bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear Optical Properties of the System CdS1−xSex
Authors: Swoboda H.‐E. , Majumder F. A. , Renner R. , Weber C. , Sence M. , Jie Lu , Noll G. , Göbel E. O. , Vaitkus J. , Klingshirn C.
Published: July 2007

The influence of localization on the nonlinear optical properties of CdS1−xSex is investigated for 0 ≦ x ≦ 1 in the temperature range from 5 to 300 K. Results from time‐integrated and time‐resolved luminescence, from pump‐ and probebeam experiments, and from measurements using laser‐induced gratings are given. From all investigations likewise free and “localized” excitons are found in the mixed crystals at temperatures below 60 K, with a spectrally rather broad transition region. The mobility of the “localized” excitons is non‐zero but is decreased by more than a factor three with respect to free excitons. Above 60 K, the optical properties approach those of the pure compounds and are dominated by the formation of an electron–hole plasma at high excitation intensities. This process reflects a delocalization of the excited electron–hole pairs due to thermal re‐excitation from “localized” into extended states.
Quantum‐Statistical Investigation on the Nonlinear Optical Oscillation in Amorphous Semiconductor GeSe2 Films
Authors: Xu Lun‐Biao , Cai Shou‐Fu , Xie Guo‐Xin
Published: July 2007

With the quantum‐statistical three‐level cascade Jaynes‐Cummings model, the relationship between the nonlinear optical oscillation phenomena in amorphous vacuum evaporated GeSe2 films and the dynamical correlation of the high‐dense defects are investigated. The collective behaviour of the system shows that the interaction between the incident photon fields and the three defect levels really causes the transmittance oscillating, which was reported recently by Hajto. The calculated results concide with the experiments very well. Also some experimental phenomena are analysed to show the origin in physical mechanism and some interesting possibilities for practices are discussed.
Optical Nonlinearity and Bistability in the Bound Exciton Energy Range of CdS
Authors: Hönig T. , Gutowski J.
Published: July 2007

Under high excitation conditions thick CdS samples show pronounced broad‐band nonlinear transmission in the bound exciton region and up to a wavelength of about 515 nm at cryo‐temperatures. This behavior is only explainable in a model based on impurity neutralization and bound exciton creation. The suitability of these nonlinearities to yield optical bistability will be shown. Bistable operation is investigated in dependence of crystal thickness, impurity concentration, excitation density, wavelength, and temperature. A strong correlation to acceptor‐bound exciton generation is obtained, and the explanation of this bistable operation fits well with that of the above mentioned transmission behavior.
Analysis of Stress Relaxation and Creep Curves for a Log‐Normal Distribution of Relaxation Times
Authors: Povolo F. , Hermida Elida B.
Published: July 2007

A procedure to determine the characteristic parameters of a log‐normal distribution of relaxation times, both for stress relaxation and creep tests, is presented. The method is based on the use of either the normalized stress relaxation or creep functions and their first derivatives. Furthermore, the limiting stress or strain can be obtained directly from the experimental data. Finally, the procedure developed is applied to actual stress relaxation curves reported for aluminum and polysulphide rubber and the results are compared with those obtained by approximate methods, based on the use of the error function.
Optical Theorem in Ultra‐Thin Film Electrodynamics
Authors: Khudik B. I. , Lozovskii V. Z. , Zhuravlev A. F.
Published: July 2007

The optical theorem in the ultra‐thin film electrodynamics is formulated. The coefficients of reflection are calculated in different cases of the incident electromagnetic wave polarization. The generalized response function of the film which is calculated in previous works, satisfies the optical theorem for the ultra‐thin films.
Binding Energy of Two‐Dimensional Excitons in Strong Magnetic Fields
Authors: Marasas R. , Spector H. N.
Published: July 2007

Because of current interest in the behavior of excitons in semiconducting quantum well systems in the presence of strong magnetic fields, variational calculations are performed of the exciton binding energy as a function of the magnetic field using two types of variational wave functions, a hydrogenic wave function which corresponds to the exact wave function in the limit of low magnetic fields and a Gaussian wave function which corresponds to the exact wave function in the limit of high magnetic fields. In the low and high field limits, the results correspond to those obtained by others using perturbation and WKB approximations. However, the variational results enable us to bridge the region of intermediate magnetic fields for which the previous approximation methods are not valid and to determine the region of validity of these approximation methods. Also calculated are the oscillator strength for 2D excitons as a function of magnetic field to determine the intensity of the exciton peak as a function of the field.
Band Corepresentations of Magnetic Space Groups
Authors: Evarestov R. A. , Smirnov V. P. , Egorov S. A.
Published: July 2007

The band corepresentations of the magnetic space groups are introduced; the procedure of their generation is considered. The band corepresentations are essential for the symmetry analysis of phonons and magnons in magnetic crystals and for the study of the magnon‐phonon hybridization. The magnetic structures of CuFeS2 and La2CuO4 crystals are analyzed. In the antiferromagnetic phase these crystals are described by Shubnikov space groups of different types. The band corepresentations for each of these groups are tabulated.
EPR Study of the Antiferromagnetic Phase Transition in (Cd, Mn)S
Authors: Goede O. , Backs D. , Heimbrodt W. , Kanis M.
Published: July 2007

