Single-particle spectrum of the degenerate electron gas

The single-particle spectrum of an interacting electron gas is discussed. There is a characteristic structure in the spectral weight function at energies that differ from the quasi-particle energy by energies of the order of the plasma energy. This structure is due to the singular Coulomb potential and the plasmon part of the effective interaction at long wavelengths. For momenta deep inside the Fermi sea a new elementary excitation of appreciable strength appears. It can be interpreted as a coupled mode of holes and plasmons.     

耦合锗量子点中空穴态对称特性研究

分别采用单带重空穴近似和六带Kronig-Penney模型, 对垂直耦合锗量子点在不同耦合距离下的空穴态特性进行了计算, 并探讨了自旋-轨道的相互作用对空穴态对称性的影响. 计算结果表明: 多带耦合的框架下, 随着量子点垂直间距的增大, 空穴基态从成键态转变为反键态, 而且价带基态能级和第一激发态能级发生反交叉现象, 这与单带模型下得到的相应结果存在较大差异. 通过分析六带模型计算得到的成、反键态波函数, 轻、重空穴态和自旋-轨道分裂态对特征空穴态波函数的贡献比例随着量子点垂直间距的增大发生了转变, 并最终导致量子点空穴基态波函数由成键态转变为反键态. 关键词： 耦合量子点 空穴态 成健态-反健态 自旋-轨道     

SU(3) spin-orbit coupled fermions in an optical lattice

We propose a scheme to realize the SU(3)spin-orbit coupled three-component fermions in an one-dimensional optical lattice.The topological properties of the single-particle Hamiltonian are studied by calculating the Berry phase,winding number and edge state.We also investigate the effects of the interaction on the ground-state topology of the system,and characterize the interaction-induced topological phase transitions,using a state-of-the-art density-matrix renormalization-group numerical method.Finally,we show the typical features of the emerging quantum phases,and map out the many-body phase diagram between the interaction and the Zeeman field.Our results establish a way for exploring novel quantum physics induced by the SOC with SU(N)symmetry.     

On the influence of the electron-velocity spread in a beam on the mechanism of Cherenkov beam–plasma interaction

The instability of an electron beam in cold plasma is considered in the linear potential approximation with different velocity-distribution functions of beam electrons. It is demonstrated that the mechanism of beam instability in plasma changes as the electron-velocity spread is increased: the hydrodynamic single-particle instability mode evolves into the hydrodynamic collective mode or the single-particle kinetic one. Instability growth rates in different modes are determined analytically and numerically.     

电磁波在非磁化等离子体中衰减效应的实验研究

针对等离子体隐身技术在航空航天领域的良好应用前景, 开展垂直入射到具有金属衬底的非磁化等离子体中电磁波衰减特性的理论与实验研究. 利用WKB方法对电磁波衰减随等离子体参数的变化规律进行了理论分析. 利用射频电感耦合放电方式产生稳定的大面积等离子体层, 搭建了等离子体反射率弓形测试系统, 进行了电磁波在非磁化等离子体中衰减效应的实验研究. 利用微波相位法和光谱诊断法, 得到不同放电功率下的等离子体电子密度, 其范围为8.17×10⁹–7.61× 10¹⁰ cm^-3. 本实验获得的等离子体可以使2.7 GHz 和10.1 GHz电磁波分别得到一定的衰减, 且电磁波衰减的理论与实验结果符合较好. 结果表明, 提高等离子体电子密度和覆盖均匀性有利于增强等离子体对电磁波的衰减效果.     

Nonlinear theory of resonant beam-plasma interaction: Nonrelativistic case

Analytic and numerical methods are used to study the nonlinear dynamics of the resonant interaction between a dense nonrelativistic electron beam and a plasma in a spatially bounded system. Regimes such as collective (Raman) and single-particle (Thomson) Cherenkov effects are considered. It is shown that in the first case, the motion of both the beam and plasma electrons exhibits significant nonlinearities. However, because of the weak coupling between the beam and the plasma, the nonlinear dynamics of the instability can be studied analytically and it can be strictly shown that saturation of instability is caused by a nonlinear shift of the radiation frequency and loss of resonance. In the second case, the nonlinear instability dynamics can only be studied numerically. In this regime, at low beam densities significant nonlinearity is only observed in the motion of the beam electrons while the plasma remains linear and saturation of the instability is caused by trapping of beam electrons in the field of the beam-excited plasma wave.     

