bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Propagation of Strong Electromagnetic Waves under Conditions of Mutual Drag of Carriers and Phonons in Semimetals
Authors: Gasymov T. M. , Katanov A. A. 
Published: July 2007

AbstractThe effect of mutual drag of hot carriers and acoustical phonons on the propagation of strong electromagnetic waves in semimetals (Bi, Sb) with equal electron and hole concentrations is investigated. In the presence of a high magnetic field the frequencies of the plasma—phonon waves are shown to depend on the amplitude of the incident wave E, through the temperatures of the heated carriers and phonons. The frequencies of these waves decrease with increasing E0. It is shown that under the action of the incident wave a semimetal becomes optically non‐uniform, i.e. the refractive index is changed from point to point. Expressions for the damping of the field and for the temperature of the carriers have been established under the conditions of a non‐linear normal skin‐effect. The ohmic and Hall static conductivities depend on E0 both in weak and strong magnetic fields. The basic characteristics of the field and temperature are calculated.
Molecular Cluster Approach to Small‐Radius Impurity Centres in Solids
Authors: Bandura A. V. , Evarestov R. A. 
Published: July 2007

AbstractThe molecular cluster approach to the problem of small‐radius impurity centres in solids is discussed. It is shown that the molecular orbitals obtained for the cluster of host atoms can be connected with the crystalline states only for clusters having the form of a large unit cell. In this case the molecular orbitals of the cluster have the sense of Wannier functions, the appropriate one‐electron energies the sense of mean values of the band energies in the large unit cell scheme of the crystalline state classification. It is found that the cluster model is realistic for solids with narrow (1 to 5 eV) energy bands. The convergence of the results with increasing cluster size is shown for lithium chloride ([LiCl6]5− [Li14Cl13]+, and [Li18, Cl18]0 are considered), the molecular cluster calculations are performed for some alkali halides and the results are compared with those obtained using band structure calculations.
On Lattice Dynamics of Substrate‐Thin Film Systems
Authors: Karasová I. 
Published: July 2007

AbstractA general method for the determination of localized modes of the substrate‐thin film system is derived. The method is applied for a computation of the mean‐square amplitudes of the film atoms at the free surface and on the film‐substrate boundary, if the substrate and the film have the structure of a simple cubic lattice.
Longitudinal Magnetoresistance and Hall Effect of CdxHg1−x Te in Strong Magnetic Fields
Authors: Tsidilkovskii I. M. , Giriat W. , Kharus G. I. , Neifeld E. A. 
Published: July 2007

AbstractThe results of measurements of the Hall coefficient and longitudinal magnetoresistance of CdxHg1−xTe (0.1 ≦ × ≦ 0.2) in the temperature range 1.8 to 300 K and in magnetic fields up to 300 koe are reported. The analysis of the data for zero‐gap semiconductors (x = 0.1) based on the two‐band model shows that hole‐like conduction in an impurity band, imposed on the conduction band, takes place. The strong rise of magnetoresistance observed in magnetic field for semiconducting compounds (x = 0.175 and x = 0.20) is attributed mainly to variation of the scattering probability at low temperatures and to the shift of the band edges in the magnetic field at higher temperatures.
Non‐Ideal Exciton Gas in Silicon and Its Condensation into Electron‐Hole Plasma Drops
Authors: Vavilov V. S. , Nolle E. L. , Fazilov A. 
Published: July 2007

AbstractExperimental data on the kinetics of the recombination via exciton states are presented for pure Si excited by a pulsed electron beam in the temperature region 4.2 to 300°K. The energy spectrum of the exciton gas is discussed as a function of the exciton concentration Δnex and exciton radius rex. It is shown that for T ⪅ 77 °K at Δnexz ⪆ 1.5 × 10−2 r the exciton gas becomes non‐ideal, and must be regarded in the limiting case, near Δnex ⪆ r as an electron‐hole plasma. At T ⪅ 20°K and Δnex ⪆ 1.5 × 10−2r in the luminescence spectrum a new band appears with a maximum at hvmax = 1.088 eV. It corresponds to the exciton condensation into electron‐hole plasma drops. The nature of an other line with a maximum at hvmax = 1.081 eV is discussed in connection with the possibility of exciton molecular complex formation.
Static Field Splitting of Zero‐Phonon Lines in Jahn‐Teller Systems
Authors: Polinger V. Z. , Rosenfeld Yu. B. , Vekhter B. G. , Tsukerblat B. S. 
Published: July 2007

