bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure of Non‐Simple Liquid Metals
Authors: Canessa E. , Mariani D. F. , Vignolo J.
Published: July 2007

A simple theoretical expression for the static structure factor a(Q) of non‐simple liquid metals is presented. The expression results from a superposition of two Ashcroft‐Lekner type expressions of the interference functions of hard sphere models, by assuming that the liquidmetal contains two types of clusters, each type being characterized by a set of four parameters. Calculations of a(Q) for liquid Hg, Ga, Sn, and Bi are made. The theoretical results are found in good agreement with experimental data and better than those predicted from the Ashcroft‐Lekner expression, in the region of interest for the well‐known Ziman theory.
Longitudinal Phonon—Plasmon Interactions in Semiconducting Plasmas
Authors: Pathak M. S. , Khan S. , Ghosh S.
Published: July 2007

The longitudinal phonon—plasmon interactions in semiconducting plasmas having piezoelectrixc or deformation potential coupling or both (viz. n‐InSb) is investigated when the electrons drift in the direction ofthe acoustic wave propagation, in presence of an magnetic field of arbitrary orientation. Using the hydrodynamic approach, the dispersion relation D(Ω, k) is derived. The conditions for excitation and the gain per radian of the acoustic wave in the collision dominated regime are studied in detail in the quasi‐static approximation. The analysis takes into account hot carrier effects and the temperature dependence of the momentum collision frequency. The variation of the gain per radian wih the system parameters is investigated. It is shown that the heating of the carrier decreases the gain.
Phonon Dispersion Curves of CsK, CsRb, and RbK Alloys
Authors: Soma T. , Ohsugi H. , Kagaya H.‐matsuo
Published: July 2007

A simplified treatment is proposed to study quantitatively the lattice dynamics of CsK, CsRb, and RbK alloy systems. The volume effect on the lattice dynamics of the pure constituent is considered, and the phonon dispersion relations of the local and band modes are obtained forthe Rb0.71K0.29, Rb0.3K0.7, Cs0.7K0.3, Cs0.7Rb0.3, and Cs0.3Rb0.7 systems. Then, the x‐dependence of the local and band mode frequencies is calculated for the Rb1−xKx, Cs1−xKx and Cs1−xRbx systems.
On the Isothermal Anderson‐Grüneisen Parameter in Solids
Authors: Dass N. , Kumari M.
Published: July 2007

Making use of the isothermal Anderson‐Grüneisen parameter as derived by Dass and Kasir, the values of the volume coefficient of thermal expansion and Grüneisen parameter are calculated as functions of pressure and temperature both in the case of sodium chloride. It is shown thatthe agreement between the calculated and the experimental values is very good. Further, it is shown that a general equation of state for solids can beeasily transferred to Birch's equation of state under the assumption that the isothermal bulk modulus varies linearly with the pressure.
Mechanical, Electrical, and Thermal Fields Produced by Moving Dislocations and Disclinations in Thermo‐Piezoelectric Continua
Authors: Minagawa S.
Published: July 2007

The stress, electrical, and thermal fields produced by a continuous distribution of moving dislocations and disclinations (defects) are studied inanisotropic thermo‐piezoelectric continua. It is assumed that the plastic deformation caused by the movement of the defect does not affect the thermo‐piezoelectric effect of the materials. The electric field is assumed as quasistatic, and the electric charges associated with the defectand the production of heat caused by the movement of the defect are neglected. The expressions for the above‐mentioned fields are given in terms of the defect‐density and defect‐flux tensors by the aid of Green's functions and the dynamic Green's potentials.
Thick Films near Phase Transitions. Green Functions, Fluctuation Spectra, and Light Scattering Theory
Authors: Filho A. Ribeiro , Tilley D. R.
Published: July 2007

