bluuebunny/crossref_metadata_2025_split huggingface dataset:
Distribution of hyperfine fields and magnetic perturbation in cobalt alloys with 3d transition metals
Authors: Shavishvili T. M. , Kiliptari I. G. 
Published: July 2007

AbstractExperimental study of 59Co NMR spectra in binary ferromagnetic Co based f.c.c. alloys with 3d transition metals is made. The analysis of the dilute alloys spectra based on the relation between the hyperfine field and the average saturation magnetization makes possible: (i) to determine the conduction electron spin‐density oscillation in the Co matrix, (ii) to obtain information about the host‐moment perturbation, and (iii) to define more precisely the magnitudes of the change in magnetization per impurity atom and the values of magnetic moments on the solute for several alloys. The hyperfine field shifts obtained in a much more consistent way than it was done previously allow to describe dilute alloys spectra in a simple additivity model. Unusual spectra of CoMn alloys are attributed to the indefiniteness of Mn moments.
Electronic structure and optical properties of rhombohedral arsenic and their variations with the internal displacement parameter
Authors: Vaidyanathan A. , Tsay Y. F. , Mitra S. S. 
Published: July 2007

AbstractThe electronic band structure, density of states, and imaginary part of the dielectric function of rhombohedral As are calculated using the empirical pseudopotential method. The electronic density of states are calculated for five different values of the internal displacement parameter u, and the results are added, weighted by a Gaussian probability distribution in u. The resulting density of states is compared with that of rhombohedral and amorphous As. The imaginary part of the dielectric function of the distorted crystal is calculated using the above density of states along with the nondirect transition model and energy dependent matrix elements. A Kramers‐Kronig transformation is performed to obtain the real part of the dielectric function. Finally, the absorption coefficient of the distorted crystal is calculated. The optical constants of the distorted crystal are compared with those of rhombohedral and amorphous As.
Vibrational spectrum of hydrogenated amorphous SiC films
Authors: Wieder H. , Cardona M. , Guarnieri C. R. 
Published: July 2007

AbstractInfrared absorption spectra are presented of amorphous Si1−xCx films made by the glow discharge process. Four bands, representing the stretching modes of SiH, CH, and SiC, and the wagging mode of SiCH3, were followed over the entire alloy composition range. It is shown that the compositional dependence of these bands varies in a manner predicted by a model in which Si and C atoms are randomly distributed throughout the film without chemical ordering. The bonded hydrogen content in the films is estimated to be of the order of 20 to 30 at%, depending on composition, with the silicon atoms bonding to a single hydrogen and the carbons bonding predominantly as CH2 and CH3 groups.
Born approximation in the Nakajima‐Zwanzig generalized master equation for the coupled coherent and incoherent exciton motion
Authors: Reineker P. , Kühne R. 
Published: July 2007

AbstractThe kernel of the Nakajima‐Zwanzig generalized master equation is derived within the Born approximation for the coupled coherent and incoherent exciton motion described according to the Haken‐Strobl model. It is shown that this generalized master equation in nearest neighbour approximation and the continuum limit is equivalent to a differential equation, which approximately has the form of a telegraphers equation. Furthermore, the kernel of the master equation in the Born approximation is compared with the exact calculated kernel for the coupled coherent and incoherent exciton motion on a linear chain. It is shown that the Born approximation modifies as well the behaviour of the kernel in space as that in time. These modifications are most distinct in the coherent limit of the exciton motion.
Surface states on Si(lll) 7 × 7 studied by low‐energy electron loss spectroscopy
Authors: Lieske N. , Hezel R. 
Published: July 2007

AbstractThe clean Si(lll) 7 × 7 surface is studied by low‐energy electron diffraction (LEED), Auger electron spectroscopy (AES), and low‐energy electron loss spectroscopy (ELS). For primary energies up to 100 eV the ELS spectra show more characteristic loss peaks than the spectra published until now. The spectra are interpreted using the dielectric model, the density‐of‐states model, and the interband excitation model applied to the surface energy band structure calculated by Pandey and Phillips. As a result the majority of the characteristic energy losses are due to electron interband transitions from filled surface states into empty surface or volume states. In contrast to that, most of the observed loss peaks for higher primary energies, as demonstrated for 400 eV, can be interpreted as interband transitions from volume to volume states.
On the deformation model of the carrier spectrum for bismuth‐type crystals II. Holes
Authors: Jung T. , Braune W. 
Published: July 2007

