bluuebunny/crossref_metadata_2025_split huggingface dataset:
Invariant Harmonic Oscillator Functions. II. An Alternative Method for the Groups Td, 0, and Oh
Authors: Wöhlecke M. , Jovanović A. 
Published: July 2007

AbstractTunneling states of off‐center impurities and Jahn‐Teller systems are examples of an application of excited states of quantum‐mechanical three‐dimensional harmonic oscillators. A method is developed, which allows the calculation of symmetrized bases with minor computing expense. Results are given for the cubic groups O, Td, and Oh.
On the Theory of Atomic Migration in Monatomic Crystals
Authors: Buchbinder G. L. 
Published: July 2007

AbstractThe frequency of the overbarrier atomic jumps into a neighbour vacant site is calculated at high temperatures. The atom adjacent to a vacancy is in a two‐well potential constructed by its neighbours. The jump into a vacant site is considered as a transition of the atom from some quantum mechanical state of this potential into another one caused by interaction with its neighbours. It is assumed that the necessary condition for a jump is the transition of the atom from some state, localized in a lattice point, to a overbarrier state. Being at a overbarrier state the atom vibrates in a region whose size is compared with the lattice constant.
Spin Wave Resonance Approach to Interdiffusion in Coupled Magnetic Layers. Theoretical Study
Authors: Maciejewski W. 
Published: July 2007

AbstractA nondestructive method for the investigation of interdiffusion process, based on spin wave resonance measurements is proposed. For the diffusion by the vacancy mechanism a procedure for determination of the approximate concentration profiles is introduced. The modified virtual crystal approximation and the exact dynamical boundary conditions are used to obtain the spin wave energies, amplitudes, and resonance line intensities. The numerical calculations show the characteristic influence of the relative movement of the two species on the shape of spin wave resonance spectra.
Surface Magnetic Properties of the Ising Ferromagnet with a Site‐Bond Diluted Anisotropie Free Surface
Authors: Yang C. Z. , Li Z. Y. 
Published: July 2007

AbstractA semi‐infinite ferromagnetic simple cubic Ising lattice which has non‐magnetic impurities substituted only at the surface with anisotropic exchange interactions is investigated by the use of a new type of effective‐field theory with correlation. Some characteristic behaviours of magnetism at the site‐bond diluted free surface are obtained.
Optical Properties of Multi‐Layer Structures. II. Reflection and Transmission
Authors: Fomin V. M. , Pokatilov E. P. 
Published: July 2007

AbstractOptical properties of multi‐layer structures with, an arbitrary number of layers are considered on the basis of the polariton theory. The reflectivity, transmissivity, and absorptivity of periodic structures are found in terms of elementary functions. The optical characteristics are calculated for superlattices GaAs/Ga1−xAlxAs with different number of periods.
Simple Description of Hydrogen‐Like Systems in Arbitrary Magnetic Fields
Authors: Chen Y. , Gil B. 
Published: July 2007

AbstractA simple description is given of an hydrogen‐like system in an arbitrary magnetic field. A new expansion of the wave function is used in terms of hydrogenic states factorized by a simple exponential factor characteristic of Landau levels for free electrons. By using parabolic coordinates, such a choice for the basic function allows an analytical calculation for both the ground state and the excited states of the system under large range of field strength.
Comparison of Optical Activity and Faraday Rotation in Crystalline Si02
Authors: van den Keybus P. , Grevendonk W. 
Published: July 2007

AbstractOptical activity (OA) and Faraday rotation (FR) in SiO2 are compared from both a theoretical and an experimental points of view. A simultaneous derivation of the one‐oscillator formulas of FR and OA is presented. For OA this formula is extended to a semi‐classical expression, in analogy with earlier derivations of FR formulae. Starting from dispersion relations for crystals without inversion symmetry, it is possible to derive the OA formula, obtained earlier by Natori with the Kubo‐Greenwood formalism. Within the limits of accuracy and in the wavelength range 300 to 700 nm the experimental curves of OA and FR differ by a numerical factor only. Nevertheless the gap energies, obtained by fitting these curves with OA and FR formulas are different. The energy E = 9 eV is believed to correspond to the real direct band gap.
Influence of Nonparabolicity on the Superlattice Band Structure
Authors: Milanović V. 
Published: July 2007

