bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonlinear Laser Spectroscopy of Exciton Absorption in MOCVD Grown ZnSe Monocrystalline Films
Authors: Gribkovskii V. P. , Zimin L. G. , Gaponenko S. V. , Malinovskii I. E. , Kuznetsov P. I. , Yakushcheva G. G. 
Published: July 2007

AbstractThe influence of intensive photoexcitation on the absorption spectrum of high‐quality monocrystalline ZnSe films grown by the MOCVD technique is investigated by two independently tunable dye lasers. With increasing photoexcited carrier density a broadening of the excitonic band, a decrease of the exctionic absorption, and a band gap narrowing are observed. The bleaching near the excitonic resonance is associated with the nonequilibrium electron–hole plasma screening of the Coloumb interaction. The considerable contribution of the excitonic band broadening and of the long‐wave shift of the fundamental absorption edge to the nonlinear crystal response permit to obtain the resonatorless optical bistability regime. The peculiarities of nonlinear absorption at sample temperatures below 88 K are associated with the influence of the polaritonic mechanism of the optical excitation energy transfer in the crystal.
Calculation of Surface‐Induced Core‐Level Shifts for Covalent Semiconductors C, Si, Ge, and α‐Sn I. (111) 2 × 1 Surfaces
Authors: Bechstedt F. , Reichardt D. 
Published: July 2007

AbstractA theory is developed for the surface induced core‐level shift. Since the many body relaxation mechanism can be neglected only the initial‐state potential effect is considered. Starting from tight‐binding assumptions the shift is related to ion charges accompanying the reconstruction, the hybridization state, the polarity of chemical bonds, and the atomic configuration. The atomic configurations are taken from total energy minimizations, dynamical LEED or ion scattering studies. The other input parameters are calculated self‐consistently. The developed theory is applied to the (111) 2 × 1 surface of group IV materials. Various fundamental reconstruction models — buckling, π‐bonded chains, and π‐bonded molecules — are studied. The shifts resulting for eight atoms per surface elementray cell and the associated core electron line shapes seem to favour the chain model in the (111) 2 × 1 case. The molecule model cannot be completely ruled out only from core‐level shift calculations because of its homopolar bond character.
Electron and Positron Distribution for the Plane (1110) in Si and GaAs
Authors: Aourag H. , Khelifa B. , Belaidi A. , Kobayasi T. , West R. N. 
Published: July 2007

AbstractThe electron and positron charge densities are calculated as a function of position in the unit cell for two diamond and zincblende semiconductors, using wave functions derived from nonlocal pseudopotential band structure calculations for the electronic part, and the positron wave functions are calculated for single‐particle approximation in manner which is free of any theoretical assumptions.
Collective Excitations of Localized Electrons and Their Effect on Magnetic‐Material Kinetics
Authors: Mitsek A. I. 
Published: July 2007

AbstractThe multielectron operators (MEO) method is used for calculating the collective excitations of unfilled shells in transition ions. The excitation dispersion law depends on a chemical bond. Decrease of the lattice stability with increasing T is determined by the MEO correlation function of the neighbour sites (the order parameter). The conduction electron scattering on such excitations provides a contribution to the electrical resistance ϱ(T) ∼ T2 in a parabolical dispersion law approximation. The effective Hamiltonian is obtained of the Cooper pairing which energy is large enough for interaction of the conduction electrons with the nearest neighbour ions. The pairing mechanism is attenuated for antiferromagnetic spin ordering of the neighbour sites. The elastic moduli defect, determining a kink of the phonon contribution to ϱ(T) near Tc or TN, is taken into account, comparing the theory with the experimental curves ϱ(T).
Electronic Specific Heat of Coulombic Systems
Authors: Rösler M. , Stolzmann W. 
Published: July 2007

AbstractThe specific heat of the electron gas is determined in the random phase approximation (RPA) using the Matsubara‐frequency summation technique which is well suited for calculating thermodynamic quantities up to relatively high degrees of degeneracy. A detailed discussion of the numerical problems is given. It is shown that widely used approximation schemes including the plasmonpole approximation (PPA) for the dielectric function are unsuitable calculating the specific heat with sufficient accuracy. The numerical evaluation shows in contradiction to previous calcutations that the specific heat ratio cv/cvid is larger than unity in the region of metallic densities.
Dislocation Recharging in Plastically Deformed Crystals of the A2B6 Type
Authors: Vardanyan R. A. , Veselko S. G. 
Published: July 2007

