bluuebunny/crossref_metadata_2025 huggingface dataset:
Covalent Bonds in Amorphous Semiconductors and Their Influence on the Structure of the Energy Spectrum
Authors: Unger H. ‐J.
Published: July 2007

The structure of the energy spectrum of amorphous semiconductors as determined by the formation of covalent bonds is analyzed. In contrast with other theoretical models all considerations are based on a realistic model of the atomic structure of a‐Si and a‐Ge. The mathematical method used throughout the paper is, within certain subspaces (cells) of the total Hilbert space, the partial diagonalization of the Hamiltonian represented in an “extended Hilbert space”. Existing model Hamiltonians, e. g. the Weaire‐Thorpe model, are generalized in such a way that real disordered solids can be described. The molecular model used in this paper yields the basic feature of the structure of the energy spectrum. For positionally disordered systems an Anderson‐like Hamiltonian is obtained. The formation of extended and localized states in disordered solids is explained by taking into account the residual interactions. Conditions for the localization of electronic states and the existence of mobility edges depending on the local and global atomic structure of amorphous semiconductors are given. A generalization of the cell model in the spirit of the scaling theory of localization leads to a method for the determination of the position of the mobility edges. Structural correlation in amorphous semiconductors manifesting itself in short‐range order and in the existence of voids, which is not taken into account e. g. in the Anderson model, is found to be the origin of the basic structural properties of the energy spectrum of disordered semiconductors. Conclusions from the theory proposed are in accordance with experimental findings and explain them.
Charge Carrier Transfer in Ferrite Spinels Affected by Magnetic Ordering
Authors: Berzhanskii V. N. , Evstafev I. I. , Ivanov V. I.
Published: July 2007

The temperature dependences of the conductivity of single crystals of nickel‐zink Ni0.39Zn0.61Fe2.00O4 (Tc = 380 K) and manganese‐zink Mn0.66 Zn0.27 Fe2.07 O4 (Tc = 464 K) ferrites are studied in the temperature range 78 to 550 K. Measurements of thermoelectromotive force show that all the samples investigated have n‐type conductivity. In the region of the phase transition to the magnetically‐ordered state the logarithm of conductivity depends anomalously on the inverse temperature with increasing conductivity.
Anderson Localization in Ferromagnetic Semiconductors Due to Spin Disorder. III. Self‐Consisten Localization Theory and Inelastic Scattering
Authors: Kogan E. M.
Published: July 2007

Theoretical investigations are made of the temperature dependence of n‐type EuS electroconductivity. The scattering of electrons by magnetic ion spin‐density fluctuations is found to be strong; selfconsistent localization theory is used to calculate the conductivity and the inelasticity of scattering due to spin dynamics is also taken into account. It is shown that due to inelasticity the states which are localized in the elastic scattering approximation become weekly conducting, and the change of the conductivity of the extended states can be neglected. Hence in the case of quasielastic scattering (though not very rigorously) the notion of the “mobility edge” i. e. the energy which separates large and small conductivity can be introduce. The conductivity in the “dielectric phase” i. e. at temperatures close enough to TC when the “mobility edge” lies above the Fermi level, is estimated. The estimation obtained agrees well with the experimentally observed values.
Scattering and Velocity Dispersion of Electromagnetic Waves in Multiphase Dielectric Materials
Authors: Shermergor T. D. , Fokin A. G. , Dikarev A. V.
Published: July 2007

The parameters are calculated of an electromagnetic wave propagating in a dielectric medium, which is a multiphase mixture of isotropic and anisotropic components. The dispersion equation is studied which is derived allowing for spatial dispersion giving rise to an additional branch in solving the equation and, correspondingly, to two waves, namely, a real wave and a virtual wave. The results are given of calculating numerically the scattering indices and the phase and group velocities of the two waves. In the case the calculations are made in terms of the Bourret approximation, the real wave alone must be treated.
Transient Energy Transfer in ps Two‐Photon Absorption Experiments in CdTe at Room Temperature
Authors: Rückmann I. , Kornack J. , Kolenda J. , Petrauskas M.
Published: July 2007

One‐beam transmission experiments and two‐beam‐coupling experiments with 35 ps‐pulses at 1.06 μm are performed in CdTe and CdTe: Ge to investigate (i) the nonlinear (two‐photon (TPA), free‐carrier and two‐step) absorption processes, (ii) their kinetics, and (iii) the transient energy transfer (TET) from stronger pump beam to the weaker probe beam, caused by coherent coupling which is observed around (with its maximum just before) zero delay. The competition between TPA and TET is demonstrated by oscillating intensity dependences of the probe‐beam transmittivity measured and calculated at small delays, which can be used to realize a continuous transition from optical beam amplification to attenuation at a fixed delay in dependence on the pump intensity only. The influence of the pump‐to‐probe intensity ratio on TET is discussed.
Photon Echoes and the Structure of Wannier Excitons
Authors: Abram I.
Published: July 2007

The coherent polarization of a Wannier exciton system, induced by a short incident resonant light pulse, is calculated within a formalism that takes into account explicitly the internal structure of excitions. By examining the phase‐space filling interactions among excitons, it is shown that the hydrogenic structure of excitions causes significant deviations in their coherent optical response when compared with the response of the traditional two‐level model of optical coherence. This suggests that photon echo experiments, which measure directly the coherent polarization, may provide information on the structure of Wannier excitons.
Nonequilibrium Description of the Intense Resonant Laser Excitation of a Semiconductor
Authors: Jahnke F. , Henneberger K.
Published: July 2007

