bluuebunny/crossref_metadata_2025_split huggingface dataset:
Field Theory of a Viscoelastic Medium Subjected to a Phase Transition
Authors: Olemskoi A. I. , Panin V. E. , Petrunin V. A. 
Published: July 2007

AbstractEvolution of a medium, which is subjected to the transition of crystallisation, martensitic type and so on, is realised as the interaction of a Higgs field, that describes a reconstruction of atomic system (transformation of potential relief), and a gauge field of displacements. It is shown, that the soliton type distribution of the fields is connected with one‐ and two‐dimensional defects. The conditions of the existence of defects are analyzed.
Contribution from the Lattice Vibrational Term and Pressure Dependence of the Phase Diagrams for Alkali Alloys
Authors: Soma T. , Iwafune K. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractThe lattice vibrational contributions to the internal energy and Helmholtz free energy of alkali metals such as K, Rb, and Cs are studied in the dynamical treatment using the previously developed electronic theory based on pseudopotentials. The pressure effect on the phase diagrams of the CsK, CsRb, and RbK systems are obtained quantitatively considering lattice vibrational contributions. A region of phase mixture is decreased under pressure, and the melting curves under compression show an increase in temperature.
Optical Study of Phase Transition from Tetrahedrally into Octahedrally Coordinated MnS
Authors: Goede O. , Heimbrod W. , Weinhold V. , Schnürer E. , Eberle H. G. 
Published: July 2007

AbstractMnS thin films on glass substrates prepared by thermal vacuum evaporation show zincblende/wurtzite and rocksalt structure, respectively in dependence of the substrate temperature. The thermal‐treatment induced transition from the tetrahedrally (ZB/W) into the octahedrally (RS) coordinated phase is studied optically by photoluminescence, excitation, and absorption spectroscopy and by X‐ray diffraction measurements. Emission bands in the red and infrared spectral region are observed being characteristic for the tetrahedrally and octahedrally coordinated phase, respectively. The excitation due to energy transfer by Frenkel excitons is studied in various stages of the ZB/W → RS phase transition. As a result of this transition a shift of the absorption edge by about 300 meV to lower energies is found ascribed to a corresponding energy‐gap difference.
Electronic Band Structure and Optical Anisotropy in InS. II. Theoretical Study
Authors: Takarabe K. , Kawamura H. , Wakamura K. 
Published: July 2007

AbstractThe electronic band structure of InS is calculated for the first time using the empirical pseudopotential method. A group‐theoretical study of the symmetry properties of InS is included. The resulting energy bands are then used to calculate the imaginary part of the dielectric function for each polarization along the principal axes of InS. The total and partial electronic densities are mapped on the (110) plane. Comparisons are made with previous experimental studies.
First Principles Prediction of Structural Properties and Pressure Dependence of the Charge Density and Energy Gaps in Diamond
Authors: Rodríguez C. O. , Casali R. A. , Blanć E. L. Peltzer Y , Cappannini O. M. 
Published: July 2007

AbstractThe possibility of predicting from first principles structural properties of solids has always been an aim of quantum theory of solids. These predictions are possible at present, and one also obtains a detailed description of many other microscopic properties. Using the ab‐initio pseudopotential approach a determination of the total energy and structural properties of diamond are made showing good agreement with experimental values. A detailed study is also given of the volume dependence of the forbidden X‐ray structure factor F(222) and of the pressure dependence of real space charge density and of different energy gaps. An analysis of the importance of transferability (norm‐conservation) of the input potentials is made.
Correlation between Chemical Shift, Plasmon Energy, and Partial Charge
Authors: Sinha S. H. , Chetal A. R. 
Published: July 2007

AbstractX‐ray chemical shifts in copper and manganese compounds are correlated with the product of partial charge and plasmon energy. A linear relation between the chemical shifts and the product is observed, with the chemical shift increasing when the product increases. The constant of proportionality for copper and manganese is of different numerical value. The relationship is used to predict the chemical shifts for other copper and manganese compounds. When correlating chemical shifts with plasmon shift alone, it is seen that the chemical shifts do not vary linearly with plasmon shifts.
On the Bleaching of the A‐Bound Exciton Absorption in GaP: N. An Example for an Electron–Hole Liquid Induced Optical Nonlinearity
Authors: Woggon Ulrike , Henneberge F. , Weinert H. 
Published: July 2007

