arXiv subjects

Luiz Felipe C. Pereira

Publications and source records attributed to Luiz Felipe C. Pereira.

At least 19 recordsLinked to original sources

arXiv2026

Parametric Glassiness in Graphene-based Electronic Lévy Glass

Complex disordered conductors can display highly structured and parameter-sensitive transport even in the absence of a thermodynamically stable glass phase. Overlap distributions originally developed for replica symmetry breaking (RSB) provide a useful diagnostic of this organization, provided that their interpretation is distinguished from the equilibrium Parisi construction. In this study, we report RSB-like overlap phenomenology and parametric mesoscopic glassiness in a graphene-based electronic Lévy glass, a device that mimics optical phenomena via electronic processes. By tuning the Fermi energy, we can control the number of propagating wave modes and observe reentrant changes from narrowly centered to broad or bimodal overlap distributions. The phenomenology is observed in both graphene-based and conventional two-dimensional electron-gas electronic Lévy glasses, indicating its generality. Sample-resolved overlap distributions show that the effect is intrinsic to each disorder landscape, whereas the normalized conductance variance shows that the growth of the absolute variance is mainly caused by the increasing mean conductance. We therefore interpret the overlap as a measure of correlation among hierarchically organized transport pathways and the reentrant behavior as evidence of pinning, parameter-induced reorganizations, and mesoscopic chaos in coherent transport.

cond-mat.mes-hall↗

arXiv2026

Spin Hall effect in electronic Lévy glasses: Enhanced spin current generation in the superdiffusive regime

In spintronics, both electronic charge and spin are used to process and store information. Generation, manipulation, and detection of spin currents are essential for the development of next-generation spintronic technologies. Here, we investigate the spin Hall effect in electronic Lévy glasses composed of graphene ribbons with randomly distributed circular regions of high spin-orbit coupling. These systems exhibit two transport regimes that can be tuned by adjusting the Fermi energy. The superdiffusive regime is characterized by low Fermi energy, low resistivity, and low magnetoresistivity, resulting in a long spin diffusion length, in contrast to the diffusive regime. Employing the Landauer-Büttiker approach in conjunction with numerically exact tight-binding simulations, we compute spin-resolved transmission coefficients to assess the spin Hall current and the spin Hall angle as functions of Fermi energy, spin-orbit coupling strength, and on-site electrostatic potential. Our findings reveal that, in the superdiffusive regime, a low charge current can be converted into a large spin Hall current, whereas in the diffusive regime, the same charge current generates a modest spin Hall current. Moreover, we observe that the spin Hall angle can reach 30% in the superdiffusive regime, whereas in the diffusive regime it is only 5%. These results demonstrate that electronic Lévy glasses provide a versatile platform for controlling spin transport and optimizing the spin Hall effect for spintronic applications.

cond-mat.mes-hall↗

arXiv2026

Engineering Delocalization in Graphene Nanoribbons via Quasiperiodic Edges and Electronic Interactions

We investigate localization effects in zigzag graphene nanoribbons with quasiperiodic Fibonacci-type edge extensions, accounting for electron-electron interactions. We employ a tight-binding model that includes first- and third-nearest-neighbor hoppings, in which electronic interactions are treated within a self-consistent mean-field Hubbard approximation. Charge transport properties are calculated using the Landauer-Büttiker formalism. Our results reveal that the combination of quasiperiodic geometry and electronic interactions gives rise to nontrivial transport phenomena. Specifically, the system exhibits three transport regimes: in the non-interacting case, we observe geometric localization. For weak interactions, the system shows a conductive regime with transmission oscillations, whose multiplicity increases with the Fibonacci generation order. In this regime, delocalization emerges from the interplay between geometry and interaction-induced correlations. Finally, for strong interactions, repulsion dominates, and the system returns to a localized state. Our results demonstrate that quasiperiodic edge engineering, combined with electronic interaction control, offers a promising path to modulate transport in graphene nanoribbons.

cond-mat.mes-hall↗

arXiv2024

Consensus effects of social media synthetic influence groups on scale-free networks

