bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic Structure and Magnetism of AFe2 Compounds with C14 and C15 Laves Structures
Authors: Terao K. , Shimizu M.
Published: July 2007

The d‐band densities of states are calculated by the recursion method for the paramagnetic AFe compounds with C14 and C15 structures, where A is occupied by 3d (Se, Ti, V), 4d (Y, Zr, Nb) or 5d (Lu, Hf, Ta) series' elements. The densities of states of the ferromagnetic and antiferromagnetic (Zr1−xNbx)Fe2 compounds with C15 and C14 structures are calculated. The pseudobinary systems are treated within a virtual crystal approximation. The trends of the crystal structures are related to the d electron number around the A site. Magnetic moment and spontaneous volume magnetostriction are calculated on the basis of the Stoner theory.
Fine Structure of the Fast Luminescence Component from BaF2 Crystal Excited by Fast Electrons
Authors: Kubota S. , Kanai N. , Ruan J.
Published: July 2007

A fine structure (a new 195 nm band) is found of the fast luminescence component from BaF2 crystal excited by electrons. This band has a decay time of (0.8 ± 0.1) ns and is observed in the case of electron excitation and not in α‐particle excitation. The observed fine structure is explained by the model of Aleksandrov et al.
On the model calculation of the excitonic‐like states and their possible role in autocatalytic processes. I. Application to the formation of autocatalytic NiP Amorphous Coatings
Authors: Demidenko V. S. , Szász A. , Aysawi M. A. , Kuznetsov V. D.
Published: July 2007

A new exciton‐like excitation mechanism is suggested for the formation of amorphous NiP coatings based on the special spatial bonds of hydrogen ions on the surface.
Study of elastic properties and their pressure dependence of zincblende structure semiconductors
Authors: Singh R. K. , Singh Sadhna
Published: July 2007

A three‐body force potential is used to derive the correct expressions for third‐order elastic constants and pressure derivatives of second‐order elastic constants for the zincblende structure semiconductors following the lines of Sharma and Verma. These corrected expressions are used for the first time to study the elastic properties and their pressure dependence of ZnS, ZnSe, and ZnTe. It is found that the inclusion of the corrections and the van der Waals interactions yield more reasonable values of the third‐order elastic constants and the pressure derivatives of second‐order elastic constants than those obtained by earlier workers from their somewhat erroneous expressions.
Representation of Energetical and Low‐Field Magnetic Properties of J = 5/2 Rare Earth Ion States in Tetragonal Crystal Fields
Authors: Fischer G. , Herr A.
Published: July 2007

The effect of a tetragonal crystal field on a J = 5/2 rare earth ion is calculated and is presented in a graphical form giving a complete description of the energy, the individual magnetic moment, and Van Vleck susceptibility of each doublet resulting from the crystal field splitting, as a function of two dimensionless parameters and a scale factor. These magnetic properties, which correspond to terms in H and H2 in the development of the energy in presence of a perturbating magnetic field, are given for both the cases, when H is either parallel or orthogonal to the c axis. The results are applied to the compound CeRu2Si2.
Multiple Scattering Study for CI K XANES of KCl, SrCl2, and CsCl Crystals
Authors: Kitamura M. , Muramatsu S. , Sugiura C.
Published: July 2007

A method for constructing crystal potentials which explicitly includes Madelung corrections due to charge transfer is presented for multicomponent crystals. In two‐component crystals, this correction is systematically taken into account by the use of a reduced Madelung constant. On the basis of the crystal potentials obtained with this method including self‐consistent field calculations, Cl K XANES of KCl, SrCl2, and CsCl crystals is studied by a multiple scattering theory within the muffin‐tin approximation. It is found that the overall profiles of experimental spectra are well explained by the calculations.
Raman Spectra and Directional Dispersion in LiNbO3 and LiTaO3
Authors: Yang Xichen , Lan Guoxiang , Li Bing , Wang Huafu
Published: July 2007

Raman spectra of ordinary and extraordinary phonons in LiNbO3 and LiTaO3 are recorded under a set of angles between wave vector and optic axis with the same backward scattering geometry, which makes all of the extraordinary phonons to appear in one directional‐dispersion spectra series, and the directional dispersion is reliably determined. The symmetry and the number of polar phonons in both the crystals are found to be the same, 4A1T + 4A1L + 9ET + 9EL. The directional dispersion of extraordinary phonons has thirteen branches with similar coupling in LiNbO3 and LiTaO3.
Optical Bleaching of the F+ Optical Absorption Bands in ZnS Crystals
Authors: Matsuura K. , Kishida S. , Yoshida K. , Tsubumi I.
Published: July 2007

The optical bleaching of the 2.3 and 2.9 eV bands related to the F+ centers in the electron‐irradiated and Zn‐treated ZnS crystals are measured from 25 K to room temperature under illumination of light from 395 to 702 nm. It is found that the 2.9 eV band is bleached in exactly the same manner as the 2.3 eV band and that under illumination of light around 2.9 eV, these bands are bleached with a decay constant independent of temperature, while under illumination of light around 2.3 eV, they are bleached by two stages, where the first stage has a decay constant independent of temperature and the second stage has a decay constant with an activation energy of (49 ± 5) meV. These bands are confirmed to be due to the same defects. It is deduced that the 2.3 eV absorption band is due to the transition of electrons from the ground state to the lower excited state located (49 ± 5) meV below the conduction band, while the 2.9 eV band is due to the transition to the higher excited state located in or closely below the conduction band.
Electron Paramagnetic Resonance of Titanium in GaP
Authors: Kreissl J. , Gehlhoff W. , Ulrici W.
Published: July 2007

