bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of an Adiabatic Potential of Simple Metals. I. Exchange and Correlation Effects of Electrons
Authors: Zarochentsev E. V. , Teplov S. V. 
Published: July 2007

AbstractA method of irreducible vertex functions for the description of many‐electron interaction is introduced allowing the exact evaluation of the electron—electron interaction in every series term of the perturbation theory in pseudopotential by which the electron part of the adiabatic potential is presented. The equations for fully many‐particle amplitudes are obtained. Fully many‐particle amplitudes are found assuming that the irreducible vertex functions depend only on the momenta q transfered to electrons scattered from the pseudopotential. Limiting values (with q → O) of irreducible vertex functions are derived using exact relations of the Fermi‐liquid theory.
Invariant Expansion of Energy of the Induced Magnetic Anisotropy
Authors: Volkov V. M. , Kustov E. F. , Maketov T. K. , Steczko G. 
Published: July 2007

AbstractUsing the reduction symmetry properties of crystals, the invariant expansions of the energy of induced magnetic anisotropy (IMA) are given for all point groups. The expansion is performed by deriving the tensor functions on the basis of polar and axial vectors. The relationship between the IMA invariant constants and the constants generally used is given. The influence of invariants of third order on IMA is discussed. The dependences of invariant constants on the composition are given for some magnetic materials.
Tunnelling Model for Quasi‐One‐Dimensional Hydrogen‐Bonded Crystals
Authors: Plascak J. A. , Salinas S. R. 
Published: July 2007

AbstractTunnelling term is included in the Hamiltonian of an anisotropic Ising model which is used to explain the thermodynamic properties of quasi‐one‐dimensional hydrogen‐bonded ferroelectric crystals. A variational approach is used to treat the strong intrachain interactions accurately, while the weak interchain interactions are accounted for in a mean‐field approximation. Also, fittings are presented of some experimental data pertaining to crystals of PbHPO4.
Charge Transfers in Structurally Disordered Alloys
Authors: Weissmann Mariana , Cohan Norah V. 
Published: July 2007

AbstractStructurally disordered binary alloys are investigated for which an atomic basis set is adequate. An iterative tight‐binding scheme within a non‐orthogonal basis and interactions among all pairs of atoms is used. The properties of the disordered systems are obtained as averages over several groups of a small number of random configurations of atoms. As the systems are structurally disordered a charge distribution is obtained for each type of atom and its average value is defined as the charge transfer. It is found that while the electrons are transferred to the atoms with higher ionization potential, as expected, they are also transferred to the larger atoms, and that both effects are almost additive. The results explain the charge transfers of several liquid alloys such as NaxK1–x AuxAg1–x, and the gold—alkali metal alloys.
Random Walk and Interaction of Vacancies with Imperfections in Diamond Lattice as a Discrete Markovian Process
Authors: Tishkovsky E. G. 
Published: July 2007

AbstractThe description of sites in diamond lattice in terms of elementary jumps is performed. The relations between the number of symmetrically arranged sites and the minimal value of elementary jumps needed to reach them from a given point are obtained. The physics of migration and interaction of vacancies with imperfections is represented by discret in space and time Markovian processes. Some characteristic features of Markovian chains and related physical processes are discussed.
Dynamics of Solitons in the Disordered Anharmonic Chain
Authors: Abdullaev F. Kh. , Abdumalikov A. A. 
Published: July 2007

AbstractThe dynamic behaviour of solitons in the random anharmonic chain in the long‐wavelength approximation is investigated. Long‐time accumulative effects are described of weak stochastic perturbations on Korteweg‐de Vries solitons. A law is found of the stochastic acceleration of solitons and the amplitude of a soliton is calculated in the case of short‐range fluctuations of the spatial inhomogeneities of the chain.
Low‐Temperature Lattice Specific Heat of CuAl
Authors: Bijalwan R. D. , Ram P. N. 
Published: July 2007

AbstractThe low‐temperature lattice specific heat of dilute copper—aluminium alloys are analysed on the basis of Grees function theory. An impurity model, which includes mass‐change at the impurity site and nearest neighbour central and noncentral force constant changes, is employed. The effect of volume change is also taken into account. The calculated results are in agreement with experimental measurements. Reduction in lattice specific heat is dominated by contribution from F1u irreducible representation. The calculated localized mode frequency on the basis of the defect model is in reasonable agreement with experimental value. The role of localized modes in understanding the change in lattice specific heat is discussed.
Self‐Interstitial in Hexagonal Close‐Packed Metals
Authors: Fendrik A. J. , Monti A. M. , Savino E. J. 
Published: July 2007

