bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effective Exchange and Correlation Interaction and Dielectric Screening in the Electron Gas. A Functional Approach to the Local‐Field Correction
Authors: Streitenberger P. 
Published: July 2007

AbstractThe basic equations for the Green's function are reformulated to incorporate the local‐field correction in the decoupling procedure for the many‐electron problem explicitly. A set of self‐consistent equations is derived, which couples the self‐energy and a mean exchange and correlation potential via an effective vertex function. In the simplest approximation a local vertex function is obtained which leads to a local‐field correction for the non‐interacting reference system involving the variational and perturbational results previously obtained. Screening and self‐energy insertions are uniquely defined, where the electron interaction potential in the self‐energy must be screened with an electron‐dielectric function defined for the interacting system.
Critical Analysis and Simplified Formulation of the Travelling Cluster Approximation for Disordered Systems
Authors: Pisani C. , Marchese E. 
Published: July 2007

AbstractThe travelling cluster approximation (TCA) for disordered systems (Mills and Ratanavararaksa) is here rederived in an axiomatic way. It is shown that a more drastic, simplified approximation (STCA) can be formulated; the corresponding equations share many attractive features with TCA, but are much easier to implement computationally, especially because they are not self‐consistent. The fundamental assumptions that underlie TCA and STCA are critically compared and discussed. It is shown that the TCA is preferable at a single‐site level of approximation; when higher levels are considered, STCA performs about as well as TCA. A number of examples are provided concerning linear chains treated with diagonal and off‐diagonal tight binding Hamiltonians.
Born‐von Karman Cell Model for Deep Impurities
Authors: Biernacki S. W. 
Published: July 2007

AbstractThe Born‐von Karman cell method of calculating the energy levels of deep, transition metal centres in semiconductors based on the linear combination of atomic orbitals representation is presented. The method can be used to calculate the energy separation Δ between impurity levels and to determine their positions with respect to some high‐symmetry points in the Brillouin zone.
The Electrical Resistivity of Clustering Alloys
Authors: Schubert G. , Richter J. 
Published: July 2007

AbstractThe electrical resistivity ϱ of clustering alloys is calculated using the force–force correlation function scheme in the weak‐scattering limit. In the high‐temperature region both signs of the extra‐resistivity Δϱ caused by clustering effects are obtained to be possible in dependence on the Fermi level. At temperatures below the critical temperature of the alloy, where a cluster‐growing process occurs, the resistivity is calculated in dependence on the cluster size. For such alloys, where clustering causes a positive extra‐resistivity Δϱ in the high‐temperature region, the well‐known maximum of the resistivity at a critical cluster size is obtained for spherical clusters. The resistivity of alloys with a negative Δϱ in the high‐temperature region decreases monotonically during a growing process of spherical clusters. Some further numerical results for elliptical and plane clusters are given.
Universal Transport Properties of Inversion Layers in Quantizing Magnetic Field
Authors: Středa P. 
Published: July 2007

AbstractThe magnetization, conductivity, thermopower, and thermal conductivity of a two‐dimensional electron gas in high magnetic field is calculated using the Kubo formula. The main attention is paid to the effect of sample edges which are responsible for universal properties of two‐dimensional systems (represented by inversion layers) as are e.g. quantum Hall effect and unusual properties of the thermopower at low temperatures. The results are in agreement with published experimental data.
Superconducting and Magnetic Order Parameters in the Coexistence Region of Ternary Superconductors
Authors: Kakani S. L. , Upadhyaya U. N. 
Published: July 2007

AbstractThe superconducting order parameter (Δ) and magnetic order parameter (M or 〈Sz〉) in the co‐existence region of the ternary superconductor, ErRh4B4, is studied using a microscopic model. The theoretical results are in good agreement with experimental observations.
On the Interpretation of Orientation Distributions and Qualitative Ghost Corrections for Hexagonal‐Orthorhombic Textures
Authors: Helming K. , Matthies S. 
Published: July 2007

AbstractSpecific, symmetry‐induced moments that have to be considered interpreting orientation distribution functions as a superposition of texture components are discussed for the case of hexagonal‐orthorhombic symmetry. Possibilities of a qualitative ghost correction using geometrical properties (hit numbers) and standard functions are described.
Radiative Optical Modes of Vibration in NiO Thin Film
Authors: Mochizuki S. 
Published: July 2007