A film of thickness L with a one‐component order parameter η is considered. It is assumed that the free energy is given by a simple Landau‐type expansion in η, that the boundary condition is linear in η and ▽η, and that fluctuations in the dielectric function depend linearly on fluctuations in η. With the use of phenomenological equations of motion the order‐parameter Green function is derived. Expressions are given, and illustrated numerically, for the power spectrum of order‐parameter fluctuations and the cross section for inelastic light scattering.
Elastic and Bonding Properties of Transition Metals
Authors: Walzer U.
Published: July 2007

A theory linking the nearly‐free‐electron theory to d‐band broadening and hybridization effects is further developed in such a way that a model, called MA, for the energy, the pressure p, the bulk modulus and its derivatives with respect to pressure as a function of the relative volume x is created. The theoretical values of MA are compared with all known experimental data for transition metals. For predictions of the relative volume as a function of pressure as well as for the predictions of the first derivative of the bulk modulus with respect to pressure at zero pressure significant improvements are obtained. The approximation of measured values in the p–x plot is very good for most transition metals, in particular for iron, too, and good for the other metals.
A Frequency Sum Rule and Spectral Moments in Lattice Dynamics
Authors: Frei V. , Deus P.
Published: July 2007

A sum rule of powers of phonon frequencies is derived generalizing a sum rule of squared frequencies given previously by Blackman, Brout, and Rosenstock. The connection of these sums with the moments of the frequency spectrum of the crystal is investigated by choosing gradually enlarged unit cells (GEUC) in the lattice and calculating the sums of the powers of phonon frequencies in suitable points of the correspondingly smaller Brillouin zones. The convergence of these sums in the GEUC‐process is shown using published dispersion curves of cubic crystals and group‐theoretical formulae for the high symmetry points in the Brillouin zones of f.c.c. lattices. Applications of the generalized sum rule are outlined.
Magnetoresistance of Ferromagnets with Domain Structure
Authors: Zakharov Yu. V. , Mankov Yu. I.
Published: July 2007

The dependence of the resistivity of a compensated ferromagnet with domain structure on a weak magnetic field is studied. It is shown that due to the change in periodicity of motion of the electrons crossing a domain wall, the conductivity near the wall has a non‐monotonic dependence on the coordinate normal to the wall plane and is larger compared to the conductivity in a domain. The process of magnetization by domain wall motion is considered. The dependence of Δϱ/ϱ on relative magnetization is shown to have a negative minimum whose value is determined by the ratio of the cyclotron diameter to the domain width.
Fundamental Zero Energy Gap States in Superlattices
Authors: de Dios Leyva M. , Alvarez R. P. , Gondar J. L.
Published: July 2007

The band structure of a model superlattice, in which the conduction band bottom in the first host semiconductor is located very close to or even below the valence band top in the other host semiconductor, is analyzed as a function of layer thickness and of the conduction band–valence band edge discontinuity. The analysis is carried out in the envelope‐function approximation and in Kane's two‐band framework. It is shown that with increasing magnitude of the discontinuity (or of layer thickness), the nature of the superlattice changes from a direct gap semiconductor to a direct zero gap semiconductor. Furthermore, it is also shown that in the direct zero energy gap states the valence and conduction bands may touch each other simultaneously over several circumferences in the Brillouin zone of the superlattice.
Angular‐Resolved X‐Ray Photoelectron Spectra of Valence and Core Levels from GaS
Authors: Chassé T. , Berg U. , Brümmer O.
Published: July 2007

Angular‐resolved X‐ray photoelectron spectra (ARXPS) are measured for valence bands and Ga core levels from the layer compound GaS. The spectra are interpreted taking into account initial and final state effects. Structures of dominating pz‐ and px,y‐like character are identified in the valence region. The core‐level spectra are qualitatively understood on the basis of scattering of photoelectrons within the solid.
Localized and Free Biexcitons in Silver Bromide
Authors: Kleinefeld Th. , von der Osten W.
Published: July 2007

