bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Intersublattice Molecular Fields in the Rare Earth–Cobalt Intermetallics
Authors: Radwański R. J. 
Published: July 2007

AbstractThe value of 9.27 × 10−23 J for the exchange coupling parameter between the Ho and Co spins in Ho2Co17 has been derived. Some experimental evidence is given to show that the R–T spin coupling parameter is rather insensitive to the kind of the rare earth atom as well as on the cobalt composition. It allows to calculate the intersublattice molecular fields for the rare earth–cobalt intermetalic compounds. This field affects the R magnetic moment and originates from the Co sublattice in the R2Co17, RCo5, R2Co7, RCo3, and RCo2 compounds. The fields in the new magnetic materials of the R2Co14B type have also been evaluated.
Determination of Titanium CNDO Parameters and Application in Cluster Calculations of Different Titanium Compounds
Authors: Haberlandt H. 
Published: July 2007

AbstractElectronic properties of the titanium clusters Ti4(Td) and Ti6(Oh) are calculated by means of the semiempirical quantum chemical CNDO method. The parameters are derived by adjusting the cluster electronic properties to the corresponding bulk data. Comparing the titanium cluster results with those of small nickel clusters calculated using Blyholder parameters, the same trends are observed as in comparing the bulk properties of both metals. An application of the titanium parameters to the calculation of the intermetallic compound Ni3Ti gives a further confirmation of their compatibility with the nickel parameters. Using the derived parameters in TiO2 cluster calculations leads to a satisfactory description of the electronic properties of this material.
Excitonic Absorption in Silicon in the Presence of Low Magnetic Fields
Authors: Donecker J. , Kluge J. 
Published: July 2007

AbstractMagnetic circular dichroism (MCD) measurements are carried out on Si monocrystals in longitudinal magnetic fields up to 5.3 T. Near the indirect excitonic absorption many oscillations occur in the MCD spectra. In comparison with wavelength‐modulated absorption measurements it is shown that the MCD oscillations are due to strongly broadened steps in the absorption edge. The characteristic energies of the absorption steps behave like that of Landau levels with a phenomenological effective mass of m* = 0.38 ± 0.04 for B | [001], obtained also by cyclotron resonance experiments. The energies of the Landau‐like steps converge with B → 0 to energies near the series limit of the exciton. It seems to be the first time that Landau levels in the magnetoabsorption in Si are measured.
Dynamical Screening, Collective Excitations, and Electron–Phonon Interaction in Heterostructures and Semiconductor Quantum Wells. General Theory
Authors: Wendler L. , Pechstedt R. 
Published: July 2007

AbstractA theory of dynamical screening in heterostructures and semiconductor quantum wells is developed which contains electron–electron interaction and electron–phonon interaction. In this theory both the types of long‐wave optical phonons, LO phonons and interface phonons, which occur in those layered structures are included. An expression is derived for the longitudinal screened interaction of subband electrons in heterostructures and quantum‐wells. The obtained screened interaction potential allows the derivation of the total longitudinal dielectric function and the dispersion relation of the coupled intra‐ and intersubband plasmon‐phonon modes. This screened interaction potential is used to develope a dynamically screened and finite‐temperature theory of the electron–phonon interaction in heterostructures and quantum wells. The leading‐order electron self‐energy is disscussed. An analytic expression of the polarization function of the quasi‐two‐dimensional electron gas is calculated within the random‐phase approximation. Further approximations, the plasmon pole approximation and the long‐wave approximation are discussed and the resulting analytic expressions of the polarization function are given.
The Pseudopotential Approach to the Shallow Donor Problem in II–VI Semiconductors
Authors: Grinberg M. 
Published: July 2007

AbstractThe problem of chemical shift of shallow donor states in compound semiconductors is investigated in the framework of pseudopotential theory. The “first principle” pseudo‐Hamiltonian including the electron–phonon interaction for shallow donor is obtained and the one‐band pseudo effective mass approximation is discussed. As an example the ionization energies for several donors in CdS and ZnSe are calculated. A good correspondence between the theory and experimental data for impurities in cation site is found.
Contribution of Medium Phonons to the Transition Probability of Reactive Processes on Solid/Solution Interfaces. Joint Treatment of Classical and Quantum Parts of the Medium
Authors: Engler C. , Rabe E. 
Published: July 2007

