bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Reflectivity for Oblique Incidence of the Uniaxial Antiferromagnetic Crystals FeF2, CoF2, and MnF2
Authors: Lehmeyer A. , Merten L. , Häussler K. M. 
Published: July 2007

AbstractBy combining the dispersion relations of the refractive index and the boundary conditions in the surface the formulae of reflectivity of the antiferromagnetic crystals FeF2, CoF2, and MnF2 can be derived for oblique incidence. This is performed for two important orientations of the surface, namely for the surface perpendicular to the optical axis and for a surface which contains the optical axis. The results are six different formulae of reflectivity for oblique incidence.
Many‐Electron Hopping
Authors: Gosar P. 
Published: July 2007

AbstractCorrelated hopping of many electrons in the impurity band of the moderately compensated semiconductor is studied. The calculation of the n‐electron cluster transition rate is based on the following assumptions: the one‐electron states in the impurity band are strongly localized, the motion of each electron is restricted to the hopping between two impurity sites, the electrons mutually interact by Coulomb forces, and the deformation‐potential‐type coupling to phonons is used. A statistical approach is applied in the calculation of transition rates for very large clusters.
Phase diagram of a spin glass of EupSr1 − pS
Authors: Katsura S. , Matsuno A. 
Published: July 2007

AbstractEupSr1 − pS is modeled as a site‐diluted Ising model with first and second neighbor interactions (J > 0, J' < 0) between Eu atoms, on a lattice with square coordination number zc. By use of the reducibility of the four‐body density matrix to the one‐body density matrix, an integral equation for the distribution function for the effective field is obtained. The integral equation for the case J' = − J/2 is solved exactly at T = 0 in the case of zc = 2 and the three solutions for the paramagnetic, ferromagnetic, and the spin glass states are obtained. The boundary between the ferromagnetic and spin glass state is given by pFG = 0.545 and the phase diagram shows a reentrant behavior.
Direct luminescence evidence for the degenerate electron—hole plasma formation in AIIBVI semiconductors
Authors: Brodin M. S. , Bandura V. M. , Matsko M. G. 
Published: July 2007

AbstractThe emission spectra of ZnTe and ZnSe crystals are investigated at T = 4.2 K at high excitation densities by a Coumarin 30 and 120 dye laser. It is shown that for excitation densities Rexc > > 0.1 MW/cm2 the emission spectrum of ZnTe exhibits the P‐band due to inelastic exciton‐exciton scattering. For Rexc > 6 MW/cm2 the emission of a degenerate electron—hole plasma (EHP) is observed. These emission bands may be differentiated by scanning the exciting quanta energy in the short‐wavelength tail region.
The theory of magnetic polarons in antiferromagnetic semiconductors
Authors: Egorov B. V. , Timofeev B. B. 
Published: July 2007

AbstractThe electron states in antiferromagnetic semiconductors with large atomic spins S and an arbitrary relation between the band width ΔE and the spin—electron interaction A are considered. It is shown that in the mean‐field approximation of atomic spins the spin—electron interaction in case of AS ≧ ΔE leads to essential transformations in the electron spectrum, while the interactions of electrons with the spin deviations from the average values (at T = 0 with virtual magnons) leads to a polaron‐type quasi‐particle formation: the antiferromagnetic polaron (AFP). With the help of the diagram technique at T = 0 the AFP Green function and its spectrum are obtained.
Biexcitons in crystals with large ortho—para‐exciton splitting
Authors: Bobrysheva A. I. , Moskalenko S. A. 
Published: July 2007

AbstractIt is shown that in a system of ortho‐ and para‐excitons two ortho‐excitons with total spin S = 0 interact attractively and biexcitons can be formed. The interaction potential of two ortho‐excitons is approximated by a generalized Morse potential depending on the electron—hole mass ratio σ. On this basis the energy of vibrational and rotational levels of the biexciton is obtained. The binding energy of the biexciton ground state is estimated for all values of σ.
Analysis of the dielectric properties of mixed alkali halide crystals
Authors: Shanker J. , Jain G. D. 
Published: July 2007

AbstractThe electronic and static dielectric constants, longitudinal and transverse optic mode frequencies, effective charge parameters, optic mode Gruneisen parameters, and volume derivatives of dielectric constants are calculated for the entire range of composition of mixed NaCl—NaBr, KCl—KBr‐and KBr—KI crystals. The calculations are performed using the knowledge of interionic potentials. The results are discussed and compared with available experimental data.
A scattering matrix calculation of very low energy electron reflection intensities for barium and magnesium oxides
Authors: Lynch D. F. , Smith A. E. 
Published: July 2007