EPR and photo‐EPR experiments are reported performed on LEC‐grown GaP:Ti with different Fermi‐level positions. An isotropic signal with g = 1.952 and a linewidth of 20.0 mT is assigned to Ti. The position of the Ti/Ti acceptor level is located at (0.5 ± 0.1) eV below the conduction band minimum.
Thermal Vibrations in Substoichiometric Vanadium Nitrides. Dynamical Deformation Effect
Authors: Čapková P. , Smrčok L. , ŠIma V. , Valvoda V. , Chalupa B. , Ettmayer P.
Published: July 2007

Thermal parameters BV and BN in substoichiometric vanadium nitrides are studied by means of X‐ray and neutron diffraction without separation of Debye‐Waller factor into dynamic and static parts. With increasing vacancy concentration in N‐sublattice the decrease of BV and increase of BN are observed. This unusual behaviour of B parameters can be explained introducing the static displacements of V atoms adjacent to N‐vacancies. The observed significant differences between BN values determined by X‐ray and neutron diffraction are interpreted as the difference between shell and core vibrations known as dynamical deformation effect.
Carrier Drift Mobilities in Some Organic Solids A Search for Organic Photovoltaic Materials. II. Charge Transport Calculations in s‐Tetrazine and 4 Phenylazoazobenzene
Authors: Kumar B.
Published: July 2007

Excess electron and excess hole mobilities of S‐tetrazine and 4‐phenylazoazobenzene are calculated using the tight binding approximation with SCF‐AO's as a basis set. The applicability of the band model in these organic solids is discussed in the light of Munn and Siebrand's theory of charge transport in organic solids. The results show that these two organic solids may be good candidate materials for organic photovoltaic devices.
Interaction between Localized and Delocalized States Indicated from Temperature‐Dependent ESR Study of Submetallic P‐Doped Si
Authors: Stesmans A.
Published: July 2007

A K‐band electron spin resonance (ESR) analysis has been carried out on submetallic Si:P powders containing (1.7 ± 0.1) × 1018 P atoms cm−3. As expected, only one signal, generally referred to as the central pair line (CPL), is observed. Accurate data of the peak‐to‐peak linewidth ΔBpp and g‐value are presented for the temperature range 1.6 K ≦ T ≦ 300 K. Unlike previous results, g shows up to be T‐dependent in the range T ⪅ 100 K, g varying from g = 1.99860 + 0.00002 at T ≈ 15 K to g = 1.99890 ± 0.00003 at T = 100 K. The implication of the experimental results regarding the physical model of the P‐in‐Si behaviour is discussed. In the range T ⪅ 4.2 K, comparison to other data reveals the existence of a significant different T dependence of g and ΔBpp between the high and low observational‐frequency situations. In the higher T range, the data are indicative of the presence of an s‐d like interaction between localized donor spins and delocalized electrons, which gradually increases with T. In that sense, it may explain the apparent “single line” behaviour of the CPL over the whole range 1.6 K ≦ T ≦ 300 K.
Atomic Level Stresses in Solids and Liquids
Authors: Vitek V. , Egami T.
Published: July 2007

In condensed matter systems there are, in general, stresses at atomic level which are related to local incompatibilities. Only in perfect crystals in which all the atoms are equivalent such incompatibilities do not exist but they are present in ordered structures with non‐equivalent atoms and in any disordered structure. In this paper evaluation of these stresses in the framework of the local density functional approximation, embedded atom method, and central force interactions is first described. The usefulness and physical significance of this concept in the description of the local atomic structure of liquids and glasses is then demonstrated using as examples atomistic studies of microscopic processes involved in structural relaxation and glass transition. Finally, it is argued that the concept of atomic level stresses provides a general means for describing atomistics of complex structures, both, ordered and disordered.
A Relationship between Prefactor and Activation Energy for Diffusion
Authors: Kirchheim R. , Huang X. Y.
Published: July 2007

Very often a relationship is observed between activation energies, Q, of diffusion and the corresponding prefactors, D0. Contrary to the Zener‐Wert relation, where activation energy and prefactor of different species migrating in the same matrix are compared, one species diffusing in a matrix with different defects or slightly varying composition is considered. It is shown that a linear relationship between In D0 and Q very often exists due to the special form of the Arrhenius equation. The slope of the corresponding graph is close to 1/kTa, where Ta is the average temperature of the range covered by the experiments. Experimental results are compiled and compared with this prediction.
Diffusion of H and D in Lutetium
Authors: Völkl J. , Wipf H. , Beaudry B. J. , Gschneidner K. A.
Published: July 2007

The anisotropy and isotope dependence of H (and D) diffusion in h.c.p. LuH0.05 and LuD0.05 is investigated in Gorsky‐effect measurements (380 K < T < 540 K). In spite of the hexagonal lattice structure, no anisotropy in the diffusion behavior can be established within experimental accuracy. The nearly isotropic diffusion can be understood from a consideration of possible atomistic jump processes. The present results are compared with previous studies on H(D) diffusion in h.c.p. metals.
Calculations of the Polarization Energy of a Complex in Alkali Halide Crystals from Zero to Fourth Order
Authors: Cardenas‐García D. , López‐Tellez E. R. , Ruíz‐Mejía C.
Published: July 2007

