Impurity Position Research Articles

Examining the influence of electric field on the photoionization cross section and spin polaronic shift in a semimagnetic double quantum well

In the current research, we performed a numerical investigation of a shallow donor impurity confined in a diluted magnetic semiconductor (DMS) double quantum well (DQW) made of a Cd1−xwMnxwTe/Cd1−xbMnxbTe under the applied electric field in the z-direction. The optoelectronic properties were carried out using the effective-mass approximation and the variational method. The binding energy and photoionization cross section were examined by considering different factors such as, well width, barrier width, impurity position, and Manganese mole fraction. Additionally, the spin polaronic shift corrections to the donor binding energy, caused by the strong exchange interaction between the magnetic moment of the Mn2+ the confined carrier spin, have been examined under the aforementioned effects.

Influence of structural factors and impurity position on second harmonic generation in double-quantum box GaAs-Ga1-xAlxAs structures

Influence of structural factors and impurity position on second harmonic generation in double-quantum box GaAs-Ga1-xAlxAs structures

Role of confinement shape and spin-orbit interactions on binding energy, temperature, transition energy, susceptibility and oscillator strength of an off-center [formula omitted] impurity in a GaAs quantum dot

This study explores the influence of confinement potential shape on the behavior of an off-center D0 impurity in a quantum dot (QD). In this study, we use the power exponential potential and Rashba spin-orbit interaction (RSOI), and Dresselhaus spin-orbit interaction (DSOI) beside an external magnetic field. Employing the variational method, we obtained the ground and first excited state energies and corresponding binding energies, transition energy, and magnetic susceptibilities across various impurity positions, QD parameters, and potential shapes. We ascertain the stable temperature by equating the maximum binding energy of an off-center D0 system. Subsequently, we computed the oscillator strength (OS) and conducted a comparative analysis with existing literature. Our findings demonstrate an exciting behavior in response to changes in potential shape, QD parameters, and spin-orbit coupling strengths. It helps us better understand how an off-center impurity behaves with different potential shapes in QDs and helps engineers to design devices in spintronics.

Impact of impurities on the topological boundaries and edge state localization in a staggered chain of atoms: SSH model and its topoelectrical circuit realization

We study the Su-Schrieffer-Hegger model, perhaps the simplest realization of a topological insulator, in the presence of an embedded impurity superlattice. We consider the impact of the said impurity by changing the hopping amplitudes between them and their nearest neighbors in the topological boundaries and the edge state localization in the chain of atoms. Within a tight-binding approach and through a topolectrical circuit simulation, we consider three different impurity-hopping amplitudes. We found a relaxation of the condition between hopping parameters for the topologically trivial and non-trivial phase boundary and a more profound edge state localization given by the impurity position within the supercell.

Effect of the electric field orientation on stark shift, dipole moment and electronic properties in a circular toroidal quantum ring: Presence of shallow donor impurity

This research investigates the influence of electric field orientation on the physical properties of a Gallium Arsenide (GaAs) Circular Toroidal Quantum Ring (CTQR) in the presence of shallow donor impurity. Using the effective mass approximation and an infinite potential well, we delve into how electric field directions specifically 0, 45, and 90 degrees on the xy-plane affect physical behaviors such as binding energy, electronic energy, the Stark effect, dipole moment and donor impurity position. Utilizing the finite difference method for our numerical analysis, we discovered interesting size-dependent behaviors. Our findings reveal intriguing insights. Initially, we observed that the electronic energy exhibits minimal sensitivity to the direction of the electric field in smaller CTQR. Notably, the ground state energy increases when the electric field’s direction shifts from φF=0 to φF=90∘. The electric field’s influence on the binding energy varies depending on its orientation. In larger structures, we observe a lower binding energy. Thus, our study unveils the influence of the electric field’s direction on Stark shifts and dipole moment which opens pathways for a deeper understanding of potential applications in this domain.

Electron-related properties in a GaAs/GaAlAs Ultra-thin Core/Shell Film through external field direction for energy and photonic devices

In this paper, we investigate electron-related properties in GaAs/GaAlAs Ultra-thin Core/Shell Film Quantum dot (UTFQD), examining the effects of external electric fields, impurity position, and aluminum fraction. Using the finite element method (FEM) within the effective mass approximation, we numerically solve the Schrödinger equation to study electron probability density, polarizability, and diamagnetic susceptibility. Our results reveal that electric fields can shift electron probability density due to the Stark effect. Without an electric field, the density centers near the shell's core. However, with electric fields, the density shifts opposite to the field's direction. Moreover, polarizability and diamagnetic susceptibility are influenced by impurity position and aluminum fraction. Polarizability increases with electric field intensity, indicating a transition from geometrical confinement to the Stark effect. Diamagnetic susceptibility rises with more aluminum, indicating stronger electron confinement. These findings suggest that adjusting electric fields, impurity position, and aluminum fraction in GaAs/GaAlAs core/shell QDs can control electron behavior, providing flexibility for photonic devices. This study offers a foundation for optimizing quantum dot-based components in photonics.

