arXiv subjects

Andre M. C. Souza

Publications and source records attributed to Andre M. C. Souza.

At least 19 recordsLinked to original sources

arXiv2026

Chesapeake Bay Food Web: Robustness Analysis via Energy Cutoff in Complex Networks

The Chesapeake Bay, one of the largest estuaries in the United States, is an ecological system of great complexity and relevance. The food web is composed of thirty-six trophic components, all of which are functionally connected. In this work, the interactions among these components are numerically analyzed using complex network methods. An energy flow cutoff paradigm is applied to a weighted ecological network. The results reveal patterns characteristic of connectivity dynamics, evidencing both the initial robustness of the system and its tendency to fragmentation at higher values of the cutoff. From an applied perspective, the findings underscore the importance of conservation strategies that protect keystone species, such as carnivorous fish, which act as crucial connectors between the two main subnetworks. Although they are positioned at the top of the food web and are often assumed to be less critical to network stability, these species play a pivotal role in regulating populations of lower-level organisms, thereby maintaining the overall integrity of the ecosystem.

physics.bio-ph↗

arXiv2023

Topological speckles

The time evolution of a topological Su-Schrieffer-Heeger chain is analyzed through the statistics of speckle patterns. The emergence of topological edge states dramatically affects the dynamical fluctuations of the wavefunction. The intensity statistics is found to be described by a family of noncentral chi-squared distributions, with the noncentrality parameter reflecting on the degree of edge-state localization. The response of the speckle contrast with respect to the dimerization of the chain is explored in detail as well as the role of chiral symmetry-breaking disorder, number of edge states, their energy gap, and the locations between which the transport occurs. In addition to providing a venue for speckle customization, our results appeal to the use of speckle patterns for characterization of nontrivial topological properties.

physics.optics↗

arXiv2022

Fractality in tumor growth at the avascular stage from a generalization of the logistic-Gompertz dynamics

The dynamics between healthy and malignant cells at the avascular stage of growth is described by a set of chemical reactions representing the populations of both types of cells. We obtain a generalization of the logistic-Gompertz dynamics and study the consequences in terms of the properties of tumor growth associated with the Warburg effect, mitosis and nutrient and space apoptosis. As a result of the stochastic nature of this process, a fractal morphology is observed in this region. Our results agree with experimental results for growth of tumor cell colonies.

physics.bio-ph↗

arXiv2019

Localization properties of a two-channel 3D Anderson model

We study two coupled 3D lattices, one of them featuring uncorrelated on-site disorder and the other one being fully ordered, and analyze how the interlattice hopping affects the localization-delocalization transition of the former and how the latter responds to it. We find that moderate hopping pushes down the critical disorder strength for the disordered channel throughout the entire spectrum compared to the usual phase diagram for the 3D Anderson model. In that case, the ordered channel begins to feature an effective disorder also leading to the emergence of mobility edges but with higher associated critical disorder values. Both channels become pretty much alike as their hopping strength is further increased, as expected. We also consider the case of two disordered components and show that in the presence of certain correlations among the parameters of both lattices, one obtains a disorder-free channel decoupled from the rest of the system.

cond-mat.dis-nn↗

arXiv2018

Disorder-safe entanglement transfer through ladder qubit chains

We study an entanglement transfer protocol in a two-leg ladder spin-1/2 chain in the presence of disorder. In the regime where on-site energies and the intrachain couplings follow aproximately constant proportions locally, we set up a scheme for high-fidelity state transfer via a disorder-protected subspace wherein fluctuations in the parameters do not depend on the global disorder of the system, accounted by $W$. Moreover, we find that the leakage of information from that subspace is actually suppressed upon increasing $W$ and thus the transfer fidelity, evaluated through the entanglement concurrence at the other end of the chain, builds up with the disorder strength.

quant-ph↗

arXiv2018

Coexistence of extended and localized states in one-dimensional systems

Mobility edge transitions from localized to extended states have been observed in two and three dimensional systems, for which sound theoretical explanations have also been derived. One-dimensional lattice models have failed to predict their emergence, offering no clues on how to actually probe this phenomenon in lower dimensions. This work reports results for a class of tight-binding models with electron-mass position dependence, for which localized-extended wave function transitions can be identified. We show that it is possible to control the density of localized and extended states by tuning the transition-related parameter for a continuous range of energy values. Mathematically exact results for extended or localized states are derived in two extreme conditions of this parameter, as well as an exact energy value for the mobility edge transition in the intermediate regime. Our framework provides a clear point of view on the phenomena and can also be harnessed for setting up experiments to probe to precisely evaluate the associated mobility edges using state-of-the-art technology.

