Shock compression and thermodynamics of highly nonideal metallic plasma

Using experimental data on compression and heating of dense metallic plasma by powerful shock waves, we have analyzed the effect of strong Coulomb interaction on both discrete and continuum bands of energy spectrum, the role of short-range repulsion, and the effect of degeneracy on the equation of state for a dense, nonideal metallic plasma. Explosive devices have been used to produce plasma for which the degree of ionization, nonideal parameter, and degeneracy varied over wide ranges. In order to increase effects of irreversible energy dissipation, metal targets of low densities have been used. Thermodynamic measurements have been compared to theoretical models taking into account Coulomb interaction, short-range repulsion, and degeneracy of electrons. The plasma models have been shown to be applicable to the equilibrium properties of multiply ionized plasma in a wide region of the phase diagram characterized by extremely high parameters [T⩾10⁴ K, P⩾10 GPa, and ρ=(0.1–1)ρ ₀], which is beyond the traditional domain of plasma physics. Zh. éksp. Teor. Fiz. 114, 1242–1265 (October 1998)     

Adhesion of metals and semiconductors analyzed by a dielectric formalism

This paper discusses a model of the adhesive interaction of metals and semiconductors, based on a dielectric formalism and using the concepts of collective excitations — plasmons of the electron-ion system. Expressions are obtained in terms of the jellium model in the longwavelength approximation for the adhesion energy and the adhesive interaction force and are determined via the dispersion dependences of the energies of surface plasma oscillations for various materials whose surfaces are separated by a gap of arbitrary magnitude. The adhesion energies and the adhesive interaction forces are calculated for a number of simple and transition metals and semiconductors, and the adhesion characteristics are also obtained for the contact of the given materials with an insulating medium. Fiz. Tverd. Tela (St. Petersburg) 39, 964–967 (June 1997)     

Phonon Scattering at Multi-Level Impurities

A Green's function technique is used to calculate the dispersion and damping of phonons at tunneling centers with internal degrees of freedom. Starting from a model for tunneling centers oriented in 〈100〉-orientations, we decouple the evolution hierarchy of Green's functions in second order. A further iteration of the resulting integral equation leads to dispersion and damping. The frequency power law differs for the even and odd parity phonons, which are involved in the local transitions. In a second approach the damping is recalculated by means of a scattering formalism, which steps directly into the fourth order. This direct method shows an extension of the renormalization of the local energy spacings and of the homogeneous linewidths.     

Magnetoplasmon replica in the recombination radiation spectra of a quasi-two-dimensional electron gas in GaAs/AlGaAs quantum wells

The radiative recombination spectra of two-dimensional electrons with free photoexcited holes are investigated for a wide variety of GaAs/ AlGaAs quantum wells, with different thicknesses and electron densities. It is found that for certain, close to integral, filling factors an intense line corresponding to an Auger process — radiative recombination with the emission of an additional magnetoplasmon — appears in the luminescence spectrum. The new line is shifted to lower energies with respect to the zero Landau level, and the magnetic field dependence of the energy splitting between these lines agrees with the theoretical concepts of the dispersion of magnetoplasmon excitations. This makes it possible to estimate the magnetoplasmon energy at the roton minimum. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 8, 539–544 (25 October 1997)     

Analytical calculation of eigen-energies for lens-shaped quantum dot with finite barriers

With the help of metadynamics it is possible to calculate efficiently the free energy of systems displaying high energy barriers as a function of few selected “collective variables”. In doing this, the contribution of all the other degrees of freedom (“microscopic” variables) is averaged out and, thus, lost. In the following it is shown that it is possible to calculate the thermal average of these microscopic degrees of freedom during the metadynamics, not loosing this piece of information. The method is tested on a two-dimensional toy system and on a small molecule, that is dialanine.     

Anharmonic interactions of elastic and orientational waves in one-dimensional crystals

Planar oscillations of a chain of dumbbell-shaped particles possessing three degrees of freedom are studied. This system models the dynamics of quasi-one-dimensional crystals consisting of elongated anisotropic molecules. A system of nonlinear differential equations describing the anharmonic interaction of the elastic and orientational waves in the lattice, corresponding to different degrees of freedom of the particles, is constructed assuming a cubic interparticle interaction potential. It is shown that in the low-frequency approximation the system obtained is equivalent to the equations of the moment theory of elasticity, widely employed for describing nonlinear and dispersion properties of layered crystals and phase transformations in alloys. Some types of three-wave collinear interactions are investigated, suggesting the possibility of exciting orientational waves in organic crystals because of their nonlinear interaction with acoustic waves. Fiz. Tverd. Tela (St. Petersburg) 39, 137–144 (January 1997)     

Role of equilibrium plasma flow on damping of slow MHD waves

In the solar corona waves and oscillatory activities are observed with modern imaging and spectral instruments. These oscillations are interpreted as slow magneto-acoustic waves excited impulsively in coronal loops. This study explores the effect of steady plasma flow on the dissipation of slow magneto-acoustic waves in the solar coronal loops permeated by uniform magnetic field. We have investigated the damping of slow waves in the coronal plasma taking into account viscosity and thermal conductivity as dissipative processes. On solving the dispersion relation it is found that the presence of plasma flow influences the characteristics of wave propagation and dissipation. We have shown that the time damping of slow waves exhibits varying behavior depending upon the physical parameters of the loop. The wave energy flux associated with slow magnetoacoustic waves turns out to be of the order of 10⁶ erg cm⁻² s⁻¹ which is high enough to replace the energy lost through optically thin coronal emission and the thermal conduction below to the transition region.     

