bluuebunny/crossref_metadata_2025 huggingface dataset:
Mössbauer Studies of the System La1−xSrxCo1−yTiyO3
Authors: Kumar V. , Singru R. M. , Parkash O. , Bahadur D.
Published: July 2007

The system La1−xSrxCo1−yTiyO3 for (a) x = 0 and (b) x = y is investigated through Mössbauer spectroscopy measurements carried out between 77 and 800 K. None of the Mössbauer spectra show hyperfine splitting even at 77 K as Ti4+ substitution restricts the generation of Co+ which is primarily responsible for itinerant electron ferromagnetism in La1−xSrxCoO3. In all the samples, two resonances are observed except in the samples with y = 0.3 and 0.5 in the system (a) where three resonances are observed. Three resonances are assigned to low spin cobalt states (i.e. CoII, CoIII and CoIV), high spin Co3+(t2g4eg2) and high spin Co2+(t2g5eg2) states, the first two being common in all the samples. The variation of the isomer shift and other data with temperature is discussed in the framework of spin‐state and valence‐state equilibria of cobalt ions in these materials. The difference in behaviour between the systems (a) and (b) is explained in terms of generation of different valence and spin states of cobalt with the increase in x and is further compared with the system La1−xSrxCoO3. The susceptibility, electron transport, and other data reported earlier support the results obtained from Mössbauer studies.
The Surface or Interface Polaron in Polar Crystals. II. Strong‐Coupling Limit
Authors: Jin‐Sheng Pan
Published: July 2007

The effective Hamiltonian and effective potential are given for the surface strong coupling polaron in polar crystals. Their binding energy and effective mass are also evaluated. When a piece of a polar crystal contacts with a piece of another non‐polar material, and the high frequency dielectric constant ε∞2 of the non‐polar material is larger than that (i.e. ε∞1) of the polar crystal, or is larger than a certain critical value (ε∞2)min, polarons can exist in the interface. Reversely, when ε∞2 < (ε∞2)min, the polaron is not able to exist near the interface. If the non‐polar material is metallic (i.e. ε∞2 = ∞), there is a deeper potential well near the interface in which the polaron may be trapped.
Influence of Collisions on the Resonances in Bounded Semiconductor Plasmas
Authors: Nikolov N. A. , Malinov P. N. , Kostov K. G. , Mihailova G. V.
Published: July 2007

The influence of the collisions on the resonances in a bounded non‐isothermal semiconductor plasma in a magnetic field is considered on the basis of the two‐component magnetohydrodynamics. The semiconductor plasma is placed between two metal electrodes. The external magnetic field is perpendicular to the exciting ac electric field. The frequencies of the excited resonances of “hole sound”‐type are found. The results can also be used in the absence of a magnetic field. They can also be applied for a bounded gaseous plasma. When the collision frequencies are neglected, and without magnetic field, the formulae derived coincide with the well‐known resonance formulae, published previously.
Short‐ and Long‐Range Ordering in Binary Alloys
Authors: Dąbrowski L.
Published: July 2007

Starting from a pair interaction model a generalized theory of ordered binary alloys is derived. Such approach is applicable for arbitrary alloy structures with any given number of long‐ and short‐range parameters and also for all possible numbers of interaction potentials and component concentrations. On the base of pair correlation functions a new definition of short‐range ordering parameters is proposed. Some explicit forms of correlation functions above critical temperature Tc are obtained. The computed results are compared with experimental data for the case of β‐brass. With the accuracy to third‐order perturbation theory, interactions and ordering in 13 coordination shells are considered.
Two‐Phonon Processes in TISe and TlInSe2
Authors: Abdullaev A. G. , Allakhverdiev K. R. , Ibragimov T. D. , Sardarly R. M.
Published: July 2007

Polarization measurements of two‐phonon absorption spectra in TISe and TlInSe2, and of the second‐order Raman scattering spectrum in TISe are carried out in the range of overtone and combination frequencies at room temperature. The observed peaks in the absorption and scattering spectra are interpreted by the selection rules for two‐phonon processes obtained for crystals of TISe type (space group D184h). The peaks which cannot be described by the phonon combination from the centre of the Brillouin zone, are successfully interpreted by selection rules involving the phonons from T and N points of the Brillouin zone.
Phonon‐Polaritons in Bilayer Systems s‐Polarized Guided Wave Phonon‐Polaritons
Authors: Wendler L.
Published: July 2007

In a bilayer system consisting of two dielectric media with local, frequency dependent dielectric functions in addition to p‐polarized phonon‐polaritons, s‐polarized phonon‐polaritons can exist. These phonon‐polaritons are associated with electromagnetic fields having standing wave character in one or in both layers in the direction normal to the surfaces. Therefore, they are guided wave phonon‐polaritons. The regions in the ω − k∥ plane where these phonon‐polaritons can exist are discussed and their principle physical properties derived. The dispersion curves and the electric fields of the s‐polarized guided wave phonon‐polaritons are calculated and presented in graphical form. The results of the developed theory of p‐ and s‐polarized polaritons in bilayer systems are discussed.
Ferromagnetism and Elementary Excitations in the Hubbard Model
Authors: Nikolaev M. Yu. , Ryzhanova N. V. , Vedyaev A. V. , Zubritskii S. M.
Published: July 2007

