bluuebunny/crossref_metadata_2025_split huggingface dataset:
Spin Wave Amplification in Ferromagnetic Semiconductors: Plasma Effects and s–d Interaction
Authors: Filho M. D. Coutinho , Miranda L. C. M. , Rezende S. M. 
Published: July 2007

AbstractWe evaluated the effects of the s–d interaction and of plasmon‐assisted processes on the spin‐wave amplification by drifting carriers in ferromagnetic semiconductors. Under the experimental conditions in CdCr2Se4 the contributions of these processes to the amplification factor are negligible compared with that one due to interaction of the current previously analyzed.
Some Applications of the Bond Orbital Model
Authors: Ciraci S. , Tiller W. A. 
Published: July 2007

AbstractThe ‘bond orbital’ model, which is based on the tight‐binding approximation, is summarized and utilized to calculate the cohesive energy of tetrahedrally coordinated solids. Several physical properties of such semiconductors are successfuly correlated with the bonding energy of the bond‐orbital. These are the band gap, the melting temperature, and the vacancy formation energy. In addition, the hardness is found to vary linearly with polarity.
Induced Scattering of Neutrons by an Electromagnetic Field
Authors: Benoit C. , Solal G. W. Cohen 
Published: July 2007

AbstractAn investigation is made of the modification of the one‐phonon scattering cross section of neutrons when the crystal is irradiated by an infrared monochromatic beam. It is found that under particular conditions an additional peak appears. The magnitude and the position of the peak depend on the intensity and the frequency of the IR beam.
Ohmic and Non‐Ohmic Transport in Undeformed and Plastically Deformed Tellurium
Authors: Thalmayr E. , Kahlert H. , Kuzmany H. 
Published: July 2007

AbstractIn order to study the influence of plastic deformation on hole transport in tellurium, the ohmic conductivity and Hall effect as well as the conductivity by warm and hot carriers have been investigated for various degrees of deformation. The temperature dependence of the mobility can well be explained by polar optical scattering, if additional scattering contributions due to lattice imperfections are taken into account which are particularly important for deformed samples. For warm carriers, positive deviations from Ohm's law are found which can be represented by σ = σ0(1 + βE2). The coefficient β turns out to increase strongly with the degree of plastic deformation. This may be caused by the variation of both the mobility and the carrier concentration with electric field strength. The two effects can be separated according to their different time‐dependent behaviour.
Separation of the Electronic and Lattice Thermal Conductivities in Bismuth Crystals
Authors: Uher C. , Goldsmid H. J. 
Published: July 2007

AbstractThe thermal conductivity of pure bismuth in a very high magnetic field has a contribution from the transverse thermomagnetic effects that is not negligible compared with the lattice contribution. It is demonstrated, however, that the lattice component in the binary direction can be determined accurately from measurements of the total thermal conductivity with a high magnetic field in the bisectrix and trigonal directions. Such measurements have shown that the lattice conductivity of bismuth is strictly inversely proportional to the absolute temperature in the range 35 to 140 K, and have allowed the electronic contribution to be evaluated.
Singlet Exciton–Charge Carrier Interaction in Anthracene Crystals
Authors: Kalinowski J. , Godlewski J. 
Published: July 2007

AbstractPrompt fluorescence in anthracene crystals is shown to be modified by the application of an external voltage to the illuminated crystal–water contact. The singlet exciton quenching due to the interaction with the injected holes is investigated. The rate constant for the interaction Kst = (3 ± 1.5) × 10−9 cm3 s−1 is determined. The results indicate that singlet exciton motion is a diffusion process and that the quenching is caused by hole‐modified crystal defects. The efficiency of detrapping of holes by singlet excitons is found to be about 30%.
Photo‐Induced Electron Spin Resonance (Photo‐ESR) in β‐Rhombohedral Boron
Authors: Nadolny A. J. 
Published: July 2007

