Coulomb Interaction Of Electrons Research Articles

INFRARED WAVELENGTH QUANTUM COMMUNICATIONS BASED ON SINGLE ELECTRON TRANSISTORS

We propose to employ a selective formation method to embed an isolated self assembled quantum dot into a n-i-n junction to implement single electron transistors (SETs). The absorption and emission spectrum of SETs are theoretically studied by the Keldysh Green function method. The electronic levels and Coulomb interactions of electrons of InAs quantum dot (QD) are evaluated by an effective mass model. It is found that Coulomb interaction and level mixing in the many body open system lead to double peaks associated with the intraband transitions involving two lowest levels of the QD. We can electrically control the SETs as a single-photon source and double-photon source for 10 μm wavelength. The single photon source can be used in the application of quantum cryptograph, and the double-photon source can be utilized in the teleportation.

Quantum-Corrected Monte Carlo and Molecular Dynamics Simulation on Electron-Density-Dependent Velocity Saturation in Silicon Metal–Oxide–Semiconductor Field-Effect Transistors

The effects of electron–electron Coulomb scattering on electron quantum transport under high electric fields in silicon metal–oxide–semiconductor field-effect transistors (MOSFETs) has been studied based on a quantum-corrected Monte Carlo and molecular dynamics simulation, where the electron–electron Coulomb interaction is split into short-range and long-range interactions. The short-range interaction is included using a molecular dynamics approach, while the long-range electron–plasmon interaction is treated in two different ways: an analytical model based on quantum mechanics, and a numerical model within semiclassical treatment. The electron velocity in the inversion layer was calculated as a function of tangential electric field using a high-resistive gate MOSFET and compared with the experimental results reported by Takagi et al., which indicated that the saturation velocity depends on surface electron concentration. The analytical model for describing the long-range interaction qualitatively agrees with the experimental results in the high electric field regime. We also evaluated the role of the plasmon scattering and short-range Coulomb scattering.

Tunneling Current Through a Single Germanium Quantum Dot

The tunneling current through a germanium quantum dot (Ge QD) of nanometer size is studied theoretically. The energy levels and Coulomb interactions of electrons in a Ge QD are calculated using an effective mass model. In small Ge QDs, the interlevel Coulomb interactions as well as the intralevel Coulomb interactions are important in the calculation of tunneling current. The Anderson model with two energy levels is used to simulate the carrier transport in a single-electron transistor (SET) composed of a single Ge QD embedded in a SiO2 matrix. The tunneling current of the Ge SET is derived by the Keldysh–Green's function technique. It is found that the differential conductance displays multipeaks for the tunneling current through an isolated QD with the two energy levels, which is due to the statistical nature of the open system. Finally, the bistable current arising from the fourfold degeneracy state of Ge QD is discussed.

Temperature-dependent carrier dynamics in metallic carbon nanotubes

The low energy states in metallic armchair carbon nanotubes can decay by the electron–electron Coulomb interactions with the intraband and the interband excitations. The inelastic scattering rate is very sensitive to the changes in the electronic distribution and the state energy (or the wavevector). The temperature dependence is linear for the Fermi-momentum state. Such dependence is hardly affected by the nanotube radius and the Fermi energy. The electron–electron interactions are more efficient in electronic deexcitations compared with the electron–phonon interactions. The calculated results are roughly consistent with the experimental measurements from the time-resolved photoemission spectroscopy.

Effect of interlevel Coulomb interactions on the tunneling current through a single quantum dot

The tunneling current through a quantum dot (QD) embedded in SiO2 matrix is studied theoretically. The energy levels and Coulomb interactions of electrons in a nanometer QD are calculated using an effective mass model. The tunneling current of a QD is calculated using the Keldysh–Green function method and two-level Anderson model. In addition to four peaks arising from the intralevel Coulomb interactions, extra differential conductance peaks are found due to the interlevel Coulomb interactions and the statistical nature of the open system.

Dynamical Singlets and Correlation-Assisted Peierls Transition inVO2

A theory of the metal-insulator transition in vanadium dioxide from the high- temperature rutile to the low- temperature monoclinic phase is proposed on the basis of cluster dynamical mean-field theory, in conjunction with the density functional scheme. The interplay of strong electronic Coulomb interactions and structural distortions, in particular, the dimerization of vanadium atoms in the low-temperature phase, plays a crucial role. We find that VO2 is not a conventional Mott insulator, but that the formation of dynamical V-V singlet pairs due to strong Coulomb correlations is necessary to trigger the opening of a Peierls gap.

