bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigating the Reliability of Local Empirical Pseudopotential for Band Structure of PbTe by Comparing Calculated Optical and Photoelectric Properties with Experimental Data
Authors: Ciucci G. , Nardelli G. F. , Antoci S. 
Published: July 2007

AbstractA comparison is made between calculations based on the empirical pseudopotential method and optical and photoelectric data of PbTe. The agreement found with such experimental data is generally good concerning conduction and high energy valence bands. In regard of optical data, the results are comparable or better than the results obtained by previous authors on the basis of the APW‐k. p method. A critical point analysis of the main structures occurring in the calculated optical properties shows that volume effects in the BZ cannot be disregarded in the critical point assignment.
Uniaxial‐Stress‐Induced Splitting of Plasma Edge in Single Crystals of MB6 Compounds
Authors: Iller A. 
Published: July 2007

AbstractUniaxial‐stress‐induced shift and deformation of the plasma edge has been observed in polarized light for single crystals of LaB6, PrB6, NdB6, and CeB6. Stress modulation technique was used. It is shown, that the shift and deformation of the plasma edge is due to the change of the parameters which determine the reflectivity in this region, i.e. free electron concentration, effective mass, relaxation time, and lattice dielectric constant. The change of the parameters was estimated and the shift of the plasma edge determined, using experimental results for all investigated compounds.
Crystal Field Determination in Rare‐Earth Oxysulfides III. Specific Heat Measurements on Gd, Tb, Ho, and Dy Oxysulfides
Authors: Rossat‐Mignod J. , Quezel G. , Berton A. , Chaussy J. 
Published: July 2007

AbstractThe specific heat of gadolinium, terbium, dysprosium, and holmium oxysulfides has been measured between 1.4 and 80 K. The lattice contribution has been obtained by the analysis of the Gd2O2S results. For the terbium, dysprosium, and holmium oxysulfides, the specific heat studies allowed to remove the ambiguities of the optical measurements and to precise the crystal field splitting of the rare‐earth ground state multiplet.
Landau Levels in Uniaxially Stressed p‐Type Germanium
Authors: Jones J. C. , Wallace P. R. , Ulmet J. P. , Carrère G. , Askenazy S. 
Published: July 2007

AbstractAn effective mass stress Hamiltonian for the Γ8 ( j = 3/2) valence bands in germanium has been used to calculate the Landau levels in p‐germanium. The magnetic fields and the stress have both been taken in the [100] direction. The stress induced changes in the band structure are related to experimentally observed shifts in the de Haas‐Shubnikov longitudinal magneto‐resistance oscillations.
Evidence from Transport Measurements at High Pressures for Donor Ions Occupying Non‐Equivalent Lattice Positions in InSb
Authors: Porowski S. , Kończykowski M. , Chroboczek J. 
Published: July 2007

AbstractMeasurements of the Hall coefficient in undoped, extrinsic n‐type InSb were made as a function of temperature at hydrostatic pressures of several kbar. The results give evidence of the existence of donor states associated with ions which can occupy two non‐equivalent positions in the lattice.
Theory of the Order Parameter of NaNO2 in Molecular Field Approximation
Authors: Bonilla I. R. , Holz A. , Rutt H. N. 
Published: July 2007

AbstractA static theory of the order‐disorder, ferro‐paraelectric phase transition in NaNO2 is developed. The Coulomb energy of the system is calculated in the point charge approximation. The model takes the relative displacement δ°(T) of the Na+ ions from their symmetrical position as a function of temperature into account; and the strong correlation of the Na+ ion position with the dipole orientation of the neighboring NO2− ion. The short range force potential acting on the Na+ ion is fitted by means of δ°(0) which can be taken from experiment. The long‐range order parameter Ω is calculated in the molecular field approximation. A first order phase transition is obtained for which the critical values Tc and Ωc are calculated as a function of the permanent electric dipole moment of NO2− and δ°(0). Only qualitative agreement with experimental results is obtained. The Made‐lung constant of the lattice is obtained as α = 1.93.
A Model of the Electrical Transport Phenomena in Imperfect Crystals of Copper Phthalocyanine. III. The Position of the Fermi Level in the Δ‐Model
Authors: Lehmann G. , Hamann C. 
Published: July 2007

