Dynamical structure factor of a one-dimensional harmonic liquid: Comparison of different approximation methods

The optical properties of Anderson-localized many-particle excitations in doped crystals are discussed assuming that the direct interaction between the active ions is greater than their interaction with the radiation field. It is shown that in this case the Anderson localization of the excitation energy on a finite number of ions has no influence in zeroth order on the absorption and emission properties at low excitation intensities used in conventional spectroscopy. Only at higher excitation intensities resulting in multiply excited many-ion states are characteristic quenching effects of the luminescence expected. These become evident by a conversion of the multiply excited states into fast relaxing, degenerate states either of the ions themselves or of the host lattice. These quenching effects offer possibilities to determine experimentally the number of coherently coupled ions forming the many-particle Anderson-localized excitations.     

An explanation of the structure in the dynamic structure factor of an electron liquid

We explain the recently observed interesting structure in the dynamic structure factor S(k, ω) of various metallic systems by considering processes that involve single-particle and multi-particle excitations.     

Self-energy contributions to the dynamic structure factor of an electron liquid

It is demonstrated that the experimentally observed two-peak structure in the dynamic structure factor of an electron liquid cannot be explained by the finite life-times of the quasiparticles in the way proposed by Mukhopadhyay et al. The two-peak structure obtained by them disappears if the frequency dependence of the one-particle self-energy is taken into account.     

Dynamical structure factor of the Frenkel-Kontorova model

We investigate the coherent dynamical structure factorS(q, ) of the Frenkel-Kontorova model with a continued fraction expansion. The model consists of harmonically interacting particles moving in a periodic potential. It applies to quasi-one-dimensional systems where two different periods and competing interactions are important. We study commensurability effects in the collective dynamical behaviour of the particles and their manifestation inS(q, ). Our theory gives detailed results for the inelastic scattering at high temperatures. For the quasielastic peak it predicts, among other things strong oscillations of the half-width as a function of the wave vectorq. Such a behaviour can be observed in neutron scattering experiments on superionic conductors.     

Comments on the presence of a peak in the static structure factor of an electron liquid

Emphasis is laid on the fact that the peak in the static structure factor S(k) observed in a recent experiment at k≈2k_F for conduction electrons in beryllium agrees well with the one predicted by us theoretically some time back. The error in the calculation of the pair correlation function g(r) using the experimental data on S(k) is pointed out. The position of the peak obtained in our g(r) clearly indicates that the effect of electron correlation is to condense into a Wigner lattice at a distance equal to the average interparticle separation rather than making a Mott type transition to an atomic-like state.     

Impact of the liquid phase shape on the structure of III-V nanowires

The III-V nanowire structure (zinc blende or wurtzite) grown by the vapor-liquid-solid process is shown to be highly dependent on the parameters which shape the droplet at the top of the nanowire. Under conditions that the droplet volume does not exceed a certain value, it is demonstrated that when the nucleation of the solid starts at the solid-liquid-vapor triple line, a relatively large droplet volume and low wetting angle favor the formation of the wurtzite structure. We show that the effective V/III flux ratio is the primary parameter controlling the structure.     

Dynamical scaling of the structure factor of some non-Euclidean systems

Predictions of nonlinear theories on dynamics of new phase formation have been examined for the hydration of calcium silicates with light water and heavy water. In the case of hydration with light water, reasonable agreement has been observed with dynamical scaling hypothesis with a new measure of the characteristic length. The characteristic length does not follow a power law relation with time. Hydrating mass is found to be mass fractal throughout hydration, with mass fractal dimension increasing with time. But, in the case of hydration with heavy water, no agreement has been observed with the scaling hypothesis. Hydrating mass undergoes transition from mass fractal to surface fractal and finally again to mass fractal. The qualitative features of the kinetics of hydration, as measured in small-angle scattering experiments, are strikingly different for hydration with light water and heavy water.     

On the electron band structure of liquid metals

The electronic structure and the density of states of simple liquid metals is discussed on the basis of a nonlocal and energy-dependent pseudopotential of the Phillips-Kleinman type. As an example we treat lithium. To calculate this pseudopotential we need to know the states and the eigenvalues of the liquid metal ion cores. For these quantities we use: first, the core data of the free atom; second, of the free ion; third, the data we have determined from the measured phonon dispersion curves. The deviations between the band structures, the density of states as calculated with these pseudopotentials and those of free electrons are considerable.     

On the dynamic form factor of an electron liquid

The mean field theories of an electron liquid at metallic densities, which go beyond the RPA, and which have been fairly successful so far, are shown to be inadequate when tested against phenomena involving high frequencies. It is also shown that by making a simple Gaussian ansatz for the imaginery part of the response function, χ″(q,ω), and using the zeroth, the first and the third frequency moments of density spectral function to determine the unknown parameters in χ″(q,ω), it is possible to understand at least semiquantitatively the available experimental information regarding the dynamic form factor. Implications of the present analysis as regards the further refinement of the present theories are indicated.     

