bluuebunny/crossref_metadata_2025 huggingface dataset:
Computer Modeling of Relaxation Peaks Involving a Gaussian Distribution of Activation Energies
Authors: Berry B. S. , Pritchet W. C.
Published: July 2007

To extend previous work in the frequency domain, as a function of temperature, the forms of anelastic or dielectric loss peaks are computed directly involving a Gaussian distribution of activation energies. The calculations provide the height, width, asymmetry, and frequency‐shift behavior of the loss peak as a function of a dimensionless parameter defining the width of the distribution. The calculations are used to determine how well the input distribution can be recovered or deconvoluted from a set of peaks, obtained for several different frequencies, by a simple empirical procedure termed a cross‐cut analysis. The procedure is found to work well for peaks whose width is more than twice the Debye width.
The Influence of Magnetic Fields on the Thermal Conductivity of the Cooperative Vibronic System Tm VO4
Authors: Mutscheller W. , Wagner M.
Published: July 2007

The influence of magnetic fields on the thermal conductivity of Tm VO4 is investigated theoretically. A method developed in an earlier paper is used in complete analogy to the case without magnetic field. The results are in a good agreement with the experimental findings.
Phase Transformation in F.C.C. Metals and Their Stability on the Path of Transformation
Authors: Thakur K. P. , Ahmad S.
Published: July 2007

Calculations are carried out to locate the stress‐free b.c.c. phase in four f.c.c. metals (Ni, Cu, Al, and Pd). Internal energies corresponding to the unstressed b.c.c. and f.c.c. phases, and the required stresses and energy changes for the f.c.c. → b.c.c. transformation in these crystals are presented. Ranges of G and S stabilities are examined according to the Born stability criterion, by calculating the values of corresponding elastic moduli on the line of deformation connecting the stress‐free b.c.c. and stress‐free f.c.c. phases of the crystal. The Morse potential model is used to carry out the calculations.
Scattering Properties of Non‐Spherical Muffin‐Tin Potentials of Surface Atoms
Authors: Rennert P. , Seifert F.
Published: July 2007

The calculation of the generalized phase shifts and of the partial wave amplitudes is described. An expansion into lattice harmonics is preferred to include the simplifications due to the symmetry in a direct way. The non‐spherical potential components are considered for a Ni atom in a surface layer of an (111) surface. Results are presented for an electron energy of 4 Ryd. Even at this relatively high energy remarkable deviations from the spherical case can be observed. It is discussed in detail, how the scattering amplitude depends both, on the direction of the incoming wave and on the azimuthal angle, that means cases are considered, in which the scattering amplitude in the spherical case has always the same value.
Exchange‐Scattering Effects on Band Energies in Magnetically Mixed Semiconductors
Authors: Ryabchenko S. M. , Semenov Yu. G. , Terletskii O. V.
Published: July 2007

Changes of the band energies of a free electron, hole, and exciton due to virtual processes of exchange scattering of these particles on the localized spin moments in magnetically mixed semiconductors with the cubic lattice are considered. The result is presented as an effective spin‐Hamiltonian governing the effects of (1) the fluctuation paramagnetic energy shift, (2) its partial compensation in the antiferromagnetic coupling within a system of magnetic ions, (3) renormalization of the exchange coupling constants in describing the giant spin splitting, (4) the non‐Heisenberg correction to the spin interaction between a hole and magnetic ions, and (5) the indirect electron‐hole exchange interaction for excitons. Numerical estimates of these effects are obtained for Cd1−xMnxTe. The results are compared with published experimental data; to verify one of the theoretical conclusions, the asymmetry of the spin splittings in the exciton spectra, a special experiment is conducted for Cd1−xMnxTe which confirms the theoretical predictions.
Electrical Conduction in Amorphous Cu10As40Se50 with Potential Fluctuations
Authors: Abdalla S. , Dongol M. , Ibrahim M. M.
Published: July 2007

Hall measurements of amorphous and annealed Cu10As40Se50 samples are performed to evaluate the carrier density and to evaluate the mobility in the temperature range 300 to 580 K. It is found that the free hole density pf, the Fermi level, and the mobility is a function of the annealing processes. The data are interpreted using the potential fluctuation theory. Differential thermal analysis (DTA) is performed. The endothermic changes of DTA have been attributed, in fact, to the shrinkage of the maximum height of the potential hills with temperature; while the exothermic changes have been regarded as a reason of the reduction of the disorder energy with annealing.
Liquid Site Model and Self‐Consistent Potentials in the Theory of Quantum Hall Effect
Authors: Ziep O. , Keiper R.
Published: July 2007

To explain the quantum Hall effect (QHE) as a macroscopic quantum phenomenon with interference character the liquid site model is discussed in more detail. The calculated thermodynamic potential containing the magnetic field energy shows minima near the filling factors v = p/(2n + 1) (p = 1, 2, …; n = 0, 1, 2, …). Electron correlation in strong magnetic fields leads to a local Hall potential satisfying the two‐dimensional Laplace equation. The liquid site model permits to discuss the necessity for an optimum degree of disorder as well as the high precision attainable in QHE measurements.
Magnetic Susceptibility of a Two‐Dimensional Electron Gas in the Strong Magnetic Field Limit and for Non‐Zero Temperatures
Authors: Wang L. , O'Connell R. F.
Published: July 2007