Online platforms for social interactions are an essential part of modern society. With the advance of technology and the rise of algorithms and AI, content is now filtered systematically and facilitates the formation of filter bubbles. This work investigates the social consensus under limited visibility in a two-state majority-vote model on Barabási-Albert scale-free networks. In the consensus evolution, each individual assimilates the opinion of the majority of their neighbors with probability $1-q$ and disagrees with chance $q$, known as the noise parameter. We define the visibility parameter $V$ as the probability of an individual considering the opinion of a neighbor at a given interaction. The parameter $V$ enables us to model the limited visibility phenomenon that produces synthetic neighborhoods in online interactions. We employ Monte Carlo simulations and finite-size scaling analysis to obtain the critical noise parameter as a function of the visibility $V$ and the growth parameter $z$. We find the critical exponents $β/\barν$, $γ/\barν$ and $1/\barν$ of and validate their unitary relation for complex networks. Our analysis shows that installing and manipulating synthetic influence groups critically undermines consensus robustness.

cond-mat.stat-mech↗

arXiv2024

Lévy flight for electrons in graphene in the presence of regions with enhanced spin-orbit coupling

We propose an electronic Lévy glass built from graphene nanoribbons in the presence of regions with enhanced spin-orbit coupling. Although electrons in graphene nanoribbons present a low spin-orbit coupling strength, it can be increased by a proximity effect with an appropriate substrate. We consider graphene nanoribbons with different edge types, which contain circular regions with a tunable Rashba spin-orbit coupling, whose diameter follow a power-law distribution. We find that spin-orbital clusters induce a transition from superdiffusive to diffusive charge transport, similar to what we recently reported for nanoribbons with electrostatic clusters [Phys. Rev. B. 107, 155432 (2023)]. We also investigate spin polarization in the spin-orbital Lévy glasses, and show that a finite spin polarization can be found only in the superdiffusive regime. In contrast, the spin polarization vanishes in the diffusive regime, making the electronic Lévy glass a useful device whose electronic transmission and spin polarization can be controlled by its Fermi energy. Finally, we apply a multifractal analysis to charge transmission and spin polarization, and find that the transmission time series in the superdiffusive regime are multifractal, while they tend to be monofractal in the diffusive regime. In contrast, spin polarization time series are multifractal in both regimes, characterizing a marked difference between mesoscopic fluctuations of charge transport and spin polarization in the proposed electronic Lévy glass.

cond-mat.mes-hall↗

arXiv2024

Length and torsion dependence of thermal conductivity in twisted graphene nanoribbons

Research on the physical properties of materials at the nanoscale is crucial for the development of breakthrough nanotechnologies. One of the key properties to consider is the ability to conduct heat, i.e., its thermal conductivity. Graphene is a remarkable nanostructure with exceptional physical properties, including one of the highest thermal conductivities (TC) ever measured. Graphene nanoribbons (GNRs) share most fundamental properties with graphene, with the added benefit of having a controllable electronic bandgap. One method to achieve such control is by twisting the GNR, which can tailor its electronic properties, as well as change their TC. Here, we revisit the dependence of the TC of twisted GNRs (TGNRs) on the number of applied turns to the GNR by calculating more precise and mathematically well defined geometric parameters related to the TGNR shape, namely, its twist and writhe. We show that the dependence of the TC on twist is not a simple function of the number of turns initially applied to a straight GNR. In fact, we show that the TC of TGNRs requires at least two parameters to be properly described. Our conclusions are supported by atomistic molecular dynamics simulations to obtain the TC of suspended TGNRs prepared under different values of initially applied turns and different sizes of their suspended part. Among possible choices of parameter pairs, we show that TC can be appropriately described by the initial number of turns and the initial twist density of the TGNRs.

cond-mat.mes-hall↗

arXiv2023

A Lévy flight for electrons in graphene: superdiffusive-to-diffusive transport transition

In this work we propose an electronic Lévy flight device, analogous to a recent optical realization. To that end, we investigate the transmission of electrons in graphene nanoribbons in the presence of circular electrostatic clusters, whose diameter follow a power-law distribution. We analyze the effect of the electrostatic clusters on the electronic transport regime of the nanoribbons, in terms of its diffusion behavior. Our numerical calculations show that the presence of circular electrostatic clusters induces a transition from Lévy (superdiffusive) to diffusive transport as the energy increases. Furthermore, we argue that in our electronic Lévy flight device, superdiffusive transport is an exclusive feature of the low-energy quantum regime, while diffusive transport is a feature of the semiclassical regime. Therefore, we attribute the observed transition to the chiral symmetry breaking, once the energy moves away from the Dirac point of graphene.

cond-mat.mes-hall↗

arXiv2022

Wave transmission and its universal fluctuations in one-dimensional systems with Lévy-like disorder: Schrödinger, Klein-Gordon and Dirac equations

