bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simple Numerical Method for the Estimation of Multiple Scattering in the Compton Effect
Authors: Das G. , Panda B. K. , Mahapatra D. P. , Padhi H. C. 
Published: July 2007

AbstractA simple numerical estimation of multiple scattering in the Compton effect is made for six different samples at 60 keV γ‐ray energy by taking the experimental collimation into account and restricting the scattering in a plane. Photon paths are generated through geometrical methods and the scattered intensities up to triple scattering are estimated. Present results are in good agreement with earlier Monte Carlo results. The double scattered spectral distributions for different sample thicknesses show shape dependence on sample thickness.
Mechanism of Concentration Quenching of Gd3+ and Eu3+ Emission in Perovskite‐Like Aluminates
Authors: de Vries A. J. , van Vliet J. P. M. , Blasse G. 
Published: July 2007

AbstractThe mechanism of concentration quenching of the Gd3+ emission in (La, Gd)AlO3 and the Eu3+ emission in (Eu, Gd)AlO3 is reported and discussed. Nearest and next‐nearest neighbors are involved in the concentration quenching process. Nearest neighbor transfer occurs by exchange interaction. Even for next‐nearest neighbors this type of interaction seems to dominate. In GdAlO3 energy migration via the 6I level is reported. After excitation of the 6I level, the excitation energy migrates at 300 K about 1350 steps over the 6I level before nonradiative decay to the 6P level occurs. The energy migration in EuAlO3 at low temperatures can be described with a phonon‐assisted process.
Diffusion Mechanisms in B.C.C. Metals. Calculation of the Correlation Factor for Mixed Nearest and Next‐Nearest Neighbour Vacancy Jumps
Authors: Neumann G. , Tuijn C. , de Vries G. , Bakker H. 
Published: July 2007

AbstractThe correlation factor for mixed nearest and next‐nearest neighbour monovacancy jumps is calculated as a function of the jump frequency ratio. The diffusion is discussed in terms of a onedefect and several two‐defect models. A pronounced temperature dependence of the diffusion energy as well as a marked divacancy contribution at high temperatures can be excluded for the refractory metals. While the measured temperature functions of the isotope effect are compatible with mixed nearest and next‐nearest neighbour jumps, there is no proof for the existence of selfinterstitial contributions to the diffusion.
Vibrational Energy as a Function of Interatomic Distance in Rare‐Gas Solids. A Universal Relationship
Authors: Mohazzabi P. , Behroozi F. 
Published: July 2007

AbstractA universal relationship between the reduced vibrational energies and average interatomic distances is derived for rare gas solids within the Lennard‐Jones (6‐12) interatomic potential model. This relationship is employed to obtain the zero‐point energies as well as the zero‐pressure heat capacities of the rare gas solids. The overall agreement with the existing data is very good.
Electronic Structure of CuCl, CuCl, and CuCl Clusters
Authors: Takeuchi T. 
Published: July 2007

AbstractElectronic properties are obtained of CuCl, CuCl, and CuCl Clusters using the SCF Xα multiple‐scattered wave method. The calculation shows that the “cluster band gap energy” in the CuCl clusters is 3.6 eV, fortuitously close to the experimental direct band gap of 3.4 eV of CuCl. Cu0 in CuCl introduces a “donor” level at Vc − 0.3 eV. In CuCl the energy levels corresponding to the upper valence bands of CuCl almost overlap and the energy gap widens substantially. The energy level 3t2 with a hole is almost at the same level as that of 1t1 of other clusters. A significant Cu 3d–Cl p hybridization is introduced in CuCl.
Dynamic Potentials for Unstable Narrow Band Systems. Application to Intermediate Valence and Heavy Fermion Compounds
Authors: López‐Aguilar F. , Balle S. , Costa‐Quintana J. 
Published: July 2007

AbstractThe one‐body propagator for interacting systems with strongly correlated electrons is determined. The self‐energy functional is constructed from a GW approximation and a self‐consistent procedure is given for determining the electronic structure of the f systems (4f and 5f). The method is applied to the intermediate valence phase of SmS and to UAl2 which is a heavy fermion compound. The resulting electronic structure is compared with available experimental results. The obtained density of states presents reasonable agreement with these results.
Dynamical Effects on the Binding Energies of Core Excitons in Covalent and Polar Semiconductors
Authors: Fliyou M. , Khan M. A. , Ringeissen J. 
Published: July 2007