Recombination luminescence in AgBr at low temperature is studied for high power quasi‐cw and pulsed excitation. The samples are nominally pure but vary systematically in iodine impurity content. Using time‐resolving techniques several new luminescence transitions are detected and found to be correlated with iodine concentration. The results can be consistently explained assuming that, besides free excitons and free biexcitons, a biexciton bound to isoelectronic iodine is created and decays. The model is supported by energy positions and shape of the observed lines as well as by the dependence of luminescence intensity on excitation power and iodine concentration. To completely account for the observed spectra, the model also takes into account intervalley exciton scattering by‐ X‐phonons known to be an effective exciton relaxation process in AgBr.
A Crystal Orbital (CO) Model for Low‐Dimensional Segregated Donor and Acceptor Stacks
Authors: Böhm M. C.
Published: July 2007

A crystal orbital (CO) model for low‐dimensional segregated donor (D) and acceptor (A) systems is developed. The approach can be traced back to two one‐dimensional (1D) tight‐binding calculations for “reference stacks” in the D and A manifolds that are coupled to the electrostatic fields created by the neighbouring 1D backbones. The Hartree‐Fock (HF) operators in the self‐consistent‐field (SCF) approximation are defined by using the grand canonical (GC) averaging procedure. This ensemble averaging allows for a straightforward determination of the mean‐field operators for fractional occupation schemes within the two 1D stacks.
Luminescence and Energy Transfer Characteristics of TbOCl
Authors: Berdowski P. A. M. , van Herk J. , Jansen L. , Blasse G.
Published: July 2007

Luminescence and energy transfer properties of the system Gd1–xTbxOCl (0 < x ≦ 1) are reported, with special stress on those of TbOCl. Concentration quenching occurs above x = 0.15 at 300 K. Transfer from intrinsic Tb3+ ions to extrinsic Tb3+ ions and to rare earth ion impurities are observed. The emission spectra of TbOCl are dominated by trap emission, which makes a quantitative analysis of the intrinsic Tb3+ luminescence properties in TbOCl cumbersome.
Instabilities and Δ‐Distributions in Solid State Physics
Authors: Englisch H.
Published: July 2007

It is not admissible to use Δ‐distributions as potentials, e.g. as central cell corrections, as it has been done by Lucovsky and Kiefer for doped semiconductors considered in effective mass approximation (EMA). Rigorous theorems like Kato's one for the wave function and Kimball's one for the pair distribution function are due to the Δ‐terms contained not appropriate to test the quality of trial functions. The intensity formula for the radiative recombination contains the dipole matrix element having in EMA two instabilities, one arising from a Δ‐term. The other one is connected with the asymptotic decay of the trial functions which also makes the usefulness of the notion of the localization length doubtful.
Vibrational Relaxation in a Localized Excited Electronic State by the GME Method
Authors: Vasilev A. N. , Čápek V.
Published: July 2007

A theory of the time evolution of the vibrational state of the lattice following an instantaneous excitation of a localized electronic state is presented for a simple model permitting both, the formal exact (in the basis of the deformed lattice states) and the second order generalized master equation (GME) treatment. The Nakajima‐Zwanzig form of the GME is used. The resulting integro‐differential equations are solved exactly by the generating function method (novel in this context) and the physical contents of the solution are discussed.
NMR Study of Dynamical Processes in Crystals of the TSCC Family
Authors: Engelke F. , Michel D. , Pille F.
Published: July 2007

Proton‐NMR Zeeman spin–lattice and dipolar relaxation and second moment measurements are performed on normal (TSCC) and deuterated (DTSCC) tris‐sarcosine calcium chloride to investigate dynamical processes near the ferroelectric phase transition of TSCC. Similar measurements are made for TSCB crystals which are isomorphous to TSCC but which are not ferroelectric. In the whole temperature range of measurements (110 to 300 K) spin–lattice and dipolar relaxation is governed by the CH3 group reorientation of the sarcosine molecules. This dynamical process explains also the increase of the second moment observed at temperatures T < 160 K for TSCC, DTSCC, and TSCB. However, a small contribution to the second moment is found for TSCB and DTSCC which is due to structural changes at the phase transition and which is absent for TSCB, where no phase transition occurs.
Isotope Diffusion in Cadmium Telluride
Authors: Suriyanarayanan V. , Madhavan Y. , Ramachandran K.
Published: July 2007