Analytic expressions are derived for the magnetic susceptibility and the Fermi energy of a non‐interacting two‐dimensional electron gas in the strong field limit and for non‐zero temperatures. The results at zero temperature agree with existing calculations but the results at finite temperature are different from those obtained recently by other authors.
General Principles of Spin‐Echo Formation in Solids
Authors: Whitaker M. A. B.
Published: July 2007

The mechanism of formation of spin‐echoes in solids is discussed, particularly in connection with the height and position of the main echo peak, and possible formation of subsidiary peaks. For values of Γ in the main part of the free‐induction decay, the value of Γ′ for the maximum will be less than τ. The value of τ′max — τ is connected with the slope of 〈Ix〉 (τ, τ). The method of time‐expansion should be regarded as descriptive, not prescriptive. Simple echo responses are analysed, and the results of a calculation for a simple cubic lattice of spins‐½‐ are discussed.
Infrared Investigation of Phase Transitions in CsHSO4
Authors: Döbler U. , Happ H.
Published: July 2007

The IR spectrum of CsHSO4(CHS) single crystals is investigated in reflection between 15 and 1500 cm−1 supplemented by absorption measurements on CHS‐KBr pellets between 2000 and 4000 cm−1, the region of OH stretching vibrations. The measurements extend from the room temperature phase up to the phase of superionic conduction above 412 K. The room temperature spectra are consistent with a structure of space group C(P21) containing HSO groups as molecular units allowing ferroelectric polarization along the crystal b‐axis. Additional dielectric measurements show that below the first known phase transition at about 360 K no further dielectric anomaly exists. The spectra in the superionic phase indicate rapid reorientational motion of SO groups and protons as mobile particles.
Magnetotransport Properties and Subband Structure of the Two‐Dimensional Electron Gas in the Inversion Layer of InSb Bicrystals under Hydrostatic Pressure
Authors: Herrmann R. , Kraak W. , Handschack S. , Schurig Th. , Kusnick D. , Schnackenburg B.
Published: July 2007

Magnetotransport properties of the n‐inversion layer formed at the grain boundary in p‐InSb bicrystals are investigated. Hydrostatic pressure up to 103 MPa is used to characterize the properties of the two‐dimensional electron gas in the inversion layer. At atmospheric pressure in addition to previous results four series of quantum oscillations are revealed, indicating that four electric subbands are occupied. From quantum oscillations of the magnetoresistivity ϱxx the characteristic parameters of the electric subbands (subband population nsi, subband energies EF — Ei) and their pressure dependences are established. A strong decrease of the carrier concentration in the inversion layer and of the corresponding subband population is observed when pressure is applied. A simple theoretical model based on the triangular‐well approximation and taking into account the pressure dependence of the energy band structure of pure InSb is used to calculate the energy band diagram of the quantum well and the pressure dependence of the subband parameters.
On the Charge Structure of Polarons in Trans‐Polyacetylene
Authors: Heiner E. , Drechsler S. L. , Malek J.
Published: July 2007

The charge structure of polarons (centered at long bonds) and antipolarons (centered at short bonds) is investigated on rings with N = 4 M sites in the SSH‐model and in the continuum model. In contrast with previous statements the charge distribution has to be described by two smooth penetrating functions. They can be reasonable well obtained within the continuum theory.
Electrical Conductivity Anisotropy in Tin‐Doped n‐Type Indium Selenide
Authors: Pomer F. , Bonet X. , Segura A. , Chevy A.
Published: July 2007

Electrical conductivity anisotropy of n‐type indium selenide samples doped with different concentrations of tin is studied between 30 and 300 K. The anisotropy ratio is found to depend exponentially on the inverse temperature, the activation energy E, and the pre‐exponential factor varying with free carrier concentration. This behaviour is explained by the existence of potential wells created by planar aggregates of ionized donor impurities screened by free electrons. A simple model in which the depth of these potential wells is calculated as a function of temperature, charge density in the planar defects, and electron concentration, gives account of the measured activation energies, but does not explain the high value of the anisotropy ratio. The existence of strictly two‐dimensional electrons bound to planar defects not contributing to the electrical conduction across the layers is proposed to explain this result.
Expression for the Diffusion Coefficient in Intermetallic Compounds with Cubic Structures
Authors: Bakker H. , Westerveld J. P. A.
Published: July 2007

A simple method is presented for obtaining an expression for the diffusion coefficient in a binary compound. Six cubic structures in which intermetallic compounds crystallize are treated as examples.
A Model of Crystallization in a One‐Dimensional Classical Liquid
Authors: Maćkowiak J.
Published: July 2007

A one‐dimensional classical mean‐field model of a liquid is presented. Each particle is located within its own cell on a circle and interacts with the others via a long‐range potential which tends to attract it towards the centre of the cell. The free energy of the liquid per particle is equal in the thermodynamic limit to that of a noninteracting system which exhibits a first‐order phase transition accompained by a discontinuous fall of the entropy and increased mean field characterizing an almost periodic particle distribution.
Thermodynamical Characteristics of Liquid Metal Droplets
Authors: Yakubov I. T. , Khrapak A. G. , Pogosov V. V. , Trigger S. A.
Published: July 2007

A gradient expansion of free energy for simple metals is performed in the framework of the density functional method. The temperature behaviour of the surface tension is described reasonably for alkali metals and the temperature dependences are obtained for the electron work function. Effects due to the surface curvature are investigated. Some exact equalities are obtained which relate the first‐order curvature corrections to the surface tension and the work function to the characteristics of the flat surface. The first‐order curvature correction to the surface tension is calculated.
Transfer Matrix in 1D Schrödinger Problems with Constant and Position‐Dependent Mass
Authors: Pérez‐Alvarez R. , Rodriguez‐Coppola H.
Published: July 2007

