bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy Band Structure and Optical Properties of Wurtzite‐Structure Silicon Carbide Crystals
Authors: Gavrilenko V. I. , Postnikov A. V. , Klyui N. I. , Litovchenko V. G.
Published: July 2007

The electroreflection spectra of hexagonal polytypes of SiC, 4H and 6H are measured in the range 1.0 to 5.6 eV. The energies of direct optical transitions are determined using a multiple oscillator model. The electronic band structures of three hexagonal polytypes of SiC (2H, 4H, and 6H) are calculated by the first‐principles self‐consistent linear muffin‐tin orbital (LMTO ASA) method. One‐electron energies and densities of states are obtained in the range ± 15 eV around the top of valence band. The results calculated are compared with experimental data measured in this work and those available in the literature.
Phonon Structure of Raman Scattering Spectra of LiH Crystals
Authors: Tyutyunnik V. I. , Tyutyunnik O. I.
Published: July 2007

Raman scattering of light in cubic 7LiH and 6LiH crystals at excitation in the range from 514 to 250 nm is investigated experimentally. Raman spectra of pure crystals are measured at 300 K. For the first time, Raman scattering is found to consist of two components. These components are (1) resonant Raman scattering and (2) nonresonant Raman scattering. Resonant Raman spectrum is obtained and identified as the density of states function of V ‐type defect, whereas the nonresonant Raman spectrum is obtained and identified as the two‐phonon spectrum of LiH. Interesting behaviour of this two‐phonon spectrum is found and used as a basis of the original assignment method. Comparison with data from lattice‐dynamics calculations gives very close agreement and identifies the modes as originating essentially from X, W, and K points at the Brillouin‐zone edges.
Non‐Local Elastic Interaction Energy between a Screw Dislocation and a Point Defect
Authors: Wang R. , Pan K. L.
Published: July 2007

The elastic interaction energy between a screw dislocation and a point defect is given in non‐local elasticity. The interaction energy has no classical singularity. The results show that the interaction energy obtained by classical elasticity is much greater (1.4 eV or so) than the experimental value. However the value obtained by non‐local elasticity is in very good agreement with the experimental value (0.5 eV). It is also proved that the nonlocal interaction energy is lower when in body‐centred cubiciron an interstitial carbon atom locates in the octahedral positions than in the tetrahedral positions.
Slow Relaxation of Bose Qusiparticless on Multilevel Systems
Authors: Safonov V. L. , Farzetdinova R. M.
Published: July 2007

A complete microscopic theory is developed for the slow linear and nonlinear relaxation of Bose‐quasiparticles on multilevel equidistant quantum systems in solids. The expressions obtained have general forms and can be used for the determination of the relaxation of the relaxation rate for magnons, phonons, and other elementary excitations in crystals, which contain impurities and defects with an internal structure. It is shown that a process of slow relaxation can influence the spin‐lattice relaxation rate of the nuclear spins of host atoms.
Vacancies and Precipitates in Al–1.9 at% Cu Studied by Positrons
Authors: Gläser U. H. , Dlubek G. , Krause R.
Published: July 2007

Experimental and theoretical investigations of positron trapping by disk shaped Guinier‐Preston zones as appearing in AlCu alloys are performed. Using positron lifetime and angular correlation S‐parameter measurements the decomposition phenomena are studied in an Al–1.9 at% Cu alloy. The energy and the wave function of a positron within a cylindrical shaped trap is calculated using Ritz's variational principle. Although a weak localization of the positrons by multilayer Guinier‐Preston zones (GP zones) is to be expected from theory, the experimental spectra are dominated by positron annihilation in vacancies surrounded by Cu atoms. Above 200 °C positron trapping by semicoherent and incoherent precipitates is found.
The Investigation of the Ferroelectric Phase Transition in Cluster Systems of Order‐Disorder Type III. Free Energy
Authors: Yukhnovskii I. R. , Korynevskii N. A.
Published: July 2007

The critical part of the free energy of ferroelectric clusters with dipole–dipole interactions between the particies is obtained. The calculation of physically different contributions to the total free energy is performed. The recursion relations for the coefficients of block Hamiltonians are solved in several approximations. The suitability is examined of each approximation to the appropriate type of critical behaviour of the system. The values of critical exponents of correlation length and heat capacity are calculated.
Impurity Centres in ZnTe Crystals Doped with Be, Mg, Cd, and Hg
Authors: Tsurkan A. E. , Rebrov S. A. , Medvetskii S. P. , Nazarenko L. A. , Shemyakova T. D.
Published: July 2007

The reflection coefficient, Raman scattering, and photoluminescence spectra are investigated in ZnTe crystals, doped by isoelectronic impurities (Be, Mg, Cd, and Hg) up to concentration ≈ 1020 cm−3. It is shown that the above‐mentioned impurities essentially influence the optical and emission properties of ZnTe crystals. It is possible only in that case when the introduced impurity forms a bound exciton complex with the local centre. The bound exciton energies of doped ZnTe crystals are determined.
Positron Radiation at Resonance Dechanneling in Superlattices
Authors: Rudko V. N.
Published: July 2007

