bluuebunny/crossref_metadata_2025 huggingface dataset:
Static Properties of the Self‐Trapped Hole in Simple Cubic Cesium Halides
Authors: Iida T. , Monnier R.
Published: July 2007

A 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

For 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

A 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

Spectroscopic 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

The 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

EPR 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

An 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

The 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

Calculations 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

Field 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

An 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

The 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

For 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

To 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

The 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

A 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

The 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

The 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

The 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

The 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

The 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

Dense 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

Using 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

Forward 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

An 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

A 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

The 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

An 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

Using 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

The “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.
Piezoemission Study of I1‐and I2‐Type Bound Excitons in CdS
Authors: Goede O. , Blaschke M. , Klohs K. H.
Published: July 2007

Deformation effects for I1‐ and I‐type bound excitons in CdS are calculated in the framework of an effective‐mass approximation using the Bir‐Pikus Hamiltonian for wurtzitetype crystals and taking into account exchange and relativistic hole‐hole interactions. By piezoemission measurements at 4.2 K for uniaxial stress, σ ∥ c and σ ⊥ c, significant differences are obtained for the stress‐induced energy shift and polarization of the two types of bound excitons. From the comparison with the corresponding calculated results the electron‐hole exchange and the relativistic hole‐hole interaction parameters for the I1 bound exciton are determined. The occurrence of a low‐energy emission line which is not observed until now, the expected stress dependence of this line, and fine‐structure effects for the I1, bound exciton are discussed.
Exciton Binding Energies in Polar Crystals
Authors: Hattori K.
Published: July 2007

The ground state of Wannier excitons in polar crystals, such as TlCl, TlBr, GaAs, and II‐VI compounds, is investigated. The exciton‐phonon coupling is taken into account by the Fröhlich‐type interaction. Exciton binding energies are evaluated by a combination of a variational method and the second‐order perturbation theory. The theoretical results are compared with those obtained experimentally. A good agreement between theory and experiment is found.
Logitudinal Anisotropy of Conductivity of n‐Si in Heating Electric Fields at Low Temperatures
Authors: Papunashvili K. I. , Frolova E. K.
Published: July 2007

The longitudinal anisotropy of the conductivity in n‐Si is studied in heating electric fields a t temperatures ranging from 35 to 77 K. The data concerning the dynamics of electron redistribution between the equivalent valleys with the temperature and electric field are reported. It is shown by extrapolation of experimental results to lower temperatures that a t these temperatures a homogeneous sample must exhibit NDC due to the electron repopulation.
Spectroscopic Investigations of Magnons in Weak Ferromagnetic RbMnCl3
Authors: Belyaev A. I. , Kotlyarskii M. M.
Published: July 2007

The temperature dependence of the RbMnCl3 absorption spectrum is investigated in the region of the C and D group bands. The detailed analysis of the fine structure allows to distinguish two characteristic intervals, 75 and 46 cm−1, corresponding to the excitation of optical and acoustic modes in the spin‐wave spectrum of RbMnCl3. In general the spectrum structure is analogous to that of isostructural CsMnF3.
Jahn‐Teller Coupling Parameters from Stress‐Dichroism Spectra for CdS:Ti2+ and CdS:Co2+
Authors: Ruszczynski G. , Boyn R.
Published: July 2007

Stress‐induced dichroism spectra are measured for the mA2→mT1(mF) and mA2→mT1(mP) transitions of CdS:Ti2+ (m = 3) and CdS:Co2+ (m = 4), at 80 K, for stress parallel and perpendicular to the hexagonal axis. The stress‐induced changes of the first moments of the absorption bands are discussed on the basis of a tetrahedral cluster model. Coupling parameters to ϵ‐ and τ2‐type distortions are estimated, and comparable values are obtained for these two symmetries in all cases. The coupling behaviour of “corresponding” levels of the two impurity systems turns out to be rather similar. The data obtained are consistent with an earlier quantitative interpretation of the absorption band shapes for CdS:Ti2+. It is found that a point‐ion model can give the correct sign of the coupling parameters, but leads to wrong results with respect to their (relative) magnitudes.
The Thermodynamic Behaviour of Charge‐Ordered Crystals
Authors: Lubimov V. S. , Manakova L. A. , Makarov E. F. , Ionov S. P.
Published: July 2007