AbstractThe zero‐phonon line structure of the singlet‐doublet transition in systems with a static Jahn‐Teller effect is investigated; the perturbation splitting of the zero‐phonon lines is supposed to be small. The results obtained can be used for the interpretation of optical spectra in tetragonal systems and dimer molecules.
Quasi‐Localized Electronic States in the Model Pseudopotential Theory of Disordered Alloys of Simple Metals
Authors: Belenkii A. Ya. , Krasko G. L. 
Published: July 2007

AbstractThe energy of disordered alloys with different ion valencies apparently cannot be described in the framework of the pseudopotential perturbation theory because of the strong electron scattering on the long wavelength concentration fluctuations. A model is suggested which provides for the existence of quasi‐localized (virtual) electronic states in alloys. A variational procedure of energy calculation is considered to modify the pseudopotential method. The concrete calculations are performed for the LiMg system. The two‐phase equilibrium, predicted by the theory is discussed.
Magnetic Susceptibility of UP and UAs
Authors: Troć R. , Lam D. J. 
Published: July 2007

AbstractThe magnetic susceptibility of UP and UAs have been measured as a function of temperature from 4.2 to 1000 K and the results are compared with published results in the literature. From the temperature dependence of the magnetic susceptibility, the most likely 5f3 electronic configuration of the uranium ion in these two compounds are deduced using a nonperturbative (full J‐mixing) crystal‐field theory.
Proton Spin–Lattice Relaxation Study of NH4+ Motion in Ammonium‐Doped Ferroelectric RbH2PO4
Authors: Blinc R. , Lahajnar G. , Levstik A. , Osredkar R. , Shuvalov L. A. 
Published: July 2007

AbstractThe temperature dependences of the proton Zeeman and dipolar spin–lattice relaxation rates have been measured in a Rb1–x(NH4)xH2PO4 mixed single crystal both in the paraelectric and the ferroelectric phase. The correlation time for ammonium ion reorientation has been determined and it is found that ultraslow reorientational motion of the H2PO4 groups exists above room temperature.
Electron Diffraction Study of the Local Atomic Arrangement in Amorphous TlCl and CuCl Films
Authors: Ichikawa T. 
Published: July 2007

AbstractThin films of amorphous TlCl and CuCl have been prepared by low temperature condensation in high vacuum, and a transmission electron diffraction study of them has been undertaken. A radial distribution analysis from the diffuse halo patterns obtained has been made and the local atomic arrangements in amorphous TlCl and CuCl are discussed by comparison of the experimental W(r) (=ϱ(r)/ϱ0) with W(r)'s calculated from disordered crystalline models.
Screening, Instability of the Uniform State, and Charge Carrier Scattering in Heavily Doped Ferromagnetic Semiconductors
Authors: Nagaev E. L. , Grigin A. P. 
Published: July 2007

AbstractA calculation of the static dielectric function ε(q) and the magnetic response function to an electrostatic perturbation χ(q) is carried out for heavily doped ferromagnetic semiconductors. Due to the spin polarization of the charge carrier a strong correlation exists between the fluctuations of electron density and magnetization. This leads to diminishing screening length and the appearance of local magnetic moments near impurities, which, in turn, causes a strong magnetic field and temperature dependence of the resistivity. On further temperature increase, the screened potential becomes oscillating, and the screening length increases, going to infinity at a temperature which corresponds to the absolute instability of the uniform state. But still earlier a first order phase transition should occur into a nonuniform state, the nonuniform state being metastable in some temperature range. It may be responsible for the resistivity hysteresis observed in some ferromagnetic semiconductors.
Linearized Effective Exchange and Correlation Potentials for One‐Particle Property Calculations in Simple Metals
Authors: Dagens L. 
Published: July 2007