AbstractThe intensity dependence of the A‐line absorption in GaP:N is investigated at various nitrogen concentrations and at different excitation conditions, i.e. for resonant and band‐to‐band excitation. For the intensity levels, which are necessary to saturate the absorption, simultaneous luminescence measurements have clearly shown the formation of an electron‐hole liquid in the excited region. An explanation is given of the experimental findings which takes into account the presence of an electron–hole liquid in the sample.
Charge Transfer in Nickel–Hydrogen System
Authors: Badirkhan Z. , Khalifeh J. 
Published: July 2007

AbstractThe local environment is considered of a hydrogen interstitial in ferromagnetic transition metals. The electronic structure of dilute hydrogen in nickel is described by a simple tight‐binding approximation. The interstitial is mainly characterized by an extra “s” effective energy level and hopping integrals between the hydrogen ls orbital and its nearest s, p, and d orbitals. The solution of such a problem requires the use of Friedel's screening rule and the equation coupling the physical parameters relevant to both spin directions. Charge transfer from metal to metalloid is present for reasonable values of the Coulomb correlation between the two electrons in the ls orbital. The change in the total saturation moment per added impurity atom and the local moment at the hydrogen site are also calculated.
Interaction of a Localized Spin Moment with Phonons Due to the Exchange Scattering of Virtual Carriers in Semiconductors
Authors: Semenov Yu. G. 
Published: July 2007

AbstractA new theory of the spin‐lattice interaction mechanism is developed for localized spins in semiconductors. In this mechanism, the coupling with phonons results from exchange scattering on a localized spin of the electron‐hole pairs accompanying the phonons. The process leads to a relaxation flip of the localized spin, provided the intermediate‐state carrier spins are flipped by spinorbit interaction. A detailed analysis of the mechanism is carried out in the approximation of the isotropic band structure of the semiconductor and the deformation electron‐phonon interactions. The experimental manifestations of the mechanism are discussed.
Stress Space and Strain Space in Continuum Mechanics
Authors: Kröner E. 
Published: July 2007

AbstractBoth, the kinematics and the statics of the mechanical state of a solid can be represented in the language of differential geometry. If the state is defect‐free then the geometry is, in general, Riemannian. The above statements are proved for the general nonlinear case. In particular it is argued that stress function tensor and stress tensor play the role of the metric and Einstein tensor, respectively, of the stress space whereas the equilibrium conditions for forces and moments (in absence of volume forces and moments) are the Bianchi identies of the stress space. Extension to solids with defects is possible.
Self‐Consistent MAPW Calculation with a Warped Muffin‐Tin Potential. I. The Electronic Structure of Al and Its Pressure Dependence
Authors: Bross H. , Eder R. 
Published: July 2007

AbstractIn the framework of the MAPW‐formalism the warped‐muffin‐tin approximation is discussed in detail. It turns out that the usually neglected terms are not only small as a consequence of wellknown facts of electrostatics but that the MAPW‐formalism has the advantage that the dominant multipole densities vanish with zero slope at the surface of the APW sphere. Using this approximation the electronic structure of Al is evaluated at seven different values of the lattice constant. This information enables the determination of the equation of state at zero temperature, the pressure dependence of the shape of the Fermi surface as well as the compressibility. At low pressures the agreement with experiments currently available is considerable. For higher pressures we expect a drastic change of the Fermi surface which should be seen by de Haas‐van Alphen experiments.
On the Anomalous Self‐Diffusion in B.C.C. Titanium
Authors: Köhler U. , Herzig Ch. 
Published: July 2007

AbstractSelf‐diffusion of 44Ti is measured in β‐Ti under UHV conditions in the whole range of existence of the b.c.c. phase. The Arrhenius plot shows a strong upward curvature in agreement with previous investigations of Murdock et al. The anomalous diffusion behaviour is related to the experimentally observed softening of the LA ⅔〈111〉 phonon mode and is explained by a monovacancy mechanism with a temperature‐dependent migration enthalpy. When separating the phonon related diffusion contribution the analysis yields a frequency factor and an activation enthalpy consistent with normal vacancy diffusion parameters.
A Model for the Calculation of Monovacancy and Divacancy Contributions to the Impurity Diffusion in Noble Metals
Authors: Neumann G. 
Published: July 2007

