bluuebunny/crossref_metadata_2025 huggingface dataset:
On the deformation model of the carrier spectrum for bismuth‐type crystals I. Electrons
Authors: Jung T. , Braune W.
Published: July 2007

Two methods of parameter determination for a complicated dispersion relation of electrons in bismuth are applied. The dispersion relation employed is obtained by Abrikosov and Falkovskii on the basis of a deformation theory. Discrepancies remaining with respect to energy dispersion in the direction of elongation of the electron part of Fermi surface are analysed and compared with k · p‐model considerations. An extended form of the Abrikosov‐Falkovskii model is presented, which should provide a more precise description of the topology of the electron Fermi surface.
The effects of magnetic field and direct interaction between impurities in the Anderson model resistivity
Authors: Zieliński J.
Published: July 2007

The method of functional derivatives is applied to investigate the Anderson model. It is shown that the presence of magnetic field and the direct interaction between impurities lead to the same form of the low‐temperature resistivity per impurity in arbitrary order of the perturbation series in the symmetric case of the Anderson model. The formal expressions for the first‐ and second‐order (with respect to intraatomic Coulomb interaction) contributions to the d‐electron Green function are given and in the limit of vanishing field (or interaction) the results obtained by Yamada and Yosida are derived. Explicit expressions for the proper self‐energy of the d‐electron are obtained up to the second order and the temperature dependence of the imaginary part of the conduction electron t‐matrix at the Fermi surface is presented.
Influence of crystal lattice defects on the ferroelectric dispersion of triglycine sulphate
Authors: Pawlaczyk Cz. , Luther G. , Müser H. E.
Published: July 2007

The influence of radiation defects and doping on the ferroelectric dispersion in triglycine sulphate (TGS) single crystals is studied. The Cole–Cole plots, temperature dependence of the distribution angle of relaxation times, as well as the temperature dependence of the static dielectric permittivity and the relaxation frequency are given for γ60‐Co irradiated TGS crystals. Deviation from the Debye‐type dispersion in the vicinity of the Curie point is found. The temperature region of this deviation is found to increase with the defect concentration.
Separation of angles in the problem of an exciton bound to an ionized donor in the case of anisotropic effective masses and dielectric constant
Authors: Munschy G. , Stauffer L.
Published: July 2007

The anisotropic exciton–ionized donor complex is studied within the effetive mass approximation. The quantum mechanical formulation of the ground‐state requires a six‐dimensional configuration space, but the problem is reducible from six to three dimensions after separation of the Eulerian angles. It remains only to solve three‐variable wave equations depending on the distances between particles.
Experimental observation of the fermi surface–Brillouin zone interaction in pure zinc by means of X‐ray photoelectron spectroscopy
Authors: Mizutani U. , Kondow T. , Uda M.
Published: July 2007

The 4s–4p valence band of pure zinc is studied by means of X‐ray photoelectron spectroscopy. A fine structure is revealed near the Fermi edge and interpreted in terms of the van Hove singularity due to the Fermi surface–Brillouin zone interaction. The observed peak is attributed to the Fermi surface contacts with the {10.1} zone planes, combined with the electron overlaps across the {10.0} zone planes. This supports the model proposed in the interpretation of the trends of the electronic specific heat coefficients in the h.c.p. Hume‐Rothery alloy phases.
Elastic properties of polytypes
Authors: Geilikman M. B.
Published: July 2007

The elastic moduli of polytypic modifications of close‐packed crystals are calculated. A microscopic calculation of the elastic moduli is made for close‐packing of atoms of the same kind and for tetrahedrally coordinated structures of ZnS‐type crystals. A new variant of a phenomenological approach is suggested, where the requirements of the general theory of internal stresses in crystals are taken into account. Two independent approaches, a microscopic and phenomenologic one, reveal a similar dependence of the elastic moduli on the polytype structure. The elastic energies of various polytypes in stressed states are compared.
Exciton reflection spectra of tetracene single crystals
Authors: Kolendritskii D. D. , Kurik M. V. , Piryatinskii Yu. P.
Published: July 2007

The exciton reflection spectra of free tetracene single crystals and those in optical contact with different substrates (quartz, glass, muscovite) are measured in polarized light at temperatures ranging from 300 to 4.2 K. Peculiarities in the reflection spectra of a free crystal are due to a phase transition in the crystal at 160 K. The phase transition is shown to result from an increase of the crystal internal pressure due to the crystal stress with lowering temperature and leads to the change of the crystal symmetry. The b‐polarized reflection spectra of free and in‐contact crystals show a structure which is related to the exciton effect in the surface region. A weak exciton‐phonon coupling in tetracene is concluded.
Band structure and electronic properties of transition metal hydrides
Authors: Kulikov N. I.
Published: July 2007