AbstractThe effective potential method of Sham and Kohn, which allows an exact calculation of one‐particle properties in an interacting electron gas of slowly varying density, is extended to the case of an arbitrary varying density. Assuming a static approximation for the mass operator, it is shown that the elastic scattering cross section can be calculated exactly from an effective scattering potential Ṽ which takes into account all vertex and self‐energy corrections. The same potential leads also to the exact Fermi surface, at least to the lowest non trivial order in the density fluctuation n(q). The matrix element of its indirect part Ṽxc = Ṽ – VH (VH is the Hartree part of the potential) is linearized as X̃(q, k) n(q) and the properties of the effective interaction X̃ are studied in great detail. The long wavelength limit X̃(0, k) is related to the linearized Sham‐Kohn one‐particle effective potential. The behaviour of X̃ in the whole range of q values is studied by means of numerical estimations, assuming a simple Thomas‐Fermi screening approximation. X̃(q, k) is found to be highly angular dependent (i.e., non local) and contact is made in this respect with a recent work of Yasuhara and Watabe. The simpler local interaction X̃(q) (equal to X̃(q, k) with k = kF = |k + q|) which is required for electronic transport property calculations is also discussed and compared to the Kohn‐Sham density‐response effective interaction.
Critical Investigation of Potentials for Band Structure Calculations
Authors: Paasch G. , Woittennek H. 
Published: July 2007

AbstractThe non‐selfconsistent calculation of potentials for band structure calculations is critically investigated. As essential properties of the potential the d‐resonance of the phase shifts and the lower band edge of the s‐band are used. The former characterizes the energy of the d‐bands. For the latter an approximate expression is given in terms of phase shifts. The influence of the atomic wave functions, configuration, and exchange on the potential is investigated. In addition the Mattheiss‐potential is compared with the renormalized atom. The possibility to obtain absolute band energies is discussed.
Cyclotron Waves in Silver – Interference Effects
Authors: Saermark K. , Lebech J. 
Published: July 2007

AbstractA discussion is given of experiments on the transmission of cyclotron waves through a thin single‐crystalline sample of silver at a frequency of 44.86 GHz. From the data information is obtained on the oscillatory dispersion relation for the extraordinary wave, i.e. turning points, slope, and width of the branches of the dispersion relation.
Estimate of the d–d Overlap of V2O5 from ESR Measurements
Authors: Sperlich G. , Lazé W. D. 
Published: July 2007

AbstractESR spectra are given of d electrons which are localized in the randomly arranged Coulomb fields of Li+ and Cu+ ions in single crystals of LixV2O5 and CuxV2O5 (x ⪅ 0.01). A localization within four vanadium 3d orbitals is derived from the hyperfine spectra. A resolved hyperfine splitting disappears at temperatures below about 15 K. The corresponding variation of the nonperiodic Coulomb field allows a rough estimate of the d‐overlap integral.
A Study of the Exchange‐Determined Absorption Lineshape Outside the Lorentzian Region
Authors: Cusumano C. , Troup G. J. 
Published: July 2007

AbstractThe wings of the EPR absorption line of an exchange narrowed spin system have been studied experimentally and theoretically. Solid solutions of DPPH in polystyrene with spin concentrations about 3 × 1020 spins/cm3 show an exponential rather than the often assumed Gaussian behaviour in the wings. The appropriate portion of the spectrum of the random frequency modulation causing the narrowing is recovered. The steepness of the exponential decrease is shown to be proportional to the exchange frequency. This result is in reasonable agreement with the high‐temperature spin correlation functions for a Heisenberg ferromagnet, obtained by some theoretical works on this subject.
Relativistic Symmetries and Lower Bounds for the Magneto‐Electric Susceptibility and the Ratio of Polarization to Magnetization in a Ferromagneto‐Electric Crystal
Authors: Ascher E. 
Published: July 2007

AbstractA definition of the relativistic symmetry of a polarized crystalline medium is proposed. The requirement of invariance of the susceptibility under this group gives rise to relations between the components of the tensor which then are used in the case of orthorhombic boracite to obtain lower bounds for the magneto‐electric susceptibility and for the ratio of the spontaneous polarization to magnetization.
Effect of Core Structure on the Determination of the Stacking‐Fault Energy in Close‐Packed Metals
Authors: Cockayne D. J. H. , Vitek V. 
Published: July 2007

AbstractThe influence of dislocation core structure upon the relationship between the separation of Shockley partial dislocations and the stacking‐fault energy (γ) of materials crystallising with a close‐packed structure is investigated. It is shown that for the same separation of the partial dislocations a wide range of values of γ can be obtained assuming various core models. The relevance of these conclusions to measurements of the separations of partial dislocations using high resolution electron microscopy is discussed, and the importance of the various core parameters in the interpretation of the microscope images is considered.
Interserial Phototransitions of Excitons in Semiconductors
Authors: Khadshi P. I. , Moskalenko S. A. 
Published: July 2007

