bluuebunny/crossref_metadata_2025_split huggingface dataset:
Single‐Site Approximation in Alloys with Short‐Range Order
Authors: Streitwolf H.‐W. , Mertsching J. 
Published: July 2007

AbstractA self‐consistent single‐site approximation in alloys with short‐range order is discussed and applied to a one‐dimensional tight‐binding model. This approximation yields some broadening or narrowing of the electron density of states due to short‐range order, but no specific cluster effects, of course.
Piezoemission Study of CdS:Te
Authors: Goede O. , Fink F. 
Published: July 2007

AbstractThe emission band of the isoelectronic impurity Te in CdS is investigated with static uniaxial stress, σ, applied to the crystal. It is suggested that the bandshape is due to strong electron‐LA‐phonon interaction, the corresponding coupling constant and the effective phonon energy are determined. The measured peak shifts and stress‐induced polarization of the emission band for σ ‖ c and the band splitting for σ ⟂ c are interpreted on the basis of first order perturbation theory. The symmetry group of the defect and the irreducible representations of the electronic states involved in the optical transition are obtained and confirm the bound exciton model proposed in [5].
On the Effects of Applied Electrostatic Fields and Hydrostatic Pressures upon F‐Centre ENDOR Spectral
Authors: Wolbarst A. B. 
Published: July 2007

AbstractIt is suggested that the effects of bulk lattice polarization are not necessarily ignorable in the analysis of F‐centre electric‐field‐effect electron‐nuclear double resonance data, as was thought previously. Estimates of those contributions to contact hyperfine interaction shifts which are attributable to electric field induced lattice polarization are found to be comparable in magnitude to the corresponding values extracted from high pressure ENDOR measurements.
Birefringence of CdS under Uniaxial Stress
Authors: Babonas G. , Reza A. , Šileika A. 
Published: July 2007

AbstractThe dependence of intrinsic birefringence of CdS on uneasily stress has been investigated at room temperature in the spectral region 0.1 to 2.3 eV. The measurements were performed for stresses parallel and perpendicular to the c‐axis of CdS single crystals up to 2500 and 300 kp/cm2, respectively. The experimental results are explained by stress‐induced changes of the parameters of the high energy peak (E1) and exciton lines (A, B, and C).
Optical Properties of Cu‐Complex Centres in KCl Single Crystals
Authors: Kishishita H. 
Published: July 2007

AbstractAbsorption and emission spectra of KCl single crystals doped with various amounts of copper have been investigated a t temperatures from 10 to 300 °K. In highly doped specimens, four new absorption bands appear in wavelength regions longer than the 260 nm absorption band which has been attributed to the lowest transition within a single Cu+ centre. These new absorption bands are found at 288 nm (B‐band), 324 nm (C‐band), 373 nm (D1‐band), and 382 nm (D2‐band) a t 77 °K. The B‐band is assigned as a transition in paired Cu centres. The D1‐ and D2‐bands are attributed t o exciton absorptions in CuCl clusters formed in KCI crystals. As these clusters are small in size, the optical properties of excitons in them are slightly different from those in bulk CuCl crystals: (1) the energy positions of exciton absorption peaks are 20 meV higher than those of bulk CuCl excitons, (2) the absorption lines show relatively large width and asymmetric shapes, (3) the Stokes shifts are large, and (4) there are no bound excitons. These results are discussed as the characterirtic feature of excitons due to the small size of a CuCl micro‐crystal.
Phenomenological Description of Aggregates of Exchange‐Bonded Paramagnetic Ions in Crystalline Environment. I. Effective Hamiltonian Formalism
Authors: Kurzyński M. 
Published: July 2007

AbstractA general effective Hamiltonian formalism is proposed and applied to the phenomenological description of energetic structure of aggregates consisting of several exchange‐bonded paramagnetic ions in a crystalline environment. The low‐lying energetic multiplets of such a system, resulting from isotropic exchange (superexchange) interaction, split under the further interactions and, for a variety of ions, can be described in terms of effective spin Hamiltonians. Such a description is highly useful from the electron paramagnetic resonance point of view, in which the transitions inside multiplets are observed. The microscopic model for the phenomenologic constants of these Hamiltonians is given in the second order of perturbation treatment, and the case of ions with orbitally nondegenerate ground crystal term is discussed in some detail.
Propagation of Electromagnetic Waves in Semiconductor Plasmas under Crossed Steady Electric and Magnetic Fields
Authors: Brauer M. 
Published: July 2007