The polarization energy of a complex is calculated for all alkali halides crystals containing Eu++ impurities. Up to 48 nearest neighbors of the complex are considered, and assumed that the field on each dipole is the one produced by the charge of the complex and by the field produced by the other induced dipoles. The results show that there are no significant changes in all alkali halides when going from second to fourth‐order. Therefore, it is not necessary to take into account a large number of neighbors when calculating the polarization energy. This is a very important result since a low symmetry defect is considered.
Effect of Thermal Expansion on Absorption Band Shift of the F‐Center in Alkali Halides
Authors: Bosi L. , Nimis M.
Published: July 2007

It is shown that the thermal expansion effect in the absorption band shift of the F‐center in alkali halides is more active than the electron lattice interaction effect. This statement is based on the analysis of detailed experimental data concerning the changes in lattice parameter as a function of temperature. The results substantially confirm those obtained in the past (but disregarded in literature) by Jacobs as well as by Brothers and Lynch.
Alloy Analogy for the Multi‐Band Hubbard Hamiltonian
Authors: Kotrla M. , Drchal V.
Published: July 2007

A systematic derivation of the alloy analogy for the multi‐band Hamiltonian of the Hubbard type is given. The formalism, of the Hubbard atomic operators is used and the decoupling procedure is applied to the double‐time Green functions. The solution is equivalent to the coherent potential approximation for a set of effective multi‐component alloys and in the single‐band case it is identical to the Hubbard III solution. The theory is valid both, for crystals and for disordered alloys. It is applicable also for the translationally non‐invariant ground state corresponding e.g. to an arbitrary magnetic ordering.
The Regularities in Ground‐ and Excited‐State Absorption Spectra of Impurity Ions of the Iron Group in Crystals
Authors: Veremeichik T. F.
Published: July 2007

The excited‐state absorption spectra (ESS) of crystalline materials doped with ions with dn‐shells are studied theoretically. The method is used of comparison of the ESS with the ground‐state absorption spectra (GSS). Classification of the ESS into three types is made using the electron distribution in the t2 and e subshells of the strong crystal field and the spin values and the regularities for each type are determined. Comparative diagrams of the transition frequencies from the excited states and from the ground states versus Dq/B are drawn. The cases are determined in which the oscillator strengths of the broad band transitions from the excited states can be calculated in the parameters which are determined using the GSS and the oscillator strengths are estimated. The results show that the GSS of the impurity ions with unfilled d‐shells can be used to evaluate the ESS characteristics.
Optical Transitions of Jahn‐Teller Local Centres
Authors: Perlin Yu. E. , Polyanovskii V. M. , Alifanov O. V.
Published: July 2007

The multiphonon optical transitions between degenerate electronic local states are considered taking into account a strong interaction of the local centre (LC) with dynamic Jahn‐Teller active lattice vibrations. The results of numerical evaluation of the band shape are listed at different values of Stokes' loss constants for T ⊗ (a + e) → E ⊗ (a + e) transition of the cubic LC.
Monte Carlo Determination of Short‐Range Parameters for Multicomponent Solid Solutions
Authors: Dimitrov V. I.
Published: July 2007

Partial atom distribution functions and short‐range order parameters are calculated for multicomponent (ternary) alloys on the face‐centered cubic lattice. The Monte Carlo method is used to obtain estimates for these quantities for the first five coordination shells. The results are compared with those predicted by an approximate short‐range order theory of multicomponent solid solutions and good agreement is observed between them.
Effective Scattering and Damping of Elastic Waves in Multi‐Component Mixtures
Authors: Bobeth M. , Diener G.
Published: July 2007

Scattering of elastic waves propagating in a strongly heterogeneous medium with aggregate topology is considered within a modified effective‐medium procedure. The calculations are restricted to long wavelengths or low frequencies and are based on results obtained in a previous paper for the fluctuations of a static strain field. Explicit results are presented for isotropic components and spherical grains. In particular, effective differential and total cross‐sections for the grains of different components are discussed. For non‐dissipative media the total cross‐sections are related to the damping rates of longitudinal and transverse waves. Numerical examples for the damping rates and the angular dependence of the differential cross‐sections are presented for some binary mixtures. In strongly heterogeneous media near the percolation threshold high values of the scattering rates and a nearly isotropic distribution are obtained.
Construction of Electronic Charge Density in Solids. Calculation of Atomic Scattering Factors of Elements and Energy of Formation of Alloys
Authors: Bhattacharya T. , Manna A. , Ghosh A. K.
Published: July 2007

A simple method to construct modified electronic charge densities in solids, ϱS(r), from their free‐atomic charge densities, ϱF(r), is described. Atomic scattering factors of seven elements representing four different crystal structures, and energy of formation of seventeen CsCl‐type intermetallic compounds of transition metals are calculated from such ϱS(r). Results thus obtained compare well with those obtained earlier from superposition of ϱF(r) through Löwdin's α‐expansion.
Influence of Non‐Magnetic Impurities on the Ferromagnetic Phase Transition and Its Critical Properties
Authors: Fazakas A. B. , Corcoţtoi I. , Ciobanu G.
Published: July 2007

