bluuebunny/crossref_metadata_2025_split huggingface dataset:
EPR Study of a Triple Fine Structure in a 1d Alternating System: Cs2(TCNQ)3
Authors: Blanc J. P. , Dugay M. , Robert H. , Thibaud C. 
Published: July 2007

AbstractThe cesium salt of tetracyanoquinodimethan Cs2(TCNQ)3 exhibits a EPR spectrum showing a fine structure consisting of two doublets of equal magnitude. A theoretical interpretation is given using the alternating Heisenberg model characterized by two exchange integrals J and γJ with γJ ≦≦ hωe ≪ J. The distance d between the lines of the triplets and the linewidth ΔωI are theoretically determined for two behaviours of the four spin correlation function Ψ(t). Measurements of the angular dependence of d and the temperature and angular dependence of ΔωI, at 9600 and 35 000 MHz, imply that Ψ(t) = exp (—ωEt). Various theoretical parameters can also be calculated. Using the values obtained the theoretical and experimental angular dependence of the linewidth are compared at room temperature. The deviation from axial symmetry is also evaluated.
Site Effects on N and O Luminescence in Electron‐Irradiated Neon Films
Authors: Sayer R. J. , Prince R. H. , Duley W. W. 
Published: July 2007

AbstractThe visible luminescence spectrum of solid neon containing small amounts of N2 or O2 is investigated at 7.8 K using low‐energy electrons. Double‐doping experiments employing N2 and × (where × is either O2, CO or Ar) are also carried out. Particular attention is given to the interpretation of the α(N2D—4S) transition of matrix‐trapped N atoms, and to a lesser extent the β(O1S—1D) transition of matrix‐isolated O atoms. The spectral intensity distribution within these transitions is photoelectrically recorded and for the long lived α transition, afterglow spectra are also presented. The structure of the α transition is shown to depend upon both the ratio of the N2 and × concentrations as well as the total [N2 + X] concentration, for total guest concentrations in the range from 0.01% to 0.1%. The components which comprise this emission arise from N atoms trapped in two characteristic sites denoted “substitutional”‐ and “impurity”‐affected. This same interpretation also applies in large part to the β transition of trapped O atoms.
APW Research of Europium Monochalcogenides. I. Band Structures and Electron—Electron Interaction in Ferromagnetic Semiconductors
Authors: Farberovich O. V. , Vlasov S. V. 
Published: July 2007

AbstractThe augmented plane wave method (APW) is used for a theoretical study of the electron properties of europium monochalcogenides. Spin‐polarized energy band calculations of the ferromagnetic EuO, EuS, and EuSe explain qualitatively the exchange interactions therein. Based on the APW data in the frame of perturbation theory the Coulomb electron—electron interaction at the 4f shell of europium is taken into account for EuO and EuS. The band structures and the multiplet terms of the f6d and 3d94f8 excited states gives a new interpretation of a known experimental spectra for these compounds.
On the Electrical Conductivity and the Density of States for the Narrow‐Band Periodic Anderson Model in the Symmetric Case
Authors: Matlak M. , Zieliński J. 
Published: July 2007

AbstractStarting from the exact atomic limit solution of the periodic Anderson model the electrical conductivity is calculated using the Kubo formula. Excluding very low temperatures the results remain in reasonable qualitative agreement with the behaviour observed experimentally for some intermediate valence compounds. The temperature dependent density of states function is also calculated and compared with the previous results.
Investigation of the Molecular Motions in Cd(NH3)6Cl2 by NMR Spectroscopy
Authors: Piśewski N. , Ferris L. T. H. 
Published: July 2007

AbstractNMR results are reported for intramolecular motion in Cd(NH3)6Cl2. Below the 180 K phase transition, the motion of the NH3 groups is well described by the Hilt‐Hubbard theory with an activation energy of 9.63 kJ/mol. The inter‐proton distance in NH3 determined from relaxational measurements is 0.161 nm. Several K below and above the transition point, two phases with different spin‐lattice relaxation times coexist.
Theory of Optical Nonlinearities in InSb
Authors: Koch S. W. , Schmitt‐Rink S. , Haug H. 
Published: July 2007