AbstractOn the basis of an earlier proposed model (Neumann and Hirschwald 1973, 1974) the impurity diffusion in noble metals is described by additionally taking into account the contribution of divacancies. The influence of the divacancy contribution on the effective diffusion energy and on the temperature dependence of the isotope effect is discussed. The divacancy contribution causes a curvature of the Arrhenius plot of the diffusion coefficient. For fast diffusing impurities the temperature behaviour of the correlation factor f leads to a distinct decrease of this curvature. A further consequence of the temperature behaviour of f for fast diffusers is that the low‐temperature value of ΔQ, the difference between the activation energies of impurity diffusion and self‐diffusion, represents an acceptable upper limit for the binding energy between impurity and vacancy.
The Magnetic Phase Transition in Amorphous and Disordered Crystalline Ferromagnets
Authors: Kellner W.‐U. , Fähnle M. , Kronmüller H. , Kaul S. N. 
Published: July 2007

AbstractThe magnetic phase transition of amorphous FeNi‐base alloys and disordered crystalline FeNi alloys is investigated, and the methods for a determination of the asymptotic critical exponents and the effective exponents are discussed critically. Two general results are obtained: 1) For the asymptotic exponents no significant deviations from the 3d‐Heisenberg exponents are found. 2) For the effective susceptibility exponent γ(T) the characteristic non‐monotonic temperature dependence is observed as predicted by the correlated molecular field theory.
Phase Transitions in Ordered and Disordered Ferrimagnets. II. Experimental Results
Authors: Haug M. , Fähnle M. , Kronmüller H. , Haberey F. 
Published: July 2007

AbstractThe magnetic phase transition is investigated by a vibration magnetometer for the homogeneous ferrimagnet Fe3O4 and the structurally disordered ferrites ZnxNi1−xFe2O4 with x = 0, 0.25, 0.5, and 0.75. For both ordered and disordered ferrimagnets the asymptotic critical exponents are compatible with the ones of a homogeneous 3d‐Heisenberg ferromagnet. Outside the asymptotic critical regime there is a strong effect of the structural inhomogeneities on the thermodynamic behaviour. In close analogy to the case of disordered ferromagnets, the effective Kouvel‐Fisher exponent γ(T) first increases with increasing temperature T for disordered systems, as predicted by the correlated molecular field theory and by Monte Carlo computer simulations, whereas it initially decreases for a homogeneous ferrimagnet. Anomalies in the modified Arrott plots at low fields are discussed.
The Influence of the Size Quantization on the Fermi Energy and the Effective Mass in Bi Films
Authors: Zaluzny M. , Lukasik A. 
Published: July 2007

AbstractThe influence of the size‐quantization on the Fermi energy, the carrier density, and the cyclotron effective mass in Bi films with normal along the trigonal, binary, or bisectrix axes is discussed. The numerical calculations are performed in the framework of the two‐band ellipsoidal model. Comparison with the results obtained in the framework of the ellipsoidal parabolic model is given.
Low‐Temperature Magnetoresistance in Medium‐Angle Grain Boundaries in Germanium
Authors: Xia Yi‐Ben , Bangert E. , Landwehr G. 
Published: July 2007

AbstractMagneto‐transport properties of grain boundaries in germanium bicrystals are studied in the liquid helium temperature range. For samples with 7° and 8° tilt angle an exponential magnetic field dependence is observed, which is analyzed in terms of two‐dimensional hopping conduction. The acceptor concentration N in the grain boundary can be deduced by comparing different magnetic field orientations. A surprising temperature dependence of N is obtained. In addition, the activation energy is determined as about 0.5 meV, typical for the hopping process, and decreases slightly with increasing magnetic field.
Three‐Branch Excitonic Polaritons in Direct Band Gap Cubic Semiconductors
Authors: Khamsasy Ch. , Van Hieu Nguyen , Viet Nguyen Ai 
Published: July 2007

