bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interaction of Current Carriers with Local Moments in a Narrow Band
Authors: Anokhin A. O. , Irkhin V. Yu. 
Published: July 2007

AbstractOne‐electron Green's functions of a narrow‐band paramagnetic insulator are calculated within the framework of the s–d exchange and Hubbard models with strong correlations. The agreement with the 1/z‐perturbation theory is discussed for the approximations employed. It is demonstrated that the analytical properties of the retarded Green's functions are violated for simple approximations in the Hubbard model and the s–d model with a negative exchange parameter I (and, for self‐consistent versions, at any sign of I). Numerical results for the corresponding densities of states are presented.
Wave Vector Dependent Magnetooptics in Semiconductors Linear and Nonlinear Interband Transitions
Authors: De Salvo E. , Girlanda R. 
Published: July 2007

AbstractA perturbative calculation, out of the electric dipole approximation, of the one‐ and two‐photon interband transition rates between the Landau levels of a semiconductor is presented. A gauge independent approach for the description of the radiation–matter interaction Hamiltonian is applied in the study. Comparisons with other naive models and experimental results are reported.
Chlorine Diffusion in CdTe
Authors: Sadaiyandi K. , Ramachandran K. 
Published: July 2007

AbstractThe experimental results of chlorine diffusion in CdTe reveal that the dominant mechanism for diffusion is through neutral defect pair such as [VCdVTe]*. Here, theoretical calculations are carried out for all the possible mechanisms such as single vacancy, single interstitial, neutral defect pair, and Frenkel defect pair. The results suggest that the most possible mechanism for Cl diffusion in CdTe is that through neutral defect pair, supporting the experiment.
Electronic Structure in Relation to the Reactivity of Nonstoichiometric AxMX2 Layered Compounds
Authors: Molenda J. 
Published: July 2007

AbstractThe data concerning the character of the discharge curve for various materials are collected and correlated with the microscopic electronic parameters such as the metal‐metal distances in the corresponding materials. On the basis of this correlation an electronic model of alkali metal ion intercalation into AxMX2 (A = Li, Na; M = V, Cr, Mn, Co, Ni; X = O, S, Se) cathode materials is proposed. The potential changes accompanying electrochemical intercalation are ascribed to the changes of the Fermi level position in the cathode material. Consequently, the step‐like shape of the discharge curve is linked with the step‐like shape of the density‐of‐states curve. Comparison of the actual metal–metal distance RM–M with the critical distance Rc given by Goodenough allows the prediction of the properties of oxide cathode materials. The materials for which RM–M < Rc prove to be among the best materials for use in batteries.
Micromagnetics of Critical Fields and Elementary Catastrophe Theory
Authors: Nieber S. , Kronmüller H. 
Published: July 2007

AbstractTaking into account the anisotropy constants up to the sixth order the critical fields for the demagnetization mode of uniform rotation in uniaxial materials are derived. The boundary curves separating regions of material parameters with distinct critical behaviour are determined. The relation between uniform rotation and FOMP is discussed in the context of elementary catastrophe theory.
Magnetocaloric Measurements on Dysprosium Phosphate (DyPO4)
Authors: Hoffmann J. 
Published: July 2007

AbstractDyPO4 orders below 3.39 K as a two‐sublattice Ising antiferromagnet with its moments along the crystallographic c‐axis. Measurements of the specific heat and the magnetocaloric effect with the magnetic field applied along c are performed to determine the phase diagram. A new intermediate ferrimagnetic phase is found at the metamagnetic transition from the antiferromagnetic to the paramagnetic state below 0.82 K. Although this phase extends only over a field range of about 20 mT, it is clearly seen since for crystals with finite demagnetising factor it produces additional mixed phases at the first‐order phase boundary. The measured phase diagram is verified by mean‐field calculations and the possibility of even more ferrimagnetic phases is discussed.
Contribution of Exciton Degenerate States to Multiphonon Resonant Raman Scattering
Authors: Riera R. , Sotolongo O. , Lang I. G. 
Published: July 2007

AbstractA general method is given for the determination of multiphonon resonant Raman scattering (MPRRS) cross section when exciton degenerate states occur. The calculation is performed for exciton states with principal quantum number n = 2, when electron and hole effective masses are equal (me = mb). The results obtained can explain the special characteristics of secondary radiation emission spectrum in InBr and InI. It is shown that the MPRRS theory can be constructed on the basis of a classical approach, as for n = 1.
Molecular Dynamics Simulation of Vitrification and Plastic Deformation of a Two‐Dimensional Lennard‐Jones Mixture
Authors: Kotelyanskii M. J. , Mazo M. A. , Oleynik E. F. , Grivtsov A. G. 
Published: July 2007