Radiation of positrons at resonance dechanneling in strained‐layer superlattices is investigated in the case when the wavelength of transverse particle oscillations in the channel is equal to the period of the superlatticeL. It is shown that for various values of the ratio,v, of the first layer thickness toL/2 (another layer thicknesses being constant) the angular dependence of channeling radiation changes from the symmetrical (atv= 1/2) to the strongly asymmetrical one (atv≈ 0 andv≈ 1). Positron radiation in superlattices with strong modulation of the average charges in neighboured superlattice layers is also investigated in the case when the wavelength of transverse particle oscillations is twice as much as the superlattice period. Depending onvthe angular dependence of channeling radiation is changed from the symmetrical one with a single maximum to various two‐maxima dependences.
Optical Absorption by Small Polarons in Palladium Hydride
Authors: Lupu D. , Chirtoc M. , Dadarlat D. , Candea R. M. , Bratu I. , Mecea V.
Published: July 2007

The optical transition of the polaron in Pd‐hydride is evidenced by both, classical and photopyroelectric spectroscopy. The results obtained from comparative studies on PdH0.65 and PdD0.65 are in agreement with the small polaron theory. The photopyroelectric spectroscopy reveals one of the main characteristics of the optical transition of the polaron: maximum phonon emission at the peak frequency.
Collective Excitations of Alpha Helical Protein Molecules
Authors: Ichinose S.
Published: July 2007

A theoretical study is given of collective excitations in long alpha‐helical proteins, including two types of peptide group displacements provided by changes of the helix pitch and its radius. The results provide two types of collective excitations in the continuum approximation called symmetric and asymmetric excited states.
Calculation of Relaxation Spectrum Function Based on the Quantum Void Model in the Amorphous Alloy Fe40Ni40B20
Authors: Phillips A. H. , Gobran N. K. , Kamel R.
Published: July 2007

The relaxation spectrum function is computed for a model representing a block of atoms forming a metallic glass involving void quanta. This is done by simulating the previously proposed atomic tilting model. By using the Monte‐Carlo method, the atomic positions in the considered block are located. The force of interaction among the atoms is computed by using the Lenard‐Jones potential function for short range order of random close packing. In terms of deduced relaxation spectrum function, the internal friction, Q−1, is calculated. Previously obtained results of Q−1 and the corresponding calculated ones are in good agreement showing the same deviation from the symmetric Debye relaxation spectrum. From a knowledge of the characteristic constants of the distribution function, together with the activation energy of formation of void quanta, the value of the free volume may be determined at any temperature. As a confirmation the amorphous‐crystalline transition temperature at which the void volume became equal to the vacancy volume is calculated and found concordant.
Tensile and Compressive Effect of Intracrystalline Pressure in Small Particles
Authors: Gamarnik M. Ya.
Published: July 2007

It is shown that the volume forces of electrostatic interaction of the crystal lattice elements — ions and electrons — result in intracrystalline pressure (IP) which depends on the size of particles and stipulates the size dependence of the unit cell parameters. Analytical expressions are obtained for the IP by the crystal energy and it is shown that the IP can increase or decrease in small particles depending on the crystal structure, i.e. has tensile or compressing action. The results of the theoretical calculations for NaCl and CeO2 give evidence for the compressing effect of IP in small particles of NaCl and for the tensile effect of IP in small particles of CeO2. These results are in good agreements with experimental data of the changes of the unit cell parameters in small particles of NaCl and CeO2.
Collective Plasmon Modes in Semiconductor Superlattice Structures in the Presence of the Effect of Image Charges
Authors: Aharonian K. H. , Sedrakian D. G.
Published: July 2007

Dispersion relations are presented of non‐retarded collective plasmon modes in superlattice structures with a strong dielectric mismatch between alternating layers in the presence of the effect of image charges (EICH).
Nonequilibrium Carrier Recombination Channels in Uniaxially Stressed Gapless Semiconductors
Authors: Bakhanova E. V. , Strikha M. V. , Vasko F. T.
Published: July 2007

Nonequilibrium carrier interband recombination channels such as radiative recombination, transitions with optical phonon emission, and Auger recombination are studied in uniaxially compressed gapless semiconductors. Energy ranges for radiative and phonon recombination are determined. The recombination process with phonon emission, the most efficient at low pressures, is dramatically suppressed when the gap becomes wider than the optical phonon energy. Energy threshold dependences are discussed for the cc → cv Auger process (the recombination energy is carried by a free electron) and for the cv → vv process (the energy is carried by a free hole). Temperature and concentration dependences of the recombination rates for these channels are obtained.
Fine Structure of 2p‐Excitons in KI Single Crystals by Two‐Photon Spectroscopy
Authors: Hasuo M. , Nagasawa N.
Published: July 2007

The fine structure of the 2p‐exciton of KI single crystals due to envelope‐hole coupling is investigated by using high resolution two‐photon excitation spectroscopy. The energies of the split‐off 2P1/2, 2P3/2, and 2P5/2 states are (6.1990 ± 0.0014), (6.1898 ± 0.0003), and (6.1947 ± 0.0004)eV, respectively. The relevant spherical parameter μ and the upper limit for the cubic parameter δ are evaluated to be (0.051 ± 0.022) and 0.004, respectively. The fine structure in the LO‐phonon assisted band is also observed. The LO‐phonon energy at Γ point is obtained to be (16.4 ± 0.4) meV.
On the Nature of the Rhenium Effect. Peculiarities of the Band Structure and Elastic Moduli of W‐ and Mo‐Based Alloys
Authors: Gornostyrev Yu. N. , Katsnelson M. I. , Peschanskikh G. V. , Trefilov A. V.
Published: July 2007