AbstractResults of calculations are presented for electrons incident on barium and magnesium oxide crystals with energies in the respective ranges 0.5 to 15 eV and 0.5 to 30 eV. Comparisons are made between these computations based on a simple pseudopotential scattering matrix approach and data from LEED and total current experiments. It is concluded that the good agreement can be explained on the basis of the dominance of the crystallography of the specimen over the precise description of the individual scattering events. The coincidence of low order kinematical Bragg reflection conditions with the features is also commented upon.
NMR study of the charge‐density‐wave state in VSe2
Authors: Skripov A. V. , Stepanov A. P. , Shevchenko A. D. , Kovalyuk Z. D. 
Published: July 2007

AbstractThe 51V NMR lineshape, Knight shift, quadrupole interaction, spin—lattice relaxation time and magnetic susceptibility in a single‐crystalline VSe2 are studied in the temperature range 4.2 to 300 K. Above the charge‐density‐wave (CDW) onset temperature T0 ≈ 110 K the linear temperature dependence of the quadrupole coupling constant and the pretransitional line broadening are found. The temperature dependence of the CDW amplitude is determined from the width of electric‐field‐gradient distribution at nuclear sites below T0. Combining the experimental data on NMR properties and magnetic susceptibility the effective electron—electron interaction parameter, J = 0.29 eV, is estimated and the density of electron states at the Fermi level. The latter is found to decrease from 2.05 to 1.60 states/eV spin V at the phase transition into the CDW state.
Crystal field splitting in NdAl3 studied by inelastic neutron scattering
Authors: Alekseev P. A. , Goremychkin E. A. , Lippold B. , Mühle E. , Sadikov I. P. 
Published: July 2007

AbstractInelastic neutron scattering experiments are performed in polycrystalline NdAl3 to determine the crystalline electric field parameters for the Nd3+ ion in its hexagonal environment. The parameters obtained are checked with the results of other measurements related to the crystalline electric field, such as magnetic susceptibility, heat capacity, and electric resistivity.
Carrier Mobility in Doped Nondegenerate Semiconductors
Authors: Khamidullina N. M. 
Published: July 2007

AbstractThe temperature dependence of the drift and Hall mobilities in compensated semiconductors at low temperatures (4 to 100 K) within the range of impurity concentration of (1013 to 1016 cm−3) is examined. Under these conditions the Born approximation for the charged impurity scattering of the charge carriers is incorrect. Therefore when calculating the mobility thee xact scattering amplitudes are used. In semiconductors with a density of states of the conventional type ϱ(E) ∼︁ √E, the curves of mobilities and Hall‐factor are obtained taking account the simultaneous charged impurity and acoustic phonon scattering; for semiconductors with a smooth random field a comparison of all scattering mechanisms is carried out and mobilities curves are obtained taking the simultaneous smooth random field and charged impurity scattering into account.
Spinless Anderson Model with a Local Phonon Mode
Authors: Kowalska J. , Zieliński J. 
Published: July 2007

AbstractThe electron‐phonon coupling in the spinless Anderson model is considered within the perturbation theory. The second‐order theory including the finite lifetime for phonons leads to some narrowing of the density of states for higher values of the ratio of the electron‐phonon coupling constant and virtual level halfwidth, λ/Δ ≈ 1. The simplified fourth‐order theory (V = 0) shows that very pronounced narrowing is expected (λ/Δ < 1) and there is no change in the height of the central peak.
Optical Phonons in GaS1‐xSex Layer Mixed Crystals
Authors: Gasanly N. M. , Goncharov A. F. , Melnik N. N. , Ragimov A. S. 
Published: July 2007