The transfer matrix method is considered for obtaining properties of standard wells and barriers in one‐dimensional Schrödinger problems with constant and position‐dependent mass. The formulae for the energy levels of a well and the transmission coefficient of a barrier are given. The continuity is demonstrated between virtual bound states in a well of position‐dependent mass and the relation between the zero energy gap states of a periodic potential problem with the corresponding energies of the non‐periodic one's with transmission coefficient equal to one. The calculations are carried out for a wide class of potentials profiles.
Transfer Matrix in the Quasiclassical Approximation with Constant and Position‐Dependent Mass. Resonant Tunneling
Authors: Pérez‐Alvarez R. , Rodriguez‐Coppola H. , López‐Gondar J. , Lago‐Izquierdo M.
Published: July 2007

A quasiclassical approximation is developed for the effective Hamiltonians describing nonhomogeneous systems and the wave function, the applicability conditions and the connection rules around the turning points are deduced. Based on the transfer matrix (TM) formalism expressions are obtained for the transmission coefficient of multiple barriers, the energy levels of multiple wells, and the quasistationary levels of a well open by one and by two sides. The dispersion relation of a periodic potential profile with variable mass problem is also given. Resonant tunneling is discussed for a system of multiple barriers. The transmission coefficient of such a barrier is maximum at energies close to the levels of the inner well when the end barriers are high enough and symmetric.
Diamagnetic Shift of Bielectrons in BiI3
Authors: Röseler J. , Shekhmametev R. I. , Neugebauer J.
Published: July 2007

In BiI3 the n = 5 and n = 6 lines of the inverse hydrogen‐like transmission spectra show a negative diamagnetic shift at 4 K for magnetic field strengths up to 50 T. Within the bielectron model the diamagnetic shift of such quasiparticle is calculated explicitly for higher‐excited states. The found results allow a satisfying quantitative explanation of the experimental findings.
Approximations to the Systematic Many‐Beam Case of High‐Energy Electron Diffraction. II. Improved Three‐Beam and Four‐Beam Solutions and Extinction Data
Authors: Kästner G.
Published: July 2007

Kinematical many‐beam corrections to the dynamical three‐beam and four‐beam approximations are derived analytically. The solutions yield refined extinction lengths and Bloch‐wave excitation coefficients tabulated for a variety of crystals and accelerating voltages (100 kV to 1 MV). Moreover, the results are used to analyse three‐beam and four‐beam features of electron transmission and anomalous absorption, and to represent many‐beam influences to critical‐voltage effects.
Dark Instability of F‐Centres in Pressure‐Treated KCl and KBr Crystals
Authors: Bagduev E. G. , Korovkin E. V. , Peresada G. I. , Ponyatovskii E. G. , Shikhsaidov M Sh.
Published: July 2007

Dark instability of colour is observed after the pressure treatment (phase transition from the NaCl‐type phase to the CsCl‐type phase and back) of coloured γ‐irradiated KCl and KBr crystals and additively coloured KCl crystals. The crystal bleaching is followed by luminescence and is strongly temperature dependent. The thermoluminescence method is employed in the studies. It is concluded that the pressure treatment leads to the formation of a great number of complex defects on the base of interstitial halide of which the diffusion or decomposition into simpler and more mobile defects leads to the phenomena observed.
Line Forces and Dislocations in Anisotropic Elastic Composite Wedges and Spaces
Authors: Ting T. C. T.
Published: July 2007

A composite wedge or a composite space is considered which consists of n wedges of different anisotropic elastic materials and wedge angles. For the composite wedge, a line force is applied at its wedge apex while the sides of the composite wedge is traction free. For the composite space, a line force and a line dislocation are applied at the center. In both cases, explicit solutions in real form are obtained for the displacement, the displacement gradient, the stress function and the stress. This is achieved by the new sum rules presented here. In most literatures, the stress in a homogeneous anisotropic elastic space subject to a line force or a line dislocation is obtained indirectly through the displacement gradient and the stress–strain laws. In this paper the stress is obtained directly from the stress function. An interesting result is that the surface traction on any radial plane vanishes for the composite wedge. For the composite space, the surface traction on any radial plane depends on r only and is invariant with respect to the choice of the radial plane.
Phase Transition and Anharmonic Properties of Semimagnetic Semiconductors
Authors: Singh R. K. , Prabhakar N. V. K.
Published: July 2007

The phase transition and anharmonic properties are investigated of semimagnetic semiconductors Cd1–xMnxTe and Cd1–xZnxTe using a three‐body force potential. The calculated values of third order elastic constants follow a systematic trend of variation with molar concentration. The values of the phase transition pressures and the pressure derivatives of second order elastic constants show reasonably good agreement with their experimental data. The possible ways of improvements are also discussed.
Phonon Spectrum in Metastable F.C.C. Lanthanum
Authors: Onwuagba B. N.
Published: July 2007

It is observed in the framework of the model pseudopotential method that the off‐diagonal components of the interatomic potentials φ(sd)‐f and φf‐(ds) associated with the s–d and d–s interactions in the s and d‐electrons make significant contribution via the local fields in the phonon spectrum of metastable f.c.c. lanthanum. The magnitude of this attractive component screens the conventional Born‐Mayer potential. Numerical results give a good agreement with experiment in f.c.c. La.
The Peculiarities of the Electronic Structure of the La2–xSrxCuO4 Compound
Authors: Timoshevskii A. N.
Published: July 2007

