Gaussian Impurity Research Articles

Tuning the Noise‐Driven Magnetocaloric Effect in Doped GaAs Quantum Dot in View of Tsallis Entropy

AbstractCurrent inspection strives to perform a detailed elaboration of the Tsallis entropy‐based magnetocaloric effect (MCE) of GaAs quantum dot (QD) doped with Gaussian impurity and under applied Gaussian white noise. Noise takes additive and multiplicative pathways for its entry to the doped QD. MCE has been found to decrease following the enhancement of temperature. The enquiry manifests magnetic field‐induced confinement and consequent decline in the disorder of the system during the gradual variation of several physical parameters. However, harnessing the extent of above confinement involves extremely sensitive and delicate control over the resultant influence of the particular physical parameter undergoing change, its range of magnitude, application of noise and its mode of inclusion. Importantly, MCE has been found to maximize only during the change in the strength of the dopant potential under multiplicative noise. And, on most occasions, multiplicative noise profoundly raises the MCE over its value under the state devoid of noise and under additive noise.

Tailoring the magnetocaloric effect in doped GaAs quantum dot under the influence of noise

Present inspection thoroughly explores the magnetocaloric effect (MCE) of GaAs quantum dot (QD) doped with Gaussian impurity and under the influence of Gaussian white noise (GWHN). Two different routes for the application of GWHN viz. additive and multiplicative have been considered. The enquiry highlights extremely subtle and complex interplay between temperature, GWHN, mode of entry of GWHN and the given physical parameters concerned that finally designs the MCE profiles. The fact that under certain conditions the MCE maximizes comes out to be technologically relevant. Deviations in the MCE profiles from the noise-free state appear to be more profound under multiplicative noise than its additive analogue. As a general trend, additive and multiplicative noise reduces and augments the MCE, respectively, from that under the noise-free situation.

Modulation of Thermodynamic Properties of Doped GaAs Quantum Dot under the Influence of Noise

In the present enquiry, an in‐depth analysis of internal energy, entropy, heat capacity, and Helmholtz free energy of GaAs quantum dot (QD) which contains Gaussian impurity as dopant and falls under the influence of applied Gaussian white noise (GWHN) is performed. GWHN takes additive and multiplicative routes for its entrance to the doped QD. In this study, highly delicate and complex interplay between temperature, presence/absence of GWHN, mode of incorporation of GWHN, and the particular physical parameters concerned is unveiled. The said interplay, in effect, designs the features of the thermal properties. The enquiry uncovers competitive behavior between thermal disorder and spatial disorder that also affects the said thermodynamic properties.

Exploring Shannon entropy and heat capacity of doped GaAs quantum dot under the influence of noise

Present enquiry explores the Shannon entropy and the corresponding heat capacity of GaAsquantum dot (QD) which is doped with Gaussian impurity and under the aegis of Gaussian white noise (GWHN). GWHN may take additive and multiplicative routes for its entrance to the doped QDs. The enquiry analyzes the features of temperature-dependence of above thermodynamic properties and also the effect of various physical parameters on them at a given temperature. The study reveals some kind of complex interplay involving the temperature zone, presence/absence of GWHN, mode of application of GWHN and the particular physical parameter concerned which ultimately shapes the profiles of entropy and heat capacity. Often, the study reveals competitive behavior between thermal disorder and spatial disorder which noticeably affects the said thermal properties. Moreover, the study also highlights some unusual behavior in the entropy profiles only under multiplicative noise of high noise strength.

Modulation of Tsallis entropy and corresponding thermodynamic properties of impurity doped GaAs quantum dot in presence of noise

Present inspection minutely explores the features of Tsallis entropy and the corresponding internal energy and heat capacity of GaAs quantum dot (QD) incorporating Gaussian impurity. Simultaneous influence of Gaussian white noise (GWHN) has also been invoked where GWHN enters the system by means of additive and multiplicative modes. The study unfolds extremely subtle interplay between temperature, entropy index, GWHN, mode of incorporation of GWHN and the particular physical parameters concerned. The resultant influence of the said interplay finally governs the traits of the Tsallis entropy-based thermal properties. The investigation manifests competitive behavior between thermal disorder and spatial disorder that prominently affects the thermal properties.

