bluuebunny/crossref_metadata_2025 huggingface dataset:
Lattice Dynamics of the Force Constant Disordered Crystal Pd0.90Ru0.10
Authors: Maliszewski E. , Sosnowski J. , Bednarski S.
Published: July 2007

Phonon dispersion relations for Pd0.90Ru0.10 single crystal at room temperature are measured along the directions [100], [110], and [111] by inelastic neutron scattering. The Born‐von Karman analysis, using the seven‐neighbour model, is carried out, and the force constants and elastic constants are calculated. The phonon frequency shifts, Δω(q), and the self‐energy functions, ∑j(q, ωj(q)), for all the branches are determined from the experimental phonon data for Pd0.90Ru0.10 and Pd. The self‐energy shows a rich and coherent structure and reveals unique information relevant to a theoretical model of a phonon induced fast diffusion in certain metals. The same structure of the self‐energy is observed in the sample after annealing at 1420°C.
Phonon Assignments in II–VI and III–V Semiconductor Compounds Having Zincblende‐Type Structure
Authors: Ram R. K. , Kushwaha S. S. , Shukla A.
Published: July 2007

The lattice infrared absorption and/or Raman spectrum peaks for ZnSe, InP, and GaSb semiconductor compounds having zincblende‐type structure are assigned to calculated critical point phonon frequencies at Γ, X, L, and W critical points. The assignments are consistent with Birman's selection rule and support lattice dynamical results. The reliability of the calculated critical point phonons for these compounds is checked by Brout's sum rule and compressibility and also comparing them with neutron or Raman data.
Comparative Analysis of Tendencies in the Temperature‐Induced Changes in Electronic Structure of Iron and Nickel
Authors: Sandratskii L. M. , Guletskii P. G.
Published: July 2007

A previously proposed symmetrized method for the calculation of the electronic structure of spiral magnetic configurations is employed in the study of non‐collinear magnetic configurations of iron and nickel. It is shown that there is a marked difference of the tendencies of changes in the electronic structure of both metals being studied due to the increase of the angle between the spins of neighbouring atoms. A qualitative interpretation of the observed changes is given in terms of a simple two‐band model. It is also shown that the difference in the behaviour of the electronic structure of both, iron and nickel leads to a substantially different behaviour of a self‐consistent local magnetic moment and total electronic energy as a function of the angle between the spins of the neighbouring atoms.
Shallow Donor Binding Energies in Semiconductors in a Magnetic Field
Authors: Sukumar B. , Navaneethakrishnan K.
Published: July 2007

The binding energies of the P donor in Si and the Si and S donors in GaP at the cation and anion sites, respectively, in strong magnetic fields are calculated using a variational procedure. The central cell effects are taken into account using an Yukawa type potential and its effects on the ionization energies are obtained for various magnetic fields. In GaP the electron—lattice coupling (polaronic effect) is also taken into account both, in fixing the parameters of the model potential and also in the computation of binding energies. It is shown that the central cell effects are important especially for magnetic fields of the order of γ ≈︁ 100. The contribution from the electron—lattice coupling is small and seen to decrease with the increase of magnetic field in confirmation with previous works. The central cell effect enhances the electron—lattice coupling appreciably, the enhancement being 30 to 100% for the range of magnetic fields investigated.
Photostimulated Acoustoelectronic Effects in Semiconductors in the Long Wavelength Region
Authors: Anh Vo Hong , Shon Nguyen Hong
Published: July 2007

The interaction of the photoelectrons with the sound waves in the long wavelength region in semiconductors is considered using the classical continuum model for the lattice motion together with the kinetic equation in the relaxation time approximation describing the electron subsystem. Currents and fields arising in the sample are calculated. An de electric field due to the deviation of the electron distribution function from the equilibrium exponential form under the action of a light wave (and in the presence of a magnetic field) is revealed that is absent in the short wavelength limit. The possibility of an experimental observation of this effect is discussed.
Josephson Properties of a Homogeneous Superconducting Film
Authors: Ilinikh A. I. , Shapiro B. Ya.
Published: July 2007

A theory of localized superconducting states arising in a thin superconducting film deposited on the surface of a ferromagnetic particle is constructed. It is shown that a periodic superconducting structure is formed in such a film. The critical magnetic field, temperature, and Josephson current are determined.
Quantum 1/f Noise Associated with Intervalley Scattering in Nondegenerate Semiconductors. I. Analytical Calculations
Authors: Kousik G. S. , van Vliet C. M. , Bosman G. , Luo Horng‐Jye
Published: July 2007

Scattering of charged particles is accompanied by the emission of soft photons. Quantum theory of 1/f noise, based on the infrared quasi‐divergent coupling of the system to the electromagnetic field, indicates that the current associated with a beam of scattered charged particles exhibits 1/f noise. Based on this quantum theory the previously obtained results are extended for mobility fluctuations to include mobility fluctuations due to intervalley f‐ and g‐type processes. The fluctuations in the scattering rates are derived, and these are related to the mobility fluctuations through the relaxation time solutions of the Boltzmann transport equation. Hooge's law for 1/f noise is derived and explicit expressions are obtained for the mobility fluctuations due to intervalley scattering. This is then applied to n‐type silicon to arrive at the overall Hooge parameter, αH, as a function of temperature. It is found that the intervalley scattering processes do contribute little to the mobility, but are quite significant for the noise. The contribution to the noise is significant because of the large changes in the electron wavevector associated with intervalley scattering processes. Excellent agreement with well known experimental results is observed for the mobility as well as the Hooge‐parameter.
Thermodynamics of Localized Magnetic Singlets and 1/2‐Spins in the Plane
Authors: Hudák O.
Published: July 2007