AbstractThe gain and absorption of an electron‐hole plasma in pure InSb is calculated by including the effects due to the band‐gap renormalization and the band‐filling and by taking into account deviations from the parabolic band form. The intensity‐dependent changes of the index of refraction are obtained with the aid of the Kramers‐Kronig relation. The results explain the large optical nonlinearities which are observed recently in InSb by Miller, Smith et al.
A Calculation of Vacancy Formation Energies in Strontium Oxide
Authors: Richardson D. D. 
Published: July 2007

AbstractA calculation of cation and anion vacancy formation energies in SrO is given after assessing three pair potentials, available in the literature, for their suitability. The calculation is done by a Born model including anharmonic potential effects and allows explicit relaxation of host ions about the defect. The vacancy formation energies are used to estimate a Schottky energy for SrO and this is compared with other available data on SrO and also several similarities of the present result with those of MgO found elsewhere are noted.
Influence of Crystal Field on the Magnetic Circular Birefringence
Authors: Malakhovskii A. V. 
Published: July 2007

AbstractMagnetic circular birefringence (MCB) is decomposed into diamagnetic and paramagnetic terms for arbitrary values of the fields on the atom and the influence of crystal field on these terms in considered. It is shown that a crystal field is the necessary condition for an existence of the temperature‐independent term in the paramagnetic part of MCB and the properties of this term are considered taking into account the mixing of states inside and between atomic terms. MCB for the transition 3d1 → 4p1 in the cubic octahedral crystal field is found taking into consideration the mixing of states inside the atomic terms. Field and temperature dependences of paramagnetic MCB are calculated for this case.
Phonon Assisted Interband Optical Transitions in Semiconductors Sustaining a Coulomb Random Field
Authors: Iskra V. D. 
Published: July 2007

AbstractThe interband optical absorption coefficient is calculated by the semi‐classical method in the case of a Coulomb random field taking account of the many‐phonon effects. The Urbach rule is reobtained with a slope of the exponential edge which generally depends upon that heat generation parameter, the random field parameter, and the temperature. The temperature dependence of the reverse slope is close to the linear one if the temperature is not low. A satisfactory interpretation of the temperature dependence of the absorption edge in chalcogenide glasses As2Se3 and As2S3 is reached.
Growth of Semiconducting CdF2:Ho3+ Crystals and Study of Their Optical and Transport Properties
Authors: Pouradier J. F. , Grimouille G. 
Published: July 2007

AbstractA method for growing CdF2:Ln3+ crystals (Ln lanthanide) is presented which results in semiconducting samples without any subsequent annealing. It is found that the main preparation parameters act on the optical and transport properties through a common parameter Eσ. The infra‐red absorption of the samples as well as their conductivity are then analysed in the frame of a model with impurity‐banding and hopping conductivity, resulting in informations on the impurity density of states.
On Quantum Theory of the Force Constant Matrix of Polyatomic Systems
Authors: Marushko I. A. 
Published: July 2007

AbstractA method is developed within the limits of the Hartree‐Fock‐Roothaan approach for calculating the force constants of a polyatomic system. The problem of differentiating the matrix P̂ with respect to atom coordinates is solved (P̂ = ĈĈ*, where Ĉ is a column vector, the components of which are the coefficients of the electron wave function expansion over the basic set). The convergence of the iterative procedure in computing the derivative ∂P̂/∂R is shown to be determined by the same parameters as the convergence of this procedure in solving the Hartree‐Fock‐Roothaan equations. Explicit account of the translational symmetry of the crystal makes it possible to escape the differentiation of the matrix and to represent the force matrix of any order in the form of an explicit function of the derivatives of the matrix elements of the Hamiltonian, the unit operator, and the matrix P̂, determined in the course of the calculations of the electronic energy structure of the system. The method proposed is applicable to any kind of calculations of the energy structure which results in the solution of the secular equation.
Dielectric Properties of the Fast‐Ion Conductor Na3Sc2P3O12
Authors: Delbecq C. J. , Marshall S. A. , Susman S. 
Published: July 2007