In the rigid band approximation the electronic structure of W–Re and Mo–Re alloys is calculated and their band contribution to the elastic moduli Cik. Critical Re concentrations are determined at which electronic topological transitions occur. An analysis of the computational results for Cik is invoked to discuss variations in the degree of “covalency” and “metallicity” of the chemical bonds in rhenium‐doped tungsten. Consideration is given to the role of the elastic anisotropy constant of W–Re and Mo–Re alloys and to its effect on the individual dislocation mobility and plastic properties of these alloys.
Excitons Bound to Defect Complexes in Heavily Doped CdS
Authors: Georgobiani A. N. , Gruzintsev A. N. , Zayats A. V.
Published: July 2007

The fine structure of the luminescence due to bound excitons is found in CdS crystals doped with alkali metals (AM): lithium or sodium 1018 to 1020 cm−3. In the spectral range of the acceptor–exciton complex emission the optical transitions are explained as recombination of excitons bound to the complexes of nearby‐located defects [AMcdCdi] or [AMcdAMi] with different distances between components: 0.2 to 0.6 nm. The Haynes rule yields Eex/Ecompl = 0.14 for such excitons.
Solutions of the One‐Dimensional Non‐Linearised Ginzburg‐Landau Equations for Optional Vector Potentials
Authors: Bläsing J.
Published: July 2007

A possibility to solve the one‐dimensional non‐linearised Ginzburg‐Landau equations is presented. The solutions describe the behaviour of the wave function and density of the Cooper pairs between two points in a weak superconductor as a function of the states in the two points. The coupling between the first and second Ginzburg‐Landau equations is attributed to the influence of the current density and the magnetic field on the solution of the first Ginzburg‐Landau equation. The solutions presented allow the description of the influence of optional vector potentials to a supercurrent in the form of the known Josephson‐current equation.
Electrical Resistivity of Compound Forming Alloys
Authors: Mishra A. K. , Sahay B. B.
Published: July 2007

The harmonic model potential is used to explain the anomalous behaviour in the electrical resistivity of LiPb and NaPb on the basis of pseudo‐binary mixture. The computed results for the electrical resistivity of LiPb and NaPb in the whole concentration range indicate that the Ziman‐Faber formula can safely be used for the study of electrical resistivity of such ternary systems.
Dielectric Properties of Mixed Alkali and Silver Halide Crystals
Authors: Sinha P. K.
Published: July 2007

The static and optical dielectric constants are calculated for the entire range of composition in twelve systems of mixed crystals of alkali halides and silver halides with NaCl‐type structure, by adopting the method developed by Kamiyoshi and Nigara (KN). Transverse and longitudinal optical mode frequencies are also evaluated using the Lyddane‐Sachs‐Teller relation. Calculated values of static dielectric constants are found to exhibit a sharp non‐linear dependence on composition near the equi‐molar region in KClKBr, KClRbCl, KBrRbBr, KIRbI, RbClRbBr, and AgClAgBr mixed crystals and a slight non‐linear dependence on composition near the NaBr end in NaCl‐NaBr mixed crystals, which is in agreement with experimental data. The usefulness of dielectric constants and optical mode frequencies is demonstrated by investigating the composition dependence of the Szigeti effective charge parameter.
Triplet relaxed excited state structure and luminescence of thallium‐doped alkali halides
Authors: Nagirnyi V. , Soovik † T. , Vaino P. , Zazubovich S. , Jaanson N.
Published: July 2007

For the first time a slow component is observed and studied in the decay kinetics of AT emission of TI+ centres in KBr, KI, RbCl, and RbI crystals. The existence is established of a singlet metastable level below the doublet emitting one in each Jahn‐Teller minimum of the triplet excited state of the TI+ centres. It is concluded that for all ns2 ions in alkali halides the structure of the relaxed excited state is qualitatively the same, and it may adequately be described in terms of a theory that considers the Jahn‐Teller effect as a main interaction in the relaxed excited states of the luminescence centres. The nature is discussed of the weak emission bands appearing on excitation in the A absorption band of TI+ centres besides the main AT and AX emission bands, earlier interpreted as hot luminescence of Tl+ centres.
EPR of new platinum‐related complexes in silicon. I. Defects of symmetry C1h formed at intermediate temperatures
Authors: Höhne M. , Gehlhoff W.
Published: July 2007

The variety of Pt‐related complex defects in silicon is enlarged by EPR detection of a new group of defects, each of them containing one Pt ion. They are formed by different annealing procedures, including a step at intermediate temperatures. Two of the new complexes exhibit an EPR spectroscopic peculiarity: Though the angular dependences evidence an apparent monoclinic symmetry, two of the line groups, typical for this symmetry, coincide for any angle of rotation. The condition for this behaviour is discussed.
Investigations of Bijvoet Differences and Anharmonicity in Gallium Phosphide
Authors: Saravanan R. , Mohanlal S. K. , Chandrasekaran K. S.
Published: July 2007

Precise X‐ray diffraction intensity data are collected at 300 K using a perfect single crystal sphere of gallium phosphide. The data are firstly analysed assuming a harmonic thermal vibration of atoms. The refined Debye‐Waller factors for this harmonic model are B(Ga) = 0.446(0.010)× 10−2 nm2 and B(P) = 0.507(0.001) × 10−2 nm2 with the residual index R = 1.2715%. Then anharmonic thermal vibration effects are included in the structure factor expressions. In the anharmonic model, two additional parameters, the individual anharmonic thermal parameters, are also included in the refinement process. The refined values are β(Ga) = −1.201(0.371) × 10−13 J nm−3 and β(P) = 2.002(0.274) × 10−13 J nm−3 with R = 1.2646%. The effect of anomalous dispersion on the structure factor is also analysed. It leads to Bijvoet differences between all odd index inverse reflections. The inclusion of anharmonic effects leads to Bijvoet differences between all even index inverse reflections. The measured Bijvoet ratios are in good agreement with the calculated Bijvoet ratios both in sign and magnitude. The individual Debye‐Waller factors, the Bijvoet ratios, observed and calculated both, for the harmonic and anharmonic models, are reported.
Theory of Macroscopic Local Single‐Particle Charge States in Quasi‐Zero‐Dimensional Structures Surface Local States
Authors: Pokutnyi S. I. , Efremov N. A.
Published: July 2007