Two pecularities of diagram technique for Hubbard operators are established. Fermi‐type excitations for the Hubbard model with strong Coulomb repulsion are investigated with the help of this technique. The cause of ferromagnetism in the Hubbard model is discovered. Bose‐type elementary excitations are investigated and the region of existence of ferromagnetic ground state is obtained.
Stimulated Emission Spectra and Valence Band Structure in the Cd3(AsxP1−x)2 System
Authors: Arushanov E. K. , Kulyuk L. L. , Lukyanova L. N. , Nateprov A. N. , Radautsan S. I. , Shtanov A. A.
Published: July 2007

Recombination radiation in Cd3(AsxP1−x)2 solid solutions near cadmium phosphide (x ⪅ 0.1) is studied. A complex structure of the stimulated emission spectra in Cd3(AsxP1−x)2 single crystals is detected. It is shown that for Cd3P2 the width of emission spectrum and its position relative to the transmission edge may be adequately described in terms of a direct interband‐transition model. The same model is used to calculate the luminescence Icv1(ω) and the optical transmission Tcv1(ω) in the presence of a small (i.e. up to 5% of the Brillouin zone size) K1 shift between the extrema of the heavy hole valence band V1 and conduction band C. It is shown that at k1 ≠ 0 the dependence Icv1(ω) may have two maxima. The structure of stimulated emission spectra and the reference data on luminescence in Cd3(AsxP1−x)2 single crystals are interpreted taking into account the calculations carried out in this work.
Transient Light‐Induced Gratings Due to Excitons in CdSe
Authors: Rückmann I. , Jarašiūnas K. , Gaubas E.
Published: July 2007

Transient light‐induced gratings due to free carriers and excitons are created in CdSe in a medium density range of 1015 to 1017 cm−3 by two coherent intense (ns) IR‐pump beams. Detailed investigations of probe‐beam diffraction due to thin excitonic gratings in the spectral region just below the An = 1 ‐exciton line at 85 K and its dependence on sample temperature and on the excitation level are presented. First‐order diffraction efficiences up to 5% and a nonlinear dependence of diffraction on the excitation level can be observed. For the first time numerical calculations of probe‐beam diffraction due to excitonic phase and amplitude gratings are presented. The comparison with the experiment shows, that the damping of a dense exciton gas increases proportional to the excitation intensity in the case of two‐photon interband excitation, and that the light‐induced absorptive changes Δ due to dense excitons dominate over the dispersive changes Δn in the spectral region under consideration.
Systems of Zero‐Phonon Lines Due to Mn2+ Pairs in ZnS
Authors: Benecke C. , Busse W. , Gumlich H.‐E. , Pohl U. W.
Published: July 2007

By time resolved and site selecting spectroscopy at ZnS doped by 0.5 wt% Mn two systems of zero‐phonon lines are detected, which appear at this concentration in addition to the zero‐phonon lines due to isolated Mn2+ ions. These zero‐phonon lines are ascribed to two independent systems of Mn2+ pairs.
Distorted Flux Lines in Bounded Type II Superconductors
Authors: Shehata L. N. , Saif A. G.
Published: July 2007

The interaction of straight or curved flux lines with the boundaries of a type II superconducting slab, ellipsoid, and sphere is considered. The surface barrier opposing the entry of the vortices into the sample shows to be of different values depending on the place of entry into the sample with iespect to the boundary. The force on different elements of the flux lines is completely determined in terms of the total current density at the position under consideration.
Coordinate Transformations Induced by the Elements of the Permutation‐Inversion Symmetry Group of a Nonrigid Molecular Crystal
Authors: Korolev A. A. , Smirnov V. P.
Published: July 2007

Special methods of nuclei labelling and of permutation‐inversion symmetry element description in nonrigid molecular crystals are suggested. These methods allow to obtain in a general form the transformation properties of coordinates (vibrational, rotational, and electronic) with respect to the permutation‐inversion elements of the crystal symmetry group. The general approach is illustrated on the example of a nonrigid sodium nitrate crystal.
Metastability and Depinning Threshold in the Random Field Ising Model
Authors: Nattermann T.
Published: July 2007

A unified description of the depinning threshold Ec for domain walls in the random field Ising model is given. The coherence length Rc ∼ E of the metastable state is proportional to h−vh, where h is the random field amplitude. For broad walls, the results interpolate between recent findings of Bruinsma and Aeppli (vH = 4/(5 – d)) valid at temperatures T ≪ Th(t) and those of Villain (vH = 2) for Th(t) < T ≪ Tco. Tco is the transition temperature of the pure system and Th(t) ∼ h2(3 – d)/(5 – d)/In t, t denotes the time. For narrow walls vH = 2/(3 – d) is found for T < Th(t), vH = 2 for T > Th(t), Th(t) ∼ h2(2 – d)/(3 – d)/In t and d ≦ 3. For d → 3 an exponential dependence is expected of Rc on h−2. Vacancies are found to be decisive for wall pinning in diluted antiferromagnets in small external fields.
Inverse Spectral Theory and Incommensurate Peierls Phases
Authors: Mertsching J.
Published: July 2007

A simple version of the inverse spectral theory for finite‐gap potentials of the Hermitean Zhakarov‐Shabat operator is presented, and the kink and polaron structures in quasi‐one‐dimensional systems with a nearly half‐filled band are discussed in terms of this theory. The gap equation for one kink band in systems with a nearly 1/3‐filled band is solved for special parameters, but no general finite‐gap solution is found in this case.
Electron–LO‐Phonon Interaction near Interfaces. Application to Scattering of Inversion Layer Electrons on SiO2Si Interfaces
Authors: Bechstedt F. , Enderlein R.
Published: July 2007

