Role of impurity influenced domain on excitation profile of doped quantum dot subject to oscillatory confinement potential

We explore the excitation profile of a repulsive impurity doped quantum dot under a periodically fluctuating confinement potential. We have considered Gaussian impurity centers. The investigation points to a minimum value of spatial extension of impurity domain below which significant excitation is not feasible. In general, excitation becomes maximum at some typical value of impurity strength depending upon the location and the spatial stretch of the dopant. The rate of transition to the excited states depends on the above spatial stretch which gets modulated by the oscillating confinement potential and explains the excitation maximization quite elegantly.     

Excitations in doped quantum dot induced by randomly fluctuating magnetic field: influence of impurity

We explore the excitation profile of a repulsive impurity doped quantum dot under randomly fluctuating magnetic field. We have considered Gaussian impurity centers. The investigation reveals the roles subtly played by the dopant coordinate, dopant strength, and the region of influence of the dopant to modulate the excitation pattern. The rate of transition to the excited states has been invoked to analyze the roles played by the above impurity parameters in influencing the excitation process. Quantum phase space plots are often exploited to support the findings.     

The randomly fluctuating impurity strength initiated excitation in doped quantum dots

We investigate the excitation behavior of a repulsive impurity doped quantum dot under the influence of randomly fluctuating dopant potential. We have considered Gaussian impurity centers doped at different locations. The investigation reveals the interplay between dopant location and dopant’s spatial stretch in modulating the excitation pattern. Maximization in the excitation rate has been observed as a function of fluctuating dopant strength owing to the conflict between opposing influences that promote and hinder excitation.     

Stability of high-current beams of relativistic electrons in cyclic systems

Stability conditions of high-current thin beams of relativistic electrons against excitation of long-wave oscillations in a stellatron and modified betatron have been investigated theoretically. The influence of self electric and magnetic fields obtained from electron beam delayed potentials has been taken into consideration. The correspondent dispersion relation has been found. The electron beam of the modified betatron has been shown to be always unstable against excitation of the oscillations considered. Necessary and sufficient conditions for the elec-tron beam confinement in a stellatron have been found.     

Optoacoustic effects in absorbing liquids under the action of pulsed bessel light

The excitation of acoustic oscillations in absorbing liquids exposed to pulsed Bessel light beams has been considered theoretically. Spatial profiles of refractive index diffraction patterns and the kinetics of their excitation and relaxation have been studied based on a numerical solution of continuous medium motion equations in a Lagrangian form and a heat-transfer equation and using the Lorentz–Lorenz formula. The conditions for optimal excitation of spatially localized acoustic pulses have been determined.     

Excitations in doped quantum dot insisted by discontinuous reversals of static electric field: Interplay between pulse and dopant site

We explore the excitation profile of a repulsive impurity doped quantum dot. The quantum dot is subject to a discontinuously reversing static electric field. The dopant impurity potential chosen assumes Gaussian form. The investigation reveals the key role played by the dopant location and the number of pulses offered by the external field to the dot in controlling the excitation rate. Time-dependent Hellman-Feynman theorem has been invoked to understand the extent of energy transfer between field direction and the direction where no field is applied. The combined transition rate from ground to other excited states is also determined to support the findings.     

Exploring electro-optic effect of impurity doped quantum dots in presence of Gaussian white noise

We explore the profiles of electro-optic effect (EOE) of impurity doped quantum dots (QDs) in presence and absence of noise. We have invoked Gaussian white noise in the present study. The quantum dot is doped with Gaussian impurity. Noise has been administered to the system additively and multiplicatively. A perpendicular magnetic field acts as a confinement source and a static external electric field has been applied. The EOE profiles have been followed as a function of incident photon energy when several important parameters such as electric field strength, magnetic field strength, confinement energy, dopant location, relaxation time, Al concentration, dopant potential, and noise strength possess different values. In addition, the role of mode of application of noise (additive/multiplicative) on the EOE profiles has also been scrutinized. The EOE profiles are found to be adorned with interesting observations such as shift of peak position and maximization/minimization of peak intensity. However, the presence of noise and also the pathway of its application bring about rich variety in the features of EOE profiles through some noticeable manifestations. The observations indicate possibilities of harnessing the EOE susceptibility of doped QD systems in presence of noise.     

Tuning third harmonic generation of impurity doped quantum dots in the presence of Gaussian white noise

We perform a broad exploration of profiles of third harmonic generation (THG) susceptibility of impurity doped quantum dots (QDs) in the presence and absence of noise. We have invoked Gaussian white noise in the present study. A Gaussian impurity has been introduced into the QD. Noise has been applied to the system additively and multiplicatively. A perpendicular magnetic field emerges out as a confinement source and a static external electric field has been applied. The THG profiles have been pursued as a function of incident photon energy when several important parameters such as electric field strength, magnetic field strength, confinement energy, dopant location, Al concentration, dopant potential, relaxation time and noise strength assume different values. Moreover, the role of the pathway through which noise is applied (additive/multiplicative) on the THG profiles has also been deciphered. The THG profiles are found to be decorated with interesting observations such as shift of THG peak position and maximization/minimization of THG peak intensity. Presence of noise alters the characteristics of THG profiles and sometimes enhances the THG peak intensity. Furthermore, the mode of application of noise (additive/multiplicative) also regulates the THG profiles in a few occasions in contrasting manners. The observations highlight the possible scope of tuning the THG coefficient of doped QD systems in the presence of noise and bears tremendous technological importance.     