Classical thermodynamics is found of localized magnetic singlets and 1/2‐spins in the plane using the monomer‐dimer approximation. Static magnetic susceptibility behaviour observed in the La2CuO4 paramagnetic phase is qualitatively explained within the theory.
Ground State of Ising Ferromagnet with Biquadratic Exchange of Negative Sign. The Case of Large Spin S = 5/2
Authors: Iwashita T. , Uryǔ N.
Published: July 2007

For spin−5/2 Ising ferromagnet with bilinear and biquadratic exchange interactions J and J′, the magnetization is calculated using the pair model approximation. The temperature dependence of the magnetization shows an anomalous behaviour at J′ = −J/10 suggesting an instability of the ferromagnetic ground state. On the other hand, the ground state spin structure is determined from the J′‐dependence of the energy of a single spin in various spin structures. The results show an occurrence of the phase transition at J′ = ‐J/10, agreeing well with the one obtained from the anomalous behaviour of the magnetization. Furthermore, the phase transitions have also been pointed out to occur at J′ = ‐J/6, J′ = ‐J/3, and J′ = ‐J.
Dynamics of Exciton Reflection Spectra on the Change of the Incidence Angle in NaI Crystals
Authors: O'Connel‐Bronin A. A. , Treshchalov A. B.
Published: July 2007

Over about sixty‐year investigations of the intrinsic absorption edge of NaI its absorption (reflection) spectra have been worked out in detail, but they have a „static”︁ character, which is one of the reasons that made their interpretation difficult. In the present work, reflection spectra at oblique incidence, including a nearly sliding one are experimentally investigated, which allows to trace their dynamics and to analyse their peculiarities from a new point of view. Thanks to that the energy of the longitudinal exciton and respectively that of the longitudinal‐transverse splitting are estimated. The structure of the high‐energy side of the n = 1 exciton line first observed by Van Sciver is analysed.
The Influence of the Vibrational Entropy on the Specific Heat of the Order—Disorder Transition in Alloys
Authors: Tuijn C. , Bakker H.
Published: July 2007

The influence is outlined of vibrational entropy on the specific heat curve of a simple cubic AB crystal, assuming nearest‐neighbour interaction. The calculation of the energy is carried out by means of a Monte Carlo method using the Ising model. For the vibrational entropy an exact analytical expression is applied. The shift in the critical temperature and the sharpening of the peak in the specific heat curve are quite considerable. A change in the vibrational entropy of 0.5k per atom is possible.
The Crystal Electron Energy and Compton Profile Calculations from X‐Ray Diffraction Data
Authors: Aleksandrov Yu. V. , Tsirelson V. G. , Reznik I. M. , Ozerov R. P.
Published: July 2007

The method of the one‐electron density matrix determination from X‐ray diffraction data is developed. It takes into account the translational symmetry and is applicable to covalent crystals. The crystal energies and directed Compton profiles are calculated in impulse approximation for silicon and diamond. The agreement with the experiments is rather good.
The Soliton Generalization of The Bipolaronic Model Proposed for the High‐Tc Superconductivity in Lanthanum and Yttrium Cupric Oxides
Authors: Mańka R. , Molak A.
Published: July 2007

A modified bipolaronic model of high‐Tc superconductivity is proposed. The model includes electron‐phonon and antiferromagnetic bipolaron mechanisms. Characteristic property of high‐Tc superconductivity is the lowered dimensionality which is essential for the formation of topological soliton. This model is related to the layered structure of La‐Sr‐Cu‐O and Y‐Ba‐Cu‐O compounds.
Theoretical Study of Density of States and Specific Heat of Itinerant Ferromagnetic Superconductors
Authors: Kakani S. L. , Paliwal R. K.
Published: July 2007

Density of states and specific heat of itinerant ferromagnetic superconductors are studied by using the mean field approximation. The results are applied to the system Y9Co7. There is satisfactory agreement between theory and experimental results.
To Magnetic Solutions of the Hubbard Model
Authors: Lindner U. , Schumacher W.
Published: July 2007

From the existence of double solutions of the Néel temperature in the Hubbard model for nearest neighbour overlap and simple cubic lattice in the framework of the Hartree‐Fock approximation as well as within the unified theory of Moriya and Hasegawa it follows that it is necessary to conclude further magnetic (commensurable and incommensurable) phases in the magnetic phase diagram. The investigation is restricted to magnetic long‐range order.
The Shape of the Multi‐Plasmon Radiation Band in Direct Gap Semiconductors
Authors: Klyukanov A. A. , Senokosov E. A. , Chibotaru L. E.
Published: July 2007

