bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Susceptibility Calculation of Zn1‐xMnxS by the Nearest‐Neighbour Isolated Cluster Model
Authors: Spasojevic V. , Bajorek A. , Szytula A. , Giriat W. , Mitic D.
Published: July 2007

Magnetic susceptibility of semimagnetic semiconductor Zn1‐xMnxS (x = 0.05, 0.10) is measured by the Faraday method. Starting from the isolated cluster model in the nearest‐neighbour approximation, and from the random distribution of Mn2+ ions, the temperature dependence is calculated of the magnetic susceptibility of Zn1‐xMnxS. By comparing these results with experimental χ (T) data, good agreement is obtained only for lower concentration x = 0.05. Treating the probabilities of finding the Mn2+ ions as singles, pairs, or triplets as adjustable parameters (modified distribution), quantitative agreement is obtained for both concentrations. Probabilities for every type of cluster, in both distributions, are given. The results show an enhancement of the clusterisation when the concentration x increases.
Analysis of Electronic Polarizabilities in Ionic Crystals
Authors: Dikshit U. C. , Kumar M.
Published: July 2007

The existing sets of additive electronic polarizabilities for alkali halides and alkaline earth chalcogenides are examined by evaluating the high frequency electronic dielectric constants and presenting a comparison with experimental data. The crystalline state values of polarizabilities are also compared with free ion values. Various physical effects responsible for changing the values of polarizabilities in the crystalline state are discussed. The differences in free state and crystalline state polarizabilities are investigated in terms of the classical model due to Havinga and quantum mechanical model due to Yamashita and Kurosawa.
Blue and Violet Emission of PbCl2
Authors: Nikl M. , Birch D. J. S. , Polak K.
Published: July 2007

The blue and violet emission of undoped PbCl2, is investigated in the temperature region from 4.2 up to 200 or 60 K, respectively. Two subbands are resolved in the blue emission and the energy transfer between them is revealed at temperatures above 80 K. The origin of blue emission and the influence of oxygen are discussed. The decay of violet emission is reported and the activation energy of its thermal quenching is calculated from the lifetime‐temperature dependence. The influence of diffusion of bromide ions into PbCl2 surface layer on the violet emission is tested.
Defect Production and Annealing Due to Relaxation of Electron Excitations in Fast Ion Tracks
Authors: Urmanov A. R.
Published: July 2007

A mechanism of defect production and annealing due to irradiation with high‐energy ions is proposed. It is shown that the degree of damage on the subsurface region of a crystal is determined by competition of two processes: migration of defects from the depth to the crystal surface and their recombination due to an increase in the mobility of defect‐forming atoms and vacancies.
Model Calculations of Nonlinear Optical Effects in Molecular Aggregates
Authors: Voigt J. , Bittner Th. , Kehrberg G.
Published: July 2007

Basing on new experimental results on nonlinear transmission of photosynthetic particles measured with the pump‐ and probe‐beam technique a reaction kinetic three‐level model involving one‐ and two‐particle excitations is developed to describe the observed phenomena quantitatively. It is shown that the nonlinear effects are caused by a competition between the one‐ and two‐particle excitations. The physical nature of the two‐particle excitations is discussed as well their role in a coherent energy transfer process in photosynthetic membrane.
Localized Hole States in a Two‐Dimensional Antiferromagnet
Authors: Rubin P. , Sherman A.
Published: July 2007

A connection between band excitations and sublattices in the Hubbard antiferromagnet leads to the appearance of two types of localized states arising due to an impurity on the “own” (for given band excitations) and “alien” sublattices. In the case of the substitutional impurity the conditions of the appearance of these localized states, their energies and symmetries are obtained in dependence on the ratio of the exchange constant to the hopping matrix element. These dependences and the number of the localized levels are different for the two types of states mentioned.
The Effective s‐Matrices in the Theory of Magnetic Breakdown with Spin Flip Magnetoresistance of a Simple Model
Authors: Proshin Yu. N. , Kh. Useinov N.
Published: July 2007

The consistent theory of magnetic breakdown in metals taking into account the existence of spin and spin‐orbit interaction of conduction electrons is developed. The effective s‐matrix and probabilities for small orbits of “diangular” and “triangular” type are calculated. The magnetoresistance of magnetic breakdown linked networks with one‐dimensional topology is calculated for the case of coherent movement of electrons on the small orbit of the network. The double‐peaked structure of magnetoresistance oscillations for a simple hypothetical metal is obtained.
Electromagnetic Fields and Power Losses for Superconducting Slabs
Authors: Refai T. F. , Saif A. G.
Published: July 2007

The distribution is investigated of the London penetrating magnetic field, vortex field, and the stray magnetic field within a semi‐infinite type II superconducting slab subjected to a vibrating wire carrying a direct current. Exact analytical solutions of the fields are obtained and the avarage time power loss on the surface of the superconductor slab is calculated. It is shown that the only field that contributes to the power loss is the London electromagnetic field. The effect of the London penetration depth on the power loss is investigated.
Temperature Dependence of the EPR Spectra of Gd0.5RE0.5 Ba2Cu3O7‐δ Compounds in the Orthorhombic and Tetragonal Phases
Authors: Guskos N. , Triberis G. P. , Lykodimos V. , Windsch W. , Metz H. , Koufoudakis A. , Mitros C. , Gamari‐Seale H. , Niarchos D.
Published: July 2007