A theory for the electron‐LO‐phonon interaction near semiconductor interfaces is developed. Starting point is the electron self‐energy in the linearly shielded potential approximation which allows to include the interface influence simply by calculating the corresponding screened Coulomb potential. Carrier scattering, screening, and interaction of electrons with longitudinal elementary excitations are treated from a unified point of view. The theory is applied to the scattering of inversion layer electrons in a MOSFET from polar SiO2Si interface phonons. These longitudinal phonons of Fuchs‐Kliewer type are not present in bulk Si. Their polar character is solely due to the polar nature of SiO2. The scattering rate and the zero‐field mobility limited by electron‐interface‐LO‐phonon interaction are calculated and compared with experimental data. It is shown that for high electron concentrations in the inversion channel the new scattering process is a serious rival of other mechanisms.
Optical Properties of the Impurity Intervalley Multiplet in Ge‐Type Semiconductors in Uniform Constant Electric Field
Authors: Savvnikh S. K.
Published: July 2007

The electric dipole transitions between states of the intervalley donor multiplet in Ge‐type semiconductors placed in an external constant electric field are considered. The assumption that a short range component of the impurity potential plays a dominant role is used in the calculations. For transitions of different types expressions for the oscillator strengths, describing their field and angle dependences, are derived.
AC Conductivity of Highly Inhomogeneous Semiconductors
Authors: Chaikovskii I. A. , Shmelev G. M. , German A. I.
Published: July 2007

The ac absorption constant of an inhomogeneous semiconductor is calculated without any assumptions of electron density fluctuations to be small. A generalized Herring's method is used for calculating the effective conductivity. The method leads to a closed formula in the case of a heterogeneous two‐phase system. The presence of a maximum in the frequency dependence of absorption is explained and its connection with the system parameters is determined.
Two‐Dimensional Electron Gas in the n‐Inversion Layer of p‐Type InSb Bicrystals
Authors: Herrmann R. , Kraak W. , Nachtwei G. , Schurig Th.
Published: July 2007

The galvanomagnetic properties of conduction electrons in n‐type inversion layers adjacent to the grain boundary in p‐type InSb bicrystals in magnetic fields up to 18 T and temperatures down to 2 K are investigated. The observed quantum oscillations of the magnetoresistivity result from a superposition of the Shubnikov‐de Haas effect in two occupied subbands. The electron densities of subbands nsi (ns1 = 3.5 × 1011 cm−2; nso = 1.1 × 1012 cm−2) and the effective cyclotron mass of the subbands mci (mc1 = (0.016 ± 0.004) m0; mco = (0.026 ± 0.003) m0) are evaluated. Besides the Shubnikov‐de Haas oscillations in high magnetic fields (B > 5 T) the Hall resistivity shows the characteristic features of the quantized Hall plateaus in finite regions of the magnetic field B. Simultaneously the diagonal resistivity ϱxx drops to a minimum. Other characteristic features of a two‐dimensional electron gas confined in the symmetrical potential well of the grain boundary are obtained.
Raman Piezospectroscopy in GaAs Revisited
Authors: Sood A. K. , Anastassakis E. , Cardona M.
Published: July 2007

The effects of a uniaxial stress on the first‐order Raman spectrum of GaAs are reported. The shifts of the long‐wavelength optical phonon frequencies and splittings of their degeneracies are obtained with improved experimental accuracy. Phonon deformation potentials and other crystal parameters are established and compared with values previously published.
Electron–Phonon Interaction in Dielectric Bilayer Systems. Effect of the Electronic Polarizability
Authors: Wendler L.
Published: July 2007

A quantum‐mechanical theory of the electron–(long‐wave optical) phonon interaction in dielectric bilayer systems is developed. The operator describing the interaction between an electron and the phonon modes of the bilayer system is calculated including the electronic polarizability. All polarization eigenmodes together with their dispersion relation are derived and discussed. The dispersion curves of the surface phonons are calculated and presented for various cases in graphical form. The interaction of electrons outside and inside the bilayer system is studied and the coupling functions are calculated and discussed and they are shown in graphical form.
A Self‐Consistent Approach to the Ideal Magnetization in Heterogeneous Ferromagnetics
Authors: Diener G. , Posselt M.
Published: July 2007

A generalization of the CPA‐like effective‐medium theory for heterogeneous media to the case of non‐linear material behaviour is proposed. The method is developed referring to the example of ideal effective magnetization of heterogeneous ferromagnetics. The treatment is based on the phenomenological description of micromagnetism. The heterogeneity is expressed by random material parameters. In comparison with the effective‐medium theory the main idea of the new procedure consists in the introduction of an additional stochastic field simulating the long‐range interaction between different grains of the heterogeneous body. In order to illustrate the method calculations are carried out for a simple ferromagnetic model system consisting of a mixture of two isotropic components.
On Static Kink Solutions for an Anisotropic Heisenberg Ferromagnetic Chain
Authors: Fischer K. G. , Heber G.
Published: July 2007

For the anisotropic Heisenberg chain nonlinear equations are derived, describing static kink properties. The equations are exactly solved for an easy axis respectively easy plane ferromagnetic chain. The influence of different forms of local anisotropy is discussed.
Exciton Impact Ionization and Electric Conductivity in Germanium at Low Temperature
Authors: Nöldeke Ch. , Metzger W. , Huebener R. P. , Schneider H.
Published: July 2007

