bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of Special‐Directions Method to the Optical Properties of Copper and Silver
Authors: Ahuja A. K. , Auluck S. , Joshi S. K.
Published: July 2007

Using the interpolation scheme (with four OPW's) the density of states N (E), joint density of states JDOS (E), and the frequency dependent dielectric function ϵ2(ω) for copper (non‐relativistic) and silver (relativistic) are calculated. The summation over the k‐vectors lying in the first Brillouin zone are performed using the special directions (SD) method. The effect of increasing the number of SD's is investigated. The optical matrix elements are evaluated by a method given by Smith. The effect of including a relaxation time τ on ϵ2(ω) is studied. Also a calculation of ϵ2(ω) for copper including 16 OPW's in the interpolation scheme is given and found that the agreement with experimental results is improved at the higher energies by increasing the number of OPW's in the interpolation scheme.
The Influence of the Variation of the Chemical Composition and of the Nitrogen Doping Level on the Energy Spectra of the Bound Excitons in GaAs1−xPx:N
Authors: Nurtdinov N. R. , Stegmann R. , Griepentrog M.
Published: July 2007

The spectras of photoluminescence (PL), photoexcitation (PE) and cathodoluminescence (CL) in GaAs1−xPx:N (x ≧ 0.67) are investigated. The spectral position of the Nx‐line can be described by a logarithmic dependence on the excitation level and on the nitrogen concentration. Different methods are worked out to determine the nitrogen concentration by measurements of PL, PE, and CL. The results allow assertions about the influence of the disorder in the As–P sublattice and of the interaction of the nitrogen atoms on the energy spectra of the bound excitons.
Heterodyne Correlation of Scattered Light from a Sr++‐Doped NaCl Crystal. A Feasibility Study
Authors: Sahoo Debendranath
Published: July 2007

A theoretical calculation of the heterodyne correlation function of scattered light is presented for a (suitably heat‐treated) NaCl crystal doped with 250 ppm divalent Sr++ impurities. It is assumed that the impurity‐vacancy complexes (A1) diffuse and aggregate to form dimers (A2) and trimers (A3) by the reactions A1 + A1 ⇌ A2 and A2 + A1 ⇌ A3. Light scattering arises due to fluctuations in concentrations of A1, A2, and A3. The correlation function, calculated under equilibrium condition, is a sum of three decaying exponentials. It reduces to 85% (of its initial value) in 10 ms at 800 K, to 30% in 10 s at 600 K, and to 6% in 10 s at 500 K, thus indicating the feasibility of the experiment at relatively high temperatures.
Free‐Carrier Absorption in n‐PbSe at Low Temperatures Due to Electron–Electron Scattering
Authors: van Huong Nguyen
Published: July 2007

Free‐carrier absorption due to electron‐electron interaction in strongly degenerate n‐PbSe is calculated using the theory developed in a previous paper. This theory is specified for the case of weakly anisotropic conduction band. Numerical results for the free‐carrier absorption are compared with those corresponding to other electron scattering processes, and with experimental data on this material at 30 K.
Modified Phase Modulation‐Only Approximation of Incommensurate Phases in K2SeO4‐Type Crystals
Authors: Mashiyama H.
Published: July 2007

The incommensurate‐commensurate transition in K2SeO4‐type crystals is studied on the base of a Landau free energy. The phase modulation‐only approximation is modified to take account of the effect of the amplitude modulation partially but in a consistent way. The soliton density decreases continuously with a logarithmic law near the lock‐in temperature. It is also shown that the specific heat and the dielectric susceptibility diverge at the transition point.
Role of Phonon‐Induced Hybridization in the Spinless Anderson Model
Authors: Zieliński J. , Kowalska J.
Published: July 2007

The spinless Anderson model accomplished by phonon‐induced hybridization is considered. It is found that in the periodic case an insulator‐metal transition appears depending on the values of parameters and temperature. In the case of an isolated impurity a pronounced temperature dependence takes place leading to an increase of the virtual state width.
Photoemission Studies of Pd80−xSi20Cox Amorphous Alloys
Authors: Hricovíni K. , Mikušík P. , Krempaský J.
Published: July 2007

X‐ray and UV photoemission measurements of the core levels and valence bands of Pd80−xSi20Cox amorphous alloys are reported. XPS spectra show a broadening of the cobalt 2p‐levels in the alloys while the binding energies are the same as in the polycrystalline Co. The behaviour of Co atoms during the alloying process is discussed. UPS spectra of the valence bands show a shift of Pd 4d‐band to higher binding energies and a cobalt contribution to the density of states above the Fermi level of PdSi alloy.
Monte carlo determination of long‐range pair interaction energies from diffuse scattering of X‐rays by alloys
Authors: Stark Yu. S. , Steinberg A. S. , Vasilev V. M. , Dimitrov V. I.
Published: July 2007