Diffusion in cadmium telluride especially the isotope effect on self‐diffusion is studied. The reaction coordinate of Achar is employed. Lattice Green's functions are used to estimate the displacement of the defect atom.
The Curie Temperature of the Ising Ferromagnet on the Honeycomb Lattice with Mixed Spins
Authors: Iwashita T. , Uryǔ N.
Published: July 2007

The Curie temperatures TC of the mixed spin systems on the honeycomb lattice are calculated in order to elucidate the effects of the biquadratic exchange interactions in the Ising ferromagnet. The mixed spin systems of S = 1/2 and S = 1, and of S = 3/2 are investigated assuming that the nearest neighbors are of the different spins and the next‐nearest neighbors are of the same spins. Bilinear and the biquadratic exchange interactions are assumed and the behaviors of TC as a function of the exchange parameters are investigated and compared with each other.
The XY Model with Nearest and Next‐Nearest Neighbour Interaction in a Transverse Field
Authors: Borges O. N. , Ribeiro L. A. Amarante , Gonclalves L. L.
Published: July 2007

The one‐dimensional XY model in a transverse field with first and second neighbour interactions is discussed, in the framework of the spectral density method, and in a first order approximation. The ground state is studied in detail and the phase transitions induced by the transverse field are determined. The phase diagram is obtained and it is shown that it presents a bicritical point.
To the Interplay of Vibrational Relaxation and Exciton Motion
Authors: Čápek V.
Published: July 2007

It is argued that todays interpretation of the Weber effect is a tribute to a special form of the approximate Markovian kinetic equations used. Using the Nakajima‐Zwanzig projection formalism with the Peier form of the projector and a subsequent Markovian approximation yields other Markovian kinetic equations. The results deviate however from those by Förster and Dexter as well as by Kenkre.
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

The 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

The 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

The 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

The 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

The 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

The 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

Specific, 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

Radiative 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

A 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

A 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

In 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

A 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

The 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

The 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

The 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

A 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

The 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

Formulas 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

Detailed 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

When 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

A 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

Angle‐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

Superconductivity 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

The 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

The 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

The 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

A 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

The 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

The 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

Concomitant 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

Strontium 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

The 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

The 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.
Alternative Quasi‐Classical Transport Equations. I. General Formalism for the Inclusion of Wave Functions
Authors: Paasch G.
Published: July 2007

The usual quasi‐classical description of transport processes does not contain directly the influence of wave functions. But the latter becomes important near interfaces. Due to the potential barrier at the semiconductor‐insulator interface the wave functions go to zero there. An expression is derived for transport coefficients which (a) within the local‐density approximation coincides in the bulk material with the standard formula and (b) contains the behaviour of the wave functions near the interface via the averaged local density‐of‐states matrix. The new approximation is discussed for a simple case. Applications and the inclusion of diffuse surface scattering will be treated in further papers.
Transport Phenomena of Ferroelectric Solid Solutions (GeTe)1−x((Ag2Te)1−y(Sb2Te3)y)x with y = 0.60, 0 ≦ x ≦ 1 at 300 K
Authors: Christakudis G. Ch. , Plachkova S. K. , Avilov E. S. , Shelimova L. E. , Abrikosov N. Kh.
Published: July 2007