Localization of electrons in the field of impurity atoms on the surface of a nanotube

The localization of electrons in the field of isolated nonmagnetic impurity atoms on the surface of a nanotube is considered. A model of a Gaussian separable impurity potential capable of localizing an electron at any intensity is used. The positions of the local level are found. The positions of the resonances are found, their widths are estimated. It is shown that the positions of the resonances experience oscillations similar to the de Haas–van Alphen oscillations, when changing the radius of the tube.

Analyzing Time‐Average Excitation Rate Among Quantum Dot Eigenstates Triggered by Time‐Dependent Noise Strength

Present investigation rigorously explores the time‐average excitation rate (TAER) of ground‐state electronic population of GaAs quantum dot (QD) to the excited eigenstates. The QD confinement potential contains Gaussian impurity (the dopant) and Gaussian white noise (GWN). GWN can be categorized as either additive or multiplicative depending upon its way of attachment to the doped QD. The excitation occurs as soon as the noise strength begins fluctuating with time in periodic or random manner. The study highlights the coupled influence of the varying physical quantity, presence/absence of noise, the mode of attachment of noise to QD, and the nature of time‐fluctuation of the noise strength (periodic/random), and finally harnesses and tailors the features of the TAER profiles. The TAER plots unveil steady rise, steady fall, maximization (linked with the emergence of large nonlinear optical response), minimization, and saturation (linked with dynamic freezing). The findings appear to be significant in the practical usage of QD‐based devices.

The Gaussian impurity effect on the electronic and magnetic properties of an electron confined in a lateral quantum dot

The Gaussian impurity effect on the electronic and magnetic properties of an electron confined in a lateral quantum dot

Simultaneous effects of Rashba, magnetic field and impurity on the magnetization and magnetic susceptibility of a GaAs-semiconductor quantum ring

The magnetization and magnetic susceptibility of GaAs/AlGaAs quantum ring (QR) with the presence of Rashba spin-orbit interaction and acceptor Gaussian impurity have been studied. We have used the shifted 1/N expansion to calculate the energy eigenvalues as a function of the magnetic field. The obtained energies show energy level crossings; transition in the angular momentum of the ground state of the QR. Furthermore, we investigate the dependence of energy eigenvalues of QR on: confinement potential strength, Rashba parameter, and the presence of acceptor impurity. The comparisons show that the present computed results are in a good agreement with the available experimental and theoretical ones.Furthermore, we have shown the variation of the magnetization and magnetic susceptibility with the Hamiltonian variables. These magnetic quantities show an oscillating behavior associated with the phenomena of energy level crossings. The computed results indicate that as the Rashba strength increases, the positions of these oscillating peaks in the magnetic susceptibility curve shift towards a lower magnetic field value.

Impurity states of electrons on the surface of a nanotube in a magnetic field

The localization of electrons in the field of isolated nonmagnetic impurity atoms on the surface of a nanotube in a magnetic field is considered. A model of a Gaussian separable impurity potential capable of localizing an electron at any intensity is used. The positions of the local level are found in the regime of strong and weak localizations. The positions of the resonances are found, their widths are estimated. They experience Aharonov-Bohm oscillations when the magnetic flux in the tube changes. It is shown that the positions of the resonances experience oscillations similar to the de Haas-van Alphen oscillations, which are not associated with a magnetic field.

The Energy of the Ground State of the Two-Dimensional Hamiltonian of a Parabolic Quantum Well in the Presence of an Attractive Gaussian Impurity

In this article, we provide an expansion (up to the fourth order of the coupling constant) of the energy of the ground state of the Hamiltonian of a quantum mechanical particle moving inside a parabolic well in the x-direction and constrained by the presence of a two-dimensional impurity, modelled by an attractive two-dimensional isotropic Gaussian potential. By investigating the associated Birman–Schwinger operator and exploiting the fact that such an integral operator is Hilbert–Schmidt, we use the modified Fredholm determinant in order to compute the energy of the ground state created by the impurity.