The materials Gd0.5RE0.5 Ba2Cu3O7‐δ (Re = Y, Sm, Eu, and La) are investigated in the orthorhombic (HTC) and tetragonal (non‐HTC) phases using EPR method. For both phases EPR signals associated with Gd ions are detected. In the tetragonal phase a strong temperature dependence of the intensities of this line is observed. These characteristics can be ascribed to the skin effect. A small polaron model is proposed to interpret the conduction mechanism of the tetragonal phase (semiconducting) of these samples.
Resonance Dechanneling in Quasiperiodic Superlattices
Authors: Rudko V. N.
Published: July 2007

Planar dechanneling of ions is investigated in strained‐layer quasiperiodic superlattices with two types of layers, A and B, arranged according to the recurrent Fibonacci rule. It is shown that in quasiperiodic superlattices withτlA+lB< λ (wherelAandlBare the respective thicknesses of the layers A and B, λ is the golden section, λ the wavelength of transverse particle oscillations in the channel) the dechanneling is a resonance process. Angular dependences of the dechanneling length are asymmetric and stepwise. The resonance dechanneling in strained‐layer quasiperiodic superlattices may be used for the determination of elastic distortions even in the case when the layer thicknesses are as small aslA,lA< λ. This feature is absent in the case of periodic superlattices.
The IR‐Optical Behaviour of Polycrystalline Dielectric Films An Anisotropic Maxwell Garnett Model
Authors: Lehmann Annemarie
Published: July 2007

The intrinsic anisotropy associated with any inhomogeneous or polycrystalline film is considered in a framework similar to the Maxwell Garnett theory by fields adjusted for a slab. While an earlier paper demonstrates this theory for small ionic volume fractions the case of high packing density of the ionic material is investigated here. Analytical solutions for vibrational frequency shifts and intensity changes in IR spectra are obtained in the approximation of a small fraction of nonabsorbing ellipsoids incorporated into the ionic film material.
Light‐Hole Non‐Parabolicity in the Single Band Approximation
Authors: La Rocca G. C. , Cardona M.
Published: July 2007

In the envelope function treatment of quantum wells and superlattices, an effective mass Hamiltonian including corrections to the quadratic dispersion relation is commonly employed to describe non‐parabolicity and other complications of the band structure. A careful definition of the boundary conditions used to connect the envelope functions at the interfaces is required to consistently take such higher order effects into account to a given order of approximation. It is possible to develop a single band scheme to describe the light‐hole non‐parabolicity implicitly accounting for the coupling to other bands. With respect to the conduction electron case, the coupling between the split‐off and light‐hole bands brings about qualitative changes in the boundary conditions. Model calculations show how the non‐parabolicity affects the energy levels not only through the modified (i.e. non‐quadratic) dispersion relation, but also through the consistently modified boundary conditions. The present simple theory compares favorably with experimental data and more refined theoretical treatments.
The Effects of Lattice Constant Variations on Electron and Positron Charge Densities in Grey Tin
Authors: Soudini B. , Aourag H. , Khelifa B.
Published: July 2007

Electron and positron charge densities are calculated as a function of the lattice constant variations in grey tin. The calculations of the electron–positron momentum densities are carried out by using the independent particule approximation coupled with the Gaussian nonlocal pseudopotential method. The results are correlated to the effects of pressure.
Dispersion of the Exciton Polariton Branches in CuCl and Their k‐Dependent Splitting in a Magnetic Field
Authors: Fröhlich D. , Köhler P. , Nieswand W. , Mohler E.
Published: July 2007

The method of three‐photon difference‐frequency generation is used to measure resonances on the lower polariton branch in CuCl. Due to the small linewidth of the resonances (smallest width 80 μeV) it is possible to determine the splitting of the lower branch in a magnetic field at different k‐values for the first time. Resonances on the upper polariton branches and on the longitudinal exciton branches can also be excited with the use of two‐ and three‐photon sum‐frequency generation and two‐photon absorption. The rather peculiar wavevector‐dependent splitting of the lower polariton branch is explained quantitatively by taking into account the field induced mixing of the Z3‐ and Z1,2‐excitons.
Optical Excitation of DX Centers in GaAlAs Alloys Doped with Si and Te
Authors: Seguy P. , Yu P. Y.
Published: July 2007

The effect of light illumination on the deep level transient spectroscopy (DLTS) and constant temperature capacitance transient spectra of DX centers in GaAlAs alloys doped with Si and Te is studied. The experimental DLTS spectra are compared with theoretical spectra based on a model in which the only effect of light is to photoionize the DX centers. The calculated spectra reproduce satisfactorily the experimental spectra only in the Te doped samples. In Si doped samples the calculated spectra cannot reproduce the light‐induced peak reported recently by Jia et al. Thus the results confirm that this peak may be associated with a light‐induced shallow metastable center related to Si in GaAlAs. The identification of this shallow metastable state based on the present work and other recent experimental and theoretical investigations is discussed.
Quantum Corrections to the Conductivity in Magnetic Field and Negative Magnetoresistance of Zinc Selenide
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N.
Published: July 2007