The form‐functions of the multi‐plasmon light absorption spectra are obtained using the fluctuation‐dissipation theorem. Transitions with photon and plasmon absorption leads to the absorption edge shift into the longwavelength spectrum region obeying Urbach's rule. It is shown, that the ground state exciton interaction with plasmons is weak due to the smallness of the Bohr radius compared to the Debye screening radius. The band shape of the multi‐plasmon own radiation of the nondegenerative electron—hole plasma is calculated. Multiplasmon transitions are direct ones whereas the radiation band consists of the superposition of equidistant Maxwell bands being apart from each other by the plasmon frequency. The amount of the multi‐plasmon satellites depends on the value of the plasma emission constant and plasma temperature. Indirect multiplasmon transitions lead to more abrupt radiation intensity decay at the short wave edge of the band. It is shown that plasmon dispersion leads to the shift of the peak value positions of the single‐plasmon satellites. The theory of multi‐plasmon transitions in semiconductors developed with account of the LO phonon replicas coincides with experimental data.
Reflectance Spectroscopy on Zn1−xMnxS in the Energy Range from 11 to 20 eV by Use of Synchrotron Radiation
Authors: Flach E. , Gumlich H.‐E. , Jung Ch. , Krause M.
Published: July 2007

Interband transitions derived from S 3s‐states and core level excitations of Zn 3d‐states are studied in Zn1−xMnxS. The investigations are performed using synchrotron radiation reflection spectroscopy both at T = 115 K and at room temperature. Below the onset of transitions from the Zn 3d‐levels into the conduction band two peaks are found due to the excitation of Zn 3d core level excitons, originating in the spin—orbit splitting of the Zn 3d‐level. The amount of the splitting is 0.23 eV for zincblende structure and 0.55 eV for wurtzite structure. Tentative assignments are given for the higher transitions and the influence of increasing manganese concentration on the shape of the reflectance spectra is discussed.
Simulation of Perfect Vacancy Loops in B.C.C. Metals
Authors: Kapinos V. G. , Osetskii Yu. N. , Platonov P. A.
Published: July 2007

Structure parameters and energies are calculated by computer simulation for faulted vacancy loops (VL) on the {110} plane in α‐Fe. The interaction between ions is described by a potential developed within the scope of the local pseudopotential theory. The size of the Frank VL dislocation core is found by comparing simulation results and continuum theory calculation. A structure simulation for small vacancy loops on the {110} plane without stacking faults with Burgers vectors b =〈100〉and b = (1/2)〈111〉 is performed.
Phase Transformation in F.C.C. Thorium and its Theoretical Stability on the Path of Transformation
Authors: Thakur K. P. , Ahmad S.
Published: July 2007

Theoretical calculations are carried out to locate the stress‐free b.c.c. phase in f.c.c. thorium on the basis of physical computations of the forces of atomic interactions. Internal energies corresponding to the stress‐free b.c.c. and stress‐free f.c.c. phases and the required stress and energy changes for the f.c.c. → b.c.c. transformation in thorium are presented. Ranges of G and S stability are identified according to the Born stability criterion, by computing the numerical values of the respective elastic moduli on the line of deformation connecting the stress‐free b.c.c. and stress‐free f.c.c. phases of the crystal. The generalised Morse potential model is used to carry out the calculations.
Two‐Component Solitary Excitations in α‐Helical Protein Molecules
Authors: Ichinose S.
Published: July 2007

Interspine interaction effects on stationary and thermodynamic properties of α‐helical protein molecules are studied using a perturbation formalism. It is shown from zeroth order condition that intrapeptide vibration Amide I corresponds to a total of three types of solitary excitations. At low temperatures, such solitary excitations are valid for obtaining information about thermodynamic properties of α‐helical protein molecules.
Structural Network and Some Photoelectrical and Optical Parameters of Amorphous Hydrogenated Silicon
Authors: Golikova O. A. , Grekhov A. M.
Published: July 2007

The results of an experimental study of a‐Si: H films are presented: dark and photoconductivity hydrogen concentration and SiH2/SiH ratio, optical gap, and Raman frequency. The deposition temperature is shown to be the main factor of the transformation of the density of localized states and corresponding shifts of the Fermi level. Theoretical calculations are made of the model of SiHSi bonds in the cluster approximation. The results concerning the Fermi level shifts are interpreted on the basis of this model.
Polariton Theory of Light Propagation in Crystals I. Connection between the Microscopic Theory of Exciton—Phonon Polaritons and Maxwell Equations
Authors: Glinskii G. F. , Koinov Z. G.
Published: July 2007

The light propagation in a crystal is considered as a polariton propagating through the crystal assuming no polariton damping. With the use of the Legendre transforms a set of nine independent exact equations is derived for the corresponding vertex and Green's functions. All possible correlation and screening effects are included in principle. Knowledge of the solutions of the above equations provide the excitation energies of the quasi‐particles (polaritons) formed by coupling of excitons with photons and phonons. Examination of the poles of the two‐particle electron—hole Green's function leads to an equation for the Bethe‐Salpeter amplitudes, as well as to the microscopic derivation of the Maxwell equations.
Optical and EXAFS Investigations of ZnS:Tm3+ Powders
Authors: Dexpert‐Ghys J. , Charreire Y. , Esteban‐Puges P. , Albert L. , Dexpert H.
Published: July 2007

The EXAFS (extended X‐ray absorption fine structure) analysis at the thulium LIII edge is applied to ZnS:Tm3+ luminescent powders. EXAFS oscillations are observed only for higher initial dopant concentrations of 1% and are attributed to oxysulfide (TmO)2S. This parasitic phase is not detected in the fluorescence spectra. By site selective excitation the emission spectrum of the same ZnS:Tm3+ (1%) powder is separated into two components. One of them is attributed to substitutional Tm on Zn sites. The nature of the other one could not be established, it is tentatively interpreted as due to a TmO complex.
Plasmons in Randomly Layered Systems
Authors: Zimpel M. , Barnas J.
Published: July 2007

