arXiv subjects

Cleverson Filgueiras

Publications and source records attributed to Cleverson Filgueiras.

At least 19 recordsLinked to original sources

arXiv2026

A Unified Description of Dirac-Cone Anisotropies in Two Dimensions

Anisotropies in two-dimensional materials are responsible for a variety of effects that significantly modify their physical properties. In this paper, we present a covariant modification of the Dirac equation that incorporates anisotropies into the effective low-energy description around the Dirac point. The model is constructed by analogy with a Lorentz-violating extension of the Standard Model of elementary particles and yields a (2+1)-dimensional framework describing physical effects such as shifted, tilted, and distorted Dirac cones through its free parameters. The proposed model thus provides a general and unified framework in which distinct anisotropy-induced modifications of the Dirac spectrum and their combinations can be systematically characterized. We further apply the model to strained graphene and show that its effective parameters can be quantitatively extracted from first-principles electronic band structures while retaining a direct geometrical interpretation. These results establish a connection between the microscopic electronic structure and a material-independent effective description of anisotropic two-dimensional Dirac systems.

cond-mat.mes-hall↗

arXiv2025

Impact of the Sagnac Effect on Thermodynamic and Magnetocaloric Properties of a Rotating Two-Dimensional Electron Gas

This work investigates the impact of the Sagnac effect on the thermodynamic properties of a non-interacting two-dimensional electron gas (2DEG) in a rotating sample under the influence of a uniform magnetic field. We derive an analytical expression for the energy spectrum using an effective Hamiltonian that incorporates inertial forces, and then apply canonical ensemble statistical mechanics to evaluate thermodynamic quantities. The results show that rotation modifies the energy levels, the application of a magnetic field leads to the formation of Landau levels further altered by rotation and gravitational mass, and thermodynamic quantities (internal energy, specific heat, free energy, entropy, magnetization, and magnetocaloric effect) exhibit a strong dependence on these parameters. In particular, the difference between effective mass $m^*$ and gravitational mass $m_G$ influences magnetization and the magnetocaloric effect, with negative rotations potentially inducing a cooling effect when these masses are distinct. We conclude that rotational effects and effective mass properties are crucial for understanding the thermodynamics of electronic systems under magnetic fields, with implications for thermal modulation in semiconductor materials.

cond-mat.mes-hall↗

arXiv2025

Modifications in the photoionization cross-section of a quantum dot with position-dependent effective mass

In this work, we investigate the photoionization cross-section of an electron confined in a quantum dot, considering the position-dependent variation of the effective mass through the parameter $\gamma$. We used a theoretical model based on the Schr\"odinger equation, in which $\gamma$ influences the energy levels and wave functions through an effective potential obtained from the harmonic oscillator potential - which, in the limit $\gamma = 0$, reduces to the original harmonic oscillator potential. Furthermore, we compared the modifications in the photoionization cross-section of these quantum systems with the constant-mass case. Our results demonstrate that even a small variation in $\gamma$ significantly impacts the photoionization process's amplitude and peak position. We also found that for specific values of $\gamma$, an inversion occurs: The amplitude, which initially increases as the quantum dot absorbs the photon, begins to decrease. Additionally, we observed that the optical transitions involving the ground state restrict the admissible values of $\gamma$ to negative values only. These results may have relevant implications for designing optoelectronic devices based on quantum dots with adjustable mass properties.

cond-mat.mes-hall↗

arXiv2025

Innovative Designs and Insights into Quantum Thermal Machines

We present a comprehensive theoretical investigation about the operational regions of quantum systems, specifically examining their roles as working media functioning between two thermal reservoirs in Quantum Thermal Machines (QTMs). This study provides relevant and novel insights, including a complete spectrum of QTMs within the operational region of these quantum systems, and introduces new QTM designs never before described in the literature. Additionally, this work introduces a standardized and cohesive classification scheme for QTMs, ensuring robustness in nomenclature and operational distinctions, which enhances both theoretical understanding and practical application. Notably, one of these designs directly addresses the need for a more appropriate explanation of the operation of a laser (or maser) as a QTM. Initial calculations were performed to achieve results applicable to any quantum system subjected to rules analogous to those used in classical thermal machine studies. These results were then used to analyze two-level quantum systems as the working medium of QTMs in the Otton cycle. In particular, we analyzed two specific quantum systems: the laser and a spinless electron in a one-dimensional quantum ring, yielding consistent and innovative results. Overall, this study offers valuable insights into the operation and classification of QTMs, establishing a clear and unified framework for their nomenclature while opening new avenues for the design and enhancement of these devices.