ELECTRON-VORTEX INTERACTION IN A QUANTUM DOT

Small numbers N<5 of two-dimensional Coulomb-interacting electrons trapped in a parabolic potential placed in a perpendicular magnetic field are investigated. The reduced wave function of this system, which is obtained by fixing the positions of N-1 electrons, exhibits strong correlations between the electrons and the zeros. These zeros are often called vortices. An exact-diagonalization scheme is used to obtain the wave functions and the results are compared with results obtained from the recently proposed rotating electron molecule (REM) theory. We find that the vortices gather around the fixed electrons and repel each other, which is to a much lesser extend so for the REM results.

Correlation between electrons and vortices in quantum dots

The exact many-body wave function for small numbers $N<5$ of two-dimensional Coulomb-interacting electrons trapped in a parabolic potential placed in a perpendicular magnetic field are investigated. The reduced wave function of this system, which is obtained by fixing the positions of $N\ensuremath{-}1$ electrons, exhibits strong correlations between the fixed electrons and the zeros of the wave function. These zeros are often called vortices. The wave functions are obtained from an exact-diagonalization scheme and the results are compared with results obtained from the recently proposed rotating electron molecule (REM) theory. We find that the vortices cluster around the fixed electrons and repel each other, which is the case to a much lesser extent for the REM results.

ELECTRON–ELECTRON INTERACTIONS IN THE QUANTUM DOT INDUCED BY THE SURFACE ACOUSTIC WAVE

In order to study the higher order quantized plateaus in the acoustoelectric current induced by the surface acoustic wave (SAW), we consider in this paper, the Coulomb interaction of electrons trapped in the SAW-induced quantum dot at the Hartree approximation level. The Hartree self-consistent potential that originates from the electron–electron interactions in the quantum dot satisfies the Poisson equation and can be solved numerically together with the Schrödinger equation; following which, the conventional tunneling mechanism can be used to interpret the step-like acoustoelectric current, in which the escape of electrons from the quantum dot determines the deviation of the current from the quantized value. It should be noted that the quantum dot is formed by both the SAW-induced potential and the Hartree self-consistent potential in our paper, which is different from previous works. We have also calculated the first and the second quantized plateaus by use of this method.

Inhomogeneous charging and screening effects in semiconductor quantum dot arrays

The electronic properties of quantum dot (QD) arrays are strongly influenced by the Coulomb interaction of electrons within the dot as well as with those in neighbouring dots. In this paper, we investigate this behaviour taking into account screening by a free electron gas in the vicinity of the QDs. We find pronounced effects for standard capacitance[ndash]voltage (CV) measurements of QD structures embedded in a pn-diode. In particular, we show that the three-dimensional nature of the problem is crucial for devices with low dot-density, whereas the self-consistency between electron depletion in the bulk layer and dot occupation is important for high dot-densities. The Coulomb interaction between the dots induces a broadening of the peaks in the CV characteristic which is comparable with the effect of disordered QD arrays, where we considered realistic size and position fluctuations obtained by a kinetic Monte Carlo simulation.

The contributions of stochastic coulomb interactions and collective space-charge field aberrations to spatial spreading in charged particle projection systems

A new computational technique based on the `nearest-neighbor' method has been used to study the effects of stochastic electron–electron coulomb interactions on the blurring of the focus spots in a lithographic electron projection system. It has been found that the collective (i.e., global) space-charge introduces two other distinct forms of spatial spreading: these are collective space-charge field aberrations and pattern-dependent aberrations. We have been able to separately simulate the first two of these three forms of blurring and to study them in isolation from lens aberrations. It has been found that the blurring is dominated by stochastic coulomb interactions when the beam pencil angle is small but conversely is dominated by collective space-charge field aberrations when the pencil angle is large. The blurring due to pattern-dependent aberrations has been found to be relatively less important. Results are presented for a range of currents and pencil angles for a representative projection system.