AbstractQuantumstatistical calculations are made of transition probabilities for reactive processes on solid/liquid interfaces, which are assisted by multi‐phonon‐transitions of the surrounding medium. A joint treatment of a classical (solvent) and a quantal (lattice) part of the medium effect upon reactive transitions is given. Numerical calculations are carried out in different approximations.
Electron Spin Resonance Studies of Light Sensitive Centers with Tetragonal Symmetry in CaO
Authors: Boas J. F. 
Published: July 2007

AbstractTwo centers with tetragonal symmetry and principal axes along 〈100〉 are observed by ESR in single crystals of CaO. The ESR signal intensity of both the centers is affected by visible light illumination. One center (g∥ = 2.0048, g⟂ = 2.0007) occurs in highly colored crystals and may be associated with carbon impurities introduced during crystal growth. The other (g∥ = 1.99905, g⟂ = 1.99956) occurs in “clear” crystals after 1 MeV electron irradiation and has the characteristics of an anion–cation vacancy pair center containing one electron (i.e. a P− or F center). The g‐values do not agree with those found for the same center in polycrystalline CaO but are consistent with a simple model of a perturbed F+ center.
The Influence of External Effects on the Proton Conductivity of an Hydrogen‐Bonded Chain
Authors: Krasnogolovets V. V. , Tomchuk P. M. 
Published: July 2007

AbstractA theoretical study is made of stimulation of hydrogen‐bonded‐chain‐proton conductivity in a constant longitudinal electric field by light‐and‐ultrasonic effects. The suggested mechanism of light effect is caused by nonactivated phonon transitions of charge carriers from the base level of one knot through an internal excited state to the base state of the neighbouring knot. The suggested mechanism of ultrasonic effect is caused by amplitude increase of acoustic fluctuations of the hydrogen bonded‐chain structure, that modulate the distance between knots, i.e. by increase of the resonance integral overlap of the carrier wave functions.
Plasmon Excitation in the Interaction of Fast Electrons with Metal Surfaces
Authors: Duy Bao Tran Thoai 
Published: July 2007

AbstractThe interaction of fast electrons with semi‐infinite metals is studied within the hydrodynamic model. Retardation effects, damping, and diffuseness of the electron density at the surface are included. The energy loss probability of surface plasmons is calculated for external electron beam travelling parallel to the metal surface. Numerical calculations are carried out for rs = 2 jellium.
Theoretical Analysis of the Oscillatory Diffusivity‐Mobility Ratio in Degenerate n‐InSb in the Presence of a Quantizing Magnetic Field
Authors: Ghatak K. P. , Mondal M. 
Published: July 2007

AbstractAn attempt is made to study theoretically the dependence of the Einstein relation for the diffusivity‐mobility ratio of the electrons on the reciprocal quantizing magnetic field in degenerate n‐InSb on the basis of the fourth order in effective mass theory and taking into account the interactions of the conduction, heavy‐hole, light‐hole and the split‐off bands. The results obtained are then compared to those derived on the basis of the well‐known three‐band Kane model since many authors have continued to use the three‐band Kane model for the same semiconductor. It is observed that the three‐band Kane model for n‐InSb exhibits smaller values of the diffusivity‐mobility ratio and the same ratio shows an oscillatory magnetic field dependence as expected in both the cases, since the origin of the oscillations in the Einstein relation is the same as that of the Shubnikov‐de Haas oscillations. Besides the corresponding results for isotropic parabolic energy bands, both, in the presence and absence of magnetic quantization, are also obtained from the expressions derived.
Many‐Exciton Theory for Multiple Quantum‐Well Structures
Authors: Manzke G. , Henneberger K. , May V. 
Published: July 2007

AbstractThe many‐exciton theory of highly excited semiconductors is reformulated in order to apply it to the case of a quasi two‐dimensional confinement of electrons and holes in a multiple quantum‐well structure. Using simple variational ansatzes for the exciton wave function in the low excitation limit density dependent exciton parameters are calculated for a GaAs‐GaAlAs multiple quantum‐well system. In contrast to bulk material but in agreement with experimental findings a blue shift of the excitonic resonance with increasing excitation intensity is obtained. The results are used to demonstrate nonlinear optical behaviour, especially bistabilities, for such systems.
Accuracy of the Transmission Coefficient across Parabolic Barriers as Obtained from a Generalized WKB Approach
Authors: Berz F. , Morice J. A. 
Published: July 2007