The exciton luminescence intensity and the electric conductivity are measured simultaneously during optical excitation in high‐purity Ge and in p‐doped Ge at 4.2 K as a function of an applied electric field. With increasing field the exciton density decreases due to exciton impact ionization. The carriers which are set free by this process result in a distinct increase in the electric conductivity. For undoped Ge the results agree well with a rate equation model based on impact ionization of the excitons. In the p‐doped Ge impurity impact ionization is found to have a strong influence in addition to impact ionization of the excitons.
Many‐Body Theory for the Dense Exciton Gas of Direct Semiconductors I. General Considerations
Authors: May V. , Boldt F. , Henneberger K.
Published: July 2007

The dense exciton gas is studied theoretically using the two‐time electron–hole pair propagator. The equation of motion for the propagator and an expression for the electron–hole pair selfenergy are transformed to a picture in which electron–hole pairs are mapped on bosons. The lowest decoupling of the selfenergy provides contributions of first and second order concerning the interaction between electron–hole pairs including electron–electron, hole–hole, and electron–hole pair exchange. It is shown that only the direct interaction between electron–hole pairs can be screened by a dielectric function. The connection with results obtained on the basis of an effective Hamiltonian for bosonic electron–hole pairs is discussed.
Shell Model for Clusters of Dense‐Packed s‐Scatterers and Calculation of the Density of States
Authors: Blaudeck P.
Published: July 2007

The local density of states is calculated a) for the central atom in real clusters of dense‐packed s‐scatterers, b) for the same atom surrounded by an appropriate spherically symmetric model potential. It is shown that in many cases the results for the model potential sufficiently approximate the original density of states.
On the Theory of Electrogyration in Dielectric Crystals. Scheelite‐Type Crystals
Authors: Stasyuk I. V. , Kotsur S. S.
Published: July 2007

The A, zz component of the electrogyration tensor for PbMoO4‐type crystals with C4h point symmetry is calculated. The ionic, crystalline and mixed contributions to the electrogyration are separated and numerical estimations are performed. The frequency dependences of different contributions are studied; the results are compared with experimental data. The relation of gyration and electrogyration effects is analysed.
A New Approach for the Diluted Ising Ferromagnet Description
Authors: Balcerzak T. , Truong V. H. , Bobák A. , Mielnicki J.
Published: July 2007

The method of diluted Ising ferromagnet description given by Kaneyoshi et al. is extended, and as a result the magnetization curve, magnetic susceptibility, and specific heat for arbitrary concentrations of magnetic atoms (larger than the critical value) are obtained.
Effect of Relativistic Mass Variation of the Electron on the Modulational Instability of Laser Beams in Transversely Magnetised Piezoelectric Semiconducting Plasmas
Authors: Ghosh S. , Dixit S.
Published: July 2007

The effect is considered of relativistic mass variation of the electron and a large transverse magnetostatic field on the modulational instability of a laser beam and consequent amplification of acoustic waves. The analysis is based on the hydrodynamic model of a plasma in the collision dominated regime. Using coupled‐mode theory the modulational instability in the medium is investigated and the threshold value of the pump electric field and the conditions of the initial growth rates of unstable acoustic waves are deduced. It is found that the condition of instability gets modified due to the presence of the relativistic mass variation. Numerical estimations are made for n‐InSb at 77 K.
Relation between Short‐Range and Long‐Range Order in Solid Solutions with Basal B.C.C. and F.C.C. Structures
Authors: Rempel A. A. , Gusev A. I.
Published: July 2007

A method is proposed to determine the number of nearest coordination spheres in which the presence of limiting short‐range order is sufficient to produce long‐range order. The use of the method is considered with reference to the example of atomic ordering in solid solutions with b.c.c. and f.c.c. structures. It is suggested that a qualitative dependence exists between the kind of order—disorder phase transition and the relation of short‐range and long‐range order in the solid solutions involved.
Attenuation Stress Hysteresis Loops and Low‐Frequency Internal Friction Associated with Thermomechanical Breakaway of Dislocations
Authors: Omri M. , Vincent A.
Published: July 2007

Measurements of ultrasonic attenuation and velocity changes are performed on 5N aluminium during the application of a low frequency bias stress. The characteristics of the attenuation‐stress Δα = f(σ) loops are studied as a function of the repetition of loading, amplitude σm of loading stress, temperature, and pretreatment of the sample (prestrain, ageing time, or temperature). The results show that at least two kinds of dislocation‐point defect breakaway mechanisms are involved in the experiments. Then a model is developed in order to calculate from the attenuation‐stress hysteretic loop a low frequency internal friction decrement δα: peak events versus amplitude (δα = f(σm)) are thus observed, in good accordance with classical models of internal friction associated with breakaway of dislocations; the activation energy for depinning and the space between pinning points are deduced from these peaks and their evolutions are followed as a function of the pretreatment of the sample. In addition, although the internal friction decrements δα and δ, obtained directly from torsion pendulum, have some similar characteristics, a noticeable difference appears in the decrement levels which is especially explained by the characters of the solicitation in bias stress and torsion pendulum experiments, respectively, one sided and alternative; their effects are discussed in terms of dislocation mechanisms.
Energy Band Structure of In1‐xGaxAsyP1‐y Lattice Matched to InP by Means of the Line Profile Analysis of the Electroreflectance Spectra
Authors: Lahtinen J. A. , Tuomi T.
Published: July 2007

