arXiv subjects

Nguyen Duy Vy

Publications and source records attributed to Nguyen Duy Vy.

14 recordsLinked to original sources

arXiv2026

A general recursion for integrals involving products of Hermite polynomials and its applications

This study presents the derivation of a recursive formula for integrals of products of $N$ Hermite polynomials, establishing a numerically stable scheme for their accurate evaluation in computer codes. The derivation is notably simple and leverages solely the well-established properties of Hermite polynomials and the method of integration by parts. Importantly, our formulation completely circumvents explicit factorials, thereby preventing potential numerical instabilities and overflows, while facilitating high-precision computations for large indices. These findings are of significant relevance to a variety of areas in physics and mathematics. In particular, they offer an efficient and accurate framework for calculating two- and three-body matrix elements in ab initio simulations of few-body systems under a 1D harmonic confinement using the Configuration Interactions approach. A numerical subroutine implementing the recursive formula is provided as supplemental material.

quant-ph↗

arXiv2025

Revealing Modeshape Complexity and Sensitivity in Torsional Vibrations of Microcantilevers with Overhang- and T-shaped Geometries

The torsional vibration of atomic force microscope (AFM) cantilevers is critical for high-sensitivity measurements, yet existing models for width-varying cantilevers often rely on approximations that lead to significant discrepancies with experimental data. Unlike prior studies, this work introduces a refined analytical framework to precisely compute resonance frequencies and mode shapes, including higher-order modes, for overhang- and T-shaped microcantilevers, validated through targeted experimental comparisons. By systematically analyzing the effects of overhang length, we reveal previously unreported multi-maxima mode shapes and demonstrate how geometric tuning can controllably shift resonant frequencies. Furthermore, we establish a quantitative relationship between modal sensitivity and cantilever-surface coupling strength, providing actionable design principles for optimizing AFM cantilever performance. Our results not only reconcile theoretical predictions with experimental observations but also offer practical guidelines for tailoring cantilever geometry to achieve specific frequency responses in applications such as nanomechanical imaging and surface property mapping. This work advances the design of next-generation AFM probes by bridging the gap between analytical models and real-world operational demands.

physics.app-ph↗

arXiv2025

Optical absorption of a Cu$_2$SnS$_3$ (CTS) layer trapped by metallic thin films in multilayer configuration

Coating and reflecting thin films for energy harvesting purposes are interesting topics in both theoretical and experimental research. The thin film could help to enhance the absorption of the system via its specific optical properties depending on the optical wavelength and the stacked layer thickness. Here, by using Maxwell's equations for the electromagnetic fields penetrating thin films, we examined in detail the absorption of a CTS layer coated by nanometer-thick thin films of several materials, Au, Ag, Cu, Al, and figured out the optimal thickness range for the outer layers of the solar cell to optimize thermal energy harvesting from the light. In particular, the absorption has been shown to be significantly enhanced thanks to the optical cavity effect, and the maximal absorption of the system could reach 60\% for ... These results could help in suitably choosing the detailed thickness for the structure of the solar cell and other energy harvesting objects.

physics.optics↗

arXiv2025

Effect of screening on Seebeck coefficient in bilayer graphene/AlGaAs electron gas

The knowledge of Seebeck coefficient is a key factor in optimization of thermoelectric materials and finding right applications for it. A high sensitivity to structural change makes thermopower measurements an excellent technique for the study on the charge transport properties of a given material. The phonondrag term dominates at low temperature in the Seebeck coefficient This study examines the temperaturedependent screening effect on the phonondraginduced Seebeck coefficient S^g in a bilayer graphene- BLG-AlGaAs-quasi-twodimensional electron gas (q2DEG) system at the temperature below 50 K. The BLG layer interacts with both deformation potential acoustic phonons and stronger piezoelectric field acoustic phonons from AlGaAs/GaAs. We compare the electronphonon interactions in BLG with and without screening by q2DEG. The screening effect reduces particularly at low temperatures and shows a strong dependence on the carrier density in the BLG layer. The doublelayer screening function increases with layer separation d paralleling the monolayer screening at large d. Additionally varying the GaAs quantum well width reveals that increases with width less than 100 Åunder doublelayer screening but remains unchanged beyond this threshold while monolayer screening decreases as the width increases. Both screening functions enhance when the BLG carrier density is lower than that of q2DEG though the magnitude difference between them is minimal

cond-mat.mes-hall↗

arXiv2025

Dielectric Substrate Dependence of Thermoelectric Transport in BLG-GaAs-BLG Heterostructures

