Effect of the dynamical collision frequency on quantum wakefields

Previous papers on the quantum wakefield around an ion moving in a dense plasma have considered the collision frequency in the static approximation. In this work, we present the results of the dynamically screened ion potential taking into account the dynamical electron–ion collision frequency. The Lenard–Balescu dynamical collision frequency and various approximations to it are considered. As a main result of our investigation for the subsonic, sonic, and supersonic regimes, we find that the frequency dependence of collisions can be safely discarded if the electronic streaming velocity (relative to an ion) is comparable to or less than the electronic Fermi velocity.     

The Influence of Dynamical Screening on the Transport Properties of Dense Plasmas

We investigate the effects of dynamical screening on the static transport properties. We review the low density expansion for the electron‐electron and electron‐ion correlation functions and give results for a 6‐moment approach within linear response theory. The expansion coefficients are given. The convergence of thermoelectric transport coefficients is examined in dependence of the rank of the collision term determinant. The results are compared with previous calculations and experiments. Effective Debye screening radii derived from the Gould‐DeWitt scheme for the inclusion of strong collisions as well as dynamical effects are discussed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

重离子碰撞中K介子和π介子产生的统一动力学模拟

用RVUU模型统一地研究了重离子碰撞中产生的K介子和π介子的动力学过程.考虑了K产生和输运过程的介质效应,同时,计入了π在核物质中的传播.用它模拟了每核子1GeV入射能量的重离子碰撞中π产生和阈下K产生过程.讨论了核介质效应对π末态性质的影响,以及对K末态性质的联带影响.计算结果表明,吸引的π光学势,影响了末态π动量分布,使横动量分布中具有小动量的π产额增大,同时明显增大了K的产额,改变了K的动量分布.这说明要合理地评价重离子碰撞的探测信息,需要统一地研究K和π的这些末态动力学作用.     

Anharmonic Excitations,Time Correlations and Electric Conductivity

We study the influence of anharmonic mechanical excitations of a classical ionic lattice on its electric properties. First, to illustrate salient features, we investigate a simple model, an one‐dimensional (1D) system consisting of ten semiclassical electrons embedded in a lattice or a ring with ten ions interacting with exponentially repulsive interactions. The lattice is embedded in a thermal bath. The behavior of the velocity autocorrelation function and the dynamic structure factor of the system are analyzed. We show that in this model the nonlinear excitations lead to long lasting time correlations and, correspondingly, to an increase of the conductivity in a narrow temperature region, where the excitations are supersonic soliton‐like. In the second part we consider the quantum statistics of general ion‐electron systems with arbitrary dimension and express ‐ following linear response transport theory ‐ the quantum‐mechanical conductivity by means of equilibrium time correlation functions. Within the relaxation time approach an expression for the effective collision frequency is derived in Born approximation, which takes into account quantum effects and dynamic effects of the ion motion through the dynamic structure factor of the lattice and the quantum dynamics of the electrons. An evaluation of the influenec of solitons predicts for 1D‐lattices a conductivity increase in the temperature region where most thermal solitons are excited, similar as shown in the classical Drude‐Lorentz‐Kubo framework. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quantum effects on elastic collisions in a two-component plasma

Eikonal method is applied to investigate the quantum effects on elastic electron–ion collisions in a two-component plasma. An effective Kelbg potential model taking into account the classical effect as well as the quantum-mechanical effect is applied to describe the electron–ion interactions in a two-component plasma. The impact parameter method is applied to represent the path of the projectile electron in order to investigate the variation of the eikonal cross section as a function of the impact parameter, thermal de Broglie wavelength, and projectile energy. In the second-order eikonal approximation, the quantum effects significantly reduce the elastic electron–ion scattering cross section. It is also found that the second-order eikonal phase is caused by the pure quantum mechanical effects.     

Influence of spin-orbit coupling induced by in-plane external electric field on the intrinsic spin-Hall effect in a Rashba two-dimensional electron gas

We study theoretically the influence of spin--orbit coupling induced by in-plane external electric field on the intrinsic spin-Hall effect in a two-dimensional electron gas with Rashba spin--orbit coupling. We show that, after such an influence is taken into account, the static intrinsic spin-Hall effect can be stabilized in a disordered Rashba two-dimensional electron gas, and the static intrinsic spin-Hall conductivity shall exhibit some interesting characteristics as conceived in some original theoretical proposals.     

Laser-induced conductivity of semiconductors at low temperatures

We consider the negative conductivity of electrons in semiconductors excited by a picosecond laser pulse at low temperatures, due to the inelastic electron-phonon collisions. For the first time, the dependence of the deformation potential on the phonon wave number is taken into account. This dependence significantly changes the region of negative electron conductivity as a function of the phonon temperature. The text was submitted by the authors in English.     

