bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical Constants of Germanium Selenide Single Crystals in the Transparency Region
Authors: Elkorashy A. M.
Published: July 2007

The refractive index, n, of GeSe single crystal is measured by the interference method in the transparency region. An effective thickness smaller than the true one is introduced to account for the photon scattering by the layer structure of the material in this region. The effective thickness hypothesis gives satisfactory explanation of the pronounced rise in reflectance for E < Eg. The extinction coefficient, k, is calculated from the measured absorption coefficient. Measurements are performed at room temperature using plane polarized light with the plane of polarization parallel to the a and c crystallographic axes which lie in the plane of cleavage. The real and imaginary parts of the complex dielectric constant (ϵr, ϵi) as well as the reflectance and its phase change (R, φ) are calculated from the values of n and k. It is shown that GeSe single crystal exhibits birefringence. Assuming that GeSe binding is partly ionic and partly covalent, the results of the optical constants are satisfactorily fitted to the model of a single effective oscillator.
Optical and Electrical Studies of GaP: Ti
Authors: Ulrici W. , Friedland K. , Eaves L. , Halliday D. P. , Payling C. A.
Published: July 2007

The results of optical absorption, photoluminescence, electrical conductivity, and Hall‐effect measurements on LEC‐grown GaP: Ti are reported. The positions of the Ti/Ti acceptor level at Ec − 0.50 eV and the Ti/Ti donor level at Ev + 1.0 eV are established and the photoionization transitions from and to these deep levels are identified in the absorption spectra and from recharging processes. The internal transitions 3A2 → 3T1(F) and → 3T1(P) of Ti are found in absorption and the 2E ↔ 2T2 transitions of Ti3+Ga are seen in the absorption as well as luminescence spectra. The interpretation of these bands and sharp lines requires to take into account different kinds of electron–phonon coupling. Photoinduced recharging experiments at low temperatures on high‐resistance GaP:Ti and GaP:Ti:Zn are consistently explained including the three charge states of TiGa, of the PGaP4 antisite defect, and of the residual FeGa impurity.
An Effective‐Field Theory of Mixed Ising Spin Systems in Transverse Fields
Authors: Kaneyoshi T. , Sarmento E. F. , Fittipaldi I. P.
Published: July 2007

An effective‐field theory is proposed and used to derive the thermodynamic properties of the mixed Ising spin system consisting of spin‐½ and spin‐1 with different transverse fields. The effects of transverse fields on the critical behavior and the magnetization curves are studied. It is shown that the present formalism, in spite of its simplicity, yields results which represent a remarkable improvement on the mean‐field treatment.
Digital Optics: Architecture and Systems Requirements
Authors: Streibl N. , Prise M. E.
Published: July 2007

Digital optics is a technology for (i) processing, (ii) transport, and (iii) storage of optical digital information. Digital optics offers both, the high temporal bandwidth known from fiber‐communications, as well as the high connectivity and information density of optical imaging. Digital optical circuits may be constructed by cascading two‐dimensional planar arrays of optical logic gates. The connection between these arrays is performed by light beams going through the free space above a chip. The system design and the architecture have to be adapted to optics. Some requirements for optical systems and for optical logic gates will be discussed.
Semiconductor Cells with N‐Type Photocurrent–Voltage Characteristic. A New Class of Nonlinear Optical Elements
Authors: Ryvkin B. S.
Published: July 2007

Electrooptic effects are shown to result in an N‐type differential negative resistance of semiconductor cells illuminated with radiation. Various types of optoelectronic elements (bistable element included) are created on the basis of these cells.
Amplitude and Frequency Modulation of Light Pulses in Semiconductor Fabry‐Perot Amplifiers
Authors: Müller R.
Published: July 2007

The amplification of Gaussian‐shaped light pulses being incident on the facet of a semiconductor diode laser which is operated below its lasing threshold (Fabry‐Perot or laser amplifier) is studied theoretically. Numerical results are presented showing the time‐dependent intensity behaviour as well as the frequency chirp, caused by self‐phase modulation, of the transmitted and reflected fields.
Exciton Parameters and Electron Miniband Structure of GaAs/AlGaAs Superlattices
Authors: Uraltsev I. N. , Ivchenko E. L. , Kopev P. S. , Kochereshko V. P. , Yakovlev D. R.
Published: July 2007

The linear optical properties of short‐period GaAs/AlGaAs superlattices (SL) with three‐dimensional conduction minibands are studied. Using spectroscopy of p‐polarized reflectance at oblique incidence the enhancement of exciton resonance features and effect of lineshape inversion at Brewster angle for the first time are observed. The heavy‐ and light‐hole exciton oscillator strength is found to decrease with shortening of the SL period. Using the optical orientation technique the splitting of electron minibands linear in wave vector is measured for the first time. An essential increase of the photoelectron spin polarization is observed in the presence of magnetic field in Faraday configuration. The magnetic field effect is described in terms of the suppression of the electron spin relaxation connected with the k‐linear splitting of miniband spin states.
On Lattice Parameters and Enthalpies of Mixing of Alkali Halide Solid Solutions
Authors: Königsberger E. , Schrunner H.
Published: July 2007

A simple unified approach to the calculation of enthalpies of mixing and deviations of lattice parameters from Vegard's rule is presented. No experimental information about the solid solution is required and the results are insensitive to small experimental errors of the relevant parameters (r,x) of the pure components. In many cases this model is superior to more sophisticated theories in reproducing experimental data of mixed crystals. The main shortcomings of these theories with respect to lattice spacings are discussed.
Time Evolution of the Refractive Index of CuCl under Picosecond Pulsed Excitation
Authors: Manar A. , Gomes M. J. M. , Hönerlage B. , Levy R.
Published: July 2007