AbstractA computer model of a two‐dimensional atomic glass is generated by molecular dynamics. This model consists of 500 Lennard‐Jones particles of two different diameters. A volume‐temperature diagram is obtained. The bend found on this diagram at T = 0.28ϵ is interpreted as the glass transition. Density fluctuations and changes in the particles coordination numbers at the glass transition are studied by means of Voronoy polygons. The spatial correlation functions for particle displacements in the liquid and glassy states are analyzed. It is found that the glass structure is always a frozen liquid structure. Below the glass transition particle displacements from their equilibrium positions become spatially correlated, and the correlation length is greater than the model's size. Unusual roton‐like collective vibrational modes are found in the glass. The simulation of shear deformation shows that these modes may play an important role in the plastic deformation. No correlation is found between the diffusional mobility of particles and their local free volumes. This fact contradicts the main physical concept upon which a free volume approach is based.
Empirical N‐Body Interatomic Potential for B.C.C. Transition Metals
Authors: Ogorodnikov V. V. , Pokropivny V. V. 
Published: July 2007

AbstractNew thermodynamical expressions are derived for the energy and bulk module of the electron gas for cubic metals as functions of the electron Grüneisen parameter, specific electron heat capacity, coefficient of thermal expansion, Caushy discrepancy, and temperature. On this basis, interatomic potentials and a semi‐empirical equation for the volume dependence of a noncentral N‐body term are obtained. A formula is proposed for the temperature of the natural ductile‐brittle transition. The tendency established of this temperature to increase as the N‐body term decreases in the row Nb–Ta–V–Mo–W–Cr. The nature of the anomalous properties of Cr, the long‐range potential problem, and connection with other potentials are discussed.
The Quasiphonon Model of Amorphous Solids and the Percus‐Yevick Approximation
Authors: Kovalenko N. P. , Krasny Yu. P. , Weck G. 
Published: July 2007

AbstractThe quasiphonon model is used to describe thermodynamical features of amorphous solids in the low temperature range (T ≈ 20 to 50 K). Using the r‐representation of the particle interaction potential and correlation functions the quasiphonon dispersion relation ωα(k) of binary amorphous solids may be calculated analytically in the Percus‐Yevick approximation. This relation is obtained in a form with the characteristic roton‐similar minimum in the shortwave range of k. Even this minimum could be the reason for anomalous thermodynamical properties of such amorphous systems.
Impurity States in Quantum Wells Structures
Authors: Beril S. I. , Pokatilov E. P. , Zotov A. S. , Madkur S. 
Published: July 2007

AbstractThe shallow impurity center binding energy in a single quantum well is calculated by using the exact electron‐interaction potential. It is shown that the binding energy value corresponding to a simple model Coulomb potential \documentclass{article}\pagestyle{empty}\begin{document}$ V_{e - i} = - e^2 /\varepsilon _{eff} \sqrt {\varrho ^2} + (z_e - z_i)^2,\,\varepsilon _{eff} = \sqrt {\varepsilon _1 \varepsilon _2,} $\end{document} is less than the value, corresponding to the potential roughly by 15%, even for structure with very slightly different layer dielectric permittivities (a GaAs/AlxGa1‐xAs structure for example).
Ordered Superstructures of Oxygen Ions in La2MeO4+δ (Me = Cu, Ni)
Authors: Loktev V. M. , Tatarenko H. M. 
Published: July 2007

AbstractTwo‐dimensional commensurable ordered superstructures that can arise in La2MeO4+δ (Me = Cu, Ni) crystals are considered. It is shown that stable superstructures with δ = 0.125, 0.25, and 0.5 are formed as long‐range ordering of superstoichiometrical oxygen. The decomposition of a nonstoichiometric La2MeO4+δ compound into the ordered phases with stoichiometric compositions is proposed.
Lattice Dynamics of Formaldehyde
Authors: Weng S. X. , Anderson A. 
Published: July 2007