AbstractA decisive advantage of the deformation theory of the carrier spectrum in bismuth — the consistent description of electrons at the L‐points and holes at the T‐points of the Brillouin zone — is pointed out. Deficiencies of the model which are specific for the dispersion in the vicinity of T‐points are analysed. An extended form of the deformation theory is presented and applied to bismuth data. A much better agreement with experimental data is obtained, demonstrating the efficiency of the deformation method.
The virial theorem for the jellium model of metal surfaces
Authors: Heinrichs J. 
Published: July 2007

AbstractExact general expressions of the virial theorem for bounded jellium systems are derived. Finite jellium systems, in contrast to infinite, unbounded ones are in equilibrium as a result of the dipole charge layer at the surface. This implies that the shape of the surface enclosing the jellium is important in the derivation of explicit forms of the virial theorem, and various cases are considered. The generalization of the Budd‐Vannimenus theorem in the case of a spherical surface is also discussed. A recent analysis of the virial theorem by Vannimenus and Budd is commented upon.
Optical properties of metal aggregates in Li+ and K+ irradiated MgO crystals
Authors: Marichy G. , Chassagne G. , Durand D. 
Published: July 2007

AbstractOptical absorption spectra of MgO crystals irradiated with high energy (250 to 450 keV) alkali ions (Li+, K+) present two bands of colloidal nature after thermal annealing of the crystal. Mie theory cannot represent all the features of this behaviour which are related to the very high dose (5 × 1016 to 1017 ions/cm2) possible to get with such a technique (up to 1022 cm−3 implanted ions). The results are interpreted using Maxwell‐Garnett theory applied to a granular metal film embedded in a dielectric host and it is possible to attribute the two observed absorption bands to plasma resonance and optical conduction absorption of the metal precipitate.
Energy band structure of Cd3P2 for real D symmetry I. Energy bands
Authors: Plenkiewicz P. , Dowgiałło‐Plenkiewicz B. 
Published: July 2007

AbstractThe pseudopotential method is used to calculate a band structure model of Cd3P2 for real tetragonal D symmetry. The calculations are performed without spin‐orbit interaction. The resulting band model is discussed and compared to the experimental data of other authors.
Temperature‐dependent density of states of n‐GaAs
Authors: Lamfried W. H. 
Published: July 2007

AbstractThe electronic density of states for nonzero temperature is calculated using the model of shortranged impurity potentials. The investigated impurity densities are limited by the maximum value n1 at which the impurity‐to‐band activation energy becomes zero. It is shown that in the case of n‐GaAs, both classical statistics and the RPA are applicable in a wide range of temperature to such doping. Thus it is possible to incorporate the screening into the model and to calculate the density of states, the activation energy, the screening, and the chemical potential in a self‐consistent manner.
First‐order resonant Raman scattering in mixed silver halides
Authors: Koumvakalis N. , von der Osten W. 
Published: July 2007

AbstractExperiments of resonant Raman scattering in mixed crystals of AgBr:AgCl at low temperatures are performed. The spectra of the mixed crystals differ in a qualitative fashion from the spectra of pure AgBr. In particular, strong first‐order resonant Raman scattering is reported hitherto not observed. The results can be interpreted in terms of a relaxation in the momentum conservation caused by the perturbing system. Intervalley scattering by TA(X) and LA(X) phonons and intraband scattering by LO(Γ) phonons are found to be effective relaxation mechanisms for the exciton.
The electronic structure of the bound exciton and bound multiexciton complexes in Al‐doped Si
Authors: Kulakovskii V. D. , Malyavkin A. V. 
Published: July 2007

AbstractThe bound exciton (BE) and bound multiexciton complexes (BMEC) luminescence in Al doped Si under uniaxial stress and in an external magnetic field is investigated to study the effects of a j–j coupling of holes. The energetic scheme of the levels of BE and BMEC is established, g‐factors of bound electrons and holes, and the constants of deformation potential for neutral acceptor (NA), BE and BMEC are determined. It is found that in stressed Al doped Si there is no thermal equilibrium between the BE including the electrons electronic from the lowest valleys and those lifted by stress. A few experimental dependences of the BE emission lines intensities on the applied stress are in contradiction with the accepted BE model.
The effect of retarded interaction on the self‐induced transparency phenomenon
Authors: Nagibarov V. R. , Khasanov O. Kh. 
Published: July 2007