quant-ph↗

arXiv2024

Nonlinear refractive index changes and absorption coefficients in mesoscopic ring induced by variable effective mass

This study explores the linear and nonlinear optical absorption coefficients (OAC) and refractive index changes (RIC) in quantum dot and quantum antidot systems with a position-dependent variable effective mass. Significant contributions to both linear and nonlinear OAC and RIC are observed. Our findings reveal that variations of the mass parameter modify the intersubband dipole matrix elements and energy intervals, leading to noticeable shifts in optical properties. The results show that higher {\gamma} values shift resonance peaks towards higher energies, while changes in the oscillator frequency result in abrupt shifts and peak diminutions. These insights provide a deeper understanding of the optical behaviors in the quantum systems under consideration, paving the way for designing devices with optimal efficiency

physics.optics↗

arXiv2024

Decoherence effects on local quantum Fisher information and quantum coherence in a spin-1/2 Ising-XYZ chain

This research explores the effects of decoherence on local quantum Fisher information and quantum coherence dynamics in a spin-1/2 Ising-XYZ chain model with independent reservoirs at zero temperature. Contrasting these effects with those in the spin-1/2 Heisenberg XYZ model reveals intricate interactions among quantum coherence, entanglement, and environmental decoherence in spin systems. Analysis of coherence dynamics highlights differences between the original and hybrid models, showcasing increased entanglement due to Ising interactions alongside reduced coherence from environmental redistribution. The local quantum Fisher information proves more resilient than coherence in specific scenarios, emphasizing decoherence is varying impacts on quantum correlations. This research underscores the complexity of quantum coherence dynamics and the crucial role of environmental factors in shaping quantum correlations, providing insights into entanglement and coherence behavior under environmental influences and guiding future studies in quantum information processing and correlation dynamics.

quant-ph↗

arXiv2023

Diamonds in Klein geometry

Recently it was suggested that the Unruh effect might occur in metamaterials at accessible Unruh temperatures. In some cases, the class of metamaterials that may be useful for this observation has a Klein instead of a Minkowski signature. Thus, confirmation of this effect in those materials requires more careful analysis. In this paper, we use the path integral formulation of Quantum Field Theory to investigate the analogous to the Unruh effect in Kleinian geometry. We calculate the analogous of the Unruh temperature for a scalar theory, provided we restrict the action in a convenient subspace of the Kleinian spacetime. As a consequence, we obtain the diamond temperature for a static observer with a finite lifetime. The result suggest metamaterials as a possible system to observe diamond regions.

hep-th↗

arXiv2023

Quantum heat machines enabled by twisted geometry

In this paper, we analyze the operation of an Otto cycle heat machine driven by a non-interacting two-dimensional electron gas on a twisted geometry. We show that due to both the energy quantization on this structure and the adiabatic transformation of the number of complete twists per unit length of a helicoid, the machine performance in terms of output work, efficiency, and operation mode can be altered. We consider the deformations as in a spring, which is either compressed or stretched from its resting position. The realization of classically inconceivable Otto machines with an incompressible sample can be realized as well. The energy-level spacing of the system is the quantity that is being either compressed or stretched. These features are due to the existence of an effective geometry-induced quantum potential which is of pure quantum-mechanical origin.

quant-ph↗

arXiv2023

Exact and approximate bound state solutions of the Schr\"odinger equation with a class of Kratzer-type potentials in the global monopole spacetime