Generation of a nonequilibrium electron hole plasma by resonant excitation above the fundamental gap but below threshold for LO‐phonon emission is theoretically investigated. At high intensities, where the Rabi frequency dominates the spectral width of the exciting pulse as well as well as the damping due to relaxation, an intensity‐dependent renormalization of bands, i. e. additional laser‐induced branches and gaps, occur. Boltzmann equations governing the generation and distribution of electron‐hole pairs in these renormalized bands and an equation of Bethe‐Salpeter type for the interband polarization governing the band renormalization are numerically solved. Beside others it is found, that virtual electron hole Coulomb interaction tends to stabilize the formation of laser‐induced gaps and enhances spectral hole burning.
Nonlinear Optical Study of Semiconductor Microstructures, CuCl Quantum Dots, and GaAs Quantum Wells
Authors: Masumoto Y. , Ideshita S. , Wamura T.
Published: July 2007

Nonlinear optical properties of zcro‐dimensional and two‐dimensional semiconductor microstructures, CuCl quantum dots and GaAs quantum wells, are studied with special attention to the bleaching and the blue shift of excitons. In CuCl quantum dots, prominent absorption bleaching of excitons is observed together with a blue shift. The optical nonlinearity is found to increase with an increase of the size of the microcrystals. The blue shift of Z3 exciton absorption increases linearly and becomes saturated with the increase of the excitation density, suggesting the possibility of quantized blue shift. In GaAsAlAs quantum wells, two‐step rise in absorption saturation of the lowest exciton is observed in a few picosecond time domain at 4.2 K under the high‐density band‐to‐band excitation. The former rise takes place simultaneously with the dynamical red shift of the electron‐hole plasma luminescence. The latter rise is accompanied with the blue shift of the exciton. The origin of two‐step rise and blue shift is discussed.
Nonlinear Optical Properties of GaAs/(AlGa)As Multiple Quantum Well Structures under Quasistationary High Excitation Conditions
Authors: Schlaad K. ‐H. , Weber Ch. , Chemla D. S. , Cunningham J. , Miller D. A. B. , Hoof C. V. , Borghs G. , Weimann G. , Schlapp W. , Nickel H. , Klingshirn C.
Published: July 2007

The optical properties are investigated of undoped and n‐modulation doped multiple quantum well structures (MQWS) under quasistationary high excitation conditions. The characteristic nonlinear optical behaviour is due to an electron‐hole plasma. Its density, temperature, and the renormalized bandgap are determined via photoluminescence and pump and probe beam measurements. A model is developed for the line shape analysis of the plasma luminescence taking into account the broadening of the single particle density of states with results deviating from those in literature, but very good agreement is achieved with the experimental findings from pump and probe beam spectroscopy. The study of the renormalization of the higher, unpopulated subbands reveals that the pure intersubband screening is weak with respect to the shift of the fundamental bandgap. The exciton resonances of the higher subbands are found to be stable against high plasma densities in the fundamental subbands and are mainly bleached by direct population. The idea of a rigid shift of the whole subband structure must be clearly rejected.
A Detailed Study Concerning the Main Aspects Influencing Thermally Induced Optical Bistability of CdS
Authors: Hollandt J. , Gutowski J. , Broser I.
Published: July 2007

Thermally induced dispersive and absorptive optical bistability of CdS is investigated in a temperature range of 20 K to RT. The influence of the geometry of the crystals, e. g., thickness, surface area size, and resonator structure, on the hysteresis feature and switching behavior is investigated. The quality of the thermal contact between the sample and the heat sink strongly influences switch‐back times. Further, starting temperature, light spot diameter, and pulse intensity are varied in order to find a set of optimization criteria for this kind of optical bistability. Experimental results are in good agreement with model calculations.
Bistability in Composites of Linear and Nonlinear Media
Authors: Jungk G.
Published: July 2007

After the introduction of a simple qualitative model for optical nonlinearity in homogeneous solids, necessary conditions for bistability are derived and the switching properties calculated. The optically nonlinear particles are assumed to be embedded into host‐media. Different effective medium theories (describing different geometrical arrangements) are used to compute reflectivity and transmissivity as function of impinging light intensity. Numerical examples demonstrate possible application for fundamental research but also for device design.
Kinks in Resonatorless Optical Bistability. Stability Limits and Formation Dynamics
Authors: Kuznetsov A. V.
Published: July 2007

The stability of the s. c. kinks which separate the two regions with quasi‐homogeneous density distributions in resonatorless optical bistability, is explicitly investigated within an exactly solvable model. Kinks are found to be stable only when they are not too close to the sample boundaries. The geometric condition of stability linking the characteristic lengths of the problem is formulated, which allows one to predict if the stable kinks are possible at all in a particular experimental situation. The possible instability is caused by the translational mode of the kink motion, and the explicit expression for the translational relaxation time enables one to distinguish between different temporal regimes.
Absorptive Optical Bistability. The Case of Fabry‐Perot
Authors: Šrobár F.
Published: July 2007

Stationary Maxwell‐Bloch equations describing saturable‐absorber‐filled Fabry‐Perot resonators are studied by the causal diagram method to bring into prominence the role of interrelations among the factors involved. The representative diagram contains three feedback loops. It is shown that cooperation of all these loops is required to produce conditions necessary for optical bistability. Similar behaviour is encountered in the case of two‐sections semiconductor injection laser. General implications are suggested.
Nonlinear Optical Absorption in I‐VII and II‐VI Microcrystallites under Quantum Confinement of Elementary Excitations
Authors: Zimin L. G. , Gaponenko S. V. , Lebed V. Yu. , Malinovskii I. E. , Germanenko I. N. , Podorova E. E. , Tsekhomskii V. A.
Published: July 2007

