Electron Confinement Induced by Diluted Hydrogen-like Ad-atoms in Graphene Ribbons

We report the electronic properties of two-dimensional systems made of graphene nanoribbons which are patterned with ad-atoms in two separated regions. Due to the extra electronic confinement induced by the presence of the impurities, we find resonant levels, quasi-bound and impurity-induced localized states, which determine the transport properties of the system. Regardless of the ad-atom distribution in the system, we apply band-folding procedures to simple models and predict the energies and the spatial distribution of those impurity-induced states. We take into account two different scenarios: gapped graphene and the presence of randomly distributed ad-atoms in a low dilution regime. In both cases the defect-induced resonances are still detected. Our findings would encourage experimentalist to synthesize these systems and characterize their quasi-localized states employing, for instance, scanning tunneling spectroscopy (STS). Additionally, the resonant transport features could be used in electronic applications and molecular sensor devices.Comment: 12 pages, 11 figures, submitted (minor changes

Bound states in the continuum: localization of Dirac-like fermions

We report the formation of bound states in the continuum for Dirac-like fermions in structures composed by a trilayer graphene flake connected to nanoribbon leads. The existence of this kind of localized states can be proved by combining local density of states and electronic conductance calculations. By applying a gate voltage, the bound states couple to the continuum, yielding a maximum in the electronic transmission. This feature can be exploited to identify bound states in the continuum in graphene-based structures.Comment: 7 pages, 5 figure

Influência da rotação de culturas no sistema radicular do milho e em algumas características químicas de um latossolo vermelho-escuro distrófico da região de Sete Lagoas.

Em experimento envolvendo rotacao de culturas e adubacao verde na cultura do milho, em um latossolo Vermelho-Escuro distrofico, observou-se um periodo de estiagem prolongada durante a fase de florescimento de milho, sintomas acentuados de murcha em areas de cultivo continuo com milho. Em areas onde se efetuava a rotacao de cultura soja-milho, mucuna-milho, milho + mucuna intercalar-milho, este sintoma nao se repetia. Procurando-se avaliar os beneficios de rotacao de culturas sobre o monocultivo, coletou-se amostras de solo de uma area com 0,20 m2, tendo-se como ponto central a linha de milho. O volume amostrado foi obtido atraves das seguintes profundidades: 0-2 cm, 2-4 cm, 4-6 cm, 6-10 cm, 10-14 cm, 14-18 cm, 18-26 cm, 26-34 cm e 34-42 cm. Apos a coleta do solo + raizes, estas foram separadas e quantificadas (peso) e o solo analisado quimicamente. Os resultados permitiram concluir que a rotacao soja-milho e mucuna-milho, promoveram maior aumento de peso de plantas de milho e maior quantidade de raizes abaixo de 30 cm de profundidade em relacao ao milho continuo e milho com mucuna intercalar. A rotacao soja-milho promoveu uma melhor distribuicao de bases nas camadas mais profundas do solo, aumentando a saturacao de calcio. Houve, nas areas com rotacao mucuna-milho, maiores teores de potassio, calcio e magnesio, em relacao aos demais manejos (soja-milho, milho continuo e milho apos milho + mucuna intercalar)

The Effective Particle-Hole Interaction and the Optical Response of Simple Metal Clusters

Following Sham and Rice [L. J. Sham, T. M. Rice, Phys. Rev. 144 (1966) 708] the correlated motion of particle-hole pairs is studied, starting from the general two-particle Greens function. In this way we derive a matrix equation for eigenvalues and wave functions, respectively, of the general type of collective excitation of a N-particle system. The interplay between excitons and plasmons is fully described by this new set of equations. As a by-product we obtain - at least a-posteriori - a justification for the use of the TDLDA for simple-metal clusters.Comment: RevTeX, 15 pages, 5 figures in uufiles format, 1 figure avaible from [email protected]