An analysis of the negative magnetoresistance (NMR) of n‐ZnSe crystals is made for the first time in frames of a new theory of this phenomenon based on quantum corrections for the conductivity in a magnetic field. The study is carried out for a wide concentration range (2.5 × 1016 to 7.4 × 1017 cm−3) at low temperature (1.65 to 4.2 K). In samples with metallic conductivity the NMR is shown to be well described by means of a localization quantum correction only for weak magnetic fields. With increasing strength of the magnetic field the contribution of anomalous positive magnetoresistance also increases, being related to the quantum correction, which arises from the state density decrease due to electron–electron interaction. The NMR is detected in heavily doped compensated (HDC) samples with low‐temperature conductivity of the Mott type, caused by the state density increase near the Fermi level in the magnetic field.
Temperature and Pressure EPR Studies of Superexchange Coupling in Cu(1‐Phenylpyrazole)2Cl2 Crystals
Authors: Goslar J. , Hilczer W. , Hoffmann S. K. , Krupski M.
Published: July 2007

Single crystal EPR data for Cu(1‐phenylpyrazole)2Cl2 in the temperature range 77 to 300 K and at hydrostatic pressures up to 500 MPa are presented. From the merging effect on the EPR lines the temperature and pressure dependence of the weak exchange coupling is determined. The exchange integral is |J| = 0.0040(2) cm−1 and it strongly increases on cooling and under pressure. Because of the large value of d |J|/dT a transition form the intermediate exchange rate (resolved lines in EPR spectrum) to the strong exchange rate (merged lines) is observed. Methods for deriving the exchange integral from the linewidth in the strong exchange range are discussed.
The Role of 4f–4f Transitions in Magnetooptics of Paramagnetic Rare–Earth Glasses
Authors: Klochkov A. A. , Valiev U. V. , Moskvin A. S.
Published: July 2007

Theoretical and experimental investigations are made of magnetooptical activity (MOA) of (parity) forbidden intraconfigurational 4f–4f transitions in Er(PO3)3 rare‐earth paramagnetic phosphate glasses. The interpretation of magnetooptical spectra in frames of a theoretical scheme similar to Judd‐Offelt's theory is carried out for the observed 4f–4f transitions. It is shown that the theory may be used successfully for the quantitative description of magnetic circular dichroism (MCD) spectra (and Faraday effect spectra) in rare‐earth paramagnetic glasses.
Evaluation of Structure and Transport Properties of NiB Glass Melts
Authors: Rao R. V. Gopala , Debnath D.
Published: July 2007

Lebowitz's solution of C(r) for binary mixtures with a square‐well attractive tail is applied to compute three partial structure factors S11(k), S22(k), and S12(k) of NiB glass melts. The total structure factors obtained from these partial structure factors are found to be in excellent agreement with experimental results. The isothermal compressibilities of these melts are calculated from the partial structure factors in the long‐wave limit through the Kirkwood‐Buff equation. An estimate of the Bhatia‐Thornton structure factors is made. The linear trajectory principle due to Helfand is utilised to calculated the diffusion coefficients of the NiB glass melts. It may be pointed out that this is perhaps the first application of Lebowitz's equations to glassy materials.
Trend to Localization of f‐States in Actinide Metals
Authors: Nikolaev A. V. , Ionova G. V.
Published: July 2007

Band‐structure calculations of actinide metals from thorium to americium in f.c.c. and b.c.c. lattices are carried out by the relativistic LAPW method with warped potential and nonfrozen core treatment to obtain their density of states at the Fermi energy. Although band‐structure calculations lead to the necessity of taking the f‐state trend to localization into account, they do not get this localization by intrinsic way. Therefore, the f‐state localization is a many electron process, which could not be obtained within density functional theory.
A Study of the Transverse Ising Model
Authors: Zhong Jia‐Lin , Yang Chuan‐Zhang , Jiang Xue‐Fan
Published: July 2007

A new method which combines the discretized path‐integral with variational approximation is proposed and used to derive the free energy of the transverse Ising model in a quantum spin system. The transition temperature dependence of both, the transverse field and the coordination number is obtained analytically. The numerical results are compared with those of other methods.
Calorimetric and Raman Study of the Phase Transition in [N(CH3)4]2ZnBr4
Authors: Igartua J. M. , Ruiz‐Larrea I. , Couzi M. , López‐Echarri A. , Breczewski T.
Published: July 2007

Raman scattering and calorimetric measurements are used to study the ferro‐paraelastic phase transition undergone by [N(CH3)4]2ZnBr4 at 287.19 K. The knowledge of its vibrational spectrum, together with the available elastic and thermal expansion data, allow to obtain the specific heat of the phase transition and the associated values for the thermodynamic functions. The transition entropy (ΔS = 1.95 R ± 0.1) confirms the order‐disorder character assigned to this phase transition. Finally, the temperature dependence of the thermodynamic functions is discussed within the frame of the Landau theory.
Features Peculiar to the Acoustic Properties of Intermetallic SmFe2 in the Spin Reorientation Region
Authors: Artma E. E. , Zinoveva G. P. , Korolyov A. V. , Gaviko V. S.
Published: July 2007

In polycrystalline specimens of intermetallic SmFe2 the temperature dependences are measured of the sound velocity and of the sound absorption coefficients. By contrast with earlier investigations, anomalies are detected in the acoustic properties at two spin‐reorientation temperatures rather than at one. The temperature dependences are characterized by a hysteresis. Possible causes of the observed anomalies in the acoustic properties of SmFe2 are discussed.
Phase Transition of Levitating Polarons
Authors: Pokatilov E. P. , Beril S. I. , Frenk M. A.
Published: July 2007