The nonlinear absorption of quantum‐confined CuCl and CdSxSe1−x crystallites imbedded in a glass matrix is investigated by means of laser spectroscopy. For CuCl in which the quantum confinement of excitons takes place a considerable light‐induced blue shift of excitonic bands is observed which is attributed to the interaction of exciton‐like excitations under quantum confinement. A decrease of the saturation intensity with decreasing size of the crystallites is detected for CuCl‐doped glasses. In CdSxSe1−x‐doped glasses where quantum confinement of free carriers predominates no distinct correlation between the crystal size and the saturation intensity is observed.
Optical Nonlinearity and Dynamics of an Exciton‐Biexciton System in CuCl in the Weak Excitation Regime
Authors: Kuwata‐Gonokami M. , Shimano R. , Iwamatsu J. , Akiyama H. , Kuga T. , Matsuoka M.
Published: July 2007

The relaxation mechanisms of biexcitons under weak excitation limit are studied in the temperature region 1.6 to 50 K. From the temporal responses of biexciton emissions, the biexciton radiative relaxation time is found to be 50 ps. Single acoustic phonon scattering determines the intraband relaxation at finite temperature. Single acoustic phonon emission process causes the broadening of the biexciton with large wave vector. The experimental data of the wave vector dependence of biexciton line width are analyzed by two‐photon polarization spectroscopy and the biexciton deformation potential of 1.5 eV is obtained.
The Exciton‐Biexciton Spectrum Renormalization in the Presence of a Polariton Pumping Wave. The New Mechanism, Exciton Level Shift, and ABC Problem
Authors: Ivanov A. L. , Panashchenko V. V.
Published: July 2007

A new mechanism of the exciton‐biexciton spectrum renormalization determined by direct virtual coupling of excitons to the biexciton owing to exciton‐exciton Coulomb interaction is proposed. Exciton and biexciton shifts depending on pumping intensity are obtained. The macroscopic equations are derived and the ABC‐problem considered. The reflection spectra modification for CdS semiconductor was calculated.
Nonlinear Luminescence of Heavily Doped CdS: In Crystals
Authors: Neukirch U. , Broser I. , Rass R.
Published: July 2007

Luminescence data of heavily doped CdS:In crystals at various exciation densities are presented. The spectra are compared to theoretical calculations, which are based upon the assumption of indirect band‐to‐band transitions. At low excitation density some highly self‐compensated samples exhibit an enhanced luminescence at energies around 2.45 cV. This is due to conduction band acceptor transitions, which are easily saturable. Samples of intermediate In concentration show a narrow‐band highexcitation line, which is attributed to an EHP recombination. The temperature‐dependent behavior of this line indicates the occurrence of optical gain in these samples.
Photoluminescence Studies of Anomalous Diamagnetic Properties of the 2D e‐h System on the GaAs Surface
Authors: Averkiev N. S. , Asnin V. M. , Rogachev A. A. , Silov A. Yu. , Stepanov V. I.
Published: July 2007

The diamagnetic properties of the 2D e‐h system on the GaAs surface are studied detailly by the photoluminescence method at T = 1.9 K. An anomalous value of the ground state energy diamagnetic shift δ∥︁, of the 2D e‐h system in magnetic parallel field is found. As well an unusual effect is observed in magnetic parallel field concerned with the self‐consistent origin of the system: a jump of δ∥︁ versus the excitation level G. It is shown that the effects are concerned with the transformation of the energy structure of the system under high magnetic field and pumping level.
Improved Calculations of Phase Shifts for EXAFS Spectroscopy
Authors: Ghatikar M. N. , Mahesh K. V. S. , Bhatia S. N.
Published: July 2007

The full curved wave formalism is used to calculate the phase shifts for the pairs FeCo, CoZr, and FeZr in the Fe54Co36Zr10 amorphous system. The estimated phase shifts are compared with those obtained from the plane wave approximation and the important differences in the region of low k‐values are discussed. The comparison with the experimental phase shift functions obtained from the measured EXAFS spectra establish the improvement in the accuray of the calculated phase shifts using the curved wave formalism.
Grain Boundary Sink Strength in Anisotropic Materials
Authors: Sarce A. , Savino E. J.
Published: July 2007

The grain boundary sink strengths for intrinsic point defects in an anisotropic lattice are calculated. It is shown that the sink strength depends on the grain size, its shape, its metallurgical state, and for hexagonal symmetry, on the anisotropy factor for the diffusivity (Dc/Da). It appears to be independent of the volume averaged diffusivity constant. For the grain shape dependence, the Holt and Ibrahim anisotropy factor is obtained only as a limit case.
Channeling of Antiprotons and Electrons
Authors: Khokonov M. Kh. , Nitta H.
Published: July 2007

Based on the diffusion model, the channeling fraction of antiprotons and electrons as a function of penetration depth is studied numerically. According to the calculations, the dechanneling length of antiprotons is of the same order of magnitude as that of electrons. It is found that, though the dechanneling length of antiprotons is much smaller than that of protons, a definite portion (≈ few %) of axially channeled antiprotons has anomalously large dechanneling length.
Analytical Representation of the Thermodynamic Functions of Simple Metals in the Model of Self‐Consistent Einstein Oscillators
Authors: Lemberg V. F. , Psakhie S. G.
Published: July 2007