A method for the determination of the long‐range interparticle interaction energies in alloys from the experimentally measured short‐range order parameters is presented. This way of determining which is based on the Monte Carlo method is applied to the problem of calculating of the first five pair interaction energies in Cu3Au. The results are compared with those obtained through the analytical theories of ordering.
Optical absorption by an exciton bound to an ionized donor impurity in anisotropic semiconductors
Authors: Stauffer L. , Stébé B. , Munschy G.
Published: July 2007

The oscillator strength is determined for the dipole absorption of the anisotropic exciton—ionized donor complex, taking into account the electronic structure and using our previously obtained anisotropic envelope wave function. It is shown that the anisotropy of the electron lowers markedly the oscillator strength, whereas the hole anisotropy does not give any significant effect. In the case of CdS, the results improve previous variational calculations made in the isotropic case.
Isotope effect of manganese and simultaneous impurity diffusion of chromium and zinc in copper
Authors: Rockosch H.‐J. , Herzig Ch.
Published: July 2007

The isotope effect E = 0.310 as a mean value is measured at T = 1200 K for impurity diffusion of 52Mn/54Mn in copper. The corresponding correlation factor f2 = 0.36 is relatively small in comparison with the published results of Fe, Co, and Ni in Cu. The small value of f2 and the faster diffusivity of Mn with regard to self‐diffusion of Cu can be explained by the strong lattice distortions of Mn in Cu. Valence effects are accordingly less important. The frequency ratios for vacancy jumps and the vacancy flow effect are calculated. The free binding enthalpy of the vacancy—impurity complex is estimated. Simultaneously to Mn, the tracer diffusion of 51Cr and 65Zn is determined. The different evaporation effects of the tracer are taken into account in the evaluation of the diffusion coefficients.
Impurity pinning, interface roughening, and the incommensurate—commensurate transition
Authors: Nattermann T.
Published: July 2007

A model of incommensurate—commensurate transition with frozen impurities which pin the domain wall is discussed. The domain wall density vanishes at the transition with an exponent β′ = = (dR — d)/2(d — d1), with dR = 5 and d1 = 1, as a function of the reduced temperature or chemical potential, in agreement with experiments in d = 3 dimensions. There is an analogy with an Ising model with a weakly fluctuating exchange coupling, which exhibits wall roughening for dimensions d ≦ 5.
On thermopower and thermal conductivity of the periodic anderson model
Authors: Schumann R. , Elk K.
Published: July 2007

The periodic Anderson model is used as a simple model describing intermediate‐valence compounds. In that model a strong electron—electron correlation is taken into account. The correlation term is decoupled using the alloy‐analogy approximation. Then the energy‐dependent conductivity σ(ω) is obtained from the Kubo‐Greenwood formula. Using σ(ω) the thermopower and the thermal conductivity can be calculated. For the absolute value of the thermopower a rapid increase with increasing temperature is found in the low‐temperature regime with a broad maximum at mean temperatures, whereas a weak decrease occurs in the high‐temperature regime. The thermal conductivity increases very rapidly with the temperature.
Electronic properties of dilute copper alloys III. Influence on the de haas‐van alphen effect
Authors: Mertig I. , Mrosan E. , Zeller R. , Dederichs P. H.
Published: July 2007

A calculation of the Dingle temperatures and changes of the Fermi surface areas of Cu resulting from alloying with 4d transition metal impurities and with sp impurities of the third, fourth, and fifth rows of the Periodic System is presented. The theoretical results are compared with experimental information obtained from de Haas‐van Alphen investigations.
Dimer center luminescence in low‐doped KI:Tl+ crystals
Authors: Benci S. , Fermi F. , Lenzi G.
Published: July 2007

The emission spectra and the polarization characteristics of the luminescence versus the temperature and the excitation wavelength in low‐doped KI:Tl+ crystals allow to determine the nature of the center observed for excitation at λ > 290 nm. From the results it can be concluded that this center is a dimer center (Tl+)2 with D2h symmetry.
Van der waals' forces in face centred cubic cobalt
Authors: Singh S. P. , Rathore R. P. S.
Published: July 2007