AbstractThe influence of the retarded part of Coulomb interaction between particles on the self‐induced transparency phenomenon is considered. This type of interaction is taken into account by introducing an effective dipole moment of an atom. Expressions for pulse area, absorption coefficient, and macroscopic medium polarization are derived. The area theorem is extended to include the retarded interaction. Estimates of the dipole moment and pulse delay are obtained. It is shown that the above parameters are substantially influenced by inhomogeneous broadening by the medium and the active centre concentration therein.
On the origin of localized magnetic states in transition metal alloys I. Wolff model
Authors: Morkowski J. , Oleś A. M. 
Published: July 2007

AbstractThe generalized Wolff Hamiltonian is solved in approximations which are exact in the limit of isolated impurity. It is shown that approximations analogical to those developed by Hubbard in the narrow band Hamiltonian overestimate the effect of Coulomb correlations. The formation of localized magnetic moments is described in the selfconsistent approach, which conserves first four moments of the spectral density function. The results indicate that the degeneracy of impurity levels is essential for transition metal systems.
Exciton—phonon interaction in the degenerate‐band case
Authors: Trebin H.‐R. 
Published: July 2007

AbstractTo consider the combined effect of valence‐band degeneracy and polar electron‐phonon interaction on the exciton binding energy in tetrahedral semiconductors two methods are generalized that have been introduced by Haken for the case of single isotropic parabolic energy bands. The first of these methods starts from polarons that form the exciton, while the second couples the bare exciton to the phonon field. In both methods the spherical part of the Luttinger matrix is used to describe the kinetic energy of the hole. There result effective Hamiltonians in configurationspin space with phonon‐induced electron‐hole interaction potentials. These consist essentially of Haken's potentials averaged over light and heavy hole bands but also contain a tensor force term. Renormalized masses must be inserted in the kinetic energy part only in the first method where the polaron is the starting point.
Resonance scattering of phonons in inhomogeneously strained n‐Ge
Authors: Singh S. , Verma G. S. 
Published: July 2007

AbstractThe resonant scattering of phonons in Sb‐doped Ge is quantitatively explained on the basis of Kwok's theory as extended by Suzuki and Mikoshiba. These expressions are modified for inhomogeneously strained n‐Ge and are used to explain the anomalous results of the strained sample for which 4Δ varies from (4Δ)min to (4Δ)max. The experimental results of the sample Sb‐306, which is believed to be inhomogeneously strained, are explained with 4Δ1 = 0.1meV, 4Δ2 = 0.32 meV, and 4Δ3 = 0.42 meV with same sharing of the electron‐phonon scattering rate such that the weighting factors are given by p1 = p2 = p3 = 1/3, where p1 + p2 + p3 = 1.
On the “anomalous” curvature of the diffusion plot of bromine in AgBr
Authors: Varotsos P. , Alexopoulos K. 
Published: July 2007

AbstractThe excessive increase of cation Frenkel defects in AgBr near the melting point should supress the number of anion vacancies through the mass action law. Therefore a downward curvature in the bromine diffusion plot would be expected whereas the experiments show a strong upward curvature. It is shown that this “anomaly” is a consequence of the usual assumption that the Schottky‐Gibbs formation energy g decreases linearly with temperature. Furthermore it is shown that g has to decrease (with temperature) faster than linearly in such a way that the term (g/2) — g exhibits an excessive decrease with temperature. Therefore the concentration of anion vacancies shows an excessive increase nea the melting poing and hence the bromine diffusion plot has to show an upward curvature. Another contribution — but a smaller one — to this curvature is the non‐linear decrease of the migration Gibbs energy of a free anion vacancy with the temperature.
Magnetoplasma Waves in Bismuth and Semimetallic BiSb Alloys at Microwave Frequencies 9 to 100 GHz
Authors: Braune W. , Schneider W. , Lebech J. , Saermark K. 
Published: July 2007