Orbital moments of CrO 2 and Fe 3O 4 studied by MCD in soft X-ray absorption

We present studies of orbital magnetic moments of CrO 2 and Fe 3O 4 by measuring magnetic circular dichroism (MCD) in soft X-ray absorption. The results show that Fe 3O 4 exhibits large orbital moments, as a consequence of the strong Coulomb interactions of Fe 3d electrons. In contrast, orbital moments of Cr in CrO 2 are nearly quenched, revealing that Cr 3d electrons are strongly hybridized with O 2p electrons and more delocalized as compared with those of Fe in Fe 3O 4. Comparing the MCD data with the band structure calculations based on local spin density approximation with on-site Coulomb energy U taken into account, we conclude that to include the on-site Coulomb interactions of 3d electrons is essential for adequately describing the electronic structure of CrO 2 and Fe 3O 4.

Test-Particle Approach to Electron Dephasing in an Open Mesoscopic Cavity

The quantum interference effect is suppressed by dephasing processes. The dephasing in mesoscopic systems at low temperatures is mainly caused by electron–electron Coulomb interactions. Usually, the magnitude of the suppression is characterized by the dephasing time . It has been shown that its T-dependence changes according to the effective dimensionality of a system. Using nano-fabrication technology, we can prepare a mesoscopic cavity which is connected to reservoirs through a pair of thin leads. A mesoscopic cavity with a weak opening can be regarded as a quasi-zero-dimensional system, and the quantum transport properties in such a system are qualitatively different from those in higher dimensional systems. We expect that the dephasing nature is also qualitatively different. We hereafter focus on the case where the classical electron motion is diffusive or chaotic. If the width of the leads is reduced, the dwelling time d for electrons becomes very long. Due to the confining effect, there arises a nearly uniform diffusion mode with the lowest eigenvalue 0 1⁄4 h = d. This mode dominantly contributes the quantum interference corrections to conductance when temperature T is sufficiently low. The present author has studied the Tdependence of for the mode by a self-consistent renormalization approach (SCRA), and found an interesting crossover behavior of . It has been shown that behaves as 1 / T when T 0=kB. If T is decreased below 0=kB, the T-dependence of crosses over to 1 / T and the dephasing effect becomes nearly negligible. In this short note, we reconsider the dephasing problem in an open mesoscopic cavity by adopting a test-particle approach. We explicitly calculate the dephasing factor for the weak-localization correction arising from a timereversed pair of paths with duration . In the long-time regime of h ðkBTÞ , the dephasing factor obeys a simple exponential law expð = 1Þ, as usually expected. However, much slower decay expð ð = 2ÞÞ is observed in the short-time regime of h ðkBTÞ . Here, 1 and 2 are characteristic time scales and satisfy h 1 1 , h 1 2 kBT . It is shown that in the case of T 0=kB is determined by the slow decay expð ð = 2ÞÞ. This is the reason why the dephasing effect becomes nearly negligible in the lowtemperature regime. On the other hand, the exponential law expð = 1Þ determines in the high-temperature regime. The resulting is in agreement with that of the SCRA apart from numerical factors. We set h 1⁄4 kB 1⁄4 1 in the following. We adapt the test-particle approach to our problem. Let us consider a time-reversed pair of paths with duration . We introduce a classical path x1ðtÞ which starts from x1ð0Þ and ends at x1ð Þ, and express its time-reversed path as x2ðtÞ. Let us assume that wave packets 1ðr; tÞ and 2ðr; tÞ follow the classical paths x1ðtÞ and x2ðtÞ, respectively. The test particle interacts with a bath of environment electrons. We introduce the density operator WenvðtÞ for the environment and the state vectors j1i and j2i which correspond to 1ðr; tÞ and 2ðr; tÞ, respectively. The test-particle state is described by a linear combination of j1i and j2i. We assume that the environment at t 1⁄4 0 is in thermal equilibrium with respect to the Hamiltonian Henv for the environment electrons including the Coulomb interactions between them. The density operator at t 1⁄4 0 is given by Wð0Þ 1⁄4 WS Wenvð0Þ, where WS 1⁄4 P i;j1⁄41;2 jiiwijhjj. The interference amplitude is Fð Þ 1⁄4 h1j trenvfWð Þgj2i. The dephasing is characterized by the dephasing factor ð Þ Fð Þ=Fð0Þ. In terms of the density of environment electrons ðrÞ and its average value 0, we define ðrÞ as ðrÞ 1⁄4 ðrÞ 0. The Coulomb interaction of the test particle with the environment electrons is expressed as

The contributions of stochastic coulomb interactions and collective space-charge field aberrations to spatial spreading in charged particle projection systems

A new computational technique based on the `nearest-neighbor' method has been used to study the effects of stochastic electron–electron coulomb interactions on the blurring of the focus spots in a lithographic electron projection system. It has been found that the collective (i.e., global) space-charge introduces two other distinct forms of spatial spreading: these are collective space-charge field aberrations and pattern-dependent aberrations. We have been able to separately simulate the first two of these three forms of blurring and to study them in isolation from lens aberrations. It has been found that the blurring is dominated by stochastic coulomb interactions when the beam pencil angle is small but conversely is dominated by collective space-charge field aberrations when the pencil angle is large. The blurring due to pattern-dependent aberrations has been found to be relatively less important. Results are presented for a range of currents and pencil angles for a representative projection system.

