bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kondo Effect in the Transport Properties of the CsCl‐Type Compounds Fe1−xTi1+x. II. Magnetic Scattering Center due to Atomic Disordering
Authors: Ikeda K. , Nakamichi T. , Yamada Y. , Yamamoto M. 
Published: July 2007

AbstractNeutron diffraction measurements were made at room temperature for the CsCl‐type compounds, Fe1−xTi1+x, in order to confirm the origins of the anomalous transport phenomena in the titanium‐rich compositions and the superparamagnetism near the stoichiometric one. On the basis of those results, it could be concluded that the former behaviour is due to the Kondo effect, originating in a magnetic cluster of nine iron atoms with a concentration of about 10−2, produced by the atomic disorder. The composition dependence of the residual resistivity also seems to be explainable from this point of view.
Effect of Magnetic Surface Reconstruction in Spin‐Wave Resonance: Twofold Resonance of the Surface Mode
Authors: Puszkarski H. 
Published: July 2007

AbstractFeasible techniques are considered, aimed at the production of a magnetic surface reconstruction (MSR) effect in thin ferromagnetic films as a result of which the surface spins orient themselves obliquely to the uniformly oriented bulk spins. It is shown that this kind of MSR admits of twofold resonance excitation of the same surface mode (in intrinsically different physical conditions): once previous to MSR, and once again subsequent to MSR.
Solution of the Onsager Ion Recombination Model in One Dimension
Authors: Singh J. , Baessler H. 
Published: July 2007

AbstractApplying Onsager's theory in one dimension it is shown that there is a finite probability for a carrier to escape geminate recombination with its image charge a t the interface of a molecular crystal and metal even in the absence of an external field. In contrast to the three dimensional case, however, the escape probability is not a strictly linear function of the field and depends on the initial pair separation, even at low fields. Good agreement between theory and experiment is obtained.
Exciton Interaction in Photoluminescence from ZnO
Authors: Hvam J. M. 
Published: July 2007

AbstractThe luminescence spectra of ZnO platelets at 1.9 K have been investigated under 3371 Å Insor excitation from 5 to 500 kW/cm2. New details in the P‐band luminescence (exciton‐exciton scattering) reveal the separation between A and B excitons in ZnO and the stimulated emission in this band is found to be strong for exciton scattering to higher excited states (n > 2). At the highest excitation powers a new emission line is observed which is associated with the decay of excitonic molecules. The molecule binding energy is estimated to be 15 to 20 meV.
Exciton Exchange and Lyddane‐Sachs‐Teller Relations
Authors: Schütz O. , Uihlein Ch. 
Published: July 2007

AbstractA consistent treatment of excitons interacting with light shows that the nonanalytic part of the exchange interaction leads to a longitudinal‐transverse splitting that equals the energy shift of transversal excitons due to polariton effects in cubic crystals (K = 0). This holds true also if excited exciton states are included.
Relaxation Process in U3+:Lacl3 Detected by Resonant Self‐Absorption of Fluorescence
Authors: Furrer R. , Seiff F. , Pelzl J. 
Published: July 2007

AbstractUsing a pulse saturation method with optical detection of the recovery of fluorescent light, the temperature dependence and angular anisotropy of the spin‐lattice relaxation rate T of U3+ in anhydrous lanthanum trichloride has been measured. In the range 1.5 K ≦ T ≦ 4.2 K the direct relaxation process was found to be dominant, leading to a relaxation rate which can be fitted to the expression T = 4.16(5)T s−1 with the anisotropy coefficient of the direct process A (θ = 90°)/A (θ = 0°) ≈ 10. Both results are comparable with the data measured for the corresponding 4f3 ion, Nd3+ in LaCl3.
Comparison of an Amorphous CBS Structure Model of Amorphous Silicon with X‐Ray and Electron Scattering Data
Authors: Boyce J. F. , McCloughrey J. K. 
Published: July 2007

AbstractAn amorphous CBS‐structure model of the form employed by Kramer et al. has been compared to electron and X‐ray scattering data from amorphous silicon. The results tend to support a distorted wurtzite structure.
Temperature Genesis of the Curves of Absorption and Dispersion of Light by Ionic Crystals in the Exciton Region
Authors: Lubchenko A. F. , Nitsovich V. M. , Tkach N. V. 
Published: July 2007