AbstractRadiative optical modes of vibration in NiO thin films on metal substrates are observed at various temperatures from room temperature to 1273 K by reflection and thermal emission methods. A comparison of the experimental spectra and the theoretical ones shows that the correlation between them is good. The upper branch of the polariton dispersion curve of NiO at room temperature is determined experimentally by analysing the reflection spectra due to the virtual mode near the longitudinal optical phonon frequency. The shift in the longitudinal optical phonon frequency with temperature is discussed in terms of thermal expansion and other anharmonic effects.
Interactions of Magnons in the Six‐Sublattice Antiferromagnet
Authors: Safonov V. L. 
Published: July 2007

AbstractA microscopic model of the six‐sublattice antiferromagnet CsMnF3is considered. Spectra and three‐magnon amplitudes of the electronic and nuclear spin waves are calculated. It is shown that in the multisublattice model there are new processes of the low‐frequency spin‐wave interactions (parallel with other processes that take place in the two‐sublattice model too). Contributions of these processes should be taken into account in the theoretical description of nonlinear properties of CsMnF3. Results obtained are compared with experimental data.
Calculation of Some Characteristics of an Intrinsic Random Field in Hydrogenated Amorphous Silicon
Authors: Khamidullina N. M. 
Published: July 2007

AbstractA calculation is presented of some characteristics of an intrinsic random field in a‐Si:H needed to interpret statistical and transport properties of this disordered heteropolar material. Numerical results are obtained for the characteristic energies related to the density of states and optical tails, etc. The results are in a satisfactory agreement with the experimental data available. On the basis of the estimated atomic radial distribution function parameters the problem of the medium‐range order in a‐Si: H is discussed.
Peculiarities of Polarization Properties of CdS Single Crystals around the Isotropic Point
Authors: Dimov T. N. , Iliev I. A. , Lange H. 
Published: July 2007

AbstractIn dependence on sample position between crossed polarizer and analyzer two effects can be distinguished in CdS crystals: the conventional birefringence and the mode coupling between ordinary and extraordinary waves. Both effects are clearly identified by comparing the ellipticity parameters. The mode coupling shows up as a spectral structure consisting of two peaks separated by a pronounced minimum at the isotropic point for as‐grown CdS platelets. The ellipticity parameters in this case exhibit principally the same features as the optical activity. The occurrence of this effect is due to non‐diagonal components of the dielectric susceptibility tensor. These components can arise as a result of higher‐order terms of the dielectric susceptibility tensor and/or internal stress. Expressions are derived which very well describe the spectral shape as well as the influence of an external magnetic field on the spectral characteristics due to mode coupling.
Green's Function Method in the Equivalent Orbital Basis. Point Defects and Complexes of Two Point Defects in Silicon
Authors: Sh. Makhmudov A. , Khakimov Z. M. , Levin A. A. , Yunusov M. S. , Khabibullaev P. K. 
Published: July 2007

AbstractA version of the Green's function method on the basis of equivalent orbitals (EO) for the calculation of localized states in diamond‐like semiconductors is described. The band structure of silicon is obtained in terms of the tight‐binding method including a bond interaction through the fourth‐next neighbours. The electronic states of point defects in silicon (vacancy, phosphorus, and sulphur impurities) and of their complexes (divacancy, phosphorus + vacancy) are calculated.
Neutral Bound Excitons in a Low Magnetic Field
Authors: Dujardin F. , Stébé B. , Munschy G. 
Published: July 2007

AbstractThe diamagnetic shift of an exciton bound to a neutral donor or acceptor shallow impurity in direct gap semiconductors is studied using the previously obtained Page and Fraser type wave function. The results are compared with the experimental observations in InP for the exciton‐neutral donor complex and in GaAs and ZnTe for the exciton‐neutral acceptor complex. In all cases qualitative agreement is found while for InP a very good agreement is obtained if an isotropic experimental effective hole mass is used.
Non‐Exponential Localization in an Inhomogeneously Disordered Chain
Authors: Hayn R. , John W. 
Published: July 2007