AbstractThe position of the Fermi level is investigated in crystals and in thin films of copper phthalocyanine. Particularly the ideal crystal, the crystal with a discrete trap level, the crystal with a continuous trap distribution on the surface, and crystals and thin films with a combination of a discrete trap level in the bulk and with a continuous trap distribution on the surface were investigated. The position of the Fermi level has a great influence on the conductivity, on the existence of p‐type or n‐type conduction, and on the population of traps. Based on the ideas of the Δ‐model [1, 2] for each case considered the position of the Fermi level is given in dependence on the temperature and on the injection of additional charge carriers by the contacts.
Resistance Minimum in Dilute “Magnetic” Alloys in the Absence of Impurity Moments
Authors: Nandiniand R. , Kumar N. 
Published: July 2007

AbstractA possible mechanism for the resistance minimum in dilute alloys in which the localized impurity states are non‐magnetic is suggested. The fact is considered that what is essential to the Kondo‐like behaviour is the interaction of the conduction electron spin s with the internal dynamical degrees of freedom of the impurity centre. The necessary internal dynamical degrees of freedom are provided by the dynamical Jahn‐Teller effect associated with the degenerate 3d‐orbitals of the transition‐metal impurities interacting with the surrounding (octahedral) complex of the nearest‐neighbour atoms. The fictitious spin I characterizing certain low‐lying vibronic states of the system is shown to couple with the conduction electron spin s via s‐d mixing and spin‐orbit coupling, giving rise to a singular temperature‐dependent exchange‐like interaction. The resistivity so calculated is in fair agreement with the experimental results of Cape and Hake for Ti containing 0.2 at% of Fe.
Toward a Dielectric Theory of Chemical Bonding
Authors: Bashenov V. K. , Alarashi R. A. , Foigel M. G. 
Published: July 2007

AbstractThe ionicities and effective energy gaps have been obtained for 32 A2B6 and A2B5 crystals using a new set of nonlocality factors. The calculation of these factors is performed by inserting the X1–X4 interband transition energies instead of the corresponding effective gaps for diamond‐type crystals. The most significant disagreement between these results and those of Van Vechten is observed at crystals composed of lighter elements belonging to the second row of the Periodic Table.
Optical Studies of Lattice Vibrations in Sphalerite Crystals — A Theoretical Approach
Authors: Talwar D. N. , Agrawal Bal K. 
Published: July 2007

AbstractAn approximate estimation of the zone‐boundary phonon frequencies has been made for the III–V compounds InP, InAs, and GaSb, using reliable theoretical approaches. Employing experimental data for the long wavelength phonons, the elastic constants, and the zone‐boundary phonon frequencies, the lattice dynamics of CuI and the III‐V compounds (crystallizing in sphalerite structure) has been discussed in a second‐neighbour‐ionic (SNI) model. The reliability of the calculated critical‐point phonons (CPP) for the III‐V compounds has been checked by Brout's sum rule and also by comparing them with the neutron or Raman data for various other compounds having similar crystal structure. The observed infrared and/or Raman spectrum peaks for the III‐V compounds have been assigned to calculated CPP at Γ, X, L, and W critical points. The assignments are consistent with Birman's selection rules and support the lattice dynamical results given here.
The Fermi Surface of White Tin from a RAPW Interpolation Compared with Experiment
Authors: Devillers M. A. C. , Matthey M. M. M. P. , De Vroomen A. R. 
Published: July 2007

AbstractFrom extensive calculations it is shown, that the relativistic APW method, used as an interpolation scheme, can describe the Fermi surface of white tin consistent in detail with all available experimental data. At the same time this model of the Fermi surface of white tin is used to confirm and to complete the interpretation of radio frequency size effect measurements presented in a preceding paper.
Helicon Waves in Semiconducting Bi1−xSbx Alloys
Authors: Herrmann R. , Oelgart G. , Krüger H. , Haefner H. 
Published: July 2007

AbstractInvestigations are made of helicon wave propagation in semiconducting BiSb alloys. The measurements were carried out at measuring frequencies between 28 and 40 GHz and at a temperature of 4.2 K in magnetic fields between 0 and 15 kG. The obtained charge‐carrier concentrations are in very good agreement with the values obtained from the direct‐current Hall effect. The influence of the displacement current on the dispersion of helicon waves is evidenced. Finally the angle dependence of the field values of the spatial resonances is discussed, which results when the magnetic field is rotated out of the direction of the surface normal.
On a Generalization of Weaire's Tight‐Binding Hamiltonian for Tetrahedrally Coordinated Networks
Authors: Streitwolf H. W. 
Published: July 2007