Conceptual design of visible spectroscopy diagnostics for DTT

The project of the Visible Spectroscopy diagnostics for the Z eff radial profile measurement and for the divertor visible imaging spectroscopy, designed for the new tokamak DTT (Divertor Tokamak Test), is presented. To deal with the geometrical constraints of DTT and to minimize the diagnostics volume inside the access port, an integrated and compact solution hosting the two systems has been proposed. The Z eff radial profile will be evaluated from the Bremsstrahlung radiation measurement in the visible spectral range, acquiring light along ten Lines of Sight (LoS) in the upper part of the poloidal plane. The plasma emission will be focused on optical fibers, which will carry it to the spectroscopy laboratory. A second equipment, with a single toroidal LoS crossing the plasma centre and laying on the equatorial plane, will measure the average Z eff on a longer path, minimizing the incidental continuum spectrum contaminations by lines/bands emitted from the plasma edge. The divertor imaging system is designed to measure impurity and main gas influxes, to monitor the plasma position and kinetics of impurities, and to follow the plasma detachment evolution. The project aims at obtaining the maximum coverage of the divertor region. The collected light can be shared among different spectrometers and interferential filter devices placed outside the torus hall to easily change their setup. The system is composed of two telescopes, an upper and a lower one, allowing both a perpendicular and a tangential view of the DTT divertor region. This diagnostic offers a unique and compact solution designed to cope the demanding constraints of this next-generation tokamak fusion devices, integrating essential tools for wide-ranging impurity characterization and versatile investigation of divertor physics.

Hybridization of an s-wave impurity with graphene lattice

Hybridization function is a quantity characterizing electron hoppings between an impurity and a host material in which the impurity resides, a full understandinging of it is crucial for studying correlation effects in various impurity problems. This work studies the hybridization function for the Anderson impurity model describing a single-orbital impurity on a honeycomb lattice simulating graphene and presents a calculation approach to obtain this function at low energy. Within this approach, the general form of the hybridization function in graphene is presented and analytical expressions of low-energy hybridization spectrum are obtained. The results quantitatively match numerical solutions for different impurity positions on the lattice. The effect of the low-energy hybridization spectrum and the capability to predict the correlated effects of the impurity problem are discussed thoroughly, suggesting that different types of pseudogap Kondo effect may occur at different impurity positions.

Effect of spin-orbit coupling and impurities on the optical properties of double quantum rings under magnetic fields

In this paper, the energy spectrum of concentric double quantum rings (CDQRs) with double well confinement under the influence of spin-orbit interactions (SOIs), magnetic fields, and hydrogen donor impurities is studied by using diagonalization. The light absorption coefficient is then calculated in the form of a compactness density-matrix. Key findings from this study include the ability to manipulate fine energy level splitting and optical absorption coefficients by tuning the magnetic field, impurity position, spin-orbit coupling, and inner rings size. Furthermore, this study reveals the bleaching effect of the optical absorption coefficient under certain conditions and demonstrates the anisotropic nature of the system through changes in the optical absorption coefficients (OACs) for different incident light polarization angles.

Electron-donor-impurity polarizability in a semiconductor nanostructure under electric field: Geometrical effects in ellipsoidal quantum dots

The features of electron-impurity polarizability in a quantum nanostructure are investigated from the knowledge of allowed electron states coupled to a shallow-donor impurity. The influence of geometry on the carrier confinement and the presence of external probes such as electric fields are explicitly considered. For the sake of illustration, the example of CdS/ZnSe-based prolate ellipsoidal core/shell quantum dot (PECSQD) configuration is chosen. This problem allows to consider a finite confinement potential model, employing both the finite element method and the effective mass approximation. Within this framework, impurity-related energies and associated polarizability for the lowest states were determined as functions of the shell thickness, core dimensions, impurity position, and applied electric field strength - while keeping the shell dimensions fixed. Electron-impurity energies are largely affected by electric field values. Under thinner shell conditions, polarizability shows variations with field strength that include “anomalous” negative values for certain states. Then, the increase in shell thickness causes a significant increment in the polarizabilities, regardless impurity position.