AbstractPhoto‐induced ESR has been investigated in the temperature range 150 to 300 K using nearly homogeneous optical excitation (hv ≈︁ 1.3 eV). The relaxation of the photo‐ESR shows, similarly to that of photoconductivity, two components which are approximately described by a logarithmical function of time, decay rate being enhanced with increasing temperature. The time and temperature dependences of the photo‐ESR as well as the relationship between the photo‐ESR and photoconductivity are interpreted on the basis of a model, with traps for electrons having various values of emptying energy continuously distributed in a certain energy range and two kinds of localized valence states.
Scattering of Phonons by Bound Holes and Phonon Conductivity of p‐GaSb
Authors: Singh M. , Verma G. S. 
Published: July 2007

AbstractThe effect of uniaxial stress along the [001] direction on the scattering of phonons by bound acceptor holes in doped semiconductors has been investigated for the situations ω < ωr and ω > ωr where ωr is the resonance frequency. The relaxation rates for the off‐resonance frequency regions are used in explaining anomalous resonance dips of the thermal conductivity curves of p‐GaSb. Two conductivity integrals, K0 < ω < ωr and K where ωD is the Debye frequency, are considered. Assuming that the phonon resonances are of very narrow width, the total conductivity is expressed as the sum of the above integrals and appropriate relaxation rates for ω < ωr and ω > ωr are used. The present approach is quite successful in explaining the experimental results of thermal conductivity of p‐type GaSb except at low temperatures.
Resonant Scattering of Phonons by Two‐Level Impurities
Authors: Joshi Y. P. 
Published: July 2007

AbstractApplication of the thermodynamic Green's functions is made to the study of phonen scattering by impurities that have two distinct integral configurations corresponding to different energy eigenvalues. Operators are defined which do the function of transferring the impurities from one state to another, and the Hamiltonian of the system is phenomenologically expressed in terms of these. Imaginary phonon Green's functious are calculated, using finite‐temperature S‐matrix expansion and diagrammatic representation. It is found that the phonon relaxation time, which is obtained from these Green's functions, explicitly involves a temperature dependent factor.
The Pseudopotential Method and the Problem of Ordering in Alloys. I. Pairwise Interaction
Authors: Krasko G. L. , Makhnovetskii A. B. 
Published: July 2007

AbstractThe thermodynamic statistical theory of ordering by Khachaturyan is formulated in terms of the pseudopotential method of second order perturbation theory. The general quantity of the theory, V(k) – the Fourier transform of alloying potential – is expressed through the pseudopotentials of the ions constituting the alloy. As an example the CaBa system is considered and an a‐priori procedure of determining the equilibrium superstructure and its thermodynamic characteristics is demonstrated. The difficulties and limitations of the theory are discussed.
On the Spectral Intensity Distribution of Donor–Acceptor Pair Recombination in GaP
Authors: Bindemann R. , Unger K. 
Published: July 2007

AbstractThe spectral intensity distribution of donor–acceptor pair spectra in GaP (donors at P sites) is theoretically investigated by use of a model recently developed for the evaluation of photon energies, and is compared with experimental data. For high excitation levels the intensity distribution is governed by the overlap integral of electron and hole wave functions and is found to depend on the impurity concentration, but hardly on the chemical nature of the impurities involved, i.e. not on the central cell correction. The implications of these observations are discussed.
Wave Vector Dependence of the Electron Energy Loss Functions of Graphite
Authors: Venghaus H. 
Published: July 2007

AbstractElectron energy loss measurements were performed on graphite single crystals with 55 keV electrons. From spectra taken with transferred momentum hq parallel to the c‐axis and recorded for different absolute values of |q| the wave vector dependent energy loss function Im [−l/ϵ‖(E, q)] was determined for 0<E ⪅ 8 eV and 0.25 Å−1<|q|< < 0.75 Å−1. Apart from the dispersion of the energy loss maximum in the 5 to 6 eV region the main feature of Im [−1/ϵ‖(E, q)] is the appearence of a band gap Eg, increasing from Eg ≪ 1 eV for |q| = 0 up to Eg ≈︁ 1 eV for |q| as 0.7 Å−1. Additional measurements made with transferred momentum ħq perpendicular to the c‐axis confirmed the dispersion of the π‐plasmon, exhibiting an anisotropy for large wave vectors and different orientation of the latter within the layer planes of graphite.
Electronic Excitations (3 to 35 eV Range) in Some Layered III–VI Compounds: GaS, GaSe, and InSe
Authors: Soukiassian P. , Cazaux J. , Perrin J. 
Published: July 2007