General regularities of the model of self‐consistent Einstein oscillators are investigated. The analytical expressions for the Einstein temperature, for thermodynamic functions, and for state equations are obtained. The range of considered values is estimated.
On the Thermodynamics of Surface Transitions Close to the Bulk Critical Point
Authors: Mishin Yu. M. , Kats D. Ya.
Published: July 2007

In the Ginzburg‐Landau functional approximation, thermodynamics of phase transitions occuring at the surface of binary alloys, ferromagnets, and similar systems are analysed in detail, including finite bulk and surface thermodynamic fields. Equations describing the lines of the Nakanishi and Fisher surface transition diagram are derived. For all the lines and (multi‐)critical points of the diagram, complete sets of thermodynamic critical exponents are obtained and scaling properties of the free energy surface excess, δfs, are examined in detail. The classical scaling of the bulk only holds at the critical prewetting lines. At the rest of the transitions, δfs is either a sum of two scaling functions with different exponents or includes a logarithmic singularity in addition to the leading one. This kind of scaling apparently represents some general properties of systems with surface‐broken symmetry or in contact with a short‐range substrate.
High Pressure Raman Study of the “Chain” Chalcogenide TlInTe2
Authors: Ves S.
Published: July 2007

The effect of pressure on the Raman spectra of the “chain” compound TlInTe2 is investigated up to 17 GPa and at room temperature using a diamond anvil cell. Three Raman peaks are observed in the low pressure tetragonal phase. The pressure coefficients and the corresponding mode Grüneisen parameters γ of their frequencies are obtained. The modes are tentatively assigned by comparison to Raman spectra of related TISe‐type compounds. The frequency dependence of γ indicates that a hierarchy of bonding forces is present. The appearance and disappearance of a new Raman peak at about 1.75 GPa is probably due to a gradual, pressure induced mutual replacement of In atoms by Tl atoms and does not indicate the occurence of a structural phase transition. Near 7.0 GPa a phase transition occurs, while at even higher pressures indications for a second phase transition are found.
Polariton–Biexciton Nonlinear Nutation and Stationary Spectrum Renormalization
Authors: Shmiglyuk M. I. , Bardetskii P. I. , Tiron S. D.
Published: July 2007

Two macrofilled coherent modes ‐ a polariton and a biexciton one ‐ are assumed to exist simultaneously in a direct‐gap semiconductor. These modes are characterized by the sets of parameters kO ωo and qo = 2ko, Ω0 = 2ω0, where k0 is the wave vector of the polariton mode and ω0 is the external pumping frequency. In the stationary case the renormalized dispersion and the particle concentrations of the strong modes k0 and q0 are obtained. A selfconsisted equation for the quasi‐momentum k0 as a function of the frequency ω0 and the external pumping intensity is deduced. in the nonstationary limit the polariton and biexciton concentrations are found to vary periodically in time within certain ranges passing through their steady equilibrium values which are the same as the stationary ones.
The Relative Energies of Ionic Structures for the High‐Tc Superconductor YBa2Cu3O7 and Implications for the Superconducting Mechanism
Authors: Floros N. , Dunne L. J. , Murrell J. N.
Published: July 2007

Madelung potentials are calculated for several choices of formal oxidation states of the ions in the high temperature superconductor YBa2Cu3O7. For p‐type CuO2 planes a slightly lower energy is found for a lattice with holes localised on copper (Cu3+) than for one with holes on oxygen (O−). Moreover, for the lattice with oxygen holes there is a negative energy for electron transfer between neighbouring Cu2+ O− sites. The near degeneracy of the ‘copper hole’ and ‘oxygen‐hole’ lattices suggests that they should be strongly mixed and this may play some role in the superconductivity behaviour.
Effect of Oxygen Concentration on the Resistive Superconducting Transition of YBa2Cu3O7−x in High Magnetic Field
Authors: Fuchs G. , Gladun A. , Drechsler S. ‐L. , Mueller R. , Ritschel M. , Krabbes G. , Koppetzki N. , Gilewski A.
Published: July 2007

The resistivity, Tc and Hc2 are studied in YBa2Cu3O7−x as a function of oxygen deficiency for 0 < x < 0.46. For small x the resistive transition is dominated by thermally activated flux creep. The temperature dependence of the activation energy is discussed. For x = 0.46, the influence of thermal activation could be neglected and a pronounced positive curvature of Hc2(T) and Hc2(0) > 45 T is found.
Hot Electron Transport in Submicron Semiconductor Devices
Authors: Kuivalainen P. , Lindberg K.
Published: July 2007

Hot electron transport is studied in small semiconductor structures by solving the coupled Boltzmann and Poisson equations using a simple relaxation time model and the integral formulation of the transport equation. Especially ballistic transport is investigated by calculating the electron distribution function f(x, v) in a submicron n+−n−−n+ diode. In the n−‐region f(x, v) is non‐Maxwellian and the ballistic electrons cause a dominant peak in f(x, v). The validity of the relaxation time approximation (RTA) is studied in the case of a large homogeneous electric field by calculating f(x, v) both, in RTA and using the full scattering rates for polar optical phonon scattering.
Analysis of Magnetostatic Modes Modified by Exchange and Anisotropy Energies
Authors: Li Shaoping , Cross L. E.
Published: July 2007

