Some properties of an ultimately nonideal metastable supercooled plasma

The formation of a metastable plasma state from an initial strongly nonideal state and certain properties of this metastable supercooled state are considered by directly modeling the dynamics of a system of many Coulomb particles. It is shown that the relaxation of the average kinetic energy of the particles can be characterized by a universal dimensionless function and, in particular, that an ultimate value degree of plasma nonidealness occurs which can be reached in the metastable state when no external action is present. The calculated binary correlation functions are in good agreement with the results of the Debye model, even outside its range of applicability. The time dependence of the total dipole moment of the system of particles is investigated. It is shown that there are oscillations of the total dipole moment. These collective oscillations take place at a frequency which is somewhat below the Langmuir frequency, the oscillations of the free and bound electrons occurring in antiphase. A hypothesis is advanced to the effect that recombination relaxation is frozen on account of the interaction of quasibound electrons with the Langmuir oscillations of the free electrons. Institute of General Physics, Academy of Sciences of the Russian Federation. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 3–16, October, 1996.     

Limiting nonideal metastable supercooled plasma

Direct modeling of the dynamics of a system of many Coulomb particles is applied to analyze the formation stage of a metastable plasma state from an initial, highly nonideal state, and also to consider some properties of this metastable supercooled state. It is shown that relaxation of the average particle kinetic energy may be characterized by a universal dimensionless function and in particular, there is a limiting degree of plasma nonideality which may be achieved in the metastable state, in the absence of any external influence. The calculated pair correlation functions agree with the results of the Debye model, even outside its limits of validity. The time dependence of the total dipole moment of the particle system is investigated. It is shown that oscillations of the total dipole moment are observed. These collective oscillations take place at a frequency slightly below the Langmuir frequency and the oscillations of free and bound electrons are in antiphase. The hypothesis is put forward that recombination relaxation is frozen as a result of interaction between quasibound electrons and Langmuir oscillations of free electrons. Zh. Tekh. Fiz. 67, 42–52 (August 1997)     

Dynamic localization of two electrons in AC-driven triple quantum dots and quantum dot shuttles

We analyze the dynamic localization of two interacting electrons induced by alternating current electric fields in triple quantum dots and triple quantum dot shuttles. The calculation of the long-time averaged occupation probability shows that both the intra-and inter-dot Coulomb interaction can increase the localization of electrons even when the AC field is not very large. The mechanical oscillation of the quantum dot shuttles may keep the localization of electrons at a high level within a range if its frequency is quite a bit smaller than the AC field. However, the localization may be depressed if the frequency of the mechanical oscillation is the integer times of the frequency of the AC field. We also derive the analytical condition of two-electron localization both for triple quantum dots and quantum dot shuttles within the Floquet formalism.     

典型甚低频电磁波对辐射带高能电子的散射损失效应

辐射带中高能电子与空间甚低频电磁波由于波粒共振相互作用发生投掷角散射, 进而沉降入稠密大气而损失. 为研究甚低频电磁波对辐射带中高能电子的散射作用机制, 本文基于准线性扩散理论, 利用库仑作用和波粒共振相互作用扩散系数的物理模型, 得到了两组典型甚低频电磁波与高能电子波粒共振相互作用的赤道投掷角弹跳周期平均扩散系数, 并分析了甚低频电磁波共振散射作用与大气库仑散射作用对不同磁壳及不同能量的辐射带电子扩散损失的影响规律. 以磁壳参数L=2.2, 能量E=0.5 MeV的辐射带电子作为算例, 采用有限差分方法数值求解扩散方程, 计算分析了电子单向通量和全向通量随时间的沉降损失演化规律. 研究结果表明: 当电子能量大于0.5 MeV, 磁壳参数大于1.6时, 甚低频电磁波的共振散射作用显著; 随着磁壳参数或电子能量的增大, 斜传播甚低频电磁波引起的高阶共振相互作用越来越大; 电子全向通量近似随时间呈指数函数形式衰减.     

Energy loss of a fast-electron beam due to the excitation of collective oscillation in hot plasma

Energy loss due to a fast-electron beam interacting with the hot plasma at a high density is analysed theoretically. By splitting the particle density fluctuations into the individual part due to the random thermal motion of the individual electrons and the collective part due to plasma－wave excitation, we are concerned with the collective interaction of the relativistic plasma electrons resulting from the Coulomb interactions. Consequently, we derive the frequency of the hot plasma and the "Debye length" with the modification of the relativistic effect. And finally we calculate the energy loss of a fast-electron beam due to the excitation of collective oscillation in the hot plasma.     

耦合量子点中的纠缠测量

运用Gurvitz提出的求解薛定谔方程的方法并结合数值计算,分析了两个自旋相反的电子在耦合双量子点中的振荡和纠缠情况,以及如何利用量子点接触读出纠缠信息.结果显示两电子通过库伦相互作用形成量子纠缠态.强库伦作用下,它们黏在一起运动,类似于单电子在量子比特中的振荡.这种情况下,把量子点接触探测器靠近耦合双量子点,可以通过探测器的电流变化率读取电子的纠缠信息.     