Gaussian impurity bands in GaN and weakening of carrier confinement in InGaN/GaN quantum wells

Gaussian impurity bands in GaN responsible for intracenter optical absorption and photoluminescence, give rise to defect-assisted carrier tunneling (hopping) through the barriers in the pn nanostructures with InGaN/GaN quantum wells (QWs). The tunneling injection of majority cariers into the QW results in the current humps and in rapid increase in the radiative recombination efficiency at low enough forward bias. As the bias increases, the carrier confinement in the QW weakens, leading to tunneling injection of minority cariers into the barriers, which results in the emission efficiency saturation and droop.

Effect of Gaussian impurity parameters on the valence and conduction subbands and thermodynamic quantities in a doped quantum wire

In this paper, the influence of impurity parameters on the energy-dispersion spectrum of electrons and holes in a doped quantum wire with Gaussian impurity is studied. The numerical calculations have shown that the energy eigenvalues enhance, if the confinement of carriers increases. Then, the energy eigenvalues rise when the magnetic field, decay length and strength of impurity increase. Also, the type of impurity affects the energy subband structures. So that, the presence of attractive impurity reduces the energy eigenvalues, as compared to repulsive impurity. Moreover, the role of impurity parameters and the external magnetic field as a control parameter on the thermal quantities has been demonstrated in details. The results show that enhancement of magnetic field, decay length and strength of repulsive impurity decreases (increases) the entropy (internal energy) of quantum wire.

The role of Rashba spin-orbit interaction and external fields in the thermal properties of a doped quantum dot with Gaussian impurity

Thermodynamic quantities such as internal energy, heat capacity, and entropy are calculated for doped quantum dot by taking into account the Rashba spin-orbit coupling. It is demonstrated that thermal properties can be controlled by Rashba coupling, Gaussian impurity parameters, and applied fields so that enhancement of Rashba coupling strength and electric field reduces the internal energy. The changes in some parameters such as the magnetic field and strength of confinement potential strongly confine the electron in a quantum dot, and consequently entropy (internal energy) decreases (increases). The results showed that the presence of impurity in quantum dot reduced heat capacity. Also, type of impurity such as repulsive and attractive cases becomes important. Moreover, the thermal properties of asymmetric quantum dot have been investigated.

Modeling the CMOS Characteristics of a Completely Depleted Surrounding-Gate Nanotransistor and an Unevenly Doped Working Region

The issues of modeling the basic electrophysical characteristics of fully depleted surrounding-gate CMOS nanotransistors with an unevenly doped working region are discussed. The case of a Gaussian impurity distribution in the radial direction with the maximum in the center of the working area is analyzed. A mathematical model of the potential distribution following from an analytical solution of the 2D Poisson equation is treated. The results of model calculations of the potential distribution of a sub-50 nm structures are in good agreement with the data obtained using the commercially available ATLASTM software package for the 2D modeling of transistor structures. Based on the obtained potential distributions, the characteristics of the current are calculated using the tested approach formulated in the charge separation concept. For the topological norms chosen, optimization of the steepness of the doping profile provides an additional opportunity to control the key characteristics, together with the radius of the working region and the thickness of the gate oxide. This is important when analyzing the applicability of the analyzed nanotransistor structures.

The Birman-Schwinger Operator for a Parabolic Quantum Well in a Zero-Thickness Layer in the Presence of a Two-Dimensional Attractive Gaussian Impurity

In this note we consider a quantum mechanical particle moving inside an infinitesimally thin layer constrained by a parabolic well in the $x$-direction and, moreover, in the presence of an impurity modelled by an attractive Gaussian potential. We investigate the Birman-Schwinger operator associated to a model assuming the presence of a Gaussian impurity inside the layer and prove that such an integral operator is Hilbert-Schmidt, which allows the use of the modified Fredholm determinant in order to compute the bound states created by the impurity. Furthermore, we consider the case where the Gaussian potential degenerates to a $\delta$-potential in the $x$-direction and a Gaussian potential in the $y$-direction. We construct the corresponding self-adjoint Hamiltonian and prove that it is the limit in the norm resolvent sense of a sequence of corresponding Hamiltonians with suitably scaled Gaussian potentials. Satisfactory bounds on the ground state energies of all Hamiltonians involved are exhibited.

