bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractA 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

AbstractFor 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractMeasurements 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractFormulae 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

AbstractThe 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

AbstractA 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

AbstractOn 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

AbstractThe 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

AbstractIn 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

AbstractThe 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

AbstractBy 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

AbstractAC 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

AbstractThe 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

AbstractThe 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

AbstractPolyacetylene 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.