AbstractDifferent symmetry configurations for an interstitial in a hexagonal close packed lattice are studied. Their stabilities are discussed and calculations are performed by means of an interatomic potential which reproduces some properties of Mg. The defect lattice eigenfrequencies and eigenvectors are calculated within the Einstein and a cluster approximation.
The Exponential Tail of Light Absorption in Disordered Solids
Authors: Szczyrbowski J. 
Published: July 2007

AbstractThe exponential shape of the optical absorption edge tail in disordered solids is discussed. An approximated calculation is made which gives an explicit relation for the steepness parameter in such materials. The model discussed predicts quantitatively the values of the steepness parameter for several amorphous and fine grained polycrystalline solids.
The Electronic Structure of a Hydrogen Impurity in Aluminium I. The Jellium Model
Authors: Craig B. I. , Smith P. V. 
Published: July 2007

AbstractAll attempts to calculate the electronic structure of a proton in a metal have involved the approximation of spherical symmetry. One possible way of including the effects of the crystal field into such calculations is to extend the Grees function method of Gunnarsson and Hjelmberg to treat the non spherical nature of the induced charge density. The aim of the present paper is therefore to establish that this basic approach can yield reliable results for the proton—jellium system and hence provide a means of studying the real metal impurity problem. The actual application of this Grees function technique to a proton interstitial impurity in aluminium is then presented in a forthcoming paper.
Heavy Doping Effects on the Energy Band Structure of n‐Type Crystals
Authors: van Cong H. , Charar S. , Brunet S. , Averous M. , Birman J. L. 
Published: July 2007

AbstractThe density of states, ϱ(E), the penetration of the Fermi level into parabolic conduction bands, En, relative respectively to optical and electrical conduction band edges Ec and E′c, the band‐gap narrowing for the optical energy gap, ΔEg, opt., the physical band‐gap narrowing (ΔEg, elec.), and the effective band‐gap narrowing (ΔEg, eff.) for the electrical energy gap, the “apparent” band‐gap narrowing due to the Fermi‐Dirac statistics effect, ΔEg, F.D., the band‐gap narrowing due to the changes in ϱ(E), Γ + Γ, are investigated for n‐type heavily doped crystals at an arbitrary temperature T, basing on a second‐order Thomas‐Fermi model and on a polaron model. It is suggested, in the n‐type heavily doped silicon at 300 K, that (i) while En is larger than the penetration of Fermi level into the unperturbed conduction band, E, for 5 × 1025 m−3 ≦ n0 ≦ 1026 m−3, En is found to be smaller than E, for n0 ≧ 2 × 1026 m−3, (ii) ΔEg, elec, is significantly larger than ΔEg, opt. because of important band edge shifts caused by the polaron effect, (iii) ΔEg, FD < 0 is much more important than (Γ + Γ), and (iv) ΔEg, eff. is thus smaller than ΔEg, elec., The results of band‐gap narrowings are in good accordance with some existing experimental results, and also compared with those obtained by other theories.
Thermodynamic properties of the s–f model (spin 7/2, atomic limit)
Authors: Matlak M. , Ramakanth A. , Skrobis K. 
Published: July 2007

AbstractThe exact solution of the atomic limit of the s–f model and S = 7/2 is given. The thermodynamic averages 〈n↑〉, 〈Szn↓〉, 〈Szn↑〉, 〈Sz(n↑– n↓)〉, 〈S+a↓+a↑〉 are calculated as functions of temperature and for different values of the average electron occupation numbers N. The validity of the factorization of some correlation functions is investigated. It is found that the factorization is acceptable only for low temperature and small values of N.
Temperature dependence of the thermoelectric power of disordered alloys
Authors: Schiller W. , Richter J. 
Published: July 2007

