bluuebunny/crossref_metadata_2025_split huggingface dataset:
Superconductivity and phonon softening in instable systems
Authors: Postnikov V. S. , Postnikov V. V. , Fedorov V. M. 
Published: July 2007

AbstractThe effect of softening of phonon modes on the coupling parameter λ for superconductors with strong electron—phonon interaction is considered by taking into account electron effects. New formulae are derived which relates the increase in coupling parameter with optical phonons λopt for the PdH system and the increase in the parameter λ for A3B‐superconductors with A15‐structure to changes in the density of states at the Fermi level. Using these formulae the role of electron factor N(0) G2 in the increasing of superconductive transition temperature Tc is discussed for the most high temperature superconductors.
The electronic structure of MgO I. Calculation method
Authors: Abarenkov I. V. , Antonova I. M. 
Published: July 2007

AbstractA method for calculating the electronic structure of an ionic crystal is developed which is an approximated self‐consistent field method. In this method the concept of an ion in crystal is used and a variational principle for the energy is employed. The method proposed is useful especially when applied to a crystal such as MgO where the corresponding free negative ion is unstable.
Study of initial stages of F‐centre aggregation in NaCl by Raman scattering
Authors: Ghomi M. , Rzepka E. , Taurel L. 
Published: July 2007

AbstractRaman spectra of F‐centres in NaCl are very dependent on colouration method. First‐order spectra of “isolated” F‐centres are very well interpreted when a 70 and 10% softening in the interionic force constant between the F‐centre and its 1 nn's and between its 1 nn's and 4 nn's, respectively, is considered and if the electron‐phonen interaction is extended up to the 5th ion shell. At the very initial stage of colloidal aggregate formation, the change of the Γ Raman spectrum may be interpreted assuming F‐centre clusters whose sizesare likely much smaller than the laser wavelength.
The influence of the valley splitting and lineshape in the density of states on the quantum oscillations of n‐type (100) inverted silicon MOSFET surfaces
Authors: Köhler H. , Roos M. 
Published: July 2007

AbstractQuantum oscillations in the channel resistance of n‐type inverted silicon (100) surfaces are investigated in quantizing magnetic fields up to 10 T as a function of the electron concentration ns. The data obtained at various tilt angles of the samples in the magnetic field are simulated numerically for ns ≧ 1 × 1012 cm−2, leaving out of consideration the range below this electron concentration, where the influence of many‐body effects is regarded to be important. The results are in good agreement with previous findings for the magnitude of the spin and valley splittings, and confirm the theoretical predictions about the lineshapes in the density of states as a function of the energy.
Temperature dependence of the electrical resistivity of disordered alloys
Authors: Richter J. , Schiller W. 
Published: July 2007

AbstractThe temperature dependence of the electrical resistivity of disordered alloys is investigated using a modified version of the model of Chen, Weisz, and Sher. Within this model the mechanism of negative temperature coefficients is discussed. For the relation between the temperature coefficient of the resistivity and the resistivity itself a qualitative agreement of the theoretical results and Mooij's experimentally observed universal rule is found.
Isomer shift of Eu2+ in fluorites
Authors: Schroeer D. , Kuo Ch. S. , Lambe R. L. 
Published: July 2007

AbstractMössbauer studies are carried out for divalent europium as dopant in the fluorites CaF2, SrF2, and BaF2. The 151Eu Mössbauer isomer shift in these materials increases, increases and decreases, respectively, as the Eu2+ concentration decreases below a few mole percent. Previous explanations of these effects as due to lattice pressure or host covalency are found to be wrong. Instead these trends are interpreted as primarily due to variations in the admixture of the prevalent defect structure of Eu2+OF (i = 1, 2, 3, or 4) which stabilizes the Eu2+ in these crystals.
Reaction field approximation for the ordered phase of heisenberg systems
Authors: Gusmão M. A. , Scherer C. 
Published: July 2007

AbstractThe approximation method to obtain the static properties of a system of interacting localized magnetic moments, called “reaction field approximation” (RFA), which is previously used for the paramagnetic phase, is extended to cover the ordered phase of a spin system with Heisenberg interaction. The presence of a small anisotropy is also considered and an application to MnF2 is made.
TO Phonon–Helicon Coupling in Polar Semiconductors
Authors: Sato K. , Kobayashi M. , Iwabuchi S. , Yokota I. 
Published: July 2007