AbstractThe behaviour of localized states is studied for a semi‐infinite chain with decreasing amount of disorder along the chain. It is shown that for slowly decreasing disorder all states are localized. In contrast to the case of homogeneous disorder, the states show non‐exponential localization and may be characterized by a generalized Lyapunov‐coefficient.
Time‐Resolved Luminescence of Charge Carriers in Localized States in Amorphous Semiconductors
Authors: Suhrke M. , Esser B. 
Published: July 2007

AbstractThe time‐dependent shift and band width of luminescence bands due to radiative transitions between carriers in localized states are calculated. As competitive to the radiative process the escape from the recombination partner over tail states with subsequent non‐radiative recombination is assumed. The low temperature case is considered where the hops away over states lower in energy dominate. The temperature dependent corrections due to back hops are found using a self consistent pair approximation for the time decay of the averaged site occupation.
The Influence of Molecular Motions on Multipulse NMR Spectra in Solids
Authors: Khitrin A. K. , Laiko V. V. , Provotorov B. N. 
Published: July 2007

AbstractA canonical transformation technique generalized for the case of a non‐periodical time dependence of the Hamiltonian is used for the analysis of molecular motion influence on multipulse NMR high resolution spectra in solids. The linewidth is shown to be described in some cases by a temperature‐dependent effective Hamiltonian.
The Role of the Zero‐Point Vibration towards Crystal Properties of Rubidium Halide Crystals
Authors: Singh R. P. , Rana J. P. S. , Daud A. , Varshney G. B. 
Published: July 2007

AbstractThe contribution of zero point vibration towards the cohesive energy, molecular force constant, reststrahlen frequency, third order elastic constants, bulk modulus and its pressure dependence are evaluated for rubidium halide crystals. The Hafemeister‐Flygare (HF) type short‐range overlap repulsive potential effective up to the next nearest neighbour is used. The zero point energy is estimated by the well known Narayan and Ramaseshan relation and the van der Waals (vdW) coefficients are calculated by the Slater‐Kirkwood variational (SKV) method. The results show a close agreement with their experimental data.
Athermal Vacancy Cluster Formation in F.C.C. Metals by High Energy PKA
Authors: Melker A. I. , Romanov S. N. 
Published: July 2007

AbstractFormulas describing the total cross sections for athermal formation of tri‐ and tetravacancies by a projectile atom are deduced using the impulse approximation. For Cu and Au, the formation probability of various configurations of these vacancy clusters created by a projectile atom with an energy E = 10 to 100 ke V is calculated. It is shown that in Cu the 120°‐ and 180°‐ clusters (linear vacancy chains) are the most probable configurations, whereas in Au the most of trivacancies are the 120°‐ and 60°‐ones and among tetravacancies prevail the 180°‐ones.
Angular Distributions of Fast Electrons at Planar Channeling in Silicon Crystals
Authors: Kaplin V. V. , Nurmagambetov S. B. , Gridnev V. I. , Rozum E. I. , Pak S. , Uglov S. R. , Vorobiev S. A. 
Published: July 2007

AbstractDetailed experimental and theoretical investigations for the orientation dependence of the angular distribution of 5.6 MeV electrons transmitted through a silicon crystal in (110) and (111) planar directions are performed. The realization of atomic‐type and molecular‐type quantum states of channeled electrons as well as the effect of preferential population of the definite states are observed.
The Role of Electron‐Hole Interaction in the Cooling Process of Highly Excited Carriers
Authors: Asche M. , Sarbei O. G. 
Published: July 2007

AbstractWhen the energy exchange by electron‐hole interaction is properly taken into account, the holes after optical excitation never achieve such a high temperature as the electrons for the concentrations usually envolved, and the cooling rate of the electrons therefore is significantly lower than in the case of an equal plasma temperature assumed until now. Theoretical expressions are obtained in Born approximation using the Thomas‐Fermi model for screening and calculations are performed for carrier relaxation in GaAs after instantaneous excitation.
Tight‐Binding Electronic Theory for Lattice Defects in Transition Metals. Correlation Effects
Authors: Masuda‐Jindo K. 
Published: July 2007