For analysing the role played by the Van der‐Waals' forces in the phonon dispersion of metals, four different models are developed for the face‐centered configuration. It is found that these forces enhance the efficacy of the models. The model parameters, calculated by the knowledge of the measured frequency, are free from the errors originating from the variation of elastic constants with temperature and the nature of the forces dominant in elastic behaviour. The least attended metal, face centered cubic cobalt, is chosen for the present analysis.
Lattice vibrations of solid hydrofluoric acid
Authors: Tse Wan‐Sun , Chang Chia‐Nan
Published: July 2007

Lattice dynamics calculations for solid hydrofluoric acid are presented. It is found that the Born‐von Karman model using six interatomic force constants is capable of giving acceptable values of the zone centre frequencies.
Parametric conversion of an electron plasma wave into an electromagnetic wave in longitudinally magnetized n‐type piezoelectric semiconductor plasmas
Authors: Ghosh S. , Khan S.
Published: July 2007

The interesting nonlinear process of parametric conversion of a high frequency electrostatic wave into an electromagnetic wave is investigated analytically in an n‐type piezoelectric semiconductor plasma to which an uniform and static magnetic field is applied along the direction of wave propagation. A general dispersion relation is obtained and solved for both the cases of excited electromagnetic waves (i.e., in the cases of left‐hand and right‐hand circularly polarized waves) to study the threshold condition and the growth rate of the unstable mode at a pump amplitude well above the threshold. Numerical estimates are made for n‐InSb at 77 K irradiated with a large amplitude electron plasma wave of frequency 1013 s−1 and wave number 5 × 107 m−1. The threshold electric field is independent of applied magnetic field and the growth rates of the excited modes have linear dependence on the magnetic field.
On the physical tensor field criterion in birman's theory of symmetry changes
Authors: Osuch K.
Published: July 2007

Birman's theory of symmetry changes at continuous phase transitions is applied to transitions induced by representations which are connected with a non‐null star, when the high‐temperature group is I4/m(C54h). It is shown that the generalized physical tensor field criterion of Birman rules out some of the low‐temperature groups which appear in Landau's theory as well as in the theory of Birman restricted to its first two criterions (the subduction criterion and the chain criterion).
Density functional theory of metal surface properties
Authors: Raykov B.
Published: July 2007

A new functional is proposed for the surface kinetic energy of an electron gas. It is a sum of the kinetic energies of two parts of the space — close to and far from the jellium surface. The decrease of the electron density is approximated by an exponential function. The values of the surface energies and surface dipole barriers thus obtained are close to those of Lang and Kohn. The errors of the method lie between those of the functional of Smith and of the functional of Ma and Sahni. The electron work function of five alkali metals is calculated and very good agreement with the experiment is found.
Nonlinear kinetics and optical properties of band charge carriers
Authors: Fomin V. M. , Pokatilov E. P.
Published: July 2007

A theory of the nonlinear response of band charge carriers in semiconductors is developed for arbitrary degeneracy conditions taking into consideration the influence of a strong electromagnetic radiation field on the scattering probability and carrier heating. A comparison of the contributions made by said sources of nonlinearity to the absorption coefficient is carried out for the main mechanisms of interaction of charge carriers with optical and acoustical phonons to first order in the intensity of the electromagnetic radiation. The temperature dependence of the absorbtion coefficient for the non‐degenerate carriers is studied.
Phonon relaxation due to anharmonism and central peak in structural phase transitions. II. Soft optic modes in uniaxial ferroelectrics and soft acoustic modes in cubic crystals
Authors: Kashcheev V. N.
Published: July 2007

In the mode—mode coupling approximation the critical exponents (CE) are calculated for the dampings and frequency shifts of soft optic modes and acoustic phonons (in uniaxial ferroelectrics) and for the dampings of soft acoustic phonons (in cubic crystals) in the structural transition point. The CE are traced back to the anharmonic interaction (of all orders) of soft phonons with the intrinsic dynamic central peak of any nature.
One‐phonon and multiphonon absorption in EuSe and Eu1—xSrxS (0 < x < 1)
Authors: Mützenich G. , Faymonville R. , Grosse P.
Published: July 2007

Transmission and reflection measurements on single crystalline samples of stoichiometric EuSe show a number of intrinsic absorption structures in the far infrared. They are explained by one‐, two‐, and three‐phonon processes. The results are consistent with measurements of second‐order Raman scattering and agree with theoretical calculations of the density of states and phonon dispersion published earlier. The reststrahl bands of the alloys Eu1—xSrx S show a typical onemode character with additional weak structures. The shift of the phonon frequencies with composition and temperature is reported.
Density functional pseudopotential calculation of the cohesive properties of disordered solid alloys of nontransition metals application to Zn—Cd
Authors: González D. J. , Zorita M. L. , Alonso J. A. , I≁iguez M. P.
Published: July 2007