Collective electronic excitations (plasmons) in layered structures with randomly distributed thicknesses are analysed theoretically in the classical approximation. The plasmon localization length λ and the density of plasmon states (DOS) are calculated numerically. Self‐averaged results are obtained for structures consisting of 105 to 106 elementary units. The dependence of λ and DOS on the disorder strength is also discussed.
Magnetic Properties of Disordered Ising Ferrimagnets
Authors: Zheng Siming
Published: July 2007

The magnetic properties of disordered Ising ferrimagnets with S = 1/2 and S = 1 are investigated by means of a new simple method. The equations for magnetization and Curie temperatures are obtained as functions of concentration p of S = 1/2 atoms. Calculations for s.c. lattice are carried out and the results discussed.
Diffraction X‐Ray Radiation under Multiwave Diffraction
Authors: Ba Ha Truong , Dubovskaya I. Ya.
Published: July 2007

The general expressions for the spectral‐angular distributions of quasi‐Cherenkov and diffraction radiations from relativistic particles are derived in the multiwave diffraction case. The transition of the expressions obtained to the well‐known formulae is demonstrated in the two‐wave approximation.
Intersubband Raman Scattering in Size‐Quantized Narrow‐Gap Semiconductor Films
Authors: Okulski W. , Załużny M.
Published: July 2007

The problem of the influence of c‐v mixing on the intersubband Raman scattering in size‐quantized narrow‐gap semiconductor films is considered in the framework of the two‐band effective mass approximation. An expression for the scattering cross section is derived in the infinite deep square well model employing the dipole approximation. A comparison with the results obtained in the one‐band effective mass approximation by Genkin and Sokolov is given. The quadrupole correction to the scattering cross section is also dicussed.
Alkali‐Metal‐Intercalated Indium and Gallium Selenides Non‐Monotonous Shift of Exciton Lines
Authors: Lukyanyuk V. K. , Voronyuk S. P. , Kovalyuk Z. D.
Published: July 2007

Absorption spectra are measured in layered semiconductors InSe and GaSe intercalated with lithium and sodium. A non‐monotonous shift is found of the free exciton lines for NaxInSe, NaxGaSe, and LixGaSe when x increases: at specific values of intercalant content the short‐wavelength shift changes into the long‐wavelength one. Interpretation of the results is made in terms of the strain effects of van der Waals and intralayer bondings which shift the electronic levels of the semiconductor.
Extension of the Crystal Chemistry Approach for the Location of Muonium in Crystals
Authors: Souiri M. , Goltzené A. , Schwab C.
Published: July 2007

By introducing a simple screening parameter, former correlation between the hyperfine coupling constant of normal muonium and the difference of cation electronegativity is improved with respect to that of hydrogen. Further crystal chemistry considerations show why small electronegativity values are required for the occurrence of bond‐centred anomalous muonium.
Theoretical Interpretation of EXAFS Results for the Relaxation in Mixed Crystals
Authors: Maiti S. N. , Sengupta S. , Roy D.
Published: July 2007

Using EXAFS technique it is possible to measure the relaxation of the nearest neighbours around a substitutional defect and at a finite concentration one obtains distinctly two types of nearest‐neighbour distances in a binary solid solution. A relation is derived containing a single parameter for the variation of these two types of nearest‐neighbour distances with concentration which predicts the results successfully both, for alkali halide solid solutions and covalently bonded tetrahedral solid solutions of zincblende structure. The parameter is calculated for alkali halide solid solutions using information of the perfect crystals only.
Calculation of Phase Diagrams in the Lattice‐Gas Model by Modified Cluster Field Method Application to High‐Temperature Superconductors
Authors: Zubkus V. E. , Lapinskas S. , Tornau E. E.
Published: July 2007

A modified cluster field method is proposed to investigate the phase transition thermodynamics and phase diagrams of systems described by the lattice‐gas model. By comparison with the exactly solved hard hexagon model and the competing interaction model on a triangular lattice the high accuracy of this method is demonstrated. The method proposed is also used to calculate the phase diagram in the high‐Tc superconductor YBa2Cu3O7‐x. The absence of two‐phase regions in this crystal at 0 ≦ x ≦ 1 and superconducting temperatures is shown. A chain mechanism for change of the oxygen content is proposed.
Thermodynamic Properties of Binary Alloy and Lattice Gas in Gaussian Fluctuation Approximation
Authors: Markowski M. , Murakowski J. , Onyszkiewicz Z.
Published: July 2007

Gaussian fluctuation approximation (GFA) is used to calculate free energy and the equation of state for two models equivalent to the Ising one: binary alloy and lattice gas. The results are compared with the results obtained within the molecular field approximation (MFA). The equations of state are used to draw phase diagrams.
Analysis of Combination Rules for Elastic Constants of Mixed Ionic Crystals
Authors: Shanker J. , Singh R. , Kumar M.
Published: July 2007

Various combination rules, proposed so far, for predicting the elastic constants of mixed ionic crystals are critically examined. The mathematical forms of different combination rules are derived, and the numerical results estimated from them are compared with one another. It is found that although the mathematical forms of the combination rules appear to be different from each other the numerical results obtained from them are closer to each other.
Generalized Formulae of Frequency Dispersion and Raman Scattering Cross‐Section of Phonon‐Polaritons
Authors: Jiang Yi‐Jian , Liao Li‐Ji , Chen Gang , Zhang Peng‐Xiang
Published: July 2007