The influence is considered of the low lying collective excitations upon thermodynamic behaviour of charge‐ordered states. The collective mode is found which provides the instability of this state relative to the Mott state when intra‐(I) and intersite (V) interactions of electrons correspond to a repulsion. If I < 0 and is stronger than the intersite repulsion, the collective excitations correspond to the motion of electron pairs. The energy and the specific heat are calculated and the phase diagram is qualitatively discussed as function of the I to V‐ratio.
The Soft X‐Ray Appearance Potential Spectra of Diamond and Graphite
Authors: Lee A. E. , Webster J.
Published: July 2007

The soft X‐ray appearance potential spectroscopic technique has been applied to diamond and graphite. The spectrum obtained from diamond is found to be similar to those obtained from other forms of carbon but to contain important differences. From the differences it is inferred that a graphitic over layer is not present. The similarities in the spectra of diamond and graphite suggest that the multiplicity of peaks observed in spectra from carbon is not due to plasmon effects. Agreement between the observed diamond spectrum and that obtained from a density of electron states model is only possible if an empty surface state band is postulated existing between the valence and lower conduction bands. The spectra of both diamond and graphite are effected by the evaporation of tungsten from the thermionic cathode. The contamination is particularly difficult to observe as the technique is shown to be relatively insensitive to evaporated tungsten films.
Bound States of Fast Electrons in Planar Channeling
Authors: Kaplin V. V. , Popov D. E. , Vorobev S. A.
Published: July 2007

A detailed treatment in the classical and quantum‐mechanical approximations of the bound motion of energetic electrons with (011) atomic planes of Si is given. For electrons with energies up to 2.5 MeV only a few resolved quantized states are obtained. The angular distributions of electrons in the ground and exited states are calculated and compared with experimental data. It is shown that electrons are effectively channeled through the crystal along the atomic planes, thereby being mainly in an excited state.
Low and very high magnetic field dependence of the magnetization and the Faraday rotation induced by the magnetic dipole transitions in YIG
Authors: Guillot M. , Le Gall H.
Published: July 2007

From Faraday rotation experiment performed at 1.15 and 0.6328 μm wavelength under low and very high magnetic fields up to 4 MOe, the magnetic field dependences are analyzed of the magnetization and the Faraday rotation induced by the magnetic dipole transitions in both the octa‐ and tetrahedral sites of YIG. The best agreement between the magneto‐optical data under intense fields and a molecular field model iniplies a choice of the exchange parameters where the intra‐sublattice interactions must be neglected. The magnetic field dependence of the sublattices magnetization, calculated from this molecular field model follows a paramagnetic behaviour up to a spin‐flop critical field as observed in our experiment near 1.7 MOe. It is shown that the Faraday rotation induced by the magnetic dipole transitions is described from two terms having a magnetic field increase of opposite sign. The first term is the usual “magnetic” Faraday rotation proportional to the total magnetization and the second one, having a dispersive character, has a quadratic dependence on the effective field defined by the applied and exchange fields.
Transport theory of ultrasonic attenuation
Authors: Sorbello R. S.
Published: July 2007

The transport theory of ultrasonic attenuation is critically examined. The Pippard expression for arbitrary band structure is derived from the traditional transport approach without introducing Pippard's fictitious forces. The validity of using the relaxation‐time approximation in the transport equation is investigated, and the analysis is extended beyond this approximation. It is pointed out that for the general collision integral the relaxation time appearing in Pippard's theory may have an imaginary part. Pippard's expression for the attenuation is shown to be valid only when the relaxation time is real, and this will occur when the mean‐free path is either much less or much greater than the wavelength of sound, and in the case of “quasi‐catastrophic” scattering. Finally, some inconsistencies in the literature are pointed out.
Steady‐state diffusion of point defects in the interaction force field
Authors: Yoo M. H. , Butler W. H.
Published: July 2007

The diffusion equation including the drift term due to the long‐range interaction between a point defect and a spherical sink is solved numerically for the steady‐state concentration of point defects. The effective capture radius of a sink is calculated from the flux integral of point defects, and the biased flux of interstitials over vacancies to an infinitesimal dislocation loop is obtained from the effective capture radii. Effects of temperature, point defect parameters, and elastic properties of the medium on the kinetics of vacancy‐inter‐stitial recombination and of dislocation loop growth are discussed.
Density of states of layer compounds. 2H‐NbSe2
Authors: Riccò B.
Published: July 2007