A theory of macroscopic local single‐particle charge states in quasi‐zero‐dimensional structures is framed. The energy spectrum of charge carriers in a small particle (semiconducting or dielectric) is investigated as well as its dependence on the size of the particle, the effective mass of the charge and relative dielectric constant under conditions when polarization interaction plays an important role. A new type of local states of charge carriers inside a small particle, namely surface states, is predicted.
Microstructural Aspect of Electron Transfer in the Blue and Red Molybdenum Bronzes
Authors: Colaitis D.
Published: July 2007

The electron transfer process is systematically examined in K0.33MoO3 semiconductor red bronze and in K0.30MoO3 metallic blue bronze as a direct consequence of cation‐anion orbital overlaps. The critical interatomic distance below which the overlap occurs is established at about 0.196 nm. In K0.33MoO3, it is shown that closed localized molecular‐type orbitals correlate the rigid units which characterize the MoO3 layers. In K0.30MoO3, the paths for collective electrons are three quasi‐one dimensional Mo–O chains, with occurrence of transverse correlations between the two among them which are equivalent. The third chain connects two staggered rigid‐unit columns. The coupling of the metal–semiconductor transition with the lattice modulation is investigated in correlation with low temperature structural slight rearrangements and atomic displacements. It is shown that a part of collective electrons can condense in collective localized orbitals which close in between two equivalent chains with the modulation periodicity. The extension of transverse correlations towards the third inequivalent chain is discussed in relation with orbital overlaps and with the two‐band states model. Finally a microstructural model is proposed, which can describe in terms of interface modulation the conduction electron modulation and its incommensurability.
EPR of New Platinum‐Related Complexes in Silicon. II. Coexistence of a Tetragonal Jahn‐Teller System and a Nearly Trigonal System in One Pair
Authors: Höhne M. , Gehlhoff W.
Published: July 2007

A spectroscopic peculiarity of two Pt‐related complex defects is interpreted for both of them by assuming one Pt ion in a crystal field, which is tetragonal, though another defect is trigonally coordinated. This coexistence is discussed in the framework of a static Jahn‐Teller effect. Wave functions, compatible with the g‐values, are sketched.
Temperature Variation of EPR Linewidth of Gd3+ and Estimation of Spin–Lattice Relaxation Time of Nd3+ in NdF3 Single Crystals
Authors: Korczak W. , Paradowski M. L. , Misiak L. E.
Published: July 2007

EPR (X‐band) linewidths of the Gd3+ ion in NdF3 and LaF3 single crystals in the temperature range 140 to 510 K are investigated. The mechanism of spin–lattice modulated narrowing is adapted to explain the temperature dependence of the Gd3+ EPR linewidths in the presence of the Kramers host Nd3+ ions (4f3, 4I9/2). The spin–lattice relaxation time (τ′1) of the host ions Nd3+ in Gd3+‐doped NdF3 single crystal is calculated, using the equation for crystals containing two different species of paramagnetic ions.
Energy Band Structure Calculation of CdGeAs2 by Pseudopotential Method with Spin–Orbit Interaction
Authors: Madelon R. , Paumier E. , Hairie A.
Published: July 2007

The electronic energy bands of CdGeAs2 are calculated at symmetry points and along symmetry directions of the Brillouin zone, using the empirical pseudopotential method and taking into account the spin–orbit interaction. The introduction of the spin–orbit interaction improves the correspondence between calculated and measured values of transition energies. The symmetry properties of the wave function are determined with and without spin–orbit interaction: this study confirms the level order and the transition polarization dependence of levels, in particular around the gap which is a direct one.
Electrical Properties of Alkaline Earth Fluorohalide Crystals
Authors: Ayachour D. , Sieskind M. , Geist P.
Published: July 2007

The ionic conductivity of undoped BaFCl, BaFBr, BaFI, SrFCl, and SrFBr single crystals is measured. The activation energies for a variety of anion vacancy mechanisms and the Schottky energy are defined. They are found to be in good agreement with Baetzold's theoretical data. Partial measurements of the static dielectric constant point out that these materials show an important dipolar contribution which is connected with their antiferroelectric character.
Processes of Hot Electrons and Lattice Relaxation in Ion Implantation
Authors: Mazzone A. M.
Published: July 2007

The relaxation processes of a hot electron gas formed under bombardment with particles of energy in the MeV and GeV range are described by using molecular dynamics simulation methods based on a classic representation. The calculations lead to a noticeable lattice disorder whose features and mechanisms of formation differ from the ones of a Coulomb explosion or of a thermal spike.
Multifractal Properties of Diffusion‐Limited Aggregates and Random Multiplicative Processes
Authors: Canessa E.
Published: July 2007

The multifractal properties are considered of irreversible diffusion‐limited aggregation (DLA) from the point of view of the self‐similarity of fluctuations in random multiplicative processes. In particular the breakdown of multifractal behaviour and phase transition associated with the negative moments of the growth probabilities in DLA are analysed.
Fourth‐Order Adiabatic Linear Compressibilities for Non‐Cubic Solids
Authors: Delannoy‐Coutris M. , Toupance N. , De Belloy J. Boistel
Published: July 2007

