bluuebunny/crossref_metadata_2025 huggingface dataset:
Anharmonic Phonon Frequency Shifts and Widths in Solid Deuterated Anthracene‐d10
Authors: Jordan J. F. J. , Kalus J. , Schmelzer U. , Eckold G.
Published: July 2007

Coherent inelastic neutron scattering measurements of the temperature dependence of the frequency shifts and widths of some phonons in deuterated solid anthracene are presented. Calculations of the explicit anharmonic phonon frequency shift and the linewidth to the lowest order are described. It is assumed that the intermolecular potential is a pairwise sum of atom‐atom potentials. Using a 6‐exp potential, and potential parameters provided by Williams, the results for all external modes at the T point (q = 0) are calculated and compared with the available experimental data. A part of the anharmonicity of two internal modes is taken into account into the evalutaion. The results from the calculation agree with some of the measurements, but are different by about a factor of two for most of the phonons.
Raman Scattering in Nb–Cu Metallic Multilayers
Authors: Zhang Xing‐Kui , Xia Hua , Hu An
Published: July 2007

Raman scattering by acoustic phonons is investigated in NbCu metallic multilayers grown by magnetron sputtering, with periods ranging from 1.7 to 20.0 nm. For larger‐periodic samples, many peaks which are analogous to those produced by Raman scattering by folded acoustic phonons in periodic superlattices, can be explained by using a perturbation elastic continuum model. On the other hand, in the samples which are layered polycrystals with textures two additional peaks at 158 and 198 cm−1 are observed and attributed to disorder‐activated transverse‐acoustic mode (DATA). The DATA shows an anomalous shift toward lower frequency as a function of film thickness and explains probably anomalies in the Rayleigh wave velocity versus modulated NbCu film thickness.
Investigation of the Transition between Large‐ and Small‐Radius Polarons in a One‐Dimensional Crystal
Authors: Feranchuk I. D. , Fisher S. I. , Komarov L. I.
Published: July 2007

The behaviour of the polaron characteristic in the intermediate range between large‐ and small‐radius approximation is considered for an one‐dimensional crystal. A discontinuous jump of the electron localization size is found. The influence of the lattice potential on the polaron characteristics is investigated.
A Theoretical Study of the FMR Surface Mode Excitation in Metals (Parallel Configuration)
Authors: Fraitová D.
Published: July 2007

Using the analytical FMR theory, the real part of the surface impedance as dependent on the magnetic field and surface anisotropy is calculated for two types of ferromagnetic metals with different exchange‐conductivity parameters. The shapes of the obtained two sets of FMR spectra (including the main and surface resonance modes) differ considerably; the discussion of the cause of this effect points to a pronounced influence of the FMR cross‐over region.
Electron Paramagnetic Resonance Study of the Dynamical Jahn‐Teller Effect on the 3d1 Impurities Ti3+ and V4+ in GaP
Authors: Kreissl J. , Ulrici W. , Gehlhoff W.
Published: July 2007

The EPR spectra of TiGa3+ and VGa4+ in GaP are studied at T = 20, 4.2, and 1.5 K. At 20 K the spectra are isotropic and become angular‐dependent for T ⪅ 4.2 K. By simulation of the spectra measured at T = 1.5 K this angular dependence is explained using the spin‐Hamiltonian for a 2E vibronic ground state arising from a weak‐to‐moderate E ⊗ ϵ dynamical Jahn‐Teller effect including internal random strains.
Electrical and Structural Properties of the Tungsten Bronze Bi4W20O62
Authors: Conan A. , Bonnet A. , Morsli M.
Published: July 2007

Transport coefficient measurements (electrical conductivity and thermoelectric power) are performed on compact bars of a bismuth tungsten bronze compound Bi4W20O62 (labelled as B‐phase) in polycrystalline form over the temperature range 100 to 500 K. Experimental results are discussed in comparison with those obtained recently on a compound, labelled as A‐phase and which is prepared at a lower temperature. A single band model accounts for all the experimental results. The main differences which are observed in the electrical properties of the two phases are a consequence of the less disordered HTB and perovskite intergrowth sequences for the high‐temperature phase.
Quasi‐Classical Trajectory of Thermal Neutrons in Elastically Deformed Crystals
Authors: Lukáš P. , Kulda J.
Published: July 2007

The propagation of thermal neutrons through distorted crystals is reconsidered on the basis of an adiabatic quantum mechanical approach which enables one to derive quasi‐classical trajectories of neutrons for an arbitrary elastic deformation of a crystal. It is shown that the quasi‐classical concept is generally applicable even in the case when interbranch scattering takes place. For demonstration, the treatment is applied to a constant gradient deformation resulting in the well known hyperbolic trajectories of neutrons.
Two‐ and Three‐Body Forces in Lattice Dynamics and Elastic Behaviour of B.C.C. Calcium and Strontium
Authors: Aradhana K. , Rathore R. P. S.
Published: July 2007

The Morse potential is transformed to represent the three body couplings among the common nearest neighbours of the b.c.c. structure. These couplings which add to the present two body potential give rise to an effective potential which is employed to predict the phonon dispersion and second, third, and fourth order elastic constants it b.c.c. forms of calcium (Ca) and strontium (Sr). Recently reported neutron scattering data for these metals support the theoretical content of the model.
Electronic Energy Structure of Substoichiometric Molybdenum Carbides in Different Crystallographic Modifications
Authors: Bazhin I. V. , Kolpachev A. B. , Nikiforov I. Ya.
Published: July 2007