The free energy functional is derived for an electron gas interacting via insite Hubbard and intersite Heisenberg terms, scattered by some dilute, interstitial, non‐magnetic impurities. The equation for the Curie temperature is deduced and discussed in various approximations. The existence is shown of a critical concentration of impurities destroing the ferromagnetism. The dirty specimen has the same critical exponents as the pure one, but the width of the critical region is modified.
The Magnetic Susceptibility of a Diluted Ferromagnetic Thin Film (Ising Model, S = 1/2)
Authors: Wiatrowski G. , Mielnicki J. , Balcerzak T.
Published: July 2007

The Dirac's delta function method is applied for the calculation of magnetic susceptibility of diluted Ising films. As a result a set of equations for magnetic susceptibility of different atomic layers of thin film is derived, hence the curves χ vs. temperature together with the reciprocal susceptibility profiles for s.c. samples with several film thickness values are obtained.
Approximations to the Systematic Many‐Beam Case of High‐Energy Electron Diffraction. I. Transition from Two‐Beam to Many‐Beam Interaction
Authors: Kästner G.
Published: July 2007

The systematic many‐beam case of electron diffraction of non‐centrosymmetric crystals is treated on solving the fundamental (eigenvalue) equation by approximate analytical diagonalization of the suitably scaled and re‐indexed dynamical matrix. Its dependence on the crystal parameters and on the accelerating voltage is used to gradually select and classify approximate dynamical solutions and kinematical corrections. The results imply a convenient, scaled version of Bethe's correction of the periodic potential terms.
Low‐Temperature Structure and Lattice Dynamics of 4,4′,‐Difluorobiphenyl
Authors: Wąsicki J. , Belushkin A. V. , Khomenko V. G. , Natkaniec I. , Telezhenko Yu. V. , Wasiutyński T.
Published: July 2007

Phonon frequencies in the centre of the Brillouin zone, dispersion relations, and phonon density of states are calculated for 4,4′‐difluorobiphenyl, following structure investigations by means of X‐ray diffraction on a monocrystalline sample at 110 K. The resulting phonon density of states, weighted with the amplitudes of hydrogen atom vibrations are compared with that obtained from the inelastic incoherent neutron scattering (IINS) data. From the calculated dispersion relations it can be inferred that the incommensurate phase transition (well established in isostructural biphenyl) does not occur in 4,4′‐difluorobiphenyl.
Plasmon Excitation in Metal Surface Layers by Fast Electrons
Authors: Bao Tran Thoai Duy
Published: July 2007

The interaction of fast electrons with metal overlayers on metal substrates is studied within the hydrodynamic model. Retardation effects and damping are included. The energy loss probability of surface and interface plasmons is calculated for external electron beam travelling parallel to the metal surface. Numerical calculations are carried out for potassium layer on aluminium substrate.
Study on the Size and Shape of CuCl Microcrystals Embedded in Alkali‐Chloride Matrices and Their Correlation with Exciton Confinement
Authors: Itoh T. , Iwabuchi Y. , Kataoka M.
Published: July 2007

In alkali chlorides heavily doped with Cu+ ions, CuCl microcrystals of different sizes are grown under different heat treatments. Their size and shape are studied using small‐angle X‐ray scattering. A clear correlation is established between the microcrystal size and the blue shift of the exciton luminescence peak. The quantum size effect on the exciton is discussed. The exciton confinement, that is, the restriction of the exciton translational motion in one‐dimensional quantum wells is found to be rather plausible for CuCl microcrystals in crystalline matrices.
Parametric Green Function Method in the Heisenberg Model
Authors: Kazakov A. A. , Kleshchev S. M.
Published: July 2007

The task of the thermodynamics of “angle magnetic phase” is solved in the spin‐wave approximation at finite temperatures by the parametrical Green's function (PGF) method. The theory application is illustrated by the low‐temperature behaviour of the magnon heat capacity and magnetization of the rare‐earth metals Tb and Dy. The received analytical dependences are in good agreement with the experimental data.
Equation of State and Pressure Dependence of the Grüneisen Parameter for NaCl Crystal
Authors: Kumar M. , Pachauri A. K. , Chaturvedi S. D. , Sharma A. K.
Published: July 2007

The equation of state for NaCl crystal is investigated using the recently revised generalized Huggins‐Mayer potentials. The calculations are performed for pressures up to about 200 × 108 Pa and at different temperatures ranging from 298 to 773 K. The calculated values are found to agree with the experimental data. An investigation of the pressure dependence of the Grüneisen parameter is also presented using different existing theories. A comparison of the calculated and experimental values reveals the superiority of one theory over the other.
Nonlinear Optics and the Mott Transition in Semiconductors
Authors: Zimmermann R.
Published: July 2007

Optical spectra below and above the Mott transition of excitons have to be calculated from the inhomogeneous integral equation for the polarization function including self‐energy, screening, and band filling. Results for gap shifts, exciton shift, exciton bleaching, and continuum enhancement are critically reviewed and extended.
Linearised Version of the Optimised Random Phase Approximation. Application to the Structure of Dense Fluids and Metallic Potentials
Authors: Regnaut C.
Published: July 2007

A linearised version (LORPA) is given of the optimised random phase approximation (ORPA) of Andersen, Weeks, and Chandler. The LORPA allows straightforward calculations of the structure of fluids interacting via hard core plus long range pair forces. Standard potentials are analyzed to show that the LORPA is as efficient as the ORPA for the prediction of the structure of dense fluids. The advantage of the method is pointed out for metallic systems by considering gallium‐like and germanium‐like oscillatory interactions. It is shown that the LORPA reproduces the special structures of these metals as well as the ORPA. Therefore this method would be particularly useful for the systematical analysis of metallic potentials in liquid alloys.
Lattice Dynamics for Superlattices
Authors: Albuquerque E. L. , Fulco P. , Tilley D. R.
Published: July 2007

