bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron—Phonon Interaction in Ferromagnetic Semiconductors
Authors: Wesselinowa Julia M. 
Published: July 2007

AbstractA Green's function technique is used to study the effects of the electron—phonon interaction in the s—d model. The renormalized energy, the polarization, and the damping of the electrons are obtained and numerically calculated taking parameters for CdCr2S4. The phonon spectrum and damping are discussed, too.
The Electronic Structure of Octahedral Platinum and Iridium Clusters (Pt6, Ir6). A Comparison between Xα‐SW and EHT Calculations
Authors: Bartel H.‐G. , Scholz G. , Neumann R. , Schmidt W. 
Published: July 2007

AbstractMO calculations are performed using the Xα‐SW and the EHT methods. The calculated DOS profiles of Pt6 and Ir6 show a good coincidence with those from relativistic bulk band structure calculations (RAPW). The use of a 5d/6s basis set with VSIP's from HFS SCF calculations allows a sufficiently good coincidence of the EHT eigenvalue spectrum with the corresponding Xα‐SW spectrum. Therefore a further adjusting of EHT parameters on Xα‐SW results is not necessary.
Polarized Positron Annihilation and Enhancement Effects in Ferromagnetic Iron
Authors: Šob M. , Szuszkiewicz S. , Szuszkiewicz M. 
Published: July 2007

AbstractBy comparison of the independent particle model calculation of the positron annihilation spectra with the spin‐polarized angular correlation results in iron, the polarization of positrons before annihilation is determined to be 0.21 ± 0.05. The character and magnitude of the differences between the independent particle model and experiment is not influenced by the presence of the magnetic field. The explanation of these deviations could be a crucial test for recent treatments of the electron‐positron interaction in metals.
Low‐Temperature Absorption Spectrum of Ni2+ Ion in Single Crystals of Ni2NbBO6
Authors: Borromei Renate , Cavalli E. 
Published: July 2007

AbstractPolarized absorption spectra of single crystals of Ni2NbBO6 in the range 5000 to 28000 cm−1 are measured at liquid‐helium temperature. The bands are interpreted in terms of “ligand field transitions” with a site perturbation expressed as the sum of two contributions, one major connected to a reduction of symmetry Oh → C3v and one minor connected to C3v → Cs. By assuming that most of the intensity derives from the static low symmetry distortion a full explanation of the intensity behaviour of the bands with the polarisation of the light is given.
SERS from Ag Colloids in Alkali Halide Crystals
Authors: Reimer H. , Fischer F. 
Published: July 2007

AbstractSurface‐enhanced Raman scattering is investigated on NaCl, KCl, KBr, and KI crystals doped with Ag. By stepwise annealing the controlled formation and growth of Ag colloids out of Ag− centres can be performed. Raman scattering and optical absorption at 20 °C under comparable conditions allow the conclusion that “active sites” at the colloid surface are responsible for the increase and decrease of the SERSspectrum. Comparative SERS at LNT show the preferred excitation near the upper limit of the crystal phonon spectrum.
Stochastic Self‐Oscillations in a Two‐Temperature Electron—Hole Plasma in a Semiconductor
Authors: Bonch‐bruevich V. L. , Ky Le Vu 
Published: July 2007

AbstractThe nonstationary states are studied of an electron—hole plasma generated and heated by an interband light absorption in a direct gap semiconductor. Account is taken of phonon and/or radiative as well as of interband impact recombination processes; adiabatic approximation (“slow recombination”) is not employed. Explicit conditions are stated underwhich the system sustains regular (periodic) or stochastic self‐oscillations of the concentration and temperature of the charge carriers.
On the Determination of Pseudopotential Parameters and the Comprehensive Study of Metallic Properties
Authors: Gohel V. B. , Acharya C. K. , Jani A. R. 
Published: July 2007