The antiferromagnetic phase transition of octahedrally coordinated (Cd. Mn)S single crystals with Mn concentrations 0.8 ≦ xMn ≦ 1 is studied by EPR measurements in the temperature range 80 to 550 K. The width of the Mn2+ EPR line is found to increase with decreasing temperature nearly proportional to (T ‐ TN)s−1 due to a corresponding decrease of the spin‐spin relaxation time. The Néel temperature TN for the transition from the paramagnetic into the (disordered) antiferromagnetic phase being determined from the linewidth divergence decreases strongly with decreasing xMn. The results are discussed in connection with actual EPR investigations of (Cd, Mn) and (Zn, Mn) chalcogenide mixed crystals with zincblende/wurtzite structure for lower Mn concentrations. The EPR signal below TN being observed in the case of polycrystalline thin films or powder samples is ascribed to surface near regions of the microcrystals.
Effect of a Random Potential on the Resonant One‐LO‐Phonon Raman Process
Authors: Klochikhin A. A. , Ogloblin S. G.
Published: July 2007

The effect is considered of Gaussian white noise potential on the one‐longitudinal‐optical (LO)‐phonon assisted Raman or photoluminescence process following the resonant excitation. The theory is based on the multiple scattering description of the excitonic state in a random potential. The Lipatov‐Brezin‐Parisi approach is extended into the multistep probability evaluation. It is shown that the joint analysis of the LO‐phonon assisted processes and the excitonic spectral density data gives new information on the exciton lifetime in the region of its localized states as well as at the positive energies where the exciton is almost free.
Monovacancy Formation Energies in Cubic Crystals
Authors: Krause U. , Kuska J. P. , Wedell R.
Published: July 2007

Using the conception of an extended object (Umezawa et al.) based on the continuum theory of elasticity, monovacancy formation energies are calculated. Anisotropy is included for cubic symmetry by means of a first order approximation to the Green's function tensor and some tensor algebraic calculations. The last considerations contribute to a better understanding of the meaning of “Voigt's average isotropic elastic constants”. Further lattice structure effects are taken into account by a common parameter for every type of structure. A comparison with experimental data or results from other theories shows either satisfactory agreement or the inconsistency of the first order approximation to the anisotropy for some materials with common properties.
The Correction Term and Core Dislocations in the Frame of the Generalized Callaway Integral
Authors: Awad A. H. , Saif J. S.
Published: July 2007

Considering four types of scattering mechanisms, viz. boundary scattering, core dislocation scattering, point defect scattering, and three phonon scattering, analytical expressions for the correction term are obtained in the low temperature approximation on the basis of the generalized Callaway integral. The expressions show that the correction term is proportional to the product of the three phonon normal process scattering strength and the square of the boundary scattering relaxation time.
Higher‐Order Terms in the Homogenized Stress‐Strain Relation of Periodic Elastic Media
Authors: Gambin B. , Kröner E.
Published: July 2007

Applying the method of two‐scale asymptotic expansions to the displacement field in periodic elastic structures the completed macroscopic stress‐strain relation of such media is derived. This relation contains beside the usually considered local part also weakly nonlocal contributions in the form of strain gradients up to infinite order. Formulae for the determination of the pertaining homogenized material tensors are derived.
Atomic and Solid State Effects in X‐Ray Absorption Spectra of Ionic Crystals
Authors: Gegsin I. I. , Datsyuk V. N. , Yumatoff A. D. , Vedrinskii R. V.
Published: July 2007

A new method for XANES calculations is offered. It allows to take into account simultaneously band structure effects as well as the core‐hole potential. The predicted K‐spectra of various ionic crystals agree well with the experimental ones. It is argued that the observed spectra correspond as a rule to the local partial densities of states of the nonperturbed crystal potential. Some of the new narrow peaks in the near‐edge region are due to electron transitions to resonance or bound‐electron states. These states are formed as a consequence of the hole potential, but exhibit essentially multicenter properties.
Two‐Photon Absorption via Deep Local Levels as Virtual Intermediate States in Semiconductors
Authors: Baltramiejūnas R. , Gavryushin V. , Račiukaitis G. , Kubertavičus V. , Kazlauskas A.
Published: July 2007

The enhancement of the coherent nonlinear losses are observed in ZnO and ZnSe crystals within the whole range of the interband two‐photon absorption (TPA) spectra. The effect is explained theoretically in terms of nonresonant participation of the deep local levels (DL) of impurities and native defects in the forbidden gap as additional intermediate virtual states of TPA. Calculations of interband TPA via DL including the influence of the momentum indeterminacy in local states are presented. The role of spatial interference of virtual contributions of the localized intermediate states in the momentum conservation is revealed. The possibility of the technological control of the additional nonlinearities is shown experimentally. The place of these phenomena among the widely investigated processes of coherent TPA via band states and the incoherent two‐step absorption through DL are discussed.
Stimulated Brillouin Scattering in Doped Centrosymmetric Semiconductors
Authors: Aghamkar P. , Sen P. K.
Published: July 2007