The variation of the transport coefficients at 300 K, Seebeck coefficient (α), specific resistivity or conductivity (ϱ = I/s̀), Hall coefficient (RH), and thermal conductivity (K) with the composition (x) for solid solution (GeTe)1−x((Ag2Te)1−y(Sb2Te3)y)x) with y = 0.60 is investigated. The Hall coefficient decreases, reaches at x = 0.40 the minimal value and increases then up to x = 1, but the variation of the other transport coefficients are monotonous with composition: α and ε increase but K decreases with composition. The results are interpreted qualitatively on the base of the band edge model of GeTe with splitting of the L‐ and ∑‐valleys of the Brillouin zone (BZ) at the ferroelectric Oh–C3v phase transition and the complicated form of the surfaces of constant energy.
Vibrational Spectrum of TlSxSe1–x Solid Solutions
Authors: Allakhverdiev K. R. , Aleshenko U. A. , Bakhyshov N. A. , Vodopyanov L. K. , Gashimzade F. M. , Sardarly R. M. , Shteinshraiber V. Ya.
Published: July 2007

The results of an experimental investigation of infrared reflection and Raman scattering spectra for TlSxSe1–x crystals are presented. The concentration dependence of infrared phonon frequencies on the composition of solid solutions is described by a modification of the isodisplacement model. The equations of motion in the model are written for a symmetrized displacement of the atoms. The results of the numerical estimations performed in the framework of this model are in good agreement with the experimental data on infrared reflection of TlSxSe1–x solid solutions (where 0 ≦ x ≦ 1). The values of the force constants and effective charges are derived from the best fitting of the estimated curves with those obtained experimentally.
Crystalline Properties of Alkali Halides Using the Generalized Huggins‐Mayer Potentials
Authors: Gupta R. K. , Shiromany A. , Bakhshi P. S. , Shanker J.
Published: July 2007

The crystalline properties of sixteen alkali halides of NaCl type are calculated using the generalized Huggins‐Mayer form of the Born model for an ionic solid. Values of potential parameters calculated from recent thermodynamic data and new van der Waals coefficients are used. The pressure dependence of bulk modulus, Grüneisen parameter, Anderson parameters, thermal expansion coefficient, volume derivatives of the Grüneisen parameter are calculated, and compared with experimental data. The present investigation is superior to other previous studies in respect of taking consistent account of the thermodynamic contribution in determining potential parameters.
On the Electronic Structure of Clusters. Convergence to the Solid State Properties
Authors: Skála L.
Published: July 2007

The relation of the electronic structure of clusters and solids, the consequences of the surface relaxation, and the conclusions following from the analytic cluster model and numerical calculations are investigated. It is shown that the electronic properties of clusters converge with increasing number of atoms at least as quickly as 1/N1/d to zero, N being the total number of atoms and d the number of dimensions of the cluster (d = 1, 2, 3). The binding energy is characterized by 1/N1/d convergence while the bandwidth, the lower band edge, and the bond order converge as the second power of this parameter.
Transition Region Effect in the SiO2–SiOx–Si System on the Si Two‐Dimensional Electron Gas
Authors: Ye Qiu‐Yi , Wang Zhi‐Chekg
Published: July 2007

The energy levels of the Si two‐dimensional electron gas (2 DEG) subband is theoretically investigated, considering a graded composition in a transition region of the SiO2–SiOx–Si system. An expression is found of an effective atomic potential of the transition, varying continually along the space coordinate, and variational calculations are performed with trial wave functions to obtain the subband energy of the 2 DEG. The theoretical results coincide satisfactorily with some known FIR experimental results about Si‐2DEG. It is shown that the properties of the Si‐2DEG are quite sensitive to the transition and, further, that if the transition width is above a certain critical value, there is no 2DEG in the SiO2–SiOx–Si system.
Electron Spin Resonance Study of Fe+ Centers in NaCl:Fe++ and Motion of the Associated Vacancies
Authors: Yang B. R. , Bouwen A. , Schoemaker D.
Published: July 2007

