bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Electron–Magnon Interaction on Electronic and Magnetic Properties of Ferromagnetic 4f Systems
Authors: Nolting V. , Nolting W.
Published: July 2007

A fully selfconsistent approach is proposed to the s‐f model of a ferromagnetic 4f‐system. A Green's function method is used for studying the mutual influence of itinerant conduction electrons and localized 4f‐moments. The striking temperature‐ and carrier concentration‐dependence is inspected of the conduction band structure, the electron spin polarization, and the Curie‐temperature Tc. A drastic Tc‐enhancement is observed with increasing band occupation, n, as a consequence of the s‐f exchange and the Coulomb interaction between the conduction electrons.
Thermoluminescence Study of Charge Traps in Polycrystalline Layers of Phenanthrene
Authors: Dreger Z. , Kalinowski J. , Davoli I. , Stizza S. , Feliziani S.
Published: July 2007

UV‐induced thermoluminescence (UVTL) experiments are carried out on polycrystalline films of phenanthrene. Applying the fractional glow technique the distribution of charge traps in energy is determined. The distribution appears to be quasi‐continuous within the energy range 0.25 to 0.60 eV, peaking at two energies Et(I) = 0.27 eV and Et(II) = 0.43 eV, and showing a cutoff at its low‐ and high‐energy edges. The peaks reflect the two maxima of the UVTL glow curves and correspond to different emission centers. It is the consequence of the distance and concomitant energy distribution of geminate trapped electron–hole pairs produced at the stage of the TL excitation. The results demonstrate that the discrete trap‐model, used extensively for the polycrystalline aromatic compounds, is not applicable to phenanthrene evaporated under vacuum onto a rigid substrate.
Incoherent Radiation and Pair Creation in Crystals
Authors: Baier V. N. , Katkov V. M. , Strakhovenko V. M.
Published: July 2007

The processes of bremsstrahlung (incoherent radiation) and incoherent electron‐positron pair creation by a photon are considered, taking the specific of particle motion in crystals into account.
X‐Ray Bragg Dynamical Diffraction in Crystals Weakly Deformed by Ultrasonic Waves
Authors: Polikarpov I. V. , Skadorov V. V.
Published: July 2007

The dynamical diffraction of X‐rays in crystals weakly deformed by transverse ultrasonic waves is investigated. Analytical expressions for the crystal reflection tensor and the modified refractive indexes for the cases of two‐and four‐level X‐ray‐acoustic resonances are obtained. It is shown that the modified refractive indexes and reflection tensor depend on the X‐ray‐acoustic resonance conditions.
Reaction of OH− and F Centers in Sodium Halides
Authors: Radzhabov E.
Published: July 2007

The influence of an additive coloration procedure on the absorption spectra of sodium halides doped with hydroxide is studied. The reaction of OH− and F centers leads to the creation of H and O2−‐vacancy centers in NaF, NaCl, NaBr crystals. The reaction yields H and O− centers in NaF doped with LiOH. Photodissociation of H and O− vacancy is studied, too. The possibility of the reaction of F and OH− centers in alkali halides is estimated on the base of the effectiveness of the reaction of free alkali metals with metal hydroxides. The reaction in alkali halides doped with LiOH is observed, too.
Atomic Diffusion in Tetrahedral Semiconductors. Approximative Treatment of Diffusion Theories
Authors: Enders P. , Schade U.
Published: July 2007

The transport of dopants in semiconductors can often be described within an interstitial–substitutional or diffusion‐reaction mechanism, e.g. for Zn in GaAs and in InP. The interpretation of experimental data, e.g. SIMS profiles, is largely complicated by that a nonlinear diffusion equation with several not precisely known coefficients has to be solved. In order to circumvent the parameter fit via the numerical solution of such a differential equation, approximately it is solved by means of the integral balance method. The usefullness of this approach is demonstrated by comparison with experimental and numerical results.
Application of the Local Environment Model to the Thermodynamics of Large Hard Core Interstitial Solutes in Binary Alloys
Authors: Oates W. A. , Mika K.
Published: July 2007

The local environment or cell model for interstitial solutes in binary alloy solvents is extended to those cases where the short range solute‐solute repulsive interactions effectively exclude or block sites adjacent to already occupied sites. The host alloy is assumed to be random and correlations between the locations of interstitial sites, which occur even in this case, are also allowed for. It is found that blocking and site correlation have a significant effect on the variation of the partial molar energy and entropy of the solute with concentration.
On the Scattering of Electrons by Confined LO Phonons in a Semiconductor Quantum Well
Authors: Leon H. , Comas F.
Published: July 2007

Scattering and momentum‐relaxation rates are calculated for a semiconductor quantum well (QW) considering electron scattering by confined LO phonons. Electron coupling with confined LO phonons is treated on the basis of an interaction Hamiltonian deduced in a previous work, while both electrons and LO phonons are assumed to be completely confined to the QW active layer. Besides the exact results, results are reported in the so‐called momentum‐conservation approximation (MCA) and the fractional error implied in the MCA is calculated. Detailed comparison with previous works (in the non‐confined phonon case) is made.
Surface Plasmons in Type II Superlattices
Authors: Sy H. K. , Song L. M.
Published: July 2007

A semi‐infinite type II semiconductor superlattice is studied using coupled Boltzmann equations. The exact equation is obtained for the surface plasma modes when the dielectric media inside and outside the surface are different. The number of solutions which are free from Landau damping depends on the parameters used.
Theory of Inelastic Low‐Energy Electron Scattering with Generation of Surface and Bulk Excitons in Molecular Crystals
Authors: Strelniker Ya. M.
Published: July 2007