Effects of electric and magnetic fields on the electronic properties in the asymmetrical biconvex lens-shaped GaAs/GaAlAs quantum dots

Theoretical investigation of electronic properties in asymmetric biconvex lens-shaped GaAs/GaAlAs quantum dots is considered in the presence of the external magnetic and electric fields. In addition, the effects of the dot size and the asymmetry of the structure on the electronic properties are also investigated. The shape of this quantum dot corresponds to the intersection of two differently centered spheres. The energy levels and wave functions of the shallow hydrogenic impurity in the structure with a finite potential are calculated numerically in cylindrical coordinates with the effective mass approach using a complex eigenvalue formalism through a two-dimensional axisymmetrical and three-dimensional finite element methods. The results reveal significant dependence of the calculated physical properties on lens dimensions, axial impurity position, and intensities of applied electric and magnetic fields.

Synthetic dimension-induced pseudo Jahn-Teller effect in one-dimensional confined fermions

We demonstrate the failure of the adiabatic Born-Oppenheimer approximation to describe the ground state of a quantum impurity within an ultracold Fermi gas despite substantial mass differences between the bath and impurity species. Increasing repulsion leads to the appearance of nonadiabatic couplings between the fast bath and slow impurity degrees of freedom, which reduce the parity symmetry of the latter according to the pseudo Jahn-Teller effect. The presence of this mechanism is associated to a conical intersection involving the impurity position and the inverse of the interaction strength, which acts as a synthetic dimension. We elucidate the presence of these effects via a detailed ground-state analysis involving the comparison of fully correlated simulations with effective models. Our study suggests ultracold atomic ensembles as potent emulators of complex molecular phenomena. Published by the American Physical Society 2024

Temperature Dependence of the Band Gap of Completely Fluorinated/Hydrogenated Carbon Nanotubes: The Role of One-Dimensional Chains

The temperature dependence of the band gap Eg(T) in zigzag single-walled carbon nanotubes at the maximum (50%) fluorination and hydrogenation has been theoretically investigated for three coating versions. It has been shown that the character of coating dramatically affects the dependence Eg(T), which may vary over a wide range from very weak (typical of pure carbon nanotubes) to strong (typical of bulk semiconductors). The character of the temperature behavior Eg(T) is directly related to the formation of one-dimensional alternating chains in nanotubes. The main factors determining this dependence are the diameter of carbon nanotube, impurity position, and impurity type.

Quantum Transport of Topological and Trivial Edge States in Sn‐Doped SbH Nanoribbons

Although the transport of topological edge states may be insensitive to impurities, impurities may induce the interedge scattering and backscattering in topological nanoribbons due to the finite size effect. It may be interesting to compare the transport of topological edge states with that of trivial edge states in nanoribbons. Here, the quantum transport of edge states in the Sn‐doped SbH nanoribbons using the density functional theory combined with nonequilibrium Green's function method is studied. Both topological and trivial edge states can be found in the zigzag SbH nanoribbons. The impurity generates a higher barrier near the doping position and leads to the scattering of the states. From calculations, the transmission of topological edge states can be smaller than that of trivial edge states due to the antiresonance behavior. Compared with topological edge states, the transport of trivial edge states is more sensitive to the impurity position. Besides, the edge impurity is more likely to induce scattering for both topological and trivial edge states than the central impurity in narrow SbH nanoribbons, since the transport channels are limited to the edges. This study may be helpful for understanding the transport of edge states in nanoribbons.

First-principles prediction of higher Curie temperature, metallic and half-metallic ferromagnetism in Zn1-x(Vx,Nix)O systems

The electronic and magnetic properties of Zn(V,Ni)O systems with 2.08 %, 4.16 %, 6.25 %, 8.3 %, and 12.5 % impurity concentrations were investigated based on ab initio simulations. The first-principles calculations were carried out using density functional theory and local spin density approximation by pseudopotential method. Analyzing the calculated density of states, the mechanism to stabilize the ferromagnetic phase in the 3d-metals doped ZnO systems is discussed. The analysis of the total density of states shows that the V-doped ZnO presents a metallic nature and Ni-doped ZnO exhibits a half-metallic character. First-principles calculations show that the stability of ferromagnetic or antiferromagnetic behaviors depends on impurity concentrations and impurity positions in related ZnO:V,Ni systems. Finally, we estimated and studied the Curie temperatures for V- and Ni-doped ZnO systems with different impurity concentrations. The Curie temperatures for VxZn1-xO and NixZn1-xO systems are higher than room temperature and these compounds are suitable ferromagnetic DMS materials for spintronic applications.