AbstractThe propagation of low frequency electromagnetic waves in single component infinite semiconductor plasmas under the combined action of dc crossed electric and magnetic fields, E0, B0, is investigated using the kinetic method. Using a modified form of the well‐known relaxation‐time approximation given by Bhatnagar for the collision term in the Boltzmann equation the dielectric tensor is calculated for propagation vectors q lying in the plane formed by E0 and B0. It is shown that only the refined relaxation‐time assumption can lead to consistent results concerning the conservation of particles. Finally the dispersion relation resulting from the dielectric tensor is discussed for q ‖ B0 and q ‖ E0.
Intra‐ and Interatomic Electron Correlation in an Orbitally Nondegenerate Narrow Band
Authors: Heiner E. , Schneider J. , Haubenreisser W. 
Published: July 2007

AbstractThe influence of interatomic interaction between the electrons on the occurrence of ferro‐magnetism in a nondegenerate narrow band is investigated. Using the Green's function technique it is shown that the unperturbed band splits due to the interatomic interaction into spin‐polarized sub‐bands. For a simple cubic tight‐binding band the ground state energy for the paramagnetic and ferromagnetic configurations are calculated and compared. It is found that in the strongly correlated limit and for sufficiently large number of electrons per atom the ferromagnetic state is stable.
Electrical and Optical Studies of Semiconducting CdF2:In Crystals
Authors: Kunze I. , Ulrici W. 
Published: July 2007

AbstractOptical absorption and electrical conductivity of In‐doped CdF2 crystals have been measured at various temperatures. The results confirm the assumption of Trautweiler et al. [12] that the In3+ centers offer two localization possibilities t o the electrons introduced by annealing the crystals in Cd vapour: an atomic ground state (In2+) and a hydrogenic ground state (In3+ :e−). From an analysis of the results 0.055 eV is obtained for the energy distance between the two ground states and approximate values for their positions below the bottom of the conduction band. The latter depend on the degree of conversion. At temperatures below 50 K the occupation ratio between the two ground states can be strongly altered permanently in favour of the In3+ : e− donor states by irradiation with visible or UV light producing a photo‐induced conductivity and absorption. From measurements of the dependence of the photo‐induced conductivity below 50 K on temperature, irradiation time, and intensity, some properties of the In3+:e− donors are deduced.
On the Derivation and the Properties of an Effective Hamiltonian for a Polaron in an External Magnetic Field
Authors: Röseler J. , Henneberger K. , Fischbeck H. J. 
Published: July 2007

AbstractThe lowest eigenvalues of Frohlich's Hamiltonian with a magnetic field are approximately determined by solving the eigenvalue problem of an effective Hamiltonian for a polaron in a magnetic field. The effective Hamiltonian can be diagonalized without approximations, and the eigenvalue problem is reduced to the determination of the energy‐momentum relation of a free polaron. In the present paper it is shown in which manner the effective Hamiltonian can be derived from Frohlich's Hamiltonian with a magnetic field. The approximations being necessary for this derivation are justified on the condition ωc/ω0 = |e| · |B|/m c ω0 ≪ 1 in the case of weak and intermediate coupling. Furthermore, the properties of the eigen‐value spectrum belonging to the effective Hamiltonian are discussed.
Infrared Reflectivity and Raman Scattering of Mg2SiO4 Single Crystal
Authors: Servoin J. L. , Piriou B. 
Published: July 2007

AbstractThe lattice vibrations of Mg2SiO4 forsterite single crystal have been studied using infrared and Raman techniques. The site symmetry method allows to study the degeneracy lifting of the silicate ion vibrational levels and to assign the modes of vibration (45 infrared active modes and 36 Raman active modes), as internal or external. The analysis of the reflectivity data between 150 and 10000 cm−l by classical dispersion theory allows to find the oscillator parameter values. Most of the infrared lattice bands could be identified. All the predicted modes have been observed in the Raman spectra and the vl1 v2, and v4 lines have been identified. For some modes, specially in the low frequency range, the difference between internal and external modes is not obvious, taking into account the SiO4 tetrahedra deformation.
Theory of Electron Galvanomagnetics in Crystals: Hall Effect in Semiconductors and Semimetals
Authors: Rode D. L. 
Published: July 2007