Expressions for the linear adiabatic compressibilities of an at least orthorhombic crystal and their pressure derivatives are derived in terms of the second‐, third‐, and fourth‐order elastic constants within a finite‐strain theory which includes thermal effects according to the quasi‐harmonic approximation of lattice dynamics. The expressions are derived in terms of the Lagrangian strain tensor and the frame‐indifferent analogue of the Eulerian strain tensor. Numerical applications are given for three hexagonal metals: cadmium, magnesium, and zinc, namely the temperature variations of the linear adiabatic compressibilities and their pressure derivatives, including recent estimations of the combinations of fourth‐order elastic constants appearing in the present work. When possible, the comparison with experimental data shows a rather good agreement with the compressibilities calculated within the present theory using the Green‐Lagrange strain measure of the deformation. About the variations of the first pressure derivatives of the adiabatic compressibilities with temperature, the present work provides us with theoretical values in the lack of experimental data.
Alloy Broadening of Semiconductor Impurity Lines Second‐Neighbor Effects
Authors: Ochi Carmen Lucia C. , Koiller Belita
Published: July 2007

The alloy broadening of impurity lines in ternary semiconductor alloys is investigated using a tight‐binding Hamiltonian with nearest‐neighbor interactions and the cluster ‐ Bethe‐lattice approach. A 17‐sites cluster connected to the alloy Bethe‐lattice effective medium within a one‐orbital per site diagonal disorder model is used for the study of a single impurity and of impurity pairs. The method is applied to InxGa1‐xP doped with Ge, and it is found that broadening occurs for the impurity on the same sublattice as the group‐III species, i.e., second neighbor to the occupationally disordered sites. This result is interpreted in terms of the cluster statistics and of the spacial distribution of the wavefunctions associated to the localized impurity states.
Electronic Structure of Bi2Sr2CaCu2O8 Doped by Sulphur in the Cluster Approximation
Authors: Kalinkin A. N. , Skorikov V. M. , Soldatov A. A. , Yu. Dobretsov V.
Published: July 2007

The electronic structure of SrBi4Cu4O4+9, SrBi4Cu4O5S4+4 clusters in the high‐Tc superconductor Bi2Sr2CaCu2O8 doped by sulphur is calculated using the relativistic self‐consistent Xα‐SW method. The effective charges of atoms and electronic densities of states are obtained. The substitution O → S in Cu‐O sheets is shown to result in hole doping and the improvement of hole hopping that may increase Tc.
Schrieffer‐Wolff Transformation of the p–d Model for Oxide Superconductors Charge Fluctuation Regime
Authors: Lovtsov S. V. , Yu. Yushankhai V.
Published: July 2007

To describe low‐energy properties of the CuO2 plane in oxide superconductors the effective interactions up to the fourth order in the p–d hybridization amplitude, V, are derived systematically by the Schrieffer‐Wolff transformation. Contrary to other analogous derivations the value of V is assumed to be comparable to the charge transfer gap, V ≈ Δ = ϵp − ϵp, that corresponds to the charge fluctuation (not spin fluctuation, V < Δ) regime in the system. Among the variety of relevant phenomena only a particular problem of magnetic frustrations in the system of Cu‐spins is examined.
Hysteresis of the Microwave Absorption in High‐Tc Superconductors
Authors: Czyzak B. , Stankowski J.
Published: July 2007

Hysteresis of Josephson microwave absorption (JMA) in the magnetic field by means of standard EPR methodology in ceramic superconducting YBa2Cu3O6.9 is investigated. The hysteresis of JMA strongly depends on 100 kHz modulation amplitude of the external magnetic field and the external magnetic field sweep rate. For a small amplitude (Bm < 1 G) of the 100 kHz modulation a fast dissipative process, independent on the sweep rate is observed. For Bm higher than 1 G Josephson‐like dissipation occurs. The hysteresis behavior of the JMA disappears for slow enough sweep rate. It disappears also for the magnetic field sweep range lower than ±25 G. A phenomenological model for explanation of the observed phenomena is proposed.
Molecular Orbital Explanation of Surface Magnetism of α‐Fe
Authors: Li Zhiqiang , Luo Helie , Lai Wuyan , Zheng Qingqi
Published: July 2007

The electronic structure and magnetic properties of bulk and surface of α‐Fe are studied by a SCF‐LCAO‐MO method within the local density functional theory. The enhancement of surface magnetic moment is observed and attributed to the decrease of overlaps of atomic orbitals on the surface, which is related to the coordination number and the occupation of localized antibonding orbitals near the Fermi level. The vacancies on the surface are found to increase the magnetic moment of the adjacent atom.
Monte Carlo Simulations for Pure and Site‐Diluted Simple Cubic Classical Heisenberg Systems
Authors: Jochims M. , Holey T. , Fähnle M.
Published: July 2007

A fully‐vectorized Monte Carlo programme is developed to investigate the critical behaviour of pure and site‐diluted classical Heisenberg systems on a simple cubic lattice of 323 spins. The finite‐size effect is much larger than that for the corresponding Ising model. It therefore must be suspected that the asymptotic critical regime could not be penetrated. An effective exponent of β = 0.33 for the root mean square magnetization is found both, for the pure and the site‐diluted case. The attempt to improve the efficiency of the computer programme by a discretization of the continuous Heisenberg model fails because of the very slow convergence with respect to the number of allowed spin orientations.
Radiative Core–Valence Transitions in Alkali‐Halide Crystals
Authors: Rodnyi P. A. , Terekhin M. A.
Published: July 2007