AbstractThe practical usefulness of the method of determination of pseudopotential parameters due to Senoo et al. and Soma is examined. It is found that this method is useful for the comprehensive study of electronic und atomic properties of simple metals. The wave vector q0, where the form factor becomes zero, plays a vital role and its correct determination is highly desirable. The present work deals with such study, calculations of band energies at major symmetry points, evaluation of electrical resistivity, and thermoelectric power of aluminium (liquid and solid phases).
The Auger Spectra from Alloys Effect of Partial Long‐Range Order
Authors: Drchal V. , Kudrnovský J. 
Published: July 2007

AbstractThe intraatomic core—valence—valence Auger spectra from partially ordered alloys characterized by the long‐range order parameter S are investigated. The combined effect of disorder and electron correlations is studied for the case of a filled valence band using the coherent potential approximation to treat disorder and the local ladder approximation for the two‐particle Green function that determines the Augerspectrum. The theory is illustrated numerically on a simplified model of analloy.
Local Optical Centers in Rare Gas Crystals
Authors: Ratner A. M. , Tarasova E. I. 
Published: July 2007

AbstractA comparison between microscopic calculated data and experimental results permits to suggest the character of crystalline surroundings of a local center and to differentiate between surface and bulk centers. The deformation of an excited atomic state is investigated which reduces due to lattice deformation. The analysis of a site exciton state provides some informationon the resonance contribution to the energy.
Luminescence Decay in NaI:Pb
Authors: Baltog I. , Mihuţ L. 
Published: July 2007

AbstractThe dependence of the photoluminescence spectra of NaI:Pb excited in the A absorption band region on crystal temperature and dispersion state of the impurity is studied. The luminescence decay time measurements are performed for each emission band. Two lifetime components can be resolved for the AX emission, the slow component value being temperature independent. Two life‐time components independent of the temperature are observed also for the emission band of the precipitated state. The luminescence of the precipitated state is supposed to be of excitonic type due to a new phase as a result of the aggregation of the impurity. The decrease of the lifetime values of each component towards the higher energy side of the spectrum is explained by modification of the potential energy surface of the luminescent centre by the lowering of symmetry.
On the Theory of Relaxation for Systems with “Remnant” Memory
Authors: Nigmatullin R. R. 
Published: July 2007

AbstractThe investigation of the universal response of an electromagnetic, acoustic, and mechanical force indicates the existence of relaxation processes with memory. It is shown that the form of the polarization current I(t) ∼︁ (ωpt)−(1+m) for (ωpt ≫ 1) can be explained on the basis of a dipole relaxation with a “remnant” memory. In accordance with theexperimental data a memory function is found which describes in one case the exponential decay I(t) ∼︁ exp (—λt) which is equivalent to the absence of memory and in the another case it transforms into a harmonic oscillator equation (full memory). From this theory theexistence of a “superslow” relaxation process also follows, in which the changing of polarization is slower than its first derivative. Such processes are also observed experimentally and are described by linear differential equations in fractional derivatives. The relationship between the experimental exponent m and the derivative exponent λ is found.
On the Calculation of the Residual Resistivity of Precipitates
Authors: Gläser U. H. 
Published: July 2007

AbstractThe change in the residual resistivity of alloys due to clustering is calculated by means of the t‐matrix and without adjusting any free parameter. A criticism of the widely used scattering potentials is given. Basing on isotropic free electron transport the applicability of the theory is limited to small clusters. An initial increase in the residual resistivity due to the formation of Guinier‐Preston zones is found for AlZn and AlCu. The different local Fermi momenta in the matrix and in the clusters have an important influence on the resistivity.
Structure of Non‐Simple Liquid Metals
Authors: Canessa E. , Mariani D. F. , Vignolo J. 
Published: July 2007

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractMaking 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

AbstractThe 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

AbstractA 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractAngular‐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

AbstractRecombination 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

AbstractA 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

AbstractLuminescence 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

AbstractIt 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

AbstractA 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

AbstractProton‐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

AbstractDiffusion 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

AbstractThe 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

AbstractThe 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

AbstractIt 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.