The acoustic and optic modes of a one‐dimensional model of a diatomic superlattice are considered. By employing a microscopic theory it is possible to explore the zone‐folding characteristics. The treatment is based on linear lattice dynamics with nearest neighbour interactions. The equations of motion for the different atoms (on either side) at two superlattice interfaces replace the boundary conditions used in continuum theories. This microscopic approach has the advantage that both optic and acoustic branches are described within a single formulation and without recourse to the long wavelength limit. The algebra, which is otherwise quite involved, is simplified by the use of transfer matrix techniques. The spectrum contains a number of interesting features whose underlying physical principles are discussed.
Theory of Compression in Some Fluorite Structure Crystals
Authors: Goyal R. P. , Gupta O. P. , Gupta B. R. K.
Published: July 2007

A theoretical method based on the phonon‐pressure theory is developed for the study of equation of state and thermodynamical properties of CaF2, SrF2, BaF2, PbF2, Sr(NO3)2, and Pb(NO3)2 crystals crystallizing in fluorite‐structure. The traditional Born method for determining the short‐range repulsive parameters is replaced by a more plausible method due to Hafemeister‐Zarht. The van der Waals dipole–dipole and dipole–quadrupole interaction coefficients are derived from the Kirkwood and Muller formula based on quantum theory. The thermodynamical properties are analysed by predicting the values of the bulk modulus and its pressure derivatives, Grüneisen, and Anderson parameters at temperatures 0 and 300 K. The values of pressure corresponding to different values of compressions are calculated using the equation of state. The results obtained in the present study are compared with available experimental data. A fairly good agreement is achieved.
Impurity Auger Spectra. Host Crystal with Unfilled Valence Band
Authors: Drchal V. , Kudrnovský J.
Published: July 2007

The intraatomic core–valence Auger spectra from a single impurity in a perfect crystal are determined for the generalized Wolff‐Clogston model with contact electron–electron interaction on the impurity as well as on the host crystal atoms. The self‐consistent T‐matrix approximation and the ladder approximation are used to determine the one‐ and two‐particle Green's functions, respectively.
Vibronic Interaction in the Absorption Spectra of Vanadium‐Doped AIIBVI Semiconductors
Authors: Melnichuk S. V. , Kramar V. M. , Tovstyuk K. D.
Published: July 2007

The vibronic interaction in AIIBVI semiconductors doped with 3d‐impurities is investigated. Ham's reduction parameter for vanadium in AIIBVI semiconductors is calculated. Comparison is made of the calculated absorption spectra with available experimental data.
Bisoliton Mechanism of High‐Temperature Superconductivity
Authors: Davydov A. S.
Published: July 2007

A moderately strong electron–phonon interaction is used to develop a nonlinear bisoliton model of high‐temperature superconductivity in ceramic oxides. The absence of an isotopic effect is explained. The dependence of the critical temperature for a superconducting transition and of the formation of a bisoliton condensate on bisoliton concentration is explained qualitatively. It is shown that at low temperatures electrons with an energy above the critical one come from a metal to a superconductor at equal time intervals only in pairs in a singlet spin state as bisolitons.
On Trigger Properties of Molecular Organizates. III. Nonlinear Waves in Stratified Molecular Structures
Authors: Gaididei Yu. B. , Yakimenko I. I.
Published: July 2007

A numerical analysis of the space–time evolution is performed for the population differences in stratified molecular systems of the donor–insulator–acceptor type with strong electron–deformation interaction. The influence of the initial population profile and pumping rate on the character of the evolution picture is studied in detail. The existence of the steady‐state nonlinear waves (the switch waves) in finite systems is proved and the velocities of these waves are calculated as well.
Tricritical Behaviour in Correlated Effective Field Theory
Authors: Mukhopadhyay S. , Chatterjee I.
Published: July 2007

Correlated effective field theory is applied to study the tricritical behaviour for a Blume‐Capel type of Hamiltonian as well as for a Hamiltonian with antiferromagnetic nearest neighbour and ferromagnetic next nearest neighbour interactions. Two different regions in the phase‐diagram are identified by estimating the slope of the double log plot of order parameter and reduced temperature. It clearly indicates that a tricritical region appears when the ratio of two competing parameters exceeds a critical value.
Dependence of Structure Factors upon Temperature for Liquid Metals, Zn and Hg
Authors: Jin Zhun‐Zhi , Zou Xian‐Wu , Yao Yong‐Qiao
Published: July 2007

The hard sphere cluster model is used to study the dependence of the structure factors upon temperature for liquid metals with the second type of liquid structures. The structure factors for liquid Zn (T = 450, 560, and 660 °C) and Hg (T = −35, 0, 20, 80, 150, 200, and 250 °C) are calculated. The theoretical results are in good agreement with experiments.
The Elastic Fields of Disclinations in a Planar Phase Boundary
Authors: Ding Di‐Hua , Deng Zicheng , Li Shuhong
Published: July 2007

First, the displacement and elastic strain fields of an infinitesimal phase boundary disclination loop (IPBDL) and a rectangular disclination loop in a planar phase boundary (RDLPPB) are derived. Then, regarding the RDLPPB as a fundamental defect unit, the displacement and strain fields of more complex dislcination configurations are calculated. All the results are presented in the form of analytical expressions of elementary functions. All the results are simplified to corresponding expressions for a homogeneous medium when both the phases have the same elastic properties.
Fast Fourier Transform Deconvolution of Positron Annihilation Doppler‐Broadened Lineshapes
Authors: Britton D. T. , Rice‐Evans P. C.
Published: July 2007