In terms of the multiple scattering theory using the crystalline muffin‐tin potential and taking into account the local distortion of the lattice the electronic structure of stoichiometric and nonstoichiometric molybdenum carbides MoC1−x for x = 0, 0.17, and 0.33 in cubic NaCl and hexagonal WC crystal structures is calculated. As the concentration of the carbon vacancies increases “atomization” of 2p states of carbon and growth of the Mo–Mo interaction take place. At the same time a new maximum of the electron density of states (DOS) appears at the carbon vacancies and in the metal d‐band near the Fermi level in cubic carbides. The Mo–Mo interaction is more important in the formation of DOS near the Fermi level of hexagonal carbides than in cubic ones. The DOS at the Fermi level depends essentially on the concentration of the carbon vacancies.
Aggregation of Bismuth in NaCl Crystals
Authors: Stoicescu Gh. , Nistor S. V. , Mateescu C. D.
Published: July 2007

The aggregation of Bi3+—vacancy dipoles in NaCl single crystals grown in a reactive atmosphere is studied by monitoring the changes in the intensity of the C‐band attributed to Bi3+ ions. An apparent third‐order reaction is observed to govern the aggregation process in the early stages, with an activation energy of 0.79 eV. No ESR signals attributed to Bi2+ centres are observed before or after X‐irradiation at 77 or 300 K.
Plasma Oscillations at the Surface of a Type II Superlattice
Authors: Sy H. K.
Published: July 2007

Semi‐infinite type II semiconductor multilayers are investigated consisting of alternating layers of two‐dimensional electron and hole carriers. By applying electromagnetic boundary conditions, a dispersion relation is derived for surface plasma modes. This is shown to be equivalent to that obtained recently starting from electrostatic image charges. Some numerical results are also discussed.
Transverse Transport in n+GaAs/AlxGa1−xAs/n−GaAs Structures
Authors: Asche M. , Friedland K. , Kostial H. , Eaves L. , Sarbey O. G.
Published: July 2007

The dc current–voltage characteristics and the real and imaginary parts of the differential conductivity of a single barrier heterostructure based on n+GaAs/AlxGa1−xAs/n−GaAs are investigated. The temperature dependence of the modulated structure related to the emission of longitudinal optical phonons is measured in the region from 1.3 to 90 K and compared with microscopic models proposed to describe it. A detailed examination of the capacitance indicates the presence of an appreciable negative charge in the barrier or at its interface, but then the current and its temperature dependence can only by explained when additionally the presence of conducting channels in the barrier is assumed.
Supertransferred Hyperfine Fields at Nuclei of Diamagnetic Copper Ions in Chalcogenide Spinels Fe1−xCuxCr2S4
Authors: Fishman A. Ya. , Mitrofanov V. Ya. , Kovtun N. M. , Prokopenko V. K. , Shemyakov A. A.
Published: July 2007

The NMR method is applied to study the local fields at diamagnetic Cu+ ion nuclei in the magnetically ordered F1−xCuxCr2S4 (0 ≦ x ≦ 0.8) system. Additional transferred hyperfine fields are revealed at the Cu+ ion which are connected with orbital (pseudospin) moments of Fe2+ ions. The obtained results are interpreted qualitatively.
Magnetic Properties of Model Multicomponent Compounds of CsCl Structure
Authors: Adamian V. E. , Artsruni A. A. , Benaissa A. , Kocharian A. N. , Melikian M. A. , Toneian A. G.
Published: July 2007

The solid solutions of CsCl type structure with controllable parameters (concentration of magnetic ions, number of conduction electrons per unit cell, and lattice parameter) are synthesized. In the systems investigated either one of the parameters is changed or all the three parameters are retained constant at different alloy compositions. X‐ray phase analysis is carried out and the magnetic properties of the alloys are investigated. The results are discussed in the approximation of the RKKY theory.
Microscopic Model of Metastable Changes in Hydrogenated Amorphous Silicon
Authors: Chen Y. F. , Wong C. K.
Published: July 2007

Concepts based on the two‐level system of structural excitations have not accounted satisfactorily for many metastable changes in hydrogenated amorphous silicon. Defects created at higher temperatures are more difficult to anneal out. Photoluminescence decreases much more after irradiation at 77 K than it does after irradiation at 300 K. After rapid cooling from 483 K, the spin signal grows with time at room temperature, etc. A microscopic explanation of these and other phenomena is given in terms of a three‐level system of structural excitations: initial state, weak SiSi bond; intermediate metastable state, SiHSi bond; final metastable state, SiH and Si dangling bond.
Eu2+‐Mn2+ Energy Transfer in NaCl and KCl Crystals
Authors: Cywiński R. , Mügeński E. , Sokólska I.
Published: July 2007

It is shown that excitation energy transfer in doubly doped (Eu2+‐donor, Mn2+‐acceptor) KCl and NaCl crystals proceeds due to the presence of various aggregation products containing both dopant ions. In simple aggregates composed of Eu2+–cation‐vacancy and Mn2+–cation‐vacancy dipoles a single stage energy transfer Eu2+‐Mn2+ is proposed due to the multipole interaction (most probably of dipole–quadrupole type) or due to exchange interaction. In the case of Eu2+‐rich precipitates with built‐in Mn2+ ions, the energy transfer, after preceded energy diffusion in the donor system, is determined by the contribution of the phonons (phonon absorption in NaCl and phonon emission in KCl) and exchange interactions.
Amplification of Acoustic Waves in Magnetised High Resistivity Piezoelectric Semiconductors. Effect of Nonuniform Electric Field Intensity and Carrier Concentration
Authors: Dey (Bose) M. , Ghosh S.
Published: July 2007