AbstractMeasurements are made of polarized Raman scattering and infrared reflection spectra of twenty two compositions of GaS1‐xSex layer mixed crystals grown by the Bridgman method. Besides the usual one‐mode and two‐mode behaviours of phonon modes, a number of more complex dependences characterized by the appearance of additional bands in the spectra of mixed crystals are observed. Their appearance is accounted for by the uncovering of the Brillouin zone due to the disturbance of the periodicity of the crystal lattice of mixed crystals. Specifically, for modes with a low dispersion in the Brillouin zone the additional modes are interpreted as vibrations of cells having mixed compositions. A number of anomalies are revealed in the concentration dependences of intensities and frequencies of optical phonons, which are attributed to the β → γ and γ → ϵ polytype transformations at x ≈ 0.6 and x ≈ 0.97, respectively.
Theoretical Calculations of the Curie Temperature for Gd1−xRExAl2 Alloys
Authors: Witański K. 
Published: July 2007

AbstractThe intermetallic compounds Gd1‐xRExAl2 (RE = Dy, Ho, Er) are considered as being disordered alloys. An indirect exchange between localized spins via narrow‐band electrons is assumed. The deviation from a linear relation between the Curie temperature and the concentration for the compounds considered is explained by a small variation of the band structure. Molecular field and Hartree‐Fock approximations combined with the coherent potential approximation are used.
The Influence of Hydrostatic Pressure on the Effective Concentration and Cyclotron Mobility of Electrons in Semiconducting Bi1‐xSbx Alloys
Authors: Požera R. , Sutkus A. , Tolutis R. 
Published: July 2007

AbstractRf electromagnetic magnetoplasma technique is used to study the influence of hydrostatic pressure (up to 1.0 GPa) on the effective concentration and cyclotron mobility of electrons in the binary plane in semiconducting pure and Te‐doped Bi1‐xSbx alloys (0.076 ≤ x ≤ 0.15) at 77 K. The pressure derivative of the energy gap at the L‐point does not depend on Sb concentration and is close to the known value at 4.2 K. The pressure and concentration dependences of electron cyclotron mobility indicates the importance of acoustic phonon scattering of electrons. An additional scattering which depends on the Sb concentration must also be taken into account in undoped samples.
Hydrostatic Pressure and Uniaxial Stress Dependence of the Silicon (222) X‐Ray Reflection Power
Authors: Pietsch U. 
Published: July 2007

AbstractThe hydrostatic pressure dependence of the silicon (222) X‐ray reflection power is calculated by means of a molecular‐theoretic model of the bond charge. The experiment, published by Yoder‐Short is explained by the variation of the s‐like portion of a/s + sp3> ‐ like model valence orbital. Furthermore, the uniaxial stress dependence of the “forbidden” reflections are calculated. Such experiments indicate the p‐like amount of the model valence orbitals in a direct manner.
Zone Edge Phonons in Gallium Phosphide
Authors: Pödör B. 
Published: July 2007

AbstractThe energies of zone edge phonons at the critical points X, L, W and along the line ∑ in GaP are deduced from an analysis of infrared absorption and Raman scattering measurements. An assignment scheme for the observed lines, based on X, L, W, and ∑ phonons is given.
The Spin‐Wave Theory of Electron and s‐f‐Exchange Magnetostriction in the Rare Earth Metals
Authors: Sadreev A. F. , Sandalov I. S. , Podmarkov A. N. 
Published: July 2007

AbstractThe magnetostriction phenomena are considered in anisotropic rare earth metals. Two mechanisms of the phenomena are investigated. The first is the s‐f‐exchange due to a distortion of the conduction electron wave functions relative to the localized f‐functions. The second is caused by a change of the single‐electron energy. It is shown for kT « Δa, gμBh, where Δa is the anisotropy energy and gμBh the Zeeman energy, that the electron striction is important to give a linear dependence on the external magnetic field. Otherwise the usual exchange striction can be used. The second mechanism is affected by the change of the single‐electron energy.
Effect of Magnetic Field on the Decay Kinetics and Polarization of the AT Emission of KCl:Tl and KI:In Crystals at 0.4 to 0.7 K
Authors: Bragina L. , Hizhnyakov V. , Liidya G. , Nagirnyi V. , Soovik T. , Zazubovich S. , Janson N. 
Published: July 2007

AbstractThe structure of emission and excitation spectra as well as the decay kinetics and polarization of the AT luminescence are investigated for Tl+ and In+ centres in KCl:Tl and KI:In at 80 to 0.4 K. The effect of a magnetic field up to 2 T on the decay times, intensities, and polarization properties of the emission occurring from the metastable tetragonal minima of the triplet excited state is studied at 0.4 to 0.7 K. The parameters of the centres are determined. Good agreement between the experimental results and theory is obtained.
Optical Properties of Molecular Crystals Phenomenological Approach
Authors: Botvich A. N. , Podoprigora V. G. , Shabanov V. F. , Shestakov N. P. , Vtyuren A. N. 
Published: July 2007

