Confinement Potential Research Articles

Exploration of the normalized intradopant transition energy of GaAs quantum dot under the influence of noise

In this work the intradopant transition energy (IDTE) and the normalized intradopant transition energy (NIDTE) of GaAs quantum dot (QD) have been minutely explored. The QD contains Gaussian impurity as dopant. Gaussian white noise, applied via two different routes (additive and multiplicative), also becomes part of the QD confinement potential. Energy values are calculated using linear variational theory. The IDTE and NIDTE exhibit (depending on presence/absence of noise, mode of entrance of noise and the given physical parameter undergoing change) steady growth, steady fall, maximization, minimization and saturation. Throughout the entire study, the NIDTE plots efficiently highlight some weak features which IDTE plots fail to do and clearly announce their superiority over the IDTE plots in realizing the influences of various physical parameters. The findings of the study are expected to be quite relevant in elucidating the optical properties of low-dimensional nanostructures containing impurity and under the sway of noise.

Mixing effects on spectroscopy and partonic observables of heavy mesons with logarithmic confining potential in a light-front quark model

Using the variational principle, we systematically investigate the mass spectra and wave functions of both 1S and 2S state heavy pseudoscalar (P) and vector (V) mesons within the light-front quark model. This approach incorporates a Coulomb plus logarithmic confinement potential to accurately describe the constituent quark and antiquark dynamics. Additionally, spin hyperfine interactions are introduced perturbatively to compute the masses of pseudoscalar and vector mesons. The present analyses of the 1S and 2S states require the consideration of mixing between them to account for empirical constraints. These constraints include the mass gap ΔMP>ΔMV, where ΔMP(V)=MP(V)2S−MP(V)1S and the hierarchy of the decay constants f1S>f2S. We find the optimal value of the mixing angle to be θ=18°, significantly enhancing the consistency between our spectroscopic predictions and the experimental data compiled by the Particle Data Group. Furthermore, based on the predicted mass, the newly observed resonance BJ(5840) could be assigned as a 21S0 state in the B meson family. The study also reports various pertinent observables, including twist-two distribution amplitudes, electromagnetic form factors, charge radii, ξ moments, and transition form factors that are found to be consistent with both available lattice simulations and experimental data. In addition, our predicted branching ratios for the channels of B+→τ+ντ as well as rare decays of B0 and Bs0 appear in accordance with experimental data. Published by the American Physical Society 2024

The electronic properties of a single electron in the GaAs/Ga1−xAlxAs oblate spheroidal quantum dot under the finite confinement potential

Quantum Dots, due to their fully quantized electronic states, have contributed to considerable progress in modern science and technology. Here we calculate the wave functions and energy spectrum of an electron confined in an oblate spheroidal quantum dot under the finite barrier potential condition, allowing the tailoring of the various energy states for specific applications. By calculating the electron wave functions outside the dot, we found that an infinite barrier is not a valid approximation for analyzing the optical properties of the structure. The effect of various geometrical and electrical characteristics of the structure, including the eccentricity, effective volume, and the height of barrier potential, is investigated. Additionally, the findings are compared with those found with prolate spheroidal quantum dot. The findings are further validated by comparing them to the exact electron energy level in a spherical quantum under the infinite barrier approximation.

Informational analysis of the confinement of an electron in an asymmetric double quantum dot

Aquasi-unidimensional one-electron double quantum dot is studied within the framework of Shannon informational entropy. Its confinement potential, which is described by an asymmetric harmonic-gaussian function, consists of two wells separated by a potential barrier, and the asymmetry of the potential in respect to the center of the barrier is parameterized by x0. In this work we employ Shannon informational entropy as a tool to investigate changes in the electronic confinement resulting from the modifications in the degree of asymmetry x0. In particular, we notice that Shannon entropy turns out to be very sensitive to the change from the symmetric to the antisymmetric regime. Moreover, we show that Shannon entropy as a function of x0 for an electronic excited state displays an irregular behavior whenever the state energy is in the vicinity of a local extreme (a maximum or a minimum); connected with this we observe an oscillatory behavior of the energy of the excited states as a function of x0.