The inelastic scattering of electrons on the surface of a semi‐infinite crystal with creation of surface and bulk molecular excitons is considered. Analytical expressions are obtained for the cross‐section of inelastic scattered electrons. The angular and energy dependences of cross‐section are investigated. A strong peak of the electron scattering is noted to be due to definite value of the wave vector of bulk exciton. The possibility to investigate the exciton band structure is discussed.
Light Quenching of Photoconductivity in Indium‐Doped Lead Tin Telluride
Authors: Möllmann K.‐P.
Published: July 2007

In strongly indium doped lead tin telluride (x > 0.2) at temperatures T < 30 K with interband excitation (hv > 3Eg) a “negative” photoconductivity is observed. This effect is attributed to quenching of the photoconductivity caused by background photon flux. The quenching of photoconductivity is discussed in terms of excitation into Jahn‐Teller centres in the conduction band at hv > 3Eg.
Comments on the EPR Spectrum of Tetravalent Chromium in Ruby
Authors: Marshall S. A. , Yu C. , Zhang Y. N.
Published: July 2007

The electron paramagnetic resonance absorption spectrum of tetravalent chromium in ruby is re‐examined at X‐band wavelengths. Spectral parameters are provided from data obtained at 4.2 K. Among these, the strength of the orthorhombic component to the crystalline electric field is given along with a suggestion of its associated direction.
Colour Centres in Alkali Metal Doped CaF2
Authors: Hamaïdia A. , Hachimi A.
Published: July 2007

Using optical spectroscopy and magnetic circular dichroism (MCD) colour centres are studied in CaF2:Li+ and CaF2:Na+. In each of these two matrices, there exists a weakly perturbed FA centre which is called F and probably a more deeply perturbed FA centre or F; the centre which is improperly named F2A has a paramagnetic ground state, its MCD is very different from that of the F2 centre in pure CaF2; there are two non‐paramagnetic centres “F3A+” and f with similar optical and magneto‐optical properties but with a long wavelengths shift of the absorption and emission spectra of the f centre.
CoK X‐Ray Absorption Near‐Edge Structure of Cobalt(III) Complex Compounds
Authors: Kitamura M. , Sugiura C. , Muramatsu S.
Published: July 2007

Experimental and theoretical studies of the CoK X‐ray‐absorption spectra for [Co(NH3)6]Cl3, [Co(NH3)5Cl]Cl2, trans‐ and cis‐[Co(NH3)4Cl2]Cl complexes are reported. The theoretical investigation is based on a multiple‐scattering theory. Overall profiles of the observed spectra are generally predicted by multiple‐scattering calculations for a single complex. Polarized spectra are presented to show that they are closely related to an arrangement of atoms along the direction of the polarization of the exciting X‐ray.
Coherent Compton Effect under Conditions of X‐Ray Dynamical Laue Diffraction
Authors: Bushuev V. A. , Kazimirov A. Yu. , Kovalchuk M. V.
Published: July 2007

A new scheme of the investigation of the coherent Compton scattering (CS), which consists in registration of the CS under conditions of the X‐ray dynamical Laue diffraction is realised. The general features of the angular dependence of the CS intensity MoKα‐radiation from the exit surface of perfect silicon crystals under the (111) reflection are investigated. The contribution of the silicon valence electrons to the atomic factor of the X‐ray scattering is experimentally determined.
Reactions for Iron Centers in Silicon under Optical Pumping
Authors: Bagraev N. T. , Polovtsev I. S.
Published: July 2007

Using the photoconductivity, EPR, and optical nuclear polarization (ONP) techniques, lightstimulated reactions leading to the rearrangement of defects in silicon doped with iron are investigated. The observed quenching and regeneration of Fe0 centers are explained on the basis of a concept suggesting the existence of a local negative‐U energy for defects with deep levels in semiconductors.
Anisotropy of the Mössbauer Effect in ß‐Sn under Pressure and the Lattice Dynamics
Authors: Opalenko A. A. , Kornilova A. A.
Published: July 2007

The Mössbauer effect probability is measured in single crystal tin samples oriented in the (100) and (001) planes under hydrostatic pressure up to 40 × 108 Pa. It is found that the anisotropy of the probability f001/f100 changes from 0.65 ± 0.02 at P = 0 to 0.90 ± 0.02 at P = 40 × 108 Pa. The experimental data for single crystals and polycrystals of tin under pressure are theoretically explained using the Brovman‐Kagan model of lattice dynamics.
Low‐Temperature Heat Capacity and Phonon Spectra of 4,4′‐Difluorobiphenyl
Authors: Wąsicki J. , Gurevich A. M. , Eropkin V. N. , Mayer J. , Natkaniec I. , Telezhenko Yu. V. , Khomenko V. G.
Published: July 2007

Heat capacity, inelastic incoherent neutron scattering and neutron diffraction experiments are performed for 4,4′‐difluorobiphenyl. The heat capacity is measured between 4.2 and 100 K using the adiabatic calorimetry technique. An interpretation of the temperature dependence of the heat capacity in terms of spectral characteristic is given. The results are finally compared with those of the isostructural crystalline biphenyl.
Effective Scattering Times of Inversion Electrons in InSb Grain Boundaries Deduced from Cyclotron Resonance Measurements
Authors: Ludwig F. , Müller H.‐U. , Herrmann R.
Published: July 2007