Effects of cross correlations between inhomogeneities of the parameters of an isotropic medium on the spectrum and damping of elastic waves

The dispersion and damping laws have been investigated for elastic waves in an isotropic medium with one- and three-dimensional inhomogeneities of the density p(x) of the material and the elastic force constants μ(x) and λ(x) with allowance for the cross correlations between these inhomogeneities. It has been demonstrated that the positive cross correlations between μ(x) and λ(x), as well as the negative cross correlations between p(x) and μ(x) or p(x) and λ(x), lead to an enhancement of the modification of the dispersion law and an increase in the damping of waves. The positive cross correlations between p(x) and μ(x) or p(x) and λ(x), as well as the negative cross correlations between μ(x) and λ(x), result in the opposite effects: a weakening of the modification of the dispersion law and a decrease in the damping. An analysis of the results obtained in this paper and in our recent work [15] has made it possible to formulate the general regularity of the effects of cross correlations, irrespective of the physical nature of the waves: the effects of cross correlations between inhomogeneities of any two parameters of the material on the wave spectrum depend on whether both parameters related by the cross correlations belong to the same part of the Hamiltonian (i.e., if they both belong to either the kinetic part or the potential part of the Hamiltonian) or they belong to different parts of the Hamiltonian. The positive cross correlations lead to a greater modification of the dispersion law and to an increase in the damping of waves in the former case and to a decrease in these characteristics in the latter case. Correspondingly, the negative cross correlations in each of these cases result in the opposite effects. This regularity has been explained qualitatively.     

Theory of the pseudospin resonance in semiconductor bilayers

The pseudospin degree of freedom in a semiconductor bilayer gives rise to a collective mode analogous to the ferromagnetic-resonance mode of a ferromagnet. We present a many-body theory of the dependence of the energy and the damping of this mode on layer separation d. Based on these results, we discuss the possibilities of realizing transport-current driven pseudospin-transfer oscillators in semiconductors, and of using the pseudospin-transfer effect as an experimental probe of intersubband plasmons.     

The Electrical Conductivity of Plasma in Wide Range of Charge Densities

The possibility of the existence of plasma oscillations in nonideal plasma and their role in effective “collision” frequency are analyzed. The simple formula for the electrical conductivity of nonideal plasma is obtained on the base of model considerations. An account is taken of a new scattering mechanism, namely, the collective plasma oscillations.     

Critical experiments in the search for fermion condensation

The specific features of fermion condensation — a phase transition associated with the rearrangement of the one-particle degrees of freedom in strongly correlated Fermi systems — by which this phenomenon can be detected experimentally are discussed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 11, 828–833 (10 June 1997)     

Plasmaschwingungen in Al,Mg, Li,Na und K angeregt durch schnelle Elektronen

We report on energy loss experiments with 50 keV electrons transmitted through thin films of the metals Al, Mg, Li, Na, and K. The valence electrons of these materials behave like a gas of free electrons to a good approximation and, in particular, give rise to significant collective effects. Since these substances oxidize rapidly they were evaporated and studied in ultra high vacuum. The apparatus and the measurement technique are described. Measurements of loss spectra for different electron scattering angles yield the volume plasmon dispersion curve and the dependence of the damping of the volume plasmon on the wave vector. New experimental values of the energy and the half width of the plasma oscillations and the coefficients of dispersion and damping are given. In addition, the results of some measurements on surface plasmons are presented. There are significant deviations from the predictions of the simple electron gas model.     

Ion cyclotron instabilities in a mildly relativistic hydrogen-deuterium fusion plasma

A dispersion relation for the perpendicular propagation of the electromagnetic ion cyclotron wave around the second harmonic of the deuterium ion gyrofrequency in a mildly relativistic, anisotropic Maxwellian plasma with hydrogen as the majority species and deuterium as the minority component has been derived. The work has been carried out in the frame of reference of the majority hydrogen ions; to these ions the waves at 2Θ_D would be at its own gyrofrequency. Using a small quantityɛ to order all relevant parameters of the plasma, it was possible to derive the dispersion relations in a simple form. To the lowest order the relativistic factors do not enter the dispersion relation. The plasma can now support two modes—one above and the other below the hydrogen gyrofrequency in agreement with the assumptions. This was also verified numerically using a standard root solver thereby justifying the correctness of the ordering scheme. In the next higher order, the dispersion relation is a quartic equation and is sensitively dependent on the relativistic factors. The plasma can now support four modes, both above and below the hydrogen gyrofrequency and consistent with the ordering scheme used. However the modes can now coalesce resulting in complex conjugate roots to the dispersion relation thereby indicating an instability. The advantage of such a scheme is that two dispersion relations — one of which is independent of the relativistic factors and the other which is sensitively dependent on them can be separated out.     