By measuring the dynamical shift of interference fringes in epitaxial layers of CuCl, using picosecond “pump and test” experiments, the temporal evolution of the nonlinear refractive index of this compound at low temperatures is obtained. This time behaviour analysed at different photon energies of the test beam is shown to depend on the intensity and photon energy of the pump beam. This observed index change is closely related to the dynamics of the polaritons created by the pump beam.
Multiple LO‐phonon Raman scattering and hot excitons
Authors: Trallero‐Giner C. , Riera R.
Published: July 2007

A theory is developed which describes multiphonon resonance Raman scattering (MPRS) processes in polar semiconductors when the incident radiation frequency ω1 is above the fundamental absorption region. A general formula for the MPRS cross‐section based on the exciton distribution function is presented as a function of ω1, the indirect creation and annihilation probabilities, the exciton lifetime, and the transition probabilities between different exciton states. The different role of hot‐exciton transitions and their main contribution to the cross‐section is investigated. It is shown that the cross‐sections depend greatly on the ratio of the electron and hole effective masses. Using that and earlier theoretical results for the exciton scattering, the scattering lines showing intensity alternation in InI and InBr are explained if the electron and hole effective masses are nearly equal. The final result corresponds to a cascade model of exciton relaxation where the main transitions are between 2p and 2s exciton states. An approximate expression for the MPRS cross‐section is given.
On the theory of roton‐like excitations in amorphous solids
Authors: Handrich K. , Resch J.
Published: July 2007

A view ofg(r)andS(k)suggests an approximately separate treatment of the short‐range order in the directk‐space and the “quasi long‐range order” (which follows from a high and sharp peak of the static structure factor) in thek‐space. The employment of structure functions leads to a widening of the reciprocalk‐space. With an approximated orthonormal and complete set of functions the Green function is decoupled from the force constants. A set of hierarchy equations follows, which is solved to obtain a structure averaged Green function. With that function the density of states is calculated and the specific heat of an amorphous system.
IR reflection spectra of manganese‐zinc ferrites
Authors: Katsnelson E. Z. , Karoza A. G. , Meleshchenko L. A. , Bashkirov L. A.
Published: July 2007

IR reflection spectra of the Mn1−xZnxFe2O4 ferrite‐spinel system are investigated in the range from 200 to 800 cm−1. The spectra of all ferrites show three reststrahlen bands ω1, ω2, and ω3, one of which ω2 splits into two components. On the basis of experimental spectra optical, dielectric, and oscillator parameters and also effective dynamic ion charges are determined by Kramers‐Kronig (K‐K) analysis, dispersion analysis (DA), and successive analysis (DA–K‐K). The position and intensities of the bands, ω1 – ω3, are changed with the change in ferrites' composition and show one‐mode behaviour. Conclusions are drawn about the preferable use of the DA–K‐K method for spectra analysis of the ferrites as well as about considerable covalency of the chemical bonds in the ferrites under investigation.
The Site‐Bond Diluted Transverse Ising Model with S = 1
Authors: Yang Chuan‐Zhang , Zhong Jia‐Lin
Published: July 2007

Within the framework of an effective‐field theory, the longitudinal and transverse magnetization, critical temperature, and critical transverse field of a site‐bond diluted transverse Ising ferromagnet on square lattice with S = 1 are calculated in detail. The dependence of these thermodynamic quantities on the concentration of the sites and of the bonds is investigated.
Nucleation Fields in Periodic Multilayers
Authors: Nieber S. , Kronmüller H.
Published: July 2007

The linearized micromagnetic equation for inhomogeneous nucleation in planar soft magnetic regions is derived and interpreted as a one‐dimensional Schrödinger equation. Based on the Kronig‐Penney model of quantum mechanics, the nucleation field for a periodic multilayer composed of two alternating layers with different crystalline anisotropies is determined.
Laser Induced Absorption of CuCl Microcrystallites in a Glass Matrix
Authors: Gilliot P. , Merle J. C. , Levy R. , Robino M. , Hönerlage B.
Published: July 2007

Using a “pump‐and‐probe” technique, the absorption changes of CuCl microcrystallites embedded in a glass matrix are studied. A blue shift of the resonance and a bleaching of the absorption at photon energies lower than the photon energy of the pump, is observed accompanied by an increase of absorption at higher photon energies.
EPR and Optical‐Absorption Studies of Cu2+‐Doped Mg(CH3COO)2 · 4H2O Single Crystal
Authors: Misra Sushil K. , Wang Chunzheng
Published: July 2007

X‐band EPR measurements on a single crystal of Cu2+‐doped magnesium acetate tetrahydrate, Mg(CH3COO)2 · 4H2O, are made at 295, 77, and 4.2 K. The Cu2+ spin‐Hamiltonian parameters are evaluated, at all these temperatures, from the EPR line positions by means of a rigorous leastsquares fitting method. The principal values of the g2 and A2 tensors indicate that the local symmetry of the Cu2+ ion, in the host lattice of Mg(CH3COO)2 · 4H2O crystal, is tetragonal. The room‐temperature optical‐absorption spectrum, recorded in the 190 to 820 nm wavelength range, is exploited to study the crystal‐field and charge‐transfer transitions of the Cu2+ ion. On the other hand, both the room‐temperature optical‐absorption and EPR data are used to estimate the core polarization contribution (K) and the molecular‐orbital coefficients for the Cu2+ ion doping Mg(CH3COO)2 · 4H2O.
Optical Effects Due to Antiferromagnetic Spin‐Ordering in (Cd, Mn)S at Highest Mn Concentrations
Authors: Heimbrodt W. , Bencke C. , Goede O. , Gumlich H.‐E.
Published: July 2007