AbstractThe temperature dependence of the curves of absorption and dispersion of light of ionic crystals in the exciton region is investigated taking into account the interaction of excitons with acoustic and optical phonons. It is shown that the shape of the curves depends on the sign of an effective exciton mass m. In the approximation linear in the phonon operators the maxima of the curves shift with increasing temperature towards lower energies when m > 0, and towards higher energies when m < 0.
Optical Phonons in CdSiP2
Authors: Bettini M. , Bauhofer W. , Cardona M. , Nitsche R. 
Published: July 2007

AbstractRaman scattering and reststrahl measurements are presented on single crystals of the chalcopyrite CdSiP2, grown from the vapour phase by iodine transport. The spectra of the zone centered phonons from 60 to 520 cm−1 show a strong similarity to those of ZnSiP2. The mode distribution of the spectra can be completely interpreted by considering that the Γ‐phonons of the chalcopyrites derive from the zincblende modes of the Γ, X, and W points. A qualitative comparison of the simpler modes in CdSiP2, to those in ZnSiP2, shows that the force constants do not deviate much from those of the corresponding binary and elemental semiconductors.
Effect of Interatomic Interactions on the Zero‐Bandwidth Hubbard Hamiltonian
Authors: Tu R. S. , Kaplan T. A. 
Published: July 2007

AbstractWe consider the linear‐chain zero‐bandwidth Hubbard Hamiltonian with added nearest‐neighbor interactions, with a magnetic field present. Exact expressions for thermo‐dynamic quantities are obtained in simple closed form for the half‐filled band. The qualitative behavior of the expressions for susceptibility and specific heat is discussed with a view toward recent studies of the organic salt NMP‐TCNQ.
Hyperfine Properties of Capper Metal
Authors: Abati S. , Borchi E. , Coppi P. G. , de Gennaro S. 
Published: July 2007

AbstractA detailed theoretical analysis is made of the hyperfine properties of metallic copper in the framework of the orthogonalized plane‐wave method and pseudopotential formalism using a reliable model for the Fermi surface of copper. The direct and exchange core polarization (ECP) contributions to the conduction electron spin density are evaluated and the role of the ECP contribution is discussed. The exchange and lattice enhancement effects on the Knight shift and the spin‐lattice relaxation time are taken into account accurately. The agreement between the theoretical results and the available experimental data is quite satisfactory.
The Spectral Distribution of Acoustical Phonons in a Plate
Authors: Iosilevskii Ya. A. 
Published: July 2007

AbstractA general expression is obtained for the spectral density, g(ω2), of acoustical phonon states in the elastically isotropic plate of arbitrary thickness, d, with stress‐free boundaries using the Green‐function method. The cases are analysed where the phonon mean free path, lph, is much larger and conversely much less than d. It is shown that the surface contribution to the thermodynamical values is additive at T ≫ πħc/kd (c is a characteristic velocity of sound) while the exact function g(02) is not additive for lph ≫ d. In this case a simple analytical expression is found for the effective distribution which allows to calculate the surface contribution to the thermodynamical characteristics of the sample of arbitrary configuration.
Behaviour of Microwave Absorption of. Tellurium at Temperatures below 10 K
Authors: Herrmann Karin , Herrmann R. , Braune W. 
Published: July 2007

AbstractTwo characteristic lines have been found in the differential microwave absorption spectrum of tellurium in low magnetic fields at temperatures below 6.4 K. These lines were observed independently of the hole concentration between p = 3.7 × 1013 and 3.4 × 1018 cm−3. The magnetic field dependence of the lines as well as their amplitudes were investigated between 1.4 and 6.4 K and showed a strong temperature dependence. The anisotropy of the lines in the magnetic field is not determined by the crystallographic orientation of tellurium, but by the orientation of the magnetic field with respect to the sample surface. A frequency dependence of the lines has not been observed within the spectral range investigated.
Investigation of Pair Interactions of Er3+ Ions in YVO4 by Paramagnetic Resonance
Authors: Kugler H. , Hillmer W. , Kahle H. G. 
Published: July 2007

AbstractEPR measurements on YVO4 doped with 1% of the erbium isotope 170 were carried out in the K‐band at T = 1.7 K to investigate the Er3+ pair interaction in this compound. The experimental results for five different neighbour pairs are described by an effective spin Hamiltonian, the parameters of which were obtained by a fit to the measured resonances for various angles between magnetic field and crystal c‐axis. The pair interaction is mostly due to magnetic dipole and only a small part is due to superexchange interaction.
Use of X‐Ray Diffuse Scattering Data for the Construction of the Fe‐Si Equilibrium Diagram
Authors: Semenovskaya S. V. , Umidov D. M. 
Published: July 2007