AbstractLight absorption in semiconductors due to interserial transitions of excitons has been investigated. Analytic expressions for the spectral and temperature dependence of the absorption coefficient have been obtained for the allowed and forbidden transitions of the exciton from one series into arbitrary discrete states of the other series, for various ratios of the translational masses of the excitons in these series. The absorption of light has a threshold or boundary frequency ω0, depending on the mass of the excitons before and after the transition. With the increase of |ω – ω0|, the absorption coefficient increases and then decreases. For the allowed transition from the Is‐exciton state of one series into the nl‐state in the other series, the oscillator strength is proportional to Tl, whereas the maximum value of the absorption coefficient is proportional to Tl–1. The temperature ignition of the absorption bands at l >1 has been predicted, which is not related to the change of the level population.
The Stress Field near the Dislocation Pile‐Up Type Defects in Anisotropic Elasticity
Authors: Solovev V. A. 
Published: July 2007

AbstractA general expression is obtained for the stress field at any point of infinite anisotropic crystals containing defects of the dislocation pile‐up type (e.g. pile‐ups, deformational twins, cracks, thin crystals of martensite). The stresses are expressed in form of an analytic continuation of the density of dislocations from the line of the pile‐up into the complex plane. The formulas obtained are valid for any geometrical arrangement of the defects, taking into account their non‐zero Burgers vectors and giving stresses due to the defects only. The interaction of a line source (i.e. a line force and a dislocation simultaneously) with the mentioned defects is investigated. The results may be used for an unified description of the adhesion forces, non‐linearity of the media, and plastic zone near the defects in terms of some integral coefficients. The concrete calculations are mainly reduced to the evaluation of the complex constants determining the stress field near a single dislocation. The constants are expressed and the stresses written in terms of elastic moduli for the defects lying in the direction of the orthotropic symmetry of the crystal. As a limiting case the general formulas for stresses near dislocation pile‐ups in isotropic media are found.
Influence of Magnetic Field on Polaritons in Uniaxial Polar Semiconductors
Authors: Gurevich L. E. , Arkhazian R. G. T. 
Published: July 2007

AbstractThe influence of a magnetic field on polaritons in uniaxial polar semiconductors is investigated. Faraday and Voigt configurations are considered in various cases of the magnetic field orientation with respect to the crystal axis. It is found that the influence of the magnetic field is very essential; for example, the number of branches and of transparency regions are changed and the resonance frequencies become dependent on the magnetic field in the Faraday configuration.
On the Static Approximation for the Hubbard Model. I. General Considerations
Authors: Puff H. , Weller W. 
Published: July 2007

AbstractStarting from the functional‐differential equation for the self‐energy, a static approximation is introduced which is shown to be equivalent to the replacement of the Hubbard model by an alloy model. By means of the single‐site coherent potential approximation an equation is derived which determines the distribution function, characterizing this alloy model self‐consistently by the Green's function. The procedure avoids shortcomings of other methods, as ad‐hoc assumptions on the distribution function or non‐unique decompositions of the interaction term.
Solvable Model for Random Systems Including Off‐Diagonal Disorder
Authors: John W. , Schreiber J. 
Published: July 2007

AbstractAnderson's model for disordered systems is considered in the case where the transfer matrix elements fluctuate according to a Lorentzian distribution. It is shown that the exact ensemble averaged Green's function may be obtained if the energy level on each site depends linearly on the overlap integrals. Using this result the stability of amorphous Heisenberg ferromagnets is studied. The Weaire model of an amorphous covalent semiconductor with fluctuating matrix elements is considered. Numerical results for the density of states are given.
Modes de relaxation électriques dans les cristaux ioniques de type NaCl dopés par des impuretés trivalentes
Authors: Brun A. , Dansas P. 
Published: July 2007

AbstractOn a utilisé un modéle á puits de potentiel pour déterminer les modes de relaxation électriquement actifs et les temps de relaxation correspondants pour un cristal de type NaCl dope par une impuretk trivalente en substitution. On a calculi! Bgalement les polarisations correspondantes A chaque mode de relaxation et discuté de l'intbrbt particulier des mesures „diélectriques”︁ dans ce cas.
Exciton‐Polariton Luminescence in Cuprous Halides
Authors: Suga S. , Koda T. 
Published: July 2007