Investigation of the Electronic Structure in GaAs/AlxGa1‐xAs Quantum Dots with Four Electrons

AbstractIn this paper, a detailed analysis of the electronic structure of four‐electron quantum dots is performed with finite confinement potential by a modified variational optimization approach based mainly on the quantum genetic algorithm and the Hartree‐Fock‐Roothaan method. For the ground and higher excited configurations, our analysis covers a range of parameters like the average energies of ground and excited states, singlet and triplet state energies, orbital energies, and two‐electron Coulomb and exchange interaction energies. One‐electron kinetic energy, the Coulomb potential energy between electrons and impurity, the confinement potential energy for the electrons, and the probability of finding an electron inside or outside the quantum well are also studied. The results demonstrate that both spatial confinement and the height of the potential barrier have a pronounced effect on all energies in the strong and intermediate confinement regions, but this influence weakens significantly in large dot radii. The most substantial difference between singlet and triplet energies occurs in the 1s22s2p configurations, with this difference decreasing in higher configurations. Significant increases in the 1s and 2s orbital energies are observed at the dot radii where the 2p, 3d, and 4f electrons from the outermost orbit begin to penetrate the well.

Valley-Hybridized Gate-Tunable 1D Exciton Confinement in MoSe2.

Controlling excitons at the nanoscale in semiconductor materials represents a formidable challenge in the quantum photonics and optoelectronics fields. Monolayers of transition metal dichalcogenides (TMDs) offer inherent 2D confinement and possess significant exciton binding energies, making them promising candidates for achieving electric-field-based confinement of excitons without dissociation. Exploiting the valley degree of freedom associated with these confined states further broadens the prospects for exciton engineering. Here, we show electric control of light polarization emitted from one-dimensional (1D) quantum-confined states in MoSe2. Building on previous reports of tunable trapping potentials and linearly polarized emission, we extend this understanding by demonstrating how nonuniform in-plane electric fields enable in situ control of these effects and highlight the role of gate-tunable valley hybridization in these localized states. Their polarization is entirely engineered through either the 1D confinement potential's geometry or an out-of-plane magnetic field. Controlling nonuniform in-plane electric fields in TMDs enables control of the energy (up to five times its line width), polarization state (from circular to linear), and position of 1D confined excitonic states (5 nm V-1).

A Backgate for Enhanced Tunability of Holes in Planar Germanium.

Planar semiconductor heterostructures offer versatile device designs and are promising candidates for scalable quantum computing. Notably, heterostructures based on strained germanium have been extensively studied in recent years, with an emphasis on their strong and tunable spin-orbit interaction, low effective mass, and high hole mobility. However, planar systems are still limited by the fact that the shape of the confinement potential is directly related to the density. In this work, we present the successful implementation of a backgate for a planar germanium heterostructure. The backgate, in combination with a topgate, enables independent control over the density and the electric field, which determines important state properties such as the effective mass, the g-factor, and the quantum lifetime. This unparalleled degree of control paves the way toward engineering qubit properties and facilitates the targeted tuning of bilayer quantum wells, which promise denser qubit packing.

Effect of magnetic and electric field on the ground state properties of weak coupling piezoelectric polaron in a quantum well with asymmetric Gaussian confinement

In this study, we employed the linear combination operation and a modified Lee-Low-Pines unitary transformation method to explore the ground state properties of an interacting electron coupled with piezo-acoustic phonons within a quantum well featuring asymmetric Gaussian confinement potential well under the influence of magnetic and electric fields. We calculated various properties, including the ground state energy, ground state binding energy, magnetic moment, magnetic susceptibility, and polarizability of the weakly coupled piezoelectric polaron. The effects of the magnetic and electric fields, electron-phonon weak coupling strength, Debye cut-off wavenumber, and confinement depth and range on these properties were thoroughly analyzed. Our findings reveal that the ground state energy decreases with increasing the Debye wavenumber, confinement range, and electron-phonon weak coupling strength. In contrast, the ground state binding energy shows the opposite trend, increasing with these parameters. Furthermore, the magnetic and electric fields, confinement depth and range, electron-phonon coupling strength, and Debye wavenumber are critical factors that significantly impact the magnetic and optical properties of the piezoelectric polaron.