The binding energy is calculated of a polaron above the liquid‐helium film placed on the polar substrate. It is shown, that in the case of thick enough films the weakly‐coupled polaron state, which is not localized in the plane of film surface, possesses the deeper energy level as compared with the strongly‐coupled and localized polaronic state. However, for thin films the inverse order in the arrangement of levels occurs. From this fact it is concluded, that a polaronic phase transition is possible when decreasing the film thickness.
Electron Paramagnetic Resonance of a CO Radical Trapped in KBr
Authors: Moens P. D. W. , Matthys P. F. A. , Callens F. J. , Maes F. R. C. , Boesman E. R.
Published: July 2007

A CO ion with axial symmetry around 〈111〉 is detected in the KBr lattice by means of electron paramagnetic resonance. This molecular ion occupies an anion vacancy and rotates rapidly around the OO axis, which coincides with a 〈111〉 direction. The spin densities on the carbon atomic orbitals are deduced from the analysis of the 13C hyperfine tensor. A comparison with the isoelectronic NO2 molecule in the same host lattice and location is made.
Change of Lattice Parameters in Highly Disperse Nickel Powders
Authors: Gamarnik M. Ya.
Published: July 2007

A monotonous increase of the lattice parameters with the decrease of particle size is established by an X‐ray study for highly disperse nickel powders in the interval of sizes from 4.9 to 35 nm. The relative changes of lattice parameters are from 4.9 × 10−3 ± 5 × 10−4 up to 3 × 10−4 ± 1 × 10−4. The effect is explained by the decrease of the intracrystalline pressure in small particles stipulated by electrostatic interaction of the elements of crystal charge lattice. A calculated dependence of the lattice parameters which agrees with experimental curve is obtained in the frameworks of the model suggested by the charge lattice represented by an ion—electron lattice of positive ions and collectivized electrons with regard of the lattice of atomic neutral cores (the contribution of the latter is proved very small as found from the calculations).
Electronic Structure Calculations for YBa2Cu3O7 by the Self‐Consistent Crystalline Orbital Method
Authors: Filonov A. B. , Borisenko V. E.
Published: July 2007

Results are given of electronic structure simulation for YBa2Cu3O7 calculated by the crystalline orbital method. The standard scheme of self‐consistency for charges and configurations is employed. Multiexponential representation for at least Cu3dO2p atomic orbitals with accounting for correct electronic configuration of the atoms entering the system are shown to be used for adequate simulation. A new modified scheme of self‐consistency for this type of materials is proposed.
Interference of Cherenkov and Parametric Radiation Mechanisms of a Fast Charged Particle
Authors: Nasonov N. N. , Safronov A. G.
Published: July 2007

The parametric X‐ray radiation of a fast charge in a medium with periodically changing refraction index is considered in the case of simultaneous fulfillment of the Vavilov‐Cherenkov radiation conditions. It is shown that if the characteristic frequencies of both types of radiation are close enough, a considerable change in the radiation structure (both, in the charge movement direction and in that of Bragg scattering) takes place. An oscillating dependence of the registered radiation versus the target thickness and viewing point is established.
K‐Shell XAFS Formation in Silicon Crystal
Authors: Pavlychev A. A. , Barry A. , Potapov S. S.
Published: July 2007

X‐ray absorption fine structure (XAFS) formation in a silicon crystal is analysed on the basis of a quasiatomic description. The spectral dependence of the XAFS formation mechanism is investigated. The existence is shown of four specific spectral regions with different electron‐optical characteristics of the atomic surroundings and different “size” effect of XAFS formation. It is shown that (i) the sensitivity of XAFS to distant coordination shells is maximum in the interval 30 nm−1 < k < 60 nm−1 and (ii) the combination of single reflections from the surroundings and photoelectron refraction in the surroundings well describes the XAFS in a very large domain k > 25 nm−1.
Compton Profile of Polycrystalline Zinc and Cadmium
Authors: Perkkiö S. , Sharma B. K. , Manninen S. , Paakkari T. , Ahuja B. L.
Published: July 2007

The Compton profiles of polycrystalline zinc and cadmium are studied. The measurements are made using 59.537 keV γ‐rays. The renormalized free atom model (RFA) and the orthonormalized linear combination of atomic orbitals (LCAO) model are used to calculate the theoretical Compton profiles. The RFA model for the electron configurations 3d104s2 and 4d105s2 for zinc and cadmium, respectively, is found to give the best agreement with the experimental profiles.
Thermodynamics and Structure of Liquid Metals from the Soft Sphere Reference Fluid
Authors: Akinlade O.
Published: July 2007

The Gibbs‐Bogoliubov inequality is used to compute the thermodynamics and structural properties of alkali metals and Mg, Cd, Al, In, Tl, Pb using the soft sphere (SS) reference fluid. The results are compared with earlier calculations using the charged hard sphere (CHS) as a reference fluid. It is concluded that the SS reference fluid gives better results than the CHS for the quantities investigated and yields, in all cases, lower values for the free energy, thus indicating that the SS is a preferred system. From the structural point of view, the SS predicts better agreement with experiments for the position of maxima and minima of the structure factor, although it tends to overemphasize the peaks in all cases when compared with the CHS. It is suggested on the basis of the calculations that the SS could be used for more calculations involving fluid variational perturbation approach because of its relative simplicity and ability to produce remarkably good results for structure and thermodynamics of liquid metals when computed values are compared with experiments.
Impurity Effects on Spectral Properties of an Adatom‐Contaminated Crystal System
Authors: Lazo E.
Published: July 2007

