2,389 research outputs found
Conductivity of suspended and non-suspended graphene at finite gate voltage
We compute the DC and the optical conductivity of graphene for finite values
of the chemical potential by taking into account the effect of disorder, due to
mid-gap states (unitary scatterers) and charged impurities, and the effect of
both optical and acoustic phonons. The disorder due to mid-gap states is
treated in the coherent potential approximation (CPA, a self-consistent
approach based on the Dyson equation), whereas that due to charged impurities
is also treated via the Dyson equation, with the self-energy computed using
second order perturbation theory. The effect of the phonons is also included
via the Dyson equation, with the self energy computed using first order
perturbation theory. The self-energy due to phonons is computed both using the
bare electronic Green's function and the full electronic Green's function,
although we show that the effect of disorder on the phonon-propagator is
negligible. Our results are in qualitative agreement with recent experiments.
Quantitative agreement could be obtained if one assumes water molelcules under
the graphene substrate. We also comment on the electron-hole asymmetry observed
in the DC conductivity of suspended graphene.Comment: 13 pages, 11 figure
Water deficit effects on the transpiration and stomatal resistance of the mango tree.
The process of mango flower induction at the northeast of Brazil through the use of water stress has not given satisfactory results mainly due to inadequate irrigation
Descompactação da panícula da mangueira pelo ácido giberélico (GA3) e controle de microlepidópteros.
bitstream/CPATSA/33063/1/COT120.pd
Magnetic exchange mechanism for electronic gap opening in graphene
We show within a local self-consistent mean-field treatment that a random
distribution of magnetic adatoms can open a robust gap in the electronic
spectrum of graphene. The electronic gap results from the interplay between the
nature of the graphene sublattice structure and the exchange interaction
between adatoms.The size of the gap depends on the strength of the exchange
interaction between carriers and localized spins and can be controlled by both
temperature and external magnetic field. Furthermore, we show that an external
magnetic field creates an imbalance of spin-up and spin-down carriers at the
Fermi level, making doped graphene suitable for spin injection and other
spintronic applications.Comment: 5 pages, 5 figure
Efeito dos teores de carboidratos nos garfos, épocas e métodos de enxertia na propagação vegetativa do umbuzeiro.
O objetivo deste trabalho, foi verificar a influência dos teores de carboidratos, épocas e métodos de enxertia, sobre o pegamento do enxerto do umbuzeiro (Spondias tuberosa Arr.), nas diferentes fases fenológicas das plantas matrizes fornecedoras de garfos
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
Influência de fatores fisiológicos de plantas-matrizes e de épocas do ano no pegamento de diferentes métodos de enxertia do umbuzeiro.
Com o objetivo de verificar a influência de fatores fisiológicos das plantas-matrizes de umbuzeiro (Spondias tuberosa Arruda.), as épocas de realização e os métodos de enxertia, sobre o pegamento de enxertos desta espécie, foram conduzidos cinco experimentos sob condições de viveiro, na Embrapa Semi-Árido, em Petrolina-PE. Os experimentos foram instalados nos meses de janeiro, março, maio, julho e setembro de 1998. O delineamento utilizado foi em blocos ao acaso, com três tratamentos e oito repetições. Os tratamentos foram: garfagem em fenda cheia e à inglesa simples e borbulhia em "T" invertido. Os garfos foram colhidos de acordo com o ciclo fenológico das plantas-matrizes, correspondendo às fases de crescimento vegetativo, reprodutivo e de dormência, quando então se realizaram as avaliações dos fatores fisiológicos. Os fatores fisiológicos (fotossíntese, potencial hídrico e condutância estomática), observados na planta-matriz, nas diferentes fases fenológicas, não influenciaram o índice de pegamento dos diferentes métodos de enxertia. Os métodos de enxertia por garfagem em fenda cheia e à inglesa simples apresentaram maiores índices médio de pegamento, de 97,1 e 92,4%, respectivamente. O material vegetativo (garfos) colhido nas diferentes fases fenológicas de planta-matriz não afetou o índice de pegamento do processo da enxertia, o que amplia a oferta de mudas ao longo do ano devido à oferta de material propagativo
Theory of Spin Fluctuations in Striped Phases of Doped Antiferromagnetic Cuprates
We study the properties of generalized striped phases of doped cuprate planar
quantum antiferromagnets. We invoke an effective, spatially anisotropic,
non-linear sigma model in two space dimensions. Our theoretical predictions are
in quantitative agreement with recent experiments in La_{2-x}Sr_xCuO_4 with . We focus on (i) the magnetic correlation length, (ii) the
staggered magnetization at and (iii) the N\'eel temperature, as functions
of doping, using parameters determined previously and independently for this
system. These results support the proposal that the low doping
(antiferromagnetic) phase of the cuprates has a striped configuration.Comment: 4 pages, Revtex. To appear in the Proceedings of the International
Conference "Stripes, Lattice Instabilities and High Tc Superconductivity",
(Rome, Dec. 1996
The infrared conductivity of graphene
We study the infrared conductivity of graphene at finite chemical potential
and temperature taking into account the effect of phonons and disorder due to
charged impurities and unitary scatterers. The screening of the long-range
Coulomb potential is treated using the random phase approximation coupled to
the coherent potential approximation. The effect of the electron-phonon
coupling is studied in second-order perturbation theory. The theory has
essentially one free parameter, namely, the number of charge impurities per
carbon, n^{{\rm C}}_i. We find an anomalous enhancement of the conductivity in
a frequency region that is blocked by Pauli exclusion and an impurity
broadening of the conductivity threshold. We also find that phonons induce
Stokes and anti-Stokes lines that produce an excess conductivity, when compared
to the far infrared value of \sigma_0 = (\pi/2) e^2/h.Comment: 4 pages, 3 figure
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