Criterion for vanishing valley asymmetric transmission in dual-gated bilayer graphene

Abstract Realizing valley asymmetric transmission(VAT) for incoming valley unpolarized Dirac carriers across an electrostatically modulated confinement potential(ECP) step, which is located at the interface of the unipolar ( n − n ′ ) junction in dual-gated Bernal-bilayer graphene(BBG), has caught growing attention because it provides a platform to study the valley polarizer. Such a junction, however, seems to preclude from supporting vanishing VAT. Based on the effective two-band Hamiltonian of BBG with wave matching approach, we demonstrate theoretically that VAT through the n/n′ interface vanishes in the following conditions: (i) the disappearing electrostatically modulated interlayer potential difference(EPD), or (ii) the invariance condition of the sum or difference of ECPs and EPDs, which physically corresponds to the zero band offset of the conduction or valence band in the band alignment of n − n ′ junction. Guided by this, it is worth mentioning that the we can derive simple, analytical valley-independent expressions for the reflection and transmission probabilities. When the same invariant conditions occur, our calculations further show the appearance of the nearly vanishing VAT for the four-band model in bilayer graphene with ‘Mexican hat’-like band. As a byproduct, we apply these findings to suggest the best design for the valley-dependent selection of momenta based on dual-gated BBG connected to two pristine BBG electrodes in which ECPs of the two outer regions are distinguishable and show that the sign of valley polarization can be switched via varying EPD. We expect our results can provide guidance for future device applications relying on ballistic and valley-selective transport.

An intriguing connection between Pisarski's fixed point and (2 + 3)-spin glasses

This paper aims to establish a connection between Pisarski's fixed point and a (2+3)-spin-glass model with sextic confinement potential. This is made possible by the unconventional power-counting induced by the effective kinetics provided by the disorder coupling in the large N-limit. Because of the absence of epsilon expansion, our approach is more attractive than the previous one. It may be relevant to the signal detection issue in nearly continuous spectra.

Landau quantization under effects of torsion and confinement potentials

In this paper, we have investigated the nonrelativistic limit of a quantum particle, subjected to a uniform magnetic field and in the presence of some confinement potentials, immersed in a background with a cosmic string and a screw dislocation. We separately examined four models, constructed the energy spectrum and cyclotron frequency for each of them, and checked the consistency of the results by considering the limit of some characteristic parameters of the potentials.

Origin of the Efficiency Roll-off in Quantum Dot Light-Emitting Diodes: An Electrically Excited Transient Absorption Spectroscopy Study.

In situ characterizations of charge injection dynamics, equilibrated concentration, and electric field distributions shed light on the critical mechanisms of quantum dot light-emitting diodes (QD-LEDs). In this work, we developed electrically excited transient absorption spectroscopy, which can provide the above key information, to investigate the efficiency roll-off of QD-LEDs. We found that the average electron populations per QD are low when QD-LEDs exhibit efficiency roll-off, excluding Auger recombination as the main cause. We also revealed that the weak electrical field inside the QD layer under forward biases has a negligible impact on the efficiency. Interestingly, we found that as the voltage increases the electron concentration in the QD layer saturates at very low levels. When combined with the concomitant efficiency roll-off, we propose electron leakage is the main loss at elevated driving voltages. We further demonstrate that increasing the electron confinement potential with the ZnS shell enables us to efficiently mitigate the efficiency roll-off.

Optical Properties of Three‐Electron GaAs/AlxGa1−xAs QDs with Finite Confinement Potential

AbstractIn the case of finite confinement potential, the average energies and corresponding wave functions for the 1s2nl configurations, in which nl = 2s, 2p, 3d, and 4f, of three‐electron GaAs/AlxGa1−xAs quantum dot with and without impurity are computed by using a new variational approach which is a combination of Quantum Genetic Algorithm procedure and Hartree–Fock–Roothaan method. Using the calculated average energies and wave functions, a detailed investigation of the linear, third‐order nonlinear and total absorption coefficients (ACs) and the refractive index changes (RICs) for the quantum dot is performed, and the obtained results are presented as a function of dot radius and photon energies. The results show that the dot radius, the impurity charge, and the height of potential barrier have a strong influence on the average energies and absorption spectra of the system. As the potential barrier height increases, the peak positions of the ACs and RICs shift toward higher energy, and there is a significant increase in the amplitudes of the absorption spectra as the potential barrier height increases. In addition, the electron wave functions begin to enter the quantum well at smaller dot radii with increasing barrier height.