AbstractThe binding energies of core excitons in covalent and polar semiconductors are obtained by the polaron model taking into account the dynamical screening by the valence electrons. The binding energies of core excitons thus obtained are comparable to the available experimental values.
The Quantum Corrections to the Conductivity in Strong Spin–Orbit Coupling Semiconductors
Authors: Bilgildeeva T. Yu. , Polyanskaya T. A. 
Published: July 2007

AbstractAn anomalous positive magnetoresistance is observed in layers of GaAs and GaAs0.94Sb0.06 doped with Ge (p‐type conductivity) which is found to be governed by quantum effects. In the analysis the degeneracy of the valence band is considered and the contribution extracted corresponding to the total moment, I = 0, of the pair of particles. The wave function phase relaxation time is found. The origin of the magnetoresistance which cannot be described by the theoretical expression for I = 0 is discussed.
Condition for Superconductivity
Authors: Krüger E. 
Published: July 2007

AbstractCommutation properties of the electronic Hamiltonian operator indicate that superconductivity is caused by a spin–phonon interaction rather than by the usually considered spin‐independent electron–phonon interaction. The proposed spin–phonon interaction is a new exchange effect which goes beyond the Born‐Oppenheimer approximation and in which the electron spins couple to phonons as a consequence of the Pauli principle, the crystal symmetry, and the conservation of spin angular momentum.
Nuclear Polarization of Atomic Hydrogen
Authors: Mertig M. , Luppov V. G. , Pilipenko Yu. K. 
Published: July 2007

AbstractThe spontaneous nuclear polarization of atomic hydrogen is calculated from the decay equations under different experimental conditions. In particular at high densities the influence of the three‐body processes described by the theory of Kagan, Vartanyants, and Shlyapnikov is investigated. To achieve a high nuclear polarization, optimum conditions are found in dependence on temperature and density.
A Recursion Method for Calculating Many‐Particle Green's Functions. Resonant Secondary Radiation and Excitation Spectra in the Exciton Region
Authors: Sherman A. V. 
Published: July 2007

AbstractA procedure for calculating many‐particle Green's functions is suggested, which is based on the information supplied by the recursion method. The advantages of the procedure are the possibility of introducing a renormalized energy spectrum of the considered system, exactly definable within the recursion method, into calculations and their relative simplicity. As an illustration of the general method a calculation of a two‐particle Green's function, describing a resonant secondary radiation in the region of a three‐dimensional isolated band of excitons interacting mainly with optical phonons, is carried out. The range of parameters covers the cases of a weak exciton‐phonon coupling and a vibronic exciton. The main attention is paid to the relation of luminescence and scattering components. The obtained spectra are compared with experimental results.
Intrinsic Luminescence of CsCdBr3
Authors: Andraud C. , Pelle F. , Pilla O. , Blanzat B. 
Published: July 2007

AbstractElectron–hole recombination luminescence is investigated in CsCdBr3 crystals. This luminescence consists mainly of a single band at 1.9 eV, assigned to a transition 3Σ → 1Σ. The comparison between this emission and emission observed under the 4 eV excitation confirms that the latter is due to Br centers.
Angle‐Resolved X‐Ray Emission Spectra (ARXES) of Carbon in Potassium Graphite C8K
Authors: Šimůnek A. , Wiech G. 
Published: July 2007

AbstractMeasurements are presented of angle‐resolved carbon K X‐ray emission (ARXES) bands for first‐stage intercalated potassium graphite C8K and pure graphite. The corresponding p‐like carbon partial densities of states are calculated by the ab‐initio pseudopotential method. It is found that in the electronic structure of graphite potassium creates new carbon pz‐like valence states near the Fermi edge. The good agreement between the measurements and the calculations makes possible a detailed analysis and interpretation of the experimental results. It appears that the terms ionicity, charge transfer, degree of hybridization, and electron occupancy are non‐adequate for the description of the potassium–carbon bond. As compared to available UPS and XPS results for C8K new features in the ARXES spectra provide complementary data for the understanding of the nature of the potassium–carbon bond.
Positron Annihilation in BaF2 and SrF2
Authors: Shishkin A. V. , Linderoth S. , Svirida S. V. 
Published: July 2007

AbstractPositron life‐time measurements are performed on the ionic crystals BaF2 and SrF2 in the temperature range 80 to 550 K. The results are discussed in terms of positron interactions with defects created by decay of excitons produced in the path of the positron.
Third‐Order Elastic Constants for Alkaline Earth Oxides and Fluorides
Authors: Hans D. 
Published: July 2007

