69 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
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
Kinetic study of the esterification of free fatty acid and ethanol in the presence of triglycerides using solid resins as catalyst
Biodiesel production is gaining more and more relevance due to its environmental advantages and because of the world situation of petroleum: decreases of reserves, augmentation of prices etc. Biodiesel is produced by transesterification of triglycerides; however, it can also be generated by the esterification of fatty acid, normally considered as an impurity. The evolution of the reaction when using oleic acid (diluted in triglycerides) and ethanol, in the presence of a heterogeneous catalyst, has been studied. Kinetics expression for the esterification reaction as well as for the esterification and transesterification taking place simultaneously have been developed and fit with the experimental data. It is shown that, when both reactions are being taking into account, the kinetics fits the experimental data better since it does consider the interaction between all the compounds involved. The kinetics expression obtained represented satisfactorily the experimental information for several operations conditions.Fil: 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; 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
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
Temperature effect on the magnetic oscillations in 2D materials
We study the magnetic oscillations (MO) in 2D materials with a buckled honeycomb lattice, considering a perpendicular electric and magnetic field. At zero temperature the MO consist of the sum of four sawtooth oscillations, with two unique frequencies and phases. The values of these frequencies depend on the Fermi energy and electric field, which in turn determine the condition for a beating phenomenon in the MO. We analyse the temperature effect in the MO by considering its local corrections over each magnetization peak, given by Fermi–Dirac like functions. We show that the width of these functions is related to the minimum temperature necessary to observe the spin and valley properties in the MO. In particular, we find that in order to observe the spin splitting, the width must be lower than the MO phase difference. Likewise, in order to observe valley mixing effects, the width must be lower than the MO period. We also show that at high temperatures, all the maxima and minima in the MO shift to a constant value, in which case we obtain a simple expression for the MO and its envelope. The results obtained show unique features in the MO in 2D materials, given by the interplay between the valley and spin.Fil: Escudero, Federico Nahuel. 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: Ardenghi, Juan Sebastian. 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: 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; Argentin
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