bluuebunny/crossref_metadata_2025_split huggingface dataset:
Debye‐Waller factors of MgO and CaO by a modified shell model
Authors: Sneh  , Dayal B. 
Published: July 2007

AbstractCalculated values of the average mean square displacements for MgO and CaO have been plotted as functions of temperature, while the Debye‐Waller B‐values and the mean square displacements for Mg and O, and Ca and O ions have been tabulated. The calculations have been done by a modified shell model, in which three‐body forces have been incorporated on the lines given by Verma and Singh, and Singh and Upadhyaya. The calculated values of the Debye‐Wailer factors and the mean square displacements are compared with available experimental values and good agreement is obtained.
Galvanomagnetic properties of MnkHg1–kTe under hydrostatic pressure
Authors: Stankiewicz J. , Giriat W. , Bien M. V. 
Published: July 2007

AbstractThe variation of the Hall coefficient and the electrical conductivity under hydrostatic pressure up to 10 katm and in the temperature range from 77 to 300 K was measured in mixed crystals of MnkHg1–kTe (k< 0.10). From the analysis of the pressure and temperature dependences of the electron concentration the energy gap E0= E(Γ6) − E(Γ8) was determined for k = 0.012; 0.05; 0.07; and 0.09 in the temperature interval from 77 t o 300 K. If is found, that the energy gap dependence is linear with composition within the investigated range of composition. It is established, that α = dE0/dT and γ = dE0/dp are positive and equal 5 × 10−4 eV/deg, and 9 × 10−6 eV/atm, respectively. This is the first attempt to determine the dependence of the energy gap on the composition in MnkHg1−kTe mixed crystals for k< 0.10. The obtained results are quite similar to the energy dependence on composition in CdxHg1−xTe, but significant differences occur in quantitative values.
Additional long‐ and short‐range potentials for direct excitons in zincblende structure solids: II. Numerical results and comparison with experiment
Authors: Ekardt W. 
Published: July 2007

AbstractThe correction formulas derived in Part I are applied to the calculation of the III‐V compound exciton spectra. Obviously only four of the many possible correction terms give appreciable contribution for these materials: dynamical corrections due to electron−electron interaction and due to electron−phonon interaction, exchange interaction, and provision of the realistic one‐particle band structure. The comparison with experiment is good.
Interlayer interaction and optical properties of layer semiconductors: 2H and 4H polytypes of PbI2
Authors: Doni E. , Grosso G. , Harbeke G. , Meier E. , Tosatti E. 
Published: July 2007

AbstractThe consequences of layer compound polytypism on optical properties and electronic band structure are investigated for the case of 2H and 4H PbI2.
On the question of exciton−phonon complexes in II−VI compounds
Authors: Georgobiani A. N. , Ozerov Yu. V. , Friedrich H. 
Published: July 2007

AbstractThe peculiarities of the λ‐modulated reflection spectra of ZnSe and CdS lying above the exciton ionization energy and located near the energy Eex1 + hω0 (Eex1 energy of the exciton ground state, hω0, energy of LO‐phonon) are investigated. The observed structures are interpreted from the point of view of the exciton‐phonon complex formation.
Multiple scattering and central limit theorem: A monte carlo approach
Authors: Desalvo A. , Rosa R. 
Published: July 2007

AbstractThe angular distribution of 1 MeV protons across layers of amorphous SiO2 of various reduced thickness τ (from 0.2 to 20) is evaluated by Monte Carlo simulation for different interaction potentials. A simple γ−2 potential and a Coulomb potential truncated at the Thomas‐Fermi screening radius turn out to be good approximations at low and high τ values, respectively, while Meyer's detailed calculations are satisfactory on the whole thickness range. The final distribution depends critically on the chosen potential: an γ−1 dependence at small impact parameters is necessary in order to satisfy the central limit theorem at large thicknesses.
Reduction symmetry method in crystal field theory (I)
Authors: Kustov E. F. 
Published: July 2007

AbstractAn account is given of a new method used to determine the matrix elements of the operators with symmetry of the point groups. Emphasis is laid to the importance of the subgroup properties of the point groups and the method of connecting matrix elements of free atoms and of atoms in the crystal field is developed. Some examples are given of the application of the reduction symmetry method (SC method) for the calculation of the matrix elements of the crystal field operators, the electrostatic, spin–orbit, and Zeeman interactions and formulae for calculating the intensities of various transitions in crystals with different symmetries are derived.
Measurements of magnetic susceptibility on amorphous boron
Authors: Kubler L. , Gewinner G. , Koulmann J. J. , Jaéglé A. 
Published: July 2007