Noise-driven optical absorption coefficients of impurity doped quantum dots

We make an extensive investigation of linear, third-order nonlinear, and total optical absorption coefficients (ACs) of impurity doped quantum dots (QDs) in presence and absence of noise. The noise invoked in the present study is a Gaussian white noise. The quantum dot is doped with repulsive Gaussian impurity. Noise has been introduced to the system additively and multiplicatively. A perpendicular magnetic field acts as a source of confinement and a static external electric field has been applied. The AC profiles have been studied as a function of incident photon energy when several important parameters such as optical intensity, electric field strength, magnetic field strength, confinement energy, dopant location, relaxation time, Al concentration, dopant potential, and noise strength take on different values. In addition, the role of mode of application of noise (additive/multiplicative) on the AC profiles has also been analyzed meticulously. The AC profiles often consist of a number of interesting observations such as one photon resonance enhancement, shift of AC peak position, variation of AC peak intensity, and bleaching of AC peak. However, presence of noise alters the features of AC profiles and leads to some interesting manifestations. Multiplicative noise brings about more complexity in the AC profiles than its additive counterpart. The observations indeed illuminate several useful aspects in the study of linear and nonlinear optical properties of doped QD systems, specially in presence of noise. The findings are expected to be quite relevant from a technological perspective.     

Plasmon mechanism of resistance magnetooscillations in a two-dimensional electron system in strong electric fields

A multielectron approach is developed to explain the resistance magnetooscillations in two-dimensional electron systems that have recently been detected under the action of microwave pumping [1] or a strong dc electric field [23]. A qualitative change in the screened impurity potential in a strong electric field is taken into account for the first time. When considered in the rest frame of the center of the cyclotron orbit, the impurity potential becomes nonstationary and, thus, should be screened dynamically. This fact substantially changes the picture of impurity scattering in a “pure” two-dimensional system: a dissipative current is induced by the excitation of two-dimensional plasmons rather than by one-electron transitions between the Landau levels. In the case of microwave pumping, every period of resistance oscillation in a reciprocal magnetic field is formed by the excitation of the corresponding magnetoplasmon branch, and the fine structure of oscillations is formed by the singularities of the magnetoplasmon density of states. In a “dirty” two-dimensional system, the role of electron-electron interaction weakens, collective excitations cease to exist, and the results transform into the well-known results obtained in terms of a one-electron approach.     

Influence of dopant concentration on electrical quantum transport behaviors in junctionless nanowire transistors

We discuss the random dopant effects in long channel junctionless transistor associated with quantum confinement effects. The electrical measurement reveals the threshold voltage variability induced by the random dopant fluctuation.Quantum transport features in Hubbard systems are observed in heavily phosphorus-doped channel. We investigate the single electron transfer via donor-induced quantum dots in junctionless nanowire transistors with heavily phosphorusdoped channel, due to the formation of impurity Hubbard bands. While in the lightly doped devices, one-dimensional quantum transport is only observed at low temperature. In this sense, phonon-assisted resonant-tunneling is suppressed due to misaligned levels formed in a few isolated quantum dots at cryogenic temperature. We observe the Anderson-Mott transition from isolate electron state to impurity bands as the doping concentration is increased.     

Giant oscillations of electron temperature during steady-state operation on Tore Supra

During fully noninductively driven discharges in the Tore Supra tokamak, large spontaneous oscillations of the core electron temperature (DeltaTe/Te>50%) have been observed for the first time. They occurred during the standard O regime, which is itself characterized by periodic oscillations of much smaller amplitude. The "giant" oscillations appear to involve distinct mechanisms with respect to the O regime and provide a spectacular example of the complex nonlinear interactions between energy confinement, noninductive current sources, and MHD that may occur in a tokamak plasma during steady-state operation.     

Orbital magnetic moment of a quantum well and a quantum dot in crossed magnetic and electric fields

A new physical effect, namely, oscillations of the orbital magnetic moment with a change in the electric field strength in two types of nanostructures, has been predicted. Explicit analytical expressions for the orbital magnetic moment of a quantum well and a quantum dot in crossed magnetic and electric fields have been derived. The oscillations of the orbital magnetic moment with a change in the electric and magnetic fields have been studied. The oscillation periods in both the electric and magnetic fields have been found and the limiting cases of the strong magnetic and quantum confinement effects have been considered.     