A Green‐function calculation is performed to investigate how the presence of impurities affects the spectral properties of the adatom and surface atoms of a semi‐infinite linear chain. The infinite set of equations is solved using the transfer matrix method, and inverting a single complex matrix that contains all information about a finite region of the chain including the adatom, the surface, and the impurity sites. The method permits to calculate the local properties on each site of the contaminated region in a very efficient form. Results of the exact calculations of the electronic densities of states are presented when a single impurity is put in many different positions and when a set of seven impurities is distributed in two different forms in the chain.
On the Electron States in a Cylindrical Quantum Box of a Wide‐Gap Semiconductor in Crossed Electric and Magnetic Fields
Authors: Das N. R. , Chakravarti A. N.
Published: July 2007

A perturbational calculation is presented for determining the energy eigenvalues of the confined electrons in a cylindrical quantum box of a wide‐gap n‐type semiconductor in the presence of crossed electric and magnetic fields. Besides, the effects of changing the fields as well as the radius and the width of the box on the lowest quantized state in such a structure are investigated, taking n‐type GaAs as an example.
The Effect of Local Field Corrections on the Electrical Resistivity of Liquid Metals
Authors: Akinlade O. , Hussain L. A. , Matthew F.
Published: July 2007

The electrical resistivity of some simple liquid metals are evaluated using the charged hard‐sphere reference system for a description of the structure, while a non‐local pseudopotential is used to describe the electron‐ion interactions. It is concluded that the inclusion of local‐field corrections leads to an improvement between calculated values and experiment. Secondly it is deduced that improvements between computed results and experiments can be obtained by using a modified form of the Ziman resistivity expression which takes into account the use of a non‐local pseudopotential.
Spectral Properties of a Chain of Polyhedra
Authors: Lazo E.
Published: July 2007

The electronic structure of a generalized linear chain formed by polyhedra joined at their vertices is studied. Our model incorporates distinct longitudinal and transverse hoppings with respect to the chain axis, producing a variety of paths between consecutive vertex atoms in the backbone chain. The problem is formulated in terms of the Green function formalism, using a tight‐binding Hamiltonian. The infinite set of equations is solved by means of the matrix inversion method. The changes produced in the electronic structure under the topological changes in the connectivity of vertex atoms is investigated when the number of basal atoms is varied. Two continuous bands, separated by a gap are obtained, even when all hoppings are the same. As a particular case of our model the local density of states of the usual linear chain is obtained.
Study on Momentum Density of Electrons and Fermi Surface in Aluminum by Positron Annihilation
Authors: Nakashima H. , Kubota T. , Kondo H. , Murakami Y. , Tanigawa S.
Published: July 2007

The three‐dimensional electron–positron momentum density in aluminum is reconstructed from measurements of two‐dimensional angular correlation of positron annihilation radiations (2D‐ACAR) followed by the image reconstruction technique based on a direct Fourier transformation. On the basis of the experimental data, the Fermi surface topology, the high momentum components (HMC), the enhancement effect, and the autocorrelation function are discussed.
Two Spin–Orbit Coupling Parameter Model of the Gyromagnetic Factor for d8 Clusters in Tetragonal Symmetry
Authors: Chen Jia‐Jun , Du Mao‐Lu , Chen Kang‐Sheng
Published: July 2007

An analytical perturbation formula of the gyromagnetic factor for the ground state 3A2 (F) of d8 ions, in which not only the contribution from spin–orbit coupling of the central transition metal ion but also that of ligand ions is included, are obtained in tetragonal symmetry. In the derivation, the contribution of all excited states for the g‐factor is considered, and no adjustable parameter is introduced. The molecular orbital coefficients are determined by means of a semiempirical method for estimating the g‐factor. The contribution of the spin–orbit coupling of ligand ions to the g‐shift is discussed in some pseudo‐tetragonal Ni(II) compounds. The results show that the contribution must be considered, especially when the ligand ions have large spin–orbit coupling parameters. The calculation results agree well with experimental findings.
On the Scattering Rates of Free Electrons in High Purity Semiconductors at Low Lattice Temperatures
Authors: Ghorai A. K. , Bhattacharya D. P.
Published: July 2007

At low lattice temperatures when the phonon energy cannot be neglected in comparison to the electron energy the influence of the mass anisotropy on the scattering rates becomes pronounced. Numerical calculations are performed for Ge and Si for electron interactions with acoustic phonons.
The Odd Voigt Effect under a Strong Electric Field in Semiconductors
Authors: Shon Nguyen Hong
Published: July 2007

The high‐frequency conductivity tensor σik(ω) in the linear approximation of magnetic field H and in quadratic approximation of external de electric field is derived by solving the Boltzmann equation. The magneto‐optical phenomena in the Voigt configuration (when the probe electromagnetic wave propagates across the magnetic field) are investigated. It is shown that birefringence and dichroism have a component that is odd (linear) in the magnetic field and predominates over the even effect in weak magnetic field.
Transient Energy Transfer by ps‐Laser‐Induced Free‐Carrier and Photorefractive Gratings in CdTe at 1 μm
Authors: Rückmann I. , Kornack J. , Kolenda J. , Petrauskas M. , Ding Y. , Smandek B.
Published: July 2007