AbstractA simple force constant model is described and applied to the vibrations of solid formaldehyde, H2CO and D2CO. Twenty adjustable parameters are used to obtain the best fit to the lattice mode frequencies and crystal field splittings observed by Raman and infrared spectroscopy. The use of symmetry coordinates to reduce the dimensions of the 96 by 96 original matrix is outlined. The dominant intermolecular interaction is confirmed to be that between carbonyl groups. The dependence of the force constants on interatomic separation is expressed in a simple exponential form.
Time‐Resolved Luminescence of Localized Excitons in CdS1—xSex under High Excitation
Authors: Urban M. , Schwab H. , Klingshirn C. 
Published: July 2007

AbstractThe temporal evolution of luminescence due to localized excitons in CdS1—xSex for various compositions from x = 0.02 to 0.55 is investigated after pulsed excitation (t ≈ 50 ps). The excitation intensity is varied from 8 × 105 W/cm2 up to 4 × 107 W/cm2. For the first time the luminescence dynamics is investigated under extremely high excitation into the extended states and it is found that the luminescence decay times, τD, become shorter and independent from the photon energy for high excitation. This behaviour is caused by the saturation of the localized states under high excitation. The x‐dependence of the “tailing parameter” and the total density of the localized states are discussed based on the experimental findings.
Temperature Dependence of the Dielectric Function of Orthorhombic GeS
Authors: Lukeš F. 
Published: July 2007

AbstractThe thermoreflectance spectra of orthorhombic GeS obtained in the 1 to 3.5 eV energy region as a function of temperature between 17 and 300 K for linearly polarized light with electric field vector E parallel to a‐ and b‐axes are used to determine the energies of the critical points Ei and broadening parameters Γi. The temperature dependence of the Ei values is analyzed in terms of average energies of phonons participating in the corresponding electron—phonon interactions. Also determined are the refractive index of GeS in the region of small absorption in the energy range of about 1 to 2 eV and its temperature dependence within the temperature interval 17 to 300 K from the interference effect.
Kinetics of A‐Luminescence in KCl:Tl Multiphonon Processes
Authors: Hlinka J. , Mihokova E. , Nikl M. 
Published: July 2007

AbstractThe decay kinetics of Tl+ UV‐emission in KCl: Tl is investigated in the wide temperature region 4.2 to 400 K. Two components — fast and slow ones are found. The results are interpreted with the help of a three level model with two excited states — radiative and metastable ones. Multiphonon nonradiative processes between these levels are involved to explain the temperature dependence of the fast component. Also the temperature dependence of transition probability between the metastable excited state and the ground state is included to improve the agreement between the experimental data and calculations.
Electronic Structure of a One‐Dimensional Superlattice
Authors: Lazo E. 
Published: July 2007

AbstractBy means of a one step matrix decimation and the transfer function method, the electronic structure of a one‐dimensional superlattice model is investigated. All the Green function components corresponding to the basic cell that form the superlattice are obtained inverting a unique complex matrix of coefficients. The method permits to calculate the local properties on each site of the basic cell. The global density of states obtained is compared with the results given by the negative‐eigenvalue theory of Dean.
Practicable Method for Estimating Thermal Depths from Phonon‐Broadened Photoexcitation Cross‐Section Bands I. Foundations
Authors: Pässler R. 
Published: July 2007

AbstractPhotoexcitation cross‐sections of deep traps in semiconductors that are thermally broadened by multiphonon (MP) emission and absorption are represented by convolutions of electronic parts with thermally averaged Franck‐Condon factors. A trap‐independent MP absorption versus emission probability relation following from analytical expressions for the limiting case of vanishing phonon dispersion is generalized to arbitrary dispersion of phonon energies assumed, however, to remain unchanged during a transition. Corresponding Franck‐Condon factors are shown to decompose into products of a universal exponential factor, exp (−ΔE/2kT), and system‐specific parts representing symmetric functions of the vibrational energy difference ΔE. On this basis an upper bound is derived for the ground‐to‐first‐excited level distance from the vertex position of the correspondingly transformed photoexcitation cross‐section band. The exemplification for the case of electron excitation from the oxygen donor level (state 1) in gallium arsenide shows reasonable agreement with results obtained by other methods.
Carrier Drag in Modulation Doped Quantum Wells
Authors: Gerlach E. , Kaser A. 
Published: July 2007

AbstractA fluctuation concept is applied to describe the ‘negative absolute mobility’ of minority carriers in ‘modulation doped quantum wells’ found experimentally by Höpfel et al. The observed linear and nonlinear effects arise from a competition of carrier–carrier and carrier–phonon and carrier–ion scattering.
An Estimate of the Dependence of the Ising Critical Exponents on the Lattice Dimensionality
Authors: Silva P. R. 
Published: July 2007

