananeira ?Prata-Anã? sob diferentes regimes de irrigação no semiárido baiano. A análise seguiu um esquema fatorial 5 x 5 x 4, cinco estratégias de irrigação, cinco distâncias do pseudocaule e quatro profundidades com três repetições em blocos casualizados. As estratégias de irrigação foram: (L1: 0,20; L2: 0,35; L3: 0,50 e L4: 0,65) x AF (área foliar) x (ETo) e L5: conforme a ETc utilizando sistema de irrigação por gotejamento no primeiro ciclo produtivo. As distâncias amostradas no sentido longitudinal e perpendicular à fileira de plantas foram: 0,15, 0,40, 0,65, 0,90 e 1,20 m do pseudocaule, e profundidades de: 0 ? 0,20, 0,20 ? 0,40, 0,40 ? 0,60 e 0,60 ? 0,80 m. O espaçamento de plantio é de 3,0 x 2,5 mem um Latossolo de textura média. As diferentes estratégias de irrigação não alteraram a distribuição do sistema radicular de bananeira ?Prata-Anã?. Não foram observadas diferenças entre o sistema radicular da ?Prata-Anã? no sentido longitudinal e no perpendicular às linhas de irrigação.A maior concentração de raízes ocorreu até a distância de aproximadamente 0,50 m do pseudocaule e a uma profundidade do solo próxima a 0,40 m

Electron waves in chemically substituted graphene

We present exact analytical and numerical results for the electronic spectra and the Friedel oscillations around a substitutional impurity atom in a graphene lattice. A chemical dopant in graphene introduces changes in the on-site potential as well as in the hopping amplitude. We employ a T-matrix formalism and find that disorder in the hopping introduces additional interference terms around the impurity that can be understood in terms of bound, semi-bound, and unbound processes for the Dirac electrons. These interference effects can be detected by scanning tunneling microscopy.Comment: 4 pages, 7 figure