The density of states of the transition‐metal layer compound 2H‐NbSe2, is calculated for both valence and conduction bands. The solid is studied by means of two different oneelectron models, one where the sandwiches of the structure interact with each other and one where instead each sandwich is treated as isolated. The densities of states given by the two models are compared with that determined by means of experiments of photoemission and transmission of synchrotron radiation. That obtained considering an isolated sandwich agrees better with the experimental curves. This seems to indicate that the oneelectron picture is inadequate to describe the intersandwich interactions in layered structures and therefore that the kz dependence of the calculated band structure E(k) should not be looked at as really reliable.
The influence of phonons and impurities on the broadening of excitonic spectra in gallium arsenide
Authors: Alperovich V. L. , Zaletin V. M. , Kravchenko A. F. , Terekhov A. S.
Published: July 2007

The absorption spectra near the fundamental edge of gallium arsenide are measured in the temperature range of 4.2 to 500 K on samples with concentration of charged impurities from 1014 to 1019 cm−3. The description of the experiment by phenomenologically broadened theoretical spectra enables to determine the broadening parameter as a function of temperature and impurity concentration. The comparison of the results obtained with microscopic theories shows the interactions of excitons with longitudinal optical phonons and charged impurities to be the main broadening mechanisms. A semiempirical equation is obtained which permits to calculate the broadening parameter in gallium arsenide for a given temperature and impurity concentration.
Electric field induced changes of the fundamental absorption and low‐temperature energy relaxation in n‐type GaSb
Authors: Obiditsch M. , Kahlert H.
Published: July 2007

The dependence of the absorption coefficient α on the photon energy is investigated for different degenerately doped samples of n‐type GaSb in the region of the fundamental absorption. A comparison of the experimental data with the theory by Dyakonov et al. shows satisfactory agreement for α > 500 cm−1. The application of pulsed electric fields at a lattice temperature of 6 K gradually removes the Burstein‐Moss shift. A comparison of the experimentally obtained absorption edges for various applied electric fields to calculated curves allows to correlate energy loss rates to certain values of the electron temperature Te. A calculation of this dependence considering acoustical and polar optical phonon scattering reveals that single phonon scattering processes are not capable of explaining the data between 12 and 40 K. Following the treatment by Ngai a calculation of the energy loss rate for two‐phonon deformation potential scattering is performed. The temperature dependence of this mechanism is in good agreement with the experimental values thus allowing to deduce a value of the two‐phonon deformation potential D2TA ≈ 5 × 103 eV.
Low‐temperature diffusion of electrons in ice evidence for polaron bands
Authors: Prince R. H.
Published: July 2007

The hopping activation energy for localized polaron states in ice is measured as (0.065 ± 0.005) eV. Below a transition temperature of ≈ 125 K, polaron band motion is observed with a temperature dependence in accordance with the density of optical phonons effective for scattering, with θ1 = 209 K in agreement with IR absorption determinations. Such observations lend support to the hypothesis of mobile electrons as precursor to fluorescence and thermoluminescence in ice.
Electron interactions and the spin‐wave stiffness constant in ferromagnetic two‐component alloys
Authors: Poo G. S. , Edwards D. M.
Published: July 2007

Electron interaction effects and the spin‐wave stiffness constant of an ordered ferromagnetic binary alloy are studied. A general condition for ferromagnetism is obtained for the system. Within a certain approximation, an explicit expression for the spin‐wave stiffness constant is derived in the limit of very weak ferromagnetism.
Exciton interactions in naphthalene single crystals
Authors: Fujiwara S. , Nakayama T. , Itoh N.
Published: July 2007

The decay of the fluorescence and T—T absorption change in naphthalene crystal induced by an intense electron pulse is measured and analyzed. It is shown from the optical absorption measurement that the decay of the triplet excitons follows bimolecular reaction kinetics. The decay of the fluorescence is found to be very much dependent on the intensity of the electron pulse. The result is analyzed with reaction kinetics comprising the singlet—singlet, singlet—triplet, and triplet—triplet annihilation processes. The values of annihilation rate constants are obtained at 77, 200, and 298 K. The singlet—triplet annihilation rate constant is calculated under Förster's long‐range resonance transfer scheme by employing the results of T—T absorption of naphthalene crystal. Good agreement is obtained for γST. It is demonstrated that the annihilation of the singlet exciton is diffusion controlled.
Structure and generation mechanism of Br centres in X‐rayed KBr
Authors: Elango A. A. , Nurakhmetov T. N.
Published: July 2007

The structure of V4 and D3 centres in KBr and KBr:Sr crystals X‐rayed at 80 K is studied by optical methods. The molecular ion Br situated in two anion and one cation lattice sites is shown to be the basic entity of the structure of these centres. The creation mechanism of such Br centres via interaction of H centres is discussed. It is assumed that the interaction of two H centres leads to the local reconstruction of the lattice. The occurrence of one particular process of this kind resulting in a new anion Frenkel pair near a cation vacancy is demonstrated.
Electron transport phenomena in narrow‐ and zero‐gap semiconductors containing magnetic impurities
Authors: Kossut J.
Published: July 2007