AbstractThe interionic potential model recently developed by taking account of the composite effect of short range repulsive and dispersion forces along with three body interactions is applied to investigate the elastic behaviour of alkaline earth oxides and fluorides. Values of third‐order elastic constants and pressure derivatives of second‐order elastic constants are obtained for MgO, CaO, SrO, BaO, CaF2, SrF2, and BaF2 crystals. The calculated values are found to present close agreement with experimental data.
On the Evaluation of Entropy and Thermodynamic Properties of 1:1 Type of Molten Salts through the Generalized Debye Inverse Screening Length
Authors: Rao R. V. Gopala , Satpathy A. 
Published: July 2007

AbstractBlum's generalized inverse screening length parameter Γ is solved numerically for 1:1 type of fused salts. Using these Γ parameters for the salts, a method is evolved for the evaluation of the entropies of fused salts by treating the different components of the salts as seperate mass entities along with the concept that the total entropy is a sum of the contributions from neutral hardspheres and that due to charging process. The entropies so calculated are found to be in good agreement with experiment. Further from the parameters Γ, the excess thermodynamic properties and the contact values of the partial radial distribution functions are calculated. A simple method is given in the evaluation of the parameter Γ which is found to yield almost similar values as that given by Blum.
Acoustic Mode Vibrational Anharmonicity in the Intermediate Valent Compound Samarium Sulfide
Authors: Gupta B. R. K. 
Published: July 2007

AbstractAnharmonic elastic properties of SmS in its semiconducting form are analysed in terms of third order elastic constants and pressure derivatives of second order elastic constants calculated using an interionic force model. This potential model consists of long‐range Coulomb and three‐body interactions and short‐range overlap repulsion, effective up to second neighbour ions. Repulsive parameters (b, ϱij) are determined using the equation of equilibrium condition and overlap integrals. The results reported are compared with experimental values and fairly good agreement is obtained.
Phonon Localization in Disordered Systems. Application of the Potential‐Well Analogy Method
Authors: Böttger H. , Theuerkauf M. 
Published: July 2007

AbstractUsing a self‐consistent equation for the diffusion coefficient of vibrational excitations, the potentialwell analogy (PWA) method for studying localization of vibrational excitations in disordered systems is formulated in analogy to the electron problem. Results obtained by the PWA‐method for vibrational systems with mass disorder are in good agreement with numerical data.
High‐Energy Tails in the Total Energy Distribution of Field Emitted Electrons from Tungsten
Authors: Bakhtizin R. Z. , Yumaguzin Yu. M. 
Published: July 2007

AbstractMethods of evaluation are considered and results presented of the study of the total energy distribution of electrons field‐emitted from tungsten at emission current densities of up to 105 A/cm2. The high‐energy tails in the energy distribution are examined and their dependence on electric field strength, emission current density, work function, and residual gas pressures in the vacuum chamber.
Statistical Operator for Thin Solid Films
Authors: Onyszkiewicz Z. 
Published: July 2007

AbstractUsing the Schrödinger variational principle for average energy in the case of a system interacting weakly with environment and for a given entropy, the equilibrium statistical operator is obtained. In the case when the interaction with the environment can be neglected this statistical operator is identical with that of the canonical Gibbs distribution. This statistical operator may be useful in describing thermodynamical properties of thin solid films and similar systems.
Investigation of Hot Exciton Interaction in ZnTe Crystals
Authors: Baltramiejūnas R. , Stepankevičius V. , Tamulaitis G. , Žukauskas A. 
Published: July 2007

AbstractRecombination‐induced heating of a gas of interacting excitons is investigated in ZnTe single crystals at a bath temperature of 80 K. The energy transfer in the system of self‐heated excitons and of nonequilibrium optical and acoustic phonons is considered. The density, the constant of bimolecular recombination, and the instantaneous lifetime of excitons in highly excited ZnTe crystal are found using the obtained experimental evidence of the effective temperature of excitons and the heat effect of the inelastic exciton–exciton collisions.
Optical Absorption and Stability of the Bipolaron Lattice
Authors: Puff H. , Streitwolf H. W. 
Published: July 2007

AbstractThe polaron lattice solution of the Brazovskii‐Kirova model is derived in the continuum approximation. The stability of the bipolaron lattice phase of this solution as well as the nature of the transition to the dimerized C‐phase are discussed. The optical conductivity is calculated for different excess electron densities and the optical sum rule is verified in each case. Finally a comparison with experimental results for polypyrrole, polythiophene, and its alkyl‐derivatives is made.
Sm3+ in ZnS on Lattice Sites and Wurtzite — Type Interstitial Sites?
Authors: Löbe K. , Boyn R. 
Published: July 2007