The effective scattering times of inversion electrons in InSb grain boundaries are investigated by means of cyclotron resonance measurements in the submillimeter wavelength range between λ = 118.8 and 513 μm. It is found that the inversion electrons in the InSb grain boundary have essentially higher scattering times than estimated from the onsets of Shubnikov‐de Haas oscillation periods. Furthermore, it is shown that the scattering times decrease with increasing magnetic field in qualitativ agreement with the theoretical result for the limit of a short‐ranged scattering potential. The scattering behaviour is discussed in the framework of this model.
Electronic and Structural Properties of Tungsten Bronzes
Authors: Bonnet A. , Conan A. , Morsli M. , Ganne M. , Tournoux M.
Published: July 2007

Transport coefficient measurements (electrical conductivity and thermoelectric power) are performed on compact bars of antimony and bismuth tungsten bronzes in polycrystalline form over the temperature range 100 to 500 K. Experimental results are discussed in comparison with those obtained recently on antimony and bismuth molybdenum bronzes in which two inverted narrow levels pin the Fermi level near the midgap. A single band model accounts for all the experimental results. In Bi4W20O62 the conduction mechanisms are governed by hopping in states near the Fermi energy. It is shown that variable range hopping occurs at low temperature whereas next neighbour hopping takes place at higher temperature. This band may be formed by the overlap of some broadened levels. The antimony phases are characterized by a non‐activated electrical conductivity and small TEP. These results are interpreted under the assumption that this narrow band broadens: this wide band is less than half‐filled and the electronic states are highly delocalized leading to “metallic” behaviour.
ESR Study of Mo3+ Containing Mixed Yttrium–Scandium–Aluminium Garnet Single Crystals
Authors: Asatryan H. R.
Published: July 2007

ESR of Mo3+ ions in mixed single crystals of yttrium–scandium–aluminium garnets Y3Al2−xScx. Al3O12, where 0 ≦ x ≦ 2 is investigated. Several new centers of Mo3+ differing from those for Y3Al5O12 single crystals are observed due to changes of symmetry and crystal field parameters associated with isomorphous substitution of octahedrally coordinated Al3+ (a) by those of Sc3+ in the third coordination sphere. Symmetry, nearest coordination, and spin–Hamiltonian parameters are estimated concerning with all Mo3+ centers in Y3Al2−xScxAl3O12 crystals for x < 0.15. It is found that in Y3Sc2Al3O12 (x = 2) the Sc3+ ions substitute also Y3+ at dodecahedral sites.
The Critical Temperature of the Axial Next‐Nearest‐Neighbour Ising Thin Film
Authors: Duda A.
Published: July 2007

The critical temperature of the disordered to ordered phase transition is calculated for the axial next‐nearest‐neighbour Ising thin film within the molecular‐field approximation. The effects originated in the finite size of the sample and the surface perturbation of the exchange coupling are discussed. It is found that for appropriate values of the surface parameter, the critical temperature can exceed the value corresponding to the infinite, ideal crystal.
On the Coercivity of Texturized Uniaxial Permanent Magnets
Authors: Elk K. , Jahn L.
Published: July 2007

To study the texture dependence of the coercivity of polycrystalline materials a model is considered taking into account coherent rotational processes and Bloch wall jumps simultaneously but neglecting a magnetic coupling between the identical grains. The texture is described by an one‐parametric distribution function. Using this model the magnetization coercivity Hc and the remanence coercivity HR are calculated. Especially the upper limits of Hc and HR are investigated. It follows that for technically attainable degrees of alignment (characterized by MR ≦ 0.98MS) a maximum value of Hc ≈ 0.677 HA cannot be exceeded.
Magnetic Properties of a Surface with an Amorphous Layer
Authors: Kaneyoshi T.
Published: July 2007

A semi‐infinite simple cubic spin‐½ Ising ferromagnet with surface amorphization is investigated by extending the mean‐field theory of amorphous bulk ferromagnets. The magnetic properties of the surface are examined as a function of averaged surface exchange 〈J〉r = J(1 + Δ) and fluctuation of the surface exchange interaction. Some characteristic behaviours of the system are found.
Single and Multiple Electron Scattering Description in X‐Ray Absorption Spectrum Theory and the Problem of Solid Structure Investigation
Authors: Vedrinskii R. V. , Bugaev L. A. , Levin I. G.
Published: July 2007

The effect of photoelectron double and threefold scattering processes on XANES (in KCl K K‐spectrum, in BaTiO3 Ti K‐spectrum) and EXAFS (in Re L3‐spectra in ReO3 at various pressures) are investigated within the spherical wave formalism. The main contributions into the near edge absorption cross‐sections are shown to be due to the photoelectron scattering processes in the approximately linear atomic chains originating and terminating at the absorbing atom. The results obtained for EXAFS show good agreement with the experiment that enables one to solve the bondangle determination problem by EXAFS.
Laser Excited Semiconductors: Light‐Induced Gaps and Saturation Kinetics
Authors: Henneberger K. , Jahnke F.
Published: July 2007

A theoretical description of the electron–hole plasma resonantly excited in the interband absorption region by a monochromatic laser is developed. A set of equations governing the spectrum and kinetics of electrons and holes as well as the nonlinear propagation of the laser wave is investigated for stationary excitation under the assumption of a local quasi‐equilibrium. Numerical results are represented concerning the spatial dependence of the electron–hole density and the laser intensity from which the saturation of absorption can be discussed.
Subpicosecond Dynamics of the Nonequilibrium Electron–Phonon System in GaAs
Authors: Mickevičius R. , Reklaitis A.
Published: July 2007