AbstractTO‐phonons coupled with helicons in a polar semiconductor are studied in detail in the Faraday configuration by the method of Green's functions technique, and are numerically analyzed for n‐InSb in two cases when the crossing would occur in‐ and out‐of‐Doppler shifted cyclotron resonance region, respectively.
On Singlet–Triplet Ferromagnet Dynamics
Authors: Szczepaniak E. 
Published: July 2007

AbstractThe spectral density method (SDM) is applied to the singlet–triplet model in the ferromagnetic region. The energy spectrum of the system and one‐site averages are obtained. A detailed analysis of these quantities at T = 0 is performed. The energy spectrum has two branches and at T = 0 two cases can be distinguished: the one when the two branches are positive, corresponding to the ferromagnetic and fully magnetized ground state, and the other when the two branches have opposite signs corresponding to the ferromagnetic but not fully magnetized ground state. Comparison between SDM and RPA results shows that RPA neglects transversal correlations in contradiction to SDM.
Anomalies in Thermal Expansion and Heat Capacity of Ferromagnets
Authors: Gurevich M. E. , Mitsek A. I. , Zhuravlev A. F. 
Published: July 2007

AbstractPolymorphic transformations (PT) f.c.c. → h.c.p. in Co are investigated on the basis of Born's thermodynamic theory. The spontaneous deformation u23 is the PT parameter; the volume exchange ω is the additional variable. The PT problem is reduced to Landau's theory with the variable u23. The elastic moduli in this case are: (C11 – C12) → 0 and C44(T) = −C44(T) in the point T = T00 (T00 is the point of the instability). The maxima of the thermal expansion coefficient (TEC) and the elastic moduli as functions of T are calculated in the case of the first‐order PT. TEC anomalies are calculated by the method of near the orientational phase transition (OPT) point in Co and Ni. TEC is measured by the method of the continual T‐excchange. Anomalies of the TEC are found in the region of the PT in Co and near OPT in Co and Ni (near 500 K). The TEC quantities are in accord with the theoretical estimations. The TEC peak in the PT region permits to find the parameters of anharmonicity.
Diffusion of the Laue Spots in Electron Diffraction
Authors: Tamura E. , Ohtsuki Y. H. 
Published: July 2007

AbstractDiffusion of Laue spots in electron diffraction is studied with changing the crystal thickness and temperature. Multiple inelastic scattering with diffraction is taken into account by coupled diffusion equations including diffusion coefficients, which are calculated humerically by the same method developed in dechanneling theory. The asymmetrical diffusion observed experimentally between the diffraction direction and its transversal direction is in agreement with the theoretical results.
Phonon‐Assisted Two‐Photon Absorption of the Excitonic Molecule in CuCl I. Bare‐Exciton Approach
Authors: Ekardt W. , Brocksch H.‐J. 
Published: July 2007

AbstractPhonon‐assisted two‐photon absorption of biexcitonic levels in CuCl is considered including damping of the nearly resonant excitonic intermediate state. A pronounced structure of the line shape due to resonance effects, threshold effects, and structure in the Fourier transform of the envelope of the excitonic molecule is predicted. A detailed discussion of both temperature and damping effects is given. Large cross sections are predicted. The most favourable energetic range to observe the effects derived here is the low energy tail of the line, on the left of the Γ⅕ exeiton.
Activation Energies for Migration of K+ and N0 in KN3
Authors: Chang Chaik , Neuberger J. , Fischer R. 
Published: July 2007

AbstractActivation energies for the migration of K+ and N0 interstitials in KN3 crystals are calculated. The total cohesive energy is obtained from a modified Born model. Both double‐spherical and triple‐spherical potentials are used as the repulsive interaction. Polarization effects according to the Hatcher‐Dienes scheme are employed. N0 interstitial migration is found to require very little energy and thus becomes a good candidate for explaining the explosive instability of the azides.
On the Symmetry Groups of Non‐Rigid Impurity Centres in Crystals
Authors: Kiselev A. A. , Lüders K. 
Published: July 2007