Three‐beam mixing is investigated in ps‐transient grating experiments carried out on (110) CdTe at 1 μm in the case of two‐photon absorption (TPA). The coupling of three transient gratings via TPA results in an amplification of the free‐carrier transient energy transfer (TET) from pump beams to the probe beam. The competition between TET and TPA as well as the TET influence on the diffraction versus intensity curve are investigated experimentally and are studied theoretically using a model including nonlinear absorption and mixed gratings. Furthermore, for the first time the contribution of the ps‐photorefractive coupling to the probe‐beam diffraction signal is observed investigating the orientational dependence of diffraction kinetics.
LO‐Phonon Generation with Energy Collision Broadening in Polar Semiconductors
Authors: Král K.
Published: July 2007

The generation of LO‐phonons in the process of the hot electron cooling in polar semiconductors is studied theoretically. The generation rate formula is derived in the frame of the theory of the nonequilibrium statistical operator. The electron energy collision broadening is included in an approximation which meets the requirements of the elementary thermodynamics. Numerical results giving the generation rate and quasi‐steady state LO‐phonon distribution function in some materials are presented. The generalization of the generation rate formula to the case of the nonthermalized electronic system is also given.
The Critical Current Density and the Curvature of the Magnetic Field in Epitaxial YBaCuO Films
Authors: Glatzer D. , Forkl A. , Theuss H. , Habermeier H. U. , Kronmüller H.
Published: July 2007

The magnetic flux density distribution in thin epitaxial YBaCuO films is detected using the magneto‐optical Faraday effect. The external magnetic field is applied perpendicular to the film plane after zero field cooling. The results for the magnetic polarization, J, the critical current density, jc, and the magnetic field, μ0H*, of complete flux penetration are compared with SQUID magnetometer measurements. The flux density gradients as derived from the detected flux density distribution reveal the importance of the radial field in the investigated thin films with respect to the critical current density jc and the magnetic polarization J.
Correlations of the X‐Ray K‐Absorption Edge Shift (Chemical Shift) in Some Cu(II) Systems with Effective Charge and Bond Length
Authors: Pandey S. K. , Chetal A. R.
Published: July 2007

X‐ray absorption Cu K‐edge spectra are recorded in some Cu(II) compounds. La2CuO4, CuSO4 · 5 H2O, CuCO3 · Cu(OH)2, CuWO4, (NH4)2SO4 · CuSO4 · 6 H2O, and Cu(OH)2 and also there of pure Cu metal using a Cauchois‐type bent‐crystal X‐ray spectrograph. The X‐ray absorption chemical‐shift, ΔE, in each of the above Cu(II) compounds is measured. The chemical‐shift, ΔE, is correlated separately with each of its two governing factors, the effective charge, q, and the bond length, R, in the systems under study on the basis of the least‐squares regression analysis. Also the extent is determined to which the chemical‐shift, ΔE, is explained by each of the two factors, the effective charge, q, and the bond length, R, separately. It is also shown that the chemical‐shift, ΔE, prominently depends on the effective charge, q, and the bond length, R, i.e. q and R explain almost the total variation in chemical‐shift, ΔE, in the systems under study.
Aluminium XAS and NMR Spectroscopic Studies of Calcium Aluminosilicate Glasses
Authors: Landron C. , Cote B. , Massiot D. , Coutures J. P. , Flank A. M. , Flank A. M.
Published: July 2007

The local geometric and electronic order around aluminium atoms in calcium aluminosilicate glasses is comparatively investigated by X‐ray absorption (XAS) and by nuclear magnetic resonance (MAS NMR). The Al absorption spectra contain features which can be decomposed into two subpeaks, the relative contribution of the subpeaks appears to be related to the silicon/aluminium ratio in the glass. MAS NMR data analysis of the same samples clearly shows differences in site structures. It is of great interest to compare the results of both techniques in order to describe a reliable picture of Al surroundings related to a number of physical properties of calcium aluminosilicate glasses.
Electronic and Optical Properties of PtSn2
Authors: Gupta A. , Gupta R. Sen
Published: July 2007

The electronic energy bands of PtSn2 are calculated using composite wave variational version of the APW method. The results show a narrowing of d‐band which indicates a weaker d‐d overlap interaction between Pt atoms. A comparative study of this band structure result with that of PtAl2 and Pt provide interesting information about d‐d interaction as a function of primary interatomic distance. From the band structure results, density of states, joint density of states, ε2(ω) spectra and the Fermi surfaces are calculated and interpreted.
A Correlation Study of Large Potassium Neutral Clusters
Authors: Kanal K. M. , Ray A. K. , Howard I. A.
Published: July 2007

Accurate ab initio molecular‐orbital calculations are performed for the neutral Kn (8 ≦ n ≦ 13) clusters. The effects of electron correlation are studied using many‐body perturbation theory. Detailed electronic structures of these clusters are studied. Stabilities from the points of view of binding and fragmentation energies are discussed and, wherever possible, results are compared with published data in the literature.
Coupled Pairs of Cu+OCN− in KCl Studied by Optical Absorption and Thermally Stimulated Depolarization Current
Authors: Oliveira L. , Magna P. , Gallo N. J. H. , Domenicucci E. C. , Li M. Siu
Published: July 2007

