bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature Dependence of Third‐Order Elastic Constants of NaCl‐Structure Alkali Halide Crystals
Authors: Varshney R. K. , Shanker J. 
Published: July 2007

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractBand 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

AbstractThe 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.
Low‐Temperature Properties of One‐Dimensional Heisenberg Systems with Random Anistropy
Authors: Gekht R. S. 
Published: July 2007

AbstractThermodynamic 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

AbstractPolarized 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.
Extended Model of Bond Charges and Its Application in Calculation of Optical Properties of Crystals with Different Types of Chemical Bonds
Authors: Tsirelson V. G. , Korolkova O. V. , Rez I. S. , Ozerov R. P. 
Published: July 2007

AbstractA method for calculating the optical characteristics of crystals with different types of chemical bonds within the framework of the dielectric theory of chemical bond put forward by Philips and Van Vechten is suggested. The calculating scheme which does not contain adjustable parameters is based on the bond charge model designed by Levine, which is generalized for the case of multiple bonds and modified involving the density functional method data on the spatial distribution of electrons in atoms. The structural elements of the method are: the screened Coulomb potentials and radii of the atomic core, bond lengths and charges, and the distances from the nuclei to the centres of gravity of the latter. The calculated characteristics of the crystals (dielectric permittivity, quadratic and cubic non‐linear susceptibilities, electrooptical constants) are in good accordance with experimental findings. An attempt is made to predict the non‐linear optical characteristics according to precision X‐ray diffraction data on the electron structure of its only representative, lithium formate deuterate LiHCO2 · D2O, whereby a fairly good fit with the experimental data is achieved.
K‐Absorption Spectra of Copper Oxides
Authors: Aggarwal O. P. , Saxena N. N. 
Published: July 2007

AbstractThe extended fine structure of K‐absorption edge of copper in its oxides is studied using a 40 cm curved crystal spectrograph. The observed shift of K‐edges of copper in the oxides is better explained with MO and SRO theories. Separations apparent between the absorption minima corresponding to copper and oxygen atoms in the lattices of two oxides support the MO viewpoints.
Quantum‐Theoretical Model of Adiabatic Rate Processes in Condensed Systems or at Interfaces
Authors: Lorenz W. , Engler C. 
Published: July 2007

AbstractA quantum‐theoretical model of rate processes in condensed systems is developed which is capable of treating partial charge transfer phenomena and chemical bond formation. Adiabatic local potential surfaces of a reactive subsystem are subjected to a unitary transformation into species potential surfaces; the phonon‐assisted conversion of chemical species can then be calculated in the common T‐matrix framework. In numerical calculations, anharmonicity of species potential surfaces and dependences of the electronic transition element upon nuclear coordinates is allowed for. As specific application, photoelectrochemical processes on semiconductor surfaces with fractional electrons or holes are considered.
Stimulated Brillouin Scattering of Laser‐Radiation by an Electron‐Acoustic Wave in Magnetised Semiconductor‐Plasmas
Authors: Guha S. , Basu C. 
Published: July 2007

AbstractUsing the hydrodynamic model of a plasma, the stimulated Brillouin scattering of laser radiation by an electron‐acoustic wave is investigated analytically in a semiconductor plasma in the presence of a dc magnetic field including the effect of the ponderomotive force. It is shown that the magnetic field decreases the threshold electric field and the growth rate.
Theory of Second‐Order Auger Recombination in Strong Degenerate Small‐Gap Semiconductors Application to PbSSe
Authors: Beiler Marion , Mocker M. , Ziep O. 
Published: July 2007

AbstractA theory to estimate the efficiency of second‐order Auger processes in strongly degenerate systems (T → 0 K) is developed, whereby a parabolic isotropic band structure model is adapted to PbS0.1Se0.9. The calculation of the net recombination rate refers to a range of doping and excitation concentration where first‐order Auger processes are strongly reduced or, in the zero temperature limit, are even forbidden. The numerically calculated small‐signal lifetime for a semiconductor with the doping concentration ND = 1017 cm−3 has the order of magnitude ≈ 10−6 s.
The Auger Processes with Energy Transfer to the Bound Charge Carriers in Multi‐Valley Semiconductors
Authors: Vorobev Yu. V. , Tolpygo E. I. , Sheinkman M. K. 
Published: July 2007

AbstractThe theory of the Auger processes of capture of charge carriers with the energy transfer to the bound charge carriers is extended to the case of a semiconductor with different valleys of the C‐band. Using hydrogen‐like Ψ‐functions for the charge carriers in the impurity centres separated with distances higher than the sum of the effective radii of the interacting states, expressions are obtained describing the dependences of the cross‐sections on the characteristic parameters for the four types of Auger processes: hole capture by the “donor—donor” complex, and the capture of the electron from the upper valley by the complexes “donor—donor”, “donor—acceptor”, “acceptor—acceptor”. It is shown that in many cases the cross‐section of the process examined can surpass the effective size of the bound electron state and reach a value ≈ 10−12 cm2. On the basis of the data obtained an interpretation is given of a number of experimental facts connecting the effects of capture and ionization in GaAs doped with deep‐level impurities (O, Fe, Cr) and InP:Fe.
Impurity Conduction along the Least Resistance Paths of Granular Insulating Thin Films
Authors: Barrière A. S. , Gevers G. 
Published: July 2007