A calculation of band structures, densities of states, and Fermi surfaces for 3d‐element hybrides is made. The results of this calculation are compared with the APW calculation by Switendick and the experimental measured values of electronic specific heat, magnetic susceptibility, and optical absorptivity. By using the Gaspari‐Gyorffy theory values of the electron‐phonon coupling constant andTcare calculated. High critical temperatures of superconductivity are predicted for chromium and nickel dihydrides.
Distribution of hyperfine fields and magnetic perturbation in cobalt alloys with 3d transition metals
Authors: Shavishvili T. M. , Kiliptari I. G.
Published: July 2007

Experimental 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 g‐factor in Cd3As2
Authors: Wallace P. R.
Published: July 2007

Using the Bodnar model, the effective mass, density of states, and g‐factor of Cd3As2 are calculated. It is found that the g‐factor is considerably more anisotropic than the effective mass, but decreases sharply with energy in all directions.
Theory of channelling of relativistic particles
Authors: Kumakhov M. A. , Wedell R.
Published: July 2007

The Fokker‐Planck equation and their solution, describing the channeling of relativistic particles in crystals, are obtained. The space and angular distributions are calculated taking multiple scattering and the influence of radiative energy loss into account. The calculations show that thereby “cooling” does not occur.
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

The 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.
Electron states associated with partial dislocations in silicon
Authors: Marklund S.
Published: July 2007

The electron energy bands associated with the glide set 90° and 30° partials in silicon are calculated. Rotations of bonds and shifts in bond lengths are taken into account. The results suggest the possibility of dislocation cores without broken bonds.
Vibrational spectrum of hydrogenated amorphous SiC films
Authors: Wieder H. , Cardona M. , Guarnieri C. R.
Published: July 2007

Infrared 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

The 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

The 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

A 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

Exact 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

Optical 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

The 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

The 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

Experiments 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

The 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

The 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

The 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

To 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

The 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

The 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

On 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

Variational 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

The 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

The 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

The 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

As 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

The 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

The 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

A 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

The 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

For 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

The 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

It 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

The 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.
Bistability and hysteresis phenomena in an optical parametric oscillator
Authors: Lugovoi V. N.
Published: July 2007

The optical parametric oscillator involving the analogue of the inverse Čerenkov effect is considered for the case when the pumping (with a frequency ωp) consists of two plane waves incident at two different angles onto an optical waveguide (terminated by mirrors). Here, a bistability of the oscillator output emission (with frequencies ωs, ωv satisfying the relation ωs + ωr = ωp) and hysteresis phenomena caused by the bistability are shown to be realized. Also, bistability and hysteresis phenomena are shown to appear in the weaves with the frequency ωp reflected from (transmitted through) the waveguide layer, and in the waves with new frequencies 2ωs, 2ωr which are due to the transformation of the pumping in the waveguide layer.
On the theory of the complex dielectric function of a heavily doped degenerate semiconductor
Authors: Quang Doan Nhat , Esser B. , Keiper R.
Published: July 2007

Starting from the Kubo formula the interband part of the complex dielectric function (DF) of a heavily doped degenerate semiconductor is calculated. In the real part of the interband DF a logarithmic singularity is obtained which is smoothed by the random impurity potential into a peak of a finite height. The peak is located at the energy of Burstein‐Moss shift of the imaginary part of the interband DF. The height of the peak is connected with the r.m.s. of the impurity potential fluctuations and particularly an estimate of the impurity concentration might be possible from its measurement.
Ebene Elastostatik anisotroper Medien mit antisymmetrischen Spannungen und ihre Anwendung auf die Theorie des Flußliniengitters
Authors: Eberhardt O.
Published: July 2007

Wie Kröner gezeigt hat, können die Probleme der ebenen Elastostatik isotroper Medien unter Berücksichtigung antisymmetrischer Spannungen so formuliert werden, daß die Verschiebungen und die Spannungsfunktionen Differentialgleichungen von derselben Form genügen. Es wird gezeigt, daß dies auch im allgemoineren Fall der anisotropen Medien möglich ist. Der Greensche Tensor der Verschiebungen und der Spannungsfunktionen für kubische und rhombische Symmetrie wird angegeben. Als Beispiel für die Verwendung antisymmetrischer Spannungen wird die anisotrope Wechselwirkung des Flußliniengitters mit dem Atomgitter in Supraleitern II. Art betrachtet.
Effect of exchange on the impurity magnetoabsorption in zero‐gap Hg1−kMnkTe mixed crystals
Authors: Bastard G. , Rigaux C. , Couder Y. , Thome H. , Mycielski A.
Published: July 2007