AbstractThe quantum transition of weakly coupled electrons from the ion to the self‐localized condenson (acoustic polaron) state on the dislocation is discussed for the case when during the plastic deformation of the crystal such ion appears in the space‐charged region of the edge dislocation. In terms of the adiabatic approximation the electron–phonon interaction is taken into account. It is shown that this interaction reduces to the multiquantum fluctuational phonon radiation and absorption in the initial and final states. The probability of the dislocation recharging elementary act is a function of the temperature, the electon–phonon interaction constant, and the distance between ion and dislocation. By numerical calculation the effectiveness for the recharging process is found for semiconductive A2B6‐compounds as a function of the deformation rate, the ionization energy of ion, the temperature, and the electrostatic field of the edge dislocation.
The Electrical Resistivity of Some Lithium Based Liquid Alloys
Authors: Akinlade O. , Belhachemi O. 
Published: July 2007

AbstractThe concentration dependent electrical resistivity of LiBi, LiIn, LiMg, and LiTl liquid alloys is studied and comparisons are made of the values of resistivity computed using the Faber‐Ziman formulation and the “2kF” scattering theory of Morgan et al. While a Heine‐Abarenkov potential will be used to describe the electron–ion pseudopotential, the structure factor will be given in the context of the mean‐spherical approximation for charged hard spheres with a Yukawa interaction. In order to explain the resistivity of Li based liquid alloys with high valency, it is necessary to go beyond the diffraction theory of Faber‐Ziman.
Spectroscopic Manifestations of Self‐Trapped Holes in Silica Theory and Experiment
Authors: Dianov E. M. , Karpechev V. N. , Sokolov V. O. , Sulimov V. B. , Chernov P. V. , Kornienko L. S. , Morozova I. O. , Rybaltovskii A. O. 
Published: July 2007

AbstractA quantitative simulation in the cluster approximation is made of an autolocalized hole in the amorphous SiO2 network. A model is suggested in which the thermal excitation of holes from Anderson localized states of the top of the silica valence band above the mobility edge corresponds to the thermally stimulated luminescence peak at 125 K, and the analogous optical transition — the radiation‐induced low‐temperature IR‐absorption. The position and form both, of the peak and absorption band and their thermo‐ and photostability are explained.
On the Representation of Orientation Distributions in Texture Analysis by σ‐Sections. I. General Properties of σ‐Sections
Authors: Matthies S. , Helming K. , Kunze K. 
Published: July 2007

AbstractThe recently suggested concept of σ‐sections of the orientation space for comprehensible representation of distributions in texture analysis is considered in detail. The properties of possible variants of variables describing orientations and of projections are characterized qualitatively as well as by numerical estimations. Two variants are recommended for the use in practice in dependence on the questions of interest for the interpretation of orientation distributions.
Possible Role of Deformation‐Induced Point Defects in Dislocation Patterning
Authors: Estrin Y. , Abromeit C. , Aifantis E. C. 
Published: July 2007

AbstractThe evolution of dislocation density is considered by taking into account the effect of deformationinduced point defects on the dislocation annihilation (recovery) rate. It is shown by linear stability analysis of the coupled equations describing the evolution of the dislocation density and the diffusion of point defects that a periodic spatial pattern can form during plastic deformation. The preferred wavelength of the emerging periodic structure is evaluated as a function of the production and annihilation bias parameters reflecting certain asymmetries in the generation and annihilation of interstitials and vacancies in the course of straining.
Second‐Order Pressure Derivatives of SOE Constants of Fluorite Structure Solids
Authors: Sharma A. K. , Goyal S. C. 
Published: July 2007

AbstractThe expressions for the second‐order pressure derivatives of the SOE constants of the fluorite structure solids are derived using the relations for SOE, TOE, and FOE constants of CaF2, SrF2, and BaF2 structure type solids. The first‐order pressure derivatives of the TOE constants, internal strain parameter, and the linear combinations of the FOE constants are also analysed for the solids under study.
Lithium Impurity States in PbTe
Authors: Tovstyuk K. D. , Polyakov I. O. , Slinko E. I. , Tovstyuk N. K. , Khandozhko A. G. 
Published: July 2007