AbstractThe electrical charge transfer is investigated through Au—FeF3—Au thin‐film structures as a function of the crystallization degree of the insulating layers. For a constant growth rate, the texture of the samples, prepared by sublimation under vacuum, depends essentially on the substrate temperature during the condensation of the vapours (Ts). Between 450 and 650 K, the FeF3 thin films are granular. The crystallized grains, the average diameter of which increases with Ts, are embedded in a disordered matter. Under these conditions, the dc conductivity of the structure greatly depends on the preparation parameter Ts. However, in all cases, as for many other insulators, the charge transfer throughout FeF3 is due to the presence of localized electronic states situated into its band gap. These states correspond to a weak lack of fluorine and are situated at 1.1 eV below the conduction energy. Now it is demonstrated that the corresponding Coulombic wells in interaction are more particularly concentrated in the intergranular zones of the layers. If their density remains constant in the whole, it grows with Ts in these regions when the volume of disordered matter decreases, which defines the least resistance paths. Along these percolation ways, the average height of the potential barriers separating two consecutive states decreases when Ts increases. In consequence, if the dc conductivity results from thermally activated jumps of electrons above these potential barriers at high temperature, below a temperature which increases with Ts a hopping process predominates.
Electron Transfer and Thermal Vibration Parameters in Titanium Nitride: An X‐Ray Diffraction Study
Authors: Field D. W. 
Published: July 2007

AbstractAn X‐ray diffraction study of titanium nitride powder of composition TiN0.89 is carried out at room temperature. The electron transfer from the Ti atom to the non‐metal sites is found to be (1.5 ± 0.3) electronic charges. The values of the r.m.s. vibration amplitudes of the atoms are uTi = (7.12 ± 0.04) pm, uN = (6.1 ± 0.3) pm, and the Debye temperature is (580 ± 20) K.
The Distribution of Magnetic Moments and the Temperature Dependence of Reduced Hyperfine Fields in Amorphous Ferromagnets
Authors: Kaneyoshi T. , Tamura I. 
Published: July 2007

AbstractThe distribution of magnetic moments in amorphous transition metal—metalloid ferromagnetic alloys is first estimated from the linewidths of hyperfine fields. The result shows that there exists a rather broad distribution of magnetic moments with some spins aligned antiferromagnetically in the alloys. The temperature dependence of reduced hyperfine fields in the alloys is evaluated by a simple molecular‐field theory, taking account of the distribution of magnetic moments in addition to the usual exchange fluctuations. Quantitative agreement between the theoretical and experimental curves is more rectified at the intermediate reduced temperature range, in comparison with the case of the usual exchange fluctuations.
Transient Coherent Anti‐Stokes Raman Spectroscopy of Surface Polaritons
Authors: Likholit N. I. , Ponath H.‐E. , Strizhevskii V. L. , Yashkir Yu. N. 
Published: July 2007

AbstractA theory of the coherent anti‐Stokes Raman spectroscopy (CARS) of surface polaritons (SP) is developed. General expressions for the intensities of ultrashort SP pulses excited by the biharmonic pump pulses and expressions for the CARS signal intensity are obtained. The specific features of the SP pulse generation and scattering are analysed.
The Theory of Double Gamma Resonance in Paramagnetics
Authors: Sadykov E. K. 
Published: July 2007

AbstractThe theory of double γ‐resonance for a paramagnetic system is suggested. The electron—nuclear (EN) state representation is used which allows to descibe the cases where the effective field approximation is not correct. The theory enables one to calculate the quasienergetic structure of the γ‐resonance spectra at the conditions of radiofrequency (rf) excitation at the frequencies of the nuclear magnetic resonance (NR) and the electron magnetic resonance (EPR) from a single point of view. The method allows also to describe consistently DGR spectra in the limit of slow electron relaxation (ER) and in the frame of a stochastic model for arbitrary relaxation rate.
Exact Density Functionals for Ground‐State Energies. I. General Results
Authors: Englisch H. , Englisch R. 
Published: July 2007

AbstractThe exact one‐particle density functionals by Levy and Lieb for the calculation of ground‐state energies are analysed. A method for the calculation of the Levy‐Lieb functional is proposed. Based on a work by Lieb, the range of validity of the exact self‐consistent equations by Kohn and Sham is determined. A self‐consistent procedure which is applicable in a wider range is presented.
Effect of Supercurrent on Charge Imbalance Relaxation in a Phase Slip Centre
Authors: Chashoo G. J. , Singh Y. 
Published: July 2007