The electron structure of La1.8Sr0.2CuO4 ceramics is theoretically studied by the cluster approach. It is found that the unoccupied 4f‐shell of La atom is located near the Fermi level which seems to be the reason of the unique physical properties of the above compound.
Hot Electron Magnetophonon Resonances in Conduction and Noise for a Nondegenerate Semiconductor
Authors: Cui H. L. , Lei X. L. , Horing N. J. M.
Published: July 2007

The nonlinear transverse magnetoresistivity of conduction electrons subject to inelastic scatterings by longitudinal optical phonons in a non‐degenerate semiconductor is determined using a balance equation approach. Magnetophonon resonances are examined in both, the linear and nonlinear transverse magnetoresistivities; and the electron temperature in an intense electric field is calculated as a function of the magnetic field, showing significant electron resonant cooling. The nonlinear current saturation in a high electric field is also studied, and is shown to be independent of the magnetic field. The thermal noise temperature for hot electrons at a nonzero bias is also examined, and exhibit its oscillatory behavior as a function of magnetic field.
Negative Magnetoresistance of Neutron‐Transmutation‐Doped Gallium Arsenide at Variable‐Range Hopping
Authors: Rentzsch R. , Friedland K. J. , Ionov A. N.
Published: July 2007

Investigations of anomalous magnetoresistance (mr) in neutron‐transmutation‐doped GaAs are performed at T = 0.05 to 4.2 K in the vicinity of the metal–insulator transition (MIT). Without as well as with magnetic field a variable‐range hopping‐law ϱ(T) = ϱ0 exp (T1/T)1/2 is found with T1 → 0 at n → nc. At low magnetic field a negative mr and for the first time T1(H) < T1(0) is found. At higher magnetic fields the negative mr saturates and eventually changes into a positive mr with T1(H) > T1(0). The dependence of T1 on n as well as on H originates from the scaling behaviour of the localization radius a and the dielectric constant ϵ0 at the MIT. From the extrapolation of the T1‐curves versus n(T = 300 K) to zero without and with magnetic field nc(H) is determined. In the range of negative mr no shift of nc with H is found. For positive mr, however, nc(H) > nc(0) = 2.18 × 1016 cm−3 is obtained. The scaling behaviour of the conductivity of barely metallic samples extrapolated to T = 0 gives for the critical index v = 0.84 ± 0.05. The comparison of v with the critical index b for the scaling relation of T1 gives the critical index ξ for the dielectric constant ξ = 1.55 and ξ/ν = 1.94.
Influence of Residual Resistance Measurements on the Superconducting Transition of Ultra‐High‐Purity Niobium
Authors: Fellmuth B. , Elefant D.
Published: July 2007

A new surprising phenomenon is discovered investigating the superconducting transitions of ultra‐high‐purity niobium single crystals (reciprocal residual resistance ratio up to 53000). It can be detected that inductively measured transition curves are broadened by more than two orders of magnitude only by the simultaneous influence of the transport current and the external magnetic field (Ha > H) applied at measurements of the residual resistance using usual experimental technique. This broadening is caused by a change of the superconducting parameters in a surface layer with a thickness of only some μm. The reproducibility of the phenomenon and the spatial dependence of the superconducting parameter change in the surface layer are carefully investigated. An interpretation of the broadened transition curves is carried out on the basis of the phenomenological Ginzburg‐Landau theory. The results obtained lead to the conjecture that the phenomenon is connected with the transition from the Meissner state to the Shubnikov state in the presence of a transport current.
Mean Field Renormalization Group for Site‐Bond Diluted Ising Ferromagnets
Authors: Yang C. Z. , Li Z. Y.
Published: July 2007

It is shown that the mean field renormalization group techniques provide a reasonable description of the critical behaviour of the site‐bond diluted Ising model, both in the two‐dimensional system and the surface of a semi‐infinite three‐dimensional system.
Solitons in TMMC. Transfer Matrix Results and Phenomenological Interpretation
Authors: da Costa B. V. , Pires A. S. T.
Published: July 2007

The statistical mechanics of the antiferromagnet TMMC is discussed, both, phenomenologically and via transfer matrix formalism. Exact results are obtained for the specific heat and compared with experimental data.
Phase Diagrams of an Amorphous Ferromagnetic Insulator with a Fractional Effective Coordination Number
Authors: Kaneyoshi T.
Published: July 2007

An amorphous spin‐one Ising ferromagnetic insulator with a fractional effective coordination number is studied by the use of an effective‐field theory with correlations. The influences of random bond and crystal‐field interaction on Curie temperature and tricritical point are investigated. A number of interesting phenomena in these quantities is found. It is suggested that the research of such an insulator may open a new field of magnetism.
Spin Dynamics in the Classical Easy‐Plane Antiferromagnet Proton Spin–Lattice Relaxation in TMMC
Authors: Gouvea M. E. , Pires A. S. T.
Published: July 2007

A spin wave calculation of the memory function for the classical anisotropic one‐dimensional antiferromagnetic Heisenberg model is applied in a calculation of the temperature dependence of the spin–lattice relaxation rate in TMMC [(CH3)4N]MnCl3. Comparison with experiment is made.
Spectroscopic Determination of the Hindered Rotational Behavior of the CN− in Alkali Halides
Authors: Wilk S. R. , Lüty F.
Published: July 2007