AbstractUpper and lower bounds are estimated of the two‐point correlation function exponent, η, of the Ising model, as a function of the lattice dimensionality, d. The average value of these two bounds together with the correlation length critical exponent v(d) evaluated by Thompson, lead to a set of critical indexes which satisfy the hyperscaling relation. This set of exponents also shows an adequate agreement with the results obtained by Le‐Guillou and Zinn‐Justin for the Ising model in non‐integer dimensions, in a large range of the parameter d.
Sublattice Structure of a Site Dilute Ising Lattice
Authors: Sikakana I. Q. , Lowther J. E. 
Published: July 2007

AbstractThe distribution of spins on a quenched two‐dimensional Ising lattice is examined using Monte Carlo techniques and related to the critical properties. A sublattice structure is defined, and the spin distribution on each sublattice investigated as dilution and temperature change.
The Shape of a Spectral Hole and Its Temporal Response at Short Burning Times in Two‐, Three,‐ and Four‐Level Systems
Authors: Rebane I. K. 
Published: July 2007

AbstractThe shape of the spectral hole in an inhomogeneous distribution function of centres over the transition frequency is calculated for the case of a quasimonochromatic burning light pulse which characteristic duration time is comparable to the relaxation times of the excited electronic level. Two‐step spectral hole‐burning in the cases of three‐ and four‐level systems as well as one‐step processes are considered. The temporal responses of the spectral holes as spectral filters on δ‐pulse of light are found.
Galvanomagnetic Luminescence Spectra of InSb
Authors: Kessler F. R. , Paul R. , Nies R. 
Published: July 2007

AbstractIn crossed electric and magnetic fields inside an intrinsic semiconductor a free carrier compression takes place due to the Lorentz force (LF). This leads to a free carrier profile containing regions of enhancement as well as of depletion of free electron–hole pairs. These deviations from the equilibrium concentration lead to a “galvanomagnetic luminescence (GL)” which is positive or negative in relation to the equilibrium temperature radiation. The measured GL spectra of InSb show a double peak at about 5.6 μm wavelength due to g‐factor splitting of the Landau level involved. The evaluation of the GL spectra (as function of magnetic field up to 14 T) by means of model calculations leads to the determination of the energy dependent band parameters: effective mass and Landé factor corresponding to the strong nonparabolicity of the conduction band of InSb. The integral radiation output of GL is also measured as function of the LF showing an increase of the quantum efficiency of emission of radiation due to (i) a saturation effect of the surface recombination velocity and (ii) a reduced diffusion length at increasing magnetic field leading to a corresponding profile enhancement.
Relationship of Triple Point Solid Volume with Thermo‐Acoustic Parameters and Structural Distortion in Quasi‐Spherical Molecular Liquids by the Corresponding State Correlations
Authors: Sharma B. K. 
Published: July 2007

AbstractThe significance and the validity of the idea of corresponding state correlations is tested by obtaining unique values for reduced triple point solid volume, Boyle temperature, critical state nearest‐neighbour number, and intermolecular separation, using critical volume and temperature as reduction parameters. The calculated values show very close agreement with experimental values for simple, non‐polar, spherical liquids. An attempt is made to obtain an expression for liquid structure distortion parameter in terms of the reduced molar volume of the liquid. It is shown that the effect of distortion parameter on structural variations with regard to change in nearest‐neighbour number with temperature in liquid argon is significant. The results are used to develop a relationship between the thermo‐acoustic parameters on the basis of liquid structure distortion and the hard‐sphere model with attractive interactions in simple liquids.
On the Intrinsic Ductility and Brittleness of Crystals
Authors: Pokluda J. , Šandera P. 
Published: July 2007

AbstractIntrinsic ductile versus brittle response of ideal crystals containing cracks is theoretically analyzed using a modified Kelly‐Tyson‐Cottrell approach. A new criterion based on the three‐axial ideal tensile strength and the normal‐stress dependence of ideal shear stress is proposed. A great variety of possible crack/slip configurations is evaluated by means of computer in order to estimate the intrinsic response of f.c.c., b.c.c., h.c.p., and diamond crystals. The result of this crystal‐calibration is, in general, in a good agreement with available experimental data.
An Investigation of Smectic A—Nematic and Nematic—Isotropic Phase Transitions
Authors: Alapati P. R. , Saran D. 
Published: July 2007