Using pulse X‐ray and synchotron radiation, the spectral and kinetic characteristics of a new type of fundamental luminescence in RbF, CsF, CsCl, and CsBr crystals are analyzed. On the basis of the experimental results obtained, a generalized consideration of the mechanism of this type of luminescence is carried out in alkali‐halide crystals, taking into account the known spectra of photoelectron emission, absorption spectra, and band structure calculations.
The Separable Potential Method A Unified Approach to Various Lattice Models
Authors: Idiodi J. O. A.
Published: July 2007

This work proposes the separable potential method (SPM) as a unified treatment of a class of lattice models. The richness in structure of the unified approach is demonstrated through contact with some of the most important lattice models in the literature, the embedded‐atom method (EAM) being one of such models. As a practical application of SPM some fairly extensive results for f.c.c. metallic copper are reported.
Atomic Hydrogen Centres in LiF–H− and LiF–H−, Mg2+ Crystals
Authors: Egranov A. V. , Otroshok V. V. , Chernyago B. P.
Published: July 2007

Atomic hydrogen centres in LiF–H− and LiF–H−, Mg2+ are studied by optical and ESR techniques. X‐irradiation of these crystals at 80 K leads to the formation of the H‐centres which are thermally stable up to 110 K. After thermal annealing of the H‐centres in LiF–H−, Mg2+ crystals a new atomic hydrogen centre is observed which is interpreted as an interstitial hydrogen atom stabilized by a complex of the Mg2+ ion and a positive ion vacancy (H(Mg)‐centre). Thermal decay of the (H(Mg)‐centres occurs at 430 K and leads to the formation of a hydrogen atom in the cation vacancy (H(Mg)‐centre).
Structural Phase Transformation (F.C.C. → B.C.C.) in Ag, Pt, and Sr and Their Stability on the Path of Transformation
Authors: Seyoum K. Belay , Thakur K. P. , Jha D.
Published: July 2007

Theoretical calculations are made to locate the stress‐free b.c.c. phase in three f.c.c. metals (Ag, Pt, and Sr). Internal energies corresponding to the unstressed b.c.c. and f.c.c. phases, and the required stress and energy changes for f.c.c. → b.c.c. transformation in these crystals are presented. To determine the range of stability (G stability) the Born criterion is used by calculating the values of corresponding elastic moduli on the line of deformation connecting the stress‐free b.c.c. and stress‐free f.c.c. phases of the crystal. The Morse potential model is used to carry out these calculations.
Chaotic Dynamics of Nonlinear Schrödinger Soliton nteracting with an Oscillating Impurity
Authors: Abdullaev F. Kh. , Abdumalikov A. A.
Published: July 2007

The problem of nonlinear Schrödinger soliton interaction with an oscillating impurity is considered. The regimes of soliton motion for the cases of periodic and random oscillations of the impurity near an equilibrium point are investigated. As shown in the first case there exist regions of parameters under which a soliton dynamics becomes chaotic. The comparison of statistic characteristics of chaos in the region of dynamic and standard stochasticity is carried out. The coefficient of the soliton diffusion is found.
On the Theory of Soliton Lattice Melting in Three‐Dimensional Incommensurate Cystals
Authors: Veshchunov M. S.
Published: July 2007

The transition into the normal phase, associated with the melting of the soliton lattice in the incommensurate phase of a three‐dimensional crystal, is theoretically studied. It is shown, that in barium−sodium niobate (BSN) crystals this transition can take place in two steps.
Experimental Quasi‐Harmonic and Leading‐Order Anharmonic Coefficients of Ag, Al, Au, Cu, Fe
Authors: Quareni F. , Mulargia F.
Published: July 2007

The recently developed procedure of estimating the leading order anharmonic coefficients (third and fourth order in the Hamiltonian) from available thermodynamic data is applied to five metals: silver, aluminium, gold, copper, and iron. Stable estimates are obtained, yielding that the leading order anharmonic contributions are comparable with the electronic ones. The quasi‐harmonic coefficients are also estimated.
Calculation‐ of Some Defect Parameters in F.C.C. Metals
Authors: Ghorai A.
Published: July 2007

The lattice statics model together with the atomistic continuum model is used for the calculation of relaxation due to a vacancy, the vacancy formation energy and divacancy binding energy in the case of some f.c.c. metals whose phonon dispersion curves are available. Using the measured phonon dispersion relations and the elastic constants as constraints the dynamical matrix is derived considering interactions up to the eighth nearest neighbouring shell. The calculation shows that in all the cases the first twelve nearest neighbours relax towards the vacancy and the magnitude of the displacements of the distant neighbours decreases systematically. The available experimental values of the monovacancy formation energy and divacancy binding energy whereever available, show fairly good agreement. Relations among monovacancy formation energy, melting temperature, and activation energy for self‐diffusion are proposed.
Replica‐Trick Study of Vibrational Properties of Dilute Scalar‐Force Networks
Authors: Böttger H. , Freyberg A.
Published: July 2007

Vibrational properties of two‐dimensional triangular bond‐percolation systems with scalar forces are studied by means of the replica trick, which allows a self‐consistent effective medium to be derived. The vibrational density of states is calculated and compared with results obtained by means of other methods. The replica‐trick approach can also be extended to models with central and bondbending forces.
Resonant Tunneling in a Symmetrical Rectangular Triple‐Barrier Structure
Authors: Yamamoto H. , Kanie Y. , Taniguchi K.
Published: July 2007