ELECTRONICS OF MOLECULAR NANOCLUSTERS

The molecular nanoclusters proved to be very promising objects for applications in electronics not only because they have absolutely identical chemical structure and allow for bottom to top approach in constructing new electronic devices, but also for the possibility to design and create great variety of such clusters with specific properties. The formation and deposition of mixed Langmuir monolayers composed of inert amphiphile molecular matrix and guest ligand-stabilized metal-core nanoclusters are described. This approach allowed to obtain the ordered stable reproducible planar monolayer and multilayer nanocluster nanostructures on solid substrates. The use of novel polymeric Langmuir monolayers formed by amphiphilic polyelectrolytes and nanoclusters resulted in fabrication of ultimately thin monomolecular nanoscale-ordered stable planar polymeric nanocomposite films. The morphology and electron transport in fabricated nanostructures were studied experimentally using AFM and STM. The effects of single electron tunneling at room temperature through molecular cluster object containing finite number of localized states were theoretically investigated taking into account electron–electron Coulomb interaction. It is shown that tunnel current-bias voltage characteristic of such tunnel junction is characterized by a number of staircase steps equal to the number of cluster's eigenlevels, however the fronts of each steps are asymptotically linear with finite inclination. The analytically obtained current–voltage characteristics are in agreement with experimental results for electron tunneling through molecular nanoclusters at room temperatures.

Many-body effects in magnetic circular dichroism at Ce L2,3 absorption edges in CeFe 2

Magnetic circular dichroism (MCD) of the X-ray absorption spectroscopy (XAS) at the Ce L 2,3 edges in a typical mixed valence compound, CeFe 2, is theoretically studied by using the impurity Anderson model combined with a cluster approach. We find that the hybridization of Ce 5d states with spin-polarized Fe 3d states is responsible for the differences between XAS and MCD, while the Coulomb interaction of a photo-excited 5d electrons plays a novel role, in addition to the many body effects yielding the two-peak structure of XAS.

Monte-Carlo calculation of Boersch energy spreading

The effects of electron–electron coulomb interactions have been simulated by a general computational technique that can be applied to almost any system, independently of the shape of the beam or the regimes that might be present, provided that the ‘closest-encounter’ approximation is valid for the system. The technique has been applied to the ‘benchmark test’ of the energy spreading in a converging round beam. The results are compared with previous analytical results.

Coulomb interaction in the spin Hall effect

The influence of the electronic Coulomb interaction on the spin-orbit-coupling induced spin Hall effect was discussed. It was shown that the electronic Coulomb interaction may decrease substantially the spin-orbit-coupling induced transverse spin accumulation in a sample when a longitudinal charge current circulates in it, and the decrease of the transverse spin accumulation due to the influences of the Coulomb interaction is determined by the ratio of the spin-drag resistivity to the ordinary resistivity of the sample.

Umklapp scattering in cuprates

The insulating Mott state is formed due to repulsive electron–electron Coulomb interaction in the presence of the lattice (or in other words, due to electron–electron Umklapp processes). The second moment conductivity sum rule is derived, and it allows us to evaluate the strength of Umklapp scattering and the static electron–lattice energy. Mid-infrared spectra of current–current and density–density correlation functions in cuprates are suggested as evidence of strong Umklapp scattering.

Correlated Charge Excitations in Quasi-Low-Dimensional Mott Insulators

We report momentum dependence of charge excitations across the effective Mott gap in quasi-low dimensional model cuprates with different effective dimensionalities ( CuGeO 3 and SrCuO 2), using high resolution inelastic X-ray scattering by working near a resonance. Particle-hole pair excitations at the gap edge in these compounds are found to be strongly dependent on the effective dimensionality of the lattice and the strength of electron–electron Coulomb interaction.