bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Properties of a Threefold Degenerate Orbital Magnetic Impurity in a Feromagnetic Crystal
Authors: Ivanov M. A. , Mitrobanov V. Ya. , Falkovskaya L. D. , Fishman A. Ya. 
Published: July 2007

AbstractThe spectrum of localized excitations of a magnetic matrix with impurity Jahn‐Teller magnetic ions with a triplet orbital ground state in a cubic crystal field is investigated. The two cases are examined of the spin‐orbit interaction of the impurity to be much less or much greater than the exchange interaction between the impurity and the matrix. The orbital exchange interaction is shown to lead to displacement and splitting of the pure spin excitation frequencies and under certain correlations between the exchange parameters it can change the ground state of the system. The specific features of the orbital degeneracy of the impurities can also occur in the electromagnetic wave absorption spectrum and in the temperature dependence of the thermodynamic characteristics of the impure crystal.
Static Properties of the Self‐Trapped Hole in Simple Cubic Cesium Halides
Authors: Iida T. , Monnier R. 
Published: July 2007

AbstractA theory of Vk centres in simple cubic Cs‐halides in the spirit of Sewell's treatment of the small polaron is presented. The stability of a hole trapped on a single site and that of the Vk centre are compared. Expressions for the peak position and width at half maximum of the uv (2Σ → 2Σ) absorption band are derived. The results are in satisfactory agreement with experiment and show that the interaction of the hole with the acoustic modes of the lattice vibrations becomes comparable to the one with the optical modes, as the mass of the halide increases.
SpinLattice Relaxation Times and Knight Shift in InSb and InAs
Authors: Braun P. , Grande S. 
Published: July 2007

AbstractFor a dominant contact interaction between nuclei and conduction electrons the relaxation rate is deduced. The extreme cases of degenerate and non‐degenerate semiconductors are separately discussed. At strong degeneracy the product of the Knight shift and relaxation time gives the Korringa relation for metals [I]. Measurements of the NMR spinlattice relaxation times of 115InSb and 115InAs were made between 4.2 and 300 K for strongly degenerate samples. The different relaxation mechanisms are discussed and the experimental and theoretical results are compared.
Long‐Wavelength Optical Phonons in Mixed Crystals : I. A System of Two Coupled Modes
Authors: Jahne E. 
Published: July 2007

AbstractA model is presented which for the first time provides a description of the long‐wavelength phonons in mixed crystals of the type AB1−xCx as a system of two coupled modes: a lattice mode in a virtual crystal approximation (VCA) and a localized (or quasi‐localized) mode of the disordered sub‐lattice. These two modes interact by effects beyond the VCA, namely by the difference of the vibrational frequencies of the atoms B and C perceived by the atom A. Two cases will occur: (i) The two modes interact only weakly over the entire composition range. Then a lattice‐like mode and – as a new result — in addition a mode in which the disordered sub‐lattice is nearly involved alone are present over the entire composition range. This leads to the traditionally named one‐mode behaviour. (ii) The two modes become resonant at a certain composition and interact strongly. This leads to the two‐mode behaviour. The dielectric function assumes a form typical for the presence of two oscillators for both types of mode behaviour.
Two‐Level Singlet Magnetism in TbAsO4 and TbVO4
Authors: Gehring G. A. , Kahle H. G. , Nägele W. , Simon A. , Wüchner W. 
Published: July 2007

AbstractSpectroscopic and specific heat measurements are reported on two singlet magnets, TbAsO4 and TbVO4. The ratios between the antiferromagnetic ordering temperature TN and the splitting Δ between the two singlets are TN/Δ = 1.58 and TN/Δ = 0.45, respectively. The experimentsshow considerable deviationsfrom a molecular field theory but remarkably better agree with a self‐consistent RPA calculation in which the experimentally determined exchange and dipole fields are used.
The Resonance Modes in the Vibrational Spectrum of a Chain with Light Impurities
Authors: Wu Shi‐Yu 
Published: July 2007

AbstractThe configurations associated with the resonance modes in the main band of a randomly disordered chain with dilute concentrations of light impurities are identified using Green's function method. By examining the eigendisplacements of the atoms in these configurations, the underlying physical reason for the existence of the resonance mode is discussed.
Variable‐Temperature EPR Study of the Semiconducting Ferromagnet EuB6
Authors: Glaunsinger W. S. 
Published: July 2007