A fast Fourier transform method for the deconvolution of positron annihilation Doppler‐broadened lineshapes and their decomposition into different components is described. Different filters are tested on the positron annihilation line for two different systems which can be described as a superposition of three components, two Gaussian curves and an inverted parabola, convoluted with a measured resolution function; Cu containing a high proportion of krypton precipitates and physisorbed oxygen on graphite. Special attention is paid to the effect of filtering on narrow and on parabolic components, both of which need higher Fourier coefficients to be described fully. In the case of oxygen on graphite, which has a narrow component due to the annihilation of para‐positronium comparison is made with analysis by repeated numerical convolution of modelled lineshapes.
The Influence of Thermal Vibrations on RBS Proton Spectra Obtained from Subsurface Regions of Si Crystals
Authors: Czerbniak J. , Moneta M. , Pawłowski B. , Piwowarski M.
Published: July 2007

The χmin experimental results for 100 keV protons, for different temperatures and planes of the Si crystal are compared with adequate evaluations obtained in a modified, continuous potential model, with geometrical approximations, and with measurements of other authors.
Cyclotron Resonance Linewidth in a Two‐Dimensional Electron Gas
Authors: Sarkar C. K. , Kundu S. , Basu P. K.
Published: July 2007

Cyclotron resonance linewidths due to scattering by phonons and alloy disorder are calculated for a two‐dimensional electron gas formed in a heterojunction. The expression of linewidth for scattering due to acoustic phonons via deformation potential and piezoelectric interaction and for alloy scattering is obtained by including the finite extent of the wavefunction along the direction of quantisation. The screening due to free carriers is considered for electron–phonon interaction. The calculated linewidths for scattering due to deformation potential accoustic phonon and alloy scattering show a B1/2 variation and a weaker field dependence is obtained for piezoelectric scattering.
The Microcontact Spectrum of Aluminium
Authors: Zhernov A. P. , Kulagina T. N.
Published: July 2007

Electron–phonon interaction spectra are analysed in the microscopic approach for Al metal. The experimental spectrum for the thermodynamic Eliashberg function is described quantitatively. Theoretical and experimental microcontact spectra are compared.
Phonon‐Assisted Two‐Photon Exciton Transitions in Semiconductors
Authors: Hassan A. R.
Published: July 2007

Phonon‐assisted two‐photon transitions to excitonic states in semiconductors are theoretically investigated. The effects of both, the nonparabolicity of the band and the degeneracy of the valence band are taken into account. Expressions for the absorption coefficient through different band models are calculated. The numerical applications to CdI2 and GaP show that the four‐band model gives the dominant contribution which leads to a final s‐exciton state. An exciton peak appears at an energy which is close to that recently observed in CdI2. The non‐parabolic effect enhances the absorption coefficient by a two‐order of magnitude.
Theory of Auger Spectra from Alloys with Partially Filled Narrow Bands
Authors: Drchal V. , Kudrnovský J.
Published: July 2007

The one‐particle and two‐particle spectra are determined of the degenerate alloy Hubbard model with partially filled bands within the local self‐consistent T‐matrix approximation and the ladder approximation, respectively. The effect of disorder is included within the coherent potential approximation. The theory is illustrated on a simple model of the copper–nickel alloy. The origin of the two‐peak structure in the Auger spectrum from Cu atoms is discussed.
Self‐Consistent Density of States of a Disordered Electron System in the Cooper Channel
Authors: Kleinert P.
Published: July 2007

On the basis of a cumulant expansion of Green's functions self‐consistent equations are derived for the Cooperon propagator of the weak‐localization theory. The density of states has been calculated. Special results are obtained for the one‐dimensional white‐noise model.
A Theoretical Study of EPR Spectra in Cu2+‐ and Mn2+‐Doped CaCd(CH3COO)4 · 6 H2O
Authors: Zhou Yi‐Yang
Published: July 2007

A theoretical EPR study of single crystals of CaCd(CH3COO)4 · 6 H2O doped with Cu2+ and Mn2+ is made separately. A comparison between the calculated results and the experimental data shows quantitatively that the Cu2+ and Mn2+ ions substitute for Cd2+ and Ca2+, respectively. This concusion is consistent with the qualitative assumption by previous authors.
Submillimetre Magnetospectroscopy of Tellurium under Hydrostatic Pressure
Authors: Lyapin S. G. , Eremets M. I. , Shirokov A. M. , Herrmann R. , Müller H.‐U. , Ludwig F.
Published: July 2007

Transmission and photoconductivity of pure Te are recorded as a function of a magnetic field up to 6 T for several radiation energies in the submillimetre range under the pressure up to 3.4 × 108 Pa. The pressure dependence of the transverse hole effective mass is obtained from observation of cyclotron resonance (CR). Three groups of impurity lines are found with different behaviour under pressure. The pressure dependence of the energy and envelope function of the ground H‐like state in Te is calculated by a variational procedure within the effective mass approximation. The comparison with experiment makes it possible to evaluate the pressure dependence of the static dielectric constant.
XANES Study of Copper Mixed Valence and Mechanism of Superconductivity in YBa2Cu3O6.5+δ System
Authors: Garg K. B. , Singhal R. K. , Rao K. V. R. , Chandra U. , Chauhan H. S. , Singh J. , Jerath K. S. , Jain D. C.
Published: July 2007