The electronic transitions E0, E0 + Δ0, E1, and E1 + Δ1 of In1‐xGaxAsyP1‐y lattice matched to InP are studied by means of the electroreflectance method (ER). The samples grown using liquid phase epitaxy cover the range from y = 0 to 0.642. The three‐point method developed by Aspnes and Rowe is commonly used for the accurate determination of the critical point parameters from the ER spectra. In this study an extension of the three‐point method is suggested for the line profile analysis of the overlapping structures in the ER spectra originating at two adjacent critical points.
Electron Screening and Mobility in Heavily Doped Silicon
Authors: Sy H. K. , Desai D. K. , Ong C. K.
Published: July 2007

The screening effect is studied in a heavily doped n‐type silicon. The Lindhard susceptibility is used for the conduction electrons. The valence susceptibility is treated as a constant parameter. The mobility of electrons is calculated using the Born approximation and by considering the dependence of the electron effective mass on dopant concentration determined empirically. The results compare favourably with recent experiments.
Investigation of Dynamical Bond Charge Transfer in GaAs by Changing X‐Ray Reflection Power under High Electric Field
Authors: Pietsch U. , Mahlberg J. , Unger K.
Published: July 2007

A direct experimental proof of the variation in amount and position of the bond charge (BC) in covalent bonded crystals under a high external electric field is given. Using a modulation technique the variation of the BC‐dependent X‐ray reflections (222, 442 …) are measured for GaAs due to an electric field of about E = 40 kVcm−1. The variation amounts to about δF2/|F|2 ≈ 10−4 for [111] oriented samples. The effect behaves linearly with respect to the external field being oriented parallel or antiparallel with respect to [111] direction. A molecule‐theoretic model is used to describe the experimental data by variation of screening constants of atomic valence orbitals. All the BC's shift against the external field direction by about (1.2 ± 0.3) × 10−5 nm. The BC is transfered from the bonds having increased ionicity of about 0.2‰ to the more covalent bonds.
Molecular Dynamical Study of ß‐AgI1−xClx
Authors: Ihara S. , Suzuki K.
Published: July 2007

A molecular dynamics study of ß‐AgI1−xClx is performed with 896 ions. It is shown that the substitution of Cl− ions in ß‐AgI increases the concentration of Frenkel defects. This result is consistent with Shahi and Wagner's conjecture.
Spin‐Flip Intraband Absorption of Intense Laser Field in the Europium Compounds
Authors: Tronconi A. L. , Nunes O. A. C.
Published: July 2007

The spin‐flip electron‐magnon scattering in the europium compounds (e.g. EuO) in the presence of intense laser light is considered. A kinetic equation for electrons is derived from which the spinflip absorption coefficient, αSF, is obtained. It is found that in the limit of ultra‐strong fields αSF, is vanishing small as a consequence of the weakening of the electron‐magnon interaction under such intense electromagnetic fields.
Exciton Absorption Spectrum
Authors: Sherman A. V.
Published: July 2007

Formulae are obtained, which enable one to develop an algorithm of an exact calculation of Green's function and the absorption spectrum of an exciton interacting with phonons for arbitrary parameters entering into the Hamiltonian at zero temperature. The expansion of Green's function into a continued fraction serves for the basis. As an illustration the absorption spectra are calculated for different parameter sets for an exciton with a three‐cosine band, which interacts with nonpolar optical phonons.
Non‐Linear Optical Nutation on Interexciton Transitions in Cu2O
Authors: Bardetskii P. I. , Shmiglyuk M. I. , Tiron Sh. D.
Published: July 2007

The non‐linear optical nutation on the transitions between IS and 2P exciton states of the Cu2O yellow series is considered theoretically taking into account their degeneracy and polarization properties. The problem is solved under various initial conditions for certain definite orientations of the electrical component of the laser field that causes the interexciton transitions. It is shown that the exciton and photon concentrations vary periodically in time within a certain range near their steady equilibrium values which coincide with the stationary ones. The nutation frequencies are found. A stationary condition is obtained and the stationary frequencies and concentrations are determined.
Electronic Properties of Ternary Superconductors
Authors: Ameta G. S. , Upadhyaya U. N.
Published: July 2007

A microscopic theory of the ferromagnetic superconductor is developed from first principles. Expressions for the electron self‐energy, electron Green's function, renormalized frequency and gap parameter are derived using the Green's function technique and the four dimensional matrix formalism considering the f‐d exchange effect up to second order. The theory is applied to explain the experimental results for the much exciting case of the rare earth ternary system ErRh4B4. The behaviour of the superconducting gap parameter (Δ) and the electronic thermal conductivity (KS) are studied and the results are compared in the coexistence region of superconductivity and magnetism in the system ErRh4B4. There is good agreement between the theoretical results and the experimental data.
The Tensor Reflection Coefficient for the Surface Diffraction
Authors: Maksimenko S. A. , Skadorov V. V.
Published: July 2007

On the basis of the covariant method the matrix equation describing the dynamical diffraction in the Laue‐to‐Bragg geometries is obtained. The tensor reflection and transmission coefficients are found for the case of symmetric surface diffraction. It is shown that unenriched Mössbauer crystals are more suitable for observing the surface diffraction.
Lattice Theory of Fourth‐Order Elastic Constants of Primitive Lattices
Authors: Goyal S. C. , Kumar K.
Published: July 2007

The theoretical expressions for the fourth order elastic (FOE) constants of the primitive lattices are derived. First the equation of wave propagation in a homogeneously strained medium is obtained and then it is compared with the equation derived from the macroscopic theory of elasticity which yields the required relations for (FOE) constants and the Kun‐Huang relation among the fourth order coupling parameters.
Dislocations and Energy of Grain Boundaries in Crystal Structures with Covalent Bonds
Authors: An Nguyen , Herrmann R. , Schurig Th. , Worm G.
Published: July 2007