AbstractThe conception of the permutation‐inversion symmetry group developed by Hougen and Longuet‐Higgins in the theory of non‐rigid molecules is applied to non‐rigid impurity centres in crystals, i.e. to impurity centres showing large‐amplitude motions of the nuclei. Examples of derivation of the symmetry groups for some molecular impurity centres are given and the transformations of the molecular coordinates induced by permutation‐inversion operations are discussed.
The Electronic Structure of MgO II. Results of Calculations
Authors: Abarenkov I. V. , Antonova I. M. 
Published: July 2007

AbstractThe method proposed in a previous paper is applied to the calculation of electronic structure of MgO. The first and the second nighbours are taken into account and well localized crystal orbitals of O2− are obtained. The results for the lattice constant, cohesive energy, and compressibility are in good agreement with the experiment.
Frequency Dependence of Some Functions Associated with Surface Polaritons
Authors: Nkoma J. S. , Rwaboona S. K. 
Published: July 2007

AbstractThe frequency dependence of the ratios of the magnitudes of the Poynting vectors and energy densities associated with surface polaritons for a semi‐infinite specimen are derived using electromagnetic theory. Strength functions characterising the quantitative composition of the surface polariton are calculated. The ratio of the tangential and normal components of the mean square electric fields is found to be a decreasing functions in the surface polariton frequency range. Graphs to illustrate the derived expressions are plotted taking parameters applicable to GaP.
The Reabsorption Mechanism of the Donor–Acceptor Energy Transfer
Authors: Serikov A. A. , Khomenko Yu. M. 
Published: July 2007

AbstractThe reabsorption mechanism of electronic excitation energy transfer between two impurities at sufficiently great distances in a crystal is investigated. The kinetics of energy transfer between the molecules of interest is considered taking into account the longitudinal relaxation of the excited terms. The spectral density of the radiation field and the quantum yield of luminescence depending on the system parameters and the temperature of a crystal‐dissolvent are discussed.
Spectra of Directionally Deformed Naphthalene Crystals and Exciton–Phonon Interaction Constants
Authors: Ostapenko N. I. , Sugakov V. I. , Chernomorets M. P. , Shpak M. T. 
Published: July 2007

AbstractThe absorption spectra of directionally deformed naphthalene crystals on anisotropic substrates of indole, deuteronaphthalene, and paradibrombenzene are investigated experimentally and theoretically. Directional deformations are created by changing the angle between the crystal and the substrate axes. A technique for determination of the thermal expansion coefficients of the crystals and substrates is worked out by which the deformation tensor for the naphthalene crystal is obtained. Using the data of the bands position in the absorption spectra and values of the deformation tensor components, the deformation potential constants Dxx = 4.2 × 103 cm−1, Dxy = Dyx = 1.9 × 103 cm−1, Dyy = 3.5 × 103 cm−1, Mxx = −2.7 × 102 cm−1, and Myy = −2.2 × 102 cm−1 are found, where Dij and Mij are the coefficients in the expansion of, respectively, the static and resonance interaction energy with respect to the deformation tensor.
Absorption Band Shape of Free Excitons in Indirect Band Gap Semiconductors at High Excitation Density
Authors: Lelyakov A. V. 
Published: July 2007

AbstractThe shape of the excitonic absorption band is studied theoretically for free Wannier‐Mott excitons in a semiconductor with an indirect band gap at high excitation density at T < Tc. The band shape is very different from the band of indirect excitons in semiconductors at small excitation density.
Localized Phonons Due to Substitutional Impurities in Dilute Copper Alloys
Authors: Kesharwani K. M. 
Published: July 2007

AbstractA detailed theoretical study of the effects of force constant changes as well as defect concentration on localized vibrational mode frequencies observed in dilute copper alloys is made after employing a localized perturbation model which includes the change in mass at the impurity site as well as the change in nearest neighbour central force constant. The force constant change, when calculated after considering exactly the effects of impurity concentration c in single site approximation, is found to be appreciably different from that calculated in very low concentration approximation (c → 0). An effective force constant, described in the framework of a nearest neighbour rigid‐ion model of lattice dynamics, is calculated in a self consistent manner and utilized to study its frequency dependence. The force constant changes introduced explicitly by volume effects due to impurity atoms are evaluated in a way which does not involve any arbitrary parameter. The experimentally measured inband‐phonon shifts in a Cu‐4.1% Al alloy are described well by the calculated force constant change.
Solitary Bound State of Magnons and Lattice Deformation in an Anharmonic One‐Dimensional Ferromagnet
Authors: Pushkarov Kh. I. , Pushkarov D. I. 
Published: July 2007