A theory of the amplification of an acoustic wave in a high resistivity piezoelectric semiconductor in the presence of a longitudinal dc electric field and a transverse magnetostatic field is developed. The static electric field intensity and the carrier concentration inside the semiconductor are taken as nonuniform even in trap‐free samples. This assumption used in the theory modifies the results obtained by the earlier theories considerably. It is also shown that this nonuniformity can explain the experimentally found asymmetric attenuation characteristic curves. Numerical estimations are made for n‐CdS at 300 K. It is found that a weak magnetic field does not have any remarkable effect on amplification, but a higher magnetic field sharply reduces the gain.
Energy Transfer of Electron Excitation. Decay Kinetics of Exciton Luminescence in a Three‐Layer System
Authors: Pokutnyi S. I.
Published: July 2007

The decay kinetics of exciton luminescence in impurity molecules in a three‐layer system near the interface of dielectric media in the presence of energy transfer of electron excitation is considered. It is shown that a change in the functional dependence of the probability of Förster energy transfer leads to new characteristic dependences in the decay kinetics of impurity luminescence in layered structures.
Critical Behaviour of Semiconductor Spin Glasses (CuCr2Se4)x (Cu0.5Me0.5Cr2Se4)1−x (Me = In, Ga; 0 ≦ x < 0.1)
Authors: Koroleva L. I. , Virovets T. V.
Published: July 2007

Magnetic susceptibility behaviour is studied in weak dc and ac magnetic fields in the spin glass–paramagnetism transition region of the system (CuCr2Se4)x (Cu0.5Me0.5Cr2Se4)1−x (Me = In, Ga). The critical exponents γ, δ, and β in the spin glasses with x = 0,0.01 and 0.03 (Me = In) determined from the nonlinear static susceptibility χnl in the region of the freezing temperature T′f are in close agreement with values predicted by the mean field theory, Tf being determined by the maximum value of χnl. The experimental points χnl satisfactorily fit the scaling function in the critical range H < 30 Oe and (T − Tf)/Tf < 0.4. The freezing temperature T′f of spin glasses with 0 < x < 0.05 (Me = In, Ga), determined from the maximum initial susceptibility in the ac field depends on the measurement frequency according to the Vogel‐Fulcher law. The constant T0 in this law is close to Tf. The fact that static scaling relation and the Vogel‐Fulcher law hold for T′f indicates that spin glass–paramagnetism phase transition occurs in the spin glasses concerned.
Calculation of Self‐Interstitial Formation Energy (Both Split and Non‐Split) in Noble Metals
Authors: Bandyopadhyay A. K. , Sen S. K.
Published: July 2007

The energy of formation of different interstitial configurations in f.c.c. metals using pseudopotential approach is formulated. A model calculation is done with a Ashcroft‐Hubbard model potential for copper, silver, and gold. The calculation is indicates that the (100) split configuration is most stable and has a minimum energy which is consistent with other theoretical predictions and experimental observations.
Global Wave Mode Theory for the Formation of Dendritic Structure on a Growing Needle Crystal
Authors: Xu Jian‐Jun
Published: July 2007

An investigation is made of the global instability mechanisms of dendritic crystal growth. In previous papers a global instability mechanism is explored which is called WEASR‐mechanism and the related global WEASR‐modes are derived. In this paper, another global instability mechanism is shown and its related global mode solution is derived, called global trapped wave (GTW)‐ mode. The quantum condition is obtained. A self‐sustaining GTW‐mode is found. This wave mode theory well explains the origin and persistence of the micro‐structure in dendritic growth.
Surface Relief and Dissipation Influence on Plasmon–Phonon Polariton Dispersion of Polar Semiconductors
Authors: Dmitruk N. L. , Fidrya N. A. , Snitko O. V. , Venger E. F.
Published: July 2007

The effect of the surface roughness by plasmon‐phonon attenuation on the surface mixed polariton (SP) dispersion is theoretically investigated. It is shown that the dispersions curve displacement is a nonmonotonous function of the attenuation in the presence of surface roughness. Epitaxial n–n+ GaAs layers are investigated experimentally by the ATR method.
On the Mechanism of Two‐Photon Absorption by Nd3+ Ions in Yttrium Aluminium Garnet and Yttrium Lithium Fluoride in the Region of 1.06 μm
Authors: Makhanek A. G.
Published: July 2007

A calculation is made of two‐photon absorption (TPA) cross‐sections by Nd3+ ions in YAG and YLF crystals in the region of 1.06 μm. It is shown that the experimental results are in good agreement with the general theory taking into account the TPA polarization characteristics and effects (for YAG‐crystals) of surrounding ligands on the TPA process. It is found that the lowest Stark component of the Nd3+ ground term in YLF does not correspond to the symmetry type earlier proposed and a new identification is given.
Theory of the Single Ion Magnetocrystalline Anisotropy of 3d Ions
Authors: Xu You , Yang Gui‐Ling , Chu Da‐Ping , Zhai Hong‐Ru
Published: July 2007

Methods for calculating the single ion magnetocrystalline anisotropy of 3d ions in the crystal field with threefold axis or higher symmetry and lower symmetry are given. Using these methods, the contributions of Fe3+ ions at all the five crystal sites of Ba‐ferrite (BaM) to the magnetocrystalline anisotropy constants and their temperature dependence are calculated. Also calculated is the single ion anisotropy of the Co2+ ion substituting the Fe3+ ion at the 12k site. The results agree well with experiments.
Phase Transition in Rb3H(SeO4)2‐Type Crystals. I. The Symmetry Analysis of Proton Ordering
Authors: Salejda W. , Dzhavadov N. A.
Published: July 2007