AbstractUsing the contraction mapping principle, we show how iterated solutions of the classical Boltzmann equation with Fermi statistics are obtained. The mathematical formalism allows manipulation of the Boltzmann equation separately from considerations of particular electron scattering mechanisms and proves existence, uniqueness, and convergence properties of the solutions. This technique potentially applies to a broad range of electronic transport problems, but in particular, Hall effects and magnetoresistance are considered in group [V, III‐V, and II‐VI semiconductors and semimetals. These results show the corrections between Hall mobility, magnetoresistance mobility, and drift mobility, e.g. Hall mobility differs from drift mobility by less than 30% for all the crystals considered. In addition, measurements of the Hall factor (rH) in GaAs from 0.1 to 90 kG are compared with theory and agreement is found to 4%.
Optical Study of Ni2+ and Co2+ Ions in Garnets with Only Octahedral Magnetic Sublattice
Authors: Sokolov V. I. , Szymczak H. , Wardzynski W. 
Published: July 2007

AbstractThe optical absorption spectra of two garnets, NaCa2Ni2V2O12 and NaCa2Co2V3O12 have been measured at various temperatures between 4.2 °K and room temperature. The data have been fitted to a crystal field theory which includes spin‐orbit coupling and the trigonal field of the S6 site. The parameters of the trigonal field for a best fit for both crystals were v = 2100 cm−1 and v′ = −500 cm−1. A discussion of the results refered to the magnetic properties of garnets is given.
Experimental Study of a New Mg Centre in NaCl and KCl
Authors: Voszka R. , Watterich A. 
Published: July 2007

AbstractIn OH‐free NaCl(Mg) and KCl(Mg) electron centres are produced by electrolytical coloration and “decoloration”. It is most probable that the centre is a Mg atom in a vacancy pair. The oscillator strength of its absorption band is determined.
Magnetic Ordering in NdS
Authors: Golosovskii I. V. , Plakhty V. P. 
Published: July 2007

AbstractA neutron diffraction study has been made of powdered NdS samples at 4.2, 27, and 293 °K. A noncollinear magnetic structure with two propagation vectors has been revealed. All spins lying in a {110} plane are collinear and arranged antiferromagnetically. From plane to plane the spin direction rotates by a right angle. The possible and really observed spin configurations are discussed within the, framework of the molecular field method.
On the Soft X‐Ray Appearance Potential Spectrum of Graphite and Less Well‐ordered Carbons
Authors: Bradshaw A. M. , Menzel D. 
Published: July 2007

AbstractThe technique of soft X‐ray appearance potential spectroscopy (APS) has been applied to pyrolytic graphite and other carbons. The prominent, sharp satellites in the spectrum are assigned, in agreement with Houston and Park, to a coupling of the CK core hole excitation to strong plasmon emission (first and higher orders of the 7 eV plasmon and first order of the 27 eV plasmon). However, the peak separations of the higher order 7 eV plasmons are found to be not constant. The broad loss peaks are assigned to coupling with interband transitions. Increasing the degree of disorder of the carbon markedly affects the spectrum. The results are discussed in the light of more direct experimental investigations of electronic excitations in graphite, and of recent theoretical considerations of plasmon coupling in APS.
The Mobility of Grown‐in Dislocations in the Intermetallic Compound MgZn2. III. Dependence of Basal Slip on Chemical Composition within the Homogeneity Range and on Temperature
Authors: Kubsch H. , Paufler P. , Schulze G. E. R. 
Published: July 2007

AbstractThe dislocation velocity, , in basal slip shows a maximum within the range of homogeneity of the Laves phase MgZn2. The temperature dependence of can be described by an thermally activated mechanism with an activation enthalpy of (1.7 ± 0.3) eV in agreement with macroscopic deformation experiments.
Localized Modes Due to Impurity Pairs in a Heisenberg Ferromagnet
Authors: Tucker J. W. , Walls J. 
Published: July 2007

AbstractThe energy of localized modes due to a nearest‐neighbour pair defect in a simple cubic Heisenberg ferromagnet is investigated. Particular attention is paid to the p‐symmetry mode oriented along the direction of the inter‐impurity bond since for this mode the energy depends on the impurity‐impurity exchange constant. It is found that the results of a two‐parameter variational calculation, along the lines suggested by Tucker and Kilby, are in very good agreement with those of an exact treatment.
Quantum‐Statistical Theory of Light Propagation in Crystals
Authors: Davydov A. S. , Serikov A. A. 
Published: July 2007