Based upon the electromagnetic treatment, stimulated Brillouin scattering (SBS) in nearly centrosymmetric doped semiconductors is investigated analytically. The origin of the nonlinear interaction is considered to be in the third‐order optical susceptibility arising due to the nonlinearly induced current density and finite electrostriction of the medium. The threshold conditions are obtained for the onset of SBS as well as the effective Brillouin susceptibility and the resulting gain constant for both, lightly and heavily doped semiconductors. The numerical estimations are made for n‐type InSb crystals at 77 K duly shined by a pulsed 10.6 μm CO2 laser. In highly doped n‐InSb, the gain constant is significantly enhanced under high power pulsed excitation below the damage threshold. The analysis establishes the possibility of occurrence of optical phase conjugation via SBS in doped semiconductors.
Theoretical study of the Raman spectrum in a‐Si1−xNx: H Films
Authors: Yu Gong , Chen Guanghua , Zhang Fangqing
Published: July 2007

The vibrational excitations in a‐Si1−xNx: H films are calculated in terms of a simplified amorphous cluster. The main vibrational modes as well as correlative frequencies and intensities are obtained. By means of a random substitution of nitrogen atoms for silicon atoms the phonon density of states at different x values are deduced. It can be found that the results are in accord with the experimental Raman spectra.
Study of electron distribution in rhodium by compton scattering technique
Authors: Mohammad F. M. , Sharma B. K. , Singh H. , Ahuja B. L.
Published: July 2007

The results of a Compton scattering study on polycrystalline rhodium are presented. The measurements are carried out using 59.54 keV γ‐rays on a sample of 0.13 mm thickness. The renormalised‐free‐atom approach is applied to calculate the spherically averaged Compton profile for Rh for various 4d‐5s electronic configurations. Best agreement between measured and calculated values is found for the 4d85s1 electron configuration. These results are also compared with the recent band structure calculation for electron momentum distribution in Rh.
Ising ferromagnet with biquadratic exchange interaction of negative sign
Authors: Iwashita T. , Uryû N.
Published: July 2007

For Ising ferromagnets with S = 1, S = 3/2, and S = 2, the magnetization 〈Sz〉 is calculated using the pair model approximation. Assuming bilinear exchange interaction J and biquadratic exchange interaction J′ of negative sign between nearest‐neighbour pair of spins, the behaviour of 〈Sz〉 as a function of these exchange parameters are investigated for the Ising spin systems. At low temperatures, an anomalous behaviour of the temperature dependence of 〈Sz〉 is obtained. With regard to these anomalous behaviours, the ground state spin structure is discussed for the Ising ferromagnet with J′ of negative sign.
Free‐carrier absorption for intervalley phonon scattering
Authors: Gashimzade F. M. , Tagirov E. V.
Published: July 2007

The frequency dependence of the free‐carrier absorption coefficient in multivalley semiconductors is calculated for intervalley deformation potential scattering between parabolic M0 and saddle M1 points. The methods of group theory are used to summarize the contributions of all the equivalent valleys to the absorption coefficient for crystals of arbitrary symmetry.
Colour centres in barium hexaaluminate (Phase I). Study by electron paramagnetic resonance, optical absorption, and thermally stimulated luminescence
Authors: Gourier D. , Gbehi T. , Visocekas R. , Thery J. , Vivien D.
Published: July 2007

Colour centres produced by X‐ray irradiation of barium hexaaluminate (phase I) with β‐alumina structure are studied by electron paramagnetic resonance, optical absorption, and thermally stimulated luminescence. It is shown that in addition to the F+ centres characteristic of β‐alumina phases, this compound presents other colour centres such as F, O−, and possibly V‐type centres. The stability of these defects is investigated by means of thermal bleaching experiments and thermally stimulated luminescence. An alternative model to the generally accepted one is proposed, for the F+ centres, together with a mechanism of defect formation.
Weak localization effects in n‐type inversion layers of InSb grain boundaries under high hydrostatie pressure
Authors: Kraak W. , Trott S. , Herrmann R.
Published: July 2007

Measurements of the low‐field magnetoresistance are reported for an n‐type inversion layer adjacent to the grain boundary in InSb bierystals. At high pressures (ρ > 4 × 102 MPa), under the conditions that only one electric subband is populated, a strong negative magnetoresistance appears. From the observed experimental data it is concluded that weak localization effects play an important role in the electronic transport properties of the grain boundary interface. Some characteristic scattering parameters of this two‐dimensional disordered system are determined.
Atomic forces in the self‐consistent tight‐binding model
Authors: Kohyama M. , Yamamoto R. , Ebata Y. , Kinoshita M.
Published: July 2007

The self‐consistent tight‐binding (SCTB) model for structural and electronic properties of solids, which can treat both ionicity and covalency on an equal footing, is re‐formulated so as to be applicable to general and disordered systems and is analyzed in comparison with the tight‐binding bond (TBB) model. It is shown that atomic forces in the SCTB model are given very simply as well as in other tight‐binding type theories. Atomic forces consist of three types of contributions, which are those from the interatomic Coulomb interaction, from the covalent energy, and from the overlap repulsion. By using the present formulation, it is possible to calculate quantum‐mechanically the structural and electronic properties of extended defects or disordered systems of sp‐bondod materials with both the properties, ionicity and covalency, which have not yet been treated enough theoretically or quantitatively.
New off‐centre system. Jahn‐Teller mercury‐like impurities in alkali halides
Authors: Liidja G. , Nagirnyi V. , Soovik T. , Zazubovich S.
Published: July 2007