Based upon the work of Born and Huang, the general dispersion relation for long‐wave phononpolaritons of Borstel and Claus is retreated as a result of crystal optics. The dispersion relation is a generalized Fresnel's equation and can be used in monoclinic and triclinic crystals. And a generalized formula of the differential cross‐section of Raman scattering by phonon‐polaritons is derived by way of fluctuation dissipation theory. This formula is applicable to monoclinic and triclinic crystals as well.
Temperature Dependence of Entropies and Specific Heats of Liquid Na and K
Authors: Joarder R. N. , Mujibur Rahman S. M.
Published: July 2007

The temperature dependence is investigated of the entropies and specific heats of liquid Na and K. The systems are primarily modelled with a hard sphere (hs) description, but contributions arising from the soft forces and electronic part are also included with the basic hs model. The hard sphere ingredients at various temperatures are determined through the consideration that the difference between the relevant pair potential and its minimum value is just equal to the kinetic energy of a free particle. The basic ingredients thus obtained are employed to calculate the entropies and specific heats of the systems at various temperatures. The calculated values are found to be in good agreement with experiments.
Surface Electromagnetic Waves in Quasiperiodic Superlattices
Authors: Goliney I. Yu. , Rudko V. N.
Published: July 2007

Dispersion equations are obtained and the conditions of existence are considered for surface electromagnetic waves in quasiperiodic dielectric superlattices with layers arranged according to the recurrent Fibonacci rule. It is shown that in the quasiperiodic superlattices an immense number of surface modes exists approximately proportional to the number of layers in the structure. Excitation of surface waves is studied in quasiperiodic superlattices using attenuated total reflection (ATR) technique. Angular and frequency dependences of reflection coefficient for ATR technique are of fractal character.
Surface Polarons at the Contact of Two Polar Crystals
Authors: Pokatilov E. P. , Beril S. I. , Fomin V. M. , Riabukhin G. Yu.
Published: July 2007

A theory of surface electron states at the contact of two polar media is developed. The electron—phonon Hamiltonian for a contact of two polar layers is given. Ground state and effective mass energies are determined in a weak coupling approximation. Conditions for polaron localization in the contact region are discussed.
Thermo‐Galvanomagnetic Phenomena in Spin Quantum Wells
Authors: Karyagin V. V. , Lyapilin I. I.
Published: July 2007

Transport phenomena in spin quantum wells (SQW) are studied based on narrow‐gap magnetically mixed semiconductors. In contrast to compositional quantum wells, the depth of SQW is easily changed under the action of temperature or magnetic field, which leads to a change in the concentration of quasi‐two‐dimensional electrons in SQW. It is shown that in this case the coefficients of transverse magnetoresistance and thermoelectric power display non‐monotonic dependence on temperature and magnetic field.
Simple Analysis of Atomic Forces Acting on Silicon Surfaces
Authors: Tomášek M. , Pick Š. , Gadiyak G. V. , Morokov Yu. N.
Published: July 2007

Extensive recursion method calculations of silicon (001), (111) and (111) surfaces, both ideal and with adatoms and steps, are analyzed and a simple, transparent picture of the origin of forces acting between surface atoms is arrived at. The results fall into three distince groups depending on the character of surface states near EF. Within each of these groups, the interactions have a pair‐wise character. The interpretation is made using the generalized Hückel rule and low order moments of the Hamiltonian. The comparison with ab initio calculations is much improved when direct interactions between surface nearest neighbours are included. The relation of the conclusions to recent empirical approaches is shortly mentioned.
Theory of Surface Polariton Excitation by Charged Particles in a Layer with Account of Retardation
Authors: Arakelian V. H. , Bagdassarian L. A.
Published: July 2007

Surface electromagnetic waves or surface polariton (SP) excitations are considered in material layer by means of moving charged particles. A general theory of the problem is given (including retardation) without any limitations for its parameters. Compact expressions for the energy spectrum of the two possible SP branches are obtained, as well as a number of calculation curves for surface phonon‐polaritons and surface plasmons. Certain particular cases of the problem are considered. SP excitation with high phase velocities is treated in detail. SP are shown to be intensively excited only at those frequencies for which ‐1 ⪅ ε (ω) < 0.
One‐Particle Excitation Spectrum in a Bisoliton Model of Superconductivity
Authors: Ermakov V. N. , Kruchinin S. P.
Published: July 2007

A bisoliton model of high‐temperature superconductivity is formulated in terms of one‐particle states. The transition to a superconducting state is shown to be accompanied by the energy spectrum rearrangement. The dielectric gap typical for BCS theory is appeared. Its dependence on concentration of carriers is of nonmonotonous character. The conditions for realization of a bisoliton mechanism of superconductivity are considered.
One‐ and Two‐Dimensional Sublattices as Preconditions for High‐Tc Superconductivity
Authors: Krüger E.
Published: July 2007

In an earlier paper it was proposed describing superconductivity in the framework of a nonadiabatic Heisenberg model in order to interprete the outstanding symmetry properties of the (spin‐dependent) Wannier functions in the conduction bands of superconductors. This new group‐theoretical model suggests that Cooper pair formation can only be mediated by boson excitations carrying crystal‐spin‐angular momentum. While in the three‐dimensionally isotropic lattices of the standard superconductors phonons are able to transport crystal‐spin‐angular momentum, this is not true for phonons propagating through the one‐ or two‐dimensional CuO sublattices of the high‐Tc compounds. Therefore, if such an anisotropic material is superconducting, it is necessarily higher‐energetic excitations (of well‐defined symmetry) which mediate pair formation. This fact is proposed being responsible for the high transition temperatures of these compounds.
On the Microscopic Theory of Optical Properties of Crystals with Incommensurate Phases
Authors: Shvaika A. M. , Mokhnyak S. M. , Stasyuk I. V.
Published: July 2007