AbstractThe ability to calculate the optical properties of molecular crystals is shown in terms of the polarizability theory. The main factors to be taken into account for such calculations are analyzed. The applicability of the method is illustrated by calculations of refractive indices and Raman and second harmonics intensities for the m‐chloronitrobenzene crystal.
Deformational Phase Transitions and Periodic Structures in a Magnetic Field
Authors: Kochelap V. A. , Sokolov V. N. 
Published: July 2007

AbstractAn instability theory of the homogeneous distribution of current carriers and lattice deformations in semiconductors with electron‐phonon interaction via deformation potential in a quantizing magnetic field is developed. It is shown that the instability takes place in a number of regions on the concentration‐temperature plane, their mutual position being connected with the alternation of electron state density peaks in a magnetic field. Each isolated region is characterized by its own maximum temperature point depending in power‐law fashion on the electron‐phonon interaction constant. At lower temperatures the Peierls‐type instability sets in. Phase diagram peculiarities associated with various types of the instability are considered. Characteristic inhomogeneity periods are calculated and their dependences on carrier concentration and temperature are investigated.
Spin Fluctuations in Alloys with Random Transfer
Authors: Fehske H. 
Published: July 2007

AbstractThe local spin fluctuation theory proposed by Hasegawa is extended to binary alloys with random transfer of the additive type. Spin fluctuations and alloy disorder are treated within an extended coherent potential approximation (ODCPA). The dc conductivity σ, including CPA vertex corrections, is derived via density‐density susceptibility from the functional integral scheme. In the paramagnetic region model calculations are presented for the averaged local moment, σ, density of states, and the distribution function of spin fluctuations.
Correlation Function Method for the Thermoelectric Power of Metals
Authors: Goedsche F. , Richter R. , Wegener H. , Röpke G. 
Published: July 2007

AbstractA general linear response theory of the thermoelectric transport is developed on the basis of Zubarev's approach to non‐equilibrium statistical thermodynamics. In the weak‐scattering limit electrical resistivity and thermopower are related to generalized dynamical susceptibilities. It is shown that the Mott formula for the thermopower is approximately correct in two cases, first in the case of elastic scattering, and furthermore, in the presence of inelastic scatterers at high temperatures. At low temperatures Mott's formula is shown to be no longer valid. The correction terms due to the inelasticity of the scattering are derived systematically and estimated for a Debye model of electron‐phonon scattering. For the same reason the Nordheim‐Gorter rule must be generalized at low temperatures. The theory is extended to homogeneously disordered systems. The phonon drag is briefly discussed.
An Analytical Theory of FMR in Bulk Metals (Parallel Configuration). II. Penetration Depths
Authors: Fraitová D. 
Published: July 2007

AbstractThe general formulae for the penetration depths of the three waves, which are excited in a bulk ferromagnetic metal in the ferromagnetic resonance (FMR) region, are evaluated for parallel configuration and compared with the antiresonance skin‐depth expression. The concept of the FMR “effective skin‐depth” is introduced.
Exoemission of Pyroelectrics
Authors: Rosenman G. I. , Pechorskii V. I. , Chepelev Yu. L. , Boikova E. I. , Issakova L. E. 
Published: July 2007

AbstractThe investigation of the current density, the angular and energy distributions, as well as the field dependence of the exoemission arising under the pyro‐ and piezoeffect conditions, shows that the electron emission occurs from a dielectric layer on the ferroelectric surface. The effect of exoemission depletion is found. The mechanism of the exoemission phenomenon is examined. The calculations of the barrier permeability show that the exoemission represents the tunnel electron emission from the polaron band or from the bottom of the conduction band.
Localized Magnetization Arising from Spin‐Dependent Impurity Potentials in the Wolff Model
Authors: Liu K. C. , Lam Kai‐Shue , George Th. F. 
Published: July 2007

