Linear response functions of a quasi-one-dimensional electron gas

The predictions for density-density-type response functions of a quasi-one dimensional electron gas are compared in detail for various models (Hubbard and Tomonaga model) and for various approximations (Monte-Carlo calculations, RPA and extended RPA). It is shown that RPA does not lead to intrinsic contradictions for electron densities larger than 1.5 inverse exciton Bohr radii. Even in this high-density regime local field corrections enhance spin- and density susceptibilities significantly.     

Exchange interaction and oscillations of the magnetization of the electron gas in a quantum cylinder

The exchange energy of the electron gas on a cylindrical surface in a constant magnetic field has been calculated. Analytical formulas describing the contribution of the exchange interaction into oscillations of the magnetization of the electron gas in a quantum cylinder have been obtained. It is shown that the magnetic response of the system exhibits Aharonov-Bohm oscillations for both degenerate and Boltzmann electron gases.     

Interacting instantons and quantum mechanical metastability

The decay by tunneling of a quantum mechanical metastable state at finite temperature is described in terms of interacting instantons. The picture of instantons with arbitrary interaction strength is developed using complex classical paths. It is shown that there exists a temperature scale at which multi-instanton configurations “freeze”. Far below this scale the partition function of the theory is that of a gas of weakly interacting particles, while far above it the contribution of only one particle dominates. It is argued that this qualitative behavior is common to all quantum mechanical systems possessing a dilute gas regime at low temperatures.     

限制在一维谐振势下的三维自由电子气的一些热力学性质

利用围路积分表达的计算系统热力学势的一个公式,得到被一维谐振子势限制、有垂直磁场作用的三维自由电子气的在任意温度下的热力学势的精确解析表达式.然后利用其研究了不同温度和尺度区域内磁化强度、磁化率和比热随磁场强度的变化情况.研究表明,低温下磁化强度、磁化率和比热随磁场强度变化出现振荡现象,其中比热还会出现两种不同的振荡模式.     

Quasi-linear analysis of Smith-Purcell free-electron amplifier

Calculations are presented of the scattering of an electromagnetic wave from a periodic structure above which flows an electron beam. The reflected fields are computed and found to comprise two separate contributions: (1) the reflection in the homogeneous case (without the beam); and (2) the contribution of the beam. Both are shown to depend on the structure by means of its reflection properties, as expressed by a reflection matrix. The beam contribution is shown to be exponentially dependent on the longitudinal position. This contribution also includes the exponential decay, which depends on the distance between the beam and the structure, and is a characteristic of Smith-Purcell devices. Expressions for the local and global gains are obtained. The local gain is found to be proportional to the first velocity derivative of the electron distribution function. Considerations of nonlinear effects introduce spatial dependence to the expression for the local gain. This dependence is determined by a nonlinear diffusion equation. The gain in the nonlinear regime is found to depend on the first and second velocity derivative of the distribution function     

Low-Frequency Behavior of the Spectral Energy Distribution Function of Equilibrium Radiation in a Degenerate Electron Gas

The low-frequency asymptotic behavior of the spectral energy distribution density of equilibrium radiation in a collisionless degenerate electron gas is studied. It is shown that the spatial dispersion in the electron gas permittivity leads to a logarithmic singularity in the spectral density distribution at low frequencies, similar to that we previously obtained for a Maxwellian plasma. In this case, the contribution of low frequencies to the total radiation energy remains finite. The results of the analytical consideration coincide with the numerical calculation.     

Interaction of spatially modulated pump and FIR waves in Raman laser

The propagation of spatially modulated IR pump and FIR generated waves interacting in the active gas medium of Raman laser is simulated numerically. Stationary nonlinear diffraction of monochromatic beams is studied for the isolated homogeneously broadened three-level system without any limitations on the values of field strength and frequency offset. It is shown that FIR radiation is trapped in the active wave guide induced owing to the nonlinear refractive index mechanism and gain inhomogeneity across the pump wave beam. Nonlinear focus positions and on-axis focal intensities for both fields are calculated.     

尿素和硫脲分子非线性光学性质的从头算研究

在B3LYP/6.31 G(2DF,2PD)水平优化气相中的尿素和硫脲分子构型,得到C2点群的非平面分子.对此构型的尿素和硫脲分子用CPHF和FF方法进行了非线性光学性质的计算,比较了尿素和硫脲非线性光学性质,讨论了极化函数、弥散函数和相关效应对(超)极化率的影响,还与固定C2v对称相同水平优化得到的平面分子计算结果进行了比较.     

Oscillatory magnetization of two-dimensional electron gas

Diamagnetic moment of the two-dimensional electron gas is calculated for finite temperature using a simple energy band model and assuming no collisional broadening of Landau levels. Numerical results are presented for GaAs band parameters. The diamagnetic moment oscillates around zero value as a function of magnetic field strength and tends to zero at low fields. It is concluded that both the diamagnetic and the paramagnetic susceptibilities of the 2D electron gas vanish in the low field limit.     

Spontaneous Faraday rotation due to strong laser radiation in a plasma

Theoretical studies on intense laser radiation interacting with plasma reveal an induced nonlinear birefringence which turns out to be spontaneous Faraday rotation. Here, this rotation is called nonlinear Faraday rotation (NFR). The expressions for the nonlinear refractive indices of the laser fields are calculated both in relativistic and non-relativistic limits for a two-component plasma. The NFR angles due to nonlinear induced birefringence are derived in the absence of externally imposed magnetic fields. It is shown that, in the relativistic limit, the electron motion plays an important role in producing NFR and so in the generation of induced magnetic fields.     