Design and electrical characteristics of a modular plasma torch

A modular system for constructing an atmospheric pressure plasma source is presented and studied. The design and construction of the plasma torch module by modifying and reassembling the structural components of two different models of spark plugs are first described. Each module can produce a torch plasma of 1 cm radius and 6 cm height and having a peak density exceeding 10¹³ cm^-3. A set of modules, each connected in series with a ballasting capacitor in the circuit, can be operated as an array sharing a common power source to produce a dense and large-volume plasma. The electrical characteristics of the module are studied for the case of a single module and two capacitively coupled modules. The discharge can be maintained, with the aid of ballasting capacitors, in a stable diffuse arc. Furthermore, the coupled discharges in an array of modules are operated with the maximum power efficiency as indicated by a near one power factor seen by the power line     

Single- and Two-Particle Energies and Thermodynamics of Dense Plasmas

Single- and two-particle states in dense plasmas differ significantly from those of ideal systems and have especially a finite lifetime. Both the bound states and the continuum edges of two-particle states are controlled by “complex single-particle energies”. Furthermore, the thermodynamics can be given by these quantities. For this reason we study the spectral weight function of the single-particle Green's function and solve the equivalent dispersion relation self-consistently in the Montroll-Ward approximation of the self energy. We give results for the continuum edges of a hydrogen plasma and of a model electron-hole plasma and discuss approximations for the equation of state.     

Structure of the ground state of a nonsuperfluid dense quark-gluon plasma

The single-particle spectrum and momentum distribution of quasiparticles in a cold dense quark-gluon plasma are calculated within the Fermi liquid approach. It is shown that this system does not behave as a standard Fermi liquid: at zero temperature, the single-particle spectrum has a plateau at the Fermi surface, while the Fermi surface itself has a nonzero volume in momentum space.     

Optical transitions in artificial few-electron atoms strongly confined inside ZnO nanocrystals

We have studied the optical transitions in artificial atoms consisting of one to ten electrons occupying the conduction levels in ZnO nanocrystals. We analyzed near IR absorption spectra of assemblies of weakly coupled ZnO nanocrystals for a gradually increasing electron number and found four allowed dipole transitions with oscillator strengths in quantitative agreement with tight-binding theory. Furthermore, this spectroscopy provides the single-particle energy separation between the conduction levels of the ZnO quantum dots.     

Influences of Temperature and Average Interparticle Distance on the Properties of Two-Dimensional Dusty Plasma

The structure and single-particle motion of a two-dimensional dusty plasma have been investigated. Pair correlation function, mean square displacement, velocity autocorrelation function, and the corresponding spectrum function have been computed by molecular dynamical simulation. The results show that the coagulation of a two-dimensional dusty plasma system is strongly affected by particle density and temperature, which are discussed in details.     

Exact calculations and a fermion pair description of the s-bosons used in the interacting boson approximation

A convenient method is proposed for exact calculations using wave functions that are products of correlated fermion pairs coupled to zero angular momentum. The method is valid for arbitrary forces and arbitrary single-particle energies. The exact results are compared to various approximations and are used to generate an equivalent s-boson Hamiltonian.     