The rotational properties of CN− substituted into various alkali halide matrices are studied through the rotational‐vibrational second harmonic absorption and excitation spectra at 2.4 μm of its vibrational emission. The variation of the spectral width with temperature is measured through the separation of the R‐ and P‐branches, the full width at half maximum, or the second moment of the spectra. The onset of T1/2 variation of the width provides a direct, if rough, measurement of the height of the barrier hindering quasifree rotation. This barrier varies from 20 cm−1 in KI to 85 cm−1 in CsCl. The coefficients of T1/2 yield the rotational constant, which varies from 0.16 cm−1 in CsI to 1.36 cm−1 in KCl. Since all measured values fall below the expected free CN− value of 1.94 cm−1, the effective moment of inertia must be increased by some mechanism, among which dressing of the ion's moment of inertia by participation of the surrounding lattice ions in rotational motion is judged to be most likely.
Band Edge Absorption Saturation Dynamics of Semiconductors
Authors: Kochelap V. A. , Kulish N. R. , Lisitsa M. P. , Malysh N. I. , Sokolov V. N.
Published: July 2007

Temporal evolution of the transmission coefficient and of the output light intensity during the laser pulse is investigated for CdSe single crystals. The nonlinear bleaching observed in the Urbach region of the absorption spectrum at room temperature has a threshold character. With the increase of the laser pulse energy exceeding the threshold value ℰ1, the transmission coefficient at first experiences a strong rise and then reaches a saturation. A phenomenological model describing the observed features is proposed assuming an abrupt dependence of the absorption coefficient on the photoexcitation density. The sequence of dynamical relationships between the transmission and the pump level is quantitatively analysed. From experimental data the threshold specific energy and the specific energy required for the bleaching of a 100 μm sample are deduced. They are equal to 2.2 × 10−11 and 1.9 × 10−10 J/μm2, respectively.
Soliton and Breather Dynamics in a Nematic Liquid Crystal under the Action of Constant and Time‐Varying Magnetic Fields
Authors: Abdullaev F. Kh. , Abdumalikov A. A. , Tsoi E. N.
Published: July 2007

The soliton and breather dynamics in a nematic liquid crystal under the action of constant and time‐varying magnetic fields are investigated. The two cases are considered: with highest gradient terms in the free energy and without them. The action of addition magnetic fields and dissipation are considered using the perturbation theory for solitons and breathers. A condition for chaotic oscillation of director is obtained. Absorption of the external alternating‐field energy in the linear approximation is studied.
Dynamics of Ionic and Bonding Defects in Quasi‐One‐Dimensional Hydrogen‐Bonded Chains
Authors: Kristoforov L. N. , Zolotaryuk A. V.
Published: July 2007

The motion of extended ion (orientational) defects in quasi‐one‐dimensional hydrogen‐bonded chains is studied for the double‐well potential model of a proton in the presence of applied external fields.
Energy Band Structure of (GaAs)m (AlAs)m Semiconductor Superlattices with Ultrathin Layers
Authors: Gushchina N. A. , Dunaevskii S. M. , Nikulin V. K.
Published: July 2007

The local band structure of the (GaAs)m (AlAs)m superlattices is calculated within the framework of the cluster recursion method of Haydock‐Heine‐Kelly. The Hamiltonian is constructed in the sp3s*‐basis of the tight‐binding method. The diagonal matrix elements and orbital populations are calculated in a self‐consistent way. The superlattice consists of alternate layers of GaAs and AlAs, each containing one to eight (110) layers of zincblende structure. The limiting cases of such a superstructure are the ideal heterojunction and a semiconductor material made up of alternate GaAs and AlAs layers. The paper presents the calculated densities of electron states for (GaAs)1 · (AlAs)1 and band discontinuities at the heterojunction. The dependence of the superlattice energy gap width on the alternate layer thickness derived here is in qualitative agreement with the experimental photoluminescence data.
On Electron States of Quantum Wells in Ultrathin Films of Wide‐Gap Semiconductors in an Oriented Magnetic Field
Authors: Bose M. K. , Majumdar C. , Maity A. B. , Chakravarti A. N.
Published: July 2007

An attempt is made to investigate the effects of a tilted magnetic field on the size‐quantized levels of quantum wells in ultrathin films of wide‐gap semiconductors, taking n‐GaAs as an example. It is found that the energy eigenvalue of the lowest Landau level corresponding to a given electric subband increases with increasing magnetic field, and reaches a maximum corresponding to a given orientation of the field, the dependence being increasingly prominent with increasing size quantum numbers. Besides, the eigenvalue corresponding to the lowest electric subband decreases with increasing film thickness, the rate of decrease being significantly dependent on the magnetic field and its orientation.
Size‐Quantized Excitons in Microcrystals of Cuprous Halides Embedded in Alkali‐Halide Matrices
Authors: Itoh T. , Iwabuchi Y. , Kirihara T.
Published: July 2007

Exciton luminescence spectra in CuCl, CuBr, and CuI microcrystals of a few nm in size which are embedded in alkali‐halide matrices are studied under selective excitation at the exciton absorption bands inhomogeneously broadened by the size distribution. The size‐quantized exciton states are found to split into various components. From the analysis of the splitting on the basis of the size‐quantization of the exciton translational motion in the microcrystals of thin platelets, the Z3 exciton translational mass, the Luttinger parameters, and k‐linear terms for the Z1,2 excitons are derived in these compounds.
On the Dynamical Stark Effect of Excitons. The Low‐Field Limit
Authors: Zimmermann R.
Published: July 2007