The antiferromagnetic phase transition in (Cd, Mn)S single crystals and thin films with highest Mn concetrations 0.8 ≦ xMn ≦ 1 is studied by luminescence emission and excition measurements. Luminescence bands near 1.5 and 1.8 eV are observed in the samples with rocksalt and zincblende/wurtzite structure, respectively, being excited by the corresponding Mn2+ d–d transitions. Below the spin‐freezing temperature TN(xMn) the Mn2+ d–d excitation bands shift to higher energies nearly proprotional to the square of the ordering parameter, due to the different spinordering induced energy relaxatio in ground and excited states. The exchange interaction parameters of the excited Mn2+ states are determined in a mean‐field approximation. Using a ligand field model the p‐d mixing and crystal field parameters for the paramagnetic and antiferromagnetic phase are obtained. The observed finestructure of the 6A1g → 4Eg, excitation band in MnSRS is ascribed to covalent bondig effects and LO phonon and magnon interaction. The measured luminescence decy parameters increase significantly below TN(xMn), indication the energy transfer rates to be influenced by the antiferromagnetic spin ordering.
The Magnetic Contribution to the Electrical Resistivity in the Ising Ferromagnet
Authors: Urbaniak‐Kucharczyk A. , Balcerzak T. , Mielnicki J. , Wiatrowski G.
Published: July 2007

On the basis of the model proposed by de Gennes and Friedel the magnetic contribution to the electrical resistivity ρm in an Ising ferromagnet is calculated using the Matsudaira approximation method for estimating the two‐spin correlation function. As the main result the dependence of ρm on the temperature T and the orientation of the Fermi wave vector kF with respect to the crystallographic axes is obtained. Especially, ρm(T, kF) for Ising ferromagnets with plane square and s.c. lattice structure is estimated and discussed in more detail.
Hydrogen Diffusion and Radiationless Electron Transfer in Metal Hydrides
Authors: Lupu D.
Published: July 2007

The activation energies of the radiationless electron transfer are calculated from the optical spectra of some Sc, Y, La, Lu, Nb, Pd, and Mg2Ni hydrides. These are practically the same with the values of the activation energies for hydrogen diffusion, pointing out to the importance of electron transfer from localized states to the conduction band in the mechanism of hydrogen diffusion. The exponential temperature dependence of the radiationless electron transfer probability together with vibrational tunneling at low temperatures can account for the temperature dependence of H diffusion in the entire temperature range. A comparison between the electronic structures of NiH and PdH qualitatively explains the higher activation energy of H diffusion in Ni. Isotopic effects in Pd hydrides and a treatment based on Frenkel defects also support the proposed model.
Electronic Structure and Optical Properties of Mgo Band Structure Calculation and Cluster Model
Authors: Stepanyuk V. S. , Szász A. , Grigorenko B. L. , Farberovich O. V. , Katsnelson A. A.
Published: July 2007

The electronic structure of MgO is calculated in the framework of local‐density theory using the LAPW resp. cluster Xα‐SW method. The results of an improved permittivity calculation is compared with optical measurements, yielding good agreement. The effect of pressure on the electronic structure is studied for NaCl symmetry. It is found that the direct gap becomes indirect already for a compression of V/V0 = 0.9.
Positron Annihilation in Si and Ge
Authors: Aourag H. , Belaidi A. , Kobayasi T. , West R. N. , Khelifa B.
Published: July 2007

A computational technique is developed to evaluate electron and electron—positron momentum densities in silicon and germanium and the use of these to provide means of interpreting the k‐space densities obtained by experimentalis's using the two‐dimensional angular correlation of positron annihilation radiation technique (2D ACAR). As a consequence of the good agreement observed in the momentum densities and the LCW folded data obtained for silicon and germanium the independent particle approximation (IPM) coupled with the use of electron pseudo‐wavefunctions represent an excellent starting point for a systematic many‐particle description of the process, since significant deviations from the experimental angular correlation distribution can be ascribed to the electron—positron and electron—electron interactions.
The Temperature Dependence of Dielectric Response in Relation to Distribution Functions
Authors: Kliem H. , Arlt G.
Published: July 2007

The transformation of temperature dependent dielectric relaxation spectra χ″(ω, T) into temperature independent distribution functions of activation energies is derived and demonstrated at the example of polyethylmethacrylat. Linear superposition of thermally activated dielectric relaxation processes is anticipated. The calculated distribution function describes the observed variation of the relaxational curves with temperature and yields for χ″(χ′) in the complex plain Cole‐Davidson plots.
Temperature Dependence of the Elastic Constants for Biaxial Nematic Liquid Crystals
Authors: Monselesan D. , Trebin H.‐R.
Published: July 2007

The elastic constants Kij of the Frank‐Oseen energy density for uniaxial nematic liquid crystals depend on the Maier‐Saupe order parameter S and hence on temperature. Longa et al. recently used an extended Landau‐Ginzburg‐de Gennes theory to expand the functions Kij(S) up to fourth order in S. Here, a similar procedure is applied for the elastic energy density of biaxial nematic liquid crystals. The three chiral and 15 achiral constants are expressed as fourth‐order polynomials in the order parameter S and the degree of biaxiality T. Via the temperature dependence of the quantities S and T also the temperature dependence of the elastic constants is fixed.
H‐Centre in LiF‐H−
Authors: Egranov A. V. , Nepomnyachikh A. I. , Otroshok V. V. , Chernyago B. P.
Published: July 2007