AbstractThe behaviour of lithium impurity in lead telluride is studied. The lithium quasi‐liquid in PbTe lattice is found to freeze out at some critical temperature. The model of light particle quasi‐liquid in a solid crystalline state is further developed.
A Search for a Phase Transition in Sr(NO3)2 by Raman Spectroscopy. Evidence for Partial Disorder
Authors: Brooker M. H. 
Published: July 2007

AbstractThe Raman spectrum of Sr(NO3)2 is measured as a function of temperature from room temperature to the melting point in a search for an explanation for reported anomalies in the electrical and thermal properties and the report of a possible phase transition in the 600 to 700 K region. Except for the expected line broading with increased temperature the Raman spectrum of Sr(NO3)2 is consistent with the Pa3(T) space group at all temperatures. Depolarization studies of an oriented single crystal confirm the fact that the Raman bands retained their Ag, Eg, and Fg character at all temperatures. There is no evidence to support the reported phase transition to a disordered structure at high temperature. However, there is good evidence to indicate the presence of a considerable fraction of the nitrate ions on disordered sites in thermal equilibrium with the nitrate ions on ordered sites. Evidence for the disordered nitrate ions comes from the presence of anomalous spectral features which appear in addition to those bands which characterize the ordered part of the crystal.
Interfacial Capacitance
Authors: Krupski J. 
Published: July 2007

AbstractAn analysis is made of experimental results on the capacitance of thin‐film condensers. To find the screened electrostatic potential in a three layer structure a specular electron reflection model is employed which takes into account quantum effects. The resulting interfacial capacitance is in semiquantitative agreement with the measured value for the thin‐film Al–Al2O3–Al condenser.
Two‐Dimensional Electron Gas in a Magnetic Field. The Non‐Degenerate Limit
Authors: Wang L. 
Published: July 2007

AbstractThe thermodynamical properties of a two‐dimensional electron gas (2DEG) in a magnetic field with an arbitrary level broadening are discussed in the nondegenerate limit first proposed by Zawadzki. It is concluded that experimental measurements in the non‐degenerate regime may open a new avenue for investigations on the density of states of a 2DEG in a magnetic field.
Percolative Treatment of the Verwey Transition in Cobalt–Iron and Nickel–Iron Ferrites
Authors: Marín M. L. , Ortuño M. , Hernández A. , Abellán J. 
Published: July 2007

AbstractA new percolation treatment of the Verwey transition in cobalt–iron and nickel–iron ferrites is performed via a large‐cell Monte Carlo simulation. It is based on the consideration of certain electronic transitions that conserve short‐range order and on their percolation properties. The presence of cobalt and nickel impurities blocks the possibility of these transitions, diminishing their electronic rearrangement capabilities. The critical impurity concentration for the disappearence of the Verwey transition obtained with this method is xc = 0.04, in agreement with experimental results.
Electron Momentum Distribution and Compton Profiles of Crystalline Rare Gases by the Augmented‐Plane‐Wave Method
Authors: Bacalis N. C. , Papanicolaou N. I. 
Published: July 2007

AbstractA systematic study of directional electron momentum distributions and Compton profiles of the inert gas solids is presented, performed within the augmented‐plane‐wave method using the exchange and correlation of Hedin and Lundqvist which is well known to be the most reliable approximation for valence band properties of the rare gas crystals. Directional anisotropies in the Compton profiles are observed which are larger than existing ones from Hartree‐Fock calculations.
Molecular Perturbation Model for the Spin–Lattice Coupling Coefficients of 6A1 States to Eθ Strains
Authors: Boulanger D. , Parrot R. 
Published: July 2007

AbstractThe proposed perturbation model involves second‐order molecular spin–orbit interactions between the fundamental state 6A1, and the components of orbital triplets 4T1 and 6T1, calculated in symmetry D2d induced by E‐strains. The matrix elements of the molecular spin–orbit interactions are first calculated for the states 4T1 and 6T1 defined from multielectronic configurations with three open shells. Then, it is shown that the second‐order molecular spin–orbit perturbation involving these states 4T1 and 6T1 is strictly zero if these states are degenerate. Finally, it is shown that the most important contribution is due to the three states 4T1, defined from multielectronic configurations with two open shells.
Metal–Dielectric Transition in n‐ZnSe Obtained by Doping with Shallow Donor Impurity
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N. 
Published: July 2007