Various transport phenomena are studied which are due to scattering of electrons in narrow‐ and zero‐gap semiconductors by magnetic impurities, namely manganese impurities. The formulae for the relaxation time corresponding to this scattering mechanism are derived and the mobility and thermoelectric power are discussed. Numerical estimations for manganese‐doped mercury telluride are presented. They show that the contribution of magnetic impurity scattering to the electron mobility, although smaller than that of ionized centre scattering, cannot be neglected at low temperatures. The thermoelectric power seems to be strongly influenced by the presence of the considered scattering mechanism. The dependence of transport coefficients on the range of the scattering potential is studied. It is particularly pronounced in the case of an inverted band structure at low electron concentrations.
X‐ray compton scattering from LiMg alloys
Authors: Berndt K. , Brümmer O.
Published: July 2007

Results are given of X‐ray Compton scattering from a series of LiMg alloys, polycrystalline Li, and Mg. The spectra indicate a contact of the “Fermi surface” of the alloy with the [110]‐Brillouin zone boundary at 30 to 40 at % Mg. LiMg seems to be a good, nearly free electron alloy. Theoretical calculations using a model alloy potential are made and the calculated momentum distributions are compared with the experimetnal results.
Thermal effects in magnetic exchange interaction
Authors: Shrivastava K. N.
Published: July 2007

The temperature dependence in the exchange interaction –2JSi · Sj in ferromagnetic K2CuCl4 · 2 H2O is interpreted to arise from the matrix elements of the phonon‐modulated nuclear potential. It is found that the temperature dependent effect is so large that at a particular temperature, called the null point, the phonon‐induced exchange cancels the static Heisenberg exchange. The contributions of anharmonicity are also estimated and correlations of exchange with interatomic distance and dependence on ionic size are established.
Energy transfer by excitons in a tetracene‐doped anthracene crystal
Authors: Golubov S. I. , Konobeev Yu. V.
Published: July 2007

A new interpretation is proposed of experimental data found by Powell on fluorescence decay of donor and acceptor molecules in binary tetracene‐anthracene solid solution. Intense direct excitation of acceptor molecules by X‐rays is assumed and a new exact relation between fluorescence decay laws of acceptor and donor molecules is derived. Using this relation it is shown that the experimental data may be satisfactorily described under the assumption that the direct impurity excitation efficiency is about four orders higher than for molecules of the host substance. Such a difference may be explained by the impurity large capture cross section of charge carriers produced by X‐rays.
Electromagnetic waves in an electron plasma in an alternating external magnetic field
Authors: Lugovoi V. N.
Published: July 2007

The generalization of the theory of plane waves in a semiconductor electron plasma located in an external magnetic field, H  H0  H1 cos pt, whose variable component is parallel to the stationary one, is given for the case of relatively low electron density in the conductivity band and for a sample inhomogeneous in the direction of the magnetic field, the waves propagating along this direction. Also the problem of the transformation of a monochromatic incident wave with a frequency co to components with new frequencies ω + np (n = ±1, ±2, …) for the wave reflected from the sample boundary and transmitted into the sample is considered. Several effects which are due to the simultaneous influence of the periodic non‐stationarity and a periodic in‐homogeneity of the medium are noted.
A Theoretical investigation of the specific heats and transport properties of the actinides
Authors: Long K. A.
Published: July 2007

The role of phonons, both optical and acoustic, is examined in the actinide metals. It is pointed out that the complicated crystal structures imply that optical phonon branches exist in the actinide metals. These branches lie at relatively low frequencies, low enough for them to contribute to the low temperature electrical resistively, and to other transport properties. In particular in plutonium it is proposed that there are two temperature regimes. The first below 100 K is that in which plutonium behaves like a normal transition metal, and where conduction is metallic in nature. In this regime the electrical resistivity is due to electron‐phonon scattering mainly by optical phonons. The second regime above 100 K is more akin to an amorphous or non‐crystalline material, than to a metal, due to the disorder caused by the lattice vibrations. In this regime conduction is by hopping of electrons from site to site. Here the interaction is so strong that plutonium can not be described even in a first approximation by a one electron band model.
The critical voltage effect in transmission electron microscopy. VII. The Influence of Absorption
Authors: David M. , Gevers R. , Serneels R.
Published: July 2007