AbstractThe transition is studied between a photon and “heavy” and “light” excitons in direct‐band gap cubic semiconductors with a fourfold degenerated highest valence band at the center of the Brillouin zone. The transition matrix elements are calculated in the second‐order approximation of the perturbation series with respect to a small constant proportional to the difference of the mass of the heavy and light holes. The algebraic equation determining the dispersion of the three‐branch polaritons is derived. The spin structure of the wave functions of the corresponding excitons is established.
Integro‐Differential Equations for the Evolution in the Athermal Pre‐Electron–Hole Plasma State of an Irradiated Direct Semiconductor
Authors: Heiner E. 
Published: July 2007

AbstractA consistent extended TDHF theory is treated for the description of electron motion of a laser irradiated direct semiconductor. Dissipation and memory is involved, therefore the theory is applicable in the athermal pre‐electron–hole plasma state of evolution. As a result the integro‐differential equations are derived which are the evolution equations for diagonal and off‐diagonal expectation values.
Multipole Theory of the Polarization of Solids by Point Defects. IV. Electronic and Spatial Structure of Single Electronic and Hole Centers and Their Pairs in LiF, KCl Crystals
Authors: Kantorovich L. N. 
Published: July 2007

AbstractA method proposed previously for calculating the electronic and spatial structure of neutral and charged point defects in ionic crystals with self‐consistent incorporation of the polarization effects into the eigenvalue spectrum is applied to the calculation of characteristics of concrete single electronic (F2, F, F) and hole (H, Vk, V2) centers and their pairs ({F, Vk}, {F, H}) in LiF, KCl crystals. The necessity of self‐consistent evaluation of polarization, as well as the dependence of calculation results on approximations used in simulating uncompensated charge density in defective region are discussed. Approximations based on point and non‐point polarizable charges (simulators) are compared. The electronic structure of defects is calculated on the basis of the INDO semiempirical method.
The Impact‐Parameter Dependence of Electron Stopping in Proton Collisions with Gas and Solid Atoms
Authors: Kabachnik N. M. , Kondratev V. N. , Chumanova O. V. 
Published: July 2007

AbstractThe semiclassical approximation with rectilinear trajectory is used to calculate the impact‐parameter dependence of electronic stopping for fast‐proton collisions with gas and solid atoms. The effects arosen from electron shell rearrangement and dynamic screening of proton charge in a solid, on the electron stopping are studied for case of solid targets. The calculation results are compared with experimental data and with approximate calculations based on sum rules and local electron density approximation.
Lattice Vibrations of CuGaSe2, CuInSe2 Ternary Compounds, and CuGaxIn1−xSe2 Solid Solutions
Authors: Bodnar I. V. , Smirnova G. F. , Smirnova T. V. , Aleshchenko Yu. A. , Vodopyanov L. K. 
Published: July 2007

AbstractOn the basis of IR reflection, transmission, and Raman spectra the frequencies of the vibrational modes of CuGaSe2, CuInSe2, and CuGaxIn1−xSe2 are obtained and identified. It is shown that the lattice vibrations of the solid solutions display mixed type behaviour. In the frequency range ω > 200 cm−1 the vibrational modes show two‐mode behaviour. Two relatively independent bands in this range are due to vibrations of GaSe atoms and InSe, respectively, in antiphase. The vibrational modes in the low frequency region (ω < 200 cm−1) display one‐mode behaviour.
Raman Scattering at the CaF2 Crystal Surface Excited by an Evanescent Optical Wave Field
Authors: Sheng Y. Q. , Recknagel E. , Weidinger A. , Gu Z. G. , Lai Z. Y. , Zhuang Z. C. 
Published: July 2007

AbstractNew results are given of Raman scattering measurements on the dispersion characteristics of surface‐phonon polaritons at the air—CaF2 interface using the Otto configuration. A phenomenological description of the dispersion relation is also given theoretically as well. The experimental results are in good agreement with the theory. For comparison, the dispersion curve of the surface‐phonon polariton under the same configuration is also measured by the ATR method in the in fared region and the agreement of the results from both the methods is also satisfactory.
Two‐Dimensional Electron Pair in a Transverse Magnetic Field
Authors: Goroshchenko S. Ya. , Ukrainskii I. I. 
Published: July 2007