Two slow decay components are found in the low‐temperature decay kinetics of the AT emission of Ga+ and In+ centres in alkali halides. The emission, excitation, and polarization spectra of these components as well as the temperature dependences of their decay times and light sums and the influence of the electric and magnetic fields on the decay kinetics of the polarized AT emission are carefully investigated. It is shown that the observed effects are caused by an off‐centre position of Ga+ and In+ ions in the triplet relaxed excited state (RES). The off‐centre displacement occurs most probably in one of the 〈100〉 directions perpendicular to the tetragonal Jahn‐Teller distortion axis. Rapid tunnelling transitions between various energetically equivalent off‐centre positions of the impurity ion lead to the tunnel splitting of each metastable tetragonal (T) minimum of the triplet RES. Both the observed slow decay components of the AT emission are connected with the radiative decay of the two lower states. The orthorhombic structure of the AT RES, found by the technique of optical detection of electron spin resonance (OD ESR) several years ago for Ga+ centres in some alkali halides, is explained here as another evidence of the same phenomenon.
On kink dynamics in media with increasing absorption optical bistability
Authors: Kiselev V. G.
Published: July 2007

The motion of the boundary between dark and light domains in a crystal with increasing absorption‐optical bistability (the so‐called kink) is considered. In the low diffusion limit the kink moves undergoing effective viscous friction which essentially affects the output intensity. The crystal boundary influence on the kink is substantial if the diffusion is sufficiently high. No jumping kink motion resulting in a sawtooth structure of the output intensity can take place in a pure crystal unless a compound material consisting of isolated semiconductor crystals is used.
Parametric amplification in magnetised piezoelectric semiconducting plasmas
Authors: Neogi A. , Ghosh S.
Published: July 2007

Assuming that the origin of the nonlinear interaction lies in the second‐order optical susceptibility χ(2) arising from the nonlinear induced current density, and using the straightforward coupled mode theory, the parametric amplification is analytically investigated in a magnetised piezoelectric semiconducting plasma. The threshold value of the pump electric field Eoth and the corresponding excitation intensities are obtained. Eoth is found to decrease with rising magnetic field. The investigation also reveals that the phenomena of self‐focusing and self‐defocusing can be enhanced in these crystals. The parametric gain constant is obtained. Numerical estimations are made for an n‐InSb crystal, at 77 K duly irradiated by frequency doubled pulsed 10.6 μm CO2 lasers. It is found that the presence of a magnetostatic field enhances the gain constant.
Theoretical INDO Investigation of the Electronic Structure of Aluminium Clusters
Authors: Fantucci P. , Pacchioni G.
Published: July 2007

A modified version of the semiempirical INDO method is developed and applied to the study of the electronic properties of Al clusters. The method is able to reproduce in a satisfactory manner the basic features of low‐nuclearity Al clusters as determined by ab initio calculations and can be considered reliable for the study of larger aggregates. In addition, the method can be adopted in a preliminary search of the geometry–energy hypersurface in order to select a few “probable” topologies to be investigated in more detail with rigorous quantum chemical approaches.
Photoconductivity of Polycrystalline Thionaphtenindol
Authors: Signerski R. , Kalinowski J. , di Marco P. , Giro G.
Published: July 2007

A systematic study of steady‐state photoconductivity within the first absorption band of polycrystalline thionaphtenindol (TNI) is made and the results are discussed in terms of charge generation and charge transport processes. Though the mechanism of photoconductivity is determined mainly from analysis of light intensity characteristics of photocurrent and their dependence on the applied voltage in the system Al/TNI/Al/g (glass), other experimental data such as action spectra, photoenhancement of the current injected from Au electrodes, or magnetic field effect on photocurrent are consistent with the inferred physical picture of the phenomenon: singlet exciton dissociation on near‐electrode defects produces electron–hole pairs, the holes being injected into the bulk of the sample. The concentration of holes in the first‐charge generation region stands for a boundary condition for their injection into the second‐charge transport region. An asymmetry in photocurrent behaviour observed when the substrate or non‐substrate electrode is illuminated can also be explained by these mechanisms.
Screening of the Coulomb Potential in the Athermal Stage in Highly Excited Semiconductors
Authors: Heiner E.
Published: July 2007

Equations for the reduced density operator are evaluated. Investigating the subdynamics of nonrelevant observables a resolvent formulation is obtained selfconsistently for the screening part of the evolution superoperator. Utilizing the diagonal representation for the time‐dependent mean field term of the Hamiltonian, a selfconsistent concrete calculation of the screened potential is possible in the high density limit of the nonequilibrium. The result is an extension of the well known RPA‐formula for nonequilibrium two‐band systems of Fermions. An extension to the semimarkovian approximation is counted for.
Planar Channeling of Electrons and Positrons in Crystals. Local‐Density Calculation of Planar Averaged Potential and Channeling Radiation Spectrum
Authors: Satpathy S. , Pathak A. P.
Published: July 2007