The relaxation of hot photoexcited electrons and the ultrashort laser pulse transmission under nonequilibrium LO phonon conditions in GaAs are studied by the Monte Carlo technique. It is shown that the electron relaxation from photoexcited levels consists of two stages. The first stage is controlled by the nonequilibrium phonons, and the second one – by intervalley processes. The laser pulse transmission is governed by the first stage.
Cavity‐Less Optical Bistability in Semiconductors
Authors: Borshch A. A. , Volkov V. I.
Published: July 2007

The way to obtain transverse cavityless OB based on the self‐defocusing of counterpropagating light waves in nonlinear medium is proposed. The theoretical analysis of the transverse OB made it possible to optimize parameters of the bistable cell involved. The experimental investigation are carried out with a semiconductor crystal of CdS. The results show a good agreement with the theory.
Effect of Optical Feedback on Self‐Induced Change of Light Polarization in Cubic Crystals with Directions Instable for Polarization
Authors: Brodin A. M. , Boiko S. A. , Valakh M. Ya. , Tarasov G. G.
Published: July 2007

Polarization optical bistability (POB) in crystals with FA‐centers mounted into a Fabry‐Perrot cavity is analysed. This type of optical bistability is caused by amplification of fluctuations of light polarization in crystals under consideration and has no threshold on radiation intensity. The range of parameters is found for impure crystals and cavity under POB conditions.
Theory of Ultrashort Pulse Generation and Amplification by Gain‐Switched Semiconductor Lasers
Authors: Schöll E. , Schell M.
Published: July 2007

A theory of the nonlinear ultrashort dynamic response of unbiased gain‐switched semiconductor laser amplifiers is presented. For suitable time delays between the incident laser pulse and the injection current pulse driving the laser amplifier, optical pulse compression due to self‐induced gain depletion is found. The finestructure of the emitted pulse resulting from multiple reflections is shown to depend crucially upon the detuning off cavity resonances and upon the ratio of input signal width to cavity round‐trip time.
Phenomenological Model for the Optical Properties of Semiconductor‐Doped Glasses
Authors: Peschel Th.
Published: July 2007

The optical properties of semiconductor‐doped glasses are determined by semiconductor crystals with diameters of 3 to 5 nm embedded in a glass matrix. The confinement of charge carriers leads to discrete energy states. The motion of the carriers is described by a Ritz ansatz for the wave function combining properties of free particles in a box with those of bulk excitons. In a first approximation the dynamical behaviour of the system can be described in analogy to a two‐level system. Since each energy level can contain only two pairs strong saturation of absorption occurs. Additionally the size distribution of the crystals is taken into account. It results in an inhomogeneous broadening of the spectral lines that can be described by convolution of the spectrum with the diameter distribution of the crystals.
Laser‐Induced Transient Grating in Semiconductor‐Doped Glasses
Authors: Feng Zhao , Li Han , Yun Zhang , Sheng Fei Hao
Published: July 2007

The characteristics are investigated of a transient grating induced by laser in glasses doped with CdSSe semiconductor and the nonlinear response time of the material is obtained. Also the properties of photoluminescence of the glasses are studied and a blue shift in luminescence spectra with increasing intensity of the input beam is observed. It is assumed that the nonlinearity of the material is due to band filling in semiconductor microcrystallites.
Dynamical Nonlinearity and Bistability of Narrow Gap Semiconductors
Authors: Allan G. R. , Chua P. L. , Hunter J. J. , Mackenzie H. A. , Pidgeon C. R. , Walker A. C.
Published: July 2007

A brief review is presented of new photo‐Hall studies of linear and nonlinear optical properties of narrow gap semiconductors with specific relevance to optical bistability. InSb is chosen as the prototype crystal for this work. The nonlinear refractive cross‐section (σ = Δn/ΔN) is determined to be −1.1 × 10−18 cm3 near 5 μm at 77K and −(2.3 ± 1) × 10−18 cm3 near 10 μm at 300 K. The two‐photon absorption coefficient is found to be β = 7 cm MW−1. The results are in good agreement with theoretical prediction.
Excitonic Electroabsorption in GaAsGaAlAs Single Quantum Well Waveguide Structures
Authors: Seisyan R. P. , Toropov A. A. , Khvostikov V. P. , Shubina T. V.
Published: July 2007

The electroabsorption spectra of GaAsGaAlAs waveguide p–n heterostructures with single quantum well grown by LPE method are studied at room temperature. The modulation spectra correspond to the quasi‐2D excitonic electroabsorption spectra. An external adjustable laser is used as a source of light propagating parallel to the epitaxial layers. A photolithographically fabricated two‐section sample consisting of LED and modulator regions is investigated as well. An on/off ratio of about 10:1 with a bias voltage U = 6 V is obtained.
Nonlinear Polarization Spectroscopy of Impure Cubic Crystals
Authors: Lisitsa M. P. , Valakh M. Ya. , Tarasov G. G. , Boiko S. A. , Brodin A. M. , Shpak A. M. , Voska R. , Feldvari I.
Published: July 2007

Nonlinear polarization spectroscopy, a new type of laser spectroscopy of solids, is used for the investigation of cubic crystals with reorienting centers. This technique based on the self‐induced change of light polarization (SICLP) is applied for the determination of fine parameters of FA(Li)‐, FA(Na)‐, F2‐centers in KCl. It is shown that the mechanism of phonon‐induced mixing of wave‐functions belonging to nondegenerate and degenerate excited electronic states of FA‐centers is responsible for SICLP manifestation in KCl with FA‐centers.
Covariant Theory of the Multiwave Bragg‐Laue X‐Ray Diffraction in Crystals
Authors: Maksimenko S. A.
Published: July 2007