AbstractDielectric properties of granular crystallites of the fast‐ion conductor Na3Sc2P3O12 are measured in the frequency range 0.05 to 26 MHz and the temperature range − 70 to + 125 °C. Plots of the loss tangent, at fixed frequency, vs. temperature show a very sharp change in tan δ accompanying a structural phase change at about 63 °C. These plots show two loss maxima in the low temperature phase which indicate the occurrence of two relaxation processes with activation energies of 0.49 and 0.77 eV. These relaxation processes are probably distinct from the process of fast‐ion conduction which occurs at temperatures above the phase change at 63 °C. The existence of the structural phase change is substantiated by heat capacity measurements.
Photogalvanic effect in piezoelectrics: Quantitative theory for interband transitions in gallium arsenide
Authors: Belinicher V. I. , Novikov V. N. 
Published: July 2007

AbstractA quantitative theory of the photogalvanic effect for interband transitions in gallium arsenide is proposed. The photocurrent is expressed through the known crystal constants, and it possesses a characteristic oscillatory dependence on polarization and frequency of light.
A theoretical study of Raman scattering and infrared absorption spectra of Ga1−xInxP mixed crystals
Authors: Kleinert P. , Jahne E. 
Published: July 2007

AbstractUsing a Green's function technique a lattice dynamical study is carried out on the local density of states and the phonon‐optical properties for low concentrations of In atoms in Ga1−xInxP. The impurity‐induced Raman scattering and infrared absorption spectra are calculated for two cases: the nearest‐neighboui force constants A and B change equally or differently. One obtains reasonable correspondence of the calculated spectra to the recently observed features in the Raman spectra lying in the TA phonon region as well as to the already known structures in the Raman and infrared reflection spectra lying in the optical phonon region by assuming ΔA/A ≈︁ −0.6 and ΔB/B ≈︁ 0.
Shell models for B.C.C. transition metals
Authors: Khanna R. N. , Rathore R. P. S. 
Published: July 2007

AbstractFour modified and simplified versions of the shell model due to Fielek are developed to describe the dispersion relations in tantalum and niobium. The models (model 1, 2, 3) thus developed adequately account for the cohesion, Cauchy's discrepancy, and anisotropy exhibited by the metals. It is found that the interactions coupling the nearby d‐shells are effectively angular for tantalum and central pairwise for niobium.
Stability of the peierls state due to impurities
Authors: Bulka B. R. 
Published: July 2007

AbstractStability conditions of the Peierls state in a one‐dimensional system with impurities is investigated. Calculations are performed in a single‐impurity approximation and two cases are considered: an impurity built in the chain and the system with solitons. In the first case the total energy of the system as a function of the atomic potential and the concentration of impurities is presented. In the case of solitons also the total energy is calculated and it is shown that for a few per cent con‐ centration of solitons the distorted phase is unstable. For polyacetylene the critical concentration of solitons is estimated to yc ≈︁ 5%.
Behavior of defects introduced by a nanosecond intense electron pulse at high temperatures in alkali halides
Authors: Toriumi K. , Itoh N. 
Published: July 2007

AbstractMeasurements have been made on decay curves of the F centers (vacancies) created with a nanosecond electron pulse in non‐treated and plastically deformed KBr or NaCl in a temperature range between 400 and 700 K. It is found that decay curves are decomposed into four decay stages: three bimolecular stages (referred to as stages I, II and III in order of increasing decay time) and a monomolecular stage (referred to as stage IV), which occurs at the last. The reaction rate constants for stages I and II are found to be not influenced by plastic deformation but those for the stages III and IV are strongly influenced. The pre‐exponential factors of the reaction rate constants for the stages I and II in KBr and for the stage I in NaCl are explained in terms of the recombination of the pairs of the isolated di‐H centers (di‐interstitials) and the F centers but those for the stage III in KBr and the stages II and III in NaCl are of the pairs of the trapped‐interstitials and the F centers. The stage IV is ascribed to the recombination of the F centers with the mobile interstitials released from the interstitial clusters, or the recombination of the mobile F centers with the interstitial clusters. The effect of the Na‐impurity on the decay curves for KBr is also studied.
Temperature dependence of the Righi‐Leduc coefficients for Na and K metals
Authors: Zhernov A. P. 
Published: July 2007