AbstractThe temperature dependence of the thermoelectric power of strongly disordered alloys is studied describing phonons in alloys by a modified Chen‐Weisz‐Sher model. Within this model the thermopower can be calculated by means of Mott's formula. For the treatment of the disorder problem the coherent potential approximation is used. Numerical results are discussed for different values of alloy concentration, number of electrons, and degree of chemical disorder with respect to experimental observations. The mixing of chemical and thermal disorder can cause strong deviations from the linear temperature variation of the thermopower.
The influence of exchange spin splitting on exciton in Cd1—xMnxTe mixed crystals
Authors: Twardowski A. , Ginter J. 
Published: July 2007

AbstractThe magnetoabsorption of Cd1—xMnx Te is measured for 0.00 ≦ x ≦ 0.10 at temperatures 1.6 to 50 K. A complicated exciton spectra consisting of split ground and excited states are observed. As a result of phenomenological analysis a continuous transition between the spectra of pure CdTe and CdMnTe is found.
Plasmon approach to the band gap of alkali halides
Authors: Kumar Srivastava V. 
Published: July 2007

AbstractQuantitative order of the band gap of Li, Na, K, and Rb halides is calculated using the plasma oscillation theory of solids. The present method is not limited to binary or ternary compounds but can be used for all the semiconducting and insulating compounds. The calculated values are in excellent agreement with the observed and calculated values of different workers.
On the theory of long‐range electron hopping in polar media
Authors: Kuznetsov A. M. , Ulstrup J. 
Published: July 2007

AbstractExpressions for the probability of a nonadiabatic electron transfer between a donor‐trap and an acceptor‐trap in a polar medium are obtained. The transition probability is expressed in terms of the zeroth‐order electron densities near the traps. The interaction of the electron with the phonon field is analyzed. A way of definition and calculation of the zeroth‐order electron states with due account for their modulation by the phonon field is suggested. The effects of deviation from the Condon approximation due to the modulation of the electron densities and of the interaction with the phonon field causing the transition are estimated. The effects of this modulation on the kinetic parameters of the transition in the Condon approximation and in the improved Condon approximation are analyzed. It is shown that these effects are rather large for the processes involving solvated, trapped, or weakly bound electrons. The deviations from the Condon approximation should be taken into account for long‐range electron transfer.
Nonhomogeneous kinetics of quasiparticles in steady‐state packet representation
Authors: Ya. Glushko E. 
Published: July 2007

AbstractThe steady‐state packet representation of exciton wave functions (WF) as a basis for nonhomogeneous kinetics description is proposed. The steadiness of the packet system of WF is reached by integration on the small region near the isoenergetic surfaces of excitons, when the packet basis is maked up. The Pauli‐master‐equation for the exciton—phonon system in steady‐state packet representation is considered. The problem of evolution of the nonhomogeneous exciton density matrix to small interactions with phonons is solved.
The cluster investigation of the q‐state potts model
Authors: Zinenko V. I. 
Published: July 2007

AbstractThe thermodynamics of the q‐state Potts model is calculated by the cluster approximation. With two, three, and four particles as the basic cluster the free energy is obtained for any q. It is found that the transition is of the first order for all two‐dimensional and three‐dimensional Potts models. In the case of planar lattices for q = 3 and q = 4 it is found that the critical point approaches the Curie‐Weiss temperature but the discontinuity of the order parameter remains almost equal to that obtained by the mean‐field approximation.
Susceptibility and specific heat of spin glasses in a magnetic field
Authors: Dubey O. N. , Tripathi R. S. 
Published: July 2007

AbstractThe susceptibility and specific heat of spin glasses for an Ising model in the presence of a magnetic field are calculated. Gaussian probability distribution is taken for exchange interaction with positive mean J0. It is shown that the presence of J0 enhances the reduction of susceptibility and specific heat around the freezing temperature.
Interaction of high power CO2 laser radiation with a nonequilibrium carrier system in Ge at low temperatures
Authors: Manenkov A. A. , Mikhailova G. N. , Prokhorov A. M. , Sidorin A. V. , Sokolov S. Yu. , Tikhodeev S. G. 
Published: July 2007

AbstractCO2‐laser produced damping of electron‐hole drop (EHD) luminescence in Ge at laser intensities of 104 to 5 × 106 W/cm2 is reported. The observed effect is explained to be due to heating of the EHD by 10.6 μm radiation and driving of e‐h plasma by phonon wind generated during absorption and relaxation of hot nonequilibrium carriers.
Autolocalized collective excitations in molecular chains with cubic anharmonicity
Authors: Davydov A. S. , Zolotariuk A. V. 
Published: July 2007