AbstractThe energy spectrum is analysed of the superlattice taking into account the nonparabolicity effect in the host materials. Starting from the Kane theory the dispersion relation is derived for the symmetric superlattice. Moreover the expression for the concentration is given. The expressions derived are general and can be applied even to cases when a potential dependence exists. An extended effective mass is introduced depending both, on the energy and the energy gap as well as on the potential. The numerical results are given for the doping superlattice, assuming a triangular dependence of the potential. It is shown that the model, neglecting the nonparabolicity effects, yields good results for smaller energies and smaller values of the transverse component of the wave vector; in the opposite case, the nonparabolicity effects must be taken into consideration.
A Dynamical Theory for a Disordered Hubbard Chain far from Equilibrium. III. The High‐Field Case
Authors: Heiner E. 
Published: July 2007

AbstractFor the high‐field limit of a ID Hubbard chain (eF0a/u) ≫ 1 the expectation values for single and double occupancy are calculated. The equation for double occupancy does not contain a diffusion term. In contrast to the low‐field case the current density is not splitted in two terms.
A Theoretical Study of the Semiinsulating Behaviour of Fe in InP
Authors: Khowash P. K. , Singh Vijay A. , Khan D. C. 
Published: July 2007

AbstractThe transition metal impurities introduce levels deep in the band gap of the host semiconductor. For neutral Fe in InP the impurity level is exactly in the mid gap and this provides a clue to its semiinsulating behaviour. A detailed MS Xα SCF calculation of the different charge states of Fe in InP is presented. The agreement with the experimental results is satisfactory and shows the promise of the method for the analysis of impurities in semiconductors. The Mössbauer isomer shift for the different charge states of Fe in InP are also calculated.
Cluster‐Bethe‐Lattice Approach to the Electronic Structure of Intrinsic Defects in v‐SiO2
Authors: Bethkenhagen Viola , Hübner K. 
Published: July 2007

AbstractA cluster‐Bethe‐lattice calculation of the local electronic densities of states of some important intrinsic defects of vitreous SiO2 is presented. Defect‐induced gap states are correlated with known optical transitions. The optical absorption at 2 eV and the luminescence at 1.9 eV can be ascribed to a non‐bridging oxygen atom. The calculations support also the experimentally found relationship of the absorption at 5.8 eV with the Ei centre. Furthermore, a threefold coordinated Si atom, the peroxy radical, and the peroxy bridge are investigated and possible optical transitions are discussed.
ENDOR Investigation of Cr3+ Centres in the Tetragonal Phase of RbCdF3
Authors: Studzinski P. , Spaeth J.‐M. 
Published: July 2007

AbstractCr3+ centres in the perovskite RbCdF2 are studied with ENDOR at 17 K. The spin‐Hamiltonian parameters obtained for 53Cr and the first, second, and third nearest set of 19F neighbours show the influence of the structural phase transition from the cubic to tetragonal phase at Tc = 124 K. The results indicate that the influence of the lattice relaxation around the impurity ion is seen even in the third shell of 19F neighbours, which limits the use of Cr3+ as a probe to study the structural phase transition.
Helicon Wave Propagation in Semiconductor Superlattices
Authors: Kushwaha Manvir S. 
Published: July 2007

AbstractA theoretical investigation is made of the collision‐induced instabilities associated with helicon wave propagation in (type‐I) semiconductor superlattices. The dispersion relation which presents a rich structure of collective excitations in the quasi 2‐dimensional systems is used to study the convective and absolute instabilities. Numerical solutions of the dispersion relation are performed including the effect of retardation. The theoretical results in the strong‐coupling limit clearly indicate the parabolic nature of the modes at small wave vectors and thus lend support to the prediction of Quinn and coworkers. The analytical diagnosis, however, leads to some paradoxial conclusions and hence keeps one in dilemma to characterize these modes precisely as helicons.
Low Temperature Resistivity Anomaly in Glassy Metals. Two‐Level Systems and Incipient Localization versus Correlations
Authors: Kaiser A. B. 
Published: July 2007

AbstractTwo‐level systems in disordered metals can contribute to the \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt T $\end{document} resistivity anomaly at low temperatures, by reducing the resistivity increment due to weak localization. A comparison is made with the generally larger effects expected from electron‐electron correlations, and with data for Mg‐Zn glassy metals.
On the Theory of Quantum Hall Effect
Authors: Ziep O. , Keiper R. 
Published: July 2007