Diffraction is considered of a plane monochromatic wave by a crystal lattice in the X‐ray fre quency region. A covariant solution of the boundary problem for the multiwave Bragg‐Laue diffraction in a plate‐like crystal is obtained on the basis of the Takagi diffraction equations written in the matrix form.
On the Integrated Intensity of X‐Ray Diffraction in Crystals with Randomly Distributed Defects
Authors: Holý V. , Kuběna J.
Published: July 2007

The dynamical theory of X‐ray diffraction in crystals with randomly distributed small defects based on an optical coherence formalism is used for calculations of integrated reflectivities (in the Laue case) of crystals with statistically placed small precipitates. It is shown that in the case of thinner crystals the integrated reflectivity is influenced mainly by the diffuse scattering, which increases the integrated reflectivity, for thicker crystals a decreasing effect of the diffuse absorption dominates. The calculated thickness dependences of integrated reflectivities are proved experimentally by projection topography of wedge‐shaped crystals with growth striations containing precipitates.
VK Centres in Alkali Halides. Direct Spin‐Lattice Relaxation and Electron‐Phonon Interaction
Authors: Stolovich A. , Liidja G.
Published: July 2007

Recent experimental results on the anisotropy of the Kronig Van Vleck one‐phonon spin‐lattice relaxation rates of self‐trapped hole centres in KBr, RbBr, and KI are used to obtain electron‐vibration interaction constants for even non‐totally symetric vibrations of VK centres. A simple centre model, consisting of the X molecule and two nearest cations with normal vibrations of β1g, β2g, and β3g symmetry, is used. A qualitative agreement with the experimental data on various cations and anions can be obtained when ion size corrections are taken into account in evaluating electron‐vibration matrix elements.
Determination of Electron Momentum Density from Electron Number Density. New Version of Semiclassical Transformation
Authors: Kokko K.
Published: July 2007

It is possible to determine the approximate momentum density of an inhomogeneous electron gas from the corresponding electron density by a semiclassical transformation. For the present by this method it is possible to calculate only isotropic total momentum densities. A method is introduced which can be used to calculate directional momentum densities in some special cases as well as partial momentum densities.
Conditions for the Occurrence of the Electric Quantum Limit in Inversion Layers
Authors: Zöllner J.‐P. , Paasch G.
Published: July 2007

In the electric quantum limit (EQL) only the lowest two‐dimensional subband of an inversion layer is populated. Whereas in some materials EQL is observed in others many subband states are populated. An almost analytical description of the inversion layer is derived. It yields conditions for the occurrence of the EQL. An upper limit for the EQL is calculated in dependence on material parameters, interface orientation, and doping concentration. Results are presented and discussed for a series of MIS systems and semiconducting bicrystals. The few available previous theoretical and experimental values for the EQL are well reproduced by the general description.
Properties of the Si‐S1 Center in Si1−xGex Solid Solutions
Authors: Bugai A. A. , Kravtsova I. N. , Maksimenko V. M. , Shanina B. D. , Shakhovtsov V. I.
Published: July 2007

Changes in the widths and integral intensities of the EPR lines of the Si‐S1 center depending on the content of germanium in a Si1−xGex solid solution are examined. The appearance of a line‐width anisotropy is accounted for by the effect of the Ge atoms in the immediate environment of the center on the spin‐spin interaction of the electron pair belonging to the center.
Optically‐Detected Magnetic Resonance of Excitons Bound at Te2 Isoelectronic Centres in CdS1−xTex
Authors: Hilton C. P. , Davies J. J. , Nicholls J. E. , Goede O.
Published: July 2007

The first ODMR experiments on excitons bound at isoelectronic traps in a II‐VI semiconductor are reported. In CdS1−xTex with x ≈ 0.02, recombination emission is obtained at 700 nm from excitons bound at Te2 pairs. The ODMR spectra obtained by monitoring polarization changes in this emission shows that the recombination occurs from a triplet state, thus confirming that the number of bound particles in the exciton is two. The symmetry of the ODMR spectra is related to the Te2 pair orientation and this, together with the spin‐Hamiltonian parameters, is consistent with the strong binding postulated for the hole in such an exciton. The additional observation of ODMR signals from shallow neutral donors is taken as evidence for efficient energy transfer between donor‐acceptor pairs and the excitons bound at the Te2 centres.
Role of Interlayer Interactions in High‐Tc Superconductors
Authors: Zieliński J. , Matlak M.
Published: July 2007

Anisotropic superconductivity is investigated for layered structures. An increase of interlayer hopping drastically reduces the transition temperature. The coupling between Cooper pairs on adjacent layers seems to be of primary importance in such systems whereas the interlayer Cooper pairs play a rather marginal role. The uniaxial pressure experiments could help to elucidate the nature of this interlayer coupling.
Superconductivity in Disordered and Ordered Niobium Carbide
Authors: Gusev A. I. , Rempel A. A.
Published: July 2007

The magnetic susceptibility, low‐temperature heat capacity, and superconducting transition temperature of an ordered and disordered niobium carbide are investigated. Features peculiar to the electronic structure of a nonstoichiometric niobium carbide are discussed. To explain the superconductive properties of the niobium carbide, a quasi‐two‐dimensional model is proposed which takes into account the peculiarities in the crystal structure of this compound. It is suggested that an exciton mechanism of superconductivity is possible which may be due to the layered structure of the niobium carbide.
Critical Relaxation of Uniform Precession of Magnetization in Cubic Ferrimagnets
Authors: Berzhanskii V. N. , Ivanov V. I.
Published: July 2007