AbstractThe cubic anharmonicity effect on the soliton motion in molecular chains with electron(exciton)—phonon interaction is investigated. This anharmonicity is shown to remove the infinite increase of the soliton energy as the soliton velocity is reaching the longitudinal sound velocity.
Estimation of second‐order Auger recombination in lead chalcogenides
Authors: Ziep O. 
Published: July 2007

AbstractThree‐electron recombination, LO‐phonon‐assisted Auger recombination; and recombination by two‐plasmon emission are qualitatively discussed by means of q‐ and ω‐dependent inverse dielectric functions in an unitary manner. In case of PbSe‐like semiconductors the effectivity of three‐electron and two‐plasmon recombination is estimated. Whereas two‐plasmon recombination is mostly less effective than Auger recombination it is predicted that three‐electron recombination neglected till now in analysis of recombination dominates at carrier concentrations 1018 to 1019cm−3 as compared to Auger recombination and should be provable experimentally.
Electric field dependent conductivity in amorphous semiconductors
Authors: Kahnt H. , Schirrmeister F. 
Published: July 2007

AbstractThe field dependence of the conductivity is related to the basic properties of the electronic structure in amorphous semiconductors, i.e. charged intrinsic defects with negative effective correlation energy and localized states in the tails at the band edges. The general formalism of the model considers the Poole‐Frenkel effect which causes an increased carrier density and the field dependence of the mobility of carriers moving by hopping among the localized states in the tails at the band edges. Special cases are discussed leading to the various types of field dependence, that have been observed experimentally.
Two‐beam interferometry in the exciton spectroscopy of CdS
Authors: Lisitsa M. P. , Terekhova S. P. , Onishchenko N. A. 
Published: July 2007

AbstractThe independence of the oscillator strength on the thickness of the sample is determined for the exciton transitions in CdS by Rozhdestwenskii method of hooks. Many‐beam interference patterns are obtained. The values of the refractive indexes and of the light group velocity are calculated. The possibility to determine picosecond times of the light flight by this method is established.
Galvanomagnetic effects in semiconductors of p‐Ge type
Authors: Ivashchenko V. M. , Mitin V. V. , Zakhleniuk N. A. 
Published: July 2007

AbstractIt is shown that the rate equations for the light and heavy hole distribution functions in p‐Ge can be solved analytically using the real anisotropic dispersion law since for acoustic lattice scattering the collision terms can be described by the isotropic relaxation time depending only on the energy of holes, which is proved by numerical computations. The even Hall effect, the transverse and longitudinal magnetoresistance (MR) as a function of the current and the magnetic field orientation with respect to the crystallographic axes in non heating electric fields E as well as the transverse γ⊥ and longitudinal γ∥ anisotropy of conductivity arising in the heating fields, and the MR linear in the magnetic field are calculated. The linear MR is determined largely by light holes (without these or with their isotropic spectrum the MR would have the reverse sign for the same direction of the magnetic field). The relative contributions of heavy holes to γ⊥ and γ∥ are nearly half of that in the earlier approximate calculations. The even Hall effect, the longitudial MR, and the anisotropy of the transverse MR are almost entirely due to the anisotropy of the heavy hole dispersion law.
On the problem of electron phase stability
Authors: Maslov V. A. , Naumov I. I. , Panin V. E. 
Published: July 2007

AbstractIn terms of the pseudopotential method the Hume‐Rothery electron phase stability is studied. Unlike the previous studies here the effects related to the nonsphericity of the Fermi surface are taken into account. The numerical calculations are carried out for the CuZn system. It is shown that the theory results in a phase alternation which is observed at rather high temperatures. The conclusion is made that the account of real Fermi surface is in principle necessary in analyzing the electron phase stability.
Recombination luminescence and energy transfer in ionic crystals at XUV excitation by synchrotron radiation
Authors: Elango M. , Pruulmann J. , Zhurakovski A. P. 
Published: July 2007