Resonant tunneling is studied theoretically in a symmetrical rectangular triple‐barrier structure. Analytical expressions for the transmission coefficient and the resonance conditions are derived. It is found that resonant tunneling with transmission 1 and resonant tunneling with transmission < 1 can occur in the symmetrical triple‐barrier structure. It is confirmed that transmission < 1 at resonance may occur when the outer barrier width is less than about one half of the central barrier width.
The Lifetime of Excited O, S, Se, and Te Centres
Authors: Hessmann W. , Fischer F.
Published: July 2007

The decay of photoluminescence of these chalcogen centres in alkali halides is purely exponential. The lifetimes being constant at low temperatures are strongly reduced as the temperature is raised above certain limits. Activation energies for thermal quenching are obtained and discussed within the frame of an anharmonic Franck‐Condon model.
Raman Spectra of [N(CH3)4]2ZnCl4 Single Crystals. III. Activation of Acoustic Phonons in Raman Spectra of the Commensurately Modulated Phases
Authors: Torgashev V. I. , Yuzyuk Yu. I. , Rabkin L. M. , Durnev Yu. I.
Published: July 2007

Low‐frequency (v < 50 cm−1) polarized Raman spectra of TMATC‐Zn crystals are studied in the temperature range between 300 and 100 K that covers the range in which the structural phase transitions of this compound occur. The appearance of lines with frequencies below 17 cm−1 is observed in commensurately modulated low‐symmetry phases. These lines correspond to the phonons of transverse acoustic branches in the Γ–Σ–X direction of the normal phase which transfer to the zone center as a result of the unit cell multiplication. A sharp drop in the relaxational contribution to the scattering spectrum is found for frequencies below 20 cm−1 in phases V and VI which is thought to be associated with ordering processes in the crystal lattice.
Diffraction of Neutrons by Superlattices in the Presence of an Alternating Magnetic Field
Authors: Goliney I. Yu. , Rudko V. N.
Published: July 2007

The peculiarities of neutron diffraction by multilayer structures, which are used in neutron monochromators and polarizers, are investigated in the presence of an alternating magnetic field. Deviations from the mirror reflection law take place due to the appearance of neutrons with a normal component of momentum equal to \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt {\chi ^2 \pm 2m\omega /\hbar}$\end{document}, where ω is the frequency of external field and χ the normal component of an incident particle. Expressions for respective reflection and transmission coefficients, R± and T±, that characterize processes with change of neutron energy, are obtained and analysed.
Low‐Temperature Heat Conduction of Disordered Crystals in the Case of Vibrational Spectrum Cross Splitting
Authors: Zhernov A. P. , Salamatov E. I. , Chulkin E. P.
Published: July 2007

A model of a crystal with nondiagonal disorder is considered. The regions of quasi‐particle localization are found. The low‐temperature heat conduction behavior is analyzed.
The Effect of Giant Striction and Thermal Expansion Anomalies in Systems with Structural Instabilities
Authors: Solontsov A. Z. , Orlov V. K.
Published: July 2007

A simple fluctuation theory analogous to the spin‐fluctuation theory of the magneto‐volume effect is presented to discuss the phenomenon of giant striction, associated with displacive phase transitions, and thermal expansion anomalies. It is argued that the giant striction accompanying the phase transition to the incommensurate charge density wave state is responsible for the low temperature anomalous expansion of α‐uranium and α‐plutonium. The spontaneous striction values in these materials are estimated to be 4.57 × 10−3 and 1.82 × 10−2 comparable with those known for systems with giant magnetostriction.
Effect of Lithium Intercalation on Lattice Dynamics of Molybdenum Disulfide
Authors: Sekine T. , Julien C. , Jouanne M. , Weber M. , Samaras I. , Balkanski M.
Published: July 2007

In order to explain new peaks in the Raman spectra of MoS2 after intercalation with Li, the lattice dynamics in LixMoS2 is calculated by applying the central force model. It is found that they can be attributed to new vibrational modes in which the intercalant atoms strongly vibrate against the host lattice. The force constants between Li and S atoms are much smaller than the intralayer force constants and have almost the same order value as the interlayer ones.
Uniaxial Stress Effect on the Charge Transfer in Highly Oriented Films of Iodinated Palladium Phthalocyanine
Authors: Tanaka M. , Tsuyoshi H. , Yudasaka M. , Kurita S.
Published: July 2007

The electronic structure of highly oriented films of iodinated palladium phthalocyanine (PdPcIx), which are obtained by vacuum‐evaporation of PdPc on mica substrates and subsequent iodine‐doping, are studied by the piezoabsorption spectroscopy. Iodines are present as linear chains of I ions in between PdPc stacks, which is confirmed by resonant Raman scattering spectroscopy. The piezoabsorption spectra is measured under a uniaxial stress along the PdPc stacking axis. It is found that the tensile stress induces charge transfer from PdPc molecules to iodines in the lightly doped films and charge back‐transfer in the heavily doped films, and the charge transfer is not induced at the critical doping level.
Electronic Structure of AgCl, AgBr, and AgI
Authors: Gordienko A. B. , Zhuravlev Yu. N. , Poplavnoi A. S.
Published: July 2007

Self‐consistent calculations are made of the band structure and charge density in the AgHal series by the density functional method using norm‐conserving pseudopotentials. The valence band top is found to be realized at the L point in the series of AgCl, Br, and I for the rocksalt structure; there are competing minima at the Γ and X points in the conduction band, the conduction band bottom being at Γ for AgCl, while that for AgBr and AgI is at X. However both, the valence band top and conduction band bottom for the zinc‐blende structure (AgI) are realized at the Γ point.
Solitary Excitations in an Anharmonic Molecular Chain with Second‐Neighbour Interaction
Authors: Primatarowa M. T.
Published: July 2007