AbstractThe density matrix method is used to investigate the passage of light (the frequency of which corresponds to the exciton excitation) through an optically isotropic crystal, The investigation is made in a wave packet representation which enables one to observe the spatial motion of photons and excitons. The radiationless energy transfer from an electronic excitation to a dissipative subsystem is taken into account.
Diffusion of Divalent Impurities from the Volume to the Surface in NaCl Crystals
Authors: Yacamán M. J. 
Published: July 2007

AbstractIn NaCl: Ca2+, NaCl: Cd2+, and NaCl: Cu2+ crystals heated in air at temperatures of 400 to 450 °C during 6 to 12 h the impurities tend to migrate to the crystal surface. There the impurities react with air and a new phase is produced on the NaCl surface. Both, transmission and scanning electron microscopy is used to study the structure and characteristics of the new phase. It is found that for NaCl: Ca2+ and NaCl: Cd2+ the new phase corresponds to CaO and CdO, respectively. The phenomenon is discussed using the theory of a double electrical layer that arises in the vicinity of the surface in ionic crystals. However this theory can not explain it completely. Diffusion to the surface must be taken into account in every work that involves a thermal treatment of a ionic crystal containing divalent impurities.
Lattice Dynamics of Crystals of the Calcite Structure II. Dispersion Curves and Phonon Densities
Authors: Plihal M. 
Published: July 2007

AbstractPhonon dispersion curves of the external and internal modes of trigonal CaCO3 have been calculated for some directions in the Brillouin zone. The one‐phonon density, the two‐phonon density, and the specific heat have also been determined. The results are compared with available experimental data on the specific heat and the two‐phonon absorption spectrum. The frequencies of the external modes have been calculated neglecting the internal degrees of freedom of the complex ions CO−3−, using a shell model which takes the short range interaction of nearest neighbours, the Coulomb interaction, and the polarizability of the complex ions into account. The variation of the frequencies of the internal modes with wave vector y has been determined by considering only the coupling of the transition dipoles of the complex ions. For this purpose the dipole‐dipole interaction formalism normally used at wave vector y = 0 to calculate the Davydov splitting of the internal modes is extended to wave vectors |y| ≠ 0.
Integral and Differential Equations of the Dynamical Theory of Electron Diffraction within a Distribution Formalism
Authors: Lannes A. 
Published: July 2007

AbstractUsing the distributions theory, an integral formulation is developed of electron dynamical theory including boundaries conditions. Two methods are proposed and the results are given in the general case of forward and backward diffusion. A differential formalism is derived in the second, first, and zeroth order. I n the column approximation, the Howie‐Whelan's formulation may be regarded as the convolution inverse of the integral form. It is suggested that this formalism is very useful as a basis for perturbation methods, diffuse scattering, and image formation.
Impurity‐Induced Far Infrared Absorption in CaF2, BaF2, and SrF2 Containing H‐Ions
Authors: Harrington J. A. , Weber R. 
Published: July 2007

AbstractThe far infrared impurity‐induced absorption has been measured for CaF2, BaF2, and SrF2 containing either H−or D−ions. In doped CaF2, only a broad one‐phonon absorption appears. For BaF2 and SrF2, H−and D−ions induce a weak continuous absorption and, in addition, resonance type modes occur at 127.0 and 139.2 cm−1, respectively. The spectra are compared with the calculated density of states curves. It is suggested that the 127 cm−1 line in BaF2 is the low lying T2 resonance mode of the H−ion.
The Kinetics of F–F′‐Transitions in Coloured Alkali Halides
Authors: Hoffmann H. J. , Stöckma F. , Tödheide‐Haupt U. 
Published: July 2007

AbstractReaction and rate equations of the kinetics of photoconductivity of the F–F′‐conversion in alkali halide crystals arc discussed and integrated for the experimentally interesting cases.
Anisotropic Chemical Shift of Nuclear Magnetic Resonance in Single Crystals of Tellurium and Selenium. I. Experimental Studies
Authors: Koma A. 
Published: July 2007