AbstractOne‐particle wave functions suitable for calculating the quantum Hall conductivity are discussed with respect to their local density of states. The new electron configurations connected with the quantum Hall effect indicate a spatial structuring in form of a Wigner‐like crystal or liquid. The calculated diagonal resistivity shows definite peaks in dependence on the magnetic field, the values of which are in good agreement with experimental data. The relationship between the filling factor and a two‐particle Green function is discussed.
Structures and Energies of Symmetrical 〈011〉 Tilt Grain Boundaries in Silicon
Authors: Kohyama M. , Yamamoto R. , Doyama M. 
Published: July 2007

AbstractThe structures and energies of a series of symmetrical 〈011〉 tilt grain boundaries in silicon are calculated for the first time using the tight‐binding type electronic theory (the bond orbital model). The boundary energies are highly dependent on the types and arrangements of the structural units which consist of 5‐, 6‐, 7‐, and 8‐membered rings of atoms. The boundary structures in the range 0° ≦ 0 ≦ 70.53° are analyzed in detail by the structural unit model, and it is shown that the comparatively simple structures of special boundaries, such as the Σ = 9 (122) boundary, are relatively stable.
Strain Derivatives of Dielectric Constants of MgO and Thallous Halides
Authors: Srinivasan K. , Raghavan S. Lakshmi 
Published: July 2007

AbstractCalculations are made to determine strain derivatives of static and high‐frequency dielectric constants of MgO, TlCl, and TlBr, using the two‐ion polarizable shell model. The calculated values of pressure derivatives of the static dielectric constant of MgO, TlCl, and TlBr are in good agreement with the experimental values. A reasonable agreement is seen between the calculated values and the measured values of strain‐optical constants for MgO. Strain‐optical constants are also calculated for thallous halides. Anisotropy in the polarizability of ions arising from strain is fairly accounted for by the shell model through the large contributions from overlap forces.
On the Calculation of Self‐Diffusion and Impurity Diffusion Coefficients with the Aid of Elastic Constants
Authors: Neumann G. 
Published: July 2007

AbstractIt is demonstrated that the diffusion model proposed by Varotsos and Alexopoulos implicitely includes a correlation between diffusion energy H and entropy S analogous that deduced by Wert and Zener. For the impurity diffusion via vacancies this correlation between H and S is not correct. Thus, the model of Varotsos and Alexopoulos is not applicable to the impurity diffusion. For self‐diffusion the model roughly approximates the temperature function of the diffusion coefficient D0, however, it is unable to describe the curvature of the Arrhenius plot of D0.
On the Diagram Technique for Green Functions of the Heisenberg Ferromagnet
Authors: Kühnel A. 
Published: July 2007

AbstractThe Green function approach to the Heisenberg ferromagnet is confronted with the difficulties connected with the commutation rules of spin operators. Recently, Baryakhtar, Krivoruchko, and Yablonskii (BKY) proposed a new diagram technique for Green functions containing spin operators based on the corresponding technique by Izyumov and Kassan‐Ogly. The new approach is compared with that proposed earlier by Haberlandt and Kühnel. Calculating some crucial terms it is shown why the diagrams of BKY do not represent the corresponding analytical terms properly if kinematic interaction due to the peculiar commutation relations is involved. The results for the low temperature spin wave energy and magnetization are discussed.
The Three‐Spin Box Product Interaction
Authors: Brown H. A. 
Published: July 2007

AbstractThe three‐spin interaction in the form of a box product, σ1 × σ2 · σ3, is investigated including additional interaction terms in the Hamiltonian in the forms \documentclass{article}\pagestyle{empty}\begin{document}$ \sum\limits_i {\sigma _{iz},} \sum\limits_{ij} {\sigma _{iz} \sigma _{jz}} $\end{document}, and πiσiz. With the relative strengths considered as parameters, the thermodynamic properties are evaluated as a function of temperature and show considerable variety. Both second‐ and first‐order phase transitions are found.
Comments on Levin's Modifications in the Phillips and Van Vechten Theory. d‐Electron Effect on Ionicity
Authors: Singh O. P. , Gupta V. P. 
Published: July 2007

AbstractBased on theoretical grounds some serious objections against Levin's modifications are discussed and an alternate approach to calculate the ionic gap Ec is presented. An attempt is made to see the validity of the theory in a wide range of structures. Calculated data show that the number of d‐electrons taking part in the bond formation depends on the ionicity which is in accordance with the earlier predictions.
On the Thermodynamics of Strongly Degenerate Two‐Component Plasmas
Authors: Rother T. , Kraeft W. D. 
Published: July 2007

