arXiv subjects

Denise Assafrão

Publications and source records attributed to Denise Assafrão.

5 recordsLinked to original sources

arXiv2026

Topological control of third-harmonic generation in a mesoscopic quantum ring with spiral dislocation

We investigate the nonlinear optical response of a two-dimensional mesoscopic quantum ring subjected to a spiral dislocation, with emphasis on third-harmonic generation (THG). The topological defect is modeled through a torsion-induced deformation of space, which modifies the effective metric without introducing curvature. By combining the minimal-coupling prescription in curved space with a radial ring confinement and a perpendicular magnetic field, we derive the effective radial Schrödinger problem, obtain the bound states, and evaluate the nonlinear susceptibilities within the electric-dipole approximation. We show that the axial symmetry of the topologically deformed ring preserves the dipole selection rule $Δm=\pm 1$ and therefore suppresses second-harmonic generation, while THG remains allowed through multistep transition chains. The study is further expanded through three complementary analyses that can be implemented without changing the Hamiltonian: a dephasing-controlled study of spectral resolution, three-dimensional waterfall spectra showing the dependence on $β$ and $B$, and a channel-resolved decomposition of the THG amplitude. Together, these results establish the spiral dislocation as a robust geometric knob for tuning nonlinear optical activity in mesoscopic ring-shaped nanostructures.

cond-mat.mes-hall↗

arXiv2025

Single-Scale Magnetoelastic Landau Quantization: Thermodynamics, Quantum Oscillations, and Metrology

We develop a unified, single-scale description of thermodynamics and quantum oscillations in electronic systems with a uniform areal density of screw dislocations under a uniform magnetic field. A single tunable gap, $\hbar|ω_{eff}|$ with $ω_{eff}=ω_{c}+ω_{cl}$, organizes all equilibrium observables obtained from a compact harmonic-oscillator partition function: free energy, internal energy, entropy, heat capacity, magnetization, magnetic susceptibility, and magnetocaloric responses collapse onto universal hyperbolic kernels in $x=\hbar|ω_{eff}|/(2k_{B}T)$. We identify a compensated-field regime where the transverse gap closes and the heat capacity reaches an equipartition plateau, providing a sharp signature of magnetoelastic interference. In transport and torque, the same scale rigidly shifts the Hall fan and compresses the $1/B$ period of de Haas-van Alphen and Shubnikov-de Haas oscillations when expressed in $1/B_{eff}$, enabling a phase-unwarping protocol that metrologizes the dislocation density from a single field sweep. In mesoscopic samples, boundary corrections to the Landau degeneracy generate finite-size calorimetric oscillations that diagnose the effective magnetic length. Moderate disorder and weak interactions preserve the kernel structure while smoothing amplitudes. We outline an experimental roadmap combining on-chip calorimetry, torque magnetometry, and transport, and discuss device-level opportunities in caloritronics and strain engineering, magnetocaloric microcooling, magnetoelastic heat switching, and dilatometric transduction, where the single scale $\hbar|ω_{eff}|$ enables rational design and optimization.

cond-mat.mes-hall↗

arXiv2025

Rotating effects on the Hall conductivity in a quantum dot

We investigate the behavior of the quantized Hall conductivity in a two-dimensional quantum system under rotating effects, a uniform magnetic field, and an Aharonov-Bohm (AB) flux tube. By varying the angular velocity and the AB flux, we analyze their impact on the formation, shifting, and structure of quantized Hall plateaus. Our results reveal that rotation modifies the energy spectrum, leading to slight shifts in the plateau positions and variations in their widths. Additionally, we identify Aharonov-Bohm-type oscillations in $σ_{\text{Hall}}$, which become more pronounced for lower values of the cyclotron frequency $ω_c$, indicating enhanced quantum interference effects in the low-field regime. These oscillations are further modulated by $Ω$, affecting their periodicity and amplitude. The interplay between the confinement frequency $ω_0$, the cyclotron frequency $ω_c$, and the rotational effects plays a crucial role in determining the overall behavior of $σ_{\text{Hall}}$. Our findings provide insights into the interplay between rotation, magnetic field, and quantum interference effects, which are relevant for experimental investigations of quantum Hall systems in rotating systems.

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 $γ$. We used a theoretical model based on the Schrödinger equation, in which $γ$ influences the energy levels and wave functions through an effective potential obtained from the harmonic oscillator potential - which, in the limit $γ= 0$, 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 $γ$ significantly impacts the photoionization process's amplitude and peak position. We also found that for specific values of $γ$, 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 $γ$ 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↗

arXiv2016

Effects of quantum deformation on the integer quantum Hall effect

In this work an application of the $κ$--deformed algebra in condensed matter physics is presented. Starting by the $κ$--deformed Dirac equation we study the relativistic generalization of the $κ$--deformed Landau levels as well as the consequences of the deformation on the Hall conductivity. By comparing the $κ$--deformed Landau levels in the nonrelativistic regime with the energy levels of a two-dimensional electron gas (2DEG) in the presence of a normal magnetic field, upper bounds for the deformation parameter in different materials are established. An expression for the $κ$--deformed Hall conductivity of a 2DEG is obtained as well. The expression recovers the well-known result for the usual Hall conductivity in the limit $\varepsilon=κ^{-1}\to 0$. The deformation parameter breaks the Landau levels degeneracy and due to this, it is observed that deformation gives rise to new plateaus of conductivity in a such way that the plateaus widths of the $κ$--deformed Hall conductivity are less than the usual one. By studying the temperature dependence of the $κ$--deformed Hall conductivity, we show that an increase of the temperature causes the smearing of the plateaus and a diminution of the effect of the deformation, whilst an increase in the magnetic field enhances the effect of the deformation.

hep-th↗