Cu+‐OCN− coupled pairs are observed through a systematic correlation study of different KCl + 1 at% CuCl, KCl + 1 at% KOCN, and KCl + 1 at% KOCN + 1 at% CuCl single crystals. The optical absorption measurements show that the forbidden 3d10 + 3d94s transition Cu+ is completely split when disturbed by an OCN− molecule. As a result new Cu+ absorption bands besides the 260 nm partially allowed transition are observed at 218, 228, 242, and 251 nm. These new bands are attributed to interaction with OCN−. The thermally stimulated depolarization current (TSDS) is best fitted when the OCN− perturbed Cu+ is considered to be a double relaxation type system rather than a single one. This is very well borne out for the two last single crystals samples. Also the presence of an unwanted isotopic impurity 18O1214N− is discussed in the doped samples. Furthermore through a thermal process it is shown that there is effectively a coupling between Cu+ and OCN−.
A New Class of Empirical Many‐Body Potential Energy Functions for Bulk and Cluster Properties
Authors: Erkoç Ş.
Published: July 2007

A new empirical many‐body potential energy function (PEF) is proposed, which comprices two‐ and three‐body atomic interactions. The two‐body potential is a kind of hybrid function and the three‐body potential is formed by additive and nonadditive functions. The additive part is expressed in terms of two‐body interactions, and the nonadditive part is expressed as triple‐dipole function. The PEF satisfies bulk cohesive energy, bulk stability condition, and bulk modulus. The PEF is parameterized for gold, silver, and copper elements in f.c.c. crystal structure. The elastic constants of the elements are calculated, and the structural stability and energetics of microclusters containing 3 to 7 atoms of the same elements are investigated. The calculated elastic constants are in good agreement with experimental values, and the most stable microcluster geometries are qualitatively in agreement with the available literature data.
A Classification of the Dislocation‐Related Photoluminescencence in Silicon
Authors: Lelikov Yu. S. , Rebane Yu. T. , Ruvimov S. , Sitnikova A. A. , Tarhin D. V. , Shreter Yu. G.
Published: July 2007

The photoluminescence (PL) spectra of the basic extended defects in Si are obtained. A new classification of the PL lines is proposed according to the squared edge components of the Burger's vectors of the dislocations which surround the structural defects. The different manifold splitting of the various dislocation‐related PL lines are predicted for external perturbations violating the crystal symmetry. The possibility of the passivation of these dislocation cores by transition metal impurities is also discussed.
Stacking Fault Energy and Phase Stability in Long‐Range Ordered Cu–Zn–Al Alloys
Authors: Ahlers M.
Published: July 2007

The close‐packed martensitic phases in Cu–Zu–Al alloys can be described as an f.c.t. ordered lattice into which stacking faults are introduced. The stacking fault energy would be essentially the same as for the disordered α‐phase, but is reduced due to an additional lattice distortion which depends on the ordering energy of the f.c.t. lattice. In the 2 H martensite with a stacking fault on each second plane, the stacking faults interact, leading to a small increase in energy. Thus, in these ordered martensites the stacking fault energy depends not only on the composition, but also on the ordering energy and on the lattice distortion associated with it. These observations can be relevant to understand the dislocation mobility in other f.c.t. long‐range ordered alloys.
Internal Friction Studies on Oxygen–Oxygen Interaction in Niobium. I. Experimental Results and Application of Previous Interpretations
Authors: Weller M. , Haneczok G. , Diehl J.
Published: July 2007

In order to further clarify the long‐lasting controversy on the origin of the broadening of the Snoek maxima of heavy solute interstitial atoms (C. N. O.) in the internal friction of b.c.c. metals due to an interaction between those atoms measurements were carried out on niobium with various oxygen contents (0.1 to 0.85 at%) by applying frequencies of about 1 Hz and about 1 kHz to identical specimens. The means activation enthalpy of relaxation as determined from the frequency shift of the peak temperatures turns out to be independent of the oxygen content, Hm = (1.15 ± 0.01) eV. The maxima are rather symmetrically broadened and shifted to higher temperature with increasing oxygen content. They are analysed in terms of previously introduced models. The clustering model proposing a superposition of discrete Debye submaxima for O pairs, triplets, etc. does not give an adequate description of the total Snock maxima. Consequently, their broadening may only be accounted for by a continuous distribution of relaxation times. Attempts with empirical approaches, like Gaussian or Fuoss‐Kirkwood distributions, yield a better but still insufficient agreement with the measurements. This indicates that an appropriate physical model for the interaction of interstitial solute atoms in b.c.c. metals is required to match the experimental data with their precision reached now.
Simulation of Plastic Deformation in a Flexible Chain Glassy Polymer
Authors: Argon A. S. , Mott P. H. , Suter U. W.
Published: July 2007

A short report of a new computer simulation of plastic deformation is given in a typical flexible chain glassy polymer–polypropylene. The model which makes no arbitrary assumptions about structure and modes of molecular segment relaxations is based on systematic static energy minimizations in a small periodic cell representing a typical molecular environment. The simulation shows that because of the relatively inflexible nature of backbone bonds and bond angles, permitting conformational changes only through alterations in torsional degrees of freedom, the size of a coherent plastic relaxation unit is typically 8 to 10 nm in dimensions. Careful scrutiny of conformational alterations revels no recurring simple kinematical configurations such as dislocations, disclinations, rotons, strophons, or the like. The best emerging picture is that plastic relaxation is by the repeated nucleation of shear transformations in a very large group of segments in a very cooperative manner resulting, however, in transformation shear strains of only about 1.5%. While such transformations are dilatant in polypropylene, they are the opposite in polycarbonate which has a more structured and stiff molecule.
Spatial and Spatio‐Temporal Patterns in pnpn Semiconductor Devices
Authors: Niedernostheide F.‐J. , Arps M. , Dohmen R. , Willebrand H. , Purwins H.‐G.
Published: July 2007