Optical parametric processes in isotropic third-order nonlinear media with magneto-optic properties

Optical parametric interaction in isotropic third-order nonlinear media with magneto-optic properties is investigated. It is shown that new phase-matching conditions with a magneto-optic contribution are possible. In particular, we study four-wave mixing and electric field-induced three-wave parametric processes in the presence of a magnetic field applied along the direction of propagation of the interacting waves. Control of the new phase-matching branches can be achieved by tuning of the magnetic field.     

Landau diamagnetism and magnetization of interacting disordered conductors

We show how the orbital magnetization of an interacting diffusive electron gas can be simply related to the magnetization of the noninteracting system having the same geometry. This result is applied to the persistent current of a mesoscopic ring and to the relation between Landau diamagnetism and the interaction correction to the magnetization of diffusive systems. The field dependence of this interaction contribution can be deduced directly from the de Haas-van Alphen oscillations of the free electron gas. Known results for the free orbital magnetism of finite systems can be used to derive the interaction contribution in the diffusive regime in various geometries.     

Directly generating vortex beams in the second harmonic by a spirally structured fundamental wave

Based on nonlinear wave mixing, we experimentally propose a scheme for directly generating optical orbital angular momentum(OAM) by a spirally structured fundamental wave interacting with a nonlinear medium, in which the nonlinear susceptibilities are homogenous. In the experiment, the second-harmonic generation of a fundamental wave carrying positive(negative) integers and fractional OAM states was investigated. This study presents a convenient approach for dynamic control of OAM of vortex beams, which may feature their applications in optical manipulation and optical communication.     

Kolmogorov-Sinai entropy of the dilute wet granular gas

We present an analytical expression for the Kolmogorov-Sinai entropy of a wet granular gas. The influence of the liquid is modeled by a hysteretic interaction force. For the dilute limit (two-particle collisions only), we find a simple expression accounting for the contribution of both the scattering states and the bound states in arbitrary dimensions. It is shown that the system is significantly more chaotic than a gas of (dry) hard spheres, as reflected by a pronounced increase of the Kolmogorov-Sinai entropy.     

Semi-empirical calculations of the magnetic properties of condensed hydrocarbons

Coupled Hartree-Fock perturbation theory is used to calculate the non-local contribution to ¹H chemical shifts and magnetic susceptibilities of alternant benzenoid, alternant non-benzenoid and non-alternant conjugated hydrocarbons. It is shown that the agreement between theory and experiment is satisfactory. For the calculation of the coupled first-order orbitals a simplified iterative procedure is proposed.     

Effect of electron-electron interaction on spin relaxation of charge carriers in semiconductors

An analysis of spin dynamics is presented for semiconductor systems without inversion symmetry that exhibit spin splitting. It is shown that electron-electron interaction reduces the rate of the Dyakonov-Perel (precession) mechanism of spin relaxation both via spin mixing in the momentum space and via the Hartree-Fock exchange interaction in spin-polarized electron gas. The change in the Hartree-Fock contribution with increasing nonequilibrium spin polarization is analyzed. Theoretical predictions are compared with experimental results on spin dynamics in GaAs/AlGaAs-based quantum-well structures. The effect of electron-electron collisions is examined not only for two-dimensional electron gas in a quantum well, but also for electron gas in a bulk semiconductor and a quantum wire.     

Spin response in nonlocal nonlinear optics

A novel effect of the electron spin in nonlinear optics is predicted. Starting from the Pauli Hamiltonian, we present the influence of the electron spin on the nonlinear optical response of a homogeneous electron gas in the low temperature limit. It is shown that the longitudinal second-harmonic response which results from a transverse incoming field differs significantly from the usual paramagnetic response when spin effects are included. The calculation is done both with and without screening.     

Microwave ponderomotive action on the inhomogeneous collisionless and collisional plasmas

The nonlinear interaction of a high-power microwave (MW) with an unmagnetized inhomogeneous plasma is investigated in collisionless and collisional regimes. The electron density distribution and the nonlinear wave equation in an inhomogeneous plasma are obtained by taking into account the ponderomotive force due to the high-power MW. It is shown that the electron density distribution becomes very steepened in the presence of the ponderomotive force. In the collisional regime, the expression for electron temperature is also found by considering ohmic heating. It is indicated that the amplitude of oscillations of the electron temperature and dielectric permittivity increases and the wavelength of these oscillations decreases with increasing energy flux, hence modulation occurs.     

Magnetism of a relativistic degenerate electron gas in a strong magnetic field

The magnetization and magnetic susceptibility of a degenerate electron gas in a strong magnetic field in which electrons are located on the ground Landau level and the electron gas has the properties of a nonlinear paramagnet have been calculated. The paradoxical properties of the electron gas under these conditions??a decrease in the magnetization with the field and an increase in the magnetization with the temperature??have been revealed. It has been shown that matter under the corresponding conditions of neutron stars is a paramagnet with a magnetic susceptibility of ?? ?? 0.001.     

Effect of excavated trapped electron distributions on ion-acoustic solitary structures in an electron-positron-ion plasma

Fully nonlinear propagation of ion-acoustic solitary waves in an unmagnetized electron-positron-ion plasma is investigated. A more realistic situation is considered in which electrons interact with the wave potential during its evolution and, follow the vortex-like excavated trapped distribution. The basic properties of large amplitude solitary waves are studied by deriving an energy integral equation involving Sagdeev potential. It is shown that effects of such electron behavior and positron concentration change the maximum values of the Mach number and amplitude for which solitary waves can exist. The small amplitude limit is also investigated by expanding the Sagdeev potential to include third-order nonlinearity of electric potential. In this case, exact analytical solution is obtained which is related to the contribution of the resonant electron to the electron density. It is shown from both highly and weakly nonlinear analysis that the plasma system under consideration supports only compressive solitary waves.