Modelling inter-dot Coulomb interaction effects in field effect transistors with an embedded quantum dot layer

By a computer simulation we study the real space and energy distributions of 0D electrons bound in a planar array of quantum dots, including both intra-dot charging and inter-dot Coulomb interaction effects, size fluctuations, as well as the screening by a parallel gas of 2D electrons.It is demonstrated that the mutual Coulomb shifts between different dots cause pronounced many-body correlation effects and in-plane potential fluctuations, which can be significant for experiments such as capacitance and tunneling spectroscopy. In addition we investigate the influence of charged dot scattering on the mobility of a conducting channel parallel to the dot layer.     

The influence of current neutralization and multiple Coulomb scattering on the spatial dynamics of resistive sausage instability of a relativistic electron beam propagating in ohmic plasma

Technical Physics - The influence of the current neutralization process, the phase mixing of the trajectories of electrons and multiple Coulomb scattering of electrons beam on the atoms of the...     

Study of optimum Q-value in 16O induced reactions on even Zr isotopes

Angular behaviour and optimum Q-value of ¹⁶O induced transfer reactions on the even Zr isotopes have been studied near the Coulomb barrier as a function of various parameters. The results are compared to semiclassical estimates including recoil effects and nuclear distortions of the Coulomb trajectories.     

Deflections of photoelectron classical trajectories in screened Coulomb potentials of H_2~+

The photoelectron momentum distribution of H+2in circularly polarized laser fields is studied based on classical trajectory calculations. We screen Coulomb potentials at different radii, and trace trajectories of an ensemble of electrons in such screened Coulomb potentials and circularly polarized laser fields. Simulations show that electron trajectories are bent by Coulomb fields, resulting in the laser-intensity-dependent drift of photoelectron momentum distributions in the laser polarization plane. This study intuitively explains how Coulomb potentials modify photoelectron momenta.     

Measurement of the interaction potential of microspheres in the sheath of a rf discharge

The interaction potential of two microspheres that are levitated in the sheath region of a radio frequency (rf) argon discharge is studied experimentally by analyzing their trajectories during head-on collisions. It is shown that the interaction parallel to the sheath boundary can be described by a screened Coulomb potential. Thus, values for an effective charge and a screening length can be obtained. The horizontal part of the interaction potential has been determined for several plasma conditions. There is no evidence for an attractive part in the potential within the accuracy of the present measurements and the given plasma conditions.     

Modification of the coulomb law and energy levels of hydrogen atom in superstrong magnetic field

The screening of the Coulomb potential by superstrong magnetic field is studied. Its influence on the spectrum of a hydrogen atom is determined.     

Fine-structure quenching and multiplet distortion in a screened Coulomb atom

Theoretical results presented in this paper reflect that the relativistic fine-structure due to the mass-velocity, spin-orbit and Darwin terms is sensitive to the screening strength parameter in an exponential screened Coulomb hydrogen atom, that is sometimes used to model a plasma-embedded atom. With stronger screening the fine-structure correction undergoes a gradual suppression in magnitude, but contributes to the total binding energy in an increasing proportion, indicating that the relativistic contribution to binding may become quite significant in the ultra-low binding regime under large screening strength. In the presence of screening the l-independence of the fine-structure correction as predicted by the Dirac theory progressively disappears, and a departure from the Z⁴-scaling law of the correction occurs along the H-isoelectronic sequence of ions - both the effects become accentuated with growing screening strength. In conjunction with screening-induced removal of the Coulomb degeneracy of non-relativistic levels, these result in a deformed multiplet structure for the screened Coulomb atom. Received 31 May 1999 and Received in final form 20 September 1999     

Effects of screened Coulomb (Yukawa) and exponential-cosine-screened Coulomb potentials on photoionization of H and He+

The screening effects due to the exponential-cosine-screened Coulomb and screened Coulomb (Yukawa) potentials on photoionization processes are explored within the framework of complex coordinate rotation method. The energy levels of H and He⁺ in both screened potentials shifted with various Debye screening lengths are presented. The photoionization cross sections illustrate the considerable screening effects on photoionization processes in low energy region. The shape resonances can be found near ionization thresholds for certain of Debye screening lengths. The relations between the appearance of resonances and the existence of quasi-bound states under shielding conditions are discussed.     

Dynamic Screening in Solar and Stellar Nuclear Reactions

In the hot, dense plasma of solar and stellar interiors, Coulomb potentials are screened, resulting in increased nuclear reaction rates. Although Salpeter's approximation for static screening is widely accepted and used in stellar modeling, the question of screening in nuclear reactions was revisited in the 1990s. In particular the issue of dynamic effects was raised by Shaviv and Shaviv, who applied the techniques of molecular dynamics to the conditions in the Sun's core in order to numerically determine the effect of screening. By directly calculating the motion of ions and electrons due to Coulomb interactions, the simulations are used to compute the effect of screening without the mean‐field assumption inherent in Salpeter's approximation. In the last few years, the USC group has first reproduced Shaviv and Shaviv's numerical analysis of the screening energy, showing an effect of dynamic screening. When the consequence for the reaction‐rate was computed, a rather surprising resulted, which is contrary to that from static screening theory. Our calculations showed that dynamic screening does not significantly change the reaction rate from that of the bare Coulomb potential. If this can be independently confirmed, then the effects of dynamic screening are highly relevant and should be included in stellar nuclear reaction rates (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Impurity effects in the optical absorption of quantum rings

We study the interplay between impurity scattering and Coulomb interaction effects in the absorption spectrum of neutral bound magnetoexcitons confined in quantum-ring structures. Impurity scattering breaks the rotational symmetry of the ring system, introducing characteristic features in the optical emission. Signatures of the optical Aharonov–Bohm effect are still present for weak scattering and strong Coulomb screening. Furthermore, an impurity-induced modulation of the absorption strength is present even for a strong impurity potential and low screening. This behavior is likely responsible of recent experimental observations in quantum-ring structures.     