Interface Engineering in Gradient Core/Shell Quantum Dots Enables Efficient Photoelectrochemical Hydrogen Production

Semiconductor core/shell quantum dots (QDs) are considered promising building blocks to fabricate photoelectrochemical (PEC) cells for the direct conversion of solar energy into hydrogen (H2). However, the lattice mismatch between core and shell in such QDs results in undesirable defects and severe carrier recombination, limiting photo-induced carrier separation/transfer and solar-to-fuel conversion efficiency. Here, we explore an interface engineering approach to minimize the core-shell lattice mismatch in CdS/CdSexS1-x (x=0.09~1) core/shell QDs (g-CSG). As a proof-of-concept, PEC cells based on g-CSG QDs yield a remarkable photocurrent density of 13.1 mA/cm2 under AM 1.5 G one-sun illumination (100 mW/cm2), which is ~54.1% and ~33.7% higher compared to that in CdS/CdSe0.5S0.5 (g-CSA) and CdS/CdSe QDs (g-CS), respectively. Theoretical calculations and carrier dynamics confirm more efficient carrier separation and charge transfer rate in g-CSG QDs with respect to g-CSA and g-CS QDs. These results are attributed to the minimization of the core-shell lattice mismatch by the cascade gradient shell in g-CSG QDs, which modifies carrier confinement potential and reduces interfacial defects. This work provides fundamental insights into the interface engineering of core/shell QDs and may open up new avenues to boost the performance of PEC cells for H2 evolution and other QDs-based optoelectronic devices.

Electric field-induced electronic structure and intersubband transitions of a hydrogen molecular ion in a gaussian-type quantum ring

In this work, the influence of an external electric field on the electronic structure and intersubband transitions of a singly ionized double-donor system in a GaAs quantum ring defined by Gaussian-type potentials is investigated theoretically. Within the framework of the effective mass approach, the two-dimensional diagonalization method is used for the solution of the Schrödinger equation to obtain the eigen energies and corresponding wave functions. Numerical results reveal that the electronic energy spectrum and the linear optical absorption coefficient of the ring are remarkably affected by the strength of the lateral electric field, internuclear distance and parameters defining the confinement potential. Also, it has been shown that beyond the anti-crossing point, the wave functions exchange their symmetries without mixing, which is a characteristic feature of energy-level anti-crossing.

Study of three-stage high-resolution ion isolation for portable ion trap mass spectrometer

Portable ion trap mass spectrometers, especially for those with continuous atmospheric pressure interfaces, usually implement vacuum pumps with limited power for miniaturization, which leads to high vacuum pressures and reduced resolutions. In this study, two three-stage high-resolution ion isolation methods of SWIFT - AC frequency sweep - SWIFT and SWIFT - RF voltage ramp - SWIFT were proposed. Compared to the 2.8 m/z isolation resolution of the traditional SWIFT ion isolation method, higher isolation resolutions of 2.2 m/z and 1.5 m/z have been achieved by SWIFT - AC frequency sweep - SWIFT and SWIFT - RF voltage ramp - SWIFT ion isolation methods at an isolation efficiency of 40 %. In addition, our detailed experiments showed that all ion isolation methods can obtain higher isolation resolution under the conditions of lower vacuum pressure, higher isolation q value, and stronger axial confinement potential barrier, like which the mass resolution behaves. In order to inspect the effectiveness of the high-resolution isolation method, the control experiments of hair samples spiked with drugs had been conducted. The signal-to-noise ratio of O6-monoacetylmorphine can be improved by a factor of 2.4 using the SWIFT - RF voltage ramp - SWIFT ion isolation method. Our research results indicate that the performance of ion trap tandem mass spectrometry can be effectively improved by using the three-stage high-resolution ion isolation methods.