AbstractA generalisation of Gell‐Mann‐Brueckner's formula is derived for two‐component systems of charged particles with any mass ratio and multi‐valley degeneracy. Higher order rs‐contribution are determined in the random phase approximation. Numerical values are given especially for hydrogen plasmas and for optically excited electron—hole plasmas in Ge and GaAs.
Interface Plasmon Modes as Collective Electronic Excitations of Semiconductor Superlattices
Authors: Bechstedt F. , Enderlein R. 
Published: July 2007

AbstractThe frequency spectrum of polar interface modes of superlattices is derived with regard of bulk spatial dispersion. The results are applied to free carrier excitations of superlattices. Dispersion relations are given for intra‐ and intersubband interface plasmon modes. It is shown that collective electronic excitations of superlattices considered in previous papers are limiting cases of interface plasmon modes. Experimental data on plasmon dispersion can be understood in terms of interface plasmon modes if carrier confinement is taken into account.
Thermodynamic Functions and Self‐Energy of Interacting Coulombic Systems. Numerical Results
Authors: Rösler M. , Stolzmann W. 
Published: July 2007

AbstractThe thermodynamics of multicomponent plasmas is investigated using a theoretical description where the free energy as a function of density and temperature is the basic quantity. The correlation contribution to the free energy and the chemical potential as well as the excess pressure (exchange plus correlation) are calculated at arbitrary degeneracy by summation over the complex Matsubara frequencies. With increasing degeneracy the numerical effort may be reduced with the help of the large wave‐number approximation or plasmon—pole expressions for the dielectric function. The temperature dependent self‐energy is calculated in the same way. Numerical results are given for the electron system, a hydrogen plasma, and for the electron—hole plasma in highly excited semiconductors.
Electronic Structure of Intrinsic Point Defects in Perovskite‐Type Crystals
Authors: Fisenko A. V. , Prosandeev S. A. , Sachenko V. P. 
Published: July 2007

AbstractUsing a tight‐binding model for the transition‐metal perovskite‐type oxides ABO3 a method of electronic Green function calculation is developed. In the framework of this technique the analytical equations for the local levels of atomic vacancies are obtained. The vacancy potential is calculated in the dielectric approximation including the ion displacements on the long ranges from the vacancy site and the electronic screening in the vicinity of the defect. It is shown that the appearance of the local levels in the forbidden gap is caused by the perturbation potential on the first neighbours of the vacancies. The energies of electronic excitations from the local levels are evaluated using the generalized transition state scheme. Donor levels close to the conduction band for the oxygen vacancy and acceptor levels for the A and B ion vacancy are obtained. The correlation between the results obtained and the physical properties of the perovskite oxides is discussed.
The Effect of Spin—Orbit Interaction on the Intensity of Transitions from 4A2 and 2E States in Strong Crystal Fields
Authors: Veremeichik T. F. , Kalinkina I. N. 
Published: July 2007

AbstractThe effect is studied of spin—orbit interaction and low‐symmetry field on the absorption ratios of the wide bands of the excited‐state absorption spectrum and similar bands of the ground‐state absorption spectrum of d3‐configuration. The study includes calculations of the energy of the pure electron transitions and the analysis of the composition of the eigenfunctions of the Cr3+ ions in ruby, magnesium oxide, and emerald in the cubic field approximation and taking mixing of all terms of the double trigonal group into account. The results are compared to the experimental values of the ratios of the oscillator strengths of the transitions compared. It is shown that the ratios depend strongly enough on the crystal field parameters and the parameter of the spin—orbit interaction. The influence of the interaction under consideration on the lasing parameters is discussed.
Influence of Macroscopic Inclusions on Excitonic Luminescence of InSe Crystals
Authors: Korbutyak D. V. , Kryuchenko Yu. V. , Demchina L. A. , Litovchenko V. G. , Sugakov V. I. 
Published: July 2007