A density functional pseudopotential method is used to calculate the heat of formation and the equilibrium volume of ZnxCd1—x as a function of the concentration x. Then an estimation of the free energy of formation is given and the results are used to explain the main features of the solid part of the phase diagram of this alloy. The influence of the form of the pseudopotential is studied by performing the calculations both with Ashcroft's and with Shaw's pseudopotentials.
Quantization procedure for phonons in an isotropic elastic half‐space
Authors: Oliveros M. C. , Tilley D. R.
Published: July 2007

In classical elasticity theory, a stress‐free surface leads to mixing of longitudinal and transverse waves with displacement in the plane of incidence, to the existence of a “pseudo‐surface” wave, and to the existence of the localised Rayleigh wave. Expressions for the quantized displacement, the quantized harmonic Hamiltonian, and the density of allowed states are presented taking proper account of these effects. The form of the cubic anharmonic Hamiltonian is outlined, and possible applications are briefly discussed.
Negative magnetoresistance in heavily doped and compensated n‐type InSb
Authors: Sethi B. R. , Goyal P. K. , Sharma O. P. , Mathur P. C.
Published: July 2007

Transverse magnetoresistance measurements are made on heavily doped n‐type InSb single crystals in the temperature range 77 to 300 K. The magnetoresistance at low temperatures is found to be negative indicating a contribution of impurity band conduction to the electrical transport phenomenon. The conductivity and Hall mobility measurements also provide evidence of impurity band conduction near liquid nitrogen temperature. The mobility of the charge carriers in the impurity band is estimated from the experimentally observed mobility.
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

The 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

The 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

The 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

The 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

In 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

A 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

An 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

Exact 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

In 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

The 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

It 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

The 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

A 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

The 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

The 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

The 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

On 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

The 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

The 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

The 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

The 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

The 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

The 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

The 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

V3 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

Vapour 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

The 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

The 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

A 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

A 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

The 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

A 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.
Temperature Dependence of Third‐Order Elastic Constants of NaCl‐Structure Alkali Halide Crystals
Authors: Varshney R. K. , Shanker J.
Published: July 2007

A method is developed for calculating the temperature dependence of third‐order elastic constants (TOEC) of NaCl‐structure alkali halides. Six independent values of TOEC for each alkali halide crystal are calculated at 0 K and at room temperature (300 K). Three pressure derivatives of second‐order elastic constants (SOEC) are also calculated at 0 K and 300 K. The calculations are performed using the concept of phonon pressure theory. The effect of Lundqvist's three‐body interactions is considered in addition to other relevant interactions operative in ionic crystals. The results are discussed and compared with other‐investigations.
Magnetic Properties of a Random Ensemble of Two‐Spin Clusters
Authors: Dusowski B. , Heber G.
Published: July 2007

The ensemble consists of N clusters each containing two spin 1/2. The energy spectrum is derived from an exchange interaction J between the two spins of one cluster, a Weiß‐molecular‐field Hm = γm (m averaged magnetization of the random ensemble), and a Zeeman‐term in an external magnetic field Hext. In special cases the four‐level‐system can be approximated by a two‐level‐system. Averages are performed over the two parameters J and γ. The averaged magnetization m of the ensemble as function of Hext and T is obtained from a nonlinear self‐consistency‐problem. The susceptibility χ(T, Hext) is also calculated. The application to experimental results is discussed.
De Haas‐Van Alphen Effect in Nearly Magnetic Transition Metals
Authors: Riseborough P. S.
Published: July 2007

The oscillatory part of the thermodynamic potential and magnetization are calculated for a paramagnetic system that is near to a magnetic instability. The dominant excitations of such an exchange enhanced Fermi liquid are persistent spin fluctuations. The electrons are scattered by processes in which the spin fluctuations are emitted and absorbed. The electron spin fluctuation interaction results in a many‐body resonance of the electronic density of states at the Fermi level. It is shown that the spin fluctuations manifest themselves in the de Haas‐van Alphen oscillations. The amplitude of the oscillations is reduced, the reduction is dependent on the enhancement of the linear T term in the electronic specific heat. The results are applied to the experiments on CeSn3 and on Pd.
Rigid Muffin‐Tin Approximation for the Electron–Phonon Matrix Element
Authors: John W.
Published: July 2007