AbstractThe Fourier‐transforms of interchange energies were determined by the method of X‐ray diffuse scattering from single crystals of disordered Fe‐Si solid solutions. The values of Fourier transforms obtained were used to calculate the free energy in the self‐consistent field approximation and to construct equilibrium Fe‐Si diagrams within the composition range of 0 to 50 at% Si. The diagram calculated contains a two‐phase α1 + α2 field at high temperatures and a two‐phase α + α1field at low temperatures. The situation of the phase boundaries is in good accordance with the experimentally observed one.
Explanation of the Magnetic Structure of Er2Ni7 with a Point‐Charge Crystal Field Model
Authors: Yakinthos J. K. , Rentzeperis P. J. 
Published: July 2007

AbstractThe magnetic structure of the intermetallic compound Er2Ni7, predicted by Bertaut's macroscopic theory, is plausibly explained by a crystal field model. The Er ions occupy two sites with anisotropy directions perpendicular to each other. The exchange energy forces the moments to deviate from these directions and form a canted structure.
Infrared Absorption and Ferroelectricity of Small BaTiO3 Crystals
Authors: Ruppin R. 
Published: July 2007

AbstractInfrared absorption spectra of small BaTiO3 crystals which have been reported by various investigators are compared with detailed theoretical calculations performed for spherical samples. The porperties of the infrared active modes and the soft mode in small crystallites are discussed. It is found that a shift of the transition temperature is not expected to occur in grains of the size usually employed in infrared absorption measurements, but will appear in extremely small crystallites, less than about 120 Å in size.
Shubnikov‐de Haas Effect in the Longitudinal Magnetoresistance of p‐Type Germanium
Authors: Carrère G. , Ulmet J. P. , Askenazy S. , Barbaste R. 
Published: July 2007

AbstractShubnikov‐de Haas oscillations in the longitudinal magnetoresistance of heavily‐doped p‐type germanium (p ≈ 3.9 × 1018 cm−3) are observed for H parallel to 〈100〉, 〈110〉, and〈111〉. The direction‐dependent behaviour of these oscillations shows the anisotropy and non‐equidistance (Luttinger effect) of the light‐hole Landau levels.
Generalization of Fick's Law for Non‐Local Complex Diffusion in Semiconductors
Authors: Jacoboni C. 
Published: July 2007

AbstractElectron diffusion in semiconductors is studied at short distances and/or times. An extension of Fick's law with higher derivatives is introduced, and a numerical method determines how many terms are to be kept and the values of the corresponding coefficients. At high applied electric fields the asymmetric diffusion introduces an imaginary part of the Fourier‐transformed diffusion coefficient, that is, even order derivatives in the diffusion equation.
On the Chemical Potential of the Hubbard Model
Authors: Monecke J. 
Published: July 2007

AbstractOn the basis of a cluster approach to the Hubbard model it is proved that the chemical potential μ as a function of the number of electrons per atom n has a jump at n = I on the insulating site and that n as a function of μ has a jump at μ = I/2 on the metallic site of the metal–insulator transition. In terms of an one‐electron picture this corresponds to an infinite density of states at the Fermi level in the metallic phase.
The Magnetic Field Distribution of Superconducting Alloys with Small Magnetization
Authors: Brandt E. H. 
Published: July 2007

AbstractThe magnetic field distribution of type‐II superconductors with arbitrary concentration of non‐paramagnetic and paramagnetic impurities is calculated near Hc2 for 0 ≦ T < Tc. At a certain temperature T, depending on the impurity concentration, minimum and saddle point of H interchange their positions. At very low T, the reduced magnetization |4πM| B/N〈|Δ|2〉 reaches a maximum at a certain impurity concentration, but even a small concentration of paramagnetic impurities inhibits this effect. The new H leads to a correction of the χ2‐theory.
Single‐Particle Excitations in Mott Insulators
Authors: Monecke J. 
Published: July 2007

