bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dielectric study of the modulated smectic C*‐uniform smectic C transition in a magnetic field
Authors: Muševič I. , Žekš B. , Blinc R. , Rasing Th. , Wyder P. 
Published: July 2007

AbstractThe in‐plane component of the dielectric constant of chiral smectic p‐decyloxybenzilidene‐p'‐amino‐2‐methylbutyl cinnamate is measured as a function of temperature and magnetic field applied parallel to the smectic layers. The transition from the modulated smectic C* to the uniform smectic C phase is accompanied by a drop in the dielectric constant in analogy to the incommensurate‐commensurate transition in ferroelectrics. The C*‐C transition line exhibits a large hysteresis and the critical field for the unwinding of the helix increases with decreasing temperature except close to the λ‐line. The obtained results are in qualitative disagreement with the predictions of the Landau‐de Gennes model and seem to suggest a different mechanism for the unwinding of the smectic C* helix.
Expansion of the Electron‐Hole Liquid Plasma at GaAs Surface
Authors: Korbutyak D. V. , Litovchenko V. G. 
Published: July 2007

AbstractThe spectral and planar distribution of the luminescence intensity of the electron‐hole plasma (EHP) created by laser excitation in the subsurface region of a direct‐band semiconductor like GaAs in contact with a dielectric medium (Si3N4) is studied. High optical excitation levels (L ≈ ≈ 5 MW/cm2) make possible to detect: (1) the appearance of stimulated radiation mainly from the regions of the sample edges; (2) the expansion of EHP from the excited region predominantly along the GaAs‐Si3N4 interface up to a distance (l ≈ 50 to 100 μm), which is several times greater than the corresponding bulk value. The assumption is made that the electron‐hole liquid is created not only at the “tails” of the expanded plasma, but also within the excited regions (in the latter case after a partial cooling of EHP, when in the process of the relaxation the electron‐hole pairs concentration achieves the EHP‐condensation value n ≈ 1016 cm−3). The mechanism of a long‐wave range tail formation in EHL radiation, which is caused by the energy losses on non‐equilibrium plasmons, is discussed.
Effect of Magnetic Field on the Decay Kinetics and Polarization of the AT Emission of KCl:Ga at 0.38 K
Authors: Hizhnyakov V. , Liidya G. , Nagirnyi V. , Soovik T. , Zazubovich S. 
Published: July 2007

AbstractThe AT luminescence of KCl: Ga is investigated at 0.38 to 100 K by spectral, kinetic, and polarization methods. At extremely low temperatures the luminescence decay curve in the magnetic field is decomposed into three components (fast, quick, and slow) with decay times dependent, but light sums independent of the field strength. Polarization degrees of the components are independent both of field and time. The experimental results are discussed in terms of a model suggesting a strong interaction of the optical electron of Ga+ with tetragonal vibrations of the crystal lattice.
Thermodynamical Properties of the Diluted Transverse Ising Model with Anisotropic Coupling Constants
Authors: Plascak J. A. 
Published: July 2007

AbstractThe thermodynamical properties of the site‐ and bond‐diluted transverse Ising model with anisotropic coupling constants are studied by using a variational procedure based on Bogolyubov's inequality. Within this approach the thermal behaviour of the system is obtained in the entire range of temperature (0 ≤ T < ∞). The results for the critical temperature, critical transverse field, and critical concentration are, in several cases, comparable to the constant‐coupling approximation.
Modified Local Density Approximation for Potentials with a Finite Step
Authors: Schnittler Ch. , Kelber J. , Paasch G. , Bartoš I. , Übensee H. 
Published: July 2007

AbstractIn the local density approximation (LDA) the density of a many‐electron system is expressed as a function of the spatially varying potential. Here a modified LDA is derived which takes into account a finite potential step at a plane interface so being applicable for semiconductor‐insulator structures and, in many cases, also for semiconductor heterojunctions. Different modifications of the standard LDA are discussed. They are compared with one another and with the exact solution of the Schrödinger equation for a model system. The simplest modification is shown to be also the best one and to give very good results for inversion layers even in the case of relatively small potential jumps and up to field strengths of some 105 V cm−1.
Analysis of Critical Voltage Data Using the Dynamical Theory of Electron Diffraction
Authors: Kim H. S. , Sheinin S. S. 
Published: July 2007