We investigate the propagation of waves in one-dimensional systems with Lévy-type disorder. We perform a complete analysis of non-relativistic and relativistic wave transmission submitted to potential barriers whose width, separation or both follow Lévy distributions characterized by an exponent $0 < α<1$. For the first two cases, where one of the parameters is fixed, non-relativistic and relativistic waves present anomalous localization, $\langle T \rangle \propto L^{-α}$. However, for the latter case, in which both parameters follow a Lévy distribution, non-relativistic and relativistic waves present a transition between anomalous and standard localization as the incidence energy increases relative to the barrier height. Moreover, we obtain the localization diagram delimiting anomalous and standard localization regimes, in terms of incidence angle and energy. Finally, we verify that transmission fluctuations, characterized by its standard deviation, are universal, independent of barrier architecture, wave equation type, incidence energy and angle, further extending earlier studies on electronic localization.

cond-mat.mes-hall↗

arXiv2020

Majority-vote model with limited visibility: an investigation into filter bubbles

The dynamics of opinion formation in a society is a complex phenomenon where many variables play an important role. Recently, the influence of algorithms to filter which content is fed to social networks users has come under scrutiny. Supposedly, the algorithms promote marketing strategies, but can also facilitate the formation of filters bubbles in which a user is most likely exposed to opinions that conform to their own. In the two-state majority-vote model an individual adopts an opinion contrary to the majority of its neighbors with probability $q$, defined as the noise parameter. Here, we introduce a visibility parameter $V$ in the dynamics of the majority-vote model, which equals the probability of an individual ignoring the opinion of each one of its neighbors. For $V=0.5$ each individual will, on average, ignore the opinion of half of its neighboring nodes. We employ Monte Carlo simulations to calculate the critical noise parameter as a function of the visibility $q_c(V)$ and obtain the phase diagram of the model. We find that the critical noise is an increasing function of the visibility parameter, such that a lower value of $V$ favors dissensus. Via finite-size scaling analysis we obtain the critical exponents of the model, which are visibility-independent, and show that the model belongs to the Ising universality class. We compare our results to the case of a network submitted to a static site dilution, and find that the limited visibility model is a more subtle way of inducing opinion polarization in a social network.

physics.soc-ph↗

arXiv2020

Suppression of coherent thermal transport in quasiperiodic graphene-hBN superlattice ribbons

Nanostructured superlattices are promising materials for novel electronic devices due to their adjustable physical properties. Periodic superlattices facilitate coherent phonon thermal transport due to constructive wave interference at the boundaries between the materials. However, it is possible to induce a crossover from coherent to incoherent transport regimes by adjusting the superlattice period. We have recently observed such crossover in periodic graphene-boron nitride nanoribbons as the length of individual domains was increased. In general, transport properties are dominated by translational symmetry and the presence of unconventional symmetries leads to unusual transport characteristics. Here we perform non-equilibrium molecular dynamics simulations to investigate phonon heat transport in graphene-hBN superlattices following the Fibonacci quasiperiodic sequence, which lie between periodic and disordered structures. Our simulations show that the quasiperiodicity can suppress coherent phonon thermal transport in these superlattices. This behavior is related to the increasing number of interfaces per unit cell as the Fibonacci generation increases, hindering phonon coherence along the superlattice. The suppression of coherent thermal transport in graphene-hBN superlattices enables a higher degree of control on heat conduction at the nanoscale, and shows potential for application in the design of novel thermal management devices.

cond-mat.mes-hall↗

arXiv2019

Thermoelectric Properties of BiSbTe Alloy Nanofilms Produced by DC Sputtering: Experiments and Modeling

Thermoelectricity refers to the conversion of thermal energy into electrical energy and vice-versa, which relies on three main effects: Seebeck, Peltier and Thomson, all of which are manifestations of heat and electricity flow. In this work we investigate the deposition of nanometric films and the effect of a thermal treatment on their thermoelectric properties. The films are based on BiSbT e ternary alloys, obtained by deposition on a substrate using the DC sputtering technique. We produced sputtering targets with repurposed materials from commercial thermoelectric modules. In this way, we explore an environmentally responsible destination for discarded devices, with in situ preparation and manufacture of film-based thermoelectric modules. Film samples show an improvement trend in thermoelectric efficiency as the annealing temperature is increased in the range 423-623 K. The experimental data regarding thermal conductivity, electrical resistivity (or electrical conductivity), and the Seebeck coefficient were analyzed with the theory of q-deformed algebra. Applying a q-deformation to our system we can model the effect of the annealing temperature on the thermal and electrical conductivities, as well as the Seebeck coefficient, and argue that the q-factor must be related to structural properties of the films. We believe that our work could pave the way for future developments in the modeling of experimental measurements via the formalism of q-deformation algebra.