New interpretation of experiments on the intermediate meson

A new theory of weak interactions is proposed in which the coupling between theV-A currents j(X) and j(X) is achieved not by vector mesons [by a propagator D ^c (X-X)], but by a scalar functionR(X – X), a fermion-antifermion loop which plays the role of a unique film joining two different pointsX andX of completely uncoupled space-times (as a result of which the space becomes a continuum). The existence of the actual currents j results from correlations between the two different spinor layers of Dirac layer formation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 25–40, February, 1996.     

Influence of the quantum dot shape on the determination of the electronic structure and electron decoherence

Theoretical calculations of electron–phonon scattering rates in AlGaN/GaN quantum dots (QDs) have been performed by means of effective mass approximation in the frame of finite element method. The influence of a symmetry breaking of the carrier's wave function on the electron dephasing time is investigated for various QDs shapes. In a QD system the electron energy increases when the QD shape changes from a spherical to a non-spherical form. In addition, the influence of the QD shape upon the electronic structure can be modulated by external magnetic fields. We also show that the electron–acoustic phonon scattering rates strongly depend upon both the QD shape and the applied magnetic field. As an additional parameter, the QD shape can be used to modify the electron–acoustic phonon interaction in a wide range. Moreover, the scattering rate of different transitions, such as Δm=0(1), presents distinct magnetic field dependency.     

Dependence of structure factor and correlation energy on the width of electron wires

The structure factor and correlation energy of a quantum wire of thickness b ? a _B are studied in random phase approximation (RPA) and for the less investigated region r _s < 1. Using the single-loop approximation, analytical expressions of the structure factor are obtained. The exact expressions for the exchange energy are also derived for a cylindrical and harmonic wire. The correlation energy in RPA is found to be represented by ? _c (b, r _s ) = α(r _s )/b + β(r _s ) ln(b) + η(r _s ), for small b and high densities. For a pragmatic width of the wire, the correlation energy is in agreement with the quantum Monte Carlo simulation data.     

Measurement and interpretation of the electron energy loss spectra of iron and its oxides

The characteristic electron energy loss spectra of high purity samples of iron and its oxides were measured using cpmbined electron microscopy and energy analysis. By comparing these with X-ray absorption spectra it was possible to identify the single electron excitation processes and to deduce the plasmon energy of the electrons in iron.     

Dynamical stability of infinite homogeneous self-gravitating systems and plasmas: application of the Nyquist method

We evolve an effective interatomic interaction potential with long range Coulomb interactions, Hafemeister and Flygare type short range overlap repulsion extended up to second neighbor ions and van der Waals interaction to discuss the pressure dependent first order phase transition, mechanical, elastic, and thermodynamical properties of NaCl-type (B1) to CsCl-type (B2) structure in lanthanum pnictides (LaY, Y = N, P, As, Sb, and Bi). Both charge transfer interactions and covalency effect apart from long range Coulomb are important in revealing the high-pressure structural phase transition, associated volume collapse, elastic and thermodynamical properties. By analyzing the aggregate elastic constants pressure (temperature) dependence, the rare earth lanthanum pnictides are mechanically stiffened as a consequence of bond compression and bond strengthening attributed to mechanical work hardening, thermally softening arose due to bond expansion and bond weakening due to lattice vibrations, brittle (ductile) nature at zero (increased) pressure and temperature dependent brittleness from room temperature to high temperatures. To our knowledge these are the first quantitative theoretical prediction of the pressure and temperature dependence of elastic and thermodynamical properties explicitly the mechanical stiffening, thermally softening, and brittle (ductile) nature of rare earth LaY (Y = N, P, As, Sb and Bi) pnictides and still awaits experimental confirmations.     

A canonical formalism and its geometric interpretation in the covariant theory of the classical electron

A canonical formalism is constructed for the covariant model of the classical electron proposed in [1, 2, 3]. For the geometric interpretation the notion of the coincidence of the tangent space to the space of outer coordinates with a subspace of the tangent space to the space of inner variables is introduced.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 88–92, June, 1976.In conclusion, the authors wish to thank Yu. G. Borisovich for his constant interest in this work.     

Fine structure of dark matter halos and its effect on terrestrial detection experiments

Terrestrial dark matter detection experiments probe the velocity-space distribution of dark matter particles in the vicinity of the Earth. We present a novel method, to be used in conjunction with standard cosmological simulations of hierarchical clustering, that allows one to extract a truly local velocity-space distribution in exquisite detail. Preliminary results suggest a new picture for this distribution which is decidedly non-Maxwellian but instead is characterized by randomly positioned peaks in velocity space. We discuss the implications of these results for experiments to detect axions and weakly interacting massive particles.