Electrical conductivity of a fully ionized plasma at high frequencies

When the frequency of the electric field is of the order of, or larger than, the electron plasma frequency, kinetic equations are no longer valid. The Klimontovich equation linearized in the applied electric field is solved systematically by means of an expansion into powers of the square root of the plasma parameter. A general expression up to second order is obtained for the conductivity σ(ω, k). There exists a large overlap with the results of an earlier paper on the conductivity at low frequencies. This overlap is used to determine a cut-off parameter. The expression for the conductivity serves as a basis for the calculation of the influence of collisions on the dispersion relation for plasma waves. It appears that for small wavenumbers the influence of electron-ion collisions is dominant compared to electron-electron collisions.     

The role of electron correlations in the double ionization of helium by fast protons

We consider the double ionization (DI) of a helium atom by fast protons and study the role of electron correlations in this process. We develop a quantum-mechanical approach that takes into account the interaction of the emitted electrons in continuum and the dynamical charge screening of the ejected particles, which depends on their ejection kinematics. The interaction of the emitted electrons between themselves and with the core is described in the model of approximate 3C functions, while the dynamical charge screening is described by introducing effective charges of the emitted electrons and the ion core, which are determined by the particle momenta. The derived closed analytical expressions for the differential ionization cross sections have been applied to the case of a coplanar particle ejection geometry at various momenta q transferred to the atom. Analysis of our calculations has shown that the developed model describes adequately the available experimental data. Including the dynamical charge screening has a significant effect on the DI cross section and improves considerably the agreement between theory and experiment.     

中能重离子碰撞中的同位旋效应

利用改进的量子分子动力学模型,研究了中心和擦边重离子反应中的同位旋效应.研究结果表明,在丰中子体系的中心和擦边反应中出射核子的N/Z都对对称势敏感,但对称势的密度依赖对中心和擦边反应的影响显示不同的特征.     

Time Relativity in the Dynamics of Open Quantum Systems

Various methods for determining the Coulomb logarithm in the kinetic theory of transport and various variants of the choice of the plasma screening constant, taking into account and disregarding the contribution of the ion component and the boundary value of the electron wavevector are considered. The correlation of ions is taken into account using the Ornstein–Zernike integral equation in the hypernetted-chain approximation. It is found that the effect of ion correlation in a nondegenerate plasma is weak, while in a degenerate plasma, this effect must be taken into account when screening is determined by the electron component alone. The calculated values of the electrical conductivity of a hydrogen plasma are compared with the values determined experimentally in the megabar pressure range. It is shown that the values of the Coulomb logarithm can indeed be smaller than unity. Special experiments are proposed for a more exact determination of the Coulomb logarithm in a magnetic field for extremely high pressures, for which electron scattering by ions prevails.     

Radiative energy loss in a finite dynamical QCD medium

The radiative energy loss of a quark jet traversing a finite size QCD medium with dynamical constituents is calculated to first order in opacity. Although finite size corrections reduce the energy loss relative to an infinite dynamical QCD medium, under realistic conditions it remains significantly larger than in a static medium. Quantitative predictions of jet suppression in relativistic heavy ion collisions must therefore account for the dynamics of the medium's constituents. Finite size effects are shown to induce a nonlinear path length dependence of the energy loss. Our results suggest a simple general mapping between energy loss expressions for static and dynamical QCD media.     

Nonlinear dissipative wave structures in planar and nonplanar geometry with quantum electron exchange-correlation potential

Taking into account the effects of electron exchange-correlation potential, particle collisions, the nonlinear dynamical properties of planar and nonplanar (cylindrical and spherical) electrostatic ion-acoustic waves (IAWs) are investigated theoretically and numerically in quantum plasmas. With the aid of quantum hydrodynamic model and the reductive perturbation technique, the planar and nonplanar dispersive-dissipative equations (modified Kakutani–Kawahara equations) are obtained to elucidate the nonlinear quantum IAW profiles. The influences of the electron exchange-correlation potential, Bohm potential and collisional effects in the wave dynamics are studied. For a typical parametric range, relevant for laboratory and astrophysical environments, it is found that the contribution from exchange-correlation potential to be prominent in comparison to the effect due to the Bohm potential. Also, numerical simulation predicts that the dissipation induced by the particle collisions leads to the evolution of low frequency shock structures in dense quantum plasmas.     

Electronic Heat Conductivity of a Partially Ionized Hydrogen Plasma

The electronic contribution of the translational heat conductivity of a partially ionized hydrogen plasma is determined, starting from a quantum kinetic equation, which takes into account the two particle scattering between the free charge carriers as well as electron-atom collisions. Plasma effects are included by statically screened potentials. In connection with a mass action law, the influence of the different collision terms on the electron heat conductivity is shown. An estimation is given for the contribution of the atoms. The pressure ionization (Mott effect) is described by a minimum behaviour of the heat conductivity.     