In covalent bounded crystal structures the construction of grain boundaries with low lattice deformation is possible by ring dislocations. The present work deals new aspects of the formation of binding rings. There will be introduced structure units of the grain boundaries as binding tetrahedrons enabling the formation of 5–7 and 5–7–n · 8‐ring dislocations. Due to these dislocations grain boundaries with rotation angles θ between 0° and 180° can be constructed. The dislocation density in the grain boundaries does not increase monotonously with the tilt angle θ, but reaches maxima for discrete rotation angles (θ = 26.53°, 109.47°, and 148.49°). It can be shown, that dangling bonds in these grain boundaries exist only in special angular ranges.
Small Vacancy Clusters in Nickel
Authors: Vasilyev A. A. , Sirotinkin V. V. , Melker A. I.
Published: July 2007

The method of molecular dynamics is used to compute binding energies of different configurations of vacancy clusters in nickel. The interatomic pair potential is obtained according to the pseudopotential theory. It is found that in the range from divacancy to hexavacancy various atomic configurations are formed which can be considered as nuclei of dislocation loops, voids, and new crystal lattices.
Theory of Absorption and Scattering of Light by Singlet–Triplet Magnetic Systems
Authors: Seidov Yu. M. , Suleimanov A. M.
Published: July 2007

By the multi‐time Green's function method the light absorption and scattering in the singlet‐triplet systems are investigated by means of the pseudospin formalism. The role of the crystal field for the two‐magnon light absorption in the singlet‐triplet ferro‐ and antiferromagnets and for the one‐magnon light scattering in the singlet‐triplet ferromagnets is elucidated.
Frequency Dependence of the AC Susceptibility of the Reentrant System CdCr2xIn2−2xS4 (0.85 < x ≦ 1)
Authors: Dormann J. L. , Saifi A. , Cagan V. , Nogues M.
Published: July 2007

AC permeability measurements of the reentrant spin glass system CdCr2xIn2−xS4 (0.85 < x ≦ 1) are performed on toroidal shaped samples by using the transformer technique since the demagnetizing factor is minimized. The complex permeability observed is very close to the true initial permeability. The abrupt decrease of μ' at low temperatures is an intrinsic effect, probably related to the transition to the reentrant spin glass state. The out‐of‐phase permeability presents a maximum at the transition temperature TRSG. The frequency dependence of TRSG is studied (130 Hz ≦ v ≦ 100 kHz). Its variation corresponds with the explanation of reentrant properties based on the existence of clusters of which the freezing destroys the ferromagnetic order.
On the Atomic Limit of the s–f Model
Authors: Karpenko B. V. , Kuznetsov A. V. , Falkovskaya L. D. , Budrina G. L.
Published: July 2007

The atomic limit of the s–f model for a system in an external magnetic field is studied. By direct calculation of traces expressions are obtained for the first time for the partition function, average number of electrons, chemical potential, magnetization, susceptibility, mean energy, and specific heat at arbitrary values of electron concentration, spin, temperature, magnetic field, and exchange and Coulomb interaction parameters. It is shown that the system behaving itself in many respects as an ensemble of “quasi‐particles” of four types, i.e. holes, down‐units, up‐units, and pairs is always paramagnetic and the susceptibility may obey both, Curie law and Curie‐Weiss law. At subnormally small intra‐atomic interactions Schottky anomalies may be observed in the system.
Self‐Consistent Tight‐Binding Method for Total Energy Calculations of Tetrahedral Semiconductors Including Surfaces and Defects
Authors: Bechstedt F. , Reichardt D. , Enderlein R.
Published: July 2007

The total energy of macroscopic electron‐ion systems as a function of ion positions is an important quantity for studies of atomic and electronic properties of ideal crystals, surfaces, and defects. For the first time a total energy calculation is presented which relies on tight binding theory and takes the electron‐electron interaction fully into account. The advantage of the method as compared to the more accurate pseudopotential‐density functional approach is its greater simplicity at still existing accuracy. The calculation relates directly to covalently bonded tetrahedrally coordinated semiconductors, but it can also be applied to ionic tetrahedral materials. The intraatomic part of the electron‐electron interaction enters the total energy through the characteristic U‐parameters whereas the long‐range interatomic contribution is approximated by a Madelung‐like Coulomb repulsion. Correlation makes that all one‐electron energy levels depend on their populations which in turn are determined by the one‐electron energies. Hence the total energy has to be calculated self‐consistently. Bonding parameters, atomic orbital energies, and parameters of electronelectron interaction are adjusted in such a way that ionization potentials of free atoms and ground‐state properties of ideal crystals as cohesive energy and bulk modulus are corectly reflected. The inclusion of the full electron‐electron interaction guarantees also the true magnitude of the total energy. The simplicity and accuracy of the presented method makes it suitable for studies of atomic rearrangements near surfaces and defects. This is demonstrated explicitly in the case of relaxed (111) 1 × 1 surfaces of covalent semiconductors.
Critical Lengths for Formation of Kink Structures in Finite Trans‐Polyacetylene Chains
Authors: Watts‐Tobin R. J.
Published: July 2007