The H‐centre in LiF is studied by optical and ESR techniques. The centre is produced by reaction between H and H‐centres. The H‐centre ESR spectrum shows three broad lines which are due to the hyperfine interaction of an unpaired electron with the two protons. The resolved superhyperfine structure (as in case of F‐centre) arises from the interaction with the lithium nuclei in a first shell and the fluoride nuclei in a second shell. Optical absorption band of the H‐centre at 5.05 eV is similar to that of the F‐band, only slightly shifted to higher energies. The centre has the character of molecule‐ion as well as of F‐centre.
Lattice Dynamics of Nitrogen and Carbon Dioxide
Authors: Binbrek O. S. , Higgs J. F. , Anderson A.
Published: July 2007

A simple force constant model is used to calculate the normal mode frequencies and eigenvectors of the cubic crystals α‐N2 and CO2. Good agreement with spectroscopic data is obtained for the lattice frequencies, and crystal field splittings of the molecular modes are found to be small in all cases. For α‐N2, the calculations suggest that the non‐centrosymmetric structure is more likely, but the possibility that this result is merely a consequence of the larger number of parameters involved cannot be ruled out. For CO2, the intermolecular CO interactions appear to play a relatively minor role.
Partial and Total Electronic Stoppings of Solids and Atoms for Energetic Ions
Authors: Kaneko T.
Published: July 2007

Partial and total electronic stopping cross sections of solids and atoms for protons are estimated by the recently developed wave packet theory and the Lindhard theory. The wavepacket theory presents the one‐shell dielectric function for the bound electrons (BE's) in the framework of RPA by adopting the momentum space representation, where the BE's are treated as an interacting electron gas. Numerical estimation of the stoppings are performed over a wide specific energy range, i.e., 1 to 104 keV/amu, on the basis of the independent shell model. The oscillatory behavior of the stopping cross sections are also shown with respect to target atomic number. The calculated results are in good agreement with the data.
Analysis of Crystal Binding and Structural Phase Transition in Alkaline‐Earth and Alkali Chalcogenides
Authors: Chaturvedi S. D. , Sharma S. B. , Paliwal P. , Kumar M.
Published: July 2007

An analysis of crystal binding and structural phase transition is presented using an analytical potential form for the overlap repulsive energy derived by Harrison from quantum mechanical considerations. The potential model is applied to calculate the cohesive energies, bulk modulus, and its pressure derivative for fifteen alkaline‐earth chalcogenides and fourteen alkali chalcogenides. Calculated values of bulk modulus are found to exhibit empirical correlationship with unit cell volume. The problem of relative stability and structural phase transition is also investigated for alkaline‐earth chalcogenides. Values of transition pressure are obtained and found to present good agreement with experimental data.
The Influence of Hybridization of the Impurity and the Conduction Bands on the Density of States of Doped Semiconductors
Authors: Radjenovic B. , Tjapkin D.
Published: July 2007

A two‐band model of a doped semiconductor is presented. The model includes both, impurity and conduction bands as well as their hybridization. Hybridization of impurity band with the unperturbed conduction band is discussed in more detail. The density of states of the impurity band of Si:P is calculated using the modified Matsubara‐Toyozawa method on the basis of the suggested two‐zone model. Physical aspects of the results obtained are analyzed as well as possible connections with experimental facts.
Luminescence Decay Times of the Sb3+, Pb2+, and Bi3+ Ions in Alkaline‐Earth Sulfides
Authors: Donker H. , Yamashita N. , Smit W. M. A. , Blasse G.
Published: July 2007

The luminescence decay times of Tl+‐type ions in MgS, CaS, SrS, and BaS are measured as a function of temperature from 4.2 to 150 K. By applying a three‐level model, the energy difference ΔE between the lower excited states 3T1u(3P1) and 3A1u(3P0) and the transition probabilities from the two excited states to the ground state 3A1g(1S0) are derived. The values of the parameters are compared with each other and with those for alkaline‐earth oxides.
Propagation of Gamma‐Radiation through a Resonance Medium with RF Modulated Magnetic Hyperfine Interaction
Authors: Sadykov E. K. , Skvortsov A. I.
Published: July 2007

The influence of the rf perturbation (magnetization reversal) in the magnetically ordered system on its Mössbauer spectrum (MS) is discussed theoretically. Similarly to the traditional MS the behaviour of the time gated MS in this condition is analysed as an extension of the time‐dependent Mössbauer spectroscopy methodology to the magnetization dynamics problem. This problem is discussed on the basis of Blume's theory generalized for time dependent hyperfine interactions. The calculations in the framework of a rotating field model reveal a remarkable distortion in MS at nonresonant radio frequencies. The phenomenon of supression of the nuclear Zeeman structure under rotating rf field is revealed. The time‐dependent effects in MS can be used to understand the high frequency magnetization reversal processes in magnetic materials.
The Intra‐ and Intersublattice Exchange Interactions in RFe12xTx Intermetallics
Authors: Stefański P. , Szlaferek A. , Wrzeciono A.
Published: July 2007

The experimental values of Curie temperatures of RFe12−xTx (R = rare earth, T = V, Ti, Si, Cr) are used to calculate the effective exchange coupling constants in iron sublattice and between rare earth and iron sublattices. A mean field approximation is used. Values of molecular field, Bmol, acting on the rare earth ion are also established. The coupling constant in Fe sublattice is found to be the largest for T = V; JFeFe = 10.14 × 10−22 J. The molecular field has its maximum value for R = Sm in each series of RFe12−xTx compounds.
About the SERS Phenomenon I. The Cross‐Section in Adiabatic Perturbation Theory
Authors: Polubotko A. M.
Published: July 2007