AbstractA method for determining critical voltage to an accuracy of 1 k V has recently been proposed by Sellar et al. The method involves an analysis of dark bands in convergent beam patterns based on the standard method for taking absorption into account in the dynamical theory of electron diffraction. The work presented in this paper shows that improved agreement between theory and experiment is obtained when an exact method of taking absorption into account is employed. The results based on the exact method support the conclusions of Sellar et al. regarding the precision with which critical voltage can be determined. The results also indicate, however, that caution should be exercised in choosing the crystal thickness at which observations should be made.
Comparison between the Self‐Consistent Continued‐Fraction and Other Continued‐Fraction Methods
Authors: Šlechta J. 
Published: July 2007

AbstractAn alternative comparison of SCCF and other CP methods to that one published recently is given. It is shown that both, conceptually and on numerical merits SCCF is the best method, in existence, of calculation of the density of states in disordered materials, in principle, as it is the optimal, that is minimal yet fully tractable, approximation of the exact problem formulated.
Second‐Order Cumulant Expansion of the Free Energy and the Effective Masses of a Polaron at Finite Temperatures
Authors: Arisawa K. , Saitoh M. 
Published: July 2007

AbstractExact perturbational results up to the second order in the coupling constant or the fourth order in the electron‐phonon interactions for the free energy, the inertial mass, and the magnetic mass of a polaron are calculated by use of the path‐integral method. New explicit analytical results are obtained for a Fröhlich polaron at finite temperatures, which in the zero temperature limit reduce to the known results.
Localization of Electronic States in Disordered Tight‐Binding Systems. I. Derivation and Study of the Model
Authors: Unger H.‐J. 
Published: July 2007

AbstractIn this and in a following paper the localization problem in real disordered systems is considered from first principles with the help of the recursion method. A Hermitian representation of the Hamilton matrix is given. The concept of the extended Hilbert space is introduced in order to find a convenient representation of the recursion method which allows us to handle the localization problem. For systems containing only nearest neighbour interactions a new useful approximation for the vector system is given within which the Hamiltonian is tridiagonal. The influence of the degree of disorder on the energy spectrum of a semi‐infinite “partially disordered chain” is studied.
Chemical Transferability of Phase Shifts in Extended X‐Ray Absorption Fine Structure
Authors: Ghatikar M. N. 
Published: July 2007

AbstractThe empirical phase shifts are calculated from the theoretical X‐ray absorption fine structure phase functions in a large number of systems with different atom‐pairs in varying surroundings. Measured extended X‐ray absorption fine structure (EXAFS) data are used to estimate the linearly dependent term on k in the phase shift and to compare it with theoretical values. Attempts are made to explain the behaviour of the phase shift of a given atom‐pair in different chemical surroundings and for different atom‐pairs in a given isoelectronic series of elements.
Excitation of Longitudinal Optical Phonons by Stimulated Raman Effect in Piezoelectric Cubic Crystals
Authors: Merten L. , Kotzott R. 
Published: July 2007

AbstractIt is shown that for special directions in piezoelectric cubic crystals Stokes and anti‐Stokes waves couple anharmonically also with longitudinal phonons. The dispersion functions of the coupled waves can be represented by simple analytic expressions, if the coupling with the anti‐Stokes waves is neglected. The wave vectors of the coupled waves are either real or pairs of complex conjugate quantities. In the frequency regions of complex‐conjugate wave vectors a coupled wave exists with an exponentially amplified longitudinal polariton wave. The properties of this wave are discussed in detail.
Structure and Bonding in Cubic IV‐VI Crystals. I. Evidence for Covalent Bonding from LCAO Parameters
Authors: Enders P. 
Published: July 2007

AbstractThe inherent instability of the cubic structure of IV‐VI compounds is considered. Alternatively to the work of Littlewood, the treatment bases on the LCAO method and relates to Harrison's approach as Littlewood's papers do to Phillips'‐Van Vechten's one. First Harrison's polarity is calculated from Slater‐Koster parameters due to Volkov and coworkers. It indicates predominantly covalent bonding character for the cubic IV‐VI compounds. A comparison is given with Littlewood's treatment. The method of special points is used to calculate integral bonding properties. Chadi and Cohen's two point set is shown to be often equivalent to a ligand‐field theoretical treatment.
Statistical Mechanics of Anharmonic Crystals
Authors: Gaveau B. , Lawrynowicz J. , Wojtczak L. 
Published: July 2007