The microscopic description and symmetry analysis of the refracting properties for incommensurate phases of dielectric crystals are performed. The contributions conditioned by anharmonicities and nonlinear electron polarizabilities are distinguished. It is shown, that the symmetry of tensors describing refracting properties is not changed at the commensurate—incommensurate phase transition.
The Gauge Theory of Point Defects
Authors: Grachev A. V. , Nesterov A. I. , Ovchinnikov S. G.
Published: July 2007

Classification of affine‐metric space theories can form the basis for geometric classification of defects. A GL(3, R) ⊳ T(3) gauge theory of linear and point defects is constructed. An asymptotic behaviour for spherical point defect is obtained by solution of fiels equations.
The Effect of a Third Component Impurity C on the Heat Capacity of A3B‐Type Ordered Alloys
Authors: Mekhrabov A. O. , Babaev Z. M. , Matysina Z. A.
Published: July 2007

For the first time theoretical (in terms of the classical theory of ordering) and experimental (with the adiabatic calorimeter method) investigations are made of the effect of a third component impurity C on the heat capacity of A3B‐type ordered alloys with FCC structure. The effect of the impurities Mn, Cr, Mo, or W on the heat capacity of Ni3Fe alloys is analysed as an example. The comparison of the theoretical results with the experimental data shows good qualitative agreement.
Calculation of the Auger Spectra of Clusters Modelling Solid Hydrogen Fluoride
Authors: Liegener C. ‐M.
Published: July 2007

The Auger spectrum of solid hydrogen fluoride is calculated by an ab initio Green's function method. Already small clusters lead to saturation with respect to cluster size. The differences which arise when going from the gas to the solid phase Auger spectrum are mainly a broadening of the lines and the emergence of an additional feature at high kinetic energies. This additional feature is assigned to transitions to delocalized final states.
Nonlinear Laser Spectroscopy of Exciton Absorption in MOCVD Grown ZnSe Monocrystalline Films
Authors: Gribkovskii V. P. , Zimin L. G. , Gaponenko S. V. , Malinovskii I. E. , Kuznetsov P. I. , Yakushcheva G. G.
Published: July 2007

The influence of intensive photoexcitation on the absorption spectrum of high‐quality monocrystalline ZnSe films grown by the MOCVD technique is investigated by two independently tunable dye lasers. With increasing photoexcited carrier density a broadening of the excitonic band, a decrease of the exctionic absorption, and a band gap narrowing are observed. The bleaching near the excitonic resonance is associated with the nonequilibrium electron–hole plasma screening of the Coloumb interaction. The considerable contribution of the excitonic band broadening and of the long‐wave shift of the fundamental absorption edge to the nonlinear crystal response permit to obtain the resonatorless optical bistability regime. The peculiarities of nonlinear absorption at sample temperatures below 88 K are associated with the influence of the polaritonic mechanism of the optical excitation energy transfer in the crystal.
Calculation of Surface‐Induced Core‐Level Shifts for Covalent Semiconductors C, Si, Ge, and α‐Sn I. (111) 2 × 1 Surfaces
Authors: Bechstedt F. , Reichardt D.
Published: July 2007

A theory is developed for the surface induced core‐level shift. Since the many body relaxation mechanism can be neglected only the initial‐state potential effect is considered. Starting from tight‐binding assumptions the shift is related to ion charges accompanying the reconstruction, the hybridization state, the polarity of chemical bonds, and the atomic configuration. The atomic configurations are taken from total energy minimizations, dynamical LEED or ion scattering studies. The other input parameters are calculated self‐consistently. The developed theory is applied to the (111) 2 × 1 surface of group IV materials. Various fundamental reconstruction models — buckling, π‐bonded chains, and π‐bonded molecules — are studied. The shifts resulting for eight atoms per surface elementray cell and the associated core electron line shapes seem to favour the chain model in the (111) 2 × 1 case. The molecule model cannot be completely ruled out only from core‐level shift calculations because of its homopolar bond character.
Electron and Positron Distribution for the Plane (1110) in Si and GaAs
Authors: Aourag H. , Khelifa B. , Belaidi A. , Kobayasi T. , West R. N.
Published: July 2007

The electron and positron charge densities are calculated as a function of position in the unit cell for two diamond and zincblende semiconductors, using wave functions derived from nonlocal pseudopotential band structure calculations for the electronic part, and the positron wave functions are calculated for single‐particle approximation in manner which is free of any theoretical assumptions.
Collective Excitations of Localized Electrons and Their Effect on Magnetic‐Material Kinetics
Authors: Mitsek A. I.
Published: July 2007

The multielectron operators (MEO) method is used for calculating the collective excitations of unfilled shells in transition ions. The excitation dispersion law depends on a chemical bond. Decrease of the lattice stability with increasing T is determined by the MEO correlation function of the neighbour sites (the order parameter). The conduction electron scattering on such excitations provides a contribution to the electrical resistance ϱ(T) ∼ T2 in a parabolical dispersion law approximation. The effective Hamiltonian is obtained of the Cooper pairing which energy is large enough for interaction of the conduction electrons with the nearest neighbour ions. The pairing mechanism is attenuated for antiferromagnetic spin ordering of the neighbour sites. The elastic moduli defect, determining a kink of the phonon contribution to ϱ(T) near Tc or TN, is taken into account, comparing the theory with the experimental curves ϱ(T).
Electronic Specific Heat of Coulombic Systems
Authors: Rösler M. , Stolzmann W.
Published: July 2007