Polyacetylene chains can have defects such as kinks in their bonding patterns. As these defects are long compared with the carbon‐carbon spacing they can be described by a continuum model. In this paper the continuum model is applied to finite chains of polyacetylene, which are of greater practical interest than very long chains. A perturbative calculation shows that there are critical lengths of polymer chain for the appearance of structures containing increasing numbers of kinks. The energy of formation of these structures is also estimated.
Pb1−xGdxTe a New Semimagnetic Semiconductor with Rare Earths
Authors: Averous M. , Lombos B. A. , Fau C. , Ilbnouelghazi E. , Tedenac J. C. , Brun G. , Bartkowski M. A.
Published: July 2007

Pb1−xGdxTe, a new semimagnetic semiconductor, containing gadolinium as a rare earth element is synthesized. Its magnetic susceptibility, transport and optical properties are determined in the temperature range of 4.2 to 300 K using magnetic field intensities up to 6 T. The interaction between the Gd3+ ions are found to be slightly antiferromagnetic. The measured Hall mobilities of the samples with low gadolinium concentration (1 at% nominal value) are extremely high (4 × 106 cm2 V−1 s−1) at 4.2 K. They are comparable with the mobilities reported in superlattices. The large static dielectric constant of the PbTe host lattice is invoked to serve to shield out the electric fields of the ionized impurities and defects, minimizing impurity scattering. In addition, at low gadolinium concentrations, no Schubnikow‐de Haas oscillations are found although all the required conditions for them are satisfied. In this sample the Fermi level is 16.9 meV above the conduction band edge. It is argued consequently, that all the Landau levels passed the Fermi level due to the internal magnetic field induced by the rare earth ions. At higher gadolinium concentrations, 2 and 5 at%, the Fermi level moves up to 338 and 478 meV in the conduction band. Consequently, the internal magnetic field does not pre‐empt the effect of the external magnetic field. This results in the appearance of the Shubnikow‐de Haas oscillations, as expected.
Temperature and High Pressure Raman Study of M3P7 (M  Li, Na, K, Rb, Cs) Compounds
Authors: Bolduan F. , Hönle W. , Hochheimer H. D. , Henkel W.
Published: July 2007

We report the results of a study of M3P7 (M  Li, Na, K, Rb, Cs) compounds by Raman scattering at various temperatures and pressures in the solid state as well as in the solution. The compounds M3P7 (M  Na, K, Rb, Cs) show a first order phase transition from a crystalline to plastic crystalline state, which has already be confirmed by X‐ray, specific heat, and DTA measurements. Above the transition temperature Tc the low frequency external Raman lines vanish completely for all compounds except Li3P7, which is characteristic for a transition from a crystalline to a plastic crystalline phase. In the case of Li3P7 the external Raman modes are still present above Tc. This result combined with the results of X‐ray and DTA investigations suggests that the phase transition in Li3P7 involves a valence fluctuation within the polyanion P.
Temperature Dependence of the Raman Spectra of Calcium Oxalate Monohydrate
Authors: Duval D. , Conurate R. A.
Published: July 2007

Analyses of vibrational spectra and X‐ray powder diffraction data demonstrate that two phases (space groups I2/m and P21/n) coexist for calcium oxalate monohydrate between 273 and 376 K. Interpretation of the Raman spectra indicates that the I2/m‐P21/n phase transition near 320 K is analogous to the cubic‐tetragonal phase transition of NH4Cl. Unambiguous Rarnan band assignments are reported for the phase with space group I2/m. Several band reassignments are made for calcium oxalate monohydrate with space group P21/n.
First Order Raman Scattering in CdSnP2
Authors: Irmer G. , Heinrich A. , Monecke J.
Published: July 2007

The optical phonon spectrum of CdSnP2 and its directional dispersion is investigated by Raman scattering. The results are compared with theoretical results, ir measurements, and the phonon mode frequencies of InP, the isoelectronic analogue of CdSnP2.
Hot‐Exciton Orientation in Indirect‐Gap GaAs1−xPx Alloys
Authors: Charfi F. F. , Zouaghi M.
Published: July 2007

Resonant Raman scattering in indirect‐gap GaAs1‐xPx alloys is studied. The multiphonon scattering intensity as a function of the incident energy and polarization correlation measurements of 2LO‐phonon scattering are presented. The intensity dependence and the depolarization associated to the participation of large momentum resonant intermediate states are consistent with the hot exciton cascade model.
Quantum Effects in Accumulation Layers of Si‐SiO2 Interfaces in the WKB Effective Mass Approximation
Authors: De Castro E. , Olivo P.
Published: July 2007

An accurate, yet simple method is given to evaluate electric potential and quantum levels in silicon accumulation layers particularly suitable for implementation in the numerical analysis of the tunneling processes in MOS (metal‐oxide‐semiconductor) structures under general conditions. The procedure makes use of the WKB (Wentzel‐Kramers‐Brillouin) approximation for the electron wave functions: Poisson's equation is then expressed in a purely integral form solved by the Ritz method (i.e. by parametrized functions). A simplified procedure, which generalizes a one‐level model is also given. It is shown that it can give a fairly accurate estimate of the accumulation layer ground state, provided the effects of a sufficient number of subbands are taken into account.
Auger Recombination of Electrons via Deep and Shallow Acceptors
Authors: Khalfin V. B. , Strikha M. V. , Yassievich I. N.
Published: July 2007