AbstractThe Wolff model for localized magnetic moments in dilute alloys is extended to include spin‐dependent impurity potentials. Two virtual levels emerge, corresponding to different spin states of the conduction electrons. As a result of this removal of degeneracy, there always exists a more favorable spin polarization for the spin state with the more attractive impurity potential, even in certain circumstances where the original Wolff model yields no magnetization. The results are obtained graphically for various situations. The physical pictures entailed can also be interpreted in terms of the Anderson model.
Asymptotic Solutions for the Differential Equation Describing Solute Drag by Dislocations
Authors: Fuentes‐Samaniego R. , Hirth J. P. 
Published: July 2007

AbstractThe differential equation describing the drag of a Cottrell atmosphere by a dislocation appears in a number of other physical moving‐frame‐of‐reference problems related to line sources of vector fields, such as vortices in fluid flow and line sources of heat. It reduces to the so‐called modified Mathieu equation. This equation is solved and the asymptotic behavior of the modified Mathieu functions is determined in the limiting situations of small velocity and small or large distance from the line source. A specific asymptotic form of the function of the second kind is found to behave like a K‐Bessel function in the limit of the argument z approaching ∞ and like an I‐Bessel function in the limit z → ∞. The solution can be used to obtained analytical results for the Cottrellatmosphere problem.
Electron—Phonon Interaction in Transition Metals. Results of Relativistic APW Band Structure Calculations
Authors: John W. , Nemoshkalenko V. V. , Antonov V. N. , Antonov Vl. N. 
Published: July 2007

AbstractThe Hopfield parameter η of the electron—phonon coupling is calculated for twelve transition metals (Rh, Pd, Ag, Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au) in the rigid muffin‐tin approximation. Using relativistic APW band structure data and a generalized Gaspari‐Gyorffy formula the influence of relativistic effects is completely taken into account. It is found that η may be calculated in remarkably good approximation using spin‐weighted averages of phase shifts and density matrix coefficients. The theoretical results for the electron—phonon parameter λ and the electronic specific heat are compared with the experimental data.
Symmetry Breaking in Organometallic Polymers Due to Interchain Interactions
Authors: Böhm M. C. 
Published: July 2007

AbstractThe electronic structure of the tetrathiosquarato nickel (II) polymer 1 is studied in the framework of an extended crystal orbital (CO) formalism where the interchain coupling between adjacent organometallic stacks is taken into account. The theoretical approach is based on the combination of a semiempirical INDO CO model for intrachain interactions with a self‐consistent‐electrostatic‐field approximation for the interchain coupling. The band structure of 1 is studied as a function of the strength of the interchain interaction for two different solid state geometries (rhombic and monoclinic lattice models). Symmetry‐broken solutions of the charge density wave type are predicted for the monoclinic solid in the case of an enhanced interstack coupling. The electrostatic potential between the one‐dimensional Ni backbones leads to a condensation of double and single bonds in the C4S4 moieties.
Localization of Electronic States in Disordered Tight‐Binding Systems. II. Mobility Edges
Authors: Unger H.‐J. 
Published: July 2007

AbstractThe model of a “partially disordered semi‐infinite chain” for disordered real systems which was obtained from first principles in a foregoing paper is further investigated. The existence of mobility edges in the spectrum is shown if the recursion coefficients tend to constant limiting values. The convergence of the sequence of recursion coefficients is discussed. Interesting relations to the theory of critical phenomena and to the percolation theory are found. The physical picture behind converging recursion coefficients, i.e. the existence of short‐range order, is cleared up. A theoretical foundation for the Mott‐CFO‐model is given. Within the framework of the recursion method the dependence of the degree of localization on the dimensionality is discussed.
On the Percolation Approach to the Hopping Conduction in Strong Electrical Fields
Authors: Böttger H. , Wegener D. 
Published: July 2007

AbstractThe non‐Ohmic hopping behaviour on random lattices is studied by solving the percolation problem by computer simulation. The dimensional “invariants” Bc (average number of open bonds per site) and vc (critical volume fraction) are shown to be not suitable for an investigation of this problem, because they are field dependent. Furthermore the field dependence of the “returns” in the percolation paths and the decrease of the conductivity at sufficiently low fields are studied.
The Morin Point as Degenerate Critical Point
Authors: Kuleshov V. S. , Popov V. A. 
Published: July 2007

AbstractThe notion of the degenerate critical point (DCP) of phase transitions is introduced. The theory of antiferromagnet properties near such points is developed. Various instances are given of realization of the Morin point as a DCP and its modifications resulting from symmetry breaking due to inclusion of new internal and external interactions. Phase diagrams show lines of zero‐order phase transition critical points.