The electron–phonon matrix element is calculated in the rigid muffin‐tin approximation for nonlocal and nonspherical potentials. It is shown that the matrix element may be expressed by the scattering properties of the muffin‐tin potential. For nonspherical potentials, which may be used to fit the Fermi surface data of cubic transition metals, an expression is derived for the Hopfield parameter η.
Resonance Magneto‐Spatial Dispersion of Crystals
Authors: Ivchenko E. L. , Kochereshko V. P. , Mikhailov G. V. , Uraltsev I. N.
Published: July 2007

The results of theoretical and experimental investigations of novel magneto‐optical effects connected with the magneto‐spatial dispersion of the principal dielectric axes are presented. For this purpose the low‐temperature transmission spectra of thin CdSe crystals are measured near the A (n=1) exciton resonance in the Voigt configuration κ ⟂H°|C6, H° being the external magnetic field and k being the light wave vector. It is observed that for the polarizer position P| C6 or P ⟂ C6 the transmitted light is polarized elliptically and the major axis of the polarization ellipse is rotated with respect to the incident light polarization plane. The derived theory of resonant magneto‐spatial dispersion of the axes is in agreement with experimental data. The constant of the k‐linear term of the exciton energy spectrum is determined from the comparison of theory and experiment.
Application of the Band Representations of Space Groups in the Theory of Electronic States of Crystalline Solids. I. General Consideration of the Band Representations
Authors: Evarestov R. A. , Smirnov V. P.
Published: July 2007

Band representations are considered in the framework of the ordinary representation theory of space groups. The band representation characterizes the symmetry of all the electronic states of an energy band. Any band representation coincides with a so‐called simple band representation or is a direct sum of the latter. The whole number of simple band representations is finite for any space group. The type of a band representation determines the symmetry of the localized functions related with a given energy band.
Nonequilibrium Kinetics of Exciton Wave Packets in Crystals
Authors: Gaididei Yu. B. , Vakhnenko A. A.
Published: July 2007

The migration in a crystal of spatially inhomogeneous electronic excitations interacting with a phonon thermostat is studied. The evolution of excitons with band widths of the order of the optical phonon energy or greater is shown to be adequately described by a mixed, site‐energy representation. A generalized diffusion equation is obtained with memory essentially dependent on the exciton energy and with an inhomogeneity term, describing the energy redistribution between the exciton band sublevels.
Electronic Structure of an Unreconstructed (1010) α‐Quartz Surface
Authors: Nylén M.
Published: July 2007

The semiemprical tight‐binding method is used to investigate the electronic structure of an unreconstructed (1010) α‐quartz surface. No localized states are found in the fundamental gap.
Low‐Temperature Properties of One‐Dimensional Heisenberg Systems with Random Anistropy
Authors: Gekht R. S.
Published: July 2007

Thermodynamic properties of classical one‐dimensional Heisenberg systems with random V (of the “easy axis” type) and regular D (of the “easy plane” type) anisotropies are considered. The expression for the free energy is obtained by the transfer‐integral techniques and by the solution of the Fokker‐Planck equations. Low‐temperature dependences of susceptibility and correlation lengths are found for a random disordered system. The expression for the square of fluctuation of the Sz spin component is obtained in dependence on the parameters V, D and temperature T.
Molecular Excitons in Quasi‐One‐Dimensional Conducting Crystals (Semiconductors and Metals)
Authors: Vlasova R. M. , Kapustin V. A. , Semkin V. N. , Sekretarczyk G. , Agroskin L. S. , Papayan G. V. , Rautian L. P.
Published: July 2007

Polarized reflection spectra are investigated of single crystals of molecular semiconductors Cs2(TCNQ)3, NMe2,6MePy(TCNQ)2 TEA(TCNQ)2, and of metals TTT(TCNQ)2, TTF‐TCNQ in the spectral region framing the band of π‐electron intramolecular transitions of TCNQ0, TCNQ−, and (TCNQ) (250 to 750 nm). Through Kramers‐Kronig relation absorption spectra are calculated and spectra of the imaginary part of the dielectric constant. In Cs2(TCNQ)3 and in TTF‐TCNQ the 370 nm electronic transition band exhibit Davydov splitting. The splitting magnitude averaged over the transition and the components polarization ratio are determined. In the crystals with asymmetric cations inhomogenious broadening of the band is observed. This broadening is associated with the influence of the chaotic potential of the crystal structure on the transition. Using the inhomogeneous broadening magnitude the magnitude of the chaotic potential in TEA(TCNQ)2 is estimated being 0.9 eV.