AbstractMagnetic susceptibility measurements on amorphous boron samples have been performed between 77 and 1300 °K. Surface impurities present in the amorphous powder (according with a small particle size) have made measurements difficult. These impurity contributions being eliminated, a paramagnetic susceptibility signal, rising exponentially with the temperature above room temperature was found, just as in β‐rhombohedral boron. The presence of the same sort of electronic states in the forbidden band gap of the two compounds is concluded.
Calculation of the electrical conductivity above and below the Verwey transition in magnetite
Authors: Lorenz B. , Ihle D. 
Published: July 2007

AbstractUsing the Cullen‐Callen model of magnetite in the region U1 » |h| (U1 nearest‐neighbour Coulomb energy, h overlap integral) the electrical conductivity is calculated above and below the Verwey transition temperature Tv. From Tv = 119 up to 250 K an increase of the dc conductivity by a factor of five is obtained. At 383 K a conductivity maximum is found. The dc conductivities normal and parallel to the c‐axis are found to change abruptly at Tv by a factor of 110 and 70, respectively. From Tv down to 75 K a decrease in dc conductivity is obtained corresponding to an activation energy of 0.11 eV. The theoretical results agree very well with experiments.
Positronium‐like Á+‐center in potassium halides
Authors: Bisi A. , Bosi L. , Dupasquier A. , Zappa L. 
Published: July 2007

AbstractThe annihilation of positrons bound in Á+‐centers is studied. From a magnetic quenching experiment the value of |Ψ(0)|2 for the bound electron‐positron pair is obtained. Reasonable agreement is found with theoretical expectations.
Scattering of cold neutrons from an imperfect flux line lattice
Authors: Labusch R. 
Published: July 2007

AbstractThe scattering of cold neutrons from an imperfect flux line lattice (FLL) is analysed. It turns out to be possible by suitable experiments to distinguish between distortions due to pinning centres and those of grown‐in intrinsic defects of the FLL, and thus to obtain valuable information on the interaction forces between pinning centres and flux lines from the shape of the scattering intensity profiles.
A shell model for molecular crystals: Orthorhombic sulphur
Authors: Luty T. , Pawley G. S. 
Published: July 2007

AbstractThe recently proposed shell model for molecular crystals has been used in the case of orthorhombic sulphur. The value of the model is assessed by calculating a goodness of fit value using the measured zone‐centre mode frequencies. These measurements include Raman, IR, and inelastic neutron scattering results. The goodness of fit value is considerably better in the case of the shell model calculations than in the unpolarisable' molecule calculations. The model results are compared with neutron measurements throughout the Brillouin zone, showing scope for further improvement. Some suggestions for improvement are made.
Crystal field splitting and superhyperfine structure parameters of Co2+ in CdTe
Authors: Biernacki S. W. 
Published: July 2007

AbstractA semiempirical LCAO method is used to study the paramagnetic impurity Co2+ in CdTe. The cubic field splitting parameter Δ, the position of the impurity level with respect to the valence band, and the parameters of SHFS tensor are calculated and compared with experiments. The theoretical value of Δ is about 50% underestimated and the parameters of SHFS tensor are in good agreement with those from experiment.
Deformation of a Ni 〈111〉 film on Cu substrate
Authors: Dragila R. 
Published: July 2007

AbstractThe discrete lattice theory has been used to determine the deformation near the free surface of Ni 〈111〉 thin film. The force constants have been chosen to fit the elastic constants and phonon dispersion data. Also the deformation of Ni 〈111〉 film near the contact with bulk Cu base is calculated in the frames of both discrete and continuum theories.
Electronic structure and EPR spectra of V4+ in TiO2, SnO2, and GeO2
Authors: Michel‐Calendini F. M. , Fichelle G. 
Published: July 2007