quant-ph↗

arXiv2018

Noncommutative quantum Hall effect in graphene

We discuss the quantum Hall effect on a single-layer graphene in the framework of noncommutative (NC) phase space. We find it induces a shift in the Hall resistivity. Furthermore, comparison with experimental data reveals an upper bound on the magnitude of the momentum NC parameter $η$ in about $\sqrtη\leq 2.5 \, \mathrm{eV}/c$.

hep-th↗

arXiv2017

Thermodynamic Framework for Compact q-Gaussian Distributions

Recent works have associated systems of particles, characterized by short-range repulsive interactions and evolving under overdamped motion, to a nonlinear Fokker-Planck equation within the class of nonextensive statistical mechanics, with a nonlinear diffusion contribution whose exponent is given by $ν=2-q$. The particular case $ν=2$ applies to interacting vortices in type-II superconductors, whereas $ν>2$ covers systems of particles characterized by short-range power-law interactions, where correlations among particles are taken into account. In the former case, several studies presented a consistent thermodynamic framework based on the definition of an effective temperature $θ$ (presenting experimental values much higher than typical room temperatures $T$, so that thermal noise could be neglected), conjugated to a generalized entropy $s_ν$ (with $ν=2$). Herein, the whole thermodynamic scheme is revisited and extended to systems of particles interacting repulsively, through short-ranged potentials, described by an entropy $s_ν$, with $ν>1$, covering the $ν=2$ (vortices in type-II superconductors) and $ν>2$ (short-range power-law interactions) physical examples. The main results achieved are: (a) The definition of an effective temperature $θ$ conjugated to the entropy $s_ν$; (b) The construction of a Carnot cycle, whose efficiency is shown to be $η=1-(θ_2/θ_1)$, where $θ_1$ and $θ_2$ are the effective temperatures associated with two isothermal transformations, with $θ_1>θ_2$; (c) Thermodynamic potentials, Maxwell relations, and response functions. The present thermodynamic framework, for a system of interacting particles under the above-mentioned conditions, and associated to an entropy $s_ν$, with $ν>1$, certainly enlarges the possibility of experimental verifications.

cond-mat.stat-mech↗

arXiv2017

Entanglement can preserve the compact nature of the phase-space occupancy

We study the one-dimensional transverse-field spin-1/2 Ising ferromagnet at its critical point. We consider an $L$-sized subsystem of a $N$-sized ring, and trace over the states of $(N-L)$ spins, with $N\to\infty$. The full $N$-system is in a pure state, but the $L$-system is in a statistical mixture. As well known, for $L >>1$, the Boltzmann-Gibbs-von Neumann entropy violates thermodynamical extensivity, namely $S_{BG}(L) \propto \log L$, whereas the nonadditive entropy $S_q$ is extensive for $q=q_c=\sqrt{37}-6 $, namely $S_{q_c}(L) \propto L$. When this problem is expressed in terms of independent fermions, we show that the usual thermostatistical sums emerging within Fermi-Dirac statistics can, for $L>>1$, be indistinctively taken up to $L$ terms or up to $\log L$ terms. This is interpreted as a compact occupancy of phase-space of the $L$-system, hence standard BG quantities with an effective length $V \equiv \log L$ are appropriate and are explicitly calculated. In other words, the calculations are to be done in a phase-space whose effective dimension is $2^{\log L}$ instead of $2^L$. The whole scenario is strongly reminiscent of a usual phase transition of a spin-1/2 $d$-dimensional system, where the phase-space dimension is $2^{L^d}$ in the disordered phase, and effectively $2^{L^d/2}$ in the ordered one.

cond-mat.stat-mech↗

arXiv2017

Noncommutative Brownian motion

We investigate the classical Brownian motion of a particle in a two-dimensional noncommutative (NC) space. Using the standard NC algebra embodied by the sympletic Weyl-Moyal formalism we find that noncommutativity induces a non-vanishing correlation between both coordinates at different times. The effect stands out as a signature of spatial noncommutativity and thus could offer a way to experimentally detect the phenomena. We further discuss some limiting scenarios and the trade-off between the scale imposed by the NC structure and the parameters of the Brownian motion itself.