The theory of SERS (surface enhanced Raman scattering) is developed. First the light interaction with molecules is considered. The wave functions of the molecule are received in the first order of the adiabatic perturbation theory. Then the cross‐section of Raman scattering with the dipole and quadrupole light interaction with a molecule taken into account is obtained.
The Parametric X‐Ray Radiation in Case of Three‐Wave Asymmetric Diffraction
Authors: Dubovskaya I. Ya , Savchuk G. K.
Published: July 2007

The spectral and angular distributions of parametric X‐ray radiation from relativistic electrons in the case of three‐wave asymmetric coplanar diffraction are obtained. A detailed numerical calculation of angular and spectral distributions in Si is derived for the case of arbitrary angle of particle incidence on the crystal target surface.
Two‐Photon Spectroscopy of PbMoO4 Single Crystals Indirect Interband Transitions
Authors: Efendiev Sh. , Darvishov N. , Shakhdgan S. , Gavryushin V. , Raciukaitis G. , Puzonas G. , Kazlauskas A.
Published: July 2007

Two‐photon interband absorption spectra are obtained first in PbMoO4 crystals. They are shown to be attributed to indirect two‐photon absorption (TPA) with the assistance of phonons to exciton state formed band transitions with the extrema in different points of the Brillouin zone. The energy parameters of excitons Eexi = 3.56 (80 K) and 3.53 eV (300 K), Ebi = 50 meV, of phonons (65, 180, and 270 meV), and of the interband absorption edge Egi = 3.61 (80 K) and 3.58 eV (300 K) are obtained. Anomalously high efficiency of electron–phonon interaction is found in crystals studied. The phonon energy observed in TPA at indirect transitions is shown to be determined probably by joint participation of several active phonon modes of MoO4−2 tetrahedral group in PbMoO4 crystal.
Free‐Carrier Optical Absorption Induced by Dislocation Scattering Mechanisms in Semiconductors Application to GaAs
Authors: Vignaud D. , Farvacque J. L.
Published: July 2007

The intraband absorption induced by the dislocation scattering mechanisms (charged line potential, piezoelectric potential, and deformation potential) is calculated. These expressions are then used to discuss the possibility to observe the dislocation scattering effect in GaAs: one finds that dislocations are rather weak scattering centres, which is confirmed by measurements.
Simple Model for the Ferroelectric Phase Transition in KTa1−fNbfO3
Authors: Vugmeister B. E. , Antimirova T. V.
Published: July 2007

The concentration dependence of niobium‐induced ferroelectric phase transition temperature Tc(f) in KTa1−fNbfO3 is explained assuming an eight‐well niobium off‐center potential. Single‐ion model and mean‐field theory is used. The best agreement between the theory and experiment is reached with the following values of parameters: barrier height U = 60 K, off‐center displacement x0 = 0.008 nm which are in good agreement with previous experimental results.
Dependence of the Line Strength of f–f Transitions on the Manifold Energy. II. Analysis of Pr3+ in KPrP4O12
Authors: Kornienko A. A. , Kaminskii A. A. , Dunina E. B.
Published: July 2007

To describe the experimental data of the line strength and the oscillator strength of electric dipole transition between manifolds a formula is suggested that takes into account the dependence on the energy of manifolds and the effect of electron correlation. It contains four phenomenological parameters and is applied to describe the experimental data of Pr3+ in KPrP4O12. It is shown that the dependence of the line strength on the energy of manifolds improves essentially the description of 3H4 → 3P2 transition.
Excited Acceptor States in II–VI and III–V Semiconductors
Authors: Said M. , Kanehisa M. A.
Published: July 2007

Higher excited states of acceptors in CdTe, ZnTe, and GaAs are obtained by using the Baldereschi and Lipari spherical model including the cubic correction and the central‐cell effect. This is done by solving the coupled radial equations by the finite‐element method with Arnoldi's algorithm, which gives several (≈ 20) low‐lying states simultaneously. The procedure permits to determine very accurately the host band‐structure parameters. In the case of II–VI compounds, the Luttinger parameters γ1 = 5.30, γ2 = 1.62, γ3 = 2.10 and the dielectric constant ϵ0 = 9.3 for CdTe and, γ1 = 3.80, γ2 = 0.86, γ3 = 1.32 and ϵ0 = 9.4 for ZnTe are obtained. For GaAs, γ1 = 7.20, γ2 = 2.15, γ3 = 3.05, and ϵ0 = 12.49 are obtained.
On the Representation of Orientation Distributions in Texture Analysis by σ‐Sections. II. Consideration of Crystal and Sample Symmetry, Examples
Authors: Matthies S. , Helming K. , Kunze K.
Published: July 2007

In this second paper on σ‐sections for representation of orientation distributions in texture analysis the results of the first one are generalized by the consequences of all crystal and sample symmetries of practical interest. The connections of σ‐sections with pole figures and inverse pole figures are given. the analytical results of both the papers are demonstrated by examples.
Bisoliton in Constant Magnetic Field
Authors: Brizhik L. S.
Published: July 2007

The dynamics of a bisoliton in three‐dimensional strongly anisotropic crystals with identified soft one‐dimensional chains, is studied in the presence of weak magnetic fields. Cyclotron mass and frequency of a bisoliton in a magnetic field are calculated.
The Electronic Structure of Copper Oxide Crystalline Compounds. II. Chemical Bonding in Copper–Oxygen Crystals
Authors: Evarestov R. A. , Veryazov V. A.
Published: July 2007