AbstractA system of coupled anharmonic oscillators with fluctuations of the crystallographic lattice is considered. The anharmonicity is included as an effective field in the form of pseudoharmonic interactions. The description of the motion far from a Brownian particle embedded in the heat bath shows that the fluctuations lead to an explanation of the origin of stochastic forces appearing in the system and having the character of a black noise. The Brownian particle is, in general, non‐Markoffian if the fluctuations are taken into account, but it can be expressed as a sum of Markoffian processes at least. The appearance of fluctuations is related to the damping of motion in the heat bath formed by harmonic oscillators.
Elastic Constants of the Layered Compounds GaS, GaSe, InSe, and Their Pressure Dependence. II. Theoretical Part
Authors: Gatulle M. , Fischer M. 
Published: July 2007

AbstractThe block diagonalization of the dynamical matrix of β‐GaS is reported in the case of propagation perpendicular to the layers. A linear chain model that includes intralayer interactions between any atoms is introduced, the principal frequencies and the elastic constants C33 and C44 are calculated. Within the model, the existence of real coupling parameters is discussed, that leads to an evaluation of the intralayer forces contribution to the elastic constants. The evolution of the interlayer interactions with pressure is studied, using previously published experimental results. Finally, as far as possible, the theoretical formulas are applied to the similar structures of ϵ‐GaSe and γ‐InSe.
Lattice Equilibrium and Phonons in Molybdenum and Tungsten
Authors: Gupta K. C. , Rathore R. P. S. 
Published: July 2007

AbstractThe deficiencies of the Fielek model, regarding the core‐shell interactions, the volume interactions, and the stability of the lattice, which so far have not been attended adequately, are removed. The improved version treats the lattice under zero stress within the framework of a mathematically more sound equilibrium condition which includes for the first time the van der Waals (vdW) attractive energy in the description of the total energy of the lattice. The vdW three‐body forces are employed in place of Krebs' scheme on account of its deficiency in respect of crystal equilibrium, arbitrary volume dependence of the screening parameter, and the assumption of the perfectly free electron gas. The isotropic force constant of the Fielek model coupling the cores with the d‐shells is replaced by the more realistic two‐body vdW forces. The theoretically sound model thus developed predicts the phonon spectrum in molybdenum and tungsten quite reliably.
The Encounter Model in Impurity Diffusion. Correlation Effects in NMR
Authors: Becker K. D. 
Published: July 2007

AbstractThe encounter model of atomic diffusion is applied to impurity diffusion in an f.c.c. lattice using the five‐frequency model. The influence of the spatial and temporal correlation of the microscopic particle motion on NMR spectral density functions is discussed in the framework of the Torrey‐Wolf theory assuming an isotropic random walk of encounters. It is shown that for fast diffusing impurities, by combination of results from NMR and macroscopic transport experiments, a criterion can be deduced by which, under certain conditions, a vacancy mechanism can be excluded as the dominating transport process. Predictions of interstitial migration mechanisms of the Cu+ ion in alkali halides based on this criterion, are in agreement with previous assignments.
On the Formation of Large Clusters of Recombining Particles of One Kind in Solids under Excitation One‐Dimensional Continuous and Discrete Models
Authors: Antonov‐Romanovskii V. V. 
Published: July 2007

AbstractOn the basis of the linear models a calculation of the average number of one‐kind particles arising in the prolonged excitation process as a result of recombination is carried out. The cluster dimensions are in a good agreement with the numerical simulation experimental data.
Characterization of the Magnetic Phases of MnAs1−xPx Crystals
Authors: Krokoszinski H. J. , Bärner K. 
Published: July 2007

AbstractThe initial magnetic susceptibility χi is used to define critical fields separating different magnetic phases in MnAs1−xPx crystals. A phase diagram in T—x—B space and sections thereof are given for 0.03 < x < 0.15, 4.2 K < T < 300 K, and 0 < B < 7 T.
Phase Diagram for the Ising Model with a Free Surface
Authors: Honmura R. , Sarmento E. F. , Fittipaldi I. P. , Kaneyoshi T. 
Published: July 2007

AbstractThe phase diagrams that occur in a semi‐infinite ferromagnetic Ising model with enhanced surface couplings are studied by means of a new‐type of effective‐field theory. A considerable qualitative and to a certain extent quantitative improvement on the traditional mean field phase diagram is obtained. The results obtained by using such a simple formalism are also in good agreement with more sophisticated techniques.
Influence of the Phase Transition in Pb1−xGexTe on the Electronic Dispersion Relation
Authors: Vassilev L. V. 
Published: July 2007