Anisotropic plasmon dispersion and damping in multilayer 8-Pmmn borophene structures

We investigate the collective plasma oscillations theoretically in multilayer 8-Pmmn borophene structures, where the tilted Dirac electrons in spatially separated layers are coupled via the Coulomb interaction. We calculate the energy dispersions and Landau dampings of the multilayer plasmon excitations as a function of the total number of layers, the interlayer separation, and the different orientations. Like multilayer graphene, the plasmon spectrum in multilayer borophene consists of one in-phase optical mode and N - 1 out-of-phase acoustical modes. We show that the plasmon modes possess kinks at the boundary of the interband single-particle continuum and the apparent anisotropic behavior. All the plasmon modes approach the same dispersion at a sufficiently large interlayer spacing in the short-wavelength limit. Especially along specific orientations, the optical mode could touch an energy maximum in the nondamping region, which shows non-monotonous behavior. Our work provides an understanding of the multilayer borophene plasmon and may pave the way for multilayer borophene-based plasmonic devices.     

Single-particle states of an arbitrarily coupled scalar field

It is shown that the method, proposed in [1, 2], for determining single-particle states and the vacuum of a conformally coupled ( = 1/6) scalar field by diagonalizing the metric Hamiltonian is not applicable if 1/6, since it leads to a physically meaningless result: an infinite number of particles is created in the model where particles should not be created at all. For this reason, it is proposed that in the method of diagonalization the metric Hamiltonian be replaced by a canonical Hamiltonian, the freedom of choosing which makes it possible to impose some necessary conditions. Implementing this program permits determining the single-particle states of an arbitrarily coupled scalar field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 49–53, October, 1990.     

Merging of single-particle levels in finite Fermi systems

Properties of the distribution of single-particle levels adjacent to the Fermi surface in finite Fermi systems are studied, focusing on the case in which these levels are degenerate. The interaction of the quasiparticles occupying these levels lifts the degeneracy and affects the distance between the closest levels on opposite sides of the Fermi surface, as the number of particles in the system is varied. In addition to the familiar scenario of level crossing, a new phenomenon is uncovered, in which the merging of single-particle levels results in the disappearance of well-defined single-particle excitations. Implications of this finding are discussed for nuclear, solid-state, and atomic systems. The text was submitted by the authors in English.     

Single-particle motion in the strongly coupled one-component plasma

We present molecular dynamics computations of the time-dependent auto-correlation function of the single-particle density in a classical one-component plasma for three thermodynamic states in the range of intermediate and strong coupling. The deviations from the Gaussian approximation are calculated and the data are analyzed by the standard memory function formalism.     

Electron interference and entanglement in coupled 1D systems with noise

We estimate the role of noise in the formation of entanglement and in the appearance of single- and two-electron interference in systems of coupled one-dimensional channels. Two cases are considered: a single-particle interferometer and a two-particle interferometer exploiting Coulomb interaction. In both of them, environmental noise yields a randomization of the carrier phases. Our results assess how the complementarity relation linking single-particle behavior to nonlocal quantities (such as entanglement and environment-induced decoherence) acts in electron interferometry. We show that in an experimental implementation of the setups examined, one- and two-electron detection probability at the output drains can be used to evaluate the decoherence and the degree of entanglement.     

Effects of Coulomb interactions on spin states in vertical semiconductor quantum dots

The effects of direct Coulomb and exchange interactions on spin states are studied for quantum dots contained in circular and rectangular mesas. For a circular mesa a spin-triplet favored by these interactions is observed at zero and nonzero magnetic fields. We tune and measure the relative strengths of these interactions as a function of the number of confined electrons. We find that electrons tend to have parallel spins when they occupy nearly degenerate single-particle states. We use a magnetic field to adjust the single-particle state degeneracy, and find that the spin-configurations in an arbitrary magnetic field are well explained in terms of two-electron singlet and triplet states. For a rectangular mesa we observe no signatures of the spin-triplet at zero magnetic field. Due to the anisotropy in the lateral confinement single-particle state degeneracy present in the circular mesa is lifted, and Coulomb interactions become weak. We evaluate the degree of the anisotropy by measuring the magnetic field dependence of the energy spectrum for the ground and excited states, and find that at zero magnetic field the spin-singlet is more significantly favored by the lifting of level degeneracy than by the reduction in the Coulomb interaction. We also find that the spin-triplet is recovered by adjusting the level degeneracy with magnetic field. Received: 14 April 2000 / Accepted: 17 April 2000 / Published online: 6 September 2000