AbstractEPR in EuB6 samples of widely separated electron density has been studied above the Curie temperature at X band. In bulk samples, narrow signals at g = 2.000 ± 0.002 have been observed and attributed to conduction electrons that are strongly coupled to the Eu2+ moments. The EPR behavior of the Eu2+ resonance is unusual in both bulk and low‐electron‐density samples. At temperatures high enough to avoid critical spin fluctuations, i.e. high temperatures, the exchange field increases linearly with temperature. Below 21 K, the Eu2+ resonance splits into two lines, and the splitting increases with decreasing temperature, with the low‐field line being considerably more intense than the high‐field line, which is unobservable near 10 K. Several models for the exchange interaction between the Eu2+ moments are examined, and it is found that to a good approximation the RKKY interaction can account for the magnitude of the exchange field at high temperatures in bulk EuB6, and probably also low‐electron‐density EuB6, but that another interaction, quite possibly the BR interaction, makes the dominant contribution to the temperature dependence of the high‐temperature exchange field. The BR model can also account for the measured Weiss constant at high temperatures, but the RKKY model fails to predict the correct low‐temperature magnetic behavior. The splitting of the Eu2+ resonance, which cannot be attributed to crystalline‐electric‐field effects, may result from a magnetic transition, possibly involving magnetic‐polaron formation.
Jahn‐Teller Effect in the 4T1(1) and 4T2(1) States of Tetrahedrally Coordinated Mn2+
Authors: Koidl P. 
Published: July 2007

AbstractAn interpretation of the 4T1(1) → 6A1 luminescence and 6A1 → 4T2(1) absorption spectrum of Mn2+ in ZnS is presented. These transitions show only two closely spaced zero‐phonon lines which is in contrast to static crystal field theory. It is shown that strong Jahn‐Teller coupling to E‐vibrations, which fully quenches the linear spin–orbit interaction, can account for the observed zero‐phonon line doublets and the size of the splittings. The results apply also to Mn2+ in CdS, GaP, and ZnSe, where similar zero‐phonon doublets have been observed.
Electron Spin Resonance of the Triplet State of Pure and Doped NaNO2 Single Crystals
Authors: Dietrich W. , Schmid D. 
Published: July 2007

AbstractThe metastable triplet state of NaNO2 single crystals, both pure and doped with 1% KNO2, has been investigated using electron spin resonance and optically detected magnetic resonance. In pure crystals homogeneously broadened lines of about 5 G linewidth are observed. The related fine‐structure constants are D/hc = (0.4480 ± 0.0007) cm−1 and E/hc = −(0.04779 ± 0.00002) cm−1. In doped crystals two pairs of triply split ESR lines are observed. The maximum splitting of these lines is about 45 G, which is large compared to the homogeneous linewidth in the pure crystal. The narrowing of the ESR lines in the pure crystal is due to the motion of the triplet energy and gives evidence for triplet excitons in these crystals.
Average Electronic Energy Loss in the Modified Firsov Theory
Authors: Latta B. M. , Scanlon P. J. 
Published: July 2007

AbstractCalculations of the average electronic stopping power Se for heavy ions in solids are performed within the framework of the modified Firsov theory. Consideration is given to the effect of the usual approximations of straight line trajectories, free‐atom electron densities, and the positioning of the dividing surface between the atoms at a fixed fraction of their separation. When Se is averaged over all impact parameters, for classical orbits, the variation of Se as a function of target atomic number Z2 is much smaller than the variation previously determined by other authors for forward‐scattered particles. The use of a simple approximation for the electron densities in solids, in conjunction with a Thomas‐Fermi estimate of their velocities during the interaction, leads to results that are very similar to the free‐atom case.
Field History Effects in Superconducting PbSn Alloys
Authors: Schafe L. M. , Rossiter P. L. , Rachinger W. A. 
Published: July 2007