AbstractThe influence of the structural phase transition on the electronic structure of Pb1−xGexTe near the band gap is investigated theoretically. It is shown that the absolute minimum of the conduction band and the absolute maximum of the valence band are shifted in the (111) plane of the Brillouin zone. The surfaces of constant energy develop from toroidal‐shaped ones near the band edge to a figure of revolution obtained from two intersecting ellipses for the usual carrier concentration of 1017 cm−3.
Electron—Phonon Coupling and Electron—Electron Coulomb Interaction in Superconductors
Authors: Surma M. 
Published: July 2007

AbstractThe coupling constant λ from the recently derived semiempirical equation for the superconducting transition temperature Tc3 = 0.5γDQD exp (−2/λ) is identified with the effective electron—electron—phonon coupling constant λexp measured in the experiment. Under this assumption the McMillan equation for Tc is written in terms of λ*, the electron—phonon coupling constant and μ*, the electron—electron interaction parameter. The method of determination of λ* and μ* from the measured λexp is presented and a numerical verification is given.
The Ordering Types in the Extended Hubbard Model with Electron—Phonon Interaction
Authors: Manakova L. A. , Ionov S. P. 
Published: July 2007

AbstractThe ground states in the extended Hubbard model are obtained taking into account polaron effects, with both, intrasite repulsion and intrasite attraction. It is shown that the function fq, characterizing the degree of lattice polarization due to the electron—phonon interaction depends on the type of the ground state and on the electron concentration. Depending on the interaction parameters, the hopping energy (the bandwidth), and the electron concentration the crystals can be in the following ground states: 1. the polaron charge‐ordered state; 2. the bipolaron chargeordered state; 3. the bipolaron state with a homogeneous electron distribution over the lattice; 4. the state with an intersite bipolaron.
Band Structure and Lifetime Determinations for GeS from Angle‐Resolved Photoemission
Authors: Cháb V. , Bartoš I. 
Published: July 2007

AbstractThe experimental determination of the electron dispersion relation, E(k‖), for a quasi‐two‐dimen‐sional system is performed by means of angle‐resolved photoemission. For the layered single crystal GeS, the whole valence band is mapped using HeI, HeII, and NeI excitation sources. Simple interpretation of peak widths in terms of hole lifetimes, based on a three‐step model of photoemission, is given.
Damping of the Transverse and Longitudinal Excitations of the Ising Model in a Transverse Field
Authors: Wesselinowa Julia M. 
Published: July 2007

AbstractThe Ising model in a transverse field is treated by means of the Green function technique to calculate the excitation spectrum and the damping of these excitations above and below Tc. The soft mode is overdamped in the disordered phase and near Tc, while it is nearly undamped at low temperatures. The temperature dependence of the transverse and longitudinal damping for zero wave vector is calculated numerically for different values of the transverse field.
V3 and FA Centers in KCl:Na Crystals. A Thermoluminescence Study
Authors: Manam J. , Ratnam V. V. 
Published: July 2007

AbstractV3 and FA centers in KCl:Na crystals are studied using thermoluminescence and TL spectra as tools together with the data on X‐ray luminescence spectra. The charge species responsible for two different glow peaks occurring around 55 and 105 °C are identified as well as the sequence of steps involved, the mechanism of recombination, and the recombination sites. The results obtained enable to establish the origin of the 435 nm emission occurring in both, the TL and X‐ray luminescence as that due to the radiative decay of the self‐trapped exciton at a cation—vacancy site.
Anisotropic Electrical Properties of GeSe
Authors: Ishihara Y. , Ohno Y. , Nakada I. 
Published: July 2007

AbstractVapour grown p‐type single crystals of Ge1+xSe, in which x is of the order less than 0.005 are prepared. The crystals include donors and acceptors. From the anisotropy of the electrical resistivity and the Hall coefficient together with the thermoelectric power in the temperature range of 78 to 300 K, the effective masses of holes along the a‐, b‐, and c‐crystallographic axes are obtained to 0.20m, 0.37m, and 6.2m, respectively, where m is the electron mass. The donor level lies 0.17 eV above the valence band, with a concentration in the range of (1.74 to 2.94) × 1024 m−3 according to the variation of x. The concentration of the acceptors is estimated to 3 × 1024 m−3.
Ultrasonic Wave Field Transport by Conduction Electrons in Indium
Authors: Gudkov V. V. , Fil V. D. 
Published: July 2007