AbstractOn the basis of a moment‐generated solution of the Hubbard model the quasiparticle energies of an extra electron or a hole in an otherwise half‐filled band are calculated in the limit of small hopping probability. In first order in the hopping probability the quasi‐particle bandwidth is zero in the case of a simple up–down spin configuration and small if zero‐point spin deviations are included. In the paramagnetic case the bandwidth is reduced to one half of the ferromagnetic one.
Correlation of Magnetic Susceptibility, Electrical Conductivity, and Structural Parameters of Ti3O5 via EPR Spectroscopy
Authors: Houlihan J. F. , Mulay L. N. 
Published: July 2007

AbstractVariable temperature EPR studies of polycrystalline Ti3O5 have been interpreted in relation to magnetic susceptibility, electrical conductivity and X‐ray diffraction data obtained on samples from the same chemical run. Electronic mobility and electrical conductivity values have been calculated in both the metallic and semiconducting regions of Ti3O5 and have been discussed in relation to the experimentally determined conductivity values of Bartholomew and Frankl. In addition, the multiplet structure observed in the EPR spectrum has been interpreted in terms of an anisotropic g‐factor and the randomness of the polycrystalline sample.
Pseudopotential Calculation of the Piezoelectric Constant of GaAs
Authors: Zeller G. R. 
Published: July 2007

AbstractA theory of the piezoelectricity of zincblende type lattices is presented. The piezoelectric polarization in a uniformly strained crystal is produced by the internal displacements of the two core ion sublattices and the distortion of the valence electron distribution. The latter is calculated applying first order perturbation theory to the empirical pseudopotential method. The computational work has been carried out for GaAs. Satisfactory agreement between theoretical and experimental values of the piezoelectric constant is achieved if the deformable ion model is applied to empirical pseudopotentials. As a test for the accuracy of the numerical calculation the transverse effective charge is evaluated.
The Electronic Structure of Chalcogenide Solids: A Photoemission Study of Sulphur
Authors: Williams R. H. , Polanco J. I. 
Published: July 2007

AbstractPhotoelectric yield and energy distribution curves for photon energies up to 11 eV, have been studied for evaporated sulphur films. For clean films the threshold occurs at 7.2 eV. The EDC's, as well as the form of the yield near threshold, agree well with calculated curves derived from the molecular orbital calculation of Chen, with levels broadened by taking into account intermolecular interactions.
Magnetic Ordering in HoAsO4 Investigated by Means of Specific Heat and Spectroscopic Measurements
Authors: Schwab M. , Berkhahn W. , Kahle H. G. , Simon A. , Wüchner W. 
Published: July 2007

AbstractThe heat capacity, optical absorption spectrum, and Zeeman effect of HoAsO4 have been measured at low temperatures. The specific heat shows a lambda anomaly at TN = = (0.557 ± 0.005) K which has to be attributed to a magnetic phase transition from the paramagnetic to the antiferromagnetic state. The anomaly is superimposed on a large contribution from the nuclear hyperfine interaction of holmium. Spectroscopic measurements indicate that the lowest lying crystal field state of the Ho3+ ions in HoAsO4 is a doublet Γ5 (gc = 15.3 ± 0.3) and that the first excited state is a singlet Γ1 at about 7.5 cm−1. The magnetic interaction in HoAsO4 has the form of Ising interaction. A simple two sublattice structure with magnetic moment direction along the optical axis is proposed for the ordered state. Assuming this structure, an estimation of exchange interaction to nearest (nn), next nearest (nnn), and third nearest (tnn) neighbours was performed. It shows that the contributions to the total exchange field of the nn and nnn are nearly compensated by those of tnn. Dipole–dipole interaction was found to be dominant for the antiferromagnetic ordering in HoAsO4.
Green's Functions Approach to the Theory of Hopping Conductivity in Disordered Semiconductors
Authors: Manucharyants E. O. , Zvyagin I. P. 
Published: July 2007

AbstractIt is shown that care should be taken when the phonon‐assisted hopping conductivity is evaluated using the formal expansion in powers of the electron–phonon coupling constant g. This expansion appears to be divergent in the low‐frequency range, and the divergent terms should be partially summed up to give a correct lowest‐order contribution to the conductivity. The resulting expressions can be obtained as well by using a standard decoupling procedure in the equations for the higher‐order Green's functions.
Anisotropy in the Optical Transitions from the π and σ Valence Bands of Graphite
Authors: Klucker R. , Skibowski M. , Steinmann W. 
Published: July 2007