AbstractThe relative quantum yield spectra of recombination luminescence for MgO, α‐Al2O3, SiO3, and several alkali halide crystals are measured by synchrotron radiation in the photon energy interval 50 to 250 eV. The main feature of the spectra of oxides is a suppression of the volume luminescence due to surface losses of electrons and holes. For alkali halides surface as well as volume recombination luminescence take place. The more intensive the surface luminescence is the larger the absorption coefficient for exciting photons. The quantum yield spectra may be interpreted quantitatively on the basis of the hot carrier diffusion theory, the diffusion lengths being 2200 Å for MgO, 1500 Å for α‐Al2O3, and 300 Å for SiO2.
Phonon dispersion in the perovskite‐type layer material K2ZnF4
Authors: Rauh H. , Geick R. , Lehner N. , Bouillot J. , Eckold G. 
Published: July 2007

AbstractThe perovskite‐type layered crystal K2ZnF4 is built up from the same structural units as the perovskite KZnF3, namely ZnF6 octahedra which have almost the same dimensions in both the materials. While the lattice dynamics has been studied in detail for the perovskites, in this investigation the first measurement of the phonon dispersion curves of K2ZnF4 is presented as an example for a perovskite‐type layer material with the K2NiF4 structure. By comparing corresponding phonon modes in the perovskite and the layer structure it is found that the interatomic forces within the octahedra do not change with the crystalline environment.
Current density near the semiconductor‐insulator interface
Authors: Paasch G. 
Published: July 2007

AbstractA modified local density approximation which takes into account that the wave functions are zero at the semiconductor‐insulator interface is used to investigate the influence of this behaviour of the wave function on the mobility. The result follows from a generalization of the classical transport description. It is shown that the decrease of the mobility due to surface scattering is reduced by the influence of the wave functions. In addition a modification of the expression for the diffusion current connected with the influence of the wave functions is given.
γ‐magnetic resonance in the presence of electronic spin relaxation
Authors: Mitin A. V. , Polyakov N. V. 
Published: July 2007

AbstractThe theory of γ‐magnetic resonance (GMR) in paramagnetic crystals in the presence of electronic spin relaxation is discussed. A general expression for the GMR lineshapes applicable to the spectrum with or without quadrupole interactions is derived. The theory is applied to the calculation of the GMR lineshapes for an 57Fe nucleus for different values of the electronic relaxation rate. The results obtained can be used to investigate the dynamics of the electronic‐nuclear system.
Solitons and proton motion in ice‐like structures
Authors: Antonchenko V. Ya. , Davydov A. S. , Zolotariuk A. V. 
Published: July 2007

AbstractThe proton motion in hydrogen bonded quasi‐one‐dimensional molecular chains is investigated It is shown that elementary processes in one‐dimensional ice lattice are nonlinear autolocalized collective exitations which can spread over macroscopic distances retaining the energy, momentum, and charge. The results obtained can be used to explain some phenomena in biological systems.
Relation of recombination radiation spectra to the concentration of structure defects in CdS single crystals
Authors: Brodin M. S. , Davydova N. A. , Shablii I. Yu. 
Published: July 2007

AbstractIt is shown that the interaction of the ruby laser radiation with a CdS single crystal leads to the formation of structure defects (largely of donor type) in a thin subsurface layer, essentially influencing the optical properties of the crystal. In particular, at low concentrations of the donors formed the radiative recombination spectra at 4.2 K exhibit a redistribution of the emission intensity in the group of lines of bound excitons whereas at higher concentrations new emission bands, 4875 and 4880 Å, appear. From the data obtained the former line is interpreted in terms of an optical transition involving donor centres and the valence band, and the latter is attributed to band‐to‐band recombination.
Raman scattering in K2SO4 at high temperatures
Authors: Ishigame M. , Yamashita S. 
Published: July 2007

AbstractTemperature dependence of Raman spectra of K2SO4 is measured in the temperature region from 300 to 1173 K. A remarkable change of the Raman frequencies is not observed through the phase transition temperature Tc. Most of the Raman spectra measured above Tc can be explained by the vibrational modes of the K2SO4 crystal with space group D. From the spectra of internal modes, however, it is suggested that a correlation between directions of two SO ions in unit cell will exist locally in K2SO4 crystal above Tc.
Investigation of Oguchi's procedure applied to the ising model
Authors: Ferreira J. R. Faleiro , Silva N. P. 
Published: July 2007

AbstractApproximate critical temperature of the anisotropic ferromagnetic Ising model is calculated using the procedure proposed by Oguchi, with better results than those obtained by the use of Bogolyubov's principle. The calculation is made with linear and double chain trial Hamiltonians.