Two high‐Tc superconductors YBa2Cu3O6.5+δ are studied with XANES technique. The two superconductor samples have a Tc (zero R) around 91 K and are orthorhombic in structure. CuK‐edge XANES measurements are made both, at room and liquid nitrogen temperature (LNT). A mixed valent state for Cu is generally considered essential for their superconducting behaviour. The measured XANES spectra are minutely examined with regard to this question. The results indicate the presence of Cu1+ and Cu2+ at RT but only Cu2+ at LNT. No evidence is found about the presence of Cu3+ state. The results tend to support an intermediate interatomic valent nature of the YBC superconducting system wherein the ground state is derived from a mixture of 3d9, 3d10L, and 3d9L configuration, L meaning the ligand hole. Mounting evidence is quoted in favour of holes being located in the oxygen valence band rather than at the Cu site and the high‐Tc superconductivity is ascribed to the pairing of the itinerant configuration 3d9L and its interaction with localized copper 3d electrons.
Spin‐Fluctuation Theory of Magneto‐Volume Effects in Itinerant Electron Magnets
Authors: Silin V. P. , Solontsov A. Z.
Published: July 2007

The magneto‐volume effects in itinerant electron ferromagnets and nearly ferromagnetic metals are discussed on the basis of a rotationally invariant microscopic theory taking account of the dynamical effects of both, transverse and longitudinal spin and electron density fluctuations. The change of volume V with temperature T in the presence of a magnetic field B due to the magneto‐volume coupling in metals is shown to be determined by the averaged squared local magnetic moment μ(B, V, T). The ratio ηC = μ(T = TC)/μ(T = 0) characterizing the invar anomalies below the Curie temperature TC is found in weak ferromagnets with account of the thermal expansion effects. The value μC is shown to decrease in the vicinity of the structural phase transition, where it vanishes. The approximations of Moriya‐Usami phenomenological theory of magneto‐volume effects are discussed.
Non‐Linear Acousto‐Optical Interaction at Deviation from Bragg Angle
Authors: Bukowski R. , Kleszczewski Z.
Published: July 2007

An influence of the deviation from Bragg's angle on the efficiency of the acousto‐optical interaction considering electrostriction is theoretically analysed. Anti‐Stokes and Stokes isotropic interaction as well as optical generation of the acoustic waves in dielectric crystals are investigated.
Optical Properties and Electronic Structure of Copper–Cobalt Alloys
Authors: Hummel R. E. , Goho W. M.
Published: July 2007

Differential reflectometry is utilized to investigate the electronic structure of α‐phase copper–cobalt alloys. It is found that copper–cobalt is a virtual bound state alloy, similar to copper–nickel and copper–gold.
Temperature Dependence of the Photoluminescence in GaAsGaAlAs Multiple Quantum Well Structure
Authors: Chiari A. , Colocci M. , Fermi F. , Li Yuzhang , Querzoli R. , Vinattieri A. , Zhuang Weihua
Published: July 2007

The temperature dependence of the photoluminescence (PL) of GaAs/GaAlAs multiple quantum wells is investigated. Emissions related to transitions between n = 1, 2, 3 electron and hole subbands are observed. Theoretical evaluation of the energy levels fits nicely the experimental data. The temperature dependence of peak position and photoluminescence intensity and the dependence of PL intensity on the power excitation show that there are three different temperature regions. At low temperatures (22 to 40 K) the main emission is ascribed to exciton recombination while at temperatures higher than 100 K it can be attributed to free carrier recombination. In the intermediate temperature region the PL involves both, excitonic and free carrier recombination. Thermally activated non‐radiative recombination processes strongly reduce the luminescence quantum efficiency.
Raman Spectroscopy of Sr Phases in Potassium Halides
Authors: Zaldo C. , Orozco E.
Published: July 2007

The formation of two different types of precipitates along 70 °C thermal annealing is deduced from the study of the Raman spectra of KCl, KBr, and KI single crystals doped with Sr. One of them is responsible for the Raman peaks present in X (YX) Z configuration and the other for the Raman peaks in the X(YY) Z one. At room temperature, peaks in X (YX) Z configuration are observed at 156, 93, and 66 cm−1 and those appearing in X (YY) Z at 189, 111, and 84 cm−1 for KCl, KBr, and KI matrices, respectively. The Sr precipitation is additionally monitored by the photoluminescence of Eu added in little quantities (<20 ppm). It is observed that Eu is only incorporated in the precipitates responsible for the Raman peaks observed in X(YX) Z configuration.
Frequency Dependence of the Soft Mode in KNbO3
Authors: Fontana M. D. , Ridah A. , Kugel G. E.
Published: July 2007

The analysis of the low‐frequency Raman spectrum of KNbO3 with a phonon–relaxator coupling model allows to reconcile the infrared results with the dielectric data. The discrepancies previously reported can be therefore explained in terms of the frequency dependence of the soft modefrequency and‐damping. The existence of the successive cubic–tetragonal–orthorhombic–rhombohedral phase transitions in KNbO3 can be coherently interpreted in this framework which emphasizes the major role of the ionic fluctuations associated with the central peak in the mechanism of transitions.
Nonlinear Propagation of Laser Pulses in GaAs‐GaAlAs MQWS
Authors: Manzke G. , Henneberger K.
Published: July 2007