AbstractThe energy levels of V4+ in a VO68− complex of D2h symmetry are computed according to an extended LCAO method with non‐orthogonal orbitals. The substitutional impurity is trapped in TiO2, GeO2, and SnO2 lattices. The results are compared with previous calculations on these structures. The interband transitions at the centre of the Brillouin zone are related to optical data with a good approximation. A first tentative is made to explain the X‐ray spectra of TiO2 according to the molecular diagram. The g‐factors and the hyperfine structure constants are computed and the covalency of molecular orbitals is taken into account. The following results are obtained for gx, gy, and gz:1.917, 1.893, 1.966 for V4+(TiO2), 1.937, 1.869, 1.953 for V4+ (SnO2) and 1.928, 1.911, 1.970 for V4+ (GeO2). The corresponding values of Ax, Ay, and Az in 10−4 cm−1 units are: 35, 40, and 141 for V4+(TiO2), 27, 40, and 148 for V4+(SnO2), and 41, 43, and 128 for V4+ (GeO2). A comparison is made with previous works using the point charge model. The LCAO calculations give results in agreement with the values deduced from EPR experiments.
Influence of magnetic anisotropy on light absorption and scattering in antiferromagnets
Authors: Gurylev V. K. , Vereshchagin V. P. , Dmitriev I. N. , Kurbatov L. V. 
Published: July 2007

AbstractThe temperature dependence of the integrated intensity of optical magnon sidebands and the differential extinction coefficient of inelastic light scattering in two‐sublattice antiferromagnets with spin S = 1 are calculated. The zeroth approximation of the self‐consistent‐field method (SCFM) with exact allowance of the single‐ion anisotropy is considered. The theory is applied to some antiferromagnets with Ni ions. The agreement of theoretical and experimental results is satisfactory.
Microtheoretical estimation of laser influence on superconductivity
Authors: Vujičič G. M. , Tošić B. S. 
Published: July 2007

AbstractThe microtheoretical estimation of the superconductive gap behaviour in the electromagnetic field is given. The approach to the problem is based on the mechanism of the retarded interaction between electrons. Ii is shown that the light quanta mainly decrease the magnitude of the superconductive gap. Also, the possibility to increase the gap is discussed, but the result is obtained under conditions near the limit of the validity of the method used.
Low‐Field Thermomagnetic Tensor for the Bi‐Like Band Structure
Authors: Uher C. 
Published: July 2007

AbstractThe low field thermomagnetic tensor components for the Bi‐like band structure have been calculated. The expressions are applicable for both the diffusion and the phonon‐drag transport mechanisms. The umkehreffect predicted for the α11(B1) coefficient is purely of phonon‐drag origin and can be used to determine the temperature range for which the phonon‐drag effect operates.
Energy Band Structure of Some Wurtzite Crystals
Authors: Chatterjee S. , Sinha P. 
Published: July 2007

AbstractA parametrized band structure for the wurtzite crystal is formulated following the tight‐binding interpolation scheme of Slater and Koster. The parametrized secular determinant is factorized using group theory at the symmetry points and axes inside the Brillouin zone. Besides the group theoretic factorization restrictive assumptions regarding the nature of the overlap integrals were needed for further factorization to facilitate the numerical evaluation of the parameters. Using the OPW data of Herman at the high symmetry points γ, A, H, and K, the parameters for wurtzite SiC, ZnS, ZnSe, and ZnTe are found and a thorough study of the energy bands throughout the Brillouin zone for these solids is performed with the help of these parameters.
Impurity‐Induced Infrared Absorption in Silver Halides
Authors: Hattori T. , Ehara K. , Hamasaki M. , Mitsuishi A. 
Published: July 2007

AbstractThe impurity‐induced infrared absorption bands are measured at low temperatures for AgBr: Li, AgBr: Na, and AgCl: Li. The absorption bands consist of those due to the localized mode, including the fundamental band, the higher frequency sidebands and the third harmonic bands, and those due to the band modes. The force constant change at the impurity site is discussed using a diatomic three dimensional model. The sideband spectra of the lithium and sodium localized mode in silver bromide are described by the theory based on two‐phonon absorption processes. There are apparent differences in the phonon coupling mechanisms to the host lattice between the lithium localized mode and the sodium one in silver bromide. It is found that for AgBr: Li, the phonon coupling mechanism due to the cubic anharmonicity is dominant and the impurity is cupled to its surrounding ions more softly. On the contrary, for AgBr: Na, the contribution due to the second‐order electric‐dipole moment mechanism is nearly equal to that due to the anharmonicity in high frequency limit of the sideband. Some absorption bands due to the impurity‐induced band mode are observed at 30, 48, and 61 cm−1 in AgBr:7Li and AgBr: Na at 2 K.
Lattice Dynamics of Covalent Ionic Compounds (II)
Authors: Altshuler A. M. , Vekilov Yu. Kh. , Izotov A. D. 
Published: July 2007