AbstractA comparison is carried out in the case of parabolic potential barriers between the transmission coefficient T obtained from the solution of Schrödinger's equation and the approximate transmission coefficient T(WKB) which is derived from a generalised WKB approach. It is shown that T(WKB) is the first term of the asymptotic expansion of T in powers of 1/X2, with X2 ∼ s \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {U_B } $\end{document}UB, where s is the width of the barrier and UB is the barrier height. Expressions are obtained which give an upper limit \documentclass{article}\pagestyle{empty}\begin{document}$ |\overline {T - T(WKB)}| $\end{document}/T(WKB) of the relative error which occurs when using T(WKB) instead of T for the transmission coefficient. It is seen that in most practical cases this error is fairly small.
Changes in the 119Sn‐site hyperfine field of iron induced by substitutional vanadium and chromium
Authors: Dubiel S. M. 
Published: July 2007

AbstractThe effect of substitutional vanadium (up to 18 at%) and chromium (in the whole composition range) on the average 119Sn‐site hf field, HSn, in metallic iron is investigated using Mössbauer‐effect spectroscopy. From the room temperature measurements for both the impurities it is observed that HSn falls with increasing impurity content much faster than the corresponding 57Fe‐site hf field. For chromium HSn is a nonlinear function of impurity concentration and indicates the following four characteristic ranges: up to x ≈ 10 dHSn/dx ≈ 390 kOe; for 10 ≦ x ≦ 45 dHSn/dx ≈ ≈ 11 kOe; for 45 ≦ x ≦ 65 dHSn/dx ≈ 210 kOe; at x = 72 HSn ≈ 0 and for x ≧ 72 HSn increases with x in a nonlinear way. From the 4.2 K measurements for iron–chromium alloys it follows that HSn passes through a minimum of 27 kOe at x = 83, but it does not compensate completely. This concentration coincides with the spin‐glass state concentrations x = 81 to 84.
Magnetic and structural properties of rapidly quenched iron–boron metallic glasses
Authors: Hermann H. , Mattern N. , Matz W. 
Published: July 2007

AbstractThe structure of rapidly quenched Fe1–xBx amorphous alloys (0.15 ≦ x < 0.25) is considered to be a stochastic arrangement of two kinds of clusters (α‐Fe and t‐Fe3B type short‐range order) and an interface region between them. The corresponding analytical structure model reproduces experimental results on density, small‐angle scattering, and radial distribution functions of atomic distances. Magnetically, each structural component is described by a certain magnetic moment of iron atoms. An expression for the average magnetic moment is derived from the structure model, and the moments of the structural components are determined by means of a least‐square fit to experimental values of the average magnetic moment. The theoretical curve agrees well with the experimental results on the concentration dependence of the average magnetic moment which deviates evidently from a linear behaviour. An extrapolation of structure and average magnetic moment to x = 0 (amorphous pure iron) is not possible at present.
Energy and Absorption Spectra of One‐Dimensional Exciton‐Phonon System
Authors: Sherman A. V. 
Published: July 2007

AbstractBased on the recursion method of the calculation of the Green's function, the energy and absorption spectra of a one‐dimensional system of Frenkel excitons interacting with dispersionless optical phonons are investigated in a wide range of parameters. It is shown that there exist three regions of parameters, which correspond to qualitatively different spectra. In the first region, the spectra reveal the features peculiar to a vibronic exciton. The second region is characterized by the existence of a large number of exciton‐phonon complexes manifesting themselves in absorption. The appearance of such complexes can be regarded as a considerable softening of the chain around excitation. In the third region, coexistence of two types of states is observed throughout the Brillouin zone. The latter are the stable states of an intermediate coupling exciton and the decaying states of a nearly free exciton, the dispersion curve of which is strongly influenced by anticrossing with a peculiarity of a combined exciton‐phonon density of states.
Impurity Breakdown in Germanium at Low Lattice Temperatures
Authors: Pramanik T. K. , Bhattacharya D. P. 
Published: July 2007