The dynamical Stark effect of excitons in semiconductors is treated in three and two dimensions (bulk material and MQW structures, respectively). Within the low‐field limit, theoretical results are presented for the gap function, the excitonic enhancement of the Stark shift, and the induced density. Higher bound states and the excitonic continuum are fully taken into account using the Coulomb Green's function.
Evolution Equations for Highly Excited Direct Semiconductors in the Athermal Stage
Authors: Heiner E.
Published: July 2007

A consistent extended time‐dependent mean field theory (TDMF) is introduced for the description of the evolution in the athermal stage of a direct semiconductor during and after a short laser pulse. A general theory involving dissipation and nonlinearity is developed from first principles. The form of the evolution equations is determined by the algebraic structure of the observation level. The collision terms are treated in a short memory approximation (SMA).
Semiconductivity in the Liquid Cu–TlTe System
Authors: Satow T. , Ishikawa H. , Uemura O.
Published: July 2007

Measurements of the electrical conductivity, the magnetic susceptibility, and the thermoelectric power for the liquid Cu–TlTe system are made in wide temperature and composition ranges. It is observed that the conductivity for the system falls abruptly at the composition of 50 mol% Cu and the themoelectric power changes its sign around this composition. The diamagnetic susceptibility also shows a sharp maximum at the corresponding composition. The experimental results of the present work are compared with the previous data of liquid telluride systems and are discussed in the light of current transport theories employed in amorphous and liquid semiconductors.
The Effect of Structural Imperfections on Macroscopic Properties of Tellurium‐Type Anisotropic Semiconductors
Authors: Shenderovskii V. A. , Tomchuk P. M. , Gorley P. N. , Gavaleshko N. P. , Tarasyuk I. I.
Published: July 2007

A theory of transport phenomena for anisotropic semiconductors is developed in which inelastic carrier scattering is dominating and the Debye screening radius of defects is large compared with the carrier mean free path. The effect of edge dislocations on electrical conductivity, magnetoresistance, and transverse and longitudinal Nernst‐Ettingshausen effects is investigated using tellurium as a model semiconductor. The defects are found to considerably affect the electrical conductivity of Te depending on the magnitude and the direction of magnetic field.
On Anisotropy of Nuclear Spin‐Diffusion Coefficient
Authors: Butkevich E. R. , Sabirov R. Kh.
Published: July 2007

The anisotropy of the spin diffusion coefficient for the simple cubic lattice is investigated. The analysis is based on using the non‐equilibrium statistical operator method. The form of the correlation function, which determines the spin diffusion coefficient, is treated by the momentum method. Exact expressions for the second and fourth moments are obtained. It is shown that usually using the Gaussian form of the correlation function as usually is unsatisfactory. Therefore, the known conclusion about the absence of anisotropy of the spin diffusion coefficient does not take place. Values of the spin diffusion coefficients are presented.
The Local Correlation Lengths in Ising Models with Free Surfaces
Authors: Korneta W. , Pytel Z.
Published: July 2007

The nearest‐neighbor Ising model of a film is considered in which couplings between spins depend on the distances to the surfaces. The local correlation lengths in directions parallel and perpendicular to the surfaces of the model near different second‐order phase transitions are studied. The random‐phase approximation is used. Analytical expressions for the local correlation lengths are obtained. Assuming that one surface of the model of a film tends to infinity, local correlation lengths in the three‐dimensional semi‐infinite Ising model are obtained.
Quantum Tunneling between AF and SF or Equivalent States in a Uniaxial Antiferromagnet
Authors: Prystasz W.
Published: July 2007

Studies are continued of tunneling effect at the first order phase transitions in the antiferromagnet with external magnetic field. By using quasiclassical approximation (WKB formalism) the probabilities are derived of the tunneling transitions between equivalent antiferromagnetic states and equivalent spin flop states. The probabilities of the tunneling transitions between the antiferromagnetic and spin flop phases are also calculated.
Influence of Rings on Electronic Structure in Topologically Disordered Systems
Authors: He H.
Published: July 2007

Green's functions are solved self‐consistently for a cluster formed by a single ring in an effective field to obtain the electronic density of states. The influence of rings of different size are then discussed.
Orientation Distribution Function Average of Second‐Rank Material Constant Tensors. Susceptibility, Conductivity, and Extinction
Authors: Ganster J. , Geiss D.
Published: July 2007

For triclinic crystal and sample symmetries material properties of polycrystals, which can be represented by symmetrical second‐rank tensors, are expressed by the generalized Fourier coefficientsC(ι = 0, 2) of the orientation distribution function (ODF) and the corresponding single crystal tensors. This relation is also given in terms ofoccurring if the ODF is expanded in real (tesseral)D‐functions. All higher symmetric cases can be treated in terms of(which belong to symmetrizedD‐functions) using the general formula and leading to drastically simplified expressions. An example is discussed. Some special cases often encountered in polymer science are expressed by orientation factors.
Conduction‐Electron Spin Resonance and Thermoelectric Power of the Mixed‐Valence Tetrathiafulvalenium Chloride
Authors: Graja A. , Sekretarczyk G. , Pukacki W. , Nešpůrrek S. , Ryba O.
Published: July 2007