AbstractThe lattice dynamics of covalent ionic compounds with ZnS structure is discussed in the light of the pseudopotential method. The calculated results of the phonon dispersion in high‐symmetry directions are given for a number of compounds. Adequacy of experiments and the “dielectric model” as well as the possibility of its further generalization are also discussed.
Magnetic Susceptibility and Electronic Structure of CoSi and CoGe Alloys at High Temperatures
Authors: Dovgopol S. P. , Antropov V. A. , Radovskii I. Z. , Geld P. V. 
Published: July 2007

AbstractThe magnetic susceptibility of CoSi and CoGe alloys is investigated by the Faraday method with the help of the pendulum scale in the temperature range 900 to 1800 °C. It is shown that the Curie‐Weiss law is fulfilled both for solid and liquid alloys with Si (Ge) concentrations up to 30 at%. For these alloys the number of noncoupled spins per Co atom and the paramagnetic Curie temperature are calculated after determination of the temperature‐independent contribution to the magnetic susceptibility. Considering the possible localization of 3d‐electrons, a band model of Co alloys is proposed. Basing on this model and considering the connection of the nearest order in the alloys with the crystalline structure of the solid state, the magnetic properties of both solid and liquid alloys are explained.
Contribution of Lattice Dilation to the Temperature Shift of the Energy Gaps in Trigonal Selenium
Authors: Lingelbagh W. , Weiser G. 
Published: July 2007

AbstractThe influence of thermal lattice dilation on the temperature shift of some optical transitions has been studied. Below 100 K the shift of both the direct gap at H and the indirect gap is determined by the lattice dilation perpendicular to the hexagonal axis c, caused by acoustical phonons which leads to an increase of the gap energy with rising temperature. At higher temperatures the electron‐phonon coupling (mainly by optical phonons) gains importance and decreases the temperature coefficient of the gap energies. The energy of the direct gap at Z is less sensitive to the thermal dilation of the lattice.
Optical Detection of Nuclear and Electronic Magnetic Resonances of Close F‐Center Pairs in KCl
Authors: Jaccard C. , Schnegg P. A. , Aegerter M. 
Published: July 2007

AbstractThe luminescence of close F center pairs (produced by short F band irradiation near RT) is measured at LHeT in a static magnetic field (kG) under the influence of a microwave and/or a rf field of suitable frequency. EPR, revealed by an increase of the luminescence, is modulated by the rf, giving ENDOR spectra similar to those obtained for single centers by conventional methods. The rf alone induces also changes of the luminescence (up to 1%) giving NMR spectra with an intensity depending on the optical excitation and the rf power. The relaxation rate, extrapolated to zero light intensity, is equal to the inverse electronic spin‐lattice relaxation time. These observations can be explained by a pair model with isotropic spin exchange, calculated in the high field limit (Zeeman energy ≫ hyperfine energy ⪆ exchange energy). The states, characterized by electronic and nuclear quantum numbers, have different luminescent probabilities and the optical cycle transfers the pairs into the non‐radiative states. Any magnetically induced transition tends to restore the population equilibrium and increases the luminescence. The calculated intensity ratio EPR:NMR:ENDOR agrees with the observations.
A Self‐Consistent Calculation of Magnetic Properties of Single‐Element Amorphous Materials beyond the Homogeneous Molecular Field Approximation
Authors: Šlechta J. 
Published: July 2007

AbstractA self‐consistent calculation of magnetic properties beyond the homogeneous molecular field approximation is given. It was found that the Curie temperature, due to fluctuations of the exchange interaction only, increases. It is also shown that the magnetic properties inherently depend on higher spatial correlations of spins then pair‐pair ones.
The Bond Orbital Model Study of the Valence Bands of Cubic‐Tetrahedrally Coordinated Semiconductors
Authors: Ciraci S. 
Published: July 2007

AbstractThe valence energy bands of cubic‐tetrahedrally coordinated semiconductor sis investigated by employing the bond orbital model. In terms of the basic parameters of the model simple expressions are obtained for the gaps and widths at X and L, which allows to learn origins of a variety of the trends. The main features of the bands are found to depend exclusively on the polarity and the s‐p splittings of the atomic term values of the cation and the anion. As a further sophistication, the second‐neighbor interactions are included. Additional energy parameters representing second‐neighbor interactions are seen to have interesting relations to the polar and the metallic character of these solids. Finally, the pressure dependence of the valence bands is studied.
Invariance Properties of a Proposed Hamiltonian for Bloch Electrons in a Magnetic Field
Authors: Wannier G. H. 
Published: July 2007