Near infrared (ħω>|ϵ0|) and submillimeter magnetotransmission experiments have been performed on zero‐gap Hg1‐kMnkTe alloys (k ≦ 2%). The observation of impurity magnetooptical transitions is crucially dependent on the Mn composition. The experimental results obtained in both the photon energy ranges indicate that the acceptor level is located below the upper valence level bV(−1) for Mn content k ≧ 0.8%.
Raman spectra of lanthanide sesquioxide single crystals with A‐type structure
Authors: Zarembowitch J. , Gouteron J. , Lejus A. M.
Published: July 2007

Phonon data are given for La2O3, Pr2O3, and Nd2O3 single crystals. The polarized Raman spectra of Nd2O3 are presented and analysed according to Pauling's structure: D3d3 (P3ml), Z = 1. A factor group analysis leads to the symmetries 2A1g + 2 Eg for the q = O lattice vibrations which give a non zero contribution in the first order Raman scattering. The experimental data are in complete agreement with these previsions. The four Raman active vibrations are shown to be those of Ln2O(II)2 entities within cages of O(I) atoms, O(I) and O(II) lying in D3d and C3v crystal sites, respectively. There are two stretching (A1g + Eg) and two bending (A1g + Eg) modes, the assignments of which are made. A tentative comparison with the oxysulphides Ln2O2S, which have also a P3ml structure, is presented. A linear correlation is found between the Ln‐O(II) stretching mode frequency of the three studied sesquioxides and the c/a ratio of their hexagonal A‐type structure.
A preliminary study of the electronic structure of uranium chalcogenides and pnictides using a relativistic single‐site scattering model
Authors: Mallett C. P. , Weinberger P.
Published: July 2007

Resonant differential Friedel summands for uranium monopnictides and monochalcogenides are calculated using a fully relativistic single‐site scattering model. It is found that relativistic effects are important in discussing the electronic structure of these compounds, especially for those with heavy non‐metal atoms. The bonding between the uranium and non‐metal constituents is predicted to have considerable covalent character, which increases with atomic number and is particularly important for the heavier group Vb elements. The calculations indicate that the uranium f‐electrons form a narrow well‐localized band.
Raman spectra and the structure of rutile at high pressures
Authors: Hara Y. , Nicol M.
Published: July 2007

Raman spectra of rutile crystals under hydrostatic pressures to 80 kbar and non‐hydrostatic stresses to 155 kbar are reported. Spectral changes near 35 kbar, previously interpreted in terms of a transformation to TiO2 II, are shown to represent an intermediate case between the spectra of a very anharmonic material at low pressures and a relatively harmonic material at pressures greater than 50 kbar.
Local and resonance vibrations in defect polymer solids
Authors: Loghinov A. P.
Published: July 2007

The problem of local and resonance vibrational frequencies in a chain with a large number of degrees of freedom in a unit cell is studied. Repeat unit normal coordinates (RUNC's) are suggested as the most convenient representation for the numerical solution of this problem. The formulas obtained are applied to the calculation of local and resonance vibrational frequencies in a polyethylene chain with a single deuterized unit.
Phase transitions in two‐sublattice biquadratic systems (S = 3/2)
Authors: Błaszczak E. , Westwański B.
Published: July 2007

The (1/z)0‐ and (1/z)1‐approximations are confronted for (1) dipolar susceptibility in the ferri‐antiquadrupolar limit for the Blume‐Emery‐Griffiths interactions, (2) antiquadrupolar susceptibility in the paramagnetic limit for the purely quadrupolar Blume‐Emery‐Griffiths and Heisenberg biquadratic interactions. The critical temperature in the first case is shown to be different than in the corresponding one‐sublattice situation (ferro‐quadrupolar limit). In the second case the critical temperature is compatible with that arising from (one‐sublattice) quadrupolar susceptibility in the paramagnetic limit.
Magnetoreflectance of exciton‐polaritons in cubic II–VI compounds. II. Semiclassical treatment
Authors: Uihlein Ch. , Feierabend S.
Published: July 2007

The magnetoreflectance of a 2 × 4‐fold degenerate S3/2excition is discussed within the semiclassical approach taking account of spatial dispersion and exchange interaction. The reflectance minimum shows a rigid shift behaviour in the Faraday configuration. The energy shift of the reflectance does not depend on the magnitude of the exchange interaction, which is in contrast to the Zeeman splitting of the pure S3/2‐exciton. It is demonstrated that the adequate analysis of magnetoreflectance allows the determination of Δexch + ΔLT and the g‐value g = −5x̃ — gc/2.
Functional integral approach for a doubly degenerate Hubbard model
Authors: Richter A. , Röpke G. , Goedsche F.
Published: July 2007