Results of calculation of channeling potentials in crystals using the local density theory are given. The linear muffin‐tin orbitals method is used in the atomic spheres approximation (LMTO‐ASA) to calculate the planar‐averaged potential seen by MeV electrons and positrons channeled along (110) planes of diamond, Si, and Ge. The calculations thus include the spherical charge relaxation effects (“solid state effects”) in the solid but omits the non‐spherical part. The calculated potentials are in excellent agreement with the empirical potentials derived from channeling radiation experiments, but are significantly different near the atomic planes from the potentials obtained from superposition of the atomic Thomas‐Fermi statistical (Molière) potentials. Agreement of the potentials with the ones obtained from superposition of atomic Doyle‐Turner potentials is reasonably good. Frequencies of emitted radiation from the channeled electrons and positrons are also calculated and compared to experiments. For the crystals considered, it is concluded that the solid state effects on the planar‐averaged potential are moderate to small. It is expected that these effects should be more important for channeling in ionic solids. The deviation of the observed positron channeling radiation from the calculated values for Si and C indicates that the non‐spherical part of the charge relaxation might be relatively important for these solids.
Physical Properties of Fractals. Mössbauer Recoilless Fraction, Raman Scattering, and Spin‐Lattice Relaxation
Authors: Shrivastava K. N.
Published: July 2007

Several different properties of a fractal are calculated: the recoilless fraction, the Raman scattering intensity, and the spin–lattice relaxation time. The recoilless fraction of a Mössbauer nucleus in a fractal is calculated from the displacement of an atom in a fractal which exhibits a scale invarince for a noninteger fracton dimensionality and found to be in good agreement with the measurements in deoxygenated myoglobin. The exponent of the normalized intensity of the Raman scattered light with frequency is calculated using fractional dimensionalities and density of states for decaying as well as nondecaying fractons. It is found that the phonon and the fracton branches may crossover or avoid crossing giving rise to new modes called as fracnons. The calculated Raman intensity is in good agreement with the measurements in silica gel, (C2H5O)4Si. A theory of the spin–lattice relaxation with the dimensionality crossover is presented. The calculated value of the spin–lattice relaxation time is found to be in good agreement with the measured value of Fe3+ in a frozen solution of metmyoglobin azide.
Polaronic Effects on Exciton States with Different Angular Momenta
Authors: Iadonisi G. , Bassani F. , Strinati G.
Published: July 2007

It is shown that exciton states with various total angular momenta (L = 0, 1, 2, 3) are differently affected by the interaction with LO phonons in polar materials. In particular, a dependence is found of the binding energy on the value of L not expected on the basis of the statically screened electron‐hole attraction. Calculations for CuCl and other ionic compounds show that the lowest L = 1 state (n = 2) is less bound than the corresponding exciton state with static screening. This effect, which is opposite to the polaronic effect on the ground state, is still present for L ≧ 2 but it decreases with increasing L. The computed binding energies of 2p excitons compare favorably with the available experimental data. The method is also applied to the calculation of bipolaron binding energies.
The Sink Strength of Dislocation Multipole and Dislocation Wall
Authors: Galimov R. R. , Goryachev S. B.
Published: July 2007

Expressions are obtained for sink strength and preference of dislocation multipole and dislocation wall both, in the absence and presence of size elastic interaction of radiation point defects with dislocations. The multipole and the wall are shown to absorb preferentially interstitials than vacancies. Multipole preference, irrespective the number of composing dislocations, may be both greater and smaller than isolated dislocation preference depending on the type of dislocations and geometry of their position in the multipole. Dislocation wall preference is much smaller than isolated dislocation preference.
Warm Electron Transport in GaAs Quantum Wells
Authors: Chattopadhyay D. , Kabasi A.
Published: July 2007

The transport of warm electrons intinerant two dimensionally in a square quantum well is studied over the temperature range 60 to 300 K, including the degeneracy of the distribution function. Scattering by polar optic phonons, deformation potential acoustic phonons, and ionized impurities is considered. Calculations with GaAs material parameters show that both the ohmic mobility and the warm electron coefficient for a quantum well of width 12 nm are greater than those for a well of width 8 nm.
Potential of Fast Neutron Damage Regions in Heavily Doped Semiconductors
Authors: Litvinov V. L. , Ukhin N. A. , Churakov Yu. I.
Published: July 2007

The potential and field of impurity—defect damage regions are calculated, employing a model which is earlier used to explain changes in properties of heavily doped silicon irradiated by neutrons. The change in initial material properties and the effect of the energy of the irradiation particles are analyzed.
The Investigation of the Ferroelectric Phase Transition in Cluster Systems of Order‐Disordered Type. II. Two‐Particle Cluster System
Authors: Yukhnovskii I. R. , Korynevskii N. A.
Published: July 2007

A new method of two‐stage integration in collective variable phase space is proposed for the calculation of the critical part of the partition function of a ferroelectric cluster system. The recursion relations for basic distribution coefficients of consequent block structures are found, taking into consideration dipole‐dipole components of intercluster interaction. A general solution of these relations is obtained. The type of critical behaviour of the system is determind. The phase transition temperature is calculated.
Calculation of Polycrystal Elastic Constants from Single‐Crystal Data
Authors: Morawiec A.
Published: July 2007

A new calculation method of determining the elastic constants of a polycrystalline material from single‐crystal elastic coefficients is presented. The averaging procedure satisfies the condition of commutation with the inversion operation. It can be applied to any crystal symmetry and allows to take texture into account. The properties of the averaging procedure are given and compared to the corresponding properties of the arithmetic averaging method.
Microstructure Dependence of Material Properties of Composites
Authors: Monecke J.
Published: July 2007

Effective material constants of composites depend not only on the material constants of the constituents and on their volume fractions but on the microstructure of the composite, too. A general structure dependent expression is derived for the effective dielectric constant of a binary composite as an example. Explicit results are given for typical microstructures. It is proved that all exactly solvable borderline cases are reproduced.
Dispersion Relation for Coupled Surface Waves in Thin Polar Semiconducting Foils
Authors: Srivastava K. S. , Tandon A.
Published: July 2007