Behavior features of phononless hopping conductivity in the vicinity of the crossover from the linear to quadratic frequency dependence

It was shown that the Coulomb interaction between electrons of “active” (resonance) pairs plays a major role in a wide frequency range. Therefore, the conventional approach to the calculation of the super-linearity of the frequency dependence of ac conductivity, based on the single-particle density of states with a Coulomb gap, is inapplicable to the calculation of high-frequency phononless conductivity. The observed superlinearity of the frequency dependence of the phononless hopping conductivity can manifest itself immediately in the region of the crossover from the linear to quadratic frequency dependence of the conductivity.     

From Faraday rotation to “Faraday oscillation”: Coherence effect between real and virtual excitons

This work provides the microscopic mechanisms responsible for circular birefringence changed into linear birefringence when the polarization of the excitons present in a semiconductor sample goes from circular to linear. This change shows up as Faraday rotation turning to “Faraday oscillation”: The probe polarization plane oscillates instead of rotates while the polarization goes from linear to elliptical and linear again. This oscillation, which reduces to zero when the probe polarization is parallel or perpendicular to the exciton polarization, comes from a non trivial coherence effect between real excitons present in the sample and virtual excitons coupled to unabsorbed photons. While Faraday rotation mainly follows from one single carrier exchange between composite excitons in the absence of Coulomb interaction, Faraday oscillation requires two Coulomb interactions plus a double carrier exchange, the virtual excitons coupled to the unabsorbed “in” and “out” photons being made with different electrons and holes, as nicely revealed by Shiva diagrams which visualize the many-body physics taking place in composite-exciton systems.     

Interference Behaviors of Resonant Transport Through a Mesoscopic System with ac Responses

Time-dependent interference behaviors on currents transporting through a mesoscopic system are investigated by using the Keldysh nonequilibrium Green function technique. The system is composed of a quantum dot coupled with two electron reservoirs. The electrons in the quantum dot are perturbed by two microwave fields (MWFs) through gate. The MWFs cause the energy level splitting in the quantum dot to form multi-channel for the tunneling current, and these branches of current interfere to produce stable oscillation. The resulting oscillation of current is strongly associated with frequency relations between MWFs. The timedependent current is the consequence of resonant effects for electrons resonating with quantum dot state and with MWFs. We present numerical calculations for the cases where the Coulomb interaction U = 0. Negative temporal current and differential conductance are observed even if the dc bias is not small. We compare the results with corresponding quantities in the system perturbed by single MWF.     

The influence of Coulomb interaction on transport through mesoscopic two-barrier structures

We investigate the influence of the Coulomb interaction on the energy spectrum of a finite number of electrons in a geometrically confined quantum mechanical system. The spectrum is calculated numerically using the Slater determinants of the one-electron states as basis set. It is found to be dominated by the Coulomb repulsion when the system is large. Coulomb and exchange matrix elements for a given combination of four one-electron states are of the same order of magnitude. As a consequence, the energy difference between the ground states of the (N+1)- and theN-electron system is an order of magnitude smaller than each of the matrix elements, although being much larger than the separation of the one-electron energy levels. We discuss the importance of the interaction effects for the explanation of the recently observed resonant behavior of the electronic transport through quantum dots.     

The influence of the s-d(f) coulomb interaction on the transition element compound superconductive critical temperature

The influence of s-d Coulomb interaction on the superconductive critical temperature T_c of transition element compounds and their dilute alloys was investigated in the frame of Anderson model. Coulomb interaction of electrons with opposite spins on the same atom was considered in a ladder approximation valid when hybridization is sufficiently small while s-d Coulomb interaction has led to the “parquet” summation. It is shown that s-d Coulomb interaction results in the decrease of T_c and hence the electron mechanism of superconductivity seems to be noneffective in systems under consideration.     

Multiplication of high-energy electrons in irradiated materials studied using the Boltzmann kinetic equation

Processes involved in the formation of electron collision cascades created by nonrelativistic high-energy electrons, which can develop in materials exposed to electron and gamma radiation fluxes, have been considered. The problem is solved using the Boltzmann kinetic equation for high-energy electrons moving in a medium. A model scattering indicatrix is constructed for this equation with an arbitrary potential of interaction between colliding particles. Using this scattering indicatrix, the distribution of the particle energies is obtained. Based on this energy distribution (with an arbitrary interparticle interaction potential), a cascade function is found that describes the multiplication of knock-out electrons (electron cascade) generated when a high-energy electron with a certain energy is scattered on the electron subsystem of the irradiated material. The cascade function has been calculated for the Coulomb potential of the interaction between a high-energy electron and atomic-shell electrons.     