Low-energy charge-density excitations in MgB2: Striking interplay between single-particle and collective behavior for large momenta

A sharp feature in the charge-density excitation spectra of single-crystal MgB2, displaying a remarkable cosinelike, periodic energy dispersion with momentum transfer (q) along the c* axis, has been observed for the first time by high-resolution nonresonant inelastic x-ray scattering (NIXS). Time-dependent density-functional theory calculations show that the physics underlying the NIXS data is strong coupling between single-particle and collective degrees of freedom, mediated by large crystal local-field effects. As a result, the small-q collective mode residing in the single-particle excitation gap of the B pi bands reappears periodically in higher Brillouin zones. The NIXS data thus embody a novel signature of the layered electronic structure of MgB2.     

Dynamics of acoustoelectromagnetic solitons as a manifestation of higher nonlinearity

The acoustoelectromagnetic interaction is examined in a regime where three mechanisms must be taken into account simultaneously: photoelasticity, quadratic photoelasticity, and elastic nonlinearity. It is shown that beyond the critical conditions, acoustic solitary waves are formed at harmonic and subharmonic frequencies in a crystal. Including damping and nonideal reflection at the boundaries does not lead to the establishment of any sort of stationary state: a soliton spatial-temporal dynamic develops. Fiz. Tverd. Tela (St. Petersburg) 39, 1101–1104 (June 1997)     

Influence of the electron damping on the properties of intermediate valence systems

The influence of conduction electron damping on the possibility of excitonic coupling in the intermediate valence systems is considered. The scattering by the internal degrees of freedom of f?-shells is shown to be the main mechanism for this damping. It is shown that both the excitonic energy gap and the damping are proportional to s-f? Coulomb integral, so the scattering considered prevents s- and f?-electrons from anomalous coupling. The growth of the resistivity near the point of valence change can be understood as the manifestation of this scattering.     

Macro-scale matter wave generation in charged particle dynamics in a magnetic field,a consequence of quantum entanglement

Matter wave interference effects on the macro-scale predicted by the author in charged particle dynamics in a magnetic field [R.K. Varma, Phys. Rev. E 64, 036608 (2001)], and observed subsequently [R.K. Varma, A.M. Punithavelu, S.B. Banerjee, Phys. Rev. E 65, 026503 (2002); R.K. Varma, S.B. Banerjee, Phys. Scr. 75, 19 (2007)] have been shown here to be an interesting consequence of quantum entanglement between the parallel and perpendicular degrees of freedom of the particle. Treating the problem in the framework of the inelastic scattering theory, it is shown that these macro-scale matter waves are generated in the ‘parallel’ degree of freedom as a modulation of the plane wave state of the particle along the field concomitantly with the excitation of Landau levels in the perpendicular degree of freedom in an inelastic scattering episode. We highlight here the role of quantum entanglement leading to the generation of this macro-scale quantum entity which has been shown to exhibit observable consequences. This case also exemplifies a situation exhibiting quantum entanglement on the macro-scale.     

Heat pulses in the second-sound regime

At low temperatures, heat propagates in crystals in the form of collective excitations—second-sound waves. How the parameters of the phonon system of the crystal can be determined from the shape of the heat pulse is considered here. Fiz. Tverd. Tela (St. Petersburg) 40, 126–127 (January 1998)     

Kinetic theory of a nonideal plasma: Dispersion relations

The kinetic theory of plasma based on the construction of propagators for the plasma particle distribution function is generalized to the case of a nonideal plasma. This theory is used for calculating the permittivity of a homogeneous nonideal plasma consisting of one species of ions neutralized by the polarized electron background. The dispersion relations are derived for ion-acoustic and low-frequency transverse waves in the plasma.     

Electron-ion Coulomb Bremsstrahlung in nonideal plasmas

The classical electron-ion Coulomb Bremsstrahlung process is investigated in nonideal plasmas. An effective pseudopotential model taking into account the plasma screening and collective effects is applied to describe the electron-ion interaction potential in a classical nonideal plasma. The classical straight-line trajectory method is applied to the motion of the projectile electron in order to visualize the variation of the differential Bremsstrahlung radiation cross-section (DBRCS) as a function of the scaled impact parameter, nonideal plasma parameter, projectile energy, photon energy, and Debye length. The results show that the DBRCS in ideal plasmas described by the Debye-Hückel potential is always greater than that in nonideal plasmas, i.e., the collective effects reduce the DBRCS for both the soft and hard photon cases. For large impact parameters, the DBRCS for the soft photon case is found to be always greater than that for the hard photon case. Received 1st December 1999