The dispersion relation for surface plasmon—surface optical phonon coupled waves is derived in nonretardation limit, using a hydrodynamical model, for thin semi‐infinite plane bounded polar semiconductor films. Due to coupling between the surface plasmons and surface optical phonons at the two surfaces of the film, it gives rise to four surface modes. Under certain conditions the dispersion relation can also describe the surface plasmon oscillations in metallic foils.
Rebuilding of Electron Spectra in One‐Dimensional Structures by Increasing the Electron—Phonon Binding
Authors: Popov A. P. , Lavrentev A. A.
Published: July 2007

The problem of the one‐electron spectra rebuilding in one‐dimensional structures by increasing the electron—phonon binding is investigated. It is shown that the non‐localized state is the ground state of the system only in the limit of weak coupling. The quality rebuilding of the one‐electron spectra occurs when the coupling constant α reaches the critical value αcr = 1.8371. The rebuilding is caused by appearance of the autolocalized state with the finite radius of localization. Autolocalized state becomes the ground state of the system when the coupling constant α reaches the value 1.8660.
An Electronic Band Structure Calculation and the Optical Properties of Alkaline‐Earth Sulphides
Authors: Stepanyuk V. S. , Szász A. , Farberovich O. V. , Grigorenko A. A. , Kozlov A. V. , Mikhailin V. V.
Published: July 2007

The electronic band structure of CaS, SrS, and BaS is calculated by linear augmented plane waves (LAPW). The calculation is applied for the explanation of the optical properties of the alkalineearth‐metal sulphides.
The Prognostication Possibility of Some Magnetic Properties for Dielectrics on the Basis of Covalency Parameters of Ligand‐Cation Bonds
Authors: Bayukov O. A. , Savitskii A. F.
Published: July 2007

The possibility to predict the exchange interaction values and Curie temperatures of magnetodielectrics is shown using the superexchange bond model and the specific dependences of the intraatomic exchange integral, the transfer parameters, and the excitation energy of electrons from ligand to cation on a number of electrons in the 3d‐shells of cations. Ability is demonstrated on examples of ferrite‐spinels and perovskites of arbitrary composition.
Characterization of Microdefects in Silicon by Means of X‐Ray Reflection Curves
Authors: Holý V. , Kubéna J.
Published: July 2007

Microdefects in an annealed Czochralski‐grown silicon crystal have been studied by means of X‐ray double crystal diffractometry. Comparing the reflection curves measured at various places of the crystal with those computed on the basis of the theory published in previous papers the effective defect size, their density, and the defect strength are determined. The results are compared with those obtained from the experimental curves using the conventional kinematical theory of diffuse X‐ray scattering.
F Centers in LiF‐Mg Crystals
Authors: Mikhalenko A. A. , Khulugurov V. M. , Dmitrieva E. I. , Salomatov V. N.
Published: July 2007

Spectroscopic characteristics of new F‐like centers in LiF‐Mg, OH crystals are studied. The role of the divalent Mg impurity in the formation of F centers in LiF is revealed. By comparison of measured and calculated energy parameters a tentative model and a mechanism for the formation of the centers studied are suggested.
On non‐Debye Linear Mechanical Response of Condensed Media
Authors: Kuklov A. B.
Published: July 2007

A phenomenological non‐Debye linear mechanical response theory for condensed media is presented which takes into account transverse diffusion currents induced by the external stresses due to the local anisotropy and inhomogeneity fluctuations (LAIF). The generalized linear shear modulus (GSM) and compliance (GSC) expressions are obtained in terms of the auto‐correlation function of the relevant LAIF representation. The theory is used to calculate the linear response fractional frequency exponent when transient diffusive creep takes place. The results are in reasonable agreement with the empirical Andrade creep law. Schoek's formula for internal friction is explained, too. To verify the theoretical predictions some experiments are proposed.
Oscillatory Temperature Dependence of Crystal Structure and Magnetic Parameters in FeGe2
Authors: Zainullina R. I. , Vlasov K. B. , Milyaev M. A. , Ustelemova E. V. , Syromyatnikov V. N.
Published: July 2007

X‐ray investigations are made of the temperature dependences of integrated Bragg reflection intensities I(T), and the tetragonal lattice parameters a and c for FeGe2 compound. The temperature dependence of the magnetic susceptibility at 80 < T < 320 K is also presented. In the range of magnetic ordering (T < 287 K) an unusual oscillatory temperature dependence I(T) for Bragg reflections is obtained, a stepped character of the a(T) and c(T) curves, and an oscillatory temperature dependence of the susceptibility for FeGe2. On the assumption that an incommensurate magnetic structure exists in FeGe2 a qualitative theory is proposed for describing the temperature oscillations of the parameters investigated.
A New Empirical Many‐Body Potential Energy Function Application to Microclusters: Elements in B.C.C., F.C.C., and H.C.P. Structures
Authors: Erkoç Ş.
Published: July 2007

A new empirical many‐body potential energy function (PEF) has been proposed recently, and it has been successfully applied to microclusters of various elements. Using the new PEF the microcluster calculations are extended to several elements in b.c.c., f.c.c., and h.c.p. structures.
Effects of Low‐Energy Electron Transport in Insulators
Authors: Adamchuk V. K. , Kuchma A. E. , Molodtsov S. L.
Published: July 2007