physics.app-ph↗

arXiv2019

Outstanding strength, optical characteristics and thermal conductivity of graphene-like BC$_3$ and BC$_6$N semiconductors

Carbon based two-dimensional (2D) materials with honeycomb lattices, like graphene, polyaniline carbon-nitride (C$_3$N) and boron-carbide (BC$_3$) exhibit exceptional physical properties. On this basis, we propose two novel graphene-like materials with BC$_6$N stoichiometry. We conducted first-principles calculations to explore the stability, mechanical response, electronic, optical and thermal transport characteristics of graphene-like BC$_3$ and BC$_6$N monolayers. The absence of imaginary frequencies in the phonon dispersions confirm dynamical stability of BC$_3$ and BC$_6$N monolayers. Our first principles results reveal that BC$_3$ and BC$_6$N present high elastic moduli of 256 and 305 N/m, and tensile strengths of 29.0 and 33.4 N/m, with room temperature lattice thermal conductivities of 410 and 1710 W/m.K, respectively. Notably, the thermal conductivity of BC$_6$N is one of the highest among all 2D materials. According to electronic structure calculations, monolayers of BC$_3$ and BC$_6$N are indirect and direct bandgap semiconductors, respectively. The optical analysis illustrate that the first absorption peaks along the in-plane polarization for single-layer BC$_3$ and BC$_6$N occur in the visible range of the electromagnetic spectrum. Our results reveal outstandingly high mechanical properties and thermal conductivity along with attractive electronic and optical features of BC$_3$ and BC$_6$N nanosheets and present them as promising candidates to design novel nanodevices.

cond-mat.mtrl-sci↗

arXiv2019

Dirac wave transmission in Lévy disordered systems

We investigate the propagation of electronic waves described by the Dirac equation subject to a Lévy-type disorder distribution. Our numerical calculations, based on the transfer matrix method, in a system with a distribution of potential barriers show that it presents a phase transition from anomalous to standard to anomalous localization as the incidence energy increases. In contrast, electronic waves described by the Schrödinger equation do not present such transitions. Moreover, we obtain the phase diagram delimiting anomalous and standard localization regimes, in the form of an incidence angle versus incidence energy diagram, and argue that transitions can also be characterized by the behavior of the dispersion of the transmission. We attribute this transition to an abrupt reduction in the transmittance of the system when the incidence angle is higher than a critical value which induces a decrease in the transmission fluctuations.

cond-mat.mes-hall↗

arXiv2017

Tuning the Fano factor of graphene via Fermi velocity modulation

In this work we investigate the influence of a Fermi velocity modulation on the Fano factor of periodic and quasi-periodic graphene superlattices. We consider the continuum model and use the transfer matrix method to solve the Dirac-like equation for graphene where the electrostatic potential, energy gap and Fermi velocity are piecewise constant functions of the position x. We found that in the presence of an energy gap, it is possible to tune the energy of the Fano factor peak and consequently the location of the Dirac point, by a modulations in the Fermi velocity. Hence, the peak of the Fano factor can be used experimentally to identify the Dirac point. We show that for higher values of the Fermi velocity the Fano factor goes below 1/3 in the Dirac point. Furthermore, we show that in periodic superlattices the location of Fano factor peaks is symmetric when the Fermi velocity $v_A$ and $v_B$ is exchanged, however by introducing quasi-periodicity the symmetry is lost. The Fano factor usually holds a universal value for a specific transport regime, which reveals that the possibility of controlling it in graphene is a notable result.

cond-mat.mes-hall↗

arXiv2017

Electronic, optical and thermal properties of highly stretchable 2D carbon Ene-yne graphyne

Recently, a new carbon-based two-dimensional (2D) material, so called "carbon Ene-yne" (CEY), was successfully synthesized. In this work, we examine electronic, optical and thermal properties of this novel material. We studied the stretchability of CEY via density functional theory (DFT) calculations. Using the PBE and HSE06 functionals, as well as the G$_0$W$_0$ method and the Bethe-Salpeter equation, we systematically explored electronic and optical properties of 2D CEY. In particular, we investigated the change of band-gap and optical properties under uniaxial and biaxial strain. Ab-initio molecular dynamics simulations confirm that CEY is stable at temperatures as high as 1500 K. Using non-equilibrium molecular dynamics simulations, the thermal conductivity of CEY was predicted to be anisotropic and three orders of magnitude smaller than that of graphene. We found that in the visible range, the optical conductivity under high strain levels is larger than that of graphene. This enhancement in optical conductivity may allow CEY to be used in photovoltaic cells. Moreover, CEY shows anisotropic optical responses for x- and y- polarized light, which may be suitable as an optical linear polarizer. The comprehensive insight provided by the present investigation should serve as a guide for possible applications of CEY in nanodevices.