Effects of High Hydrostatic Pressure on the Structural, Electronic, and Elastic Properties, and Li-Ion Diffusion Barrier of Lithium Lanthanum Titanate Electrolytes: A DFT Study

Lithium lanthanum titanate perovskites (LLTO) are excellent solid electrolytes because of their good ionic conductivity and elasticity. In this work, the effects of high hydrostatic pressure and the impact of the position of Li impurities on the structural, electronic, elastic, and Li-ion diffusion properties of LaTiO3 perovskite (LTO) and its LLTO substitutional solid solutions, were studied. Density-Functional Theory (DFT) and Hubbard-corrected Local Density Approximation (LDA+U) were used. Due to hydrostatic pressure, the octahedral distortion of LTO, LLTO-layered (L), and -rock-salt (RS) electrolytes decreases, while it increases for the LLTO-columnar (C). On the other hand, the energy band gap () of LTO and LLTO-C decrease as hydrostatic pressure increases. For the LLTO-L, increases with pressure. For the LLTO-RS, decreases from zero to 20 GPa and increases from 20 to 30 GPa. Pugh’s criterion indicates that all systems are ductile regardless of applied pressure. Poisson’s ratio shows that bonds in the LTO are metallic, and LLTO-C is ionic-covalent. Likewise, LLTO-L and -RS electrolytes have a transition from ionic-covalent to metallic behavior, as pressure increases. Li-ion diffusion barriers of LLTO electrolytes increase with increasing hydrostatic pressure, indicating a decrease in Li ionic conductivity.

Binding Energy Stark-Shift, Polarizability and Dipole Moment Response of Shallow Donor Impurity in GaAs Quantum Dots

In this study, we have examined, under the influence of an electric field applied along the z-direction, the binding energy Stark-shift, the dipole moment and the polarizability of a confined shallow donor impurity in GaAs conical-shaped quantum dots (CSQD). With square infinite confinement system, the calculations are based on the approximation of the effective mass by using the finite difference method. Our results show that increasing the radius of the CSQD structure and the electric field intensity increases the Stark shift binding energy and it has a mixed behavior as a function of the impurity position. Furthermore, the polarizability and the dipole moment vary in a quasi-linear way as a function of the dot radius and they follow a decreasing function as a function of the electric field intensity. These two physical parameters have a double behavior, they decrease with the position of the impurity in the strong confinement regime and they increase in the top regions of the quantum dot. These results provide a lot of information about the behavior of the electronic wave function which give more interesting ideas for the fabrication of optoelectronic devices.

Unveiling the Role of Donor Impurity Position on the Electronic Properties in Strained Type I and Type II Core/Shell Quantum Dots under Magnetic Field.

In this theoretical investigation, we delve into the significant effects of donor impurity position within core/shell quantum dot structures: type I (CdTe/ZnS) and type II (CdTe/CdS). The donor impurity's precise location within both the core and the shell regions is explored to unveil its profound influence on the electronic properties of these nanostructures. Our study investigates the diamagnetic susceptibility and binding energy of the donor impurity while considering the presence of an external magnetic field. Moreover, the lattice mismatch-induced strain between the core and shell materials is carefully examined as it profoundly influences the electronic structure of the quantum dot system. Through detailed calculations, we analyze the strain effects on the conduction and valence bands, as well as the electron and hole energy spectrum within the core/shell quantum dots. The results highlight the significance of donor impurity position as a key factor in shaping the behaviors of impurity binding energy and diamagnetic susceptibility. Furthermore, our findings shed light on the potential for tuning the electronic properties of core/shell quantum dots through precise impurity positioning and strain engineering.

Laser field effect on the normalized self-polarization, self-polarization and binding energy in square quantum wells made of different materials

In this study, we examine the effect of the laser field on normalized self-polarization, self-polarization, and binding energy in square quantum wells made of four different materials under effective mass approximation. The effects of well width, laser field, and impurity position on normalized self-polarization, self-polarization, and binding energies are shown in detail. The subband energies are obtained by the finite difference method, and the impurity energies are calculated by the variational method. The laser field significantly affects binding energy, self-polarization, and normalized self-polarization. The term normalized self-polarization is defined for the first time in this study. This allows a more detailed examination of the self-polarization change depending on the impurity position. Examining the laser field effect, especially in square quantum wells made of different materials, will provide researchers with helpful information about the importance of material selection in calculating binding energy, self-polarization, and normalized self-polarization.

Tuning the Diamagnetic Susceptibility and Electron Average Position in a GaAs Hemi-Spherical Quantum Dot with an Off-Center Donor Atom

The Langevin theory of diamagnetism is used to examine the effects of geometric confinement and hydrogenic impurity location on the diamagnetic susceptibility in a GaAs hemispherical quantum dot with an infinite confinement potential considered as vacuum. Using the finite difference approach and the effective mass approximation, the electron-donor Schrödinger equations are derived. As a function of the size of the hemi-spherical quantum dot, the mean value of the electron location and electron to ionized donor atom distance are investigated, taking into account the various impurity positions. The results show that shrinking the size of the hemi-spherical quantum dot improves the diamagnetic susceptibility by reducing the electron-donor distance. The major findings show that the donor impurity location has a significant impact on the diamagnetic susceptibility. We believe that the findings from our work into the diamagnetic susceptibility of quantum dots will be crucial in determining how well optoelectronic devices will operate.