Transport of excited electrons with an energy less than the band gap value in the conduction band of insulators is described analytically. Interaction of electrons with optical phonons is assumed to be the predominant process in scattering. By solving the diffusion equation obtained on the basis of the kinetic equation it is possible to find the energy distribution of the electrons in the solid and vacuum. Photoelectron spectra for CsI are calculated. Comparison of theoretical and experimental results yields the structure of the density of states in the conduction band, the energy loss intensity, and the free path time of excited electrons with respect to the electron—phonon scattering.
Incommensurate Magnetic Structures in Triangular Antiferromagnet CsCuCl3
Authors: Gekht R. S. , Fedoseeva N. V. , Dolina V. A. , Balaev A. D.
Published: July 2007

The helical magnet CsCuCl3 in an applied field higher than the critical field is shown to have sinusoidal phase with linear polarization of spins. The new intermediate phase is due to a conical‐point instability caused by weak dipole interactions. Therefore in different temperature ranges two modulated structures are actually realized. Results found theoretically are in good agreement with the experimental data.
On the Phase Shift and Bound States in a One‐Dimensional Antiferromagnetic Chain
Authors: Costa B. V.
Published: July 2007

The behavior of small oscillations in an antiferromagnetic chain with an external magnetic field applied when a static kink is present is investigated. By using a Green's function approach the bound states and phase shifts are obtained and it is possible to show that a purely anisotropic model can generate the same thermodynamics.
Simulation of Vacancy Migration in B.C.C. Metals
Authors: Fritzsch B. , Zehe A. , Fritzsch R.
Published: July 2007

With the help of moleculardynamic calculations the diffusion via vacancies as the dominant mechanism in b.c.c. metals is studied. The interaction between atoms in the block are described by potentials of the Lennard‐Jones type. For selfdiffusion a linear dependence between the migration and binding energy of the crystal is found, unrestricted by the lattice constant. On the contrary, for impurity diffusion in the model the size of the diffusing atom influences essentially the diffusion behaviour.
A Comparative Study of the Phenomenological Potentials for Ionic Crystals of Alkali Halides (II)
Authors: Khwaja F. A. , Razmi M. S. K. , Naqvi S. H.
Published: July 2007

A comprehensive study of some phenonenological interionic potentials is continued by developing further tests based on the calculation of cohesive energy, relative stability, and pressure induced solid‐solid phase transformation of alkali halides. A comparison of the results with some previous calculations and with experimental data is made.
Transient Response of Hot Electrons in Semiconductor Quantum Well Wires
Authors: Mulimani B. G. , Ramakrishna C. H. , Krishnamurthy B. S. , Sarkar C. K.
Published: July 2007

Transient response of hot electrons in quantum well wires of a polar semiconductor to a step electric field is studied using the displaced‐Maxwellian distribution function and the energy and momentum balance conditions. Numerical results are given for the variation of drift velocity and electron temperature with time for parameters characteristic of GaAs. Momentum relaxation is found to be faster than the energy relaxation. Also, both the relaxation rates are found to increase with the increase of lattice temperature and become faster with the decrease of transverse dimension of the wire.
The Quantum Well in an Electric Field A Density of States Approach
Authors: Enderlein R. , Holz T. , Gondar J. L.
Published: July 2007

A quantum well (QW) in the presence of a homogeneous electric field forms a system with continuous energy spectrum. Its density of states (DOS) is calculated. A general DOS formula is applied which avoids the well‐known difficulties for systems with continuous spectra. The Schrödinger equation is solved exactly, and the 1D DOS is expressed in closed analytical form by means of Airy functions of first and second kind. Quasistationary energy levels are defined as zeros of a certain 4 × 4 matrix. Their positions are calculated in dependence on the field strength over a wide range. The 1D DOS peaks arising from quasistationary levels are studied for different field strengths. The same is done for the 1D DOS in a larger energy interval ranging from far below the QW bottom up to far above the QW barriers. Franz‐Keldysh oscillations as well as QW interferences are observed above the barriers.
Doping Dependent Bandgap Narrowing in Silicon and Germanium
Authors: Noor Mohammad S. , Abdus Sobhan M.
Published: July 2007

A simple model for bandgap narrowing in doped silicon and germanium is developed. The model assumes that bandgap narrowing in doped semiconductors results primarily from electron—electron, electron—hole, electron—donor, and hole—donor interactions. Based on the suggestion of Hermanson and Phillips that in an impure crystal spatially dependent dielectric screening represents a measure of electron—hole, electron—donor, and hole—donor interactions, the model attempts to determine electron—donor, hole—donor, and electron—hole interactions by making use of the DYP (Dingle/Yakawa potential) modified by including spatially variable dielectric constant. The electron—hole interaction energy is estimated on the basis of many‐body techniques of Mahan and Abram et al. Physics justifying the use of modified DYP for calculating bandgap narrowing is discussed in some details. It is noted that the use of the DYP is valid for doping concentrations up to about 4 × 1020 cm−3. Calculated results are displayed in figures, which show good agreements with available experiments.
The Acceptor States of Hydrogen in Silicon
Authors: Gutsev G. L. , Myakenkaya G. S.
Published: July 2007