AbstractThe dye‐laser site‐selective excitation technique is used to investigate 4f–4f optical spectra of three Sm3+ centers in mixed‐polytype ZnS bulk crystals at 4.2 K. Measurements are made on crystals grown by the Bridgman method and by iodine transport, the latter containing Li as a codopant. One center (C), which obviously has cubic (Td) symmetry, is assigned, on the basis of a crystal‐field analysis, to Sm on (AN‐type) Zn sites. For the other two species (A and D), each of which is the dominant center in one of the two types of crystals, polarisation data indicate trigonal (C3V) symmetry, with symmetry axes parallel to [111]w. For these centers models are suggested involving “wurtzite‐type” interstitial site occupation, with local charge compensation by intrinsic defects and Li impurities, respectively.
Interplay between Superconductivity and Antiferromagnetism in the Triplet Local‐Electron‐Pair System
Authors: Li Yan‐Min , Zhang Li‐Yuan 
Published: July 2007

AbstractThe interplay between superconductivity and antiferromagnetism in the homogeneous triplet local‐electron‐pair system is investigated by using the self‐consistent broken‐symmetry Hartree approximation. A phase diagram of the antiferromagnetic, the superconducting, the mixed, and the nonordered phases is obtained from the calculation of free energies of these phases. It is found that there exists rather complicated competition and coexistence between superconductivity and antiferromagnetism in this system.
Magnetoresistance and Hall Effect in Bi2Te3〈Sn〉 in Ultrahigh Magnetic Fields and under Pressure
Authors: Kulbachinskii V. A. , Brandt N. B. , Cheremnykh P. A. , Azou S. A. , Horak J. , Lošták P. 
Published: July 2007

AbstractThe resistance and Hall effect are investigated in p‐Bi2Te3 and Bi2Te3〈Sn〉 with tin content x = 0.1 and 0.25 at% and hole concentrations p = (2 to 4) × 1018 cm−‐3 in the temperature range 0.5 K ≦ T ≦ 300 K, at stationary magnetic fields 0 ≦ B ≦ 22 T and under hydrostatic pressure 0 ≦ P ≦ 5.3 × 108 Pa. In the samples containing Sn the oscillations of resistance (Shubnikov‐de Haas effect (SdH)) show an anomalously high amplitude and the oscillations of Hall voltage show plateaus. In the ultrahigh region of magnetic fields the magnetoresistance and Hall resistance are practically constant. Under hydrostatic pressures P > 3 × 108 Pa all peculiarities of oscillations disappear. It is proposed that tin doping of Bi2Te3 leads to the appearance of an impurity band with high density of states not far from the maximum of the heavy hole band which stabilizes the Fermi level. Under hydrostatic pressure the light hole band rises relatively to the heavy hole band and carriers flow from the impurity band into the light hole band, which leads to the disappearance of peculiarities of oscillations in tin doped samples.
An Improved Mean Field Approximation
Authors: Ferreira J. R. Faleiro 
Published: July 2007

AbstractAn upper bound for the free energy may generate an approximation which preserves short order range effects even when a sum of single spins is used as the auxiliary Hamiltonian. Unlike the usual mean field approximation it may distinguish the cubic lattice from the planar triangular lattice. Its application to the Ising chain recovers some exact results.
Colour Centres in Alkali Metal Doped SrF2
Authors: Hamaïdia A. 
Published: July 2007

AbstractColour centres in SrF2:Na+ and SrF2:K+ are studied by optical spectroscopy, magnetic circular dichroism (MCD) and by EPR. It is shown that, in each of these two materials, there exist two kinds of FA centres, the weakly perturbed F and the more strongly perturbed F. The improperly named F2A centre is paramagnetic and its MCD has no similarity at all with the one of the F2 centre in SrF2. In SrF2:A+, non paramagnetic colour centres of the “F“ type are observed, as in CaF2:A+, but no defect corresponding to the f centre of CaF2:Na+. On the other hand, in SrF2:Na+ can be produced a centre which is called c', comparable to “F“, but with a spectral shift toward shorter wavelengths.
Optical Nonlinearity and Phase Coherence in CdSe and CdSexS1−x
Authors: Hvam J. M. , Dörnfeld C. , Schwab H. 
Published: July 2007