An investigation is made of magnetostatic modes modified by exchange interaction in anisotropic ferromagnets; and it gives a macroscopic description of influence of exchange interaction on Damon‐Eshbach surface modes. The classic Damon‐Eshbach (DE) and De Wames and Wolfram (DWW) theories of magnetic excitations in thin films is extended. A remarkable qualitative difference from previous theory is that all the spin wave vectors normal to the film are related to the exchange parameter. In case of weak exchange interaction, the critical angle between surface wave and bulk wave is modified according to the new circumstance and the spin wave dispersion relation is analysed.
Optical Absorption in Heavy Transition B. C. C. Metals
Authors: Ostanin S. A. , Shilkova N. A. , Shirokovskii V. P.
Published: July 2007

The complete relativistic calculation of electron states in heavy b. c. c. d‐metals is performed by the Green's function method to interpret the experimental optical absorption data. The interband optical conductivity is computed in the framework of the single‐particle density matrix formalism taking into account the dipole transition matrix elements. It is shown that consequent relativistic approach permits to interpret reliably the experimental results for the main band of the optical absorption. The effect of the spin‐orbit interaction on the absorption in the infrared region is investigated.
IR‐Spectroscopic Data of Thin Insulating Films on Semiconductors. New Methods of Interpretation and Analysis
Authors: Teschner U. , Hübner K.
Published: July 2007

On the basis of the Fresnel theory special IR optical equations for the description of the transmission (T), reflection (R), and attenuated total reflection (ATR) of thin films on semiconductors are derived. It is shown that these relations (quadratic approximations of film thickness) lead to a theoretical explanation for the detection and identification of transverse and longitudinal phonon‐polaritons by means of oblique incidence of polarized light realized in different experimental modes (T, R, ATR). A comparison of calculated model spectra of SiO2 with corresponding experimental spectra shows good quantitative agreement. Furthermore, in this framework a very effective method of determination of the dielectric functions of thin films from their IR spectra is developed and applied to an Al2O3‐film on silicon.
Optical Spectrum Model for a Substitutional Isoelectronic Impurity in Binary Semiconductors
Authors: Hugel J. , Parlebas J. C.
Published: July 2007

The effect of a substitutional isoelectronic impurity on the optical absorption spectra in binary semiconductors is investigated using a one‐electron NaCl crystal model containing two independent bands. It appears that wave‐vector conserving and wave‐vector non‐conserving transitions are responsible for the structures observed in the differential imaginary part of the dielectric function. However, the direct impurity induced transitions are dominant.
A Theoretical Study of Diffuse Scattering by Clusters in Alkali Halides
Authors: Augst G. R. , Vladislavskii Yu. I.
Published: July 2007

It is shown that in the case of dipoles located in one sublattice (divalent impurity with compensating vacancy), or its complexes, diffuse scattering very near to the Bragg reflections is determined only by short range non‐Coulomb forces affecting the lattice by the defect; in the case of dipoles in different sublattices (divacancies) or their complexes, the electrostatic forces also make a contribution to the amplitude of scattering, Strong compensation of contributions of this forces in the range near the Bragg reflection causes low cross‐section of scattering by divacancies and their complexes, in comparison with the cross‐sections by vacancies and divalent impurities with vacancies. In the case of the diffuse scattering far away from the Bragg reflection the cross‐sections of the same defects have a comparable value. The amplitude of near‐to‐Bragg‐reflection scattering on clusters is proportional to the number of dipoles in the cluster.
The Electronic Structure of the Alkaline‐Earth Oxides. II. Crystalline Cluster Approach Formalism
Authors: Lobatch V. A. , Sobolev A. B. , Rubin I. R.
Published: July 2007

Crystalline cluster approach based on the multliple scattering technique is discussed within the context of its precision to reproduce the valence band top in oxides insulators. Possible types of boundary conditions are analysed. Detailed calculations are presented for the magnesium oxide.
Specific Features of Kinetic Effects Measured in (Cd, Hg) Te in Quantizing Magnetic Fields
Authors: Baranskii P. I. , Belyaev A. E. , Gorodnichii O. P.
Published: July 2007

Magnetic‐field (0 ≦ B ≦ 5 T) and temperature (1.6 ≦ T ≦ 4.2 K) dependences are investigated of resistivity, ϱ, and Hall coefficient, R, in perfect enough and weakly compensated narrow‐gap (NG) and zero‐gap (ZG) n‐(Cd, Hg)Te crystals. A monotonic decline of R(B), observed in both the cases, is ascribed to an uncontrollable contribution of size‐quantized surface enrichment layers to the conductivity. The temperature dependence of ϱ⊥(B) in NG samples is related to the freeze‐out of electrons into an impurity donor band. An absence of such a dependence in the ZG samples studied evidences an absence of donor states even at the appearance of a gap. An anomalously strong dependence ϱ⊥(B) ∼ B5, measured in this case, is a consequence of a change of dielectric constant, ε, in magnetic field.
Amorphization of the Transverse Ising Model with Spin‐1
Authors: Zhong Jia‐Lin , Li Jia‐Liang , Yang Chuan‐Zhang
Published: July 2007

The amorphization of the transverse Ising model on square lattice with S = 1 is discussed by using the effective‐field approximation. The longitudinal and transverse magnetization, the fluctuation of spin operator Sz, Δ = (y – m)1/2, associated with the order parameter y  ≪(S)2≫r and the initial parallel susceptibility χ‖ are calculated in detail. Some interesting properties in their behavior are investigated.
The C3h Symmetry EPR Spectral Parameters for (0.005Gd, 0.995La) (C2H5SO4)3. 9 H2O and 9 D2O
Authors: Buckmaster H. A. , Kumar K.
Published: July 2007