AbstractFor the first time the values of the Righi‐Leduc coefficient ARL for Na and K are determined within the framework of a microscopic pseudopotential model at low temperatures. It is shown, when neglecting the nonequilibrium state of the phonon subsystem that in order to find ARL for these alkali metals, it is sufficient to consider a set of one‐dimensional integral equations instead of the standard kinetic equation. An explanation is given of the experimentally revealed significant difference in the low‐temperature dependence of the Hall and Righi‐Leduc coefficients for Na and K.
Magnetic spin phenomena in the chlorophyll “a” photoconductivity
Authors: Frankevich E. L. , Tribel M. M. , Sokolik I. A. , Kolesnikova L. I. , Stolovitseii Yu. M. 
Published: July 2007

AbstractModulation of the chlorophyll “a” (Chl) photoconductivity by an external magnetic field due to variations of the rate of non‐equilibrium spin processes under the action of a magnetic field is observed. These processes are charge carrier generation and charge detrapping by Chl triplet. Application of a magnetic field causes two types of variations of the photoconductivity of Chl films in vacuum: (i) instantaneous (τ < 1 s ) increase of the photoconductivity and (ii) slow decrease with time constant τ = 10 to 100s. The influence of temperature and intensity of the exciting light on the magnetic field effects is investigated. A scheme of energy transformation processes in Chl involving electron‐excited and ionized states is presented. The presence of oxygen leads to an increase of the photoconductivity of Chl, as compared with the vacuum values, and to a change in the dependence of photoconductivity on magnetic field. These changes are shown to occur due to the appearance of new acceptor centres arising from unstable products of Chl photooxidation.
Direct absorption inside the electron‐hole liquid in Ge: Warping effects and final state interactions
Authors: Zimmermann R. , Rösler M. , Asnin V. M. 
Published: July 2007

AbstractEarlier absorption experiments in highly excited Ge are successfully explained and quantitatively fitted by a theory including Moss‐Burstein shift in warped hole bands, self‐energy effects, and multiple electron‐hole scattering via screened Coulomb potential. The corresponding Bethe‐Salpeter equation is solved numerically in momentum space. At frequencies above Moss‐Burstein influence, calculated absorption spectra are close to the exciton continuum independent of excited carrier concentration in agreement with experiment, which disqualifies a one‐particle description of direct absorption in the electron‐hole liquid of Ge.
Absorption coefficients in the dynamical theory of electron diffraction for the non‐symmetrical Laue case
Authors: Sheinin S. S. , Kim H. S. 
Published: July 2007

AbstractIn previous investigations of diffraction contrast in the non‐symmetrical Laue case, the standard expressions for Bloch wave absorption coefficients, which are based on the assumption of symmetrical Laue diffraction conditions, are used. An expression for absorption coefficients which is specifically applicable to the non‐symmetrical Laue case is derived. For strong beam diffraction conditions it is shown that small errors result from the use of symmetrical Laue absorption coefficients in the non‐symmetrical Laue case. For weak beam diffraction conditions, on the other hand, considerable error can result. These errors increase with increasing crystal thickness and for increasing departure from symmetrical Laue diffraction conditions.
Calculations of Deformation‐Potential Constants in InSb
Authors: Gorczyca I. 
Published: July 2007

AbstractThe deformation‐potential constants for nonpolar optical‐phonon scattering and for acoustical‐phonon scattering in InSb are calculated. Wave functions obtained in the previous papers by orthogonalized plane wave (OPW) method and empirical pseudopotential method (EPM) are used to perform present calculations. The results are compared with those obtained from other theoretical methods and experimental data.
The Electronic Theory of the Alloy Systems Composed of Alkali Metal Elements. II. Phase Diagrams
Authors: Soma T. , Matsuo H. , Funaki M. 
Published: July 2007

AbstractThe phase diagrams of the Cs‐K, Cs‐Rb, Rb‐K, Cs‐Na, Rb‐Na, and K‐Na systems are investigated using the pseudo alloy atom model and the local Heine‐Abarenkov model potential. For the Cs‐K, Cs‐Rb and Rb‐K systems, the curves obtained near the melting point show reasonable agreement with experimental data, and the calculated results predict the presence of a mixture of two phases at low temperatures. Then, the Cs‐Na, Rb‐Na, and K‐Na systems show complete immiscibility.
Comparison of the s Band Structure of Face Centred Cubic and Hexagonal Close Packed Solids: II. Energy Correspondence
Authors: Betteridge G. P. 
Published: July 2007