Proton ordering is analysed at the phase transition in superionic crystals of the type Rb3H(SeO4)2. The method of concentration waves is applied. The observed ordering of protons is described using basis functions of the irreducible representations of the groups of wave vectors at the L and Γ points of the Brillouin zone. Possible directions of the crystallographic axes of the low‐temperature phase are determined in the framework of the approach proposed. The jump of entropy is calculated. The results obtained are in good agreement with experiment.
The Electronic Structure of the Alkaline‐Earth Oxides. I. The Differences between MgO and LiF, NaF Electronic Structures
Authors: Lobatch V. A. , Kulyabin B. E. , Zhukov V. P. , Medvedeva N. I.
Published: July 2007

The energy band structures of MgO, LiF, and NaF are calculated by the LMTO method with a set of different atomic spheres radii. It is shown that MgO is distinct from fluorides in that a pure ionic charge distribution is not achieved. Such a behaviour of the electron density is explained by the presence of a potential barier inside the oxygen atomic sphere near its boundary. As a consequence the charge configuration of MgO is suggested to be close to Mg2+O− plus one electron distributed in the interionic region.
Compton Profile Anisotropies of GaAs
Authors: Panda B. K. , Mahapatra D. P. , Padhi H. C.
Published: July 2007

Directional Compton profiles along the [100] and [111] directions of GaAs are measured using 59.54 keV γ‐rays from a 3 Ci241 Am annular source. A pseudo‐potential calculation is performed to calculate the Compton profile and autocorrelation anisotropies. Inclusion of a non‐local term in the pseudopotential appears to give better agreement with experimental result. The calculated period of the oscillatory anisotropy tends to be shorter than that experimentally observed. The experimental autocorrelation anisotropy has a small peak near the origin which is not accounted for by the theory.
Electronic Structure of F‐Centers in LiH by the SCF Xα Method
Authors: Takeuchi T.
Published: July 2007

The electronic structure of F‐centers in LiH is obtained by SCF Xα method. The F‐center transition energy is found to be 4.76 eV. Differences between the electronic structure of F‐centers in ionic oxides and that in LiH are discussed.
Optical Absorption near Excitonic Resonance of MOCVD‐Grown ZnSe Single Crystals
Authors: Gribkovskii V. P. , Zimin L. G. , Gaponenko S. V. , Malinovskii I. E. , Kuznetsov P. I. , Yakushcheva G. G.
Published: July 2007

The exciton and band‐to‐band absorption spectra of monocrystalline ZnSe films produced by MOCVD‐technique on GaAs substrates are studied in the temperature interval 80 to 300 K by laser spectroscopy technique. Violation of the Bouguer law and the temperature dependence of the integral absorption coefficient in the region of the excitonic band are revealed. The distinctive features of the transmission spectra near the excitonic resonance are interpreted in terms of the polaritonic approach to light propagation in crystals.
On the Possibility of Describing Lattice Properties of Iridium in Terms of Pseudopotential Theory
Authors: Greenberg B. A. , Katsnelson M. I. , Koreshkov V. G. , Osetskii Yu. N. , Peschanskikh G. V. , Trefilov A. V. , Shamanaev Yu. F. , Yakovenkova L. I.
Published: July 2007

The possibility is discussed of describing lattice properties of iridium in terms of pseudopotential perturbation theory with allowance for second and third order. Values of pseudopotential parameters are proposed which provide a good description of the lattice properties of iridium under zero pressure, the contributions of the three‐ion forces being small. The total energy, pressure, elastic moduli, Debye temperature, low‐temperature Grüneisen parameter, pairwise potentials, and also effective solid sphere packing parameters are calculated. In addition, by invoking molecular dynamic methods, the vacancy formation and migration energies and the stacking fault energies are computed. The electron energy spectrum and group velocity calculations suggest that the electron density of states curve of Ir exhibits no van Hove singularities near the Fermi level, a fact which apparently accounts for the successful description of lattice properties in terms of the pseudopotential perturbation theory.
Two‐Band Envelope Function Model for Graded Interfaces
Authors: Rodríguez‐Coppola H. , Martínez‐Cuellar J. L. , Pérez‐Álvarez R.
Published: July 2007

An analytical calculation is given of the energy minibands of a superlattice with graded interfaces and the sawtooth superlattice applying a simple two band model to describe electrons in coduction band and light holes, and a single band equation for heavey holes with good agreement with calculations reported before. The effective energy gap in the superlattice with graded layers as a function of the thickness of the graded interfaces shows a different behavior than reported before for small superlattice period. It is shown that with simple enough envelope function models such composite graded systems can be treated with good results.
Photoluminescence of a Dense Quasi‐2D Electron‐Hole System in a Modulation‐Doped Heterostructure with Strained InGaAs QW
Authors: Butov L. V. , Kulakovskii V. D. , Andersson T. G.
Published: July 2007

The photoluminescence of dense homogeneous quasi‐2D electron‐hole (e‐h) system in the strained InGaAs QW is investigated for the modulation‐doped n‐AlGaAs‐InGaAs‐GaAs heterostructure under excitation density up to 105 W/cm2 and magnetic field H ≦ 8.3 T. The many body effects are found to become well pronounced in the emission spectra when the concentration of the photoexcited e‐h pairs exceeds the electronic density due to modulation doping (1012 cm−3). There are found and investigated i) the band gap renormalization, ii) the effective mass renormalization, and iii) the change of the damping of one‐particle states in the dense e‐h system.
Multistability of Absorption Domains in Bulk CdS Due to Band Edge Nonlinearities
Authors: Stadnik V. A.
Published: July 2007