AbstractThe presence of excited spins in ferromagnetic systems can change the potential energy of interaction between atoms. In a ferromagnetic anharmonic linear chain the deformation formed and the spin excitations can create a bound state which can move along the chain with constant velocity without changing its shape. The quantum‐mechanical treatment of the problem leads to a nonlinear Schrödinger‐like equation with nonlinearity of third and fifth powers which has soliton solutions.
Certain features of semiconductor behaviour in strong parallel magnetic and electric fields. IV. Zener tunnelling
Authors: Berezhkovskii A. M. 
Published: July 2007

AbstractAn expression is derived for the tunnelling current density in a semiconductor subjected to a strong magnetic field parallel to an electric field, in regard to the Wannier‐Stark levels generated in an electric field. Tunnelling in InSb under magnetic field is investigated.
Anisotropy of the electron—phonon interaction in copper. II. Scattering and transport properties
Authors: Schmidt H. , Mann E. 
Published: July 2007

AbstractBy use of the electron‐phonon matrix elements for Cu derived in a preceding paper (in the form with plane‐wave parts only) the anisotropic functions of the scattering rate and the mass enhancement, as well as the electrical resistivity and the Hall coefficient for several orientations of the magnetic field are calculated as functions of the temperature. The agreement with the experimental data is satisfactory, though the local maximum of the Hall coefficient, characteristic for the scattering anisotropy, appears at lower temperatures than measured. This and other deficiencies, however, may be uniquely related to the simplified form of the matrix elements and should be overcome when the d‐parts of the pseudo wave functions are retained. The present considerations are thought to explain also some discrepancies reported for Al.
Bound magnetic polaron in magnetic semiconductors
Authors: Kuivalainen P. , Sinkkonen J. , Kaski K. , Stubb T. 
Published: July 2007

AbstractThe bound magnetic polaron (BMP) model is studied for a ferromagnetic non‐degenerate semiconductor. Using Zubarev's Green's function technique a set of coupled equations for the nonuniform spin polarization around an impurity is obtained and the binding energy of a shallow impurity state. A variational solution of these equations indicates that near the magnetic transition temperature the binding energy increases and the orbit of the bound electron shrinks. The application of a magnetic field decreases the binding energy and increases the electron orbit. The calculated temperature and magnetic field dependences of the resistivity are compared with the measured values for a EuSe sample.
Excitation spectroscopy of the I2 bound exciton and the excitonic molecule in CdS. I. Excited states of the I2 bound exciton
Authors: Puls J. , Voigt J. 
Published: July 2007

AbstractUsing a narrow band dye laser three excited states of the I2 bound exciton in CdS can be detected in the excitation spectrum of luminescence. Their behaviour at different excitation intensities is investigated giving essential conclusions to distinguish EM‐ and I2‐emission. From the corresponding lines in the transmission spectrum the oscillator strengths are estimated. The properties of the excited states refer to a deuteron‐like model of exciton weakly bound to the donor.
Theoretical description of elastic atom—atom scatteringd
Authors: Gärtner K. , Hehl K. 
Published: July 2007

AbstractRecent measurements of Lindhar's scattering function are used as starting point for some theoretical investigations of the elastic atom‐atom scattering within the quasistatic model. Good agreement is found for scattering of light ions on heavy atoms. For heavy collision partners the theoretical results agree in average with the experiments but don't provide the oscillations in full magnitude. This deviation is caused by neglecting the deformation of electron distributions.
Conduction electron spin resonance and inhomogeneous broadening due to local moments
Authors: Witters J. , Stesmans A. , van Meijel J. 
Published: July 2007

AbstractA simple theory is developed for the interaction of conduction electron spins with local moments in the bulk or at the surface of the metal, with emphasis on the conduction electron system, which is considered most important. When considering a local moment system with a distribution in g‐values and introducing an interaction strength in the electron system, this can give rise to extra linewidth terms, depending on the coupling strengths between the d‐s, d‐d, and s‐s subsystems, as compared to the width of the g‐distribution in the d‐system.
Calculations on the properties of helium in silicon
Authors: Kaplan D. R. , Weigel C. , Corbett J. W. 
Published: July 2007