Melting of strongly coupled,negatively charged,two-dimensional dust cluster: The role of charge fluctuation amplitude

Structural and melting characteristics are investigated for negatively charged dust particles in the presence of a two-dimensional electrostatic parabolic confinement potential. For a restricted number of dust particles that are subject to the permanent flow of electrons and ions, numerical simulation is conducted taking into account the random charge fluctuation. The amplitude of the charge fluctuation affects the ground-state configuration and melting characteristics of a finite number of particles interacting through Coulomb potential. The melting temperature decreases when the amplitude of the charge fluctuation increases as a result of particles' strong repulsive interaction.     

Charged particles on a two-dimensional lattice subject to anisotropic Jahn-Teller interactions

The properties of a system of charged particles on a 2D lattice, subject to an anisotropic Jahn-Teller-type interaction and 3D Coulomb repulsion, are investigated. In the mean-field approximation without Coulomb interaction, the system displays a phase transition of first order. When the long-range Coulomb interaction is included, Monte Carlo simulations show that the system displays very diverse mesoscopic textures, ranging from spatially disordered pairs to ordered arrays of stripes, or charged clusters, depending only on the ratio of the two interactions (and the particle density). Remarkably, charged objects with an even number of particles are more stable than with an odd number of particles. We suggest that the diverse functional behavior-including superconductivity-observed in oxides can be thought to arise from the self-organization of this type.     

氢团簇在飞秒强激光场中的动力学行为

利用分子动力学方法研究了氢团簇在飞秒强激光场中的动力学行为. 与库仑爆炸模型所预言的不同, 团簇的膨胀是各向异性的, 质子平均动能沿激光场极化方向上的分量要明显大于垂直于激光场极化方向上的分量. 讨论了团簇各向异性膨胀产生的原因, 分析了激光和团簇参数对各向异性程度的影响.     

Derivation of the Euler Equations¶from a Caricature of Coulomb Interaction

A caricature of collisionless plasma involving 2N particles of opposite charge is introduced. The N first particles are called "ions" and don't move. The N other particles are called "electrons". At each time, there is a one-to-one matching between electrons and ions and each pair is linked by a "spring" so that each electron oscillates with fixed frequency )^у. The essential point is that the matching between electrons and ions is updated at every discrete time n‰, n˸,1,2,..., so that the total potential energy of the system stays minimal. This leads to a non trivial interaction which turns out to be a caricature of Coulomb interaction. It is proven that, provided the N ions are equally spaced in a bounded domain D and ), ‰ and N^у tend to zero at appropriate rates, the electrons behave as the fluid parcels of an incompressible inviscid liquid moving inside D according to the Euler equations. Our proof relies on a result of P. Lax on the approximation of volume-preserving transformations by permutations.     

Dynamic transport characteristics of side-coupled double-quantum-impurity systems

A systematic study is performed on time-dependent dynamic transport characteristics of a side-coupled double-quantum-impurity system based on the hierarchical equations of motion. It is found that the transport current behaves like a single quantum dot when the coupling strength is low during tunneling or Coulomb coupling. For the case of only tunneling transition, the dynamic current oscillates due to the temporal coherence of the electron tunneling device. The oscillation frequency of the transport current is related to the step voltage applied by the lead, while temperature $T$, electron--electron interaction $U$ and the bandwidth $W$ have little influence. The amplitude of the current oscillation exists in positive correlation with $W$ and negative correlation with $U$. With the increase in coupling $t_{12}$ between impurities, the ground state of the system changes from a Kondo singlet of one impurity to a spin singlet of two impurities. Moreover, lowering the temperature could promote the Kondo effect to intensify the oscillation of the dynamic current. When only the Coulomb transition is coupled, it is found that the two split-off Hubbard peaks move upward and have different interference effects on the Kondo peak at the Fermi surface with the increase in $U_{12}$, from the dynamics point of view.     

Two Electron States in a Thin Spherical Nanolayer: Reduction to the Model of Two Electrons on a Sphere

Two electron states in a thin spherical nanolayer are discussed. Adiabatic approach is used to divide the system to fast (radial) and slow (angular) subsystems. This leads the Coulomb interaction to be dependent on angular variables, more precisely, on the relative angle between electrons. Approximated Coulomb interaction potential is discussed. Analytical solutions for angular part of Schrödinger equation as well as for energy spectrum for the case of harmonic approximation are obtained. Also the first order of correction energy is discussed by using perturbation theory. For the ground state an analytical expression for the first order correction energy dependent on effective radius of the nanolayer is obtained. Obtained results are compared with exact Coulomb interaction model presented by Loos and Gill.     

Coexistence of the chiral superconductivity and noncollinear magnetic order in the ensemble of Hubbard fermions on a triangular lattice

For the system of strongly correlated electrons on a triangular lattice, the possibility of coexisting superconductivity with the chiral order parameter and the 120°-type noncollinear spin ordering is demonstrated. The integral self-consistency equation for the superconducting order parameter is derived using the diagram technique for Hubbard operators taking into account the spin structure, exchange interaction within two coordination spheres, and intersite Coulomb repulsion.