Spatial and spatio‐temporal patterns of the current density and the potential distribution in silicon pnpn devices are expermentally investigated. In dependence on various parameters we observe homogeneous current distributions and the spontaneous appearance of stationary standing, rocking, and travelling well‐localized current density filaments. Model calculations reproduce the main features of the experiments.
Superconductivity of Fullerenes Doped with Alkali Metals
Authors: Davydov A. S.
Published: July 2007

The properties of the alkali‐metal‐doped fullerene C60 are discussed. It was shown that a superconductivity of this crystal is determined by a quasi‐one‐dimensional spreading of a planar bisolation condensate. The condensate is formed when the energy of the electron–phonon interaction exceeds the energy of the one‐dimensional zeor vibrations caused by local pairing. Under very strong electronphonon interaction small‐radius, spherically symmetric bisolitons are created instead of planar bisolitons. Their formation needs overcoming of a potential barrier. The localized bisolitions are moving through the crystal by a hopping mechanism only.
Ambipolar Diffusion of Electron–Hole Pairs in β‐Rhombohedral Boron
Authors: Werheit H. , Kristen F. , Franz R.
Published: July 2007

In β‐rhombohedral boron the electronic transport is essentially determined by deep electron traps of different bonding energies. The ambipolar diffusion of optically excited electron–hole pairs on diffusion paths of up to 5.37 mm length was investigated. The diffusion length at stationary conditions is 21 mm and the mean diffusion velocity is 5.8 × 10−6 m s−1. From these data a lifetime of 3620 s results. By Fick's second law the diffusion coefficient was determined to increase from about 5 × 10−3 to 101 cm2 s−1 with the diffusion velocity increasing from 10−5 to 10−1 m s−1. The Einstein relation yields the corresponding mobilities, which increase accordingly from about 0.2 to about 50 cm2 V−1 s−1. These mobilities are mean values for electrons and holes. The relaxation of the excited state of the sample into the thermal equilibrium is determined by five relaxation times (6.6, 50, 514, 5650, 14700 s), which are immediately related to the thermal excitation of the electrons from the traps with the bond energies 0.18, 0.37, 0.58, 0.77, and 0.89 eV.
Magnetic Susceptibility of Electrons in Quantum Wires of Wide‐Gap Semiconductors
Authors: Das N. R. , Chakravarti A. N.
Published: July 2007

A transverse perturbing magnetic field is assumed to be applied to a rectangular quantum wire of a wide‐gap semicondutor, to determine the magnetic susceptibilities of electrons. The computations are perfomed for a low value of the temperature, taking degenerate n‐GaAs as an example of such semiconductors, It is interesting to note that, not only the paramagnetic‐to‐diamagnetic susceptibility ratio for electrons in a semiconducting quantum wire deviates from that (⅓) in conventional semiconductors, but also that there is a critical region, governed by the concentration of the electrons and the transverse dimensions of the wire within quenching of the diamagnetism occurs.
Nucleation Field for Three‐Dimensional Rotation in Inhomogeneous Ferromagnets
Authors: Hu Jifan , Kronmüller H.
Published: July 2007

Based on the method developed for the one‐dimensional rotation process the nucleation field for three‐dimensional rotation is deduced from the linearized micromagnetic equation for magnetic inhomogeneities due to a spatial variation of the magnetocrystalline anisotropy energy. Comparing the nucleation field of the one‐dimensional rotation with that of three‐dimensional rotation, it turns out that one‐dimensional rotation describes experimental data of sintered magnets much better than the latter one. The physical process of the nucleation is dominated by the low‐dimensional rotation – especially the one‐dimensional rotation – due to the limited freedom of magnetization state by the alignment of the magnetization within grains and the existence of an easy axis in uniaxial magnets.
The Effect of Germanium Overlayers on the Magnetization of Chromium Films
Authors: Schröder K. , Nayak S.
Published: July 2007

The magnetic moment of chromium films with and without germanium overlayers is determined in an ultra‐high vacuum oscillating torque magnetometer at room temperature. Films deposited with growth rates from 0.002 to 0.01 nm/s at pressures of about 10−5 to 10−6 Pa show frequently strong diamagnetism. This diamagnetism usually increases if Ge overlayers are deposited on the Cr film. It seems difficult to associate this increase with the magnetization of the germanium film. It is suggested that one should try to explain the observed susceptibility values with a kind of exciton mechanism.
Parametrization of S‐ and P‐Magnetoexcitons in Quantum Wells
Authors: Engbring J. , Zimmermann R.
Published: July 2007

An analytical formula is proposed that describes magneto‐optical data of heavy hole S‐ and P‐magnetoexcitons in quantum welis quite well. The open coefficients in this formula have been fitted to numerically derived magnetoexciton energies. Experimental results for S‐ and P‐magnetoexcitons are presented obtained from one‐ and two‐photon excitation spectroscopy. It is possible to extract parameters for conduction band and valence band separately, while band mixing is taken into account by nonparabolicity parameters. The investigation shows that the dominant features of the spectra can be quantitatively described in the frame of a two‐band model.