We theoretically study the thermoelectric transport S in a double-layer bilayer graphene (BLG-GaAs-BLG) system on dielectric substrates (h-BN, Al2O3, HfO2). Electrons interact with GaAs acoustic phonons via both the deformation potential (acDP) and piezoelectric (acPE) scattering. Results show that piezoelectric scattering dominates the total transport, especially at low carrier density and high dielectric constant. Substrate dielectric constant significantly influences thermopower S, and the thermopower of the materials is in the order of HfO2 > Al2O3 > h-BN. When densities on two BLG layers are unequal, the contribution from acDP scattering Sd decreases (increases) at low (high) densities versus equal densities, while acPE scattering Sg remains stable, making S largely Sg-dependent. Increasing interlayer distance d enhances S, while higher temperature boosts Sd (notably at low densities) with minimal effect on Sg. These insights and substrate-dependent trends demonstrate substrate engineering as a key parameter for optimizing BLG thermoelectric devices

cond-mat.mes-hall↗

arXiv2025

Significant Mobility Enhancement in Coupled AlGaN/GaN Quantum Wells considering Inter-Well Distance and Asymmetric Widths

We demonstrate that coupled AlGaN/GaN quantum wells with asymmetric widths ($L_1-L_2<30 $ A achieve up to 4.5 times higher mobility than single wells at optimal separation (d = 100 A). Crucially, mobility surpasses single wells when d>40 A reversing the trend at smaller distances. This enhancement stems from double-layer screening that suppresses remote/background impurities and dislocations, while LO phonon scattering remains unaffected. For identical wells, coupled systems underperform single wells at d<40 A but exceed them beyond this threshold. Peak gains occur at cryogenic temperatures (77 K). Our results provide a robust theoretical framework to optimize mobility in AlGaN/GaN heterostructures, reducing experimental trial-and-error in quantum device engineering.

cond-mat.mes-hall↗

arXiv2025

Competition between heating and cooling effects in an optomechanical oscillator using a squeezed field

Squeezed light is a useful phenomenon that can be exploited to improve the sensitivity of specific classes of detectors based on optomechanical effects. Recently, there has been significant interest in the potential application of a squeezed field in the cooling of an optomechanical oscillator. It has been shown that this field could cool an oscillator below the standard limit of a coherent field. In this study, the effect of squeezed light was evaluated by explicitly examining the role of the squeezing parameters on the final effective temperature of the oscillator. The results show that the observed cooling and heating effects are strongly dependent on the squeezing parameters and the phase. Using an oscillator of 2$π\times$10.1 MHz driven by a 1064-nm laser, the lowest effective temperature and quantum number are three orders of magnitude smaller compared to the case of no squeezing; especially, these minimum values are obtained at the squeezing phase of about 0.8$π$. This study highlighted important insights for the optimization of cooling efficiency using squeezed light.

quant-ph↗

arXiv2025

Tuning the flexural frequency of overhang-/T-shaped microcantilevers for high harmonics

High-harmonic (HH) frequencies in microcantilever impose several applications in precision detection thanks to the higher sensitivity of the higher modes in comparison to the fundamental modes. In this study, we showed that by tuning the cantilever length via changing the clamped position, the dimensional ratio of the overhang to the main cantilever part is altered and the HHs could be effectively obtained. Multiple HH frequencies have been achieved, from 4th to 8th order of the second- and from 11th to 26th order of the third-mechanical mode versus the first mode, and these orders are much higher if higher modes are used. The analytical calculation is in agreement with available results of other groups. HH behavior when the cantilever is interaction with sample is also examined and is strongly depending on the overhang parameters. These results could guide the experimentalist in the tuning and controlling of the HHs in detecting objects.

physics.app-ph↗

arXiv2025

Tuning the lasing threshold of quantum well exciton-polaritons under a magnetic field in Faraday geometry: a theoretical study

Polariton lasing is a promising phenomenon with potential applications in next-generation lasers that operate without the need for population inversion. Applying a perpendicular magnetic field to a quantum well (QW) significantly alters the properties of exciton-polaritons. In this theoretical study, we investigate how the lasing threshold of QW exciton-polaritons depends on the magnetic field. By modifying the exciton's effective mass and Rabi splitting, the magnetic field induces notable changes in the relaxation kinetics, which directly affect the lasing threshold. For low-energy pumping, an increase in the magnetic field delays the lasing threshold, while for high-energy pumping, the threshold is reached at much lower pump intensities. Furthermore, increasing both the pump energy and the magnetic field enhances relaxation efficiency, leading to a substantially larger number of condensed polaritons. Our result gives insights into the modulation of exciton-polariton condensation through magnetic fields, with potential implications for the design of low-threshold polariton lasers.

cond-mat.mes-hall↗

arXiv2025

Significant Enhancement of Carrier Mobility in Finite vs. Infinite Square Quantum Wells: A Comparative Study of GaAs/In$_x$Ga$_{1-x}$As/GaAs Heterostructures