The method of the functional integral is applied to a doubly degenerate Hubbard model with arbitrarily filled bands. The relation between the number of electrons per atom n, and the chemical potential μ, the local moments, and the static susceptibilities corresponding to the magnetic, orbital, and charge‐ordered states are studied. At zero temperature a phase diagram is obtained in dependence on the electron concentration n, correlation energy U, intra‐atomic exchange energy I, and half bandwidth Δ. The exchange energy is important for the stability of the ferromagnetic state. Additionally to magnetic long‐range ordering an ordering of the orbital states within the ferromagnetic region is possible.
Single‐site theory of Wannier excitons in disordered semiconductors. I. General considerations
Authors: Fischbeck H. J. , Strehlow R.
Published: July 2007

Starting from the general theory of interacting disordered systems a Bethe‐Salpeter equation is derived which describes Wannier excitons in disordered semiconductors. It contains both the Coulomb and the disorder vertex. The former is taken in the static vs approximation whereas the latter is derived from a single‐site approximation. Replacing the Coulomb vertex by an approximate product kernel this equation can be solved. An expression for the imaginary part of the dielectric function is obtained which is accessible to numerical evaluations.
Investigation of the reproducibility of electronic properties in n‐type inverted silicon MOSFET surfaces
Authors: Roos M. , Köhler H.
Published: July 2007

The magneto‐quantum oscillations in the channel resistance as a function of the magnetic field or the gate voltage are used to investigate the reproducibility of the electronic properties in n‐type inverted silicon surface channels depending on the history of the same sample. A model is proposed in order to explain the variable data up to ns ≈︁ 1.5 × 1012 cm−2 for (100) surfaces, where the lowest electric subband edges are less distant than supposed before. The additional assumption of elastic intervalley scattering at low electron concentrations and tunnelling of electrons into traps in the SiO2 near the Si/SiO2 interface allows a thorough discussion of all the properties in the “activated” and “metallic” conduction range. The variable data seem to depend on the density and distribution of trapped electrons deep inside the SiO2.
One‐dimensional ising model with an infinite radius of interaction in a transverse magnetic field. Some thermodynamic properties of the rigorously solvable part
Authors: Georgiev G. I. , Sandalski M. P.
Published: July 2007

The rigorously solvable (quadratic in Fermi creation and annihilation opreators) part of the Hamiltonian of the ID Ising model (S = 1/2) with an infinite radius of interaction is studied in a transversal magnetic field H. After diagonalization of the Hamiltonian, an analytical and numerical investigation is made for the spectrum and some basic thermodynamic quantities at two long‐range interaction laws. The spectrum has some peculiarities; the energy gap vanishes only in the centre of the zone at H = H/cr which leads to singularities in some quantities and is reflected in the phase transition in the model considered. Some dependences of the thermodynamic quantities on H and on the coupling constants are obtained from the numerical data.
Energie dispersive dans les semiconducteurs
Authors: Ance C.
Published: July 2007

Nous avons analysé pour plusieurs semiconducterus l'énergie dispersive Ed, définie dans le modèle de Wemple et Didomenico, en relation avec les énergies covalentes et ioniques Eh et C. Une courbe continue de l'ionicité est donnée en fonction du rapport de deux énergies EA et EB reliées à Eh et C. Le modèle développé par Afromowitz, à partir des moments optiques, est appliquè au composé ternaire Ga1−xAlxSb. A partir de ces résultats, l'énergie du gap moyen Eg est donnée par Eg = D0M/(ϵ1(0) ‐ 1) où M est la contribution des transitions interbandes au moment optique M0.
Electronic structure and optical properties of AlP, AlAs, and AlSb
Authors: Sarkar R. L. , Chatterjee S.
Published: July 2007

The composite wave variational version of the APW method is used in conjunction with the semiempirical tight‐binding interpolation scheme to obtain the electronic band structure and optical absorption characteristics of the compounds AlP, AlAs, and AlSb. The results show that all these materials are indirect band gap semiconductors. The overall feature of the energy bands and the optical characteristics agree fairly well with existing theoretical and experimental results. The implication of the interpolation parameters is also emphasised.
Infrared studies of lattice vibrations in Bi12GeO20 and Bi12SiO20 crystals
Authors: Wojdowski W. , Łukasiewicz T. , Nazarewicz W. , Żmija J.
Published: July 2007