AbstractBy means of dosed variation from 2 × 1016 to 2 × 1018 cm−3 of the shallow donor Al impurity concentration in n‐ZnSe a transition from activated conductivity to non‐activated one is obtained in the low‐temperature limit. In the temperature range from 1.6 to 300 K the peculiarities of resistivity, Hall coefficient, and electron mobility dependences on temperature are investigated while transiting from a metallic conduction to an activated one. On the dielectric side of the transition as the temperature decreases the conduction with an activation energy ϵ1 induced by electron excitation from the impurity states into the conduction band is replaced by the hopping conduction with a constant activation energy ϵ3, which in the lowest temperature region is transferred to a hopping conduction of variable activation energy. It is established that the replacement of the activated conduction by a metallic one occurs at ND = 1.3 × 1017 cm−3 and takes place within the impurity band before it attains the bottom of the conduction band. The electron concentration at the transition from the metallic state to the dielectric one is continuously varied as a consequence of a chaotic distribution of donors in the crystal.
Hall Coefficient of Dilute CuPd, CuRh, CuZr, and CuY Alloys d‐Resonance Scattering
Authors: Flouda E. , Boukos N. , Papastaikoudis C. 
Published: July 2007

AbstractMeasurements of the Hall coefficient of the dilute CuPd, CuRh, CuZr, and CuY alloys are made in a magnetic field up to about 3 T and 4.2 K. The Hall coefficients show the trend to depend on the valence of the 4d impurities. The results are discussed in the spirit of the Friedel‐Anderson model of virtual bound states in Cu.
Electron Paramagnetic Resonance Spectra Observed in Single Crystals of YBa2Cu3O7–δ
Authors: Yu C. , Lai C. , Marshall S. A. , Yoder‐Short D. R. , Zhang Y. N. 
Published: July 2007

AbstractAn electron paramagnetic resonance absorption study is conducted on four separately prepared single crystal groups of the superconductor YBa2Cu3O7–δ, each group consisting of from four to six crystalline platelets. This investigation confirms conclusions reached by other regarding the EPR silence of this superconducting oxide while demonstrating that EPR spectroscopy can be used to determine certain properties of superconducting oxides. Such determinations include detection of paramagnetic impurity phases, noninvasive means for determining Tc, and estimating the depth of penetration of a microwave radiation field in these materials. Some comments are provided on the nonresonant, zero field absorption in both, the powders and single crystal platelets.
Functional Approaches to Superconductivity within an Extended Attractive Hubbard Model
Authors: Teubel A. , Kolley E. , Kolley W. 
Published: July 2007

AbstractOn the basis of an extended attractive Hubbard model with nearest‐neighbour interaction of opposite spins two functional methods are adopted for deriving a self‐consistent equation for the superconducting order parameter. The functional‐integral formalism is exploited in saddle‐point approximation. The functional‐derivative technique using Schwinger source fields leads via the self‐energy in Hartree‐Fock‐Bogolubov approximation to a nonlinear gap equation. The superconducting transition temperature is investigated for the case of s‐wave pairing.
Charge Fluctuation in the High Tc Superconductor YBaCuO in the Transition Temperature Region
Authors: Chen Ling , Wang Guanghou , Teng Mingkang 
Published: July 2007

AbstractPositron annihilation rates in both, high and low Tc superconductors are calculated by considering the interaction between the thermalized positrons and electrons in superconducting and normal state in the framework the of KSS model. By properly chosen parameters (for instance, EF = 0.7 eV) the anomaly of positron annihilation rate in the high Tc superconductor YBaCuO at the transition temperature is predicted and is in agreement with recent experimental results.
Antiresonances in the Fundamental Spectra of CdI2–4H and CdBr2–6R Crystals
Authors: Dovgyi Ya. O. , Kityk I. V. 
Published: July 2007