The domain instability phenomenon in semiconductors of CdS are investigated. Multistability of high absorption states is explained by features of the nonlinear behaviour of the absorption coefficient and the longitudinal transport of photoexcitations. It is shown that for the explanation of the observed effects besides the thermal mechanism of the nonlinearity the process of the saturation of the excitonic absorption should be taken into account.
Quantum Confined DC Stark Effect in Microcrystallites
Authors: Rossmann H. , Schülzgen A. , Henneberger F. , Müller M.
Published: July 2007

This paper reports on the electric field induced absorption change in the situation of zero‐dimensional quantum confinement. We have studied CdS microcrystallites embedded in glass by a sensitive modulation spectroscopy technique at room temperature. We observe a two‐line spectrum and a quadratic dependence on the applied field. This absorption change is related to the Stark shift of the lowest electron‐hole pair state of the quantum dot.
Excitonic Optical Nonlinearity in II‐VI MOCVD‐Grown Crystals
Authors: Zimin L. G. , Gaponenko S. V. , Malinovskii I. E. , Lebed V. Yu. , Kuznetsov P. I. , Yakushcheva G. G. , Kuznetsov A. V.
Published: July 2007

Using the method of single‐ and two‐beam laser spectroscopy, the nonlinear optical properties of high‐quality MOCVD‐grown ZnSe and CdSe samples are studied. At nitrogen temperatures the dominating mechanism of absorption nonlinearity is the plasma screening of excitons. Along with this, in the nonlinear response of ZnSe crystals the exciton‐exciton interaction causing band broadening takes place. At room temperatures, in CdSe a strong dependence is revealed of absorption spectrum deformation on the exciting radiation quanta energy which is associated with slowing down of electron‐hole plasma cooling.
The Concept of Production Bias and Its Possible Role in Defect Accumulation under Cascade Damage Conditions
Authors: Woo C. H. , Singh B. N.
Published: July 2007

In the study of microstructural evolution and macroscopic property changes due to radiation damage, the point defects are usually modelled as being produced continuously in time and uniformly in space. Furthermore, the excess of vacancies required to sustain the void growth is assumed to arise entirely due to the preferential trapping of interstitial atoms at dislocations. It is shown that this approach may not be appropriate for cascade damage conditions where both vacancies and interstitials are produced in a highly localized and segregated fashion. A model is presented which takes into account the effects of both, vacancy and interstitial clustering in the cascade zones on the defect accumulation rate (e. g. swelling rate) under cascade damage conditions. The consideration of interstitial clustering in the cascade yields a production bias which is found to be a potent driving force for void swelling in addition to the one provided by the dislocation bias.
Adsorption of H2O (Molecular and Dissociative) on Si(100) and Si(111) Surfaces Considered by an Empirical Pair Potential Method
Authors: Engler C.
Published: July 2007

The adsorption of H2O on Si(100) and Si(111) surfaces is examined by an empirical method, which connects pair potential considerations with the BEBO‐concept. For both surfaces, only small energetic differences between molecular SiH2O and dissociative SiH and SiOH species are obtained, which lie within the margin of error of the method. For the dissociation process of adsorbed H2O‐molecules on Si(100)−(2 × 1), the course of the total energy along a possible reaction path is discussed.
Scattering of Two‐Dimensional Electron Gas on the Semibounded Three‐Dimensional Electron Gas
Authors: Boiko I. I. , Sirenko Yu. M.
Published: July 2007

From first principles, basing on the averaging of the equation for exact fluctuating distribution functions, the classical kinetic equation is derived for a two‐dimensional electron gas (2DEG), interacting with a random potential of an external system. Using the approximation of a Fermi function with a shifted argument for the 2DEG distribution function the frequencies of energy and momentum relaxation are obtained. In the case of equilibrium external system the frequencies are expressed in terms of the dielectric functions of the 2DEG and external system. Energy and momentum relaxation frequencies of 2DEG, scattered on the three‐dimensional electron gas, are calculated.
Positron Band Structures of GaAs and CdTe
Authors: Aourag H. , Khelifa B. , Belaidi A. , Tadjer A. , Rezki M. , Gamoudi M.
Published: July 2007

The problem of positron band structure in aperiodic lattice is similar to its electron counterpart. GaAs and CdTe positron band structures are calculated a comparison between the electron and positron energies is discussed.
Calculation of Local‐Field Correction in the Two‐Dimensional Electron Gas
Authors: Tanatar B.
Published: July 2007

The frequency independent local‐field correction factor G(k) is calculated for the two‐dimensional electron gas. The method is based on decoupling and solving the equations of motion for the charge‐density operator by a moment‐conserving scheme. The expression obtained for G(k) is evaluated by a Monte Carlo integration. The results for G(k) and the static dielectric function ε(k) are tabulated.
Foundations of the Quasi‐One‐Dimensional Bisoliton Model of Superconductivity of Ceramic Oxides
Authors: Davydov A. S.
Published: July 2007

It is shown that in the plane square lattice the most stable self‐localized states are of quasi‐one‐dimensional character. This may serve to substantiate the applicability of a quasi‐one‐dimensional bisoliton model of high‐temperature superconductors containing square plane layers of alternating copper and oxygen ions.
On Mössbauer Spectrum Analysis for Spin Orientation in Fe2As
Authors: Kulshreshtha S. K.
Published: July 2007