AbstractThe dielectric tensor \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \varepsilon \limits^ \wedge $\end{document}(ω) of pyrolytic graphite, cleaved with its surface perpendicular to the c‐axis, has been determined using polarized synchrotron radiation of photon energies 3 eV ≦ hω ≦ 40 eV. For this purpose the reflectivities were measured for nine angles of incidence between 15° and 75°, the electric field vector E lying parallel and perpendicular to the plane of incidence. The complex dielectric functions \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \varepsilon \limits^ \wedge $\end{document} ⊥and \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \varepsilon \limits^ \wedge $\end{document} ‖ for E perpendicular and parallel to the c‐axis were obtained by a least squares fitting of the measured reflectivities to the calculated ones. In addition \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \varepsilon \limits^ \wedge $\end{document} ⊥ was determined independently by a dispersion analysis of the reflectivity at 15° angle of incidence. The results showing strong anisotropy over the whole energy range are compared with previous optical data for \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \varepsilon \limits^ \wedge $\end{document} and electron energy losses. On the basis of recent two and three dimensional band structure calculations the spectra are attributed to direct interband transitions from the π‐ and σ‐type valence bands to π(σ)‐and σ(π)‐conduction bands for E ⊥ c (E ‖ c), respectively.
Herzberg‐Teller Interaction and Vibronic Coupling in Molecular Crystals. III. Influence of the Phonon‐Assisted Exciton Transfer and Phonon Propagation on the “False” Origin of the Absorption Spectrum
Authors: Zgierski M. Z. 
Published: July 2007

AbstractThe influence is discussed of the phonon‐assisted exciton transfer induced by the Herzberg‐Teller interaction, and of the propagation of phonons participating in the Herzberg‐Teller coupling on the creation of vibronic and scattering states in the region of a “false” origin of an absorption spectrum of an one‐dimensional molecular crystal.
Observation of High‐Temperature Heisenberg Ferromagnet Spin Relaxation by EPR
Authors: Cusumano C. , Troup G. J. 
Published: July 2007

AbstractThe previously observed exponential lineshape in the wings of an exchange‐narrowed system, namely solid solution of DPPH in polystyrene, is interpreted as being the result of the spin‐relaxation function of the high‐temperature Heisenberg ferromagnet. This is possible because the exchange frequency was of the same order as the hyperfine width, and because the system is amorphous and disordered.
The Kinetics of Recombination Radiation and the Temperature of the Electron–Hole Plasma in Silicon
Authors: Dite A. F. , Lysenko V. G. , Timofeev V. B. 
Published: July 2007

AbstractThe temperature of the excitonic gas as well as the temperature and the carrier density in electron‐hole drops (EHD) under intense optical excitation are determined from the analysis of the spectrum of recombination radiation in silicon. The temperature range within which EHD exist is determined (the critical temperature is Tc ≈︁ 33 °K) and the upper branch of the state diagram, excitonic gas–excitonic condensate, is constructed. The kinetics of the radiative recombination spectrum of EHD and excitons is studied, as well as that of the decay of the electron‐hole plasma at temperatures above Tc. The dependence of the boundaries of the radiative recombination spectrum on the carrier density in the plasma is analysed.
A Non‐Parametric Model Pseudopotential and Electronic Transport Coefficients
Authors: Srivastava S. K. 
Published: July 2007

AbstractA non‐parametric model pseudopotential for metals is proposed. The cut of region of the form factors lies between 1.4<q/kF<2. The various electronic transport coefficients of liquid metals obtained for this model potential agree reasonably well with experiment. The influence of electron–lattice interaction parameter K on the various electronic transport coefficients is discussed.
Localization of Electron Wave Functions in One‐Dimensional Disordered Systems
Authors: Hermann H. 
Published: July 2007

AbstractResults are presented of numerical calculations of the eigenvalues and eigenvectors of one‐dimensional systems with diagonal and off‐diagonal disorder. Two possible definitions of the localization length are discussed. Using a formula of Thouless the quantity Lexp(E) describing the exponential decay of a wave function far away from the localization centre is calculated for chains containing up to 400 lattice sites. The energy dependence of Lexp for off‐diagonal disorder differs from that of the well‐known case of diagonal disorder. It is found that the wave functions of an infinite one‐dimensional system with statistically distributed hopping terms are extended at least over an half infinite part of the complete infinite system.