AbstractIntroducing two interaction operators for interactions at the atom and the bond Weaire's tight‐binding Hamiltonian is extended to take into account all interactions between nearest neighbour bonds. The integrated density of states is derived and the energy spectrum is discussed. It consists of two bands with δ‐peaks at the upper band edges. In a special representation the Green's function is calculated.
The Excitation Spectrum of a Rare‐Earth Alloy
Authors: Tucker J. W. 
Published: July 2007

AbstractThe dispersion relation for the coupled nuclear and electronic spin wave modes that exist in magnetically ordered materials due to the hyperfine interaction is derived for arbitrary concentrations of nuclear spins. The calculation makes use of a diagrammatic technique in which the evaluation of the thermal averages of products of spin operators is fa cilitated by the use of the drone‐fermion representation. Criteria are established for the validity of the proposal by Jones (1973) that the results of molecular field theory hold for arbitrary concentrations.
Magnetic Susceptibility and Electrical Properties of p‐Pb1−xSnxTe
Authors: Lasrkarev G. V. , Migley D. F. , Shevchenko A. D. , Tovstyuk K. D. 
Published: July 2007

AbstractThe results of the measurements of magnetic susceptibility, Hall effect, and resistivity of the p‐type Pb1−xSnxTe solid solutions with x = 0.11 to 0.31 and a hole concentration of (3.1 to 7.9) × 1019 cm−3 are given. The magnetic susceptibility was measured in a temperature range of 78 to 450 °K, the Hall effect and resistivity in a range 4.2 to 450 °K. At T > 80 °K the Hall coefficient essentially increases with temperature, which can be explained by the presence of light and heavy hole bands. The temperature dependence of the magnetic susceptibility shows that the latter is paramagnetic for the holes, and the Pb1−xSnxTe valence band has a complex structure. Near T = 300 °K the temperature dependence of the magnetic susceptibility has peculiarities. It is supposed that the latter are connected with the conversion of the g‐factor to zero when the hole effective mass increases with temperature.
Wave Scattering Processes on Fluctuations in Non‐Equilibrium Semiconductor Plasma with Isotropic Non‐Parabolic Dispersion Law of Carrier Energy
Authors: Tomchuk P. M. , Shenderovskii V. A. 
Published: July 2007

AbstractAn effect is investigated of the energy band non‐parabolicity on the scattering and transformation processes of electromagnetic waves on fluctuations in the non‐equilibrium semiconductor plasma. It is shown that the deviation of the carrier energy dispersion law from the isotropic parabolic one in a high electric field leads to a new mechanism of the light scattering which does not occur in the equilibrium plasma. The cross section of the electromagnetic waves scattering and transformation on fluctuations in the non‐equilibrium semiconductor plasma essentially depends on the energy band shape and magnitude and orientation of the external electric field.
Correlation Functions of Weakly Bonded Impurity Spin in a Ferromagnet at High Temperatures
Authors: Los V. F. 
Published: July 2007

AbstractCorrelation functions have been calculated for the operator of a weakly bonded impurity spin in the Heisenberg ferromagnet in the temperature range whose lower limit is determined by the condition kT ≫ S|ω0| (S is the magnitude of impurity atom spin, ω0 the excitation energy of a weakly bonded impurity spin) with the exception of a close neighbourhood around the point of the phase transition of second order. The calculation was performed by summation of the infinite series of the perturbation theory for correlation functions. No representation of the Holstein‐Primakoff type was used for the spin operators of the impurity atom and the spins of the matrix atoms.
Hot‐Electron Magnetic Susceptibility of Degenerate Semiconductors at Low Temperatures: Effect of Non‐Parabolicity
Authors: Pal B. P. 
Published: July 2007