AbstractThe phenomenon of electronic transport of ultrasonic fields corresponding to a circularly polarized wave is observed and studied in a single crystal of superpure indium under propagation of transverse ultrasonic radio‐wave pulses along tetragonal crystallographic axis under Doppler‐shifted acoustic cyclotron resonance conditions in a longitudinal magnetic field. The most effective transport is proved to be in the range of sufficient deformation interaction of conduction electrons with the ultrasonic wave. A Gaussian curvature of the resonant band of electrons is determined.
Regular Method in X‐Ray Scattering Analysis of Amorphous and Liquid Metals
Authors: Eeshov N. V. , Ageev A. L. , Serikov A. V. , Babanov Yu. A. , Vasin V. V. 
Published: July 2007

AbstractThe capabilities of the regularization method in the problem of extracting the radial atomic distribution function from X‐ray scattering data for amorphous and liquid metals are studied. The results are compared to the data obtained by the conventional Fourier transformation procedure, with reference to the examples of liquid Ga and Fe80B20 metallic glass.
Lattice Dynamics and Thermal Properties of SiGe Solid Solution
Authors: Soma T. , Kitani Y. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractA simplified treatment is proposed to study quantitatively the lattice dynamics and thermal properties of SiGe solid solutions. The volume effect on the lattice dynamics of the pure constituent is considered, and the phonon dispersion relations of the local and band modes are obtained for Si0.9Ge0.1 and Si0.1Ge0.9 systems.
Calculation of Lattice Defect Saddle‐Point Configurations
Authors: Savino E. J. , Monti A. M. 
Published: July 2007

AbstractA numerical method for calculating lattice defect atomic configurations corresponding to energy local extrema is presented. It is designed for locating and calculating the defect saddle‐point configuration. The method is used for obtaining the vacancy and divacancy migration energy in a h.c.p. lattice. The lattice atoms are identified by their coordinates and bonded together by a short‐range pair interatomic potential fitted to some Mg properties.
Electronic Structure of YCx
Authors: Ivashchenko V. I. , Lisenko A. A. , Zhurakovskii E. A. 
Published: July 2007

AbstractThe band structures of YCx for concentrations x ‐ 1.0, 0.8, 0.7, and 0.6 are calculated using the coherent‐potential approximation (CPA) in the linear combination of atomic orbitals (LCAO) basis. The LCAO Hamiltonian is derived from augmented plane wave (APW) calculations performed for a hypothetical stoichiometric compound with x ‐ 1.0. The results reveal that YCx is most stable for about 42 at% C. Most of the theoretical values are compared with experimental data.
Parametric Conversion of an Electromagnetic Wave into an Acoustic Wave in Magnetised Cubic Piezoelectric Semiconducting Plasmas
Authors: Ghosh S. , Saxena R. B. 
Published: July 2007

AbstractA detailed analytical investigation is made of parametric conversion of an electromagnetic wave into an acoustic wave in a magnetoactive n‐type cubic piezoelectric semiconducting crystal belonging to class 43m under a geometrical configuration which can also be employed in analysing the phenomenon under either Voigt or Faraday orientation. The electric vector E0 of an spatially uniform pump electromagnetic wave (applied along the y‐axis) is normal to propagation direction (along the z‐axis) of the generated low‐frequency transverse‐acoustic wave (Ω, k) and the scattered electromagnetic wave (Ω1, k1). The magnetostatic field is applied in the xz plane making an arbitrary angle θ with propagation vectors k, k1 (antiparallel to each other). The dispersion relation is obtained by using a hydrodynamic model of an homogeneous, piezoelectric, one‐component (electron) semiconductor plasma, and the threshold value of pump electric field and the growth rate of unstable acoustic mode well above the threshold are discussed for isotropic (B0 = 0) and magnetoactive (B0 ≠ 0) plasmas. The analysis is applied to a specific semiconductor, n‐InSb at 77 K duly irradiated by a pulsed 10.6 μm CO2 laser for numerical estimation. The laser wave intensities used are in the range of 109 to 1011 W m−2 which is assumed to be less than the damage threshold of the InSb crystal.