AbstractThe energy losses suffered by a 40 keV electron beam through some monocrystalline layered III–VI compounds have been measured. By means of a Kramers Kronig analysis, the complex dielectric constant, in the 3 to 35 eV energy range, is computed for GaS (∥ and ⊥ to c‐axis), GaSe (∥ and ⊥ to c‐axis) and InSe (⊥ to c‐axis) and the e2 sum rule is applied. Attempts of interpretation are suggested with a special attention for the outer shell core electron excitations.
Localized Plasmon Modes in Lattice Defects of Metals
Authors: Nieminen R. M. 
Published: July 2007

AbstractThe localized modes of plasma oscillations in defects of free‐electron metals are discussed within the random phase and hydrodynamic approximations. The trapped plasmon frequency is calculated as a function of the defect size for spherical voids in several metals. The relevance of the defect modes to experimental detection techniques is discussed.
Raman Spectra and Optical Absorption Edge of Li3P04 Single Crystals
Authors: Harbach F. , Fischer F. 
Published: July 2007

AbstractLarge single crystals of the high‐temperature form of lithium phosphate have been grown from the melt. The Raman spectrum of these single crystals is reported in detail at room temperature and at liquid nitrogen temperature. The frequencies can be divided into groups of internal modes, librations and translational modes of the PO tetrahedra and into two groups of vibrations of the lithium ions against the oxygen lattice, split in consequence of the different site symmetries of the lithium atoms. The optical absorption edge in Li3PO4 (HT) single crystals is studied additionally. Li3PO4 single crystals are transparent up to 8.16 eV at 20°C or 8.37 eV at 78 K referred to an absorption constant K = 100 cm−1.
Anisotropic Hyperfine Interaction of Pb3+ Ions in 2S1/2‐State EPR
Authors: Born G. , Hofstaetter A. , Scharmann A. , Vitt B. 
Published: July 2007

AbstractFrom the angular dependences of EPR‐spectra of the 2S1/2‐state system Pb2+ in CaWO4 an anisotropic hyperfine interaction with the 207 Pb nucleus is inferred. The weak anisotropy (≈︁10/00) of the hyperfine A‐tensor is caused by the admixture of covalent ligand orbitals to the central s‐function in D2d symmetry.
The Contribution of Electric Quadrupolar Interactions to Nuclear Spin Relaxation by Vacancy‐Type Self‐Diffusion Mechanisms in Metals
Authors: Cavelius E. 
Published: July 2007

AbstractThe spectral densities determining the quadrupolar contribution to the NMR relaxation times are calculated for randomly diffusing vacancies in cubic metals. For the computation of the field gradients due to the vacancies Friedel's oscillating potential for the screening of a vacancy by conduction electrons is used. It is shown that the quadrupolar relaxation rate can be used to determine separately the energies of migration and formation of a vacancy. Detailed numerical results and estimates are given for the metals aluminium and rubidium.
Cluster Theory of Spin Excitations of Mixed Antiferromagnets. Application to MncCo1−cF2 and KMnCCo1−cF3
Authors: Dzyub I. P. 
Published: July 2007

AbstractThe cluster theory which takes into account the fluctuations in the longitudinal and transverse parts of the exchange interaction is generalized for studying mixed antiferromagnets. It is shown that the spin‐excitation widths reach their maximum values for the wave vector at the zone boundary. It is demonstrated that the coherent wave approximation generalized for a mixed antiferromagnet describes rather well the wave‐vector dependence of the spin‐excitation frequencies and their structure factors measured in mixed fluorides by means of the slow neutron scattering.
Indirect Transitions in Spectra of BiI3 Crystals at Low Temperatures
Authors: Shekhmametev R. I. 
Published: July 2007