AbstractThe phases and phase transitions in two homologues of the 4‐(4′‐n‐alkyloxy‐benzoyloxy) benzylidene‐2″‐methylaniline (decyloxy and dodecyloxy) are characterized using a variety of experimental techniques. These are differential scanning calorimetry, thermal microscopy, X‐ray diffraction, ESR spectroscopy, and density determination. The nematic—isotropic transition is found to be of first order but with a smaller transition entropy, in both of the compounds, than expected. The smectic A—nematic transition is found to be of weak first order in both of the compounds. The experimental results are compared to those of other compounds which have comparable molecular lengths and with the predictions of a molecular field theory of smectic A liquid crystals.
On a Dislocation Core Tensor
Authors: Maruszewski B. 
Published: July 2007

AbstractAn attempt is made that may lead to a new definition of the dislocation density field. The idea is based on the fact that dislocation cores form a kind of network of infinitesimally thin pores or capillary tubes in the crystal lattice. The main aim of the new description of the dislocation density field is focused on a way which differs from the definition based on a local distortion field coming from lattice line defects.
Theorie du ferromagnétisme itinérant dans des semimétaux supraconducteurs
Authors: Tran C. Do , Manh D. Nguyen , Van C. Nguyen 
Published: July 2007

AbstractUne théorie du ferromagnétisme itinérant dans des semimétaux supraconducteurs est proposée. Une aimantation moyenne apparait dans l'état supraconducteur due à l'interaction (interférence) des ondes: onde de densité de spin, onde de densité de charge et onde des paires de Cooper. Le diagramme des phases et les propriétés physiques des états examinés sont étudiés analytiquement et numériquement.
Raman Spectra of [N(CH3)4]2ZnCl4 Single Crystals IV. Isomorphous Substitutions. Raman Spectra of [(CH3)2NH2]2ZnCl4 and [(CH3)2NH2]2CoCl4 Crystals
Authors: Torgashev V. I. , Yuzyuk Yu. I. , Rabkin L. M. , Durnev Yu. I. , Bobrova Z. A. 
Published: July 2007

AbstractThe polarized Raman spectra of recently synthesized [N(CH3)4]2ZnCl4 and [(CH3)2NH2]2CoCl4 crystals are obtained. The structure of these spectra exhibits strong similarities with that of [N(CH3)4]2ZnCl4. The vibration spectra of these crystals at room temperature are analyzed and the similarity of the spectra with those of the ordered low‐symmetry phase (176–155 K) of the [N(CH3)4]2ZnCl4 crystal is discussed.
Excitonic Excitation of Cu Luminescence in ZnSCu, Cl Crystals
Authors: Brandt S. , Jaszczyn‐Kopec P. 
Published: July 2007

AbstractAn excitation peak is observed at Ax energy (A = intrinsic exciton) for the Cu blue (CuB), and at AxLO for the Cu green (CuG) luminescence in a ZnSCu, Cl cubic crystal. It is shown that the difference in the two peaks position is due to the localization of CuB luminescence centers at the surface and that of the CuG in the bulk of the crystal. The excitonic excitation of the blue emission is attributed to the Auger process decay of the excitons bound to the (CuZnCui) complex. The possibility of exciting the CuGDA pairs, not only via binding the excitons, but also by the energy transfer from the excitons bound to other impurities, is considered.
Fluorescence and Upconversion in CaF2:Ho3+
Authors: Tang S. H. , Zhang H. Y. , Kuok M. H. , Kee S. C. 
Published: July 2007

AbstractLaser excitation studies of CaF2 crystals doped with 0.01 to 10% Ho3+ using the second harmonic wavelength 532 nm of a pulsed Nd: YAG laser are carried out. Three fluorescence bands belonging to the 5F4, 5S2 → 5I8, 5F4, 5S2 → 5I7 and 5F5 → 5I8 transitions are detected. Fluorescence lifetimes of the first two transitions are measured and used for site‐identification of new lines. Four upconverted fluorescence bands belonging to the 5F3 → 5I8, 5G4 → 5I8, 5G5 → 5I8, 5H5, 5H6 → 5I8 transitions are also detected. A comparative study is made of two pairs of energy transfer mechanisms, which are multiphonon relaxation versus ion‐pair relaxation and two‐photon absorption versus ion‐pair relaxation. The analysis of the concentration dependence of fluorescence intensities shows that ion‐pair relaxation is the chief mechanism responsible for the fluorescence and upconversion behaviour of CaF2:Ho3+.