Tuning diamagnetic susceptibility of impurity doped quantum dots by noise-binding energy interplay

In the present work we explore the role of noise-binding energy (BE) interplay on the diamagnetic susceptibility (DMS) of doped GaAs quantum dot (QD). Gaussian white noise has been invoked for the above exploration. And Gaussian impurity acts as a dopant in the present study. The mode of inclusion of noise to the system significantly affects the above interplay and thus prominently modulates the DMS profile. The outcomes of the inspection unfolds the way by which DMS of doped QD can be regulated by prudent adjustment of noise-BE interaction.

Many-body dissipative flow of a confined scalar Bose-Einstein condensate driven by a Gaussian impurity

The many-body dissipative flow induced by a mobile aussian impurity harmonically oscillating within a cigar-shaped Bose-Einstein condensate is investigated. For very {small and large driving frequencies} the superfluid phase is preserved. Dissipation is identified, for intermediate driving frequencies, by the non-zero value of the drag force whose abrupt increase {signals the spontaneous downstream emission of an array of gray solitons. After each emission event, typically each of the solitary waves formed decays and splits into two daughter gray solitary waves that are found to be robust propagating in the bosonic background for large evolution times.} In particular, a smooth transition towards dissipation is observed, with the {\it critical} velocity for solitary wave formation depending on both the characteristics of the obstacle, namely its driving frequency and width as well as on the interaction strength. The variance of a sample of single-shot simulations indicates the fragmented nature of the system; here it is found to increase during evolution for driving frequencies where the coherent structure formation becomes significant. Finally, we demonstrate that for fairly large particle numbers in-situ single-shot images directly capture the gray soliton's decay and splitting.

Analyzing the correction factor relevant to Kerr nonlinearity in impurity doped quantum dots for a passage from non-absorbing to absorbing media: Role of noise

kerr nonlinearity is an important nonlinear optical property exhibited by quantum dot (QD). Present study endeavors to explore the correction factors (CFs) relevant to kerr nonlinearity for nonlinear refractive index (RI) and nonlinear absorption coefficient (AC) of GaAs QD. The CF arises owing to a shift from non-absorbing to absorbing media. The QD is doped with Gaussian impurity and special stress has been given on appreciating the role of Gaussian white noise. The CFs for RI and AC have been scrutinized following the variations of a large number of important physical parameters. These parameters include e.g. electric field, magnetic field, confinement potential, dopant location, dopant potential, noise strength, aluminium concentration (only for AlxGa1−xAs alloy QD), carrier density, relaxation time, position-dependent effective mass, position-dependent dielectric constant, anisotropy, hydrostatic pressure and temperature. It has been found that the CF profiles are governed by the concerned physical parameter, presence/absence of noise and the route (additive/multiplicative) through which the ingression of noise to the system can take place. The CF for RI has been found to be orders of magnitude greater than that of CF for AC. Present study helps us identify the various conditions when CF would be extremely small, or, more preferably, minimized.

Impurity-related optical properties of a laser-driven quantum dot

In this paper, we explore theoretically the effect of an on-center Gaussian impurity on the optical properties of a laser-driven parabolic quantum dot system under uniform magnetic field. Laser radiation with circular polarization has been treated within the framework of high-frequency Floquet approach. The linear and third-order nonlinear optical absorption coefficients and refractive index changes have been examined by means of the compact-density matrix approach. Numerical results reveal that the position and magnitude of the resonant peaks of absorption coefficients and refractive index changes are sensitively affected by magnetic field, the depth and the range of the impurity potential. Besides, the presence of intense laser field causes a red-shift in the positions and reduction in the amplitudes of the resonant peaks of optical characteristics.