AbstractNuclear magnetic resonances of 125Te and 77Se have been observed in single crystals of tellurium and selenium, respectively. They consist of three resonance lines, each of which shows a highly anisotropic chemical shift. The anisotropy of the chemical shift has been investigated in detail. Especially in the case of tellurium the difference in the anisotropy has been made clear between the right and the left‐handed crystals. The chemical shift tensors of tellurium and selenium are determined from the experimental results.
Valence Band Structure of CdTe
Authors: Čápek V. , Zimmerman K. , Koňák Č. , Popova M. , Polivka P. 
Published: July 2007

AbstractThe valence band structure near the I‐point in CdTe has been investigated. Experimentally, the absorption curves obtained for p‐type CdTe doped with Te, P, As are presented, discussed, and compared with theory [18]. This comparison yields the ratios of the hole effective masses m/m; = 7.5 and m/m = 5. The theoretical valence band structure near the r‐point is fitted to correspond with the optical absorption measurements.
On the influence of electronic exchange and correlation on pseudopotential calculations
Authors: Hafner J. 
Published: July 2007

AbstractThe influence of different local statistical exchange and correlation approximations for the core‐core and conduction band‐core interactions on a calculation of binding energies and stable crystal structures within Harrison's first principles pseudopotential formalism is discussed. It is shown that with a convenient choice of the exchange parameters it is possible to calculate the binding energies with high accuracy and to predict the correct crystal structure in each case. These exchange parameters agree well with those yielding the best form factors and effective interionic pair potentials in a previous paper [1].
On positronium‐like state in F‐centres of potassium chloride
Authors: Hautojárvi P. , Nieminen R. , Jauho P. 
Published: July 2007

AbstractThe trapping of positrons in F‐colour centres in KCl is investigated in some model calculations. The wave function of the bound state of the positron and F‐centre is determined in various approximations with and without the electron‐positron correlation, and annihilation parameters are evaluated using this function. It is suggested that the screening of the electron‐positron interaction in the bulk of the crystal has a strong influence on the trapping by promoting the localization of a neutral positronium‐like state in the vacant anion site. In this case agreement with experiments is obtained.
Thermoelectric power of n‐type Bi2Se8 in strong transverse magnetic fields
Authors: Middendorff A. , Köhler H. , Landwehr G. 
Published: July 2007

AbstractFrom the saturation values of the magneto‐Seebeck coefficient and Hall constant in strong transverse magnetic fields the density of states and the chemical potential were determined as a function of electron concentration in the conduction band of Bi2Se3 single crystals. The results confirm in an independent manner the non‐parabolic one‐valley model for the lowest conduction band, which was derived from Shubnikov‐de Haas investigations.
On the description of multiple scattering processes in amorphous and crystalline semiconductors
Authors: Maschke K. , Overhof H. , Thomas P. 
Published: July 2007

AbstractThe electronic properties of amorphous semiconductors can be calculated from the configurational averaged Green's function. In this method the atomic structure of the system is incorporated into the scattering correlation function (SCF). To get a tractable form, the SCF is factorized into products of two‐center SCF's. The approximations involved in this decomposition are discussed. A comparison is made to similar approximations common in KKR energy band calculations for crystals (Ewald's summation technique). The connection with scattering by “frozen” hot crystals is demonstrated. For the amorphous case, it is shown that at least one and two‐center scattering contributions to the Green's function can be treated correctly.
On non‐local extensions of the ginsburg‐landau theory for type‐II superconductors valid at all temperatures
Authors: Brandt E. H. 
Published: July 2007

AbstractThe free energy of a superconductor is expressed as a two‐dimensional infinite series which may be interpreted in three different ways: as an expansion with respect to a) the gap parameter, b) the gauge‐invariant gradient, or c) the temperature difference Tc‐ T. By partial summation of the series we obtain a simple non‐local functional containing as special cases the extended Ginsburg‐Landau theory (Neumann‐Tewordt) and the nonlocal electrodynamics (Pippard, Gorkov). For small magnetization it gives the exact gap (Helfand‐Werthamer) and the magnetic field distribution (Delrieu) in the entire temperature range 0≦ T < TcIn the general case the functional is expected to be a good approximation for T > 0.7 Tc By numerical minimization of the functional one may hope to solve fairly complicated problems such as, e.g., the perturbed flux‐line lattice.