AbstractThe electronic properties, lattice location, and diffusion coefficient of helium are investigated in silicon by extended Hückel theory calculations. The electrical properties are unchanged, the helium sits in the tetrahedral interstitial position, and the calculated diffusion coefficient is (1.28 ± 0.11) × 10−3 cm2s−1 exp (− 1.8 eV/kT).
Mixing of frenkel excitons and ionic excited states in a linear crystal of donor‐acceptor complex
Authors: Petelenz P. 
Published: July 2007

AbstractThe Merrifield model of the coupling between neutral and ionic excited states of a linear molecular crystal is applied to a crystal of a weak donor‐acceptor complex. The interaction of the ionic excited states with Frenkel excitations of donor (acceptor) molecules is taken into account. The results are discussed in relation to recent experimental data. Some other possible experimental consequences are pointed out.
Oxidation of clean cleaved Ge (111) surfaces
Authors: von Wienskowski J. , Froitzheim H. 
Published: July 2007

AbstractThe oxidation process of clean Ge (111) surfaces is followed up with low‐energy electron loss spectroscopy (ELS). Quasimolecular binding with a characteristic loss at 9.2 eV is recognized first. As oxide is formed at the surface an intense loss at 7.2 eV governs the spectra up to complete oxidation. In comparison with recent results on cleaved Si (111) surfaces the oxide is determined to be non‐stoichiometric.
Critical temperature of a compressible ising magnet
Authors: Chakrabarti B. K. , Barua B. P. , Sinha S. K. 
Published: July 2007

AbstractThe shift in critical temperature due to spin‐phonon interaction in a two‐dimensional compressible Ising magnet under zero pressure is obtained using a self‐consistent field approach. Fluctuations near the shifted critical temperature are also discussed. The observed shift in critical temperature is compared with that of Matsudaira.
Optical identification of substitutional acceptors in refined ZnTe
Authors: Magnea N. , Bensahel D. , Pautrat J. L. , Pfister J. C. 
Published: July 2007

AbstractA systematic study of acceptors incorporated by diffusion is carried out on refined melt‐grown ZnTe. The properties of five substitutional acceptors are investigated by low‐temperature photoluminescence. Since the binding energy of excitons on neutral acceptors is almost unaffected by the central cell potential, the neutral acceptors are identified by the two‐hole transitions which give accurate values of acceptor ionization energies. The two dominant acceptors “b” at 61 meV and “a” at 149 meV are identified as LiZn and CuZn, respectively, while the hole binding energies on NaZn, AgZn, and AuZn are established as 62.8, 123, and 272 meV, respectively. These experiments show that all the relatively shallow acceptors involve impurities and not stoichiometric defects.
An extended deformable shell model for ionic crystals including quadrupolar deformation of the charge cloud
Authors: Ghosh S. , Basu A. N. , Sengpta S. 
Published: July 2007

AbstractIt is well known that the dipolar and scalar deformation of the charge cloud around an ion in ionic crystals are quite significant in describing the different lattice mechanical properties. Even after the inclusion of the above deformations systematic discrepancies between theory and experiment persist. An attempt is made to incorporate the effect of the quadrupolar distortion of the charge cloud in the framework of the deformable shell model. All the relevant equations and lattice sums are evaluated for the CsCl structure and a preliminary application of the complete model which takes into account simultaneously the scalar, the dipolar and the quadrupolar deformation considered for a CsCl structure crystal. So far there is no estimate of the effect of the quadrupolar distortion on the different properties of a crystal belonging to CsCl structure. The calculation indicates that the effect is quite considerable for certain properties and its inclusion improves the overall agreement with experiment.
Angle‐resolved UPS of GaS, GaSe, and GaS0.6Se0.4
Authors: McGilp J. F. , Parke A. W. 
Published: July 2007

AbstractAngle‐resolved photoemission spectra are recorded from cleaved single crystals of GaS, GaSe and the alloy GaS0.6Se0.4. While energy band dispersion curves obtained for the three crystals are very similar, the azimuthal dependences of the emission from the top of the valence bands show considerable differences.