AbstractThe effect of electron—electron interaction on the quantization of the motion of two‐dimensional electron pair in a transverse magnetic field is studied. It is shown that the energy spectrum of inner motion of the system is not degenerate when the magnetic field strength exceeds a certain value. Decreasing the field strength below this value a variety of level crossings is obtained. In the field region with a nondegenerate spectrum there exists a significant overlap of pair wave functions with those for the case of noninteracting electrons.
Characteristic Features of the Electronic Structure of Carbon Films
Authors: Gavrilenko V. I. , Klyui N. I. , Litovchenko V. G. , Strelnitskii V. E. 
Published: July 2007

AbstractStudies of the electroreflectance spectra of microcrystalline carbon films make it possible to reveal two energy gaps E1 and E2 within the spectral range from 1.0 to 5.6 eV. Using the strong‐bond method, a model of the electronic energy structure (EES) of microcrystalline carbon is developed explaining the emergence of semiconductor properties of this material and describing the available experimental data. An analysis of the data published in literature and of those obtained during these investigations allows to specify, within the limits of the model mentioned, additional features in the changes of the electronic structure of carbon by structural disordering. Characteristic features of the EES of hydrogenated carbon films are studied and substantial difference between the EES of a‐C:H and a‐C is shown.
Transition Probability of Impact Ionization by Holes in Silicon
Authors: Gautam D. K. , Khokle W. S. , Garg K. B. 
Published: July 2007

AbstractAn analytical expression is developed for the transition probability per unit time for impact ionization by holes. The approach is based upon time dependent perturbation calculations and the Bloch functions for the states of electrons and holes. The threshold energy of ionization by holes is calculated for the valley L1 for the electron band structure of silicon. The results obtained for the probability are in good agreement with experimental results for threshold energy and theoretical results for the ionization probability.
Calculation of Electrical Resistivity of Some Liquid Metals by the Mode‐Coupling Method
Authors: Jha D. N. 
Published: July 2007

AbstractThe resistivities and temperature coefficients of resistivity (TCR) of some liquid metals (Ag, Au, Fe, Ni, Eu) are calculated by the mode‐coupling approximation method of Götze and compared with respective experimental values. Good agreement is found for some of them. The sign of TCR is closely related to the variations in the values of the electron‐phonon coupling parameter.
On the Luminescence of CaO:Sn2+
Authors: Donker H. , Smit W. M. A. , Blasse G. 
Published: July 2007

AbstractThe luminescence spectra and decay times of CaO:Sn2+ are studied in the temperature range between 4.2 and 295 K. The emission spectra show one emission band with a maximum at 490 nm at 4.2 K. In the diffuse reflection spectra and the luminescence excitation spectra the A, B, and C bands are observed at 365, 324, and 294 nm, respectively. CaO:Sn2+ shows a very long after‐glow when excited at room temperature. The observed temperature dependence of the decay time may be fitted to a three level scheme leading to the parameter values τ0 = 350 μs, τ1 = 0.7 μs, and ΔE = 43 cm−1. A comparison is made with the luminescence of Sn2+ and Pb2+ in other calcium chalcogenides.
EXAFS in ZnxCd1−xGa2S4 Defect Chalcopyrite Solid Solution
Authors: Lottici P. P. , Antonioli G. , Razzetti C. 
Published: July 2007

AbstractThe structure of the nearest neighbours environment in the mixed defect chalcopyrite ZnxCd1−xGa2S4 is investigated by the EXAFS (extended X‐ray absorption fine structure) spectroscopy at the Zn and Ga K‐edges. The bond distances in the end member crystals and for different compositions in the alloy are determined. In addition to a conversation of the tetrahedral bond lengths with composition, the EXAFS analysis suggests an internal distortion in the ZnGa2S4 compound, in contradiction with literature data.
Collective Action Formalism on the Keldysh Contour for Disordered and Hubbard‐Correlated Electrons
Authors: Kolley E. , Kolley W. 
Published: July 2007

AbstractA real‐time finite‐temperature field theory on the Keldysh contour is used to describe the dynamics of an electron system within a random Hubbard model. The effective, i.e. quenched‐averaged, fermionic action under the functional integral is bosonized by introducing both a matrix field and an exchange field via Hubbard‐Stratonovich transformations. The resulting collective action permits the loop expansion, giving rise to a systematic approximation scheme. The saddle point and Gaussian fluctuations around it are calculated.