AbstractThe kinetic processes which take part in the phenomenon of impurity breakdown in n‐Ge are known to be the impact ionisation of the neutral donor atoms by the relatively energised free electrons and the thermal recombination of the latter. The electric field dependence of the coefficients of these processes, AI(E) and BT(E) is calculated numerically. The calculations are carried out in the approximations of an effective electron temperature and a parabolic law of dispersion. The impurity breakdown characteristics of the material are then investigated. When compared with other calculations and with the available experimental data, the results obtained here show a better agreement in some of the characteristics with the experimental observations. The anomalous type behaviour obtained here in respect of some other characteristic is also discussed.
Sensitized Luminescence of Pure and Doped NaNO2 Single Crystals. II. Time‐Resolved Experiments and Preliminary Analysis
Authors: Pufahl H. , Köhler J. , Schmidt Th. , Schmid D. , Kenkre V. M. 
Published: July 2007

AbstractThe fluorescence decay times of pure NaNO2 and of NaNO2 doped with KNO2 are measured for varying temperature and dopant concentration. Both, time‐resolved and steady measurements are carried out and are found to be in agreement with each other. Energy transfer rates are deduced from the measurements and an attempt is made to interpret them with the help of a generalization of the standard sensitized luminescence theory which includes detrapping effects. The result of this attempt is a strong indication that the rates for trapping and detrapping in NaNO2 are not interrelated via detailed balance and the conclusion drawn is that a deeper theoretical investigation is necessary to analyze the experiment quantitatively. However, a rough estimate of the singlet exciton hopping rate can be made, and is found to be in agreement with the results of an interpretation of the lineshape asymmetry. For triplet excitons in NaNO2, it is shown that it is natural to conclude that energy transfer is motion‐limited and that the motion is one‐dimensional, in agreement with expectations based on the crystal structure of NaNO2.
On the Free Energy of the Hard Sphere Fluid
Authors: Edgal U. F. 
Published: July 2007

AbstractThe equilibrium properties of the hard sphere fluid are investigated in the low/medium density regime by finding upper and lower bounds for the free energy of the system. It is shown that the coincidence of the bounds in the low density limit justifies the Van der Waal's approximation at very low densities. A better approximation is obtained valid for moderately higher densities. Similarities and properties of the equilibrium packing and parking processes are employed, allowing a simple expression to be obtained for the partition function of the hard sphere fluid.
Thermodynamics of Superconductors with Charge‐ and Spin‐Density Waves
Authors: Gabovich A. M. , Gerber A. S. , Shpigel A. S. 
Published: July 2007

AbstractUsing thermal Green's function technique the thermodynamics of superconductors with charge‐ and spin‐density waves is considered. The Δ/Tc ratio and the paramagnetic limit Hp are calculated for various values of the dielectric gap σ and the parameter ν = Nnd(0)/Nd(0), where Nnd(0) and Nd(0) are the electron densities of states for non‐dielectrized and dielectrized Fermi surface sections, Δ(0) is the zero‐temperature value of the superconducting order parameters, and Tc is the critical temperature. It is shown that for the charge‐density wave‐superconductors the values Δ(0)/Tc are substantially less than in the conventional BCS theory. The theoretical conclusions are in a good agreement with the experiment.
Dispersion and Damping Properties of Plasmon Polaritons in Superlattice Structures. I. Infinite Superlattice
Authors: Haupt R. , Wendler L. 
Published: July 2007

AbstractThe dispersion and damping properties of plasmon polaritons in infinite superlattices are analyzed using a local theory with retardation. The band structure and the zone folding of the plasmon polaritons are discussed. It is shown that in a definite range of the thickness ratio of the single‐layers of the superlattice a degeneracy point of the two interface‐like plasmon‐polariton bands occurs. An analytic expression for the damping function is derived by means of a perturbative method. The different behaviour of the damping of plasmon polaritons in various infinite superlattice structures is discussed. The dispersion curves and the damping function are calculated and presented in graphical form.
Spectrum of Excitations of an Easy‐Plane Ferromagnet (S = 3/2) in a Magnetic Field
Authors: Valkov V. V. , Valkova T. A. , Ovchinnikov S. G. 
Published: July 2007

AbstractThe quantum spectrum of elementary excitations of easy‐plane ferromagnet with S = 3/2 in a magnetic field is calculated by the diagram technique for Hubbard operators. It is established that the collective excitation spectrum in the low‐temperature region consists of one longitudinal and two transverse branches. The limiting cases of strong and weak anisotropy are analysed in detail. In the region of small values of quasimomentum the intervals are determined in whose limits the ω(q) dependence is quadratic and linear in quasimomentum modulus.
Transport Properties of Ferrous Oxide Fe1−yO at High Temperature
Authors: Molenda J. , Stokłosa A. , Znamirowski W. 
Published: July 2007