AbstractOn the basis of the low temperature spectra measured for CdI2 (4H‐polytype) and CdBr2 (6R‐polytype) crystals in the region of UV radiation in the exciton resonance vicinity the distinct antiresonance are discovered. The exciton interaction with the continuous spectrum corresponding to interband transitions is determined to cause a self‐ionization and a band widening. That is the Fano effect manifestation. The exciton dynamical instability in the cadmium dihalide crystals is shown to be caused by energy band structure pecularities. According to the analysis of the absorption curve profiles and antiresonances parameters and types at T = 77 K the matrix element values of the exciton state hybridization with the continuous spectrum states are obtained. A significant dispersion of the antiresonance parameter being caused by the complex structure of the valence bands in cadmium dihalide is discovered.
Interstitial Atom in the Zincblende‐Type Lattice
Authors: Soma T. , Tahata S. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractThe formation energy of an interstitial atom in the zincblende‐type lattice is investigated using the perturbational formalism presented earlier and considering the relaxation effect around the interstitial atom. The interstitial atom Ga or As in GaAs seems favourable at the tetrahedral site neglecting relaxation, but is found to be most stable at the hexagonal site considering the relaxation effect.
Energy Loss Distributions of Relativistic Charged Particles in Crystals
Authors: Kudryashov N. A. , Petrovskii S. V. , Samsonov V. M. , Strikhanov M. N. 
Published: July 2007

AbstractThe kinetic equations are derived which describe the energy loss for fast charged particles with account for their correlated motion in the field of atomic planes and multiple scattering. The numerical calculations for relativistic proton beams demonstrate that for large beam incident angles θ0 > θL (where θL is the Lindhard angle) the energy loss distributions coincide with the Landau theory with good accuracy. At small incidence angles θ0 < θL of a narrow positively charged particle beam the distribution maximum is shifted to anomalously small energy losses. The problem of particle selection according to the small energy loss criterion is considered. A comparison between the theory and experiment is made.
Lattice Dynamics of Binary Alloys
Authors: Gurskii Z. A. , Chushak Ya. G. 
Published: July 2007

AbstractLattice dynamics of binary alloys is investigated by the collective variables method. The relation between a developing technique and the well‐known virtual crystal and coherent potential approximations is analysed. The characteristic property of the theory presented consists in taking into account explicitly the short‐range order. The influence of pair correlations on the vibrational density of states and the Debye temperature for K–Rb alloys is calculated and discussed. The short‐range‐order effects on the dynamic properties are shown to be strong near the order–disorder phase transition temperature.
Calculation of Surface‐Induced Core‐Level Shifts for Covalent Semiconductors C, Si, Ge, and α‐Sn. II. (100) 2 × 1 Surfaces
Authors: Bechstedt F. , Reichardt D. 
Published: July 2007

AbstractThe theory developed for the surface‐induced core‐level shift is applied to (100) 2 × 1 surfaces of group IV materials. The initial‐state potential effect is related to ion charges (of the ground state), changes of the atomic hybridization state, and the polarity of chemical bonds accompanying the atomic configuration due to reconstruction. The many‐body relaxation mechanism is neglected. The atomic configurations are taken from total energy minimizations, dynamical LEED or ion scattering studies. In the case of Si and Ge the results are compared with experimental shifts. A tendency is observed for the confirmation of symmetric dimer formation during the reconstruction.
Determination of the Surface Magnetization of Fe(110) by Spin‐Polarized Low‐Energy Electron Diffraction
Authors: Tamura E. , Feder R. , Waller G. , Gradmann U. 
Published: July 2007

AbstractExchange and spin‐orbit scattering asymmetries of spin‐polarized low‐polarized low‐energy electrons from Fe(110) are measured at room temperature for several beams at constant energies as functions of the polar angle of incidence (“rocking curves”). Corresponding calculations by means of a relativistic multiple scattering formalism gave results in good agreement with the experimental data. The sensitivity of part of the calculated curves to changes in the layer magnetization implies an enhancement of the topmost layer magnetization by about 36 to 40% relative to the bulk and possibly a reduction in the second layer. Further, a dominance of spin‐down over spin‐up inelastic scattering is deduced associated with 3p → 3d excitation.
Hot LO‐Phonon Quasi‐Steady State Distribution Function in Polar Semiconductors
Authors: Král K. , Hejda B. , Khás Z. 
Published: July 2007

AbstractThe quasi‐steady state hot LO‐phonon distribution function, as it is produced by hot electron cooling in laser excitation experiments, is calculated induding the effect of electron energy collision broadening (EECB) and screeing. Numerical computations performed in several compound polar semiconductors reveal a rather strong effect of EECB.