AbstractOn the first time extensive investigation of magnetoplasma waves is reported for the whole semimetallic range of the alloy BiSb (0 ≦ x ⪅ 6 at% Sb). It is possible to deduce the qualitative, in some cases as well the quantitative, behaviour with alloy composition of the so‐called mass‐density function under the condition that this quantity is independent of the applied magnetic field. This is achieved by appropriate variation of the microwave frequency in the range 9 to 106 GHz, the sample thickness and, finally, the field configuration of the measurement. The determination of the magnetic field independent mass density function turns out to be difficult for alloys with an antimony concentration close to the one for the semimetallic to semiconducting phase transition.
Hydrogen‐Like Systems in Arbitrary Magnetic Fields A Variational Approch
Authors: Aldrich C. , Greene R. L. 
Published: July 2007

AbstractVariational calculations using a cylindrica Gaussian basis are applied to the problem of hydrogenlike systems in an arbitary magnetic feld. This choic of basis functions allows us to calculate energies and dipole matrix elements for levels corresponding to the ls through 4f levels of the free hydrogen atom. Comparison of the results with earlier calculations in both the high and low field limit show excellent agreement. In the intermediate field regime two previous calculations show marked disargreement in one of the excited state energies. Our results are in agreement with the results of Lee et al.
Self‐Consistency in the Calculation of Electron Effective Mass
Authors: Halder N. C. 
Published: July 2007

AbstractThe self‐consistency of the energy in powers of the nonlocal, energy dependent pseudopotential equation in perturbation series is examined. An appropiate expression for the electron effective mass is derived from the well‐known parameters in band structure. The present results are interpreted in context to the results obtained earlier by different methods.
Evaluation of Third‐Order Elastic Constants and Pressure Dependence of Second‐Order Elastic Constants of Ionic Crystals
Authors: Singh R. P. , Shanker J. 
Published: July 2007

AbstractThe third order elastic constants and the pressure dependence of second‐order elastic constants are evaluated for alkali halides with NaCl and CsCl structures, and for alkaline earth oxides with NaCl structure on the basis of the Löwdin‐Lundqvist three‐body potential theory for ionic solids. The potential parameters are derived from the knowledge of the overlap integrals. An exponential form suggested by Cochran is used for the variation of the three‐body overlap parameter. It is considered that the second‐neighbour repulsive as well as the van der Waals interactions contribute to the short‐range energy. The analysis presented uses only two parameters and determines six third‐order elastic constants, three pressure derivatives of second‐order elastic constants, and the cohesive energy of 22 crystals. The results obtained are in good agreement with experimental data.
Dynamical Effects in Inelastic Scattering of Thermal Neutrons by a Crystal
Authors: Dzyublik A. Ya. 
Published: July 2007

AbstractThe cross‐section for one‐phonon inelastic scattering of thermal neutrons by a perfect crystal slab with simple cubic lattice is calculated taking into account multiple elastic collisions of neutrons with atoms and also the role of atomic vibrations in elastic diffraction. The pendellösung effect in the one‐phonon peak is considered when the Bragg condition corresponding to Laue diffraction is fulfilled for the incident wave.
Propagation of Electromagnetic Waves in a Direction Perpendicular to the Magnetic Field in Semiconductive BiSb Alloys II. B ⊥ C2 ∥ k
Authors: Stegmann R. , Oelgart G. , Herrmann R. 
Published: July 2007

AbstractAs a supplement to a previous work the wave propagation is shown to exist within the entire binary plane. The polarization of the wave in the material is discussed as a function of the external magnetic field. In the quasi‐classical case, the anisotropy of the spatial resonance field values of the waves decreases due to the redistribution effects of the carrier between the individual parts of the Fermi surface.
Magnetic Interactions in α‐MnSO4 and β‐MnSeO4
Authors: Wegener W. , Vanderhaeghen J. , Scheerlinck D. , Hautecler S. , Legrand E. , Will G. 
Published: July 2007

AbstractThe energy distributions of neutrons scattered by α‐MnSO4 and β‐MnSeO4 in their paramagnetic state are measured by means of a time‐of‐flight technique. From a simultaneous analysis of the second moment of these energy distributions and of the Néel temperature computed in the Green's function approximation it is concluded that the exchange interactions between fourth neighbours play an important role in these manganese compounds. Values for J1 and J4 are obtained from which reasonable values for Θ and χ(TN) are predicted in the case of α‐MnSO4.
Valence Instabilities in CeSn3 and YbAl3
Authors: Buschow K. H. J. , Goebel U. , Dormann E. 
Published: July 2007

