Orbital symmetry fingerprints for magnetic adatoms in graphene

In this paper, we describe the formation of local resonances in graphene in the presence of magnetic adatoms containing localized orbitals of arbitrary symmetry, corresponding to any given angular momentum state. We show that quantum interference effects which are naturally inbuilt in the honeycomb lattice in combination with the specific orbital symmetry of the localized state lead to the formation of fingerprints in differential conductance curves. In the presence of Jahn-Teller distortion effects, which lift the orbital degeneracy of the adatoms, the orbital symmetries can lead to distinctive signatures in the local density of states. We show that those effects allow scanning tunneling probes to characterize adatoms and defects in graphene.Comment: 15 pages, 11 figures. Added discussion about the multi-orbital case and the validity of the single orbital picture. Published versio

Avaliação de controle leiteiro de bovinos usando análises de medidas repetidas.

O objetivo deste trabalho foi analisar os dados de produção de leite de sete vacas, obtidos com intervalos de 14 dias, de vacas da raça Holandesa submetidas a três tratamentos em pastejo de alfafa [T1: controle (confinamento em área de descanso com silagem de milho+11,0 kg de concentrado); T2: pastejo restrito de alfafa+silagem de milho+11,0 kg de concentrado, e T3: pastejo de alfafa à vontade+silagem de milho+8,0 kg de concentrado], em delineamento inteiramente casualizado. Os dados foram analisados por meio de modelos mistos (procedimento MIXED), considerando medidas repetidas, em que cada animal representou um indivíduo. Para modelar a estrutura de variância e covariância dos erros das avaliações dentro de indivíduos, foi selecionada a matriz Huynh-Feldt, estrutura que atende à condição de esfericidade, indicando que, além do modelo linear misto utilizando máxima verossimilhança restrita, também podem ser utilizados recursos do modelo linear padrão, considerando as (co)variâncias no tempo constantes. Pela análise de medidas repetidas, houve redução da produção de leite (p ≤ 0,01) ao longo dos três tratamentos; entretanto, não houve diferença significativa (p > 0,05) global entre tratamentos e nem entre tratamentos dentro de controles (p > 0,05)

Avaliação de controle leiteiro de bovinos usando análises de medidas repetidas.

O objetivo foi analisar dados de produção de leite (y) de sete controles a cada 14 dias de 24 vacas da raça holandesa submetidas a três tratamentos em pastejo de alfafa (T1 - confinamento em área de descanso com silagem de milho + 11,0 kg de concentrado; T2 - pastejo restrito de alfafa (menor participação na dieta) + silagem de milho + 11,0 kg de concentrado e T3-pastejo de alfafa à vontade (maior participação na dieta) + silagem de milho + 8,0 kg de concentrado), em um experimento completamente casualizado, desenvolvido na Embrapa Pecuária Sudeste, São Carlos, SP, em 2008. Os dados foram analisados na forma de medidas repetidas, em que a vaca representou o indivíduo e os controles a avaliação dentro do indivíduo. A estrutura de variância e covariância dos erros das avaliações dentro de indivíduos foi a Huynh-Feldt (HF), indicando que para o presente caso os dados de y poderiam ser analisados tanto pelo modelo linear padrão quanto pelo modelo misto; para os usuários do SAS, significa usar ambos os procedimentos: GLM e MIXED

Transmission through a biased graphene bilayer barrier

We study the electronic transmission through a graphene bilayer in the presence of an applied bias between layers. We consider different geometries involving interfaces between both a monolayer and a bilayer and between two bilayers. The applied bias opens a sizable gap in the spectrum inside the bilayer barrier region, thus leading to large changes in the transmission probability and electronic conductance that are controlled by the applied bias.Comment: 10 pages, 8 figures, extended versio

Optical Properties of Strained Graphene

The optical conductivity of graphene strained uniaxially is studied within the Kubo-Greenwood formalism. Focusing on inter-band absorption, we analyze and quantify the breakdown of universal transparency in the visible region of the spectrum, and analytically characterize the transparency as a function of strain and polarization. Measuring transmittance as a function of incident polarization directly reflects the magnitude and direction of strain. Moreover, direction-dependent selection rules permit identification of the lattice orientation by monitoring the van-Hove transitions. These photoelastic effects in graphene can be explored towards atomically thin, broadband optical elements

Strained graphene: tight-binding and density functional calculations

We determine the band structure of graphene under strain using density functional calculations. The ab-initio band strucure is then used to extract the best fit to the tight-binding hopping parameters used in a recent microscopic model of strained graphene. It is found that the hopping parameters may increase or decrease upon increasing strain, depending on the orientation of the applied stress. The fitted values are compared with an available parametrization for the dependence of the orbital overlap on the distance separating the two carbon atoms. It is also found that strain does not induce a gap in graphene, at least for deformations up to 10%

Colloquium: The transport properties of graphene: An introduction

An introduction to the transport properties of graphene combining experimental results and theoretical analysis is presented. In the theoretical description simple intuitive models are used to illustrate important points on the transport properties of graphene. The concept of chirality, stemming from the massless Dirac nature of the low energy physics of the material, is shown to be instrumental in understanding its transport properties: the conductivity minimum, the electronic mobility, the effect of strain, the weak (anti-)localization, and the optical conductivity.Comment: As publishe

Observation of Intra- and Inter-band Transitions in the Optical Response of Graphene

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 Pauli blocking and induced absorption from the intra-band transitions of the carriers. The latter dominates at low electronic temperature, but, despite an increase in Drude scattering rate, is overwhelmed by the former at high electronic temperature. The time-evolution of the optical conductivity in all regimes can described in terms of a time-varying electronic temperature.Comment: 10 pages (4 pages manuscript + Supplemental Info.