The specific heat of the electron gas is determined in the random phase approximation (RPA) using the Matsubara‐frequency summation technique which is well suited for calculating thermodynamic quantities up to relatively high degrees of degeneracy. A detailed discussion of the numerical problems is given. It is shown that widely used approximation schemes including the plasmonpole approximation (PPA) for the dielectric function are unsuitable calculating the specific heat with sufficient accuracy. The numerical evaluation shows in contradiction to previous calcutations that the specific heat ratio cv/cvid is larger than unity in the region of metallic densities.
Dislocation Recharging in Plastically Deformed Crystals of the A2B6 Type
Authors: Vardanyan R. A. , Veselko S. G.
Published: July 2007

The quantum transition of weakly coupled electrons from the ion to the self‐localized condenson (acoustic polaron) state on the dislocation is discussed for the case when during the plastic deformation of the crystal such ion appears in the space‐charged region of the edge dislocation. In terms of the adiabatic approximation the electron–phonon interaction is taken into account. It is shown that this interaction reduces to the multiquantum fluctuational phonon radiation and absorption in the initial and final states. The probability of the dislocation recharging elementary act is a function of the temperature, the electon–phonon interaction constant, and the distance between ion and dislocation. By numerical calculation the effectiveness for the recharging process is found for semiconductive A2B6‐compounds as a function of the deformation rate, the ionization energy of ion, the temperature, and the electrostatic field of the edge dislocation.
The Electrical Resistivity of Some Lithium Based Liquid Alloys
Authors: Akinlade O. , Belhachemi O.
Published: July 2007

The concentration dependent electrical resistivity of LiBi, LiIn, LiMg, and LiTl liquid alloys is studied and comparisons are made of the values of resistivity computed using the Faber‐Ziman formulation and the “2kF” scattering theory of Morgan et al. While a Heine‐Abarenkov potential will be used to describe the electron–ion pseudopotential, the structure factor will be given in the context of the mean‐spherical approximation for charged hard spheres with a Yukawa interaction. In order to explain the resistivity of Li based liquid alloys with high valency, it is necessary to go beyond the diffraction theory of Faber‐Ziman.
Spectroscopic Manifestations of Self‐Trapped Holes in Silica Theory and Experiment
Authors: Dianov E. M. , Karpechev V. N. , Sokolov V. O. , Sulimov V. B. , Chernov P. V. , Kornienko L. S. , Morozova I. O. , Rybaltovskii A. O.
Published: July 2007

A quantitative simulation in the cluster approximation is made of an autolocalized hole in the amorphous SiO2 network. A model is suggested in which the thermal excitation of holes from Anderson localized states of the top of the silica valence band above the mobility edge corresponds to the thermally stimulated luminescence peak at 125 K, and the analogous optical transition — the radiation‐induced low‐temperature IR‐absorption. The position and form both, of the peak and absorption band and their thermo‐ and photostability are explained.
On the Representation of Orientation Distributions in Texture Analysis by σ‐Sections. I. General Properties of σ‐Sections
Authors: Matthies S. , Helming K. , Kunze K.
Published: July 2007

The recently suggested concept of σ‐sections of the orientation space for comprehensible representation of distributions in texture analysis is considered in detail. The properties of possible variants of variables describing orientations and of projections are characterized qualitatively as well as by numerical estimations. Two variants are recommended for the use in practice in dependence on the questions of interest for the interpretation of orientation distributions.
Possible Role of Deformation‐Induced Point Defects in Dislocation Patterning
Authors: Estrin Y. , Abromeit C. , Aifantis E. C.
Published: July 2007

The evolution of dislocation density is considered by taking into account the effect of deformationinduced point defects on the dislocation annihilation (recovery) rate. It is shown by linear stability analysis of the coupled equations describing the evolution of the dislocation density and the diffusion of point defects that a periodic spatial pattern can form during plastic deformation. The preferred wavelength of the emerging periodic structure is evaluated as a function of the production and annihilation bias parameters reflecting certain asymmetries in the generation and annihilation of interstitials and vacancies in the course of straining.
Second‐Order Pressure Derivatives of SOE Constants of Fluorite Structure Solids
Authors: Sharma A. K. , Goyal S. C.
Published: July 2007

The expressions for the second‐order pressure derivatives of the SOE constants of the fluorite structure solids are derived using the relations for SOE, TOE, and FOE constants of CaF2, SrF2, and BaF2 structure type solids. The first‐order pressure derivatives of the TOE constants, internal strain parameter, and the linear combinations of the FOE constants are also analysed for the solids under study.
Lithium Impurity States in PbTe
Authors: Tovstyuk K. D. , Polyakov I. O. , Slinko E. I. , Tovstyuk N. K. , Khandozhko A. G.
Published: July 2007

The behaviour of lithium impurity in lead telluride is studied. The lithium quasi‐liquid in PbTe lattice is found to freeze out at some critical temperature. The model of light particle quasi‐liquid in a solid crystalline state is further developed.
A Search for a Phase Transition in Sr(NO3)2 by Raman Spectroscopy. Evidence for Partial Disorder
Authors: Brooker M. H.
Published: July 2007