cond-mat.mtrl-sci↗

arXiv2017

Thermal conductivity decomposition in two-dimensional materials: Application to graphene

Two-dimensional materials have unusual phonon structures due to the presence of flexural (out-of-plane) modes. Although molecular dynamics simulations have been extensively used to study heat transport in such materials, conventional formalisms treat the phonon dynamics isotropically. Here, we decompose the microscopic heat current in atomistic simulations into in-plane and out-of-plane components, corresponding to the in-plane and out-of-plane phonon dynamics, respectively. This decomposition allows for direct computation of the corresponding thermal conductivity components in two-dimensional materials. We apply this decomposition to study heat transport in suspended graphene, using both equilibrium and non-equilibrium molecular dynamics simulations. We show that the flexural component is responsible for about two thirds of the total thermal conductivity in unstrained graphene, and the acoustic flexural component is responsible for the logarithmic divergence of the conductivity when a sufficiently large tensile strain is applied.

cond-mat.mes-hall↗

arXiv2017

Anomalous strain effect on the thermal conductivity of borophene: a reactive molecular dynamics study

Borophene, an atomically thin, corrugated, crystalline two-dimensional boron sheet, has been recently synthesized. We investigate mechanical properties and lattice thermal conductivity of borophene via reactive molecular dynamics simulations. We performed uniaxial tensile strain simulations at room temperature along in-plane directions, and found 2D elastic moduli of 188 N/m and 403 N/m along zigzag and armchair directions, respectively. The anisotropy is attributed to the buckling of the borophene structure along the zigzag direction. We also performed non-equilibrium molecular dynamics to calculate the lattice thermal conductivity. We predict room-temperature lattice thermal conductivities of $75.9 \pm 5.0$ W/m-K and $147 \pm 7.3$ W/m-K, respectively, and estimate effective phonon mean free paths of $16.7 \pm 1.7$ nm and $21.4 \pm 1.0$ nm for the zigzag and armchair directions. The anisotropy is attributed to differences in the density of states of low-frequency phonons, with lower group velocities and possibly shorten phonon lifetimes along the zigzag direction. We also observe that when borophene is strained along the armchair direction there is a significant increase in thermal conductivity along that direction. Meanwhile, when the sample is strained along the zigzag direction there is a much smaller increase in thermal conductivity along that direction. For a strain of 8\% along the armchair direction the thermal conductivity increases by a factor of 3.5 (~250\%), whereas for the same amount of strain along the zigzag direction the increase is only by a factor of 1.2 (~20\%). Our predictions are in agreement with recent first principles results, at a fraction of the computational cost. The simulations shall serve as a guide for experiments concerning mechanical and thermal properties of borophene and related 2D materials.

cond-mat.mtrl-sci↗

arXiv2017

Thermal Conductivity and Mechanical Properties of Nitrogenated Holey Graphene

Nitrogenated holey graphene (NHG), a two-dimensional graphene-derived material with a C2N stoichiometry and evenly distributed holes and nitrogen atoms in its basal plane, has recently been synthesized. We performed first principles calculations and molecular dynamics simulations to investigate mechanical and heat transport properties of this novel two-dimensional material at various temperatures. First principles calculations based on density functional theory yield an elastic modulus of 400 +/- 5 GPa at 0 K, 10% larger than predicted by molecular dynamics simulations at low temperatures. We observed an overall decreasing trend in elastic modulus and tensile strength as temperature increases. At room temperature, we found that NHG can present a remarkable elastic modulus of 335 +/- 5 GPa and tensile strength of 60 GPa. We also investigated the thermal conductivity of NHG via non-equilibrium molecular dynamics simulations. At 300 K an intrinsic thermal conductivity of 64.8 W/m-K was found, with an effective phonon mean free path of 34.0 nm, both of which are smaller than respective values for graphene, and decrease with temperature. Our modeling-based predictions should serve as guide to experiments concerning physical properties of this novel material.

cond-mat.mtrl-sci↗