AbstractA tight‐binding type electronic theory is used to calculate the atomic relaxation (δRi), formation and binding energies (Efv and Ebin) of vacancy‐type lattice defects in transition metals. The short‐range repulsive energies between atomic sites i and j are simulated by the Born‐Mayer potential. An electronic correlation contribution is taken into account using a second‐order perturbation theory within the Hubbard model. It is shown that correlation effects play a significant role in determining the physical properties of the lattice defects (δRi, Efv, and Ebin) in transition metals. This tendency is observed for the lattice defects on the surface as well.
Tight‐Binding Calculations for the Angle‐Resolved Local Density of States of InP(110) Surfaces
Authors: Jalaj S. , Singh I. , Joshi S. K. 
Published: July 2007

AbstractAngle‐resolved electronic local density of states and layer density of states of indium phosphide(110) surfaces are calculated using empirical tight binding methods. The slab method is used for the purpose. The results are compared with recent angle‐resolved photoemission spectroscopy (ARUPS) findings.
Superconductivity of Metals with a Superlattice of Voids
Authors: Rudko V. N. , Sugakov V. I. 
Published: July 2007

AbstractSuperconductivity of metals with a superlattice of vacancy or gas voids is investigated in the presence of magnetic fields around the second critical field Hc2. At H ⪆ Hc2 the porous superconductor appears to be a system of an immense number of superconducting regions localized near the voids. The paper represents following results: (i) the dependence of the third critical field Hc3 on the void radius; (ii) the diamagnetic properties of the system; (iii) the Bloch states of the superconducting condensate. It is shown that in type‐II superconductors with a lattice of voids Josephson effects due to Cooper pair tunneling between the voids occur.
Galvanomagnetic Effects of Bismuth in Non‐Quantising Magnetic Fields. Pseudo‐Parabolic Model
Authors: Hansen O. P. , Mikhail I. F. I. 
Published: July 2007

AbstractThe non‐parabolicity of the L‐point carriers and the temperature dependence of the band structure are incorporated in a model for the transport properties of bismuth. Results are given for elements of the resistivity tensor versus magnetic field at temperatures around 80 and 300 K. A comment is made to the papers of Gitsu et al.
Lattice Specific Heat and Superconducting Transition Temperature of a V:W Alloy
Authors: Maithani P. C. , Tiwari M. D. 
Published: July 2007

AbstractThe changes in lattice specific heat and transition temperature of vanadium doped with tungsten impurities are studied systematically by using the low‐concentration Green's function theory. The nearest neighbour radial and angular force‐constant‐changes are evaluated by fitting the measured enhanced phonon heat capacity of the alloy. The electron‐phonon interaction as well as electronimpurity scattering are discussed in detail. The present theory shows reasonably good agreement with the experimental measurements on specific heat and with those on superconducting transition temperature of the alloy.
Anharmonic Properties of Sodium Halides
Authors: Prabhakar N. V. K. , Singh R. K. 
Published: July 2007

AbstractThe anharmonic properties of sodium halide crystals are investigated using a three‐body interaction potential. This includes the prediction of second, third, and fourth order elastic constants, the pressure dependence of second and third order elastic constants, and the temperature variation of second order elastic constants. The agreement between experimental and the theoretical results is, generally, good. The inclusion of anharmonic terms in the potential might lead to further improvements.
Pressure Effect on Band Structure of Neon
Authors: Zarochentsev E. V. , Tolpygo K. B. , Troitskaya E. P. 
Published: July 2007

AbstractA study is made of an excess electron placed in a perfect Ne crystal subjected to hydrostatic compression. The conduction bands (excess electron energy spectrum) are calculated from first principles using the OPW method. The Phillips‐Kleinman potential is constructed using atom‐like Wannier functions. At normal pressure the band structure is very similar to that calculated by other methods which involve the expansion of the basis in plane waves and agrees well with available experimental data. As the crystal is compressed the conduction bands are deformed, they become broader in energy, the actual minimum remains in the centre of the Brillouin zone, and the effective mass at this point decreases.
Consistent Evaluation of Long‐Range and Short‐Range Contributions to the Quasi‐Particle Energies of Transition Metal Solids
Authors: Böhm M. C. 
Published: July 2007