AbstractResonance luminescence spectra of the free exciton are investigated in cuprous halides by uniaxial‐stress and magneto‐optical measurements. Apart from the perturbation‐induced structures due to the longitudinal and spin‐triplet excitons, the characteristic‐doublet structure is conclusively ascribed to the exciton‐polariton effect. Temperature‐dependent spectral shapes of these polariton luminescences are analyzed to derive the distribution of polaritons in the upper and the lower branches. The bottle‐neck effect of the polariton decay process is also discussed.
Influence of Magnetic Fields on the Lineshape of the Exciton‐Polariton Reflectance in GaAs
Authors: Fischbach J. U. , Dreybbodt W. , Suga S. , Willman F. 
Published: July 2007

AbstractThe influence of high magnetic fields on the line shape of the exciton‐polariton reflectance is investigated in epitaxial GaAs at helium temperature. The changes of the line shape can be understood from the variation of the Bohr radius, the binding energy, and the oscillator strength of the exciton in a magnetic field. From the analysis of the spectra it is shown that the longitudinal‐transverse splitting of the ground state can be obtained from the experimental reflectance curves. In addition to the well‐known exciton free layers at the crystal surface, the influence of a transition layer, where the excitons get partially ionized, is established.
The Fine Structure of Wannier‐Mott Excitons in a Cubic Crystal and Its Behaviour in an Electric Field
Authors: Agekyan V. T. , Monozon B. S. , Shiryapov I. P. 
Published: July 2007

AbstractThe anisotropy of the forbidden transitions in the absorption spectrum of the exciton yellow series of cuprous oxide in an electric field has been studied. The group‐theoretical analysis of electric field effect on transitions with different orbital quantum numbers l makes it possible to reveal the P‐, S‐, and D‐series of exciton levels on the basis of experimental data. The position of dipole‐active and ‐inactive levels has been determined by extrapolation to zero field, which enables one to study the l‐splitting in a cubic crystal. With the l‐splitting, the P‐series remains exactly hydrogen‐like, the D‐series preserves an approximate hydrogen‐like behaviour, and the S‐series looses its hydrogen‐like behaviour.
Spin Wave Amplification in Ferromagnetic Semiconductors: Magnetoresistance and Non‐Ohmic Behavior
Authors: Filho M. D. Coutinho , Miranda L. C. M. , Rezende S. M. 
Published: July 2007

AbstractThe influence of magnon amplification on the magnetoresistance of ferromagnetic semiconductors is analyzed microscopically. A simple model for the non‐linear relaxation of magnons is proposed which can explain the existing measurements in CdCr2Se4.
Cross‐Relaxation Studies of a Four‐Spin Flip Transition
Authors: Mai Chan Khanh 
Published: July 2007

AbstractA theoretical investigation of the process of four‐spin flip cross‐relaxation transitions has been carried out in the case of three types of spins in the crystal 2ω1 = ω2+ω3+Δ; |Δ|≪ ω1, ω2, ω3, The dipole–dipole reservoir is taken into account. Using the method of the nonequilibrium statistical operator of Zubarev, a system of equations describing the evolution of the temperatures of the Zeeman subsystem and of the dipole–dipole reservoir is obtained. The stationary solution in the case of saturation of one of the Zeeman spin subsystems is studied.
Effect of Spatial Correlations on Hopping Transport
Authors: Pollak M. 
Published: July 2007

AbstractSpatial fluctuations of the potential are inherent in hopping transport. The effect is considered of the stochastic dependence between the potentials of hopping sites, specifically the case when the correlation length of the potential is considerably longer than the hopping distance. The percolation approach is used. The behavior is found to depend on certain characteristics of the equipotential surface at the Fermi energy. If this surface is non‐connected, an activated conductivity is expected. If the surface consists of parts connected through narrow channels, a T−l/2 dependence is predicted. For stronger connectivity, a T−1/3 dependence is deduced. The T−1/4 dependence, characteristic of hopping in the absence of spatial correlation, is not expected to occur.
Band Structure and Fermi Surface of In3Sn Alloys in the ß‐Phase
Authors: Maciejewski S. 
Published: July 2007

AbstractBand structure calculations are performed for In3Sn alloys with Sn concentrations from 16.2 to 30 at% by the pseudopotential method with the Animalu‐Heine model potential. From the dispersion relations E(k) obtained, the Fermi surface parameters of the alloys are determined. In the point R of the Brillouin zone, the influence of Spin–orbit interaction is calculated.