The theory of Auger recombination via deep and shallow acceptors in p‐type AIIIBV semiconductors is investigated to determine the influence of free and localized carrier wave functions orthogonality. The extension of zero radius potential model to the case of several bands is used for the treatment of the deep acceptor wave function. The asymptotic wave function of the shallow acceptor for the range of the great wave vectors, and the scattering amplitude in the case of elastic scattering of the free carriers by a deep centre, are obtained, taking into account complex band structure. The results of the theory are applied to GaAs, and InGaAsP solid solutions. The rates of the various processes of Auger recombination are compared.
Quantumchemical Study of Imperfect Semiconductor Surfaces Including Step and Kink Sites
Authors: Katterle T. , Lorenz W.
Published: July 2007

The influence of semiconductor surface imperfections upon elementary processes of chemisorption and charge transfer is studied. Taking as simple model a silicon (111) surface with [211]‐step and kink site, chemisorption of H, OH, and H2O in different positions is investigated in TB approximation. Local and difference densities of states are calculated and adsorbate charges, relative charges of the chemisorption complexes, and adsorption energies determined.
Influence of Local Environment on Bound Excitons and Bound Excitonic Molecules in III‐V Alloys. I. Theory and Numerical Results for GaAs1−xPx:N
Authors: Müller H.‐J.
Published: July 2007

A calculation of the local‐environment effect on nitrogen bound excitons and excitonic molecules in III‐V‐mixed crystal alloys is represented. The stochastic alloy potential is treated by means of perturbation theory, and a random distribution of As and P atoms in the appropriate sublattice is assumed. Because of special considerations concerning the concentration dependence of the averaged alloy potential the method is free of adjustable parameters. The density of states and its statistical momenta are calculated including electrons and holes simultaneously. The method is applied to GaAs1−xPx:N. Good agreement with measured bandwidths for bound excitons is obtained.
Hall Factor in p‐Ge with Anisotropic Energy Spectrum
Authors: Gutsul I. V. , Kirnas I. G. , Litovchenko P. G. , Marusyak V. I. , Nitsovich V. M. , Ostapov S. E. , Petrosyan E. E.
Published: July 2007

By solving the kinetic Boltzmann equation, a quasi‐momentum distribution function for charge carriers in p‐Ge is found taking into account the non‐sphericity of the constant energy surfaces of light and heavy hole bands. Account is also taken of the anisotropic carrier scattering by ionized impurities and acoustic lattice vibrations. The magnetic field and temperature dependences of the Hall‐factor rH are calculated for fields 0 < B ≦ 5 T and temperatures 77 K ≦ T ≦ = 260 K. The results calculated are compared with measured τH values obtained on oriented p‐Ge samples with free carrier concentration p ≈ 1.7 × 1014cm−3.
Three‐Body Interaction in H.C.P. Metals
Authors: Dutta B. , Sarkar S. K. , Roy D.
Published: July 2007

The consideration of two‐body central forces cannot explain the correct ordering of dispersion branches in the I'KM direction in many h.c.p. metals. The importance of three‐body forces in these metals is also indicated by the fact that for these metals the sum rule of Waren is not satisfied. Pseudopotential theory demonstrates that the total energy of a metal consists of an effective two‐body central interaction and a purely volume dependent part. Starting from this basis, a model expression for the energy of a metal is developed. It is shown that the interpretation of the volume strain as the local strain, as demanded by the adiabatic hypothesis, leads to an effective three‐body interaction between the ions. The model is applied to study the lattice dynamics of Mg and Be. It is found that the model predicts the correct ordering of the dispersion branches and fairly good agreement is obtained in the case of phonon frequencies and elastic data.
Spin–Phonon Excitations in Paramagnetic Crystals. Heat Transfer at High Temperatures
Authors: Kokshenev V. B.
Published: July 2007

An analysis is made of high‐temperature thermal conduction (above the Debye temperature) of a paramagnetic crystal in the conditions of exciting coupled spin–phonon modes. It is shown that the rearrangement of crystal spectra connected with these excitations changes drastically the character of heat carriers that may lead to considerable anomalies in the temperature behaviour of thermal conduction of a crystal formed by paramagnetic ions.
Some aspects of raman scattering in Cd3As2 single crystals
Authors: Weszka J. , Renucci M. , Zwick A.
Published: July 2007

Raman scattering measurements in the tetragonal Cd3As2 single crystals are carried out at temperatures of 300 and 77 K. The spectra obtained are interpreted in terms of phonon‐electron and electron‐electron interactions. The features in the low‐frequency interval are due to contributions from phonon and single particle scattering. The electronic RS involving intra‐ and interband excitations is dominant at frequencies higher than 80 cm−1. The resonant enhancement of the band at 300 cm−1 arises from the incident light frequency being in the vicinity of ∑1 – ∑4.
Multiple scattering approach to the XANES theory of alkali halide crystals. I. Crystalline potential in the X‐Ray absorption spectra problem
Authors: Bugaev L. A. , Gegusin I. I. , Datsyuk V. N. , Novakovich A. A. , Vbdbinskii R. V.
Published: July 2007

Two schemes of the crystalline potential for the slow electron in the conduction band of alkalihalides are proposed. The first one (semiempirical) is based on the assumption that in the case of an ion in the crystal one can use the same energy dependence of logarithmic derivatives (of radial solutions at the atomic sphere radius) as in the case of the isolated ion. The modifications required consist in some potential corrections, that are due to the Madelung field as well as to the relaxation and polarization response for both, hole and electron. The second model (ab initio) suggests the straightforward solution of Poisson's equation. Both approaches are compared, so it is found that they lead to satisfactory agreement for a wide energy interval in the continuum.