AbstractThe magnitude of the optical nonlinearity and its phase coherence are investigated at low temperatures in single crystals of CdSe and CdSexS1−x, using picosecond time resolved degenerate four‐wave mixing. In the pure compound semiconductors, the optical nonlinearity as well as the dephasing is governed by free exciton and biexciton interactions. In the mixed crystals, excitons localized by the alloy disorder play the dominant role, giving rise to larger nonlinearities and longer dephasing times than in the pure compounds.
Periodic and Stochastic Self‐Pulsations in the System of Coherent Excitons, Photons, and Biexcitons
Authors: Moskalenko S. A. , Rotaru A. H. , Zaloi V. A. 
Published: July 2007

AbstractPossible appearance of quasiperiodic and chaotic self‐pulsations in a system of coherent excitons and photons as well as in the processes of one‐ and two‐photon exciton–biexciton conversions are established for the first time. In the last two cases the generalized Lorenz equations are obtained. Lyapunov analysis of the stationary state stability and computer experiments are made. The main bifurcations in the three considered systems of quasiparticles are found.
Femtosecond Studies of Room Temperature Optical Nonlinearities in Wide‐Gap II–VI Compounds
Authors: Puls J. , Rudolph W. , Henneberger F. , Lab D. 
Published: July 2007

AbstractFs‐excite‐and‐probe measurements are made on wide‐gap II–VI compounds at room temperature. A variety of nonlinear processes are observed and their ultrafast transients are studied. The results emphasize the use of these materials for fs optical switching.
Optical Stark Effect in an Exciton–Phonon System
Authors: Higashimura T. , Iida T. , Komatsu T. 
Published: July 2007

AbstractA theoretical study is made of the optical Stark effect in an exciton‐phonon system in which the Fano effect takes place due to the interference between two exciton bands through the exciton‐LO‐phonon interaction. Formal expressions of spectra are derived for the absorption and the time‐resolved resonant secondary emission of probe light, using the resolvent method. The spectral change of absorption induced by the optical Stark effect corresponds to Im (χ(3)). Carrying out numerical computations for a model system, it is demonstrated what spectral structures and temporal behaviors are expected to be observed when there coexist the optical Stark effect and the Fano effect.
The Exciton Reflection Shifting and Modification in Presence of Intensive Polariton Wave Interacting with LO‐Phonons in Polar Semiconductors
Authors: Ivanov A. L. , Vygovskii G. S. 
Published: July 2007

AbstractA set of macroscopic phonoriton equations describing exciton, photon, and LO‐phonon spectra renormalization in presence of intensive polariton wave is analyzed. New specific additional boundary conditions are introduced and corresponding exciton reflection spectra are calculated for the problem of probe wave reflection at the crystal boundary. The appearance of the new phonoriton spike and the exciton line shifting in reflection spectra are determined by the intensity of the pumping wave.
Remarks on Optical Nonlinearity and Bistability in Composite Media
Authors: Jungk G. 
Published: July 2007

AbstractNecessary conditions for intrinsic (without external feedback) bistability are discussed for the field‐intensity dependent dielectric function within the most simple homogeneous model. Some of the restrictions imposed in this way can be relaxed in composite media by local‐field corrections. The results are illustrated with stationary bistable reflectivities and transmissivities as function of the impinging light intensity.
Resonatorless Dissipative Optical Bistability of Electronic Origin in Direct‐Gap Semiconductors
Authors: Kochelap V. A. , Kuznetsov A. V. , Sokolov V. N. 
Published: July 2007

AbstractThe results of numerical calculations of the band edge absorption dependence on photoexcitation density for hexagonal CdS, CdSe, and cubic ZnSe are presented. The calculations are based on the recent plasma screening theory of Banyai and Koch modified to take into account the band structure and anisotropy of these materials. At low temperatures the resonatorless optical bistability is predicted for all three materials provided their quality is high enough. It is shown that the proper material and parameter choice apparently may lower the corresponding intensities down to kW/cm2 range.
Spatial Resolution of Dynamic Thermo‐Optical Hysteresis in CdS
Authors: Nguyen H. X. , Egorov V. D. 
Published: July 2007

AbstractTransverse effects in the thermo‐optical switching processes in CdS crystals a t room and liquid N2 temperature are investigated experimentally by recording the time–space distribution of the transmitted laser beam. Numerical solving the nonstationary two‐dimensional heat transport equation confirms the formation of a ring structure in the transmitted beam profile due to the induced absorption mechanism of the switching at room temperature. For the interpretation of the experimental findings at 77 K, probably dispersive effects must be taken into account as well.