Impurity effects on the magnetization and magnetic susceptibility of an electron confined in a quantum ring under the presence of an external magnetic field

The magnetization and the magnetic susceptibility of a single electron confined in a two-dimensional (2D) parabolic quantum ring under the effect of external uniform magnetic field and in the presence of an acceptor impurity have been studied. The shifted 1/N expansion method was used to solve the Hamiltonian quantum ring within the effective mass approximation. The computed energy spectra, the magnetization and magnetic susceptibility have been displayed as a function of the quantum ring parameters: confinement strength ω₀, magnetic field strength (ω_c), and temperature (T). The obtained energy results show level-crossings, in the absence and presence of acceptor impurity, which are manifested as oscillations in the magnetization and magnetic susceptibility curves.     

Exploring diamagnetic susceptibility of impurity doped quantum dots in presence of Gaussian white noise

We explore diamagnetic susceptibility (DMS) of impurity doped quantum dot (QD) in presence of Gaussian white noise. Noise has been introduced to the system additively and multiplicatively. In view of these profiles of DMS have been pursued with variations of several important quantities e.g. magnetic field strength, confinement frequency, dopant location, dopant potential, and aluminium concentration, both in presence and absence of noise. We have invariably envisaged noise-induced suppression of DMS. Moreover, the extent of suppression noticeably depends on mode of application (additive/multiplicative) of noise. The said mode of application also plays a governing role in the onset of saturation of DMS values. The present study provides a deep insight into the promising role played by noise in controlling effective confinement imposed on the system which bears significant relevance.     

Hydrostatic pressure,impurity position and electric and magnetic field effects on the binding energy and photo-ionization cross section of a hydrogenic donor impurity in an InAs Pöschl-Teller quantum ring

Using the variational method and the effective mass and parabolic band approximations, the behaviour of the binding energy and photo-ionization cross section of a hydrogenic-like donor impurity in an InAs quantum ring, with Pöschl-Teller confinement potential along the axial direction, has been studied. In the investigation, the combined effects of hydrostatic pressure and electric and magnetic fields applied in the direction of growth have been taken into account. Parallel polarization of the incident radiation and several values of the applied electric and magnetic fields, hydrostatic pressure, and parameters of the Pöschl-Teller confinement potential were considered. The results obtained can be summarised as follows: (1) the influence of the applied electric and magnetic fields and the asymmetry degree of the Pöschl-Teller confinement potential on the donor binding energy is strongly dependent on the impurity position along the growth and radial directions of the quantum ring, (2) the binding energy is an increasing function of hydrostatic pressure and (3) the decrease (increase) in the binding energy with the electric and magnetic fields and parameters of the confinement potential (hydrostatic pressure) leads to a red shift (blue shift) of the maximum of the photo-ionization cross section spectrum of the on-centre impurity.     

Exciton energy transfer between adsorbates

The electron excitation energy transfer between adsorbed molecules on a solid surface via virtual and real surface excitons is considered. The rate of energy transfer via virtual excitons is calculated analytically. The nonradiative energy transfer to surface impurity centers is considered in the case of rapid migration of virtual or real excitons leading to repeatedly changed distances between centers of excitation localization. A theoretical model of the kinetics of “surface exciton-T-center” cross annihilation is constructed as a mirror image of the theory of cross annihilation of oxygen-containing objects adapted to a system of quasiparticles.     

含顺磁杂质超导体中的束缚态

本文利用广义正则变换和自洽场方法,讨论了单个杂质对超导体的影响。证明在磁性杂质附近,可能形成一个束缚态的元激发,其能量位于能隙之中。求出了能级和波函数的解析表达式,并计算了束缚能级所引起的附加电磁吸收。讨论了与此有关的隧道和高频吸收实验。此外,还讨论了非磁性杂质对连续谱元激发的影响及杂质附近能隙的变化。     

Impurity Cu+ centers in LiF single crystals

LiF single crystals with copper impurity (0.0004–0.002%) have been grown by the Czochralski method and investigated. The luminescence, excitation, and optical absorption spectra have been recorded. The luminescence spectrum contains a band at 450 nm upon 250-nm excitation. This band is attributed to Cu⁺ centers in the samples grown. The mechanisms of capture and recombination during thermoluminescence are considered.     

Formation of impurity bands in iodine cation substitutionally doped TiO2 and its effects on photoresponse and photogenerated carriers

First-principles calculations based on the plane-wave pseudopotential (PWP) method were performed to investigate the electronic structure of iodine cation substitutionally doped anatase TiO₂ (referred to as I_sTiO₂). A 2×2×1 anatase supercell, in which one Ti atom was substituted by one iodine atom, was constructed for calculations. The calculated results reveal that iodine dopant contributes part of its 5s states to form one isolated impurity band in band gap and part of its 5p states to form some impurity bands at the bottom of conductive bands. The visible light response of I_sTiO₂ should be the consequence of the excitation between the two types of impurity bands (2.77 eV, about 450 nm). According to the distribution of impurity states, iodine dopant is considered to serve as a recombination center or an efficient trap for photogenerated carriers. This deduction was partly approved by water photosplitting under visible light irradiation.