16,562 research outputs found
Self-similar transmission properties of aperiodic Cantor potentials in gapped graphene
We investigate the transmission properties of quasiperiodic or aperiodic
structures based on graphene arranged according to the Cantor sequence. In
particular, we have found self-similar behaviour in the transmission spectra,
and most importantly, we have calculated the scalability of the spectra. To do
this, we implement and propose scaling rules for each one of the fundamental
parameters: generation number, height of the barriers and length of the system.
With this in mind we have been able to reproduce the reference transmission
spectrum, applying the appropriate scaling rule, by means of the scaled
transmission spectrum. These scaling rules are valid for both normal and
oblique incidence, and as far as we can see the basic ingredients to obtain
self-similar characteristics are: relativistic Dirac electrons, a self-similar
structure and the non-conservation of the pseudo-spin. This constitutes a
reduction of the number of conditions needed to observe self-similarity in
graphene-based structures, see D\'iaz-Guerrero et al. [D. S. D\'iaz-Guerrero,
L. M. Gaggero-Sager, I. Rodr\'iguez-Vargas, and G. G. Naumis,
arXiv:1503.03412v1, 2015]
Interplay between Zeeman interaction and spin-orbit coupling in a two-dimensional semiconductor system
We analyse the interplay between Dresselhaus, Bychkov-Rashba, and Zeeman
interactions in a two-dimensional semiconductor quantum system under the action
of a magnetic field. When a vertical magnetic field is considered, we predict
that the interplay results in an effective cyclotron frequency that depends on
a spin-dependent contribution. For in-plane magnetic fields, we found that the
interplay induces an anisotropic effective gyromagnetic factor that depends on
the orientation of the applied field as well as on the orientation of the
electron momentum.Comment: 5 page
Intrinsic spin dynamics in semiconductor quantum dots
We investigate the characteristic spin dynamics corresponding to
semiconductor quantum dots within the multiband envelope function approximation
(EFA). By numerically solving an Hamiltonian we treat
systems based on different III-V semiconductor materials.It is shown that, even
in the absence of an applied magnetic field, these systems show intrinsic spin
dynamics governed by intraband and interband transitions leading to
characteristic spin frequencies ranging from the THz to optical frequencies.Comment: to be published in Nanotechnology. Separated figure file
Temperature and doping dependence of normal state spectral properties in a two-orbital model for ferropnictides
Using a second-order perturbative Green's functions approach we determined
the normal state single-particle spectral function
employing a minimal effective model for iron-based superconductors. The
microscopic model, used before to study magnetic fluctuations and
superconducting properties, includes the two effective tight-binding bands
proposed by S.Raghu et al. [Phys. Rev. B 77, 220503 (R) (2008)], and intra- and
inter-orbital local electronic correlations, related to the Fe-3d orbitals.
Here, we focus on the study of normal state electronic properties, in
particular the temperature and doping dependence of the total density of
states, , and of in different Brillouin zone
regions, and compare them to the existing angle resolved photoemission
spectroscopy (ARPES) and previous theoretical results in ferropnictides. We
obtain an asymmetric effect of electron and hole doping, quantitative agreement
with the experimental chemical potential shifts as a function of doping, as
well as spectral weight redistributions near the Fermi level as a function of
temperature consistent with the available experimental data. In addition, we
predict a non-trivial dependence of the total density of states with the
temperature, exhibiting clear renormalization effects by correlations.