Various vacancy complexes are considered in crystalline silicon containing from one to four hydrogen atoms and possessing acceptor levels in the band gap. Their geometrical and electronic structure are calculated by the discrete variational Xα‐method in the cluster approach. It is concluded that for the creation of such acceptor states in the band gap of silicon it is necessary to use some appropriate experimental conditions.
EPR of Lithium‐Induced Silicon‐5dn Pairs in Silicon
Authors: Höhne M.
Published: July 2007

A platinum‐analogue to the lithium‐induced silicon‐gold pair, previously investigated, is now detected by EPR. The results underline the close similarity of platinum‐ and gold‐related defects in silicon and suggest a remark concerning the absence of an EPR‐proof of the isolated gold defect, contrary to the platinum defect.
Dependence of Tc on the Hole Concentration in the High‐Tc Superconductors Bi1.5Pb0.5Sr2Ca1−xGdxCu2O8+z
Authors: Kiemel R. , Wischert W. , Kemmler‐Sack S.
Published: July 2007

Substitution of Gd for Ca in the high‐Tc superconductor Bi1.5Pb0.5Sr2Ca1−xGdxCu2O8+z (0 ≦ x ≦ 1.0) is accompanied by a decrease in hole concentration with increasing x. Nevertheless, Tc ≈︁ 90 K remains nearly constant in the interval 0 ≦ x ≦ 0.25. Compounds with x = 0.35 and 0.5 are still superconducting; the increased width of the transition points on a percolation of superconductivity. Compounds with x ≧ 0.75 are semiconductors. The presence of variable range hopping in the insulating regime strongly suggests that the metal—insulator transition is of Anderson type.
Interband Critical Point Parameters Determined by Ellipsometry in CdxHg1−xSe
Authors: Kumazaki K. , Viña L. , Umbach C. , Cardona M.
Published: July 2007

The dielectric function of CdxHg1−xSe crystals, with x = 0 to 0.30, is measured by ellipsometry at room temperature between 1.8 and 5.5 eV. The E1 and E1 + Δ1 gaps and the Δ1 spin—orbit splitting show a upwards quadratic dependence on composition. The broadening of the observed structures increases with x due to alloying effects and disorder or to the difference in chemical activity of the surfaces. The results are discussed in comparison with those obtained for ZnxHg1−xSe and CdxHg1−xTe.
Phonon Localization in Disordered Systems Application of a Probabilistically‐Based Self‐Consistent Theory
Authors: Böttger H. , Theuerkauf M.
Published: July 2007

The probabilistically based self‐consistent theory of localization proposed by Abou‐Chacra et al. and simplified by Logan and Wolynes is extended to phonon localization. For systems with mass disorder, results are derived for the mobility edges and the extent of the localization domain.
A Study for Critical Behaviour of Ferromagnetic Thin Films
Authors: Hai T. , Li Z. Y.
Published: July 2007

The critical behavior of ferromagnetic thin film with two surfaces is investigated by the use of effective field theory with correlations. Surface magnetic order phase is found under certain conditions. The effects of couplings at surface, couplings between surface and nearest neighbouring layer, film thickness, and concentration of magnetic atoms at surface on surface magnetism are discussed.
An Improved Linear Chain Approximation for the Free Energy
Authors: Faleiro Ferreira J. R.
Published: July 2007

Some previous results obtained through a new variational approach recently proposed can be improved by using a sum of linear chains as the trial Hamiltonian. That approximation preserves short‐range order effects above the approximate critical temperature.
Mean‐Field Solution of Strongly Correlated Systems Using Hubbard Atomic Operators. Hubbard Model with Infinite U
Authors: Kotrla M. , Drchal V.
Published: July 2007

The hierarchy of equations of motion for double‐time Green functions for Hubbard atomic operators is solved using moment‐conserving decoupling. The lowest order gives a new type of meanfield solution which depends on nonlocal correlation functions. The case of Hubbard model with infinite Coulomb interaction is studied and magnetic properties of the mean‐field solution are investigated employing an additional approximation for correlation functions.
Magnetization Processes of the Rare‐Earth and Fe Sublattices in R2Fe14B (R = Tb, Dy, Ho, Er, and Tm)
Authors: Zhao Tiesong , Fan Zhongzhi , Jin Hanmin
Published: July 2007

The magnetization processes of the rare‐earth and Fe sublattices in R2Fe14B compounds (R = Tb, Dy, Ho, Er, and Tm) along the principal crystal axes at 0 K in fields up to 200 kOe are analysed. The analysis based on the classical three‐sublattice model reproduces fairly well the magnetization processes which are predicted by the analysis based on the crystalline electric field model. The noncollinearity between the magnetic moments of the rare‐earth and Fe sublattices is striking during the magnetization processes, and the Sucksmith‐Thompson method widely used for the evaluation of the magnetocrystalline anisotropy constants cannot be used for the R2Fe14B compound system.
Critical Behaviour of the Magnetic Resonance in KNixMn1−xF3
Authors: Skrzypek D.
Published: July 2007

A series of KNixMn1−xF3 (0.3 < x < 0.8) with cubic structure is examined by electron paramagnetic resonance in the region of the magnetic phase transition. The broadening of the linewidth ΔB and the shift of the resonance field Br at a fixed frequency are caused by the onset of magnetic ordering. This work proves Huber's theory that the effects observed near magnetic phase transitions in antiferromagnets depend on the symmetry of the system examined.