AbstractField history effects in directionally solidified eutectic PbSn alloy specimens are defined and analyzed in terms of the dependence of the flux trapped (at zero applied magnetic field) and the decreasing applied magnetic field minor magnetization paths on magnetic history. The temperature and sweep rate dependence of these effects and the direct measurement of flux profiles along minor magnetization paths may be explained in terms of the hypothesis that the effective pinning force in these specimens depends not only on the nature of the pinning features but also on the density, density distribution, and mobility of defects in the flux line lattice.
Moments of the Phonon Spectrum in Lithium Chloride
Authors: Duraiswamy S. , Haridasan T. M. 
Published: July 2007

AbstractAn analysis of the available experimental data of specific heat on lithium chloride by Shirley has been made to obtain the moments of the phonon spectrum. These moments are compared with the theoretical results obtained by using a shell model calculation of the lattice dynamics. The use of these moments for understanding the various other physical properties is indicated. The results are discussed in the light of the lattice dynamical model. Suggestions for further improvements are also made.
Sample Size Effects on the Spin Resonance of Conduction Electrons in Aluminium
Authors: Sharp‐Dent G. , Hardiman M. , Sambles J. R. , Cousins J. E. 
Published: July 2007

AbstractThe CESR residual line widths of cold rolled aluminium foils and evaporated aluminium films have been measured at 9.27 GHz for samples of thickness 0.1 to 38 μn. An increase in line width with decrease in thickness is observed at low temperatures. This increase is attributed to spin scattering of the conduction electrons at the aluminium surface. Below 20 K, ϵ, the probability for an electron losing its spin memory on colliding with the surface, is found to be less than 2.3 × 10−3 for foils and lies within the range 1.0 × 10−4 to 1.9 × 10−3 for films.
Impurity Effects in the Hc2 Anisotropy of Cubic Superconductors
Authors: Pohl H. W. , Teichler H. 
Published: July 2007

AbstractFor cubic type II superconductors the Hc2 anisotropy is evaluated in the non‐local regime, i.e., for metals with moderate impurity content at arbitrary temperatures below Tc. In particular it is shown that the contributions of Hc2 anisotropy originating from anisotropic electron‐electron coupling and those resulting from Fermi surface anisotropies differ in their impurity and temperature dependences.
Wave Function for the Interstitial Hydrogen Atom in SrF2
Authors: de Matos M. O. M. , Brandi H. S. , Maffeo B. 
Published: July 2007

AbstractTo interpret the EPR and ENDOR results for the H center in SrF2 two different models are used to describe the wave function of the unpaired electron. Using the Heitler‐London and the molecular orbital models the importance of the Pauli repulsion and covalence to the evaluation of the magnetic hyperfine constants is discussed. Introducing covalence in a phenomenological manner the measured data are reproduced fairly accurately. Also the inconvenience of introducing covalence using the Heitler‐London scheme together with the Löwdin transformation is discussed.
Anharmonic Vibrations of a Small Linear Chain
Authors: Mazumdar R. , Kothari L. S. 
Published: July 2007

AbstractThe anharmonic vibrations are investigated of a small linear chain under fixed end points and periodic boundary conditions. Numerical results as well as perturbative solution of the problem are given. It is observed that even in cases where one should expect a large effect of anharmonic terms, the numerical results are very close to the harmonic motion. The perturbative solution developed here gives a change in frequency in second order without having to take recourse to the “tucking‐in‐technique”.
On a Peculiarity of Ordering in F.C.C. Binary Alloys with a Distribution Function Containing Two Long‐Range Order Parameters
Authors: Ratishvili I. G. 
Published: July 2007

AbstractA binary ordered solid solution of f.c.c.‐type is considered. The free energy of the system is calculated for several numerical values of external and internal parameters. It is shown that for a distribution function containing two long‐range order parameters and for restricted values of energetic constants the free energy function can possess more than one minimum inside the ordered phase, providing a possibility of sharp change of order parameters in several small temperature intervals.
Study of the Size Quantization in p‐Type Silicon Inversion Layers by Means of Magnetoresistance
Authors: Holyavko V. N. , Dragunov V. P. , Morozov B. V. , Skok E. M. , Velchev N. B. 
Published: July 2007