AbstractThe dependence of hot‐electron magnetic susceptibility (χ) in a non‐parabolic conduction band on external dc electric field (E) has been investigated theoretically. The non‐parabolicity is accounted for by Kane's model for the conduction band and the “effective‐electron‐temperature model” has been used to describe the electron distribution function. Ionized impurity scattering has been assumed to be the dominant momentum relaxation process while energy loss was assumed to be accounted for by scattering due to acoustic phonons via the screened deformation potential, the screened piezoelectric interaction and scattering by polar optical phonons. Individual energy loss rates have been calculated using the corresponding analytical expressions which take account of the non‐parabolic nature of the energy bands both in the density of states and electron wave functions. Numerical results are presented for the typical case of an n‐InSb sample for fields up to ≈ 2 V/cm. The plot of susceptibility (χ) as a function of the dc electric field (E) leads to a kink at a field strength of ≈ 370 mV/cm corresponding to an electron temperature ≈︁ 18.5 °K. This is attributed to the onset of the spontaneous emission of polar optical phonons. Results are compared with those obtained on assuming a parabolic model for the energy bands. Non‐parabolicity, in general, leads to a lower value of the hot‐carrier magnetic susceptibility (absolute magnitude) as compared to its value in the parabolic band model for the same value of the electric field.
Energy Transfer between Heated Carrier Systems in a Semiconductor by Inter‐Carrier Scattering
Authors: Hearn C. J. 
Published: July 2007

AbstractAn analysis is made of the rate of transfer of energy between two heated carrier systems in a semiconductor via the inter‐electronic interaction. The systems can be either two electron systems, in different valleys of a semiconductor, or an electron system and a hole system. The systems are taken to have different mean energies and drift velocities and their momentum distributions are approximated by displaced Maxwellian functions. It is shown that this process can be of importance in certain types of hot carrier calculations.
The Mechanism of Luminescence of Crystals of the Complex Formed by Manganese (II) Chloride with 3‐Ethyl‐4‐Methylpyridine Hydrochloride
Authors: Burić I. , Nikolić K. , Aleksić A. 
Published: July 2007

AbstractThe luminescent properties of crystals of the complex formed by manganese(II)chloride with 3‐ethyl‐4‐methylpyridine hydrochloride were studied at different temperatures by measurement of absorption, excitation, reflectance, and luminescence spectra. From the reflectance and excitation spectra in this compound 4T1g, 4T2g and 4A1g, 4Eg energy levels are found. It was established that there is a tetrahedral coordination of the manganese (II) ion, which brings about a green luminescence. The mechanism of the process of absorption and emission is explained in terms of the theory of the configurational model. The parameters required for plotting a configurational coordinate diagram were computed. Theoretically determined values for the maxima of excitation and luminescence are in good agreement with those determined experimentally. It is established that the phenomenon of luminescence is due to the 4T2g → 6A1 transition.
The Van Hove Diagonality Conditions and the Ionic Configuration Average in the Theory of Liquid Metals
Authors: Schaich W. L. 
Published: July 2007

AbstractThe justification of the ionic configuration average within the limitation of infinite order perturbation theory is considered. The diagonality conditions of Van Hove are shown to result from this average if the momentum matrix elements are appropriately coarse grained. An omission in a previous proof of these conditions is thereby rectified. Finally a comment is made on the generality of the results.
Pseudopotential Spherical Functions in Metals
Authors: Srivastava S. K. 
Published: July 2007

AbstractA theory of the new defined spherical function known as pseudopotential spherical function s1(yr) has been presented. This spherical function is similar to other well known spherical functions: Bessel spherical function ji(qr) Neuman spherical function n1(qr), and Hankel spherical function h1(qr). The spherical function is used in description of the electron‐ion potential and the effective density of metals. The results of the effective density for Na, Mg, and Al are presented. The obtained values are similar to the values obtained from the atomic orbital method.
Crystal Field Theory Interpretation of the Magnetic Susceptibility of CdYb2Se4 Spinel
Authors: Pokrzywnicki S. , Czopnik A. , Wróbel B. , Pawlak L. 
Published: July 2007

AbstractThe paramagnetic susceptibility of polycrystalline CdYb2Se4 spinel has been measured between 4 and 300 K. The data are interpreted within the crystal field approximation and a correction is made taking into account exchange interactions. The energy levels and crystal field parameters b4 and b6 have been calculated.
Parametric Excitation of Spin Waves in Ferromagnets with Domain Structure
Authors: Filippov B. N. , Lukomskii V. P. , Lebedev Yu. G. 
Published: July 2007