The crystalline structure of copper‐oxygen compounds with copper atom in the oxidation states I, II, and III is reviewed. A calculation is made of the electronic structure of the row of crystals with copper‐oxygen bonding. It is shown that the covalence effects are essential for copper oxide compounds containing copper atoms in oxydation states CuII and CuIII LUC‐CNDO calculations of La2CuO4 and YBa2Cu3Ox (x = 6,7) crystals are made. It is concluded that the higher copper valency is favourable for superconductivity.
Thermal Conductivity and Thermoelectric Figure of Merit of Thin Antimony Films
Authors: Völklein F. , Kessler E.
Published: July 2007

The thermal conductivity λ and thermoelectric figure of merit z of Sb films with thicknesses from 27 to 230 nm are measured in the temperature range 80 to 400 K. The lattice thermal conductivity λφ is determined from the measured total thermal conductivity λ and the calculated charge carrier contribution λe. The results are discussed in the framework of a two‐band model for the charge carriers and of a grain boundary and surface scattering model for phonons. The transport properties of isotropic and texturized films are compared.
Pulse Propagation and Carrier Kinetics in Laser Excited Semiconductors
Authors: Schäfer W. , Henneberger K.
Published: July 2007

Propagation of an intense ultrafast pulse (100 fs) of Gaussian shape with its central frequency above band gap in a GaAs halfspace is investigated theoretically. Nonequilibrium occupation of one particle states, memory effects in the polarization, Coulomb interaction, LO‐phonon Scattering, and spatial inhomogeneities, i. e. the deformation of the pulse shape are taken into account in a strict microscopic approach. The numerical analysis allows to follow the various mechanisms involved on a fs‐time scale, e. g. (1) saturation, spectral hole burning, and relaxation of the one particle distribution, (2) memory effects, dephasing processes, and Coulomb‐enhancement of the polarization and (3) the interplay between that during pulse propagation. The resulting behaviour cannot be simulated by phenomenologically introduced dampings and/or relaxations, thus underlining the importance of accounting for the above mentioned effects in a microscopic way.
Time‐Resolved Four‐Wave Mixing Experiments in CuCl
Authors: Gomes M. J. M. , Kippelen B. , Levy R. , Grun J. B. , Hönerlage B.
Published: July 2007

By a light‐induced grating technique with three degenerate laser beams, the diffusion constants and the decay times of optical nonlinearities in CuCl are determined. By comparison with results from induced absorption, the nonlinearities may be identified as being due to different excitonic populations as well as to thermal effects.
Excitons and Phonons in CdTe/MnTc and ZnTe/MnTc Single Quantum Wells. Aspects of Confinement and Optical Phonon Coupling
Authors: Nurmikko A. V. , Gunshor R. L.
Published: July 2007

With the incorporation of wide gap cubic zineblende MnTe, a range of optical studies are carried out on single quantum wells of ZnTe/MnTe and CdTe/MnTe. By using thin MnTe barrier layers the highly strained structures appear to be nearly pseudomorphic and show evidence for good electron hole confinement. This has provided a means to examine the exciton‐LO‐phonon coupling through different indicators.
Carrier‐Induced Pulse Narrowing in Indium‐Doped CdS
Authors: Hönig T. , Gutowski J. , Broser I.
Published: July 2007

Strong optical nonlinearities and bistability in the band‐gap region are known to occur in CdS doped with indium by 1016 to 1018 cm−3, which are due to the neutralization of ionized acceptors. In time‐resolved single‐beam measurements an absorptive effect becomes dominant for excitation densities higher than 1 MW/cm2 in addition to the known induced transmission. The combination of both processes yields a narrowing of the shape of the transmitted pulse. This phenomenon is studied in dependence of the laser wavelength, intensity, and polarization, as well as on the temperature and the dopant concentration. The experimental results can be understood in a model of interaction of free carriers with photonic polaritons.
Electron–Hole Plasma in Cross‐Over‐Near Ga(As, P)
Authors: Fieseler H. , Schwabe R. , Staehli J. L.
Published: July 2007

The spontaneous emission spectrum of an electron–hole plasma (EHP) in direct‐gap Ga(As, P) near the Γ‐X cross‐over is investigated as a function of the excited electron–hole pair density. Special attention is paid to a multicomponent EHP, i. e. to the case of an additional occupation of the conduction band X valleys. The EHP luminescence bands and the excitation induced band gap shrinkage are calculated in random phase approximation (RPA). The theoretical results for the reduction of the band gaps are compared with data obtained from luminescence experiments. The EHP luminescence is investigated at T = 2 K on high‐purity direct‐gap GaAs0.55P0.45 islands using an intense band‐edge resonant dye‐laser excitation.
Dissipation of Excitonic Polaritons in CdS
Authors: Pantke K.‐H. , Over H. , Broser I.
Published: July 2007

Experiments are discussed wherein scattering of excitonic polaritons with acoustic phonons between different polariton modes can be observed. Information about this dissipation process is given by the luminescence of deep impurities acting as microscopic detectors within the crystal which are sensitive to the distribution of energy to the different polariton branches. The calculated intensity for an ensemble of ideal micro‐detectors containing constant quantum yield and absorption probability agrees excellently with measurements.
Instrinsic and Impurity‐Related Point Defects in Amorphous Silica. A Spectroscopic Study
Authors: Pio F. , Guzzi M. , Spinolo G. , Martini M.
Published: July 2007