The geometry of quantum wells (QWs) critically influences carrier mobility, yet systematic comparisons between finite and infinite square QWs remain scarce. We present a comprehensive study of GaAs/In$_x$Ga$_{1-x}$As/GaAs heterostructures using a variational-subband-wave-function model, analyzing key scattering mechanisms: remote impurities (RI), alloy disorder (AD), surface roughness (SR), acoustic (ac) and piezoelectric (PE) phonons, and longitudinal optical (LO) phonons. The mobility ratio $R=μ_{fin}/μ_{inf}$ reveals distinct trends: $R_{RI}$ and $R_{LO}<$ 1 (long-range Coulomb/inelastic scattering), while $R_{AD}$, $R_{ac}$, $R_{PE}$, $R_{SR}>$ 1 (static potentials). Finite QWs achieve higher mobility at low temperatures (77 K), narrow widths ($<$ 100 Å), and low densities, enhanced by high indium content. Conversely, infinite QWs outperform at 300 K due to dominant LO scattering. These findings provide actionable guidelines for optimizing QW-based devices such as HEMTs and lasers across operational regimes.

cond-mat.mes-hall↗

arXiv2025

Effect of linear and quadratic coupling on dynamical parameters of an optomechanical oscillator

Dynamics of icrocantilevers are of important interest in micro-mechanical systems for enhancing the functionality and applicable range of the cantilevers in vibration transducing and highly sensitive measurement. In this study, using the semi-classical Hamiltonian formalism, we study in detail the modification of the mechanical frequency and damping rate taking into account both the linear and quadratic coupling between the mechanical oscillator and the laser field in an opto-mechanical system. It has been seen that, the linear coupling greatly enhances the modification of the effective mechanical frequency and the effective damping rate while the quadratic coupling reduces these quantities. For a MHz-frequency oscillator, the damping rate could be 10^5 times increased and the frequency is several times modified. These results help clarifying the origin of the modification of the susceptibility function for cooling of the mechanical mode

quant-ph↗

arXiv2024

Impact of cut-off frequency effect on resonance energy transfer and Casimir-Polder interaction

Using the Green's function approach, we investigate the resonance energy transfer (RET) rate between two parallel, identical two-level atoms in the presence of three types of cylindrical system: a distributed Bragg reflector (DBR), a perfectly reflecting wall (PRW), and a two-layer silicon fiber. Our analysis, incorporating the cut-off frequency condition, reveals significant suppression of the RET rate for atoms positioned along the axis of the cylinder with the PRW. In contrast, for atoms located within the DBR, the RET rate is enhanced in the far zone. Additionally, we find that for atoms oriented radially are placed inside or near the surface of the silicon fiber, the RET rate is entirely inhibited. We also investigate the Casimir-Polder (CP) interaction between a cut-off-frequency DBR and an excited atom, discovering a fully attractive potential towards the surface for the atom within the waveguide.

physics.optics↗

arXiv2024

Effect of magnetic field on the Bose-Einstein condensation of quantum well exciton-polaritons

We theoretically investigate the nonlinear effects of a magnetic field on the relaxation process of exciton-polaritons toward Bose-Einstein condensation in GaAs quantum wells. Our study reveals that the modification of the exciton's effective mass, Rabi splitting, and dispersion significantly alters the relaxation rate of polaritons as they approach condensation. By employing a quasi-stationary pump, we clarify the dynamics of the total and condensed polariton populations in response to varying magnetic field strengths. Notably, we demonstrate that under low-energy pumping conditions, the presence of a magnetic field significantly suppresses condensation. This suppression is attributed to the decreased scattering rate between energy levels, which is a consequence of the reduced steepness in the high-energy dispersion. Conversely, increasing both the pump energy and the magnetic field can enhance relaxation efficiency, leading to a substantially larger number of condensed polaritons.

quant-ph↗

arXiv2024

A revisit on the hydrogen atom induced by a uniform static electric field

In this paper, we revisit the Stark effect of the hydrogen atom induced by a uniform static electric field. In particular, a general formula for the integral of associated Laguerre polynomials was derived by applying the method for Hermite polynomials of degree n proposed in the work [Anh-Tai T.D. et al., 2021 AIP Advances \textbf{11} 085310]. The quadratic Stark effect is obtained by applying this formula and the time-independent non-degenerate perturbation theory to hydrogen. Using the Siegert State method, numerical calculations are performed and serve as data for benchmarking. The comparisons are then illustrated for the ground and some highly excited states to provide an insightful look at the applicable limit and precision of the quadratic Stark effect formula for other atoms with comparable properties.

quant-ph↗