X‐irradiation at 77 K of a NaCl:Fe++ crystal produces orthorhombic and axial Fe+ ESR spectra of comparable intensities. The corresponding Fe+ (ortho) and Fe+ (tetra) centers are identified with, respectively, a substitutional Fe+ perturbed by a nearest and a next nearest cation vacancy. At 170 K the cation vacancy of Fe+ (ortho) jumps to the next nearest neighbour position enhancing the Fe+ (tetra) intensity. Above 215 K the vacancy moves away completely and the unperturbed Fe+ (cubic) is formed. It is concluded from this study that before X‐irradiation Fe++ perturbed by either nearest or next nearest cation vacancies occur in roughly comparable amounts and that the activation energy for cation vacancy motion in NaCl is 0.72 eV.
A Refinement of the Mollwo‐Ivey Rule for F‐Centres in Alkali Halides
Authors: Maduemezia A. , Vega‐Catalan F. J.
Published: July 2007

It is found that the simple formula , where A = 328, B = 9.3118, and a = 1/x the nearest‐neighbour distance in Bohr radii, is a very good fit for the detailed variation of the F‐centre peak absorption energy, E (in Ryd), with a, for the 16 alkali halides with NaCl structure, excluding CsF. The first term arises from incoherent photon scattering leading to electronic level transitions. The second term is a diffraction term, arising from the coherent scattering of photons from relaxed ionic aggregates around F‐centers separated on the average by distances of the order of optical wavelengths.
Isotopic Impurity Modes and Polariton Dispersion in Li2GeO3 Crystals
Authors: Orel B. , Klanjšek M. , Moiseenko V. , Volnyanskii M. , Le Calvé N. , Pasquier B. , Novak A.
Published: July 2007

Infrared reflection and Raman spectra of single crystals of 7Li2GeO3 and 6Li2GeO3 containing 7.42 and 9.10% of 6Li and 7Li, respectively, are measured and the oscillator parameters \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \nu $\end{document}LO, \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \nu $\end{document}TO, γLO, and γTO determined using the Kurosawa dispersion relation. The experimental attenuated total reflection spectra are in good agreement with the calculated polariton dispersion curves. The resonance type interactions between parent and isotopic impurity deformation modes are interpreted; the behaviour of the corresponding phonons depends on their symmetry species.
Soft Mode Spectroscopy in Potassium Dihydrogen Phosphate
Authors: Brehat F. , Wyncke B.
Published: July 2007

The infrared reflectivity spectra polarized along the c‐axis of potassium dihydrogen phosphate are studied for both, the ferro‐ and paraelectric phase, over a wide temperature range: 10 to 420 K. The reflectivity spectra are fitted to the factorized form of the dielectric function. The temperature dependence of the optical mode parameters: frequencies, damping, and oscillator strengths are reported for both the phases. The analysis shows that besides the soft mode, a relaxational process of the very low‐frequency region plays an important role near the phase‐transition temperature.
Two‐State Mean‐Field Theory of Reentrant Phase Transitions
Authors: Kventsel G. F. , Katriel J.
Published: July 2007

A generalized mean‐field theory allowing for the possibility of the microscopic constituents to be in two different internal states with an ordering interaction in each one of them, is formulated. The explicit criterion of reentrance is established and a corresponding Landau theory is presented. A two‐state extension of McMillan's model is discussed, exhibiting a large variety of sequences involving reentrant nematic, smectic, and isotropic phases. Some of these sequences, such as I → N → S → rN → rS → rI, have not yet been observed experimentally.
Magnetic Properties of the Transition Metals in a Superconductor
Authors: Bortel K.
Published: July 2007

The superconductivity as a sensitive probe of the magnetic properties of transition metals is investigated. A theory of magnetic impurities in a superconductor is presented within the Nagaoka‐Suhl approximation (with the double renormalization of energy parameters). Application of Anderson's theory to superconducting host metals permits to determine the relation of the interactions responsibles for magnetic properties of transition metals.