Absorption, photoluminescence emission, and excitation measurements of “as grown” and neutron irradiated amorphous silica characterized by different impurity and OH content, confirm the composite nature of the ≈ 5.1 eV (B2) absorption band and make it possible to distinguish between structural defects and impurity‐related centers. A detailed analysis of the published results on the subject shows that none of the up to date existing models fully accounts for the complex of the experimental observations. A new scheme is proposed in which all the available data find a consistent collocation. It is suggested that two structurally different centers, with optical absorptions in the B2 region, can be simultaneously present in amorphous SiO2; they exist in two variants: bare defect (also produced by neutron irradiation) or impurity‐perturbed center. Some proposals for a deeper understanding of absorption and photoluminescence in glassy SiO2 are finally advanced.
Chemical Trends in the Formation and Binding Energy of Native Defects in III‐V Semiconductors
Authors: Gu Y. M. , Fritsche L. , Christensen N. E.
Published: July 2007

Chemical trends are reported in the formation and binding energy of mono‐ and divacancies in nine III‐V semiconductors. In addition, results are given on self‐interstitial energies. The calculations are carried out within the density functional theory. In self‐consistently solving the scalar‐relativistically extended Kohn‐Sham equations for defect‐specified supercells, Andersen's LMTO‐method is used and the atomic sphere approximation (ASA). The exchange‐correlation energy per particle and the associated one‐particle potential is assumed to have the local spin density form suggested by von Barth and Hedin.
The High‐Frequency Quantum Size Effect in the Impedance of Metal Films
Authors: Zakharov S. P. , Ustinov V. V.
Published: July 2007

A novel high frequency quantum size effect in the surface impedance of metal films under quantum anomalous skin effect conditions is predicted. The suppression of the Landau damping by the size quantization leads to reconstruction of the skin layer and to specific magnetic field dependence of the impedance near the cyclotron resonance conditions.
On Conditions of Spectroscopic Manifestation of the Dynamical Jahn‐Teller Effect
Authors: Fugol I. Ya. , Ratner A. M. , Yurtaeva E. M.
Published: July 2007

Impurity level splitting in a crystal due to the lowering of the lattice symmetry under its vibrations is considered. Since the interaction of low‐symmetry vibrations with the optical center is generally weaker than that of the full‐symmetry one which makes the optical lines broader, the dynamic level splitting is masked by the broadening. The dynamic splitting manifests itself by a mechanism which promotes weakening in the interaction of the optical center with the full‐symmetry vibration rather than with the low‐symmetry ones. In the case of rare‐gas crystals with atomic impurities such a mechanism is associated with the compensation of contributions of repulsive forces and the Van der Waals attraction to the line brodening. The degree of compensation correlates with that of spectral separation of the splitting components in experimental absorption spectra.
A Generalized Ballistic Aggregation Model for the Simulation of Thin Film Growth with Special Consideration of Nodular Growth
Authors: Müller‐Pfeiffer S. , Anklam H.‐J. , Haubenreisser W.
Published: July 2007

Starting from the well‐known idea of atomic shadowing during growth (i. e. ballistic aggregation) a computer model is developed which includes surface relaxation by thermally induced surface diffusion, desorption, angular distribution of the oncoming atoms, and atomic attraction as well for one‐and two‐ (or more‐) component systems. This enables to consider such deposition parameters as substrate temperature, energy of oncoming particles, deposition geometry, and inert gas pressure. The model is applied to investigate the influence of various deposition parameters on the morphology of thin films, especially on the structure of nodular defects.
The Influence of the Size Quantization on the Cyclotron Effective Mass and the Density of States in Bi Films
Authors: Zaluzny M.
Published: July 2007

The influence of the size quantization on the cyclotron effective mass and the density of states at the Fermi level in Bi films with normal along the trigonal axis is discussed. Calculations are performed in the framework of the Cohen non‐ellipsoidal non‐parabolic model. A comparison with the results obtained in the framework of the ellipsoidal non‐parabolic model is given. A critical discussion of the results reported by Mustafaev and Shakhtakhtinskii is also given.
Interpretation of the Group‐Theoretically Unexpected Shape of the Contour Appearing in the Experimental LCW Data for Si and Ge
Authors: Aourag H. , Khelifa B. , Belaidi A. , Kobayasi T.
Published: July 2007

The discrepancies between the measured and the calculated LCW folding distribution in silicon and germanium are discussed on the basis of symmetry considerations.
Charge Ordering of Multielectronic Clusters in Mixed‐Valence Molecular Crystals
Authors: Klokishner S. I. , Koryachenko A. V. , Tsukerblat B. S.
Published: July 2007

Mixed valence molecular crystals consisting of multielectronic clusters of transition metal ions of the type of d2–d3 are considered. A theory of charge ordering in these crystals is developed. The conditions for the occurence of one, two, or three phase transitions are eludicated. The peculiarities of the temperature behaviour of the magnetic moment are investigated.
Determination of the Effective Absorption Cross‐Section of F‐Centres in KBr—In by Photostimulated Luminescence
Authors: Kalniņš A. , Pļaviņa I. , Popov A. I. , Tāle A.
Published: July 2007

Using photostimulated luminescence of F, In2+ defect pairs in KBr‐In are proposed to be a very sensitive method for the determination of the effective absorption cross‐section of F‐centres. It is shown that the effective absorption cross‐section of F‐centres equals to 2.0 × 10−16 cm2. Some criteria for the applicability of this method are analysed.
Investigation of the Thermodynamic Properties of Anharmonic Crystals by the Momentum Method. II. Comparison of Calculations with Experiments for Inert Gas Crystals
Authors: Tang Nguyen , Van Hung Vu
Published: July 2007