An analysis is given of precision data sets describing the zx‐ and zy‐plane angular variation of the 9.396 GHz, 292.2 K EPR spectra for 0.5% Gd3+ impurity ions in both, the nonahydrated and nonadeuterated lanthanum ethyl sulfate host lattices. This analysis parameterized the spectral data to both a phenomenological spin Hamiltonian and a restricted symmetry‐adapted generalized spin Hamiltonian with C3h symmetry zero field splitting terms. It reports more precise values for the g‐factors and zero field splitting parameters for Gd3+ ions in the nonahydrated lattice than available previously and, for the first time, the values of these factors and parameters for the nonadeuterated lattice.
Particuliarities of Diffusion in Two‐Dimensional Systems with Random Forces
Authors: Dugaev V. K. , Tovstyuk K. D.
Published: July 2007

The diffusion is investigated of a classical particle in a two‐dimensional system with anisotropic random forces. It is shown that at largest time scales the renormalized diffusion coefficient is isotropic, and the diffusion laws at various time scales are obtained. The renormalization of the mobility in an external field is examined as well. Also the generalization of the results to dimensionalitics d = 2 – ε is presented.
Weak Localization and Interaction Effects in Thin Disordered Zinc Films
Authors: Meikap A. K. , Jana A. R. , De S. K. , Chatterjee S.
Published: July 2007

The low temperature resistance ΔR(T)/R and magnetoconductance Δσ(H, T) is measured of thin and quasi two‐dimensional disordered zinc films. At low temperatures, the thinnest films show a logarithmic temperature dependence of resistance. This is well explained by the localization and electron–electron interaction theory. The electron–phonon and electron–electron contributions to the resistance are described in detail. From the magnetoconductance data, the inelastic and spin–orbit scattering times are calculated and compared with theoretical values.
Interactions on Silicon Surfaces and Theory of Moments
Authors: Pick Š. , Tomášek M. , Gadiyak G. V. , Morokov Yu. N.
Published: July 2007

Extensive recursive method calculations for high‐symmetry silicon surfaces both, ideal and non‐ideal, with matrix elements up to 2nd nearest neighbours included are analyzed using low order moments of the Hamiltonian. The relevance of the results for chare transfer and bond‐bending forces are mentioned. Some results obtained previously by the present authors are revised.
The Electronic Structure of the Alkaline‐Earth Oxides. III. Resonant Behaviour of the MgO Valence Band Top
Authors: Lobatch V. A. , Rubin I. R.
Published: July 2007

Crystalline cluster approach (CCA) calculations show that in MgO, as contrasted to NaF, the valence band is situated above the “muffin‐tin” zero (MTZ). Self‐interaction correction results solely in lowering the MgO valence band bottom below the MTZ level. In this case valence band top states are assumed to be bonded by a barrier, appearing in the effective one‐particle potential due to the centrifugal potential contribution. It follows that such states are resonant ones and provide a substantial contribution to the electron scattering, which by Friedel's sum rule results in the appearance of additional electron density in the anion vicinity. Such an electron charge is localized in the interstitial region. Thus, MgO charge configuration can be defined as Mg2+ O− plus one electron, distributed in the inter‐ion region, which implies that a hole is to be found on the anion in the ground state. Such an interpretation may turn to be applicable to other oxides.
The Electronic Structure and Cohesive Energy of HfO2, ZrO2, TiO2, and SnO2 Crystals
Authors: Medvedeva N. I. , Zhukov V. P. , Khodos M. Ya. , Gubanov V. A.
Published: July 2007

Energy band structure calculations for tin, titanium, zirconium, and hafnium dioxides are made according to the LMTO method. The values of cohesive energies as well as of the total and partial densities of states are calculated. The results are used for the analysis of the change of the forbidden gap width in the series of dioxides. Relative values of the cohesive energy for TiO2 and SnO2 are explained as a result of repulsion between the oxygen atoms forming pairs, and – in the case of SnO2 – of the absence of hybridization between O2p‐ and d‐states as well.
Strain‐Induced Superconductivity in Lead Salt Superlattices
Authors: Agassi D. , Chu T. K.
Published: July 2007

Recent data on lead salt superconducting superlattices are interpreted in terms of an electronic pairing mechanism. The strain in these structures is estimated within the uncertainties in the deformation potential parameters and boundary conditions. The results indicate that the PbS/PbTe superlattice on KCl [100] substrate is particularly susceptible to band inversion in the PbTe layers. Consequently, electrons (or holes) are trapped in the ensuing localized states associated with the PbS/PbTe interface. By virtue of an exciton‐exchange mechanism these electrons condense into a superconducting state. The estimated Tc is in reasonable agreement with the data. Finally the observed superconductivity in another IV–VI superlattice is discussed in light of the present model.
Charge Density Wave and Contact Effects in NbSe3 Observed with Microwave Harmonic Mixing
Authors: Mayr W. , Philipp A.
Published: July 2007