AbstractAn investigation is made of the mechanism of the influence of an rf field on ferromagnets with different domain structures leading to a modulation of the internal effective magnetic field, in which the magnetization vector precesses. The calculations are made for the case when external polarizing magnetic field H0 = 0. It is shown that the mechanism of the parametric excitation investigated is strongly sensitive to the type of the domain structure. It turns out that the parametric excitation of the spin waves in a ferromagnet with a Shirobokov domain structure is impossible. However, in a ferromagnet with a striped domain structure the investigated mechanism leads to the excitation of wall and intra‐domain modes and to the simultaneous excitation of both the modes as well. The excitation thresholds are found of all the modes under consideration and analysed.
Unpinning of Dislocations within the Framework of the Vibrating‐String Model
Authors: Frank W. , Frydman R. 
Published: July 2007

AbstractWithin the framework of the vibrating‐string model the frequency of thermally activated unpinning of dislocations from point obstacles is calculated with the aid of a dynamical theory. It is found that the unpinning frequency Γ has the form of an Arrhenius equation, Γ = Γ0e−ΔG/kT, where ΔG is the portion of the free enthalpy of activation which may be obtained by means of elasticity theory using isothermal elastic constants. The pre‐exponential factor Γ0 is shown to decrease with increasing length of the pinned dislocation segments, contrary to the result obtained on the basis of the absolute rate theory.
Inelastic Neutron Scattering by Cerium Hydrides. II. Lattice Dynamical Approach
Authors: Vorderwisch P. , Hautecler S. , Deckers H. 
Published: July 2007

AbstractA central force lattice dynamical model, previously applied by Slaggie to the CaF2 structure of ZrH2, is extended to the BiF3 structure. It is used for the analysis of inelastic neutron scattering data on cerium hydrides CeH1.98 and CeH2.72. For both samples the force constants are derived. The values of the corresponding force constants in both hydrides are different. The additional hydrogen in the CeH2 structure is found to be weakly bound.
Optical Absorption and Photoconductivity in Liquid Selenium
Authors: Rabit J. , Perron J. C. 
Published: July 2007

AbstractThe optical absorption and photoconductivity is measured in liquid selenium. Urbach's spectral rule is satisfied and explained with the Dow and Redfield model. The optical gap is close to 1.8 eV at 230 °C and its temperature dependence is 8 × 10−4 eV/K. Optical absorption and quantum efficiency curves are not energy shifted in contrast to amorphous selenium. The low energy photogeneration is due to a “dynamically”‐assisted separation of electron–hole pairs. Two lifetimes are found and the shorter is related to the structural relaxation. The values of photoconduction and conduction gaps are about 1.8 eV in agreement with the optical result but the Fermi level must be shifted towards the valence band.
Longitudinal Photon Drag in p‐Type Tellurium
Authors: Auth J. , Genzow D. , Herrmann K. H. , Wendt M. 
Published: July 2007

AbstractThe longitudinal photon drag has been studied for free holes in tellurium using a Q‐switched CO2 laser. A great effect is expected due to the great interband matrix element for allowed direct hole transitions between the sub‐valence bands H4 and H5. Due to the low crystal symmetry interesting anisotropy phenomena take place. The measurements have been performed for a set of samples, oriented either parallel or perpendicular to the c‐axis. The drag effect connected with sub‐band transitions is dominating as predicted by the theory (tensor coefficient σ1133 = 5 × 10−12 cm/V at T = 77 K). The coefficient σ3311 connected with the absorption of radiation polarized Fω ⊥ c was found to be −1 × 10−12cm/V at 77 K.
A New Exchange Interaction Operator for Magnetic Materials
Authors: Popović‐Božić M. 
Published: July 2007

AbstractGirardeau's second quantization representation for compound particles is used to derive, starting from first principles, a new approximate Hamiltonian for the exchange interaction of two atoms in their ground states. As distinct from the conventionally used Dirac‐Heisenberg Hamiltonian, the new operator comprises the effects of exchange of one, two, three etc. pairs of electrons. Assuming that the exchange interaction in a many‐atom system can be taken as a sum over the operators for interaction of pairs of atoms, a new approximate Hamiltonian for magnetic crystals is derived.
On the Relativistic Electronic States of a Monatomic and a Diatomic One‐Dimensional Lattice
Authors: Sen Gupta N. D. 
Published: July 2007

AbstractA new method has been developed to obtain directly wave functions and relations between the energy and momentum of an electron in a linear array of δ‐potentials obeying the Dirac equation, both for a monatomic and a diatomic one‐dimensional lattice.