On the basis of results obtained in a previous paper by the moment method the thermodynamic quantities of the inert gas crystals are calculated. The obtained results are compared with the experimental data and with the ones of other authors.
Size Changes of Lattice Parameters in Ultradisperse Diamond and Silicon
Authors: Gamarnik M. Ya.
Published: July 2007

A relative increase of the lattice parameters equal to 2.05 × 10−3 ± 1.8 × 10−4 is established by X‐ray analysis in ultradisperse powder diamond with average size of crystallites equal to 4.6 ± 0.4 nm as compared with the lattice parameter of a large‐crystal sample. The effect found for diamond as well as the experimental data of the increase of the lattice parameters in ultradisperse samples of silicon established previously are explained by the size change of intracrystalline pressure stipulated by the interaction of the excess negative charges arranged on the bond lines CC (or SiSi), and the positive cores of the atoms of the covalent crystal. The size dependences of the relative change of the lattice parameters are calculated in the frameworks of the point model of the charge lattice for diamond and silicon. The dependences show a monotonous increase of the lattice parameters when decreasing the sizes of the crystals. Calculated dependences are in good agreement with experimental data.
Electron and Positron Distributions in Grey Tin
Authors: Aourag H. , Soudini B. , Khelifa B. , Belaidi A.
Published: July 2007

Electron and positron charge densities are calculated as a function of position in the unit cell for grey tin,α‐Sn. Wavefunctions are used derived from pseudopotential band structure calculations and the independent particle approximation (IPM), respectively, for the electrons and positrons. Detailed plots of the distributions are along the 〈111〉 (the bond axis). Electron and electron‐positron momentum densities are calculated for (001, 110) plane. The results are used to analyze the positron effect in α‐Sn.
Electronic Structure and Charge State of Oxygen Vacancies in Perfect ZrO2 Crystals
Authors: Sobolev A. B. , Varaksin A. N. , Keda O. A. , Khaimenov A. P.
Published: July 2007

Calculations are given for clusters, modeling the electronic structure of the oxygen vacancies in ZrO2 crystals by means of the self‐consistent scattered waves method. The crystalline cluster model is used for the description of the properties of a perfect crystal, while the properties of a defect are described by the embedded cluster model. Forming of vacancies in a ZrO2 perfect crystal is shown to result in trapping of one or two electrons on a vacancy and forming of F+‐ and F‐centers with local states in the perfect crystal energy gap. The characteristics obtained of the electronic structure of F+‐ and F‐centers are in satisfactory accord with the known experimental data.
Two‐Dimensional Character of Electron Gas in Layered InSe Crystals
Authors: Dmitriev A. I. , Kovalyuk Z. D. , Lazorenko V. I. , Lashkarev G. V.
Published: July 2007

An analysis of investigation results of kinetic, galvanomagnetic, and quantum oscillation properties in the range of 4.3 to 300 K permits to construct a phenomenological spatial energy model of the spectrum of the layered semiconductor InSe, pure and intercalated by metal atoms. The dynamics of the temperature variations of the character of kinetic phenomena is suggested. The model suggested serves to prove in experiment and to explain the two‐dimensional character of the current carrier gas in the range of low temperatures as well as the peculiarities of the temperature dependence of transversal and longitudinal specific resistance, magnetoresistance, oscillation, and resonance phenomena in the range of 4.3 to 300 K. An analogy is drawn between the band structure of a single crystal of the layered semiconductors InSe and semiconductor superlattices.
Model Calculation of the Dislocation Resistivity for Copper
Authors: Diallo A. O. Donghol , Mrosan E. , Ziesche P.
Published: July 2007

Starting from a cylindrically symmetric scattering potential as a model for the dislocation core and the strain field in the vicinity of the core the specific dislocation resistivity for copper is calculated within the free electron model. Several model potentials are considered. The results are compared with experimental values.
Temperature Dependence of the EPR Spectra of GdBa2Cu3O7−δ Compounds in Orthorhombic and Tetragonal Phases
Authors: Guskos N. , Triberis G. P. , Calamiotou M. , Trikalinos Ch. , Koufoudakis A. , Mitros C. , Gamari‐Seale H. , Niarchos D.
Published: July 2007

EPR measurements are presented for two samples of GdBa2Cu3O7−δ of which one is superconducting (orthorhombic phase) and one is nonsuperconducting (tetragonal phase). For the superconducting sample signal associated with Cu2+ and Gd3+ ions are detected above and below Tc (with gGd = 1.999 (2)). The sample with oxygen deficiency gives an EPR signal with a strong temperature dependence up to 30 K coming from Gd3+ ions in GdBa2Cu3O7−δ, with g = 2.063 (3). These characteristics can be ascribed to the semiconducting properties of the tetragonal phase of GdBa2Cu3O7−δ. Below T = 30 K, the sample with tetragonal structure gives an additional EPR line associated with Cu2+ ‐Cu2+ ion pairs. The intensity of the EPR signal strongly depends on the temperature.
Effect of Magnetic Phase Transition on the Electronic Specific Heat Coefficient of Lu(Co1−xAlx)2
Authors: Wada H. , Inoue T. , Hada M. , Shiga M. , Nakamura Y.
Published: July 2007

The low temperature specific heat of Lu (Co1−xAlx)2 is measured between 1.4 and 6.5 K. The electronic specific heat coefficient, γ, is enhanced around the critical concentration for the onset of ferromagnetism, while it is sharply reduced in a ferromagnetic region with a substantial moment. The results are discussed in relation with the magnetism in this system.