hep-th↗

arXiv2016

Quantum-state transfer in staggered coupled-cavity arrays

We consider a coupled-cavity array, where each cavity interacts with an atom under the rotating-wave approximation. For a staggered pattern of inter-cavity couplings, a pair of field normal modes each bi-localized at the two array ends arise. A rich structure of dynamical regimes can hence be addressed depending on which resonance condition between the atom and field modes is set. We show that this can be harnessed to carry out high-fidelity quantum-state transfer (QST) of photonic, atomic or polaritonic states. Moreover, by partitioning the array into coupled modules of smaller length, the QST time can be substantially shortened without significantly affecting the fidelity.

quant-ph↗

arXiv2014

Anderson localization on the Falicov-Kimball model with Coulomb disorder

The role of Coulomb disorder is analysed in the Anderson-Falicov-Kimball model. Phase diagrams of correlated and disordered electron systems are calculated within dynamical mean-field theory applied to the Bethe lattice, in which metal-insulator transitions led by structural and Coulomb disorders and correlation can be identified. Metallic, Mott insulator, and Anderson insulator phases, as well as the crossover between them are studied in this perspective. We show that Coulomb disorder has a relevant role in the phase-transition behavior as the system is led towards the insulator regime.

cond-mat.str-el↗

arXiv2010

Describing the ground state of quantum systems through statistical mechanics

We present a statistical mechanics description to study the ground state of quantum systems. In this approach, averages for the complete system are calculated over the non-interacting energy levels. Taking different interaction parameter, the particles of the system fall into non-interacting microstates, corresponding to different occupation probabilities for these energy levels. Using this novel thermodynamic interpretation we study the Hubbard model for the case of two electrons in two sites and for the half-filled band on a one-dimensional lattice. We show that the form of the entropy depends on the specific system considered.

cond-mat.stat-mech↗

arXiv2009

Thermal entanglement witness for materials with variable local spin lengths

We show that the thermal entanglement in a spin system using only magnetic susceptibility measurements is restricted to the insulator materials. We develop a generalization of the thermal entanglement witness that allows us to get information about the system entanglement with variable local spin lengths that can be used experimentally in conductor or insulator materials. As an application, we study thermal entanglement for the half-filled Hubbard model for linear, square and cubic clusters. We note that it is the itinerancy of electrons that favors the entanglement. Our results suggest a weak dependence between entanglement and external spin freedom degrees.

quant-ph↗

arXiv2008

Hölder mean applied to Anderson localization

The phase diagram of correlated, disordered electron systems is calculated within dynamical mean-field theory using the Hölder mean local density of states. A critical disorder strength is determined in the Anderson-Falicov-Kimball model and the arithmetically and the geometrically averages are found to be just particular means used respectively to detect or not the Anderson localization. Correlated metal, Mott insulator and Anderson insulator phases, as well as coexistence and crossover regimes are analyzed in this new perspective.

cond-mat.str-el↗

arXiv2007

Local electronic properties in nanoscale systems

The local electronic structure on nanoscale chains is investigated theoretically. We propose a mechanism to explain the even-odd oscillation of length distribution of atom chains. We study the spatial peak structure as obtained by scanning tunneling microscopy (STM) constant-current topography as a function of the electron-electron interaction, band filling and temperature. The site-dependent magnetic moment is also examined.

cond-mat.str-el↗

arXiv2006

A simple model for magnetism in itinerant electron systems

A new lattice model of interacting electrons is presented. It can be viewed as a classical Hubbard model in which the energy associated to electron itinerance is proportional to the total number of possible electron jumps. Symmetry properties of the Hubbard model are preserved. In the half-filled band with strong interaction the model becomes the Ising model. The main features of the magnetic behavior of the model in the one-dimensional and mean-field cases are studied.

cond-mat.stat-mech↗

arXiv2006

Correlated electrons systems on the Apollonian network

Strongly correlated electrons on an Apollonian network are studied using the Hubbard model. Ground-state and thermodynamic properties, including specific heat, magnetic susceptibility, spin-spin correlation function, double occupancy and one-electron transfer, are evaluated applying direct diagonalization and quantum Monte Carlo. The results support several types of magnetic behavior. In the strong-coupling limit, the quantum anisotropic spin 1/2 Heisenberg model is used and the phase diagram is discussed using the renormalization group method. For ferromagnetic coupling, we always observe the existence of long-range order. For antiferromagnetic coupling, we find a paramagnetic phase for all finite temperatures.

cond-mat.str-el↗