The static (magnetization M(T) and susceptibility X(T) and the dynamic (magnetic resonance line width Δ‐B(T) properties of cubic ferrimagnets Y3Fe5O12 and MnFe2O1 are studied experimentally in the vicinity of the phase transition (PT) into the magnetically‐ordered state. The critical “speeding‐up” of the spin relaxation rate Γ which is available in cubic ferrimagnets is found to be absent. Scattering of the uniform precession of magnetization on the spin waves, including the optical ones, is shown to be the process dominating the relaxation below the Curie temperature Tc but not the fluctuation mechanism.
Anisotropic Ferromagnet with Biquadratic Exchange
Authors: Chaddha G. S. , Kalsi G. S.
Published: July 2007

Effect of biquadratic exchange on Curie temperature of a spin‐1 ferromagnet with anisotropic exchange interaction is studied using the Green function approach in the Anderson‐Callen decoupling approximation. The variation of Curie temperature with biquadratic exchange interaction is calculated for crystal lattices of different coordination numbers and for spin systems of various anisotropy parameters of the exchange interaction. Anisotropy parameters for which biquadratic exchange interaction has no effect on the Curie temperature are determined. The results of various approaches are compared.
Two‐Photon Absorption of Bismuth Germanate
Authors: Casalboni M. , Francini R. , Lohmeier F. J. , Grassano U. M.
Published: July 2007

Two‐photon absorption of BGO is observed between 4.8 and 5.7 eV. The results confirm and extend previous investigations on two‐photon excited luminescence. In particular the two‐photon spectra do not show the first three structures observed in the reflectivity measurements. Therefore these structures should be assigned to excitonic transitions and to Bi3+ ion transitions that are parity forbidden in two‐photon spectroscopy. In the region just above the onset, the two‐photon absorption coefficient increases with the photon energy in reasonably good agreement with the theory. Above 5 eV it increases more rapidly than predicted by the present theories for direct interband two‐photon transitions.
Optical Properties of High‐Refractory Disilicide Thin Films
Authors: Henrion W. , Lange H.
Published: July 2007

Optical reflectivity spectra are measured for TiSi2, TaSi2, and WSi2 thin films in the spectral range from 0.05 to 6 eV. The optical constants are obtained by Kramers‐Kronig analysis. The spectra are characterized by two spectral regions: the low‐energy free‐carrier response and the interband part. The spectra are discussed on the basis of presently existing band structure information and bonding trend calculations.
A Double Bond Charge Model for Si
Authors: Klenner M. , Falter C. , Ludwig W.
Published: July 2007

Starting from a picture of bonding dynamics of covalent crystals based on ab‐initio density response calculations, a phenomenological model is constructed which more clearly shows the principles governing the microscopic density redistribution than does the usual bond charge model. A tetrahedral configuration is introduced of four bond charges rigidly attached to each ion, but free to rotate. The resulting system is treated by means of methods used in the lattice dynamics of molecular crystals. The accuracy of the phonon dispersion curves obtained is comparable to that of the best other models. The analogies are worked out to the microscopic partial density model and the importance of the “chains” in the crystal structure to the lattice dynamics of zinc‐blende materials demonstrated by computing the effective force constants.
Multiple Scattering Approach to the Density of States and Electron Energy Loss Spectra of Amorphous Carbon
Authors: Mühling I. , Blaudeck P.
Published: July 2007

For a set of different carbon clusters the electronic density of states per atom is computed by multiple scattering. Electron energy loss experiments with thin films of sputtered amorphous carbon are carried out as well. By comparing the ε2E2 function with the joint density of states and the C Is near‐edge structure with the conduction band density of states some information about the film structure is obtained.
Potential Surfaces for Chemisorption on Semiconductor Surfaces from Pair Potential Considerations
Authors: Engler C.
Published: July 2007

A pair potential method, recently proposed by Tersoff, is extended in order to treat chemisorption problems on semiconductor surfaces. The modified version is tested for chemisorption of atomic hydrogen and oxygen on Si(100)‐surface. The calculated data are compared with experiments and ab‐initio results.
Magnetic Resonance in Magnetically Diluted Solids at Low Temperatures
Authors: Dzheparov F. S. , Henner E. K.
Published: July 2007

The paramagnetic resonance in the disordered spin systems with dipole‐dipole interactions is considered. The theory is extended into the region where βĒ ≪ 1 (β is the inverse dipole temperature, Ē is the interaction energy at the average distance between the spins). The kinetic equations are formulated and the heat capacities for real systems and the resonance form function for the Anderson model are calculated. The correlation expansion is advanced to calculate the form function and the heat capacities are calculated using the concentration expansion.
Influence of the Magnetostatic Interaction on the Outer Hysteresis Loop
Authors: Elk K. , Christoph V.
Published: July 2007

To study the magnetostatic interaction, clusters of N magnetic particles in an infinite sample are considered. The magnetic hardness of a single particle is described by its coercivity field being distributed with different distribution functions. On the base of analytical solutions the shape of the hysteresis loop and information on the remagnetization process result.
Anisotropy of the Optical Band Edge Absorption in CuInTe2 Single Crystals
Authors: Medvedkin G. A. , Prochukhan V. D. , Rud Yu. V. , Tairov M. A.
Published: July 2007