AbstractThe 27Al NMR in YbAl3 is studied by spin echo techniques in the temperature range 4.2 to 300 K. The temperature dependence of the Knight shift exhibits a minimum close to the temperature where the susceptibility shows a maximum. A comparison is made with NMR and susceptibility data of CeSn3. For CeSn3 supplementary susceptibility measurements are made in the range 300 to 650 K. All data are analysed in terms of a two‐level model with a nonmagnetic ground state and excited state with a degeneracy of 2J + 1. This excited state, corresponding to the 3+ integral valence state, largely determines the magnetic properties of these systems. The quadrupolar splitting of the 27Al NMR in YbAl3 is independent of temperature over the whole temperature range considered. Thus, it is concluded that the presumed change in valence of Yb with temperature does not involve major changes in charge distribution around the Yb atoms.
A Quasi‐Polycrystalline Approximation for Electronic States in Liquid Transition Metals and Tetrahedrally Bonded Semiconductors
Authors: Brown D. , Fairbairn S. , Morgan G. J. 
Published: July 2007

AbstractA simple method, analogous to the Thomas‐Fermi approximation, is described for constructing approximations to electronic states in structurally disordered ‘solids’ when at least part of the Hamiltonian may be represented in terms of localised orbitals and when the range of interaction of the orbitals is comparable with short‐range order present in the solid. A resistivity formula is also proposed for liquid transition metals.
Theoretical Calculation of the Electron‐Phonon Coupling Parameters of the F‐Centre in Alkali Halides
Authors: Dochy F. 
Published: July 2007

AbstractThe coupling parameters of the F‐centre to lattice modes of cubic, tetragonal, and trigonal symmetry are calculated using the pseudopotential theory of Bartram, Stoneham, and Gash, for all 20 alkali‐halides. Different analytical forms for the trial pseudo wave function are used. The results are compared with uniaxial stress and hydrostatic pressure experiments. General trends for the whole series of alkali‐halides agree with experiments.
Electronic Structure of Ti2O3 from Single Crystal Thermoreflectance Spectroscopy
Authors: Bianconi A. , Stizza S. , Bernardini R. , Nannarone S. 
Published: July 2007

AbstractFor the first time studies are made of the polarized thermoreflectance of an oriented Ti2O3 single crystal. The spectra in the photon energy range 1 to 3.5 eV are taken at room and liquid nitrogen temperature. Optical transitions involving the 3d electrons, which play a crucial role in the semiconductor‐to‐metal transition, are studied. The optical transition at 2.9 eV is identified as a transition at a M2 critical point by Kramers‐Kronig analysis of the thermoreflectance spectra. A clear evidence of a plasmon excitation at 1.82 eV in the semiconducting Ti2O3 is reported. The temperature shift of the bands is in agreement with the band‐crossing model of the semiconductor‐to‐metal phase transition.
Eu2+ Luminescence in KY3F10
Authors: Boulon G. , Gacon J. C. , Trottier D. , Vedrine A. 
Published: July 2007

AbstractThe luminescent properties of divalent europium in KY3F10 are investigated. Emission and excitation spectra and decay‐time measurements are presented. The nature of the Eu2+ centres responsible for the observed luminescence is discussed. It is concluded that KY3F10:Eu2+ is a possible candidate for an ultraviolet solid state laser.
LO Phonon Raman Lineshape in Highly Excited GaAs
Authors: Turtelli R. S. , de Castro A. R. B. 
Published: July 2007

AbstractIt is shown that the LO phonon Raman line in bulk GaAs excited with pulsed IR radiation of high intensity is shifted, broadened, and distorted. The TO line is not affected. These phenomena cannot be explained by trivial lattice heating but are quantitatively accounted for by invoking mixing of the LO phonons with photo‐excited carrier collective modes.
Problems of the OPW method. I. Transition metals
Authors: Farberovich O. V. , Kurganskii S. I. , Domashevskaya E. P. 
Published: July 2007

AbstractThe main problems of the OPW method are discussed including (a) consideration of core states; (b) effect of overlap of wave functions of external core states upon the band structure; (c) calculation of d‐type states. The modified orthogonal plane wave method (MOPW method) of Deegan and Twose is applied in a general form to solve the problems of the usual OPW method. For the first time the influence on the spectrum of the main parameters of the MOPW method is studied systematically by calculating the electronic energy spectrum in the transition metals Nb and V.