This work investigates the motion of a non-relativistic charged particle within the spacetime of a global monopole. We introduce the Schr\"odinger equation to describe the particle's motion with two interactions by considering the Kratzer and the screened modified Kratzer potential. The problem's eigenfunctions and eigenvalues are obtained by deriving and solving the radial equation. The effective potential encompasses both the Kratzer and electrostatic self-interaction potential and leads to bound states solutions. The energy spectrum is investigated, particularly emphasizing its dependence on the system's physical parameters. The screened modified Kratzer potential and the screened self-interaction potential reveal an important role in influencing both the effective potential and the energy spectrum. Additionally, it also accommodates the existence of bound states. All these behaviors are illustrated with graphs and discussed in detail.

quant-ph↗

arXiv2023

Optical and electronic properties of a two-dimensional quantum ring under rotating effects

This work presents a study on the nonrelativistic quantum motion of a charged particle in a rotating frame, considering the Aharonov-Bohm effect and a uniform magnetic field. We derive the equation of motion and the corresponding radial equation to describe the system. The Schr\"odinger equation with minimal coupling incorporates rotation effects by substituting the momentum operator with an effective four-potential. Additionally, a radial potential term, dependent on the average radius of the ring, is introduced. The analysis is restricted to motion in a two-dimensional plane, neglecting the degree of freedom in the $z$-direction. By solving the radial equation, we determine the eigenvalues and eigenfunctions, allowing for an explicit expression of the energy. The probability distribution is analyzed for varying rotating parameter values, revealing a shift of the distribution as the rotation changes, resulting in a centrifugal effect and occupation of the ring's edges. Furthermore, numerical analysis demonstrates the significant rotational effects on energy levels and optical properties, including optical absorption and refractive coefficients.

cond-mat.mes-hall↗

arXiv2021

Two Coupled Double Quantum Dots Systems as an working substance for Heat Machines

This paper presents a conceptual design for quantum heat machines using a pair of coupled double quantum dots (DQDs), each DQD with an excess electron to interact, as an working substance. We define a compression ratio as the ratio between the Coulomb couplings which describes the interaction between the electrons during the isochoric processes of the quantum Otto cycle and then we analyse the arising of different regimes of operations of our thermal machine. We also show how we can achieve a classically inconceivable Otto engine, when considering the effects due to the parameters related to the quantum tunneling of a single electron between each individual DQD.

quant-ph↗

arXiv2020

Thermal entanglement and correlated coherence in two coupled double quantum dots systems

In this work, we investigate the thermal quantum correlations in two coupled double semiconductor charge qubits. This is carried out by deriving analytical expressions for both the thermal concurrence and the correlated coherence. We study, in detail, the effects of the tunneling parameters, the Coulomb interaction and the temperature on the thermal entanglement and on the correlated coherence. It is found that the Coulomb potential plays an important role in the thermal entanglement and in the correlated coherence of the system. The results also indicate that the Coulomb potential can be used for significant enhancement of the thermal entanglement and quantum coherence. One interesting aspect is that the correlated coherence capture all the thermal entanglement at low temperatures, i.e, the local coherences are totally transferred to the thermal entanglement. Finally, we focus on the role played by thermal entanglement and the correlated coherence responsible for quantum correlations. We show that in all cases, the correlated coherence is more robust than the thermal entanglement so that quantum algorithms based only on correlated coherence may be more robust than those based on entanglement. Our results also show that the entanglement can be tuned by varying the Coulomb interaction between electrons.

quant-ph↗

arXiv2020

Quantum particle motion on the surface of a helicoid in the presence of harmonic oscillator

The geometric potential in quantum mechanics has been attracted attention recently, providing a formalism to investigate the influence of curvature in the context of low-dimensional systems. In this paper, we study the consequences of a helicoidal geometry in the Schrödinger equation dealing with an anisotropic mass tensor. In particular, we solve the problem of an harmonic oscillator in this scenario. We determine the eigenfunctions in terms of Confluent Heun Functions and compute the respective energy levels. The system exhibit several different behaviors, depending on the adjustment on the mass components.

quant-ph↗

arXiv2020

Study of electronic properties, Magnetization and persistent currents in a mesoscopic ring by controlled curvature

