32 research outputs found
Statistical repulsion/attraction of electrons in graphene in a magnetic field
The aim of this work is to describe the thermodynamic properties of an
electron gas in graphene placed in a constant magnetic field. The electron gas
is constituted by Bloch electrons in the long wavelength approximation. The
partition function is analyzed in terms of a perturbation expansion of the
dimensionless constant . The statistical
repulsion/attraction potential for electrons in graphene is obtained in the
respective case in which antisymmetric/symmetric states in the coordinates are
chosen. Thermodynamic functions are computed for different orders in the
perturbation expansion and the different contributions are compared for
symmetric and antisymmetric states, showing remarkable differences between them
due to the spin exchange correlation. A detailed analysis of the statistical
potential is done, showing that, although electrons satisfy Fermi statistics,
attractive potential at some interparticle distances can be found.Comment: Physica B, 201
Valley properties of doped graphene in a magnetic field
The aim of this work is to describe the electronic properties of graphene in
a constant magnetic field in the long wavelength approximation with random
binary disorder, by solving the Soven equation self-consistently. Density of
state contributions for different valleys in each sublattice sites are obtained
for different values of magnetic field strength showing remarkable differences
between K and K' valleys. A band gap is obtained by an asymmetric on-site
impurity concentration and the graphene electrons acquire an anomalous magnetic
moment, which is opposite in different valleys, which depend highly in the
interplay between the impurity band, the band edges and the broadening of the
Landau levels. In turn, magnetization as a function of B for different on-site
random impurities is computed showing that by decreasing the on-site impurity
energy values, maximum magnetization is shifted towards higher values of B
which can be used to create and manipulate polarized valley currents. Finally,
conductivity and local vertex function are obtained as a function of energy
showing that scattering contributions from A and B sublattices differ
significantly. Effective medium local two-irreducible vertex is computed
showing that scattering from sublattices A and B do not contribute equally,
which can be related to weak anti-localization. From these results, it could be
possible to explore how the valley pseudospin can be used to create polarized
currents by populating asymmetrically the sublattice sites, where the
population can be tuned with the applied magnetic field strength
Dynamical diffusion and renormalization group equation for the Fermi velocity in doped graphene
The aim of this work is to study the electron transport in graphene with
impurities by introducing a generalization of linear response theory for linear
dispersion relations and spinor wave functions. Current response and density
response functions are derived and computed in the Boltzmann limit, showing
that in the former case, a minimum conductivity appears in the no-disorder
limit. In turn, from the generalization of both functions, an exact relation
can be obtained that relates both. Combining this result with the relation
given by the continuity equation, it is possible to obtain general functional
behavior of the diffusion pole. Finally, a dynamical diffusion is computed in
the quasistatic limit using the definition of relaxation function. A lower
cutoff must be introduced to regularize infrared divergences, which allow us to
obtain a full renormalization group equation for the Fermi velocity, which is
solved up to order O(h^2).Comment: 20 pages, 2 figure
Ballistic transport properties in pristine-doped-pristine graphene junctions
We investigate the ballistic electron transport in a monolayer graphene with
configurational averaged impurities, located between two clean graphene leads.
It is shown that the electron transmission are strongly dependent on the
concentration of impurities and the incident energy. In turn, the conductance
computed using the Landauer formalism shows a similar behavior to those found
in experimental works as a function of the applied voltage for different
concentrations of impurities in the limit of low temperatures. In the limit of
zero bias voltage, the conductance shows a minimum value which reduces to zero
for high concentration of impurities which disentangle graphene sublattices.