AbstractThe Hall‐mobility and transverse magnetoresistance (MR) in p‐type inversion channels on (100) and (111) surfaces of silicon are investigated as functions of the strength and direction of magnetic field and the carrier density Γp at 4.2, 77, and 295 K. A characteristic peculiarity of the obtained results is a considerable MR anisotropy: a magnetic field oriented in the plane of the channel causes a minimum MR. The evaluation of the energetic positions of quantum levels is made to analyze the experiment, two types of holes and nonparabolicity of the band are taken into account. Results of the calculation and the observed MR anisotropy permit to conclude that the quantization of the transverse motion of holes in the channel plays an important role at 77 K for all Γp, and at 295 K for high Γp values. Conclusions about the scattering mechanisms of charge carriers are drawn from the analysis of the Γp dependence of MR.
Band Structure of Ga1−xInxAs
Authors: Schulze K.‐R. , Neumann H. , Unger K. 
Published: July 2007

AbstractThe band structure of Ga1−xInxAs is calculated in the virtual crystal approximation using the empirical pseudopotential method. A simple model is proposed and tested to consider the change of the screening due to alloying accounting for the nonlinear relationship between bare and effective ion potentials. The bowing parameters found in this manner are smaller than the experimental ones and disorder effects must be included to achieve agreement between theory and experiment.
Electronic Structure of TiC and VC from the Iterative Extended Hückel Theory
Authors: Yip Kwok Leung , Kunz A. B. , Williams W. S. 
Published: July 2007

AbstractThe iterative extended Huckel theory has been applied to compute the electronic structure of TiC and VC by using various clusters of different sizes. The calculated valence‐band structures are consistent with the results of APW calculations and with the X‐ray spectro‐scopy and ESCA data. The bonding is found to be mostly covalent but with an ionic contribution from positive metal atoms and negative carbon atoms in TiC and VC indicating an electron transfer from metal to carbon atoms when computed using a Mulliken population analysis.
Dynamical Conductivity and Plasmon Excitation in Bi
Authors: Gerlach E. , Grosse P. , Rautenberg M. , Senske W. 
Published: July 2007

AbstractThe reflectivity of bismuth crystals is measured in the spectral range 50 to 500 cm−1. From the measured data the dielectric function is determined by a'Kramers‐Kronig analysis. The dispersion of this function is explained by the dynamical conductivity of a free electron gas. At frequencies above the plasma edge there is a contribution which is due to the excitation of plasmons by the interaction of the free electrons with the Coulomb fields of impurities. This contribution can be expected from model calculations of the dynamical conductivity, considering ionized impurity scattering and screening effects.
Interband Faraday Rotation in Germanium
Authors: Kessler F. R. , Metzdorf J. , Müller R. H. 
Published: July 2007

AbstractThe doping dependence of the resonant interband Faraday rotation (IFR) in germanium shows a screening influence of free carriers. This proves that the IFR is due to transitions in exciton states split up by spin and not to transitions between Landau levels. At the critical doping concentration the Debye radius is equal to the Bohr radius of the excitons. A second transition energy in connection with a greater exciton radius must be interpreted as an indication of excitons with smaller reduced mass (“light excitons”). The measurements embrace a concentration range of 5 × 1013 to 6 × 1017 cm−3 and are carried out at 297 K and 2 T on single crystals. The interpretation in terms of excitons is supported by the optical isotropy of the IFR observed in intrinsic Ge.
Scattering Properties of Dense Random Packings of Hard Spheres
Authors: Graczyk J. F. , Chaudhari P. 
Published: July 2007

AbstractDense random packings of hard spheres are used as structural models for amorphous metallic solids. These describe the short range atomic order in a number of amorphous metallic binary alloys. Results are presented of a calculation of the structure factor, dark‐field and interference contrast from two such models. These models consist of 7928 and 1000 atoms clusters. It is shown that these models contain structural anisotropy similar to the models used for amorphous semiconductors. Also, the scattering properties of these models are in qualitative accord with transmission electron microscopy observations.
Pinning in Superconducting Films with Modulated Concentration of Impurities
Authors: Kulić M. , Dobrosavljević L. 
Published: July 2007

AbstractUsing the London theory, the flux pinning in inhomogeneous superconducting films with ϰ ≫ 1 is studied. A periodic variation of the impurity concentration in the direction perpendicular to the film is assumed. Beside the pinning by the film boundaries, the pinning of vortices in the interior of the film occurs whenever the period of the vortex lattice is commensurable with the period of the concentration variation. This leads to an increase of the critical current density in the film.
Polaritons in an Ensemble of CuI Crystallites
Authors: Wiener‐Avnear E. 
Published: July 2007