A theoretical approach is presented for the description of nonlinear optical properties of GaAs‐GaAlAs MQWS connected with the blue‐shift of the 1s‐exciton resonance at high excitation. An experimental situation is considered where the MQWS is resonantly excited by a pump pulse of narrow spectral width creating a high density of excitons, and where the optical spectra are recorded by an ultrafast broad‐band probe pulse at different time delays. The densities of excitons in the single GaAs wells are determined by the simultaneous solution of the exciton diffusion and the optical problem of wave propagation. With increasing pump intensity jumps of the exciton densities in certain layers appear when the maximum of absorption crosses the pump frequency due to the blue‐shift of the resonance. The mechanism of the corresponding bistabilities in the reflection and transmission spectra is similar to that observed in connection with the quantum‐confined Stark effect.
The Complete Set of Polar Optic Phonon Modes of Superlattices. Confined Bulk and Interface Modes
Authors: Enderlein R. , Bechstedt F. , Gerecke G.
Published: July 2007

The complete set of polar optic phonon modes of an infinite superlattice is considered within the macroscopic theory. Eigenfunctions are given for confined bulk modes as well as interface modes. Interface modes arise from forbidden longitudinal and p‐transverse confined bulk modes. It is shown that the totality of confined bulk and interface modes form a complete orthonormalized set of basis functions.
Magnetic Polarons in EuO
Authors: Samokhvalov A. A. , Viglin N. A. , Gizhevskii B. A. , Arbuzova T. I. , Chebotaev N. M.
Published: July 2007

The existence of spin‐polarized complexes or magnetic polarons in magnetic semiconductors has been suggested theoretically some time ago, but up to now there is little experimental evidence of this phenomenon. With this in view, electron paramagnetic resonance is investigated (g‐factor and linewidth temperature coefficient) and also several other electrical and magnetic parameters of EuO‐based magnetic semiconductors with various donor concentrations (oxygen vacancies or Gd3+ ions substituting Eu2+ ions). The results of the investigation show that in a limited region of donor concentrations and temperatures there occurs a localization of charge carriers which may be attributed to the formation of magnetic polarons.
Theory of Infrared Transmission Spectra of Thin Insulating Films
Authors: Lehmann A.
Published: July 2007

It will be demonstrated that the so‐called LO–TO splittings in the infrared spectra of thin amorphous insulating layers are a consequence of boundary conditions.
The Improper Ferroelastic Phase Transition in Superionic Rb3H(SeO4)2 Crystals
Authors: Plakida N. M. , Salejda W.
Published: July 2007

A phenomenological theory of improper ferroelastic Phase Transition, that superionic hydrogen‐bonded Rb3H(SeO4)2, crystals undergo at Tc = 447 K, is presented. The temperature dependences of components of the spontaneous deformation tensor, elastic coefficient tensor, and electric conductivity in the vicinity of phase transition are calculated. A possible microscopic model of order–disorder type of the phase transition in the proton subsystem is discussed briefly.
On the Einstein Relation in n‐Channel Inversion Layers on Ternary Semiconductors under Magnetic Quantization
Authors: Ghatak K. P. , Mondal M.
Published: July 2007

An attempt is made to investigate the Einstein relation for the diffusivity–mobility ratio of the carriers in n‐channel inversion layers on ternary semiconductors in the presence of a quantizing magnetic field, on the basis of the fourth order in effective mass theory and taking into account the interactions of the conduction, heavy‐hole, light‐hole and split‐off bands, without any approximations of weak or strong electric field limits and incorporating the influences of electron spin and Dingle temperature, respectively. It is found, taking n‐channel inversion layers on Hg1−xCdxTe as an example, that the Einstein relation exhibits an oscillatory magnetic field dependence and the oscillatory spikes are much sharper with large numerical magnitudes even in the presence of broadening in inversion layers. The nature of oscillation is quite different to those obtained for bulk specimen of the same material under magnetic quantization. In addition, the corresponding well‐known results for isotropic parabolic energy bands form the special cases of the generalized expressions.
The Application of Thermally Stimulated Processes to the Study of Defects in Perovskite Type Fluorides
Authors: Kristianpoller N. , Trieman B. , Chen R. , Kirsh Y.
Published: July 2007

Thermally stimulated processes are studied in nominally pure, as well as in doped, perovskite type fluorides. The TSL and TSC, induced by X and monochromatic UV irradiations, are measured and their relations with other thermally stimulated processes are discussed. The excitation and emission spectra of the main TSL peaks are also measured, and their kinetic parameters are evaluated. From the comparison of the TSL and TSC curves, valuable information concerning the processes which occurred during the irradiation and the subsequent heating of the samples is obtained. The main TSL peaks seem to arise in this type of crystals from the thermal release of holes and their subsequent recombination with electron centres.
Mass Defects in Polyethylene and the Role of Mass Weighting in Phonon Green's Function Theory
Authors: Hägele P. C. , Wolf S. , Schmid C.
Published: July 2007

In phonon Green's function theory two representations of the defect matrix operator are used, a frequency‐dependent and a frequency‐independent. Care has to be taken when changing from one definition to the other: Not all results are independent of the definition chosen. Since such dependencies are not mentioned in the literature, one may be easily misled, e.g. in numerical calculations. Therefore a systematic comparison of the two representations is given. The theory is applied to the calculation of the defect density of states for mass defects in the polyethylene chain.