The reports of the analysis of 57Fe Mössbauer spectra of Fe2As and the derived spin orientation are inconsistent. To understand the reasons for this inconsistency, the spectra are recorded at various temperatures between 4.2 and 375 K and least squares fitted by solving the complete nuclear hyperfine Hamiltonian matrix using different sets of fitting parameters. The trade off in the fitting of the spectra corresponding to the two iron sites is responsible for this inconsistency. The incorporation of magnetically induced asymmetry parameter in the fitting procedure as suggested in a recent study, did not produce consistent results at all temperatures. The possible reasons for the reported discrepancies are discussed.
A Study of the Disorder in Heavily Doped Ba1–xLaxF2+x by Raman Scattering
Authors: Kolesík M. , Tunega D. , Sobolev B. P.
Published: July 2007

The Raman spectra of the Ba1–xLaxF2+x solid solutions (0.005 ≦ x ≦ 0.31) are presented. The low‐frequency scattering is studied in some detail. The spectra indicate that no large clusters are present in solid solutions studied. A cross‐over which can be interpreted in terms of the fracton model is observed.
Modification of the INDO Calculation Scheme and Parametrization for Ionic Crystals
Authors: Stefanovich E. , Shidlovskaya E. , Shluger A. , Zakharov M.
Published: July 2007

A new parametrization of the semiempirical quantum‐chemical INDO method is proposed for the study of the electronic structure of a wide class of perfect and defective ionic insulating crystals. The applicability of the “cut‐off function” concept for the calculations of exchange interactions in the large unit cell (LUC) model is also briefly discussed. Both, the proposed calculation scheme and the parametrization are tested on a number of molecules, ionic crystals (LiH, LiF, LiCl, KCl, MgO, K2SO4), and (100) crystal surfaces of LiF, KCl, MgO.
Point Defects in Electron‐Irradiated Stoichiometric Magnetite
Authors: Walz F. , Kronmüller H.
Published: July 2007

High‐purity, stoichiometric, single crystalline magnetite (Fe3O4) has been electron (e−)‐irradiated below 45 K to a dose of 1023 electrons/m2. Radiation‐induced point defects give rise to both drastic modifications of intrinsic electronic processes and the occurrence of reorientation‐type magnetic relaxations. Both phenomena offer deeper insights into the mechanisms of (i) electronic charge transport and (ii) thermally activated reactions of interstitials and vacancies. Coordination between migration of elementary defects and corresponding anncaling stages can be established in Fe3O4 with higher precision than in any other magnetic system investigated so far.
Computer Simulation on the Threefold Coordinated Oxygen Atom in Vitreous Silicon Dioxide
Authors: Dianov E. M. , Egibyan A. V. , Akopyan S. A. , Rustamyan A. É. , Sokolov V. O. , Sulimov V. B.
Published: July 2007

Dissociation of SiO bonds in vitreous silicon dioxide is proved to yield threefold coordinated oxygen atoms with three silicon atoms or one oxygen and two silicon atoms being the nearest neighbours. Electronic spectra, wave functions, and transition probabilities are investigated for three charge states of both the defects by the semiempirical LCAO MO method MINDO/3 in a cluster approach.
The Model of Rotation of the NO Impurity Molecule in KCl Crystal
Authors: Sild O.
Published: July 2007

As a result of an analysis of the data on Raman scattering and polarized luminescence of the NO impurity molecule in KCl crystal, the model of one‐dimensional rotation of the NO molecule around the crystal axis of three‐fold symmetry is verified.
Strength and Stability of Silver
Authors: Singh G.
Published: July 2007

Semiquantitative calculations are made of the theoretical strength and range of stability of a perfect uniaxially stressed crystal of silver by using a pseudopotential. The rigorously estimated total binding energy of the metal consists of kinetic, exchange, and correlation parts along with ion‐ion and electron‐ion interactions. The computed value of tensile strength is 1.01 × 109 N/m2 with a corresponding strain of 2.72%. These values are fairly close to 1.7 × 109 N/m2 tensile strength and about 3% strain observed experimentally for silver whiskers.
On the Effect of Three‐Body Interactions and Proximity of the Fermi Level to the Brillouin Zone Faces on Elastic Modules of Simple Metals
Authors: Fomichev S. V. , Katsnelson M. I. , Koreshkov V. G. , Trefilov A. V.
Published: July 2007

A discussion is made in the model of the local pseudo‐potential V(q) ≡ Vq on effects going beyond the scope of the second‐order terms of the Vq perturbation theory for describing the static properties of simple metals. It is shown that the allowance for third order in Vq hardly improves the description of static properties (energy, pressure, elastic modules, etc.), being nevertheless apparently essential for Ba and Al. The effect of non‐sphericity of the Fermi surface ignored in the third order in Vq is discussed in the two‐wave approximation. The ranges of parameters in which the simple perturbation theory in Vq is not adequate are found for the b.c.c., f.c.c., and h.c.p. structures of simple metals alloys in the rigid‐band approximation.
Reflectivity and Photoreflectivity in Superlattices and Quantum Wells
Authors: Ivchenko E. L. , Kochereshko V. P. , Uraltsev I. N. , Yakovlev D. R.
Published: July 2007

Oblique‐incidence reflectance and photoreflectance of heterostructures near the resonance frequencies of excitons confined in a single quantum well are studied. Under illumination with above barrier band gap light at low temperature, the relative change ΔR/R of the reflectivity is found to reach 10% and even more. The experimental results can be explained by a photo‐induced decrease in the exciton damping and attributed to neutralization of the barrier impurity centres under the illumination.
Experimental and Theoretical Study of Heavy Ion Irradiation Processes in Polymer Materials
Authors: Danziger M. , Andrassy G.
Published: July 2007