Enhancing compressive behavior of concrete with novel low-cost hybrid passive confinement including large rupture strain cotton ropes: Experimental findings and a design-oriented model

Recent research have highlighted the potential of hybrid confinement, combining high tensile strength fiber-reinforced polymers with large rupture strain confinement. This study presents experimental findings on 64 cylindrical and square-shaped specimens tested under axial compression, introducing a novel hybrid confinement method utilizing low-cost fiberglass chopped strand mat sheets and cotton ropes (COFS confinement). The experimental and analytical results yielded several key conclusions. Firstly, circular specimens exhibited significant peak strength increases in various subgroups, with enhancements ranging from 97.5 % to 285.5 %, and ultimate strain improvements ranging from 588.6 % to 1650.0 %. Similarly, square specimens under COFS confinement also demonstrated notable enhancements in ultimate strength and strain, with increases up to 244.7 % and 1083.0 %, respectively, particularly evident with higher levels of confinement. The influence of cross-sectional shape on compressive strength, strain, and energy dissipation was noted, with COFS confinement notably improving these factors for circular sections. Additionally, the study found that as the unconfined compressive strength increased, the enhancement in compressive strength, ultimate strain, and energy dissipation decreased. Moreover, the confinement ratio positively affected axial behavior improvement, with a proportional enhancement observed. However, the efficacy of the confinement ratio was influenced by cross-section type and plain concrete strength, emphasizing the need for considering these factors in COFS-based confinement design. Lastly, an analytical design-oriented model proposed for approximating stress vs. strain curves of COFS-confined concrete showed close agreement with experimental results, providing valuable insights for future design considerations.

Effects of interlayer spacing and applied pressure on the lanthanide transport in MoS2-based two-dimensional channels

ABSTRACT Rare-earth elements (REEs) are critical to modern industry but difficult to separate due to their subtle and monotonic changes in physicochemical properties. MoS2-based two-dimensional (2D) materials offer novel opportunities for enhancing REE separation, exhibiting a distinct volcano-shaped transport performance distribution that peaks at Sm3+. However, the specific contributions of thermodynamic and kinetic factors to ion transport within 2D confinement remain unclear. In this study, we conducted a series of non-equilibrium all-atom molecular dynamics (MD) simulations to explore the effects of interlayer spacing and external pressure on the transport of lanthanide ions in Å-scale acetate functionalized 2D MoS2 (MoS2-COOH) channels. We examined ion entry and permeation rates, water flux, dehydration, and binding modes. The simulation results reveal that the transport trends of lanthanide ions are jointly driven by the dehydration degree and the relative-binding strengths of ions to water and to the acetate within the 2D channels. Notably, the dehydration pattern of lanthanide ions during permeation is closely linked to kinetic factors. Overall, this study provides a detailed atomistic understanding of the mechanisms underlying lanthanide ion transport under confinement. These findings point to the significant potential for tuning confinement and chemical functionalization within Å-scale channels for more efficient REE separation.

Skewed generalized parton distributions of proton from basis light-front quantization

We obtain all the leading-twist quark generalized parton distributions (GPDs) inside the proton at nonzero skewness within the basis light-front quantization framework. We employ the light-front wave functions of the proton from a light-front quantized Hamiltonian in the valence Fock sector consisting of a three-dimensional confinement potential and a one-gluon exchange interaction with fixed coupling. We find that the qualitative behaviors of our GPDs are similar to those of other theoretical calculations. We further examine the GPDs within the boost-invariant longitudinal coordinate, σ=12b−P+, which is identified as the Fourier conjugate of the skewness. The GPDs in the σ-space show diffraction patterns, which are akin to the diffractive scattering of a wave in optics.

Magnetoelectric fractals, Magnetoelectric parametric resonance and Hopf bifurcation

In the present work, we study the dynamics of the magnetic nanodisc coupled through a magnetoelectric coupling to a ferroelectric crystal. The model of our interest is nonlinear, and we explore the problem under different limits of weak and strong non-linearity. By applying two electric fields with different frequencies, we control the form of the confinement potential of a ferroelectric subsystem and realize different types of dynamics. We proved that the system is more sensitive to magnetoelectric coupling in the case of double-well potential. In particular, in the case of strong non-linearity, arbitrary small values of magnetoelectric coupling lead to chaotic dynamics. In essence, magnetoelectric coupling plays a role akin to the small perturbations destroying invariant tori according to the KAM theorem. We showed that bifurcations in the system are of Hopf’s type. We observed the formation of magnetoelectric fractals in the system. In the limit of weak non-linearity, we studied a problem of parametric nonlinear resonance and enhancement of magnetic oscillations through magnetoelectric coupling.