A conduction‐electron spin resonance study together with thermoelectric power measurements for the TTF‐Cl0.71 salt are presented. One‐dimensionality and eclipsed stacking of TTF molecules are confirmed by ESR. It is shown that the Coulomb interaction is comparable with the intermolecular exchange interaction. The anomalies of the ESR linewidth, the spin susceptibility, the electrical conductivity, the thermoelectric power, and the specific heat at 250 K are associated with a commensurate Peierls transition.
Approximations for the Scattering of Excited Electrons in Solids
Authors: Fritzsche V.
Published: July 2007

The errors of several approximations for photoelectron scattering are systematically studied as a function of the electron energy in the range from 10 to 1000 eV. The accuracy of the approximations does not improve with rising energy, as it was commonly supposed. The errors increase considerably with the angular momentum of the incident wave. The large discrepancies of the small‐scattering‐centre approximation (SSCA) are substantially reduced by means of effective scattering amplitudes in the modified small‐scattering‐centre approximation (MSSCA). Above all the reduced angular momentum expansion (RAME) has such a high degree of accuracy that allows reliable calculations of multiple‐scattering contributions for all purposes. Both the MSSCA and the RAME are further simplified in order to facilitate applications.
Diffusion Coefficient of F− Ions in Perfect β‐PbF2 Crystals
Authors: Sekar P. , Haridasan T. M.
Published: July 2007

In the quasi‐harmonic approximation, the mean square velocity of F− ions in β‐PbF2, along different directions is estimated. A critical square of the velocity is fixed by equating the experimental value of the migration energy to the minimum kinetic energy (E) required by the F– ion to make the jump. The ratio of the calculated kinetic energy to E is assumed to govern the probability term appearing in the Arrhenius equation. The diffusion coefficient is estimated for migration along 〈100〉 and 〈111〉 directions. The calculation is repeated in the reaction coordinate approach for migration along 〈111〉 direction. The estimated attempt frequencies of the ions in this approach are compared with that from Debye approximation. The diffusion coefficient thus calculated compares well with that of experiment. The requirement that the amplitude of the mobile ion should fluctuate to values just enough to cross the first ring of obstructing ions is found to be justified for these fluorite type crystals.
The Advantage of Internal Force Calculations in the X‐Ray Crystal Structure Analysis
Authors: Pietsch U.
Published: July 2007

According to the Hohenberg‐Kohn‐theorem the valence electron density (VED) determines the electronic ground state of crystal. The VED can be constructed measuring the X‐ray scattering amplitudes. Parametric density models are developed in order to complete the experimental data and to enable a generalization of the solved structure parameters. Caused by experimental and methodic errors various density models are able to describe the experimental data with comparable accuracy. However, electrostatic criterions can be applied in order to select a density model, which describes also the dynamical structure–property connections of semiconductor. A quantitative calculation of internal forces is possible by use of the generalized Berlin‐Theorem. The electrostatic model contains the ion–ion‐ and the electron–ion interaction in the crystal. The latter one can be calculated in the Fourier space using experimental or theoretical structure amplitudes. A model is proposed specially designed for diamond and zincblende structure compounds. The elastic properties of covalently bonded materials are described sufficiently precise by a bond charge model, taking into account the variation of amount and extension of the bond charge by deformation of lattice. The so fitted VED response of binary compounds can be transfered to solid solutions in order to interprete quantitatively the measured internal deformations in such materials.
Optical Absorption Coefficient in Cylindrical Quantum Wells
Authors: Pérez‐Alvarez R. , Pajón‐Suárez P.
Published: July 2007

Using the envelope function approximation and a one band model, the absorption coefficient of a quantum wire with arbitrary transverse section is studied. The selection rules for direct allowed transitions are reported. The results are particularised for the cylindrical case with infinite potential barrier, and numerical results for GaAs are given.
Effect of Pressure on Electrical Resistivity and Crystal Structure of Quasi‐Two‐Dimensional Mo4O11
Authors: Koyano M. , Ōhara S. , Negishi H. , Sasaki M. , Inoue M. , Nomura M. , Fujiwara H.
Published: July 2007

Electrical resistivities ϱ and lattice parameters of quasi‐two‐dimensional crystals of monoclinic η‐Mo4O11 and orthorhombic γ‐Mo4O11 are measured under hydrostatic pressure up to 1.2 GPa at room temperature. Both crystals have negative pressure coefficients of ϱ, which can be qualitatively explained by a phonon stiffening effect. In particular, the pressure dependence of ϱ for γ‐Mo4O11 shows a drastic drop or jump at Pc = 0.3 GPa, whose magnitude and the pressure coefficients are strongly dependent on the sample resistivity or degree of stoichiometry. It is suggested that the change of a small amount of MoO4 tetrahedra into MoO6 octahedra induced by excess oxygen atoms is responsible for such structure‐sensitive properties.
Green Function Formalism and Superfluid Properties of 4He
Authors: Bahadur R. , Kachhava C. M.
Published: July 2007

The excitation spectrum of superfluid HeII is studied using the Lennard‐Jones form of the potential and the reaction matrix of the Green's function method. The parameters of the theory are determined from the experimental data only. The results on energy values and equation of state amply justify the proposed philosophy.
A Phenomenological Model for the Magnetic Resistivity of NM‐TM Spin Glasses
Authors: Sheikh A. W. , El‐Fazani M.
Published: July 2007