Due to the fact that the anomalous behaviour of most different physical characteristics in vitreous solids compared with crystalline solids can be described by the action of a system of additional low‐energy excitations, the application of this model to processes in polymer films irradiated with heavy ions, is studied. The irradiated polymer films were etched with simultaneous electrical conductivity measurements. It is shown that the dependence of the radial etching rate on the distance from the trajectory of the heavy ion up to a determined radius can be described by the response function developed from the model of low‐energy excitations.
The Effect of Quantum Screening on the Energy Loss Rates of Hot Electrons in n‐Hg0.8Cd0.2Te in the Extreme Quantum Limit at Low Temperatures
Authors: Bhowmik S. , Sarkar C. K. , Santra K.
Published: July 2007

A theoretical model is proposed to calculate the energy loss rates of hot electrons in semiconductors in high magnetic fields at low temperatures. The energy loss due to the acoustic phonon scattering via deformation potential and piezoelectric coupling is considered for lowest Landau level occupancy, i.e. the extreme quantum limit. The model includes the effect of the modified free carrier screening due to Landau quantisation, on the acoustic phonon scattering, assumed to be the dominant loss mechanisms. The band nonparabolicity, the non‐equipartition of acoustic phonons, and the Landau level broadening due to electron‐impurity interactions are also included. The model is used to interpret the experimental results obtained from the specific heat measurements in n‐Hg0.8Cd0.2Te at 1.5 K. The theoretical values of the energy loss rate are found to be larger compared to the experimental values. The inclusion of quantum effects on the free carrier screening overestimates the theoretical energy loss rates.
Impact Ionization of Free and Bound Excitons by Free Carriers in an Electric Field in CdS. Investigation by Optical Methods
Authors: Jakobson M. A. , Kagan V. D. , Katilius R. , Müller G. O.
Published: July 2007

Quenching of the exciton luminescence of cadmium sulfide at 1.8 K in a static electric field is observed and attributed to impact ionization of free excitons and delocalization of bound excitons by hot electrons. A continuous transition from the T ownsend‐Shockley to the Davydov‐Wolf law is observed when the field is increased to 1 kV/cm. A theoretical analysis of the results on the quenching of luminescence lines of bound excitons makes it possible to identify the mechanisms of relaxation of high‐energy electrons dominating in CdS at low temperatures. It turned out that these electrons lose their quasi‐momentum by spontaneous emission of piezo‐phonons in “pure” samples and are scattered by impurities in “less pure” samples. The mean free path of 4 meV electrons in moderate fields is 10−4 cm in the “pure” samples and 5 × 10−6 cm in the remaining samples.
Synchrotron Radiation, Radiative Losses, and Polarization Effects for Relativistic Beams in Bent Crystal
Authors: Arutyunov V. A. , Kudryashov N. A. , Mishin O. A. , Samsonov V. M. , Strikhanov M. N. , Sytsko Yu. A.
Published: July 2007

Expressions for the intensity of specific radiation accompanying the deflection of high‐energy particles by a bent crystal are presented. It is shown that when R → ∞ (R is the bending radius) the corresponding formulas are transformed into those for channeling radiation in an unbent (straight) crystal. Dipole, synchrotron‐like radiation, and polarization effects are analysed. Numerical calculations of the radiation and polarization in the bent planes using a realistic potential are made for beams with different parameters.
The Size‐Quantized States of the Wannier‐Mott Exciton in Structures with Superthin Films of CdTe
Authors: Pokatilov E. P. , Beril S. I. , Fomin V. M. , Kalinovskii V. V.
Published: July 2007

The results of experimental investigations of excitonic spectra of the CdTe superthin films on MgFe2 are theoretically discussed. The significance of different terms in the experimentally measured quantity — the energy of a photon which generates an exciton — is analysed. The theory is in good quantitative and qualitative agreement with experiments.
A Model Theory of Structural and Superconducting Phase Transitions in Chain‐Like Systems
Authors: Kiselev A. A. , Liaptsev A. V.
Published: July 2007

A model Hamiltonian for the study of non‐adiabatic effects caused by orbital degeneracy of electronic states in conducting systems is obtainded basing on the dynamics of a quasi‐one‐dimensional chain of tri‐atomic linear molecules, each in the ground electronic ∏‐state. The Renner‐type electron‐phonon interaction which arises in such systems, differs essentially from Fröhlich's one: it is non‐diagonal with respect to the electronic quantum numbers and quadratic in the phonon operators. This interaction is shown to induce structural and superconducting phase transitions, the structural one lowers the symmetry of the charge density and cause the enlarging of the gap in the electronic spectrum. An example of the Renner‐type interaction in the high‐Tc superconductor is given.
Systematization of Binary Intermetallic Compounds
Authors: Walzer U.
Published: July 2007

Norm‐conserving pseudopotentials derived from the Dirac equation serve for the derivation of new characteristic quantities. For each chemical element and each electron shell, two characteristic energy and two characteristic spacing quantities are calculated. Therefrom, functions are formed for binary compounds and alloys of type AB. If two each of these functions are plotted in pairs, an arrangement is obtained according to regions with crystals of the same structure type and same space group, of the same melting temperature class etc. This systematics enables one to eliminate unfavourable combinations in the search for specific physical properties. A few results are plotted.
A Green's Function Estimation of Lattice Relaxation for Isovalent Substitutional Defects in Alkali Halide Crystals over the Entire Composition Range
Authors: Roy (Paul) S. Datta , Sengupta S.
Published: July 2007

A Green's function calculation is presented for dilute concentration isovalent substitutional defects in alkali halides. A simple model is suggested to extend this calculation to the high concentration range. Comparing the values of lattice relaxation obtained from this estimation to EXAFS measurement, a very good agreement is noticed over the entire composition range.
Anisotropic Diffusion of Point Defects to Spheroidal Cavities
Authors: Grande N. Smetniansky‐De , Tomé C. N. , Passianot R.
Published: July 2007