Screening and attraction of dust particles in plasmas

The potential around a dust particle in a plasma is found using the collisional hydrodynamic equations of dusty plasmas, taking into account ion-dust and ion-neutral collisions and considering the plasma source proportional to the dust density. The linear screening is strongly influenced by the collisions and can substantially differ from Debye screening. Attraction of negatively charged dust particles can occur due to overscreening by the ion fluxes in the presence of friction forces.     

Dynamical and static spin conductivities in the Heisenberg model on honeycomb lattice: The effects of magnetic long range ordering

We have studied both dynamical and static spin conductivities of Heisenberg antiferromagnet on honeycomb lattice in the presence of a magnetic long range ordering. The effects of spatial anisotropy as weak Dzyaloshinskii–Moriya interaction and next nearest neighbor exchange coupling on the behaviors of conductivities are discussed. A sublattice antiferromagnetic long range ordering has been considered for localized electrons on honeycomb lattice structure. Using Holstein–Primakoff bosonic transformations, the behaviors of spin transport properties have been studied by means of excitation spectrum of mapped bosonic gas. We have found the temperature dependence of static spin conductivity in the field induced gapped spin-polarized phase for various Dzyaloshinskii–Moriya interaction strengths. Furthermore we have studied the frequency dependence of dynamical spin conductivity for various Dzyaloshinskii–Moriya interaction strengths and different next nearest neighbor coupling constants. We find that the height of peak in the temperature dependence of static spin conductivity increases upon increasing the anisotropy parameter. The static spin conductivity is found to be monotonically increasing with anisotropy parameter due to increase of the energy gap in the excitation spectrum. Furthermore we have studied the temperature dependence of the spin conductivity for different next nearest neighbor coupling constants.     

Isospin effects of the Skyrme potential and the momentum dependent interaction at intermediate energy heavy ion collisions

We improve the isospin dependent quantum molecular dynamical model by including isospin effects in the Skyrme potential and the momentum dependent interaction to obtain an isospin dependent Skyrme potential and an isospin dependent momentum interaction. We investigate the isospin effects of Skyrme potential and momentum dependent interaction on the isospin fractionation ratio and the dynamical mechanism in intermediate energy heavy ion collisions. It is found that the isospin dependent Skyrme potential and the isospin dependent momentum interaction produce some important isospin effects in the isospin fractionation ratio.     

Spectroscopic properties of the molecular ions BeX+ (X=Na,K, Rb): forming cold molecular ions from an ion–atom mixture by stimulated Raman adiabatic process

In this theoretical work, we calculate potential energy curves, spectroscopic parameters and transition dipole moments of molecular ions BeX⁺ (X=Na, K, Rb) composed of alkaline ion Be and alkali atom X with a quantum chemistry approach based on the pseudopotential model, Gaussian basis sets, effective core polarisation potentials and full configuration interaction. We study in detail collisions of the alkaline ion and alkali atom in quantum regime. Besides, we study the possibility of the formation of molecular ions from the ion–atom colliding systems by stimulated Raman adiabatic process and discuss the parameters regime under which the population transfer is feasible. Our results are important for ion–atom cold collisions and experimental realisation of cold molecular ion formation.     

Influence of Chiral Mean Field on Kaon In-plane Flow in Heavy Ion Collisions

The influence of the chiral mean field on the K⁺ in-plane flow in heavy ion collisions at SIS energy is investigated within covariant kaon dynamics. For the kaon mesons inside the nuclear medium a quasi-particle picture including scalar and vector fields is adopted and compared to the standard treatment with a static potential. It is confirmed that a Lorentz force from spatial component of the vector field provides an important contribution to the in-medium kaon dynamics and strongly counterbalances the influence of the vector potential on the K⁺ in-plane flow. The calculated results show that the new FOPI data can be reasonably described using the Brown & Rho parametrization, which partly takes into account the correction of higher order contributions in the chiral expansion. This indicates that one can abstract the information on the kaon potential in a nuclear medium from the analysis of the K⁺ in-plane flow.     

Hopping Transport and Stochastic Dynamics of Electrons in Plasma Layers

We investigate the stochastic dynamics and the hopping transfer of electrons embedded into two‐dimensional atomic layers. First we formulate the quantum statistics of general atom ‐ electron systems based on the tight‐binding approximation and express ‐ following linear response transport theory ‐ the quantum‐mechanical time correlation functions and the conductivity by means of equilibrium time correlation functions. Within the relaxation time approach an expression for the effective collision frequency is derived in Born approximation, which takes into account quantum effects and dynamic effects of the atom motion through the dynamic structure factor of the lattice and the quantum dynamics of the electrons. In the last part we derive Pauli equations for the stochastic electron dynamics including nonlinear excitations of the atomic subsystem. We carry out Monte Carlo simulations and show that mean square displacements of electrons and transport properties are in a moderate to high temperature regime strongly influenced by by soliton‐type excitations and demonstrate the existence of percolation effects (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)