Nonlinear effects caused by the interaction of an exciton with phonons in deformable molecular chains are considered in the second‐neighbour approximation. The cubic anharmonicity of the intermolecular potential leads to a nonlinear Schrödinger equation with nonlinearities of third and fifth power with respect to the function. Two types of solitary bound states are shown to appear situated at the bottom and the top of the exciton energy band, respectively. The parameters of the solitary excitations are calculated.
Study on Momentum Density and Fermi Surface in Paramagnetic Cr and W by Positron Annihilation
Authors: Kubota T. , Kondo H. , Nakashima H. , Murakami Y. , Tanigawa S.
Published: July 2007

The three‐dimensional electron‐positron momentum densities in paramagnetic Cr and W are reconstructed from measurements of two‐dimensional angular correlation of positron annihilation radiations (2D‐ACAR) by the image reconstruction technique based on a direct Fourier transformation. The experimental momentum density for paramagnetic Cr and W shows the contribution of the Fermi surface sheets; the electron surface at Γ, the hole surface at H, the hole surface at N. The Fermi surface topology obtained from the present results agrees with the theory and other experiments.
Theory of High‐Temperature Superconductivity
Authors: Chen Liangheng , Lu Tianquan
Published: July 2007

A new mechanism for the high‐Tc superconductivity is suggested. The antiferromagnetic order of the Cu spins between two neighbour O holes, i.e. the localized antiferromagnetic correlation may be the origin giving rise to the hole pair. The maximum of Tc is calculated for the YBaCuO superconductor using the similar method of calculating the antiferromagnet Neel temperature. The conclusion is made that the maximum of Tc for the YBaCuO superconductor is between 107.9 and 155.2 K, and the energy gap 2Δ(0) = 3.54kBTc.
Effect of Antisymmetric Strain‐Order Parameter Coupling on Elastic Constants in Unconventional Superconductors
Authors: Thalmeier P.
Published: July 2007

The coupling of strains to the superconducting order parameter leads to step anomalies in the elastic constants at the transition temperature. In a unconventional cubic superconductor a very specific step asymmetry of transverse (ex, kz)‐ and (ex, kz) c44‐modes may exist in an external field. It is due to a coupling of pseudoangular momentum of the condensate to rotational, antisymmetric strains which is genuine for a superconducting order parameter belonging to a representation with broken T‐invariance. This effect is calculated on the basis of a Ginzburg‐Landau approach and an estimate of its size is given.
Magnetoconductivity of Disordered Two‐Dimensional Electron Systems
Authors: Kleinert P.
Published: July 2007

The magnetoconductivity of a disordered two‐dimensional electron gas is calculated for low‐intermediate magnetic field strengths. Vertex corrections from the Cooper scattering channel are treated and the influence of the self‐energy is investigated. Special attention is paid to cases where both, Shubnikov‐de Haas oscillations and a negative magnetoresistance appear.
Symmetry and Eigenstates of the 3D Hubbard Model in an Electromagnetic Field
Authors: Su Gang , Ge Mo‐Lin
Published: July 2007

The symmetry and the eigenstates of the 3D Hubbard model in the presence of an external electromagnetic field on a periodic simple cubic lattice are investigated within the pseudospin and spin framework. It is shown that the magnetic flux through the periodic lattice is quantized in units of hc/2e, and in this situation the Hubbard system possesses SO4 symmetry which is proved to be spontaneous breaking in the eigenstates obtained explicitly of the model. The information of ODLRO in those eigenstates is also discussed. The absolute ground state of the Hubbard model is yet obtained, and found that the state may not show superconducting transition.
On the Multispike Structure of a Transmitted Pulse in Monocrystalline Films with Absorption Bistability
Authors: Perelman L. T. , Vitkin E. I.
Published: July 2007

The dynamics of motion of boundaries between strongly and weakly absorbing regions in monocrystalline films with increasing absorption bistability is considered. It is shown that the multispike structure of a transmitted pulse is attributed to the simultaneous influence of the film boundary effects and bleaching of the sample at large exciton concentrations.
Stochastic Resonance under Propagation of Electromagnetic Waves in a Three‐Dimensional Random Medium
Authors: Shermergor T. D. , Dikarev A. V.
Published: July 2007

The Bourret approximation for a many‐component medium, which is homogeneous and isotropic statistically under an exponential coordinate dependence of the permittivity correlation function, is used to calculate the mean Green tensor of the electromagnetic wave equation. The frequency dependence of the wave component amplitudes of the mean Green tensor is calculated numerically. The results of the calculations suggest that a stochastic resonance effect occurs in the frequency band determined by the structure of the medium.
Optical Properties of Zn2CuGaSe4 and Zn2CuGaSe4:Co2+ Single Crystals
Authors: Choe Sung‐Hyu , Yu Ki‐Su , Kim Chang‐Dae , Kim Wha‐Tek
Published: July 2007

Zn2CuGaSe4 and Zn2CuGaSe4 :Co2+ single crystals are grown by the slow cooling method. The optical energy gaps of these single crystals are found to be 1.510 and 1.490 cV at 298 K, respectively. In the Zn2CuGaSe4 :Co2+ single crystals, the impurity optical absorption peaks are attributed to the electronic transitions between the electron energy levels of Co2+ ions sited at the Td symmetry of the Zn2CuGaSe4 host lattice. The crystal field, Racah, and spin—orbit coupling parameters are given as Dq = 425.5, B = 404, and λ = −348 cm−1, respectively.