Interestingly, investigating the origin of this predicted behaviour by
analyzing the evolution with temperature of the k-dependent self-energy
obtained in our approach, we could identify a number of specific Brillouin zone
points, none of them probed by ARPES experiments yet, where the largest
non-trivial effects of temperature on the renormalization are present.Comment: Manuscript accepted in Physics Letters A on Feb. 25, 201
Normal state electronic properties of LaOFBiS superconductors
A good description of the electronic structure of BiS-based
superconductors is essential to understand their phase diagram, normal state
and superconducting properties. To describe the first reports of normal state
electronic structure features from angle resolved photoemission spectroscopy
(ARPES) in LaOFBiS, we used a minimal microscopic model to
study their low energy properties. It includes the two effective tight-binding
bands proposed by Usui et al [Phys.Rev.B 86, 220501(R)(2012)], and we added
moderate intra- and inter-orbital electron correlations related to Bi-(,
) and S-(, ) orbitals. We calculated the electron Green's
functions using their equations of motion, which we decoupled in second-order
of perturbations on the correlations. We determined the normal state spectral
density function and total density of states for LaOFBiS,
focusing on the description of the k-dependence, effect of doping, and the
prediction of the temperature dependence of spectral properties. Including
moderate electron correlations, improves the description of the few
experimental ARPES and soft X-ray photoemission data available for
LaOFBiS. Our analytical approximation enabled us to
calculate the spectral density around the conduction band minimum at
, and to predict the temperature dependence of
the spectral properties at different BZ points, which might be verified by
temperature dependent ARPES.Comment: 9 figures. Manuscript accepted in Physica B: Condensed Matter on Jan.
25, 201
The continuum description with pseudo-state wave functions
Benchmark calculations are performed aiming to test the use of two different
pseudo-state bases on the the Multiple Scattering expansion of the total
Transition amplitude (MST) scattering framework. Calculated differential cross
sections for p-6He inelastic scattering at 717 MeV/u show a good agreement
between the observables calculated in the two bases. This result gives extra
confidence on the pseudo-state representation of continuum states to describe
inelastic/breakup scattering.Comment: 4 pages, 2 figures. Published in Physical Review
Heterogeneous Extractive Batch Distillation of Chloroform - Methanol â Water : Feasibility and Experiments
A novel heterogeneous extractive distillation process is considered for separating the azeotropic mixture chloroform â methanol in a batch rectifying column, including for the first time an experimental validation of the process. Heterogeneous heavy entrainer water is selected inducing an unstable ternary heteroazeotrope and a saddle binary heteroazeotrope with chloroform (ternary diagram class 2.1-2b). Unlike to well-known heterogeneous azeotropic distillation process and thanks to continuous water feeding at the column top, the saddle binary heteroazeotrope chloroform â water is obtained at the column top, condensed and further split into the liquid â liquid decanter where the chloroform-rich phase is drawn as distillate. First, feasibility analysis is carried out by using a simplified differential model in the extractive section for determining the proper range of the entrainer flowrate and the reflux ratio. The operating conditions and reflux policy are validated by rigorous simulation with ProSim Batch ColumnÂź where technical features of a bench scale distillation column have been described. Six reproducible experiments are run in the bench scale column matching the simulated operating conditions with two sequentially increasing reflux ratio values. Simulation and experiments agree well. With an average molar purity higher than 99%, more than 85% of recovery yield was obtained for chloroform and methanol
The Stationary Phase Method for a Wave Packet in a Semiconductor Layered System. The applicability of the method
Using the formal analysis made by Bohm in his book, {\em "Quantum theory"},
Dover Publications Inc. New York (1979), to calculate approximately the phase
time for a transmitted and the reflected wave packets through a potential
barrier, we calculate the phase time for a semiconductor system formed by
different mesoscopic layers. The transmitted and the reflected wave packets are
analyzed and the applicability of this procedure, based on the stationary phase
of a wave packet, is considered in different conditions. For the applicability
of the stationary phase method an expression is obtained in the case of the
transmitted wave depending only on the derivatives of the phase, up to third
order. This condition indicates whether the parameters of the system allow to
define the wave packet by its leading term. The case of a multiple barrier
systems is shown as an illustration of the results. This formalism includes the
use of the Transfer Matrix to describe the central stratum, whether it is
formed by one layer (the single barrier case), or two barriers and an inner
well (the DBRT system), but one can assume that this stratum can be comprise of
any number or any kind of semiconductor layers.Comment: 15 pages, 4 figures although figure 4 has 5 graph
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