The Raman spectrum of Sr(NO3)2 is measured as a function of temperature from room temperature to the melting point in a search for an explanation for reported anomalies in the electrical and thermal properties and the report of a possible phase transition in the 600 to 700 K region. Except for the expected line broading with increased temperature the Raman spectrum of Sr(NO3)2 is consistent with the Pa3(T) space group at all temperatures. Depolarization studies of an oriented single crystal confirm the fact that the Raman bands retained their Ag, Eg, and Fg character at all temperatures. There is no evidence to support the reported phase transition to a disordered structure at high temperature. However, there is good evidence to indicate the presence of a considerable fraction of the nitrate ions on disordered sites in thermal equilibrium with the nitrate ions on ordered sites. Evidence for the disordered nitrate ions comes from the presence of anomalous spectral features which appear in addition to those bands which characterize the ordered part of the crystal.
Interfacial Capacitance
Authors: Krupski J.
Published: July 2007

An analysis is made of experimental results on the capacitance of thin‐film condensers. To find the screened electrostatic potential in a three layer structure a specular electron reflection model is employed which takes into account quantum effects. The resulting interfacial capacitance is in semiquantitative agreement with the measured value for the thin‐film Al–Al2O3–Al condenser.
Two‐Dimensional Electron Gas in a Magnetic Field. The Non‐Degenerate Limit
Authors: Wang L.
Published: July 2007

The thermodynamical properties of a two‐dimensional electron gas (2DEG) in a magnetic field with an arbitrary level broadening are discussed in the nondegenerate limit first proposed by Zawadzki. It is concluded that experimental measurements in the non‐degenerate regime may open a new avenue for investigations on the density of states of a 2DEG in a magnetic field.
Percolative Treatment of the Verwey Transition in Cobalt–Iron and Nickel–Iron Ferrites
Authors: Marín M. L. , Ortuño M. , Hernández A. , Abellán J.
Published: July 2007

A new percolation treatment of the Verwey transition in cobalt–iron and nickel–iron ferrites is performed via a large‐cell Monte Carlo simulation. It is based on the consideration of certain electronic transitions that conserve short‐range order and on their percolation properties. The presence of cobalt and nickel impurities blocks the possibility of these transitions, diminishing their electronic rearrangement capabilities. The critical impurity concentration for the disappearence of the Verwey transition obtained with this method is xc = 0.04, in agreement with experimental results.
Electron Momentum Distribution and Compton Profiles of Crystalline Rare Gases by the Augmented‐Plane‐Wave Method
Authors: Bacalis N. C. , Papanicolaou N. I.
Published: July 2007

A systematic study of directional electron momentum distributions and Compton profiles of the inert gas solids is presented, performed within the augmented‐plane‐wave method using the exchange and correlation of Hedin and Lundqvist which is well known to be the most reliable approximation for valence band properties of the rare gas crystals. Directional anisotropies in the Compton profiles are observed which are larger than existing ones from Hartree‐Fock calculations.
Molecular Perturbation Model for the Spin–Lattice Coupling Coefficients of 6A1 States to Eθ Strains
Authors: Boulanger D. , Parrot R.
Published: July 2007

The proposed perturbation model involves second‐order molecular spin–orbit interactions between the fundamental state 6A1, and the components of orbital triplets 4T1 and 6T1, calculated in symmetry D2d induced by E‐strains. The matrix elements of the molecular spin–orbit interactions are first calculated for the states 4T1 and 6T1 defined from multielectronic configurations with three open shells. Then, it is shown that the second‐order molecular spin–orbit perturbation involving these states 4T1 and 6T1 is strictly zero if these states are degenerate. Finally, it is shown that the most important contribution is due to the three states 4T1, defined from multielectronic configurations with two open shells.
Metal–Dielectric Transition in n‐ZnSe Obtained by Doping with Shallow Donor Impurity
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N.
Published: July 2007

By means of dosed variation from 2 × 1016 to 2 × 1018 cm−3 of the shallow donor Al impurity concentration in n‐ZnSe a transition from activated conductivity to non‐activated one is obtained in the low‐temperature limit. In the temperature range from 1.6 to 300 K the peculiarities of resistivity, Hall coefficient, and electron mobility dependences on temperature are investigated while transiting from a metallic conduction to an activated one. On the dielectric side of the transition as the temperature decreases the conduction with an activation energy ϵ1 induced by electron excitation from the impurity states into the conduction band is replaced by the hopping conduction with a constant activation energy ϵ3, which in the lowest temperature region is transferred to a hopping conduction of variable activation energy. It is established that the replacement of the activated conduction by a metallic one occurs at ND = 1.3 × 1017 cm−3 and takes place within the impurity band before it attains the bottom of the conduction band. The electron concentration at the transition from the metallic state to the dielectric one is continuously varied as a consequence of a chaotic distribution of donors in the crystal.
Hall Coefficient of Dilute CuPd, CuRh, CuZr, and CuY Alloys d‐Resonance Scattering
Authors: Flouda E. , Boukos N. , Papastaikoudis C.
Published: July 2007

Measurements of the Hall coefficient of the dilute CuPd, CuRh, CuZr, and CuY alloys are made in a magnetic field up to about 3 T and 4.2 K. The Hall coefficients show the trend to depend on the valence of the 4d impurities. The results are discussed in the spirit of the Friedel‐Anderson model of virtual bound states in Cu.