The problem of point defects diffusing anisotropically towards spheroidal sinks is solved using an analytical treatment. Depending on the ratios between the sink semi‐axes (a0, b0) and the diffusivity main components (D⟂, Dz), two different situations are solved separately: the prolate and the oblate cases. For each case two boundary conditions are considered: a) periodic sink distribution and b) a constant boundary concentration condition. The results of this study allow to derive qualitative conclusions with respect to the influence of the diffusion anisotropy, the boundary conditions, and the cavity shape on the point defect concentration profiles around spheroidal sinks. In a coming paper these results are applied to study the diffusion of irradiation produced point defects towards cavities and to calculate defect bias and cavity sink strength.
EPR Parameters and Spectral Fine Structure of Ni2+ in LiNbO3
Authors: Zhou Kang‐Wei , Zhao Sang‐Bo , Wu Ping‐Feng , Xie Jun‐Kai
Published: July 2007

By means of the eigenvalues and eigenvectors of the complete energy matrix of the C (d8) ion and the spin Hamiltonian theory, the Spectral fine structure, the EPR parameters (D, g) and the ground state Zeeman splitting of Ni2+ in LiNbO3 are calculated in a unified scheme for the first time. The results agree well with the findings, thus the optical and paramagnetic properties of LiNbO3:Ni2+ are uniformly explained. The theoretical methods, including the g formulae, are suitable for any C (d8,2) ion.
Nonlinear Oscillations and Chaos in CdS Single Crystals under Temperature‐Electric Instability Conditions
Authors: Golik L. L. , Gutman M. M. , Pakseev V. E.
Published: July 2007

Low‐frequency chaotic and complex regular oscillations of photocurrent and temperature in CdS single crystals occurring at constant applied voltage and illumination are investigated. Routes from periodicity to chaos are studied. Explanation of the complex behaviour is presented on base of a rate‐equation model of temperature‐electric instability in semiconductors with two types of electron trap levels. Numerical results of computer calculations of the model are in agreement with the experimental results.
On Functional Integral Representations Satisfying the Constraints in the Correlation Models of High‐Temperature Superconductors
Authors: Weller W.
Published: July 2007

Functional integral representations are constructed for Fermions with spin 1/2, in which the fields satisfy directly by construction the constraints (e.g., exclusion of double occupancy of a site) appearing in recent models in the theory of high‐temperature superconductivity. Thus, the enforcement of the constraints by delta functions in the integration measure is avoided. Perelomov's concept of generalized coherent states is used. However, in constructing such representations, exponential functions of linear combinations of operators (which are difficult to disentangle) are avoided, as is the construction and reduction of the invariant measure. Instead, an ansatz is used for the resolution of the unity operator. This approach also provides more freedom in choosing the appropriate fields. Several new and simple representations with only few elementary fields are given. The representation already used by Wiegmann is recovered. In this case and in any other cases the integration measure is explicitly given. In all these representations, the original Fermi operators are substituted by the product of a spin independent Graßmann field and a spin dependent bosonic (complex) field in accordance with the physical idea of separation of charge and spin degrees of freedom. It is further shown how a change in the integration measure eliminates also zero occupancy (the case of the Heisenberg antiferromagnet). The absence of an explicit delta function constraint in the functional integral is reflected in a special form of the kinetic part of the action. The considered representations are compared with that of the slave boson method.
The Temperature Dependence of the Optical Second Harmonic Generation Coefficientd11of Quartz Homeotypic AlPO4(Berlinite)
Authors: Defregger S. , Engel G. F. , Krempl P. W.
Published: July 2007

The nonlinear optical properties of quartz homeotypic AlPO4(Berlinite) are studied. The second harmonic generation (SHG) coefficientd11is determined experimentally in the range from 296 to 783 K (the upper temperature limit is due to precipitation effects). At higher temperaturesd11decreases (approximately 35% decrease at 783 K). The order parameter associated with the α–β transition (at about 860 K) and derived from the measured temperature dependence ofd11agrees well with the corresponding results derived from previous birefringence measurements. Theoretical calculations using Levines bond charge model are also made at various temperatures up to the α–β phase transition. The strong decrease of the calculatedd11to values near zero about 25 K below the α–β transition is discussed in terms of the mean rotation angles of the AlO4and PO4tetrahedra as deduced from literature X‐ray data.
The Energy of Constrictions in Extended Dislocations
Authors: Püschl W.
Published: July 2007

The shape and energy of screw dislocation constrictions is calculated numerically according to the principles of linear, anisotropic elasticity theory, in contrast to previous treatments which did not correctly take into account all interaction energies. The energy of the whole constriction configuration can be conveniently written as the energy of two isolated half‐constrictions plus the energy of the completely compressed straight piece between them. Suitably normalized, the half‐constriction energy does not depend very strongly on specific material properties. In first approximation, it can be calculated by a simple rule, provided extension width or stacking fault energy are known.
Investigation of the Thermodynamic Properties of Anharmonic Crystals by the Momentum Method. III. Thermodynamic Properties of the Crystals at Various Pressures
Authors: Tang Nguyen , Van Hung Vu
Published: July 2007

By the momentum method established in the preceding papers the thermodynamic properties of strongly anharmonic crystals are considered with face‐centred cubic structure being under action of pressure. In the application properties as the thermal expansion coefficient, the specific heats cv and cp etc. at various pressures are calculated numerically for the inert gas solids and compared with experimental data.