arXiv subjects

J. Milton Pereira Jr

Publications and source records attributed to J. Milton Pereira Jr.

6 recordsLinked to original sources

arXiv2020

Electronic and transport properties of anisotropic semiconductor quantum wires

Within the effective-mass approximation, we theoretically investigated the electronic and transport properties of 2D semiconductor quantum wires (QWs) with anisotropic effective masses and different orientations with respect to the anisotropic axis. The energy levels in the absence and presence of an external magnetic field are analytically calculated, showing: (i) a strong dependence on the spacing of energy levels related to the alignment QW angle and the anisotropy axis; and (ii) for non-null magnetic field, the quantum Hall edge states are significantly affected by the edge orientation. Moreover, by means of the split-operator technique, we analyzed the time evolution of wavepackets in straight and V-shaped anisotropic QWs and compared the transmission probabilities with those of isotropic systems. In the anisotropic case we found damped oscillations in the average values of velocity in both x and y directions for a symmetric Gaussian wavepacket propagating along a straight wide QW, with the oscillation being more evident as the non-collinearity between the group velocity and momentum vectors increases.

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arXiv2018

Dirac spectrum in gated multilayer black phosphorus nanoribbons

We investigate the effects of a perpendicular electric field applied to multilayer phosphorene nanoribbons with zigzag and armchair edges. Within the context of the tight-binding model, we explore the electronic properties of these systems giving emphasis to the appearance of Dirac-like spectra, a transition that occurs when the gate density associated with the applied displacement field is greater than the critical value $n_c$. We show that the confinement properties and the screening effects in such systems play an important role on the determination of $n_c$, suggesting a scheme to determine the thickness, width and edge orientation of multilayered phosphorene nanoribbons. We also explore how this transition affects the electronic transport properties of such systems.

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arXiv2017

Boundary conditions for phosphorene nanoribbons in the continuum approach

We investigate the energy spectrum of single layer black phosphorene nanoribbons (BPN) by means of a low-energy expansion of a recently proposed tight-binding model that describes electron and hole bands close to the Fermi energy level. Using the continuum approach, we propose boundary conditions based on sublattice symmetries for BPN with zigzag and armchair edges and show that our results for the energy spectra exhibit good agreement with those obtained by using the five-parameter tight-binding model. We also explore the behaviour of the energy gap versus the nanoribbon width $W$. Our findings demonstrate that band gap of armchair BPNs scale as $1/W^2$, while zigzag BPNs exhibit a $1/W$ tendency. We analyse the different possible combinations of the zigzag edges that result two-fold degenerate and non-degenerate edge states. Furthermore, we obtain expressions for the wave functions and discuss the limit of validity of such analytical model.

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arXiv2011

Dirac and Klein-Gordon particles in one-dimensional periodic potentials

We evaluate the dispersion relation for massless fermions, described by the Dirac equation, and for zero-spin bosons, described by the Klein-Gordon equation, moving in two dimensions and in the presence of a one-dimensional periodic potential. For massless fermions the dispersion relation shows a zero gap for carriers with zero momentum in the direction parallel to the barriers in agreement with the well-known "Klein paradox". Numerical results for the energy spectrum and the density of states are presented. Those for fermions are appropriate to graphene in which carriers behave relativistically with the "light speed" replaced by the Fermi velocity. In addition, we evaluate the transmission through a finite number of barriers for fermions and zero-spin bosons and relate it with that through a superlattice.

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arXiv2011

Bilayer graphene with single and multiple electrostatic barriers: band structure and transmission

We evaluate the electronic transmission and conductance in bilayer graphene through a finite number of potential barriers. Further, we evaluate the dispersion relation in a bilayer graphene superlattice with a periodic potential applied to both layers. As a model we use the tight-binding Hamiltonian in the continuum approxi- mation. For zero bias the dispersion relation shows a finite gap for carriers with zero momentum in the direction parallel to the barriers. This is in contrast to single-layer graphene where no such gap was found. A gap also appears for a finite bias. Numerical results for the energy spectrum, conductance, and the density of states are presented and contrasted with those pertaining to single-layer graphene.

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arXiv2005

Dipole-exchange spin waves in Fibonacci magnetic multilayers

A microscopic model is employed to calculate the spectrum of spin waves in quasiperiodic magnetic multilayers in the dipole-exchange regime. Results are presented for structures in which thin ferromagnetic films are separated by non-magnetic spacers following a Fibonacci sequence and extend previous magnetostatic calculations. The results show the splitting of the frequency bands and the mode mixing caused by the dipolar interaction between the films as a function of spacer thickness, as well as the fractal aspect of the spectrum induced by the non-periodic aspect of the structure.

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