The influence is studied of the absorption on the dynamical behaviour of a linear (2N + 1)‐beam system close to the second order Bragg orientation and around the critical voltage. When a small imaginary potential is introduced into the dynamical matrix for such situations, the eigenvalues and the eigenvectors of the latter are drastically altered. In particular the mechanism of symmetry exchange of the first two Bloch waves, and its consequences on the vanishing of the second order DF bend contour are examined. A qualitative effect of absorption on the behaviour of the bend contour with varying voltage, seems unlikely to be observable in most materials. However, one finds that absorptionless calculations may underestimate the critical voltage of heavy materials by an amount of the order of 50 kV.
Ultraviolet reflectivity spectra of CoCl2 and CoBr2 crystals
Authors: Pollini I.
Published: July 2007

The reflectivity spectra of CoCl2 and CoBr2 magnetic crystals in the 2 to 11eV region, at 300 and 80 K, are reported. The optical constants are derived by means of a Kramers‐Kronig analysis of their reflectivity data. It is suggested that peaks up to ≈ 8eV are due to electron transfer processes, in which halogen p‐ and cobalt d‐states are involved in localized excitations. The structures beyond 8eV are due to onset of band‐to‐band transitions, from p halogen to s metal states.
Isotope effects of diatomic CH and CD complexes in Ni single crystals
Authors: Kronmller H. , König N. , Walz F.
Published: July 2007

The magnetic relaxation spectrum of Ni single crystals containing different amounts of carbon interstitials is measured after charging with hydrogen or deuterium. A relaxation maximum observed after hydrogen charging at 133 K is attributed to the reorientation aftereffect of diatomic C‐H complexes of orthorhombic symmetry. Similarly after deuterium charging a relaxation maximum at 139 K is observed. The relaxation times of both these relaxation maxima show significant isotope effects of the activation energies as well as the pre‐exponential factors. These results are discussed within the framework of an harmonic oscillator model.
XPS and APS studies of V3Si
Authors: Nilsson P. O. , Curelaru I. , Jarlborg T.
Published: July 2007

The occupied and unoccupied parts of the valence band of V3Si single crystal are studied by means of XPS and APS techniques, respectively. Agreement with calculated band structure data is obtained.
Phonon spectra of the laves phase intermetallic compound CaMg2
Authors: Eschrig H. , Feldmann K. , Hennig K. , Matz W. , Paufler P.
Published: July 2007

A pseudopotential calculation of the phonon dispersion curves and the phonon density of states of CaMg2 is done using Shaw's model pseudopotential in second order. Moreover on a polycrystal‐line sample the phonon density of states is determined by coherent inelastic neutron scattering following the suggestion of Bredov et al. Good agreement between the calculated and measured results is obtained. The experimental accuracy is investigated by calculating the neutron scattering cross section from the theoretical phonon spectrum.
Self‐consistent cellular methods for the ising problem
Authors: Billard L.
Published: July 2007

A variational method is used based on various cluster hamiltonians. Thus a self‐consistent scheme is obtained to treat approximatively the Ising hamiltonian. Results are compared with the classical ones by Bethe and Oguchi.
Phenomenological description of dynamics in a diluted anisotropic heisenberg paramagnet at high temperatures
Authors: Tahir‐Kheli R. A. , Kawasaki K.
Published: July 2007

A recent work on space and time dependent spin correlation function for a diluted isotropic Heisenberg paramagnet at infinite temperature is generalized in two important directions: firstly, now also lattices are considered which, admit nearest neighbour triangles, e.g. f.c.c. lattice, and, secondly, now the exchange interaction is allowed to be uni‐axially Anisotropic. The latter generalization necessitates the consideration of two different types of spin‐correlations: longitudinal and transverse. As limiting cases, the longitudinal correlation is examined for XY model and the transverse spin correlation for the Ising model. Between these limits, correlations are computed for J0/J+ = 2 and 0.5, for several concentrations, and the results are compared with those for the isotropic case, i.e. J0/J+ = 1.
Extra‐atomic relaxation and X‐ray spectra of narrow‐band metals. I. Formalism
Authors: Grebennikov V. I. , Babanov Yu. A. , Sokolov O. B.
Published: July 2007

For narrow band metals the distortions of the form of X‐ray and X‐ray photoelectron spectra are investigated under the influence of the vacancy on the inner level. A calculation method over the whole energy interval of the distoring influence of the hole field is proposed and realized numerically. The site formalism is developed to describe the X‐ray spectra. Equations are obtained in the energetic representation which allow to effect a numerical analysis.