AbstractIt is shown that an exact, one‐to‐one correspondence between the s band energies of the face centred cubic (3C) and hexagonal close packed (2H) structures exists throughout the common zone, when nearest neighbour interactions only are considered. The form of this correspondence throughout the zone, its physical basis, and the effects of more distant neighbour interactions, are discussed.
Non‐Local Calculations of the Dispersion of Electromagnetic Waves in Bismut: Dispersion Relation for the Voigt Configuration: q ∥ n ∥ C1, q ⟂ B
Authors: Saermark K. , Lebech J. , Braune W. , Kubicki N. 
Published: July 2007

AbstractThe dispersion and damping of Alfvén waves propagating through bismuth samples are calculated for the two Voigt configurations: B ∥ C2, q ∥ C1, E ∥ C3 and B ∥ C3, q ∥ C1, E ∥ C2 by means of a non‐local formalism developed earlier. A comparison with experimentally observed results is performed for a number of frequencies of the incoming microwaves.
Collective Motions in a Metal‐Doped Molten Salt
Authors: Kobayashi M. , Yokota J. 
Published: July 2007

AbstractGekoppelte Plasmon‐LO‐Phonon‐Moden und Polaritonen in einem metalldotierten geschmolzenen Salz werden als Kollektivbewegung mittels einer hydrodynamischen Beschreibung untersucht.
Lifetime of Photogenerated Carriers in TCNQ Single Crystals
Authors: Eley D. D. , Kinnear S. , Willis M. R. 
Published: July 2007

AbstractMeasurement of photocurrents using the variable frequency chopped light technique shows that the reported photocurrents are due to photogeneration of carriers rather than a bolometric effect. The carrier lifetime, which is 10 to 40 ms at room temperature is independent of wavelength, but dependent on temperature according to the equation τ = τo eE/kT with E = 0.255 eV.
The Coulomb Shift of the Charge Transfer Band in Donor‐ Acceptor Compounds
Authors: Mikhailov I. D. , Novikov S. V. , Vannieov A. V. 
Published: July 2007

AbstractThe mechanism of the shift of the charge transfer band ina three‐component donor‐acceptor system due to collective long‐range Coulomb interaction is considered. Correlations determining the critical value of the concentration of a third component, at which a dramatic leap of the charge transfer band to the long‐wave region occurs, are obtained.
Cluster Approximation and Perturbation Theory for Band Models with Coulomb Interaction
Authors: Lorenz B. 
Published: July 2007

AbstractBand models with intrasite (Hubbard) and intersite Coulomb interactions are treated in a cluster approximation taking into account the interactions and the transfer within clusters of sites rigorously. Between different clusters the interaction is decoupled in a mean field approximation and the transfer term is treated as a perturbation. The ground‐state energy of the one‐dimensional Hubbard model is calculated up to fourth order in the perturbation and is compared with other approximations and the exact result. In the one‐dimensional spinless fermion model the perturbation is treated without further approximations by solving Dyson's equation for the one‐particle Green's function. The order‐disorder transition in this model is discussed.
Semiempirical Pseudopotential Calculations for the Electronic Structure of Zincblende Semiconductors
Authors: Singh I. , Srivastava G. P. 
Published: July 2007

AbstractA semi‐empirical pseudopotential calculation is made for the electronic structure of zincblende semiconductors InP, GaAs, and CdTe. Using the local approximation, it is started with an ionic model potential, and screening it through the Heine‐Abarenkov dielectric function the pseudo‐potential is obtained. Various parameters in this pseudopotential are chosen so as to obtain good fit for important interband transition energies with experimental results. Band structures and electronic densities of states are presented and compared with earlier local ‐ and nonlocal‐pseudopotential calculations as well as with the available experimental results.
Thomas‐Fermi Approximation for the Valence Electron Densities in Cubic Semiconductors and Insulators
Authors: Baldereschi A. , Maschke K. , Milchev A. , Pickenhain R. , Unger K. 
Published: July 2007

AbstractThe validity of the Thomas‐Fermi approximation for the calculation of valence charge densities in cubic semiconductors and insulators is investigated. Starting from local soft‐core pseudopotentials the valence charge densities are calculated via full band structure calculations and by using the Thomas‐Fermi approach. The results obtained by the two different methods agree surprisingly well. It is found that the validity of the Thomas‐Fermi approximation decreases with increasing ionicity and covalency of the considered compounds.