AbstractA matrix equation has previously been proposed for the equation governing the motion of a Bloch electron in a magnetic field. The matrix was obtained by concentrating on irrational fields. The matrix elements vary continuously with the parameters of the problem. It is shown that this Hamiltonian matrix has the normal invariance properties expected from quantum theory. When derived in a Landau base it has an energy spectrum which is invariant with respect to a rotation of the Landau axes about the field. The same matrix equation results for rational and irrational fields if one works in a cylindrical magnetic base.
Exciton Superradiance
Authors: Kopvillem U. Kh. , Samartsev V. V. , Sheibut Yu. E. 
Published: July 2007

AbstractThe statistical aspects of exciton systems are considered. Calculations show that the non‐Bose character of the statistics plays a fundamental role in forming the exciton echo signal, self‐induced transparency, and other superradiant effects. As application of the general theory new phenomena as exciton nutation and forced exciton induction are considered. Comparison with experiment is made for the self‐induced transparency in CdS0.75Se0.25.
Linear Electroabsorption Due to Substitutional Deep Impurities in Wurtzite‐Type Crystals. III. Model Analysis of Co2+ in CdS
Authors: Gardavský J. 
Published: July 2007

AbstractAxial crystal field and Stark effect splittings are calculated and compared with experimental values. Reversed splitting pattern of 4T1(4F) is accounted for by the equivalent even‐parity field. The field‐induced changes of the absorption band intensities are explained as being due to the field‐induced change of the equivalent even‐parity dipole moment operator. The perturbed absorption spectra obey sum rules suggesting a conservation of the f‐sum rule already within the 3d7 configuration. A pronounced enhancement of the Stark effect through the axial crystal field is discussed.
Stimulated Extraordinary Polaritons in α‐Quartz
Authors: Chapet M. , Laval S. 
Published: July 2007

AbstractFrom an experimental study, dispersion curves are plotted of three extraordinary and one ordinary polariton modes in α‐quartz in the range 350 to 500 cm−1. A theoretical formulation of the two‐beam method, experimentally used, makes the possible coupling between E and A2 vibration modes obvious and the simultaneous existence of ordinary and extraordinary polaritons. The experimentally obtained dispersion curves are compared to the corresponding calculated branches. The agreement is quite good.
Effective Electron–Hole Interaction for Intermediate and Strong Electron–Phonon Coupling
Authors: Barentzen H. 
Published: July 2007

AbstractThe interaction of an electron‐hole pair is studied in a polar semiconductor, each particle being coupled to the lattice by the Fröhlich interaction. The theory of Gross and Tulub is used for the description of a single polaron. This theory which gives satisfactory results for both intermediate and strong coupling is then generalized to the problem of two interacting polarons. For not too strong coupling the effective electron‐hole potential will be presented in form of a series with increasing powers of the coupling constant. The first term of this series gives the well known Haken potential, whereas the higher terms are corrections to the potential which will become important for stronger coupling. The results are discussed in connection with exciton screening in the thallous and cuprous halides.
Linear Magnetoresistance in Parabolic Semiconductors
Authors: Arora V. K. 
Published: July 2007

AbstractA density matrix approach is described to calculate the complete ohmic magnetoresist‐ivity tensor for a non‐degenerate and non‐polar semiconductor with isotropic effective mass. The conventional methods using the Boltzmann transport equation cannot be used in a satisfactory way with magnetic fields of arbitrary strength. The presence of a magnetic field in a crystal introduces some non‐diagonal elements of the velocity operator, which could be averaged properly by using the density matrix. The results obtained agree with those obtained from the Boltzmann transport equation in the limit of low magnetic field including the value of zero.
The H− Ion as a Diffusion Trap for Divalent Ions in KCl
Authors: Castro J. C. , Robert R. , de Souza M. 
Published: July 2007

AbstractThe interaction between divalent ions such as Ca++, Sr++, and Ba+ + and its associate positive ion vacancy with substitutional H− and D− ions is studied. A model is proposed for the trapping of the divalent ion by the H− anions. The strong perturbation on the H−, and D− localized vibration introduced by the divalent ion and its vacancy is reported. The decrease on the barrier height for I.V. dipole relaxation was studied by dielectric loss technique.