AbstractAbsorption and luminescence spectra of BiI3 crystals have been studied in a temperature interval of 1.6 to 77°K. In the vicinity of the intrinsic absorption edge steps in the absorption contour have been detected (steps A, B, C, AT, BT), having a positive coefficient of temperature shift. These steps can be related to indirect exciton transitions with phonon emission and absorption. Emission of the indirect exciton has been observed, which belongs to the spectral region where the inverse hydrogen‐like series lines of absorption and luminescence are located. The energy of the indirect exciton formation (Eik = 16205 cm−1) and of phonons taking part in indirect transitions have been determined.
The s–d Bond and the Hyperfine Field on the Nucleus of Iron Atoms in FecPd1−c Alloys
Authors: Galperin F. M. , Kizhaev F. G. 
Published: July 2007

AbstractIt is shown t at in consequence of s–d bond oscillations of the charge (spin) density of 3d–electrons appear in disordered ferromagnetic alloys of 3d and 4d transition metals. The origin of these oscillations is different from those in the RKKY and Friedel theories. The contribution of these oscillations to the hyperfine field on the nucleus of iron atoms in FecPd1−c alloys is calculated. The concentration of iron changes from c = 0 to c = 0.25.
The Effective Mass of Holes in p‐Type AIIIBV Compounds
Authors: Filipchbnko A. S. , Lang I. G. , Naslbdov D. N. , Pavlov S. T. , Radaikina L. N. 
Published: July 2007

AbstractA rigorous calculation is made of the concentration dependence of the effective masses of holes in a series of p‐type AIIIBv compounds. The density‐of‐states effective masses and the optical effective masses (conductivity masses) in the compounds investigated are shown to differ essentially from each other both by their absolute value and by the character of their concentration dependences. These discrepancies are accounted for by the complexity of the valence band structures in the AIIIBv compounds.
Diffuse X‐Ray Determination of the Energy of Mixing and Elastic Constants of GeSi Solid Solutions
Authors: Bublik V. T. , Gorelik S. S. , Zaitsev A. A. , Polyakov A. Y. 
Published: July 2007

AbstractThe short‐range order and elastic properties of GeSi solid solutions of 28, 54, and 64% Si are studied by means of X‐ray diffuse scattering measurements. The mixing energy of the system taking into account the existence of two f.c.c. sublattices in the diamond structure is determined by extrapolating the long‐wave Fourier transforms of the concentration fluctuations Cq to q = 0 points corresponding to the node (400) and equals for q = 0 to W(q=o) = (2.5 ± 0.2) kcal/mol. The elastic constants of the GeSi solid solutions are determined and their positive deviations obtained from the additive values which are in good agreement with the data of the lattice parameter of the system.
Self‐Consistent Phonon Width Calculations in Alkali Halides
Authors: Fischer K. 
Published: July 2007

AbstractThe cubic anharmonic phonon decay process is reinvestigated. The δ‐functions which describe energy conservation in the harmonic approximation are replaced by Lorentzians in the self‐consistent theory, whose widths are given by the sum of the line widths of the interacting phonons. For KI at room temperature, the critical points in the damping function are “washed out” almost completely by this line broadening effect and the shift function is reduced considerably, as compared to conventional calculations with constant width parameters.
Magneto‐Thermoelectric Power of Bismuth in Weak Magnetic Fields
Authors: Hansen O. P. , Nielsen H. 
Published: July 2007

AbstractThe element α33(H) of the thermoelectric power tensor for bismuth has been measured at five temperatures between 15 and 37 K, and in magnetic fields up to 40 G. The analysis of the experimental data is based on the expansion of 4aL33(H) to second order in H. The coefficients in this expansion are calculated from the theory of Korenblit. Disagreement with the experimental results is found.
Shallow Donor States in Semiconducting CdF2
Authors: Langer J. M. , Langer T. , Pearson G. L. , Krukowska‐Fulde B. , Piekara U. 
Published: July 2007

AbstractThe origin of near infrared absorption spectra in semiconducting CdF2 crystals is reviewed. Good agreement between theoretical calculations and experimental data for CdF2:Gd or Ga gives strong support to the photoionization origin of the near infrared absorption. Lack of an evident “chemical shift” for the different shallow impurities studied indicates the intrinsic nature of the shallow donors responsible for both the infrared absorption and conductivity of CdF2. Arguments are presented for attributing the line spectrum observed in lightly doped CdF2 with phonon replicas of zero‐phonon ls–2p absorption masked by reststrahlen absorption of the host. It is proposed that for systems like semiconducting CdF2 such states should be described in terms of Fano's theory of discrete states degenerate with the continuum.
Optical Absorption of Defects in V205 Single Crystals: As‐Grown and Reduced V2O5
Authors: Clauws P. , Vennik J. 
Published: July 2007