It is shown that the method of phase resolved harmonic mixing (PREHM) at microwave frequencies provides a powerful tool in the investigation of the non‐ohmic behaviour of NbSe3. The latter is due to the formation of two distinct charge density waves (CDW), one below T1 = 144 K and the other below T2 = 59 K. The observed PREHM signal is investigated in view of the contacts necessary for the detection of the PREHM signal possibly being a source of nonlinear behavior, too, and hence contributing to the signal. Several positions of the NbSe3 crystal in the waveguide are chosen to expose either the contact region or the undisturbed part of the sample to the microwave radiation and in this way separating corresponding contributions to the PREHM signal. For comparison, harmonic mixing by a rectifying microwave diode is observed for the first time in order to investigate the principal physical behavior of a rectifying contact. The measurements show that in NbSe3 there is a clear dominance of the CDW contribution over a negligible contact contribution at temperatures below T1 = 144 K.
On the Theory of the Faraday Effect in Dielectric Ionic Crystals and Crystals with Structural Phase Transitions of Jahn‐Teller Type
Authors: Stasyuk I. V. , Kotsur S. S. , Tupychak V. P.
Published: July 2007

The expressions for the components of the tensor of linear magnetooptical effect in ionic dielectric crystals and crystals with structural phase transitions of Jahn‐Teller type are obtained in general form. The Faraday effect in KH2PO4‐type crystals is considered. Calculations are made of the components of the tensor of linear magneto‐optical effect for TmAsO4 crystals and their temperature dependences are investigated.
Structural Stability and Energetics of F.C.C. Metal Microclusters. Empirical Many‐Body Potential Energy Function Calculation
Authors: Erkoç Ş.
Published: July 2007

The structural stability and energetics of microclusters containing 3 to 7 atoms of f.c.c. metal elements are investigated. A recently developed empirical many‐body potential function (PEF) is used in the calculations, which comprises two‐ and threebody atomic interactions. The PEF satisfies both, bulk cohesive energy and stability condition. It is found that the energetically most stable structures of microclusters are in compact form.
Optical Properties of GaSe Crystals Containing Mn Impurity Atoms. I. Exciton‐Phonon Interaction
Authors: Gnatenko Yu. P. , Zhirko Yu. I. , Kovalyuk Z. D.
Published: July 2007

The experimentally observed growth of the integrated intensity of the n = 1 exciton absorption band in GaSe crystals is due to its energy degeneracy with the indirect conduction band. Participation of a phonon in such a process is needed to meet the conservation laws. Introduction of a light impurity atom into the interlayer space gives rise to a local interlayer mode capable of controlling the exciton‐phonon processes.
Optical Properties of GaSe Crystals Containing Mn Impurity Atoms. II. Excitonic and Impurity Emission
Authors: Gnatenko Yu. P. , Zhirko Yu. I. , Kovalyuk Z. D.
Published: July 2007

The impurity band (Emax = 1.842 eV) observed in photoluminescence (PL) spectra of GaSe: Mn crystals is demonstrated to be due to intracentre transitions of the Mn2+ ion. The energy of a zero‐phonon transition (EZPL = 1.928 eV) and of optical phonons participating in the formation of the PL of the electronic‐vibrational band is determined. Emission of excitonic polarons — ferronic states, resulting from a spin polarization of the electron and hole, included in the exciton, and of local antiferromagnetic‐ordered magnetic moments of Mn2+ ions is observed at T < 20 K.
Calculation of Diffraction Effects Due to Double Positioning in (111) Gold Bicrystals
Authors: Wang D. , Bristowe P. D.
Published: July 2007

The diffraction effects from doubly positioned [111] twist boundaries are calculated using an embedded atom model for gold. It is found that the kinematical scattering from any two boundaries related by double positioning is always superimposed. However, in a limited misorientation range near 30°, the superimposed intensities in the boundary plane are equal and can therefore be separated. Consequently, the projected atomic structure of each doubly positioned boundary can be determined by X‐ray diffraction. It is found that the displacement field of [111] twist boundaries is generally characterized by rotational‐like displacements centered around ‘O’ lattice elements. Since these displacements are largest for near‐Σ1 and near‐Σ3 orientations, these boundaries have the largest scattering power per unit area.
Monte Carlo Simulation Analysis of Proton‐Energy Spectra for Axial Channeling in Silicon in the Intermediate Energy Region
Authors: Lenkeit K. , Trikalinos Ch. , Balashova L. L. , Kabachnik N. M. , Shulga V. I.
Published: July 2007

A detailed theoretical analysis of experimental energy spectra of axial‐channeled protons transmitted through thin silicon targets is performed by Monte Carlo calculations. Energy spectra are calculated for 〈110〉, 〈111〉, and 〈112〉 channels in the energy region from 50 to 300 keV. The Monte Carlo program is based on the continuum string model. The energy loss on valence electrons is calculated on the basis of a modified Lindhard model for channeling energy loss and the stopping number is taken from the local density approximation of the Lindhard‐Winther formalism. The anisotropic distribution of the valence electron density in a semiconductor is taken into account. Stopping due to core electrons is considered by a semiclassical approximation. Multiple scattering and energy straggling are included in the simulation program. The calculated energy spectra and channeling stopping powers are in good agreement with experimental ones.
LCAO Recursion Approach in k‐Space Representations for the Treatment of Bulk and Surface Problems
Authors: Hergert W. , Rennert P.
Published: July 2007

The recursion method in a k‐space representation is used to calculate the electronic density of states for bulk and surface problems. The separability property of the Hamiltonian and the Green function is consequently used to avoid the discussion of the asymptotic behaviour of the recursion coefficients. The results of the recursion calculations in k‐space representation are compared with recursion calculations in a local basis and conventional LCAO calculations. Results are presented for silicon. The connection of local and k‐space representations for the treatment of adsorbate systems is discussed.
Microscopic Derivation of a Transport Equation for the Acoustic Polaron
Authors: Liu S. , Sak J.
Published: July 2007