We study the model of a noninteracting spinless electron gas confined to the two-dimensional localized surface of a cone in the presence of external magnetic fields. The localized region is characterized by an annular radial potential. We write the Schrödinger equation and use the thin-layer quantization procedure to calculate the wavefunctions and the energy spectrum. In such a procedure, it arises a geometry induced potential, which depends on both the mean and the Gaussian curvatures. Nevertheless, since we consider a ring with a mesoscopic size, the effects of the Gaussian curvature on the energy spectrum are negligible. The magnetization and the persistent current are analyzed. In the former, we observed the Aharonov-Bohm (AB) and de Haas-van Alphen (dHvA) types oscillations. In the latter, it is observed only the AB type oscillations. In both cases, the curvature increases the amplitude of the oscillations.

cond-mat.mes-hall↗

arXiv2019

Quantum motion of a spinless particle in curved space: A viewpoint of scattering theory

In this work, we study the scattering of a spinless charged particle constrained to move on a curved surface in the presence of the Aharonov-Bohm potential. We begin with the equations of motion for the surface and transverse dynamics previously obtained in the literature (Ferrari G. and Cuoghi G., Phys. Rev. Lett. \textbf{100}, 230403 (2008)) and describe the surface with non-trivial curvature in terms of linear defects such as dislocations and disclinations. Expressions for the modified phase shift, S--matrix and scattering amplitude are determined by applying a suitable boundary condition at the origin, which comes from the self-adjoint extension theory. We also discuss the presence of a bound state obtained from the pole of the S--matrix. Finally, we claim that the bound state, the additional scattering and the dependence of the scattering amplitude with energy are solely due to the curvature effects.

quant-ph↗

arXiv2019

Effects of curvature on the electronic states of a two-dimensional mesoscopic ring

The effects of surface curvature on the motion of electrons in a mesoscopic two-dimensional ring on a cone in the presence of external magnetic fields are examined. The approach follows the thin-layer quantization procedure, which gives rise to a geometry induced potential. Due to the annular geometric shape of the sample, only the mean curvature has relevant effects to the model. Nevertheless, the most significant contribution of the mean curvature occurs in the state $m=0$, which tends to decrease the energies when the magnetic field is null. The effects of curvature are also manifested in the cyclotron frequency as well as in the effective angular momentum through the $α$ parameter, which can be controlled in such a way that the magnitude of these effects becomes explicit. This is verified in the energies and wave functions of the system. A decrease in the number of occupied states in the Fermi energy is observed. As a consequence, there is an alteration in the radial range of the conducting region of the sample. This fact is confirmed by studying the variations in the radii of the states.

cond-mat.mes-hall↗

arXiv2019

On the effects of an impurity in an Ising-$XXZ$ diamond chain on the thermal entanglement, on the quantum coherence and on the quantum teleportation

The effects of an impurity plaquette on the thermal quantum correlations measurement by the concurrence, on the quantum coherence quantified by the recently proposed $l_{1}$-norm of coherence and on the quantum teleportation in a Ising-$XXZ$ diamond chain are discussed. Such an impurity is formed by the XXZ interaction between the interstitial Heisenberg dimers and the nearest-neighbor Ising coupling between the nodal and interstitial spins. All the interaction parameters are different from those of the rest of the chain. By tailoring them, the quantum entanglement and quantum coherence can be controlled and tuned. Therefore, the quantum resources -- thermal entanglement and quantum coherence -- of the model exhibit a clear performance improvement in comparison to the original model without impurities. We also demonstrate that the quantum teleportation can be tuned by its inclusion. The thermal teleportation is modified in significant way as well, and a strong increase in average fidelity is observed. We furnish the exact solution by the use of the transfer-matrix method.

quant-ph↗

arXiv2019

Quantum heat machines enabled by the electronic effective mass

In this letter, we analyze a conceptual design for the operation of an Otto cycle heat machine driven by adiabatic modifications on the electronic effective mass. Such tailoring of it can be implemented, for instance, via the application of external electron fields in some materials, as in Gallium Nitride (GaN). We show that due both the energy quantization on this structure and the adiabatic transformation of the effective mass, the machine performance can be improved. The realization of classically inconceivable Otto machines, with an incompressible working substance, can be realized as well. Our finds hold in cases where the electronic effective mass, in the low temperature regime, remains constant during the isochoric strokes.

quant-ph↗