Optical absorption of p‐CuInTe2 (I42d) single crystals is studied near the band edge in linearly polarized light in the temperature range 370 to 77 K. Band edge absorption in E ∥︁ c and E ⟂ c polarizations follows Urbach's rule and is described by an electron‐phonon mechanism. The minimal optical transitions in CuInTe2 are allowed primarily in E ⟂ c polarization and correspond to a band gap of 0.983, 0.994, and 1.038 eV for T = 370, 300, and 77 K, respectively. The single crystals reveal optical linear dichroism near the band edge reaching an amplitude 𝒫T ≈ 70%. The optical anisotropy correlates with the deformation of the chalcopyrite lattice, the transmission in linearly polarized light obeying the generalized Malus law. The CuInVI2 (VI = S, Se, Te) crystals are found to have a temperature coefficient of band gap width substantially smaller than that typical of their binary analogs, the II‐VI compounds.
Dynamical theory of electron diffraction for quasicrystals
Authors: Cheng Yifan , Wang Renhui
Published: July 2007

The dynamical theory of electron diffraction for crystals in the wave‐optical and the wave‐mechanical formulations is extended to quasicrystals. In these formulations the basic equations satisfied by the electron wave amplitudes have the same forms for both crystals and quasicrystals.
The structure of the defect chalcopyrite ZnGa2Se4 studied by EXAFS
Authors: Antonioli G. , Lottici P. P. , Razzetti C.
Published: July 2007

EXAFS (extended X‐ray absorption fine structure) measurements on the defect chalcopyrite ZnGa2Se4 are performed at the K‐absorption edges of all the atomic species. The bond lengths and the internal distortion parameters are determined by standard EXAFS data analysis techniques in the plane wave approximation, using CuGaSe2 and ZnSe as structural standards for the EXAFS phase shifts. It is shown that the EXAFS radial distribution function contains informations also on the second and third neighbours coordination shells.
Volume capture of 1.5 to 5.7 MeV electrons in quantum channeling states
Authors: Kaplin V. V. , Gridnev V. I. , Khlabutin V. G. , Rozum E. I. , Vorobiev S. A.
Published: July 2007

Volume capture of (1.5 to 5.7) MeV electrons into the quantum states of planar and axial channeling along (100), (110), (111), and 〈110〉 directions of Si crystal is investigated. The measurements carried out on crystals with the thickness of 2 and 7 μm reveal two different mechanisms for the volume capture: a small‐angle multiple scattering and strong single scattering of electrons. In the former case the near‐barrier weakly bound states are populated basically, in the latter one they are strongly bound states.
The force constant of a bijellic interface
Authors: Streitenberger P. , Ziesche P. , Nafari N.
Published: July 2007

The equivalence of different expressions for the force constant of a bijellic interface is shown. Within the local density approximation of the universal functional, G[n], the force constant can be expressed solely in terms of bulk quantities. The Thomas‐Fermi‐Dirac approximation is applied and the results are compared with other ones obtained recently within the gradient expansion method.
Subsurface hydrogen exciton‐like states in solid catalysts
Authors: Szász A. , Fabian D. J.
Published: July 2007

Subsurface hydrogen electronic levels are discussed in terms of exciton‐like states generated by vacancy‐hydrogen interaction in transition‐metal catalysts. Trapped hydrogen atoms have binding energies that depend exponentially on the density of electronic states at the Fermi level.
Band tails in the density of states of mixed crystals
Authors: Monecke J.
Published: July 2007

The Saxon‐Hutner theorem proves the existence of band tails in the density of states for a wide class of models of mixed crystals. These band tails are discussed in detail by Lifshitz. They are not obtained, however, in self‐consistent theories like the coheren, potential approximation or in the theory of Klauder. The non‐existence of band tails in the self‐consistent theories is related to a wrong percolation behaviour of the self‐energy and it is proved that a recently proposed alternative theory results in a density of states which fulfils the Saxon‐Hutner theorem. Further it is shown that the density of states of binary mixed crystals exhibits all Van Hove singularities of both pure constituents.
Chromium centres in 3 CdSO4 · 8 H2O single crystals
Authors: Prasad P. Sathya Sainath , Radhakrishna S.
Published: July 2007

The optical absorption spectra of 3 CdSO4 · 8 H2O single crystals doped with Cr3+ is recorded at 300 and 80 K; the crystal field transitions are assigned and the B, C, Dq parameters evaluated. Polarisation investigations are undertaken to establish the exact electric dipole transitions and the exact magnetic dipole transitions. Splitting of the bands (differences between the parallel and perpendicular polarised spectra) due to the non‐cubic fields acting on the chromium (III) ion are not observed though two inequivalent cadmium atoms exist in the lattice. Also no lowering of symmetry is observed either from the low temperature spectra or the polarised spectra. Radiation damage studies are undertaken to study the mechanism of the formation of Cr3+ to Cr+ and the valence state effect on the electronic transitions. The effect of space charge compensating vacancies on the electronic transitions and its effect on the crystal field strength is studied using the radiation damage spectra. The formation of Cr+ from Cr3+ through Cr2+ is well explained. The theoretically calculated values coincide well with the experimentally observed values for the octahedral symmetry for both, Cr3+ and Cr+ ions in 3 CdSO4 · 8 H2O lattice.
Strong‐field scheme for C (d3) and the Spectra of Ruby and Cr2O3
Authors: Zhao Sang‐Bo , Zhou Kang‐Wei
Published: July 2007