AbstractLow temperature (from 4.2 up to 30 K) photoluminescence spectra of InSe crystals containing macroscopic inclusions of neutral slightly soluble impurities (gadolinium, anthracene, fluorene etc.) are studied. The inclusions are of 0.1 to 0.5 μm in size. A substantial rise (by one or more orders in magnitude with respect to the initial spectrum of undoped crystals) of the exciton luminescence intensity is observed at relatively moderate doping doses (the impurity concentration less than 0.5 wt%) in the region of longitudinal exciton frequency ωL. To explain this effect a model is developed, which takes into account the scattering of lower branch polaritons at macroinclusions and their transformation into polaritons of the upper branch without changes in energy. The calculated temperature and frequency dependences of upper polariton branch luminescence are close to those measured experimentally despite of the practically non‐parametric way of the calculations.
Multipole Theory of the Polarization of Solids by Point Defects. III. Transition Energy Calculations, the Approximation of Non‐Point Charges
Authors: Kantorovich L. N. 
Published: July 2007

AbstractThe method developed in Parts I, II for calculating the polarization energy of crystals by point defects self‐consistently with their electronic structure is extended. (i) Along with the initial (e.g. ground) state the final (e.g. excited) electronic state of the crystal containing the defect and the corresponding vertical transition energy is considered. (ii) The uncompensated charge density simulating the defect and its neighbourhood is treated now by a set of non‐point charges. (iii) The polarization potential is calculated. This generalized method may be useful for self‐consistent calculations of a wide class of actual point defects in ionic solids.
Orbit—Lattice Interaction and Mössbauer Quadrupole Splitting of 57Fe2+ in GeFe2O4
Authors: Choudhary S. N. , Sinha T. P. , Srivastava K. K. P. 
Published: July 2007

AbstractThe temperature dependence of Mössbauer quadrupole splitting of 57Fe2+ in GeFe2O4 is theoretically analysed by taking into account the effect of orbit—lattice interactions from 77 to 1000 K. It shows a good agreement between theoretical and experimental results, brings consistency between Mössbauer and magnetic susceptibility measurements, and emphasizes the importance of the dynamic crystal field approach over a wide range of temperatures.
Damping of Polaritons in Bilayer Systems. Long‐Range Surface Phonon‐Polaritons
Authors: Wendler L. , Haupt R. 
Published: July 2007

AbstractThe damping properties of surface phonon‐polaritons, especially long‐range surface phonon‐polaritons in bilayer systems are analysed. An analytic expression is derived for the damping function by means of a perturbative method. The different behaviour of the damping properties of surface phonon‐polaritons for various physically different bilayer systems are discussed. It is shown that not all possible cases yield long‐range surface phonon‐polaritons. In some cases one or two modes show the behaviour of long‐range surface phonon‐polaritons. In special cases, there two longe‐range surface phonon‐polariton modes exist, one of these shows in a small frequency range a significantly increased propagation length. The propagation properties are analyzed numerically in dependence of frequency and of the thicknesses of the two layers of the bilayer system. Dispersion curves, the electromagnetic fields, the energy flow, the power flow, and the propagation length of the surface phonon‐polaritons are given in graphical form and in tables.
Photoluminescence Study of the Gallium Defect Spectrum at ≈ 0.928 ev (ga3) in Irradiated Silicon
Authors: Thonke K. , Schall U. , Sauer R. 
Published: July 2007

AbstractA detailed investigation is made of the Ga3 luminescence spectrum observed in gallium doped silicon after electron irradiation and annealing at ≈ 250 °C. The spectrum exhibits exciton singlet—triplet pair no‐phonon transitions at 0.9291 or 0.9272 eV, respectively, and quasi‐localized modes of vibration energy 10.3, 24.4, and 56.9 meV along with combination modes and lattice phonon bands. An additional higher energy no‐phonon transition is due to an excited exciton state at excess energy of 3.8 meV thermalizing with the singlet—triplet states. The isotropic Zeeman splitting of the triplet (g = 2.00 ± 0.05) shows that the orbital momentum of the excitonic hole is entirely quenched. This and the low thermal dissociation energy of the exciton (16 meV) are used to deduce a strong hole binding energy (≈ 226 meV) whereas the 16 meV energy is attributed to the electron localization. The low electron binding energy is consistent with uniaxial stress measurements which are quantitatively explainable in terms of effective‐mass valley—orbit electron states. This defect represents the first example of a luminescent center in silicon which under uniaxial stress exhibits the whole multiplicity of valley—orbit‐states. The valley—orbit nature of the electron and the quenching of the hole orbital momentum render a symmetry classification of the defect impossible.