Starting with the Kubo formula, a transport equation for the acoustic polaron is derived. The collision integral in the transport equation contains not only irreducible vertex parts, but also “products” of them. These are products of irreducible verteces connected by non‐singular parts of Green's functions. They are important when one considers the second or higher order perturbations, as in the case of an acoustic polaron at very low temperatures.
Spin–Lattice Coupling Coefficients Gij for Trigonal Al2O3:Fe3+ and ZnSiF6 · 6H2O:Ni2+ Crystals2)
Authors: Zheng Wen‐Chen
Published: July 2007

By expressing the six spin–lattice coupling coefficients G in trigonal symmetry in terms of the coefficients G and G in cubic symmetry, the coefficients G for trigonal Al2O3 : Fe3+ and ZnSiF6 · 6 H2O : Ni2+ crystals are calculated from the values of G and G obtained from a simple and uniform method within the framework of cubic symmetry approximation. The results for the Al2O3 : Fe3+ crystal is in agreement with the experimental findings, whereas for ZnSiF6 · 6 H2O : Ni2+, the agreement for part of coefficients is poor. The reasons for the disparity are discussed.
On the Carrier Spectrum of CuO2 Planes in High‐Tc Superconductors and Its Dependence on Stoichiometry
Authors: Loktev V. M.
Published: July 2007

An attempt is made to analyse the problem of the conduction band type (σ or π) in HTSC copper oxides. It is established that the σ‐character of this band may take place only under the condition of strong pd‐hybridization between p‐ and d‐holes from the upper Hubbard subband. The effect of nonstoichiometry on delocalized carriers consists in a possible appearance of discrete levels or a change in the spectrum as a whole. The estimate of these carriers damping as a function of nonstoichiometry shows that the damping may be a nonmonotonous function of doping that makes it possible to speculate of various HTSC properties dependent on lattice disordering.
Superconducting Current in a Bisoliton Superconductivity Model
Authors: Ermakov V. N. , Kruchinin S. P. , Ponezha E. A.
Published: July 2007

It is shown that the transition into a superconducting state with the current which is described by a bisoliton superconductivity model is accompanied by the deformation of the spectrum of one‐particle states of the current carriers. The deformation value is proportional to the conducting current force. The residuary resistance is absent in such states.
The Capture of an Extra Electron by Supersonic Acoustic Solitons in a Molecular Chain in the Presence of Thermal Vibrations
Authors: Kadantsev V. N. , Lupichev L. N.
Published: July 2007

The possibility for an extra electron to be transferred by a supersonic acoustic soliton in a thermalized one‐dimensional (1D) lattice with quintic anharmonism is studied. Existence conditions for solitonic solutions and electron states in a distorting potential produced by the acoustic soliton are analyzed. The effect of thermal vibrations of the molecules on the state of an extra electron held by a periodic molecular chain is demonstrated.
Absorption of Impurity Centres of a Crystal in the Field of a Strong Monochromatic Wave
Authors: Apanasevich P. A. , Kruglov V. I. , Tralle I. E.
Published: July 2007

On the basis of the non‐Markovian kinetic equation the nonlinear susceptibility and the absorption coefficient are investigated for different models of the impurity centre and electron—phonon interaction in the field of a strong electromagnetic wave. An analytical expression is obtained for the nonlinear absorption coefficient which differs greatly from the formula of the Bloch theory.
Accurate Numerical Calculation of the Electron Density at a Bijellic Interface within the Gradient Expansion Method
Authors: Kaschner R. , Vojta Th.
Published: July 2007

The differential equations of the gradient expansion method (concerning corrections to the kinetic, exchange, and correlation energies of the local density approximation) for the electron density at a bijellic interface are solved accurately by means of a discretization of the Euler and Poisson equations. The resulting set of nonlinear algebraic equations is solved by iteration (Newton‐Raphson method). The results are checked by means of several rigorous theorems. The accuracy of earlier approximate solutions of this problem is estimated. A comparison of the adhesive forces with the results of Vannimenus and Budd is performed.
Induced Absorption Spectroscopy by Lattice Defects in Sillenite‐Type Crystals
Authors: Efendiev Sh. M. , Gavryushin V. , Raciukaitis G. , Bagiev V. E. , Kazlauskas V. , Puzonas G. , Aliev R. A. , Mustafaev E. R.
Published: July 2007

In sillenite‐type crystals. Bi12XO20 (BXO) (X = Si, Ti, Ge), the effects of laser modulation of two‐step absorption (LM TSA) by deep local centres with spectroscopic regularities common to all the crystals of such type are observed. It is shown that to explain the nature of LM TSA, the indirect energy‐band structure of such crystals and the direct optical transitions from strongly localized states of deep defects extending in k‐space both, to “indirect” minimum and “direct” extremum of the conduction band should be taken into account. In sillenite‐type crystals the LM TSA processes involve intercenter optical transitions from the states of dominant intrinsic defects of extremly great concentration.
Phonon Spectrum of the One‐Dimensional Two‐Component Quasiperiodic Crystal
Authors: Gumen L. N. , Usatenko O. V.
Published: July 2007

The properties of an one‐dimensional quasicrystal consisting of two types of atoms with masses m and M, and with nearest neighbour elastic interaction constants k and K, are studied. The velocity of long‐wavelength phonons and the dependence of the maximum oscillation frequency on lattice parameters are derived analytically. The classification procedure of quasicrystal spectra is performed in the limit of large difference of masses and elastic constants. Five different limiting kinds of the spectra are shown to occur.