AbstractThe quasiparticle charge imbalance relaxation time in the nonequilibrium state of a phase slip centre in indium whiskers is calculated taking into account the depairing effect due to supercurrent and the finite size of the core. The normal‐like length for the first phase slip centre for various temperatures below the transition temperature is calculated and compared with the experimental data. The analysis shows that the core of phase slip centre is about four times the Ginzburg‐Landau coherence length. This result is new. Further the effect of pair breaking due to supercurrent on the charge imbalance relaxation time for various values of τE is calculated for temperatures 1 to 50 mK away from the transition temperature.
Electrical Resistivity Calculations for Amorphous CuxAl1−x
Authors: Knuyt G. 
Published: July 2007

AbstractThe electrical resistivity ϱ and its temperature coefficient α are calculated for different compositions of the CuxAl1−x amorphous alloy using a pseudopotential theory. The calculated resistivity ϱ(x) agrees well with the experimental data when hybridization effects for copper are included. Different pseudopotentials are tested on their validity. The calculated α(x) curve does not reproduce the experimental CuxAl1−x data accurately, but has characteristics found in other experimental data. Finally a mechanism is suggested which can be responsible for the resistivity minimum at low temperatures for amorphous alloys in certain cases.
Time‐Dependent Ginzburg‐Landau Equations for Anisotropic Superconducting Alloys
Authors: Vones G. , Schachinger E. 
Published: July 2007

AbstractIn the framework of space and time dependent Green's functions an implicite expression for the energy integrated electron Green function is presented for anisotropic superconducting alloys. Normal and paramagnetic impurity scattering is included as well as relaxation processes due to inelastic electron scattering. The theory is later on specialized for an anisotropic system with normal momentum scattering only in order to study the ‘smearing’ out of the anisotropy. A separable model is finally employed to describe the anisotropy of the Fermi velocity and of the electron—phonon interaction. Within this model the influence is studied of the mean square anisotropy and of the normal impurity concentration on the Ginzburg‐Landau parameter, on the critical temperature, on the upper critical magnetic field, and on the penetration velocity of the flux vortices.
Fluctuations in a Nonequilibrium System of Electrons and Magnons in Ferromagnetic Semiconductors
Authors: Ya. Korenblit I. , Tankhilevich B. G. 
Published: July 2007

AbstractThe fluctuations in the electron and magnon systems of a ferromagnetic semiconductor in strong electric fields are investigated. The expressions for the correlation functions of the magnon temperature and the longitudinalmagnetic moment fluctuations are derived. The magnon noise temperature is obtained and it is shown that it may exceed the magnon temperature.
On the Theory of Solitary Wave Excitation in Molecular Crystals by a Coherent Electromagnetic Field
Authors: Kruglov V. I. 
Published: July 2007

AbstractA closed integro‐differential equation is obtained which describes solitary wave propagation in a molecular crystal. It is shown that from this equation a system of differential equations for the module of the exciton amplitude and the slow part of phase follows, as well as the dispersionrelation. On the basis of the method proposed for solving nonlinear equations two types of solitary waves are found, as well as a system of algebraic equations for defining the soliton parameters. All the results are obtainedwithout using truncated equations and taking into account Pauli statistics for excitons.
Nonlinear Exciton Transmission in CdS Non‐Homogeneous and Non‐Stationary Model Calculations
Authors: Nguyen Hoang Xuan , Zimmermann R. 
Published: July 2007

AbstractThe transmission of a thin semiconductor platelet is studied by solving Maxwell's equation together with a rate equation for the exciton concentration. The concentration induced exciton broadening serves as nonlinear mechanism. Numerical results for the diffusion‐controlled concentration profile in the sample are presented. As a second case, the temporal transmission lineshape of a Gaussian input pulse is calculated and compared with our experimental results on CdS. The hysteresis phenomenon found is interpreted in terms of a transient effect.
Dispersion and Absorption Anomalies in Three‐Level Systems
Authors: Hönerlage B. , Bigot J. Y. 
Published: July 2007

AbstractUsing the density‐matrix formalism, the dielectric function of athree‐level system under high excitation conditions is determined. The density matrix being calculated by a continuous matrix inversion, non‐resonant contributions and saturation effects can be fully accounted for and the stability of absorption and dispersion anomalies may be discussed.
Infrared Reflectivity Plasma Spectra of TlBiTe2 Single Crystals
Authors: Paraskevopoulos K. M. , Siapkas D. , Economou N. A. 
Published: July 2007

AbstractInfrared reflectivity plasma measurements performed in the range 300 to 4000 cm−1 on TlBiTe2 single crystals with a high density of coherent and semicoherent twins, at room temperature, reveal a frequency relaxation time of the form τ−1(ω)  τ0−1 + bωn. With n = 2.35 satisfactory fits to the experimental plasma reflectivity data are obtained incorporating the above expression for τ(ω) in the Drude model. Discrepancies between the classical theory and the experiment are attributed to the scattering of free electrons by twin boundaries.