AbstractElectrical conductivity and thermoelectric power of ferrous oxide are measured as a function of temperature (1090 to 1580 K) and oxygen pressure in the whole range of its stability. The results are analysed with reference to the measurements of its deviation from stoichiometry. It is shown that at temperatures exceeding 1070 K the total electrical conductivity of Fe1−yO is a sum of intrinsic and extrinsic conductivity related to the ionic defect concentration. It is shown that a simple band model is insufficient to describe the electrical properties of Fe1−yO. A semiconductor–metal transition is revealed in Fe1−yO. The semiconductor–metal transition corresponds to the stability limits of wustite pseudophases (w1, w2). A qualitative model of electronic structure of Fe1−yO is proposed.
Investigation of p‐CdTe and p‐ZnxCd1−xTe Single Crystals by ps‐Laser‐Induced Gratings and by Photoluminescence
Authors: Rückmann I. , Petrauskas M. , Netikšis V. , Tamulaitis G. , Halfpap J. 
Published: July 2007

AbstractFrom the measured erasure times of transient gratings created in the volume and on the surface of non‐intentionally doped p‐type CdTe and ZnxCd1−xTe (x ≦ 0.11) single crystals the free‐carrier lifetime and the surface recombination velocity at room temperature are determined, respectively. The erasure time of the surface grating in CdTe is found to be 130 ps, which is one order smaller than that of the volume grating. A lifetime shortening is observed in mixed crystal. Moreover, using cw‐laser excitation the samples are characterized additionally by photoluminescence investigation at low temperatures to test the quality, to determine the mole fraction, and to identify impurities. The A0X‐line observed is interpreted as due to a single acceptor on Te site. In the mixed crystals at x ≧ 0.09 the two‐mode behaviour of LO‐phonons and an up to now not observed splitting of the A0X‐line are found.
X‐Ray Dynamical Diffraction in Crystals Being Subjected to the Action of Ultrasonic Waves
Authors: Polikarpov I. V. , Skadorov V. V. 
Published: July 2007

AbstractA dynamical theory is given of X‐ray diffraction in crystals being subjected to the action of longitudinal or transversal ultrasonic waves. Analytical expressions for the X‐ray field diffracted on nonstationary crystals in Bragg and Laue geometry are obtained.
Aggregation Kinetics of Divalent Impurity–Vacancy Dipoles in Alkali‐Halide Matrix. II. KCl:Eu2+ System
Authors: Berg G. , Poźniak J. , Macalik B. 
Published: July 2007

AbstractThe decay curves of the Eu2+–cation vacancy dipole concentration in KCl crystals isothermally annealed at 75, 100, 140, and 240 °C are presented. On the basis of a theoretical model discussed in Part I, the rate constants of association and dissociation of the dimers and trimers as well as the enthalpy of these reactions are evaluated.
Intramolecular Excitation Dynamics in a Thermalized Chain. I. Formation of Autolocalized States in a Cyclic Chain
Authors: Kadantsev V. N. , Lupichov L. N. , Savin A. V. 
Published: July 2007

AbstractA numerical study of the Davydov soliton dynamics in a thermalized cyclic molecular chain is performed. Account is taken of the effect of thermalized molecular vibrations within the scope of the quantum‐mechanical theory. It is shown in contrast to results of a number of works, where account of the thermal vibration effect is taken within the framework of the classical model, that using the quantum‐mechanical description the thermal vibrations not only don't prevent but also favour autolocalization of intramolecular excitation.
The Influence of Next‐Nearest‐Neighbour Exchange Coupling on the Spin‐Wave Resonance Spectrum in Uniaxial Ferromagnetic Thin Films
Authors: Duda A. 
Published: July 2007

AbstractThe spin‐wave resonance spectrum is calculated for a uniaxial ferromagnetic thin film with both' nearest‐neighbour and next‐nearest‐neighbour exchange coupling. The profiles of the resonance modes, the positions of the absorption lines, and their intensities are analysed for various values of the nnn coupling parameter. It is found that the spectrum is strongly affected by the nnn coupling, especially by the coupling of antiferromagnetic type.