Low Energy D(p, p)D Elastic Scattering Including Coulomb Force

The motivation of this paper is to obtain the three-body amplitudes for the Coulomb potential plus a nuclear force in momentum space. Not only the two-body off-shell nuclear amplitude but also the two-body off-shell Coulomb amplitude is important in the three-body calculation. For calculating the Coulomb amplitude, the modified Coulomb potential whose Fourier transformation is analytically equivalent to the pure configuration space Coulomb potential, is introduced. In addition, the decisive screening range parameter is also utilized instead of the screening range. The modified Coulomb potential plus the parameter is called decisive modified Coulomb potential. The three-body proton-deuteron elastic scattering is calculated by using the proper two-body off-shell amplitude for the decisive modified Coulomb potential.     

KeV channeling effects in the Mott scattering of electrons and positrons

High-energy scattering experiments mandate a point-like charge on the electron. However, the spectroscopic properties of the electron suggest an overall Compton-sized geometry. Adopting the model of a Compton-sized electron or positron that has a equatorial point charge, we use detailed computer calculations of classical Coulomb scattering off atomic nuclei to delineate the boundaries of a narrow energy window, in the KeV range, in which finite-size effects should be observable. Some experimental evidence for these finite-size effects can be found in the published literature.1. This work was performed under the auspices of the U. S. Department of Energy by the Lawrence Livermore National Laboratory under contract No. W-7405-ENG-48.2. The impact parameters shown in Fig. 1 were obtained by numerical integration of point-particle trajectories, with relativistic effects and nuclear screening included.3. When rotational and recoil effects are set equal to zero, the calculated large-positron elastic differential cross sections are accurately point-like at all incident energies.4. The calculations shown here required more than 10,000 hours of computer time on a network of seven Sun SPARC 1 and SPARC 2 computers.     

Short distance behaviour of the pair correlation function for classical plasmas

The screening effects on two like charges at short distances in a classical plasma are computed using a cluster expansion for the pair correlation function. We obtain numerically accurate results for the intermediate screening region, Λ 1, where Λ is Coulomb interaction parameter.     

The Coulomb problem in superstrong B: Atomic levels and critical nuclei charges

The spectrum of atomic levels of hydrogen-like ions originating from the lowest Landau level in an external homogeneous superstrong magnetic field is obtained. The influence of the screening of the Coulomb potential on the values of critical nuclear charges is studied.     

Completely bound motion of a positive-energy electron in the coulomb field of a motionless nucleus and a uniform magnetic field

We show that the completely bound classical motion of a positive-energy electron is realized in the Coulomb field of a motionless nucleus and a uniform magnetic field. Such a motion exists due to conservation of the so-called invariant tori in the phase space of the system for not only the negative, but also for the positive energy of an electron. The completely bound trajectories occupy a much larger interval of the velocity directions compared with free trajectories for the same energy in a range of distances from the nucleus in which the typical time of the electron transit near the nucleus is larger than the cyclotron-gyration period, while the negative energy of Coulomb interaction is larger (in absolute value) than the total electron energy. The indicated range of distances is realized in the case of a low electron energy or a strong magnetic field when the Larmor radius of the electron is smaller than the characteristic impact parameter of the close Coulomb collisions in the absence of a magnetic field. The required conditions are realized in the photospheres of isolated magnetic white dwarfs and in the experiments on creation of antihydrogen.     

Ab initio many-body treatment of the electronic structure of metals

We propose and apply a combination of an ab initio (band-structure) calculation with a many-body treatment including screening effects. We start from a linearized muffin-tin orbital (LMTO) calculation to determine the Bloch functions for the Hartree one-particle Hamiltonian, from which we calculate the static susceptibility and dielectric function within the standard random phase approximation (RPA). From the Bloch functions we obtain maximally localized Wannier functions, using a method proposed by Marzari and Vanderbilt. Within this Wannier basis all relevant one-particle and unscreened and screened Coulomb matrix elements are calculated. This yields a multi-band Hamiltonian in second quantization with ab initio parameters, for which screening has been taken into account within the simplest standard approximation. Then, established methods of many-body theory are used. We apply this concept to a simple metal, namely lithium (Li). Here the maximally localized Wannier functions turn out to be of the sp³-orbital kind. Furthermore, only the on-site contributions of the screened Coulomb matrix elements are relevant, and a generalized, four-band Hubbard model is justified. The screened on-site Coulomb matrix elements are considerably smaller than the band width because of which it is sufficient to calculate the selfenergy in weak-coupling approximation. We compare results obtained within the screened Hartree-Fock approximation (HFA) and within the second-order perturbation theory (SOPT) in the Coulomb matrix elements for Li and find that many-body effects are small but not negligible even for this simple metal.     

Electromodulated reabsorption of luminescence in GaAs-MOS and Schottky systems

The electromodulated reabsorption of luminescence in GaAs-MOS and Schottky systems have been investigated. It is indicated that this study gives important information about reabsorption with polaron effects and dissociation of free or bound excitons due to screening of the Coulomb interaction.     

Quantum-trajectory approach to time-dependent transport in mesoscopic systems with electron-electron interactions

It is proved that many-particle Bohm trajectories can be computed from single-particle time-dependent Schr?dinger equations. From this result, a practical algorithm for the computation of transport properties of many-electron systems with exchange and Coulomb correlations is derived. As a test, two-particle Bohm trajectories in a tunneling scenario are compared to exact results with an excellent agreement. The algorithm opens the path for implementing a many-particle quantum transport (Monte Carlo) simulator, beyond the Fermi liquid paradigm.