The reflection spectra of Bi12GeO20 and Bi12SiO20 single crystals are studied in the spectral region 50 to 1000 cm−1 at 90 and 300K. Both the single crystals are found to exhibit several reflection bands which are ascribed to the interaction of electromagnetic radiation with normal modes of F‐symmetry in the central region of the Brillouin zone. The frequencies of the longitudinal (LO) and the transverse (TO) component is calculated from the obtained reflection spectra by the Kramers‐Kronig method. The results are compared with Raman data. In order to verify the applicability of the notion of molecular crystal to the compound studied, the frequencies of the normal modes of the groups GeO4 and SiO4 are calculated and the results are compared with the experimental data obtained in this work.
Phenomenological theory of electromagnetic and sound energy attenuation in many‐domain magnetics
Authors: Mitsek A. I. , Sirota D. I. , Kolmakova N. P.
Published: July 2007

The attenuation of the electromagnetic and sound waves interacting with a transitional domain structure in the neighbourhood of orientational phase transitions of the first‐order type is calculated. It is taken into account that the domain wall displacement under wave action is irreversible, i.e. the magnetoelastic or magnetic hysteresis occurs. It is shown that in the general case contributions of reversible and irreversible domain wall displacements into the wave attentuation are not additive.
Electron spin‐echo (ESE) investigations of critical paramagnetic relaxation anomalies in X‐irradiated triglycine sulphate (TGS:X)
Authors: Völkel G. , Brunner W. , Windsch W. , Steudel D.
Published: July 2007

The relaxation behaviour of a stable free radical in X‐irradiated triglycine sulphate is investigated by means of the electron spin‐echo method in the vicinity of the ferroelectric phase transition. A critical behaviour of the transverse relaxation as well as of the longitudinal relaxation is detected. The critical shortening of the phase memory time TM can be explained by the order parameter fluctuations at the phase transition of TGS. To the contrary the spin–lattice relaxation time T1 critically increases at the phase transition. This unusual behaviour cannot be understood on the basis of a direct interaction with the order parameter fluctuations via direct relaxation processes but points at a coupling of the acoustic lattice modes to the ferroelectric relaxational mode.
Comparison between spontaneous radiation in channelling, coherent bremsstrahlung, and synchrotron radiation
Authors: Greschner O. , Wedell R.
Published: July 2007

A detailed comparison is made of the spontaneous radiation in channelling which has been considered recently by Kumakhov, with the coherent bremsstrahlung and the synchrotron radiation. The coherent bremsstrahlung is shown to be suppressed under channelling conditions. It is found that the mechanism of appearance of the Kumakhov radiation differs greatly from that for the coherent bremsstrahlung. The Kumakhov radiation is shown to be more intensive than the synchrotron radiation, especially in the region of high‐energy quanta. It is proposed to set a thin single crystal in the peripheral part of a storage ring in order to obtain intensive fluxes of polarized hard γ‐quanta.
Cluster bethe lattice treatment for phonons in pseudobinary alloy systems
Authors: Kleinert P.
Published: July 2007

The cluster Bethe lattice method is extended to study vibrational properties of pseudobinary alloy systems AB1−cCc. As an example, the phonon density of states and the infrared response function of the alloy system In1−cGacP is calculated. The calculations are in agreement with experimental results. In the approach presented here longitudinal modes do not appear and hence there is not any longitudinal–transversal splitting observed in the first order Raman spectrum.
Disorder‐induced Raman scattering in non‐crystalline films of alkaline‐earth halides
Authors: Harbach F.
Published: July 2007

Above 50 cm−1 the Raman spectrum of quench‐condensed thin films of SrCl2, BaCl2, and BaFCl can be interpreted as a weighted one‐phonon density of states according to the theory of Shuker and Gammon. The weighting emphasizes those normal modes that are related to the Ramanactive F2g mode of the chlorine ions in a fluorite lattice: The maximum of the weighted density of states of non‐crystalline SrCl2 is situated at 180 cm−1, of BaCl2, and BaFCl at 160 cm−1. Above 50 cm−1 the depolarization ratio is approximately frequency independent and fluctuates around 0.5.
Deviations from matthiessen's rule in the low‐temperature resistivity of iron
Authors: Möbius A. , Goedsche F. , Elefant D. , Berthel K.‐H. , Vojta G.
Published: July 2007

The electrical resistivity of iron is measured between 2 and 30 K. The results can be extremely well explained by fitting the data to a simple two‐current model including electron–magnon, electron–phonon, and electron–impurity scattering. Below 10 K large deviations from Matthiessen's rule are observed arising from the two‐current character of the conduction.