A phenomenological expression is developed of magnetic resistivity of NM‐TM spin glasses by incorporating “effectively free” spin populations and “interacting” spin populations into modified Kondo and spin‐diffusion theories, respectively. Analyses of the data on AuMn, AgMn, and CuMn through a successful best‐fitting of the model reveal two new conduction electron scattering mechanisms: static magnetic disorder scatterings and spin‐orbit scatterings in addition to s‐d, spin‐spin and non‐magnetic scatterings. It is found that the magnetic resistivity maximum at temperature Tm originates from the suppression of spin‐diffusivity effect and rise of Kondo effect as the temperature increases. The temperature TSG of a new resistivity maximum in “interacting” spin resistivity, is related to Tm. Unlike previous studies, Tm is found to depend explicitly on impurity spins and the ratio of level width with level splitting for spin‐split impurity virtual bound states.
Photocarrier Drift Mobility in Bulk Vitreous GeSe3 in the Temperature Range 60 to 300 K
Authors: Calas J. , Abdel‐Maksoud S. M. , Averous M.
Published: July 2007

From the transit time technics with two blocking electrodes, the drift mobility for the two types of carriers is determined for the bulk GeSe3 in the temperature range 50 to 300 K. These values at room temperature are respectively μdn = 10−2 cm2 V−1 s−1 and μdp = 10−1 cm2 V−1 s−1. Initial photocarrier densities n(0) = 5 × 107 cm−3 and p(0) = 3 × 107 cm−3 are also reported. Successively microscopic mobilities are deduced respectively, μon = 6 × 10−2 cm2 V−1 s−1 for electrons and μop = 10−1 cm2 V−1 s−1 for holes. From these values an estimation of the ratio Nc/Ntn ≈︁ 1 and Nv/Ntp ≈︁ 0.5 is lastly provided as well as trap densities Ntn ≈︁ 1020 cm−3 and Ntp ≈︁ 1021 cm−3.
Heavy Fermion Superconductivity via Kondo‐Type Pairing
Authors: Svozil K.
Published: July 2007

A consistent quantum field theoretical approach to Kondo‐type pairing in heavy fermion superconducting systems is presented. This pairing mechanism allows both “singlet” and “triplet”, as well as l > 1 pairing, depending on the system parameters. Associated with the superconducting transition is the appearance of hybridization (dielectric gap) between localized f‐states and the conduction band. The parquet approximation is used to calculate the superconducting and excitonic (dielectric) gaps.
Many‐Body Effects in Resonantly Excited Dense Exciton Systems
Authors: Schäfer W. , Schuldt K.‐H. , Treusch J.
Published: July 2007

The nonlinear optical properties of semiconductors, which are excited by a strong laser pulse at the excitonic resonance are investigated. The concepts to describe the time‐evolution of the initially coherently excited system in the framework of a nonequilibrium Green's function theory are discussed in general. Numerical results are presented for a quasistationary limit and compared with recent experimental data.
Kinetic Theory of Chemically Reacting Systems
Authors: Kremp D. , Schlanges M. , Bornath T.
Published: July 2007

A kinetic approach for chemically reacting systems is derived on the basis of a nonequilibrium Green's function method. This approach is used to take into account nonideality effects in the rate equation for the exciton density in a semiconductor. Numerical results, especially for the impact ionization coefficient, are given in the case of germanium.
A Raman Investigation of the Polymorphism of Potassium Nitrite
Authors: Tse W. S. , Fang C. S. , Pai K. F. , Lih W.
Published: July 2007

Raman spectra of crystalline KNO2 in the region of lattice and anion internal modes are obtained over the temperature range 80 to 480 K. The temperature dependent results are consistent with the X‐ray and calorimetric work that two transitions occur around 170 and 265 K, respectively.
Sensitized Luminescence of Pure and Doped NaNO2 Single Crystals, III. Excitation Spectroscopy and Time Resolved Trap Fluorescence
Authors: Schmidt Th. , Köhler J. , Kryschi C. , Schmid D.
Published: July 2007

Energy transfer processes in the first excited singlet state of NaNO2 single crystals doped with KNO2 are studied using fluorescence excitation spectroscopy and time resolved spectroscopy of the trap fluorescence. In the latter case either pulse excitation of host excitons or selective resonant pulse excitation of trap states is used. Three pairs of trap states, each of which consists of a shallow trap (trap depth less than 100 cm−1) and a deep trap (trap depth in the order of 1000 cm−1), are identified. At low temperatures energy transfer from the shallow to the deep trap is effective only within the pair. At higher temperatures the shallow traps can also transfer the excitation energy to the host exciton band. The temperature dependence of these processes is discussed on the basis of the generalized master equation.
Curved Wave and Multiple Scattering Corrections in Calculated EXAFS Spectra
Authors: Rennert P. , van Hung Nguyen
Published: July 2007

The curved wave theory RAME (reduced angular momentum expansion) is used to develope an expression for EXAFS. Systematic errors of the standard plane wave evaluation SSCA are found. Partially they can be corrected by a suitable choice of the energy zero E0 in the SSCA expression. But different values E0 have to be used for different neighbour shells at the distance R. An analytical expression E0(R) is given. Furthermore it is shown that there are other important multiple scattering contributions besides those due to the focussing effect for shadowed atoms. The comparision of RAME and the modified small scattering centre approximation MSSCA shows that MSSCA is sufficient accurate for EXAFS. In the XANES region below electron energies of 50 eV RAME is needed. For the first nearest neighbour RAME corrects MSSCA up to 100 eV.