In order to calculate the energy spectra of Cr3+ ions in a C3v symmetry crystal field, a radial orbit function is used for the d‐electrons in bounded ions having a form between the SCF wave functions of Richardson and Watson. In addition the complete strong field matrices of C(d3) are built up for the first time by a simplified strong‐field scheme, in which the Griffith standard bases of the O double group are taken as the starting point. Then the absorption spectra (including the spin‐allowed and spin‐forbidden spectra) of Cr3+ in ruby and Cr2O3 crystals are calculated. The theoretical results, with consideration of vibronic, are quite consistent with experiments. Thus the mechanism of the absorption spectra of Cr3+ in these two crystals is well explained. This scheme of calculating spectrum parameters by radial orbits greatly reduces the number of fitting parameters. This simplified strong‐field scheme can be extended to any dn system and any subgroup of Oh.
Theoretical calculation of the optical constants of transition metal silicides
Authors: Huang Tzu‐Yu , Lue Juh‐Tzeng
Published: July 2007

A quantum theory of screening charges exploiting orthogonalized pseudowave functions to evaluate the conduction electron charge density due to d–p hybridization is used to solve the optical constants of transition‐metal silicides. The dependence of the complex refractive indices on photon wave vector, carrier relaxation time, valence charges, and core binding energies for TiSi2 is calculated. The results show much better agreement with the observed values than those from the classical Drude model.
Energetic and temporal characteristics of picosecond pulse self‐diffraction in silicon
Authors: Apanasevich P. A. , Asimova V. D. , Zaporozhchenko V. A. , Zaporozhchenko R. G. , Pilipovich I. V.
Published: July 2007

Self‐induced diffraction of ultrashort pulses in silicon crystals at high incident light intensities is studied. A theoretical model is presented which takes into account the band‐filling effect as a major mechanism of light‐induced grating anharmonicity. Experimental results on the energetic and temporal characteristics of four orders of diffraction are in good agreement with this theoretical model.
A new empirical many‐body potential energy function. Application to microclusters
Authors: Erkoç S.
Published: July 2007

A new empirical many‐body potential energy function is proposed which comprises two‐ and three‐body interactions. The two‐body potential is a kind of hybrid function and the three‐body potential is expressed in terms of the two‐body interactions. The parameters of the potential energy function can be easily evaluated using dimer data and the bulk cohesive energy of the system considered. The proposed potential energy function is parameterized for several elements in f.c.c., b.c.c., and diamond structures and is applied for the investigation of structural stability and energetics of microclusters. The agreement between the present results and literature values is good.
Incommensurate–commensurate transition driven by concentration in rare gas mixtures adsorbed on graphite
Authors: Marti C. , de Beauvais C. , Ceva T. , Croset B. , Goldmann M.
Published: July 2007

An unexpected anomaly is observed in the phase diagram of argon‐xenon and krypton‐xenon mixtures adsorbed on graphite: less krypton than argon is needed to drive the incommensurate–commensurate transition. A mean lattice model is developed, which describes the krypton‐xenon mixture, however, local disorder terms must be added to obtain agreement with the argon‐xenon results.
Exciton‐grating induced metamorphoses of the degenerate four‐wave mixing spectra in the giant two‐photon resonances of the excitonic molecules in CuBr and CuCl
Authors: Mizutani G. , Nagasawa N.
Published: July 2007

It is demonstrated that the spectral shape of the DFWM generation in CuBr and CuCl show remarkable metamorphoses when the polarization of the incident two beams is set parallel to each other. According to the polarization character of the nonlinear polarization, these phenomena are concluded to be due to higher order non‐linearity than χ(3) where the really populated exciton grating contributes.
Double periodic peierls phases
Authors: Mertsching J.
Published: July 2007

Double periodic Peierls phases may arise in quasi‐one‐dimensional conductors containing two groups of electrons with different Fermi wave numbers, e.g. in very strong magnetic fields. For a nearly half‐filled conduction band, the Peierls distortion may be a kink lattice, a polaron lattice, or a nonlinear superposition of a kink lattice and a polaron lattice. The lattice distortion, the band structure, the magnetic moment, and the chemical potential in the ground state are calculated as a function of the magnetic field strength and the density of electrons.
An interpretation of the pressure dependence of EPR zero‐field splitting of Mn2+ in Na2ZnCl4 · 3 H2O
Authors: Lu Ke‐Qin , Guo Sheng‐Li , Wu Ping‐Feng
Published: July 2007

The relationship between the zero‐field splitting parameter D and the C3v crystalline potential components for Mn2+ ions is established by using the parametrization d‐orbital theory proposed by Zhao et al. The pressure dependence of D of Mn2+ in Na2ZnCl4 · 3 H2O is calculated. The results agree well with the values measured experimentally indicate that the D‐value increase with increasing pressure is caused most dominately by changing in the angle θ and next by the change in the bond length R under pressure.
Observation by ESR of electrons localized at intrinsic shallow traps in silver halide systems
Authors: Eachus R. S. , Olm M. T. , Janes R. , Symons M. C. R.
Published: July 2007

Electrons shallowly trapped at intrinsic sites in single‐crystal and polycrystalline samples of AgBr, AgCl, and mixed iodohalides are observed by ESR. The results are consistent with a model in which the electron is localised by a silver ion in an effective mass state. The observed ESR linewidths are explained in terms of exchange narrowing. The effect of iodide on the free or nearly‐free electron g‐value is determined. Addition of iodide to AgCl or AgBr resulted in alloy line broadening. The amount of shallow trapping depended in part on dislocation density. In polycrystalline samples of AgBr, cyclotron resonance of the free electron polaron is observed simultaneously with the ESR signals from localized electrons. From the linewidth of the cyclotron resonance signal, the mobility of the free electron polaron in some polycrystalline samples is determined to be the same as that measured previously in very pure single crystals of AgBr.