AbstractForward Raman scattering at small angles (0.3° < < θ < 0.5°) from a transparent pellet of CuI multi‐crystallites allows to follow the lower polariton branch. The obliquity of the propagation vectors versus the major axes of each zincblende crystallite does not affect the polariton dispersion relation, thus allowing the tracing of the polaritons in the ensemble.
Effect of Thermal Fluctuations on the Electronic Density of States in Disordered Binary Alloys. Numerical Results of CPA Model Calculations
Authors: Kolley E. , Kolley W. 
Published: July 2007

AbstractAn extended coherent potential approximation is applied to electron‐phonon interaction in disordered binary alloys. Numerical calculations are performed for a stochastic tight‐binding model including off‐diagonal randomness in the additive limit and results for the temperature dependence of the electronic self‐energy and density of states are presented. The density of states can display in the minority band fine structure caused by combined impurity and electron‐phonon scattering. The role of the phonon‐modulated hopping integrals is discussed.
Solitons in One‐Dimensional Molecular Chains
Authors: Davydov A. S. , Kislukha N. I. 
Published: July 2007

AbstractA theory of collective excitations in one‐dimensional chains of weakly bound molecules which correspond to intramolecular excitations is developed. It is shown that these excitations are described by solitary waves (solitons) propagating (without “smearing”) along the chain together with local deformation. The theory is developed without applying the assumption of inertialess motion of molecules. It is shown that the ultimate velocity of solitons is the velocity of sound waves corresponding to longitudinal vibrations of molecules. The problem of soliton stability is discussed.
Nuclear Magnetic Resonance and Susceptibility Measurements of Transition Metals and Alloys V‐Ta, V‐Nb, and Nb‐Ta Systems
Authors: Kalantarian V. P. , Chechernikov V. I. 
Published: July 2007

AbstractThe Knight shift of V51 and Nb93 and the magnetic susceptibility have been measured in binary alloys of 3d, 4d, and 5d transition metals including vanadium, niobium, and tantalum. The experimental results and estimates of the various contributions to K and χ show that the orbital contribution due to d‐electrons is dominant in these alloys. In the calculations of the various contributions, both the electron‐phonon interaction and s‐d hybridization are taken into account.
Alloy Analogy Approximation of the Degenerate Hubbard Model
Authors: Brouers F. 
Published: July 2007

AbstractAn expression of the degenerate Hubbard model energy in the alloy analogy approximation is given. A two sublattice system is considered in order to allow for spin or orbital antiferromagnetism ordering solutions. The Hartree‐Fock and Hubbard I approximations are shown to be specific limits of the CPA alloy analogy solutions.
Pressed‐Pellet Infrared Absorption Spectra of Molybdenum Dichalcogenides
Authors: Garg A. K. 
Published: July 2007

AbstractUsing infrared absorption spectra obtained by CsI pellet technique an investigation is made of the long wavelength optical phonon spectrum of trigonal prismatic type dichalcogenides of molybdenum. Both infrared active modes, E ⊥ C and E ∥ C, a have been observed. These observations are used to calculate the values of various shear and compressional force constants using Wieting's linear chain model. It is found that anisotropism of the force constants decreases as sulfur of MoS2 is being replaced by selenium and tellurium atoms.
Bloch Electrons in Magnetic Fields. Rationality, Irrationality, Degeneracy
Authors: Obermair G. M. , Wannier G. H. 
Published: July 2007

AbstractThe “irrational” equations for determining the energy eigenvalues developed earlier are studied. It is shown that, for rational fields, they can be transformed into the “rational” equations which are generally preferred. The two energy spectra are therefore the same, and there exists no conflict. Further, the question of infinite degeneracy familiar from the Landau functions is taken up. It was established earlier that as long as the field is irrational, this degeneracy is also present for Bloch electrons; now a criterion is developed for the condition under which this degeneracy may be lifted. The criterion comes out to be a rationality condition on the field: it differs in general from the usual (Brown) rationality; it is called “green” rationality.