These results can be very helpful for exploring the tunneling mechanism of
electrons through doped thermodynamically stable graphene
Landau level transitions indoped graphene in a time dependent magnetic field
The aim of this work is to describe the Landau levels transitions of Bloch
electrons in doped graphene with an arbitrary time dependent magnetic field in
the long wavelength approximation. In particular, transitions from the m Landau
level to the m + 1 and m + 2 Landau levels are studied using time-dependent
perturbation theory. Time intervals are computed in which transition
probabilities tend to zero at low order in the coupling constant. In
particular, Landau level transitions are studied in the case of Bloch electrons
travelling in the direction of the applied magnetic force and the results are
compared with classical and revival periods of electrical current in graphene.
Finally, current probabilities are computed for the n = 0 and n = 1 Landau
levels showing expected oscillating behavior with modified cyclotron frequency.Comment: 18 pages, 7 figure
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Minimum Information about a Biosynthetic Gene cluster
A wide variety of enzymatic pathways that produce specialized metabolites in bacteria, fungi and plants are known to be encoded in biosynthetic gene clusters. Information about these clusters, pathways and metabolites is currently dispersed throughout the literature, making it difficult to exploit. To facilitate consistent and systematic deposition and retrieval of data on biosynthetic gene clusters, we propose the Minimum Information about a Biosynthetic Gene cluster (MIBiG) data standard.Chemistry and Chemical Biolog
DFT study of CO adsorption on Pd-SnO2(110) surfaces
We studied the effect of Pd on the adsorption of CO on the tin oxide surface SnO2(110) by Density Functional Theory calculations. Molecular CO adsorbs more strongly in the presence of Pd pre-deposited on the surface. The most stable adsorption sites are those bonded to the Pd atom near a Pd top position on a tilted configuration. In this case the C-O distance increases, producing a bond weakening, and the calculated stretching frequency decreases. Analysis of the atomic orbital interactions reveals that Pd-CO bonding involves C s - O p and p orbitals from CO, with Pd d orbitals. For CO sites bonded to Pd, CO bonds to the surface producing a weakening on the surface Pd-O bond. The electronic configuration analysis shows that in all cases the CO molecule withdraws charge from the surface.Fil: Bechthold, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Pronsato, Maria Estela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Pistonesi, Carolina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin
A first-principles study of formic acid adsorption on CaO (001)
Formic acid adsorption on CaO (001) is analyzed using Density Functional Theory (DFT) with Van der Waals corrections, implemented through the Vienna ab Initio Simulation Package (VASP). Our calculations reveals two possible adsorption sites at low coverage with adsorption energies of −2.38 eV and −2.07 eV. For both sites we found a similar structural behavior, with a considerable elongation of the formic acid OH bond with respect to the molecular distance. The analysis of the electronic structure and bonding show a stabilization of formic acid as a result of a shift in their states to lower energies, with respect to the gas phase. There is a small charge transfer (0.03e−) from the hydrogen to the surface. At the same time, formic acid oxygens also experiment a charge decrease of 0.15e− and 0.13e−, being the ones with the greatest charge variation during the adsorption process.Fil: Bechthold, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Orazi, Valeria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; ArgentinaFil: Marchetti, Jorge Mario. Norwegian University of Life Sciences; Noruega. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentin
Hydrogen adsorption on PdGa(110): A DFT study
H and Pd bonding is analyzed using density functional theory (DFT) calculations. Changes in the electronic structure of PdGa(110) surface upon the introduction of one or two hydrogen atoms are addressed. H locates only on Pd atop geometry and no interaction with Ga is detected. The Pd-Pd bond strength decreases as the new Pd-H bond is formed. The effect of H is limited to its first Pd neighbor. An analysis of orbital interaction reveals that Pd-H bonding mainly involves Pd 5s and H 1s orbitals with less participation of Pd 5p and 4d orbitals. © 2012 American Chemical Society.Fil: Bechthold, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Jasen, Paula Verónica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Gonzalez, Estela Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Nacional del Sur. Departamento de Física; ArgentinaFil: Juan, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Física del Sur. Universidad Nacional del Sur. Departamento de Física. Instituto de Física del Sur; Argentina. Universidad Nacional del Sur. Departamento de Física; Argentin