AbstractThe validity of widely‐used approximations for the determination of quasi‐particle (QP) energies in solids with transition metal atoms is critically investigated. It is shown that the combination of “true” many‐body procedures for the description of the long‐range (LR) contributions and mean‐field (electronic relaxation) corrections for spatially localized short‐range (SR) reorganizations is insufficient for strongly metal‐centered nd electrons. The influence of electronic correlation in localized holes is so strong that these elements cannot be neglected in comparison to orbital relaxation. Interrelations as well as differences between perturbational expansions beyond the Hartree‐Fock picture in the LR and SR regimes are discussed. The significance of physically feasible LR and SR contributions to the total QP energies of the solid is analyzed. Simplified relations are given to estimate improved SR contributions to the quasi‐particle spectrum of complex solids.
Mixed Basis Method with Overlapping Atomic Orbitals
Authors: Reser B. I. 
Published: July 2007

AbstractThe LCAO‐PW mixed basis method is considered in its most general formulation, i.e. with due account for overlapping AO's as well. By approximating atomic wave functions and potentials with Gaussian‐type functions analytical expressions are derived for all elements of the Hamil‐tonian and non‐orthogonality matrices. As an example, a silicon crystal is considered.
Photoluminescence and Recombination of Excess Carriers in Amorphous Hydrogenated Silicon
Authors: Andreev A. A. , Zherzdev A. V. , Kosarev A. I. , Kougia K. V. , Shlimak I. S. 
Published: July 2007

AbstractConcomitant simultaneous investigations of both, photoluminescence (PL) and photoconductivity (PC) decay from steady‐state levels are carried out for the first time under the same conditions for the same a‐Si:H samples. It is found that there is no competition between radiative and non‐radiative recombination channels for excess carriers. A general model of tunnel distant‐pair recombination based on the experimental data is proposed for explanation of both, PL and PC.
Electron Paramagnetic Resonance Study of Copper (II) Ions in Single Crystal of Strontium Formate Dihydrate
Authors: Chand Prem , Umar M. 
Published: July 2007

AbstractStrontium formate dihydrate is one of the examples of eight‐coordination forming a distorted antiprism around strontium sites and provides a suitable site to observe the effects of low symmetry on EPR of copper(II) in this lattice. Results of an X‐band EPR study show that copper (II) ions enter the host lattice in two different ways (i) substitutionally and (ii) interstitially, the latter being more favourable. The principal axes of the g‐ and A ‐tensors do not coincide for the former case in conformity with the low symmetry of the site as determined by X‐ray work. From the obtained experimental data, the ground state wave function for the copper(II) interstitial complex which displays a rhombic symmetry, is constructed. The interstitial complex is of highly covalent nature and the |x2 – y2〉 ground state has an about 5% admixture of |3z2 – r2〉.
The Surface or Interface Polaron in Polar Crystals. I. Weak‐Coupling Limit
Authors: Jin‐Sheng Pan 
Published: July 2007

AbstractThe effective Hamiltonian and effective potential are given for surface weak‐coupling polarons in polar crystals. Their binding energy and effective mass are also evaluated. When a sample of polar crystal contacts with another sample of non‐polar material, and the high frequency dielectric constant ε∞2 of the non‐polar material is larger than that (i.e. ε∞1) of the polar crystal, or is larger than a certain critical value (ε∞2)min, the polaron may exist in the interface. Reversely, when ε∞2 < (ε∞2)min, the polaron is not able to exist near the interface. If the non‐polar sample is metallic (i.e. ε∞2 = ∞), there is a shallow potential well near the interface, in which the polaron may be trapped.
Crystal Structure Dependence of Hole Stability in Ionic Crystals
Authors: Nakaoka Y. 
Published: July 2007

AbstractThe stability of self‐trapped holes in ionic crystals with NaCl and CsCl structures is studied on the basis of the small polaron theory. The model Hamiltonian contains four free parameters: the coupling constants for hole with acoustic and optical phonons, the site off‐diagonal coupling, and the mass ratio of cation to anion. The overall and systematic features of the hole stability are investigated by means of phase diagrams in the space spanned by the parameters. It is found that the stability drastically depends on the crystal structure. By fitting the parameters, results are obtained which agree with the experiments.