AbstractAbsorption spectra are presented of V2O5 single crystals in the range 0.5 to 2.1 eV. From the behaviour of the optical absorption upon reduction, reoxidation, and annealing it follows that two different centres are active. The bands observed at 1.25 and 1.52 eV for a polarization parallel to the a‐axis (E‖a) and at 1.0 eV for E‖c increase after homogeneous reduction and are attributed to oxygen vacancies. The remaining structure in the range 0.6 to 1.1 eV is influenced by annealing and quenching and is probably due to a centre related with stacking faults. A possible centre is the V–V pair proposed by Perlstein.
Strong Coupling of the Proton–Phonon System in KDP. I. Isotope Effect on the Transition Temperature TC
Authors: Godzik K. D. , Blumen A. 
Published: July 2007

AbstractA mixed mode model is proposed for KDP (KH2PO4), which includes explicitely the coupling of the proton to the O…︁O vibrations of its hydrogen bond. The Hamiltonian is formulated in the framework of the tunnelling model using delocalized states of single H‐bonds as a basis set. The linear transverse coupling term is handled by a canonical transformation in infinite order perturbation theory. Uncoupling the protonic and vibrational motion a Tokunaga‐Matsubara type Hamiltonian is obtained with a renormalized tunnelling frequency and a renormalized interaction between different hydrogen bonds, both effects being mass dependent. This mass dependence explains fully the isotope effect of the transition temperature.
The Lattice Vacancy in Si and Ge
Authors: Yip Kwok Leung 
Published: July 2007

AbstractThe extended Hückel theory is used to study the electronic structure of the vacancy in Si and Ge. Localized levels associated with the vacancy are found in the forbidden gap near the valence‐band edge. The equilibrium positions of the four neighboring atoms around the vacancy after symmetric relaxation are predicted for the four different charged states of the vacancy. Jahn‐Teller effects are found to he small. The migration energies for vacancies in Si and Ge are also estimated. Results are compared with other calculations and experimental data.
A Study of Spin–Phonon Interactions in Ferromagnetic Insulators. I. The Spin Wave Spectrum
Authors: Jones M. J. , Cottam M. G. 
Published: July 2007

AbstractA field‐theoretical perturbation method is used to study the effects of Spin–phonon interactions in a Heisenberg ferromagnet. The calculations are carried out by employing an expansion in powers of the high‐density parameter 1/z, where z is the number of spins interacting with any given spin. In lowest order (1/z)0 this leads to molecular field theory, and the effects of spin fluctuations and Spin–phonon interactions are then introduced in higher orders of the perturbation expansion. The renormalised energy and damping of the spin wave excitations are evaluated to second order in the Spin–phonon coupling, and the dependence of these quantities on temperature, wave vector, and magnetic field is obtained. The calculations are valid over a wide range of temperature below Tc.
Electrical Properties of Tellurium under Hydrostatic Pressure. I. Effects on Its Effective Mass and Energy Gap
Authors: Koma A. , Tani T. , Tanaka S. 
Published: July 2007

AbstractConductivity and Hall coefficient have been measured in undoped and Sb‐doped tellurium at 77 and 273 K under hydrostatic pressure up to 7000 bar. It is found that the hole mobility increases with pressure and that the sample with its c‐axis perpendicular to the current direction shows a more rapid mobility increase than the parallel one. The mobility increase under pressure in undoped tellurium is interpreted as resulting from the decrease in the hole effective mass under pressure, and the pressure coefficients of the hole effective mass are derived from the experimental results. The pressure coefficients of the energy gap including the second order one are also obtained from the precise measurement of the pressure dependence of the Hall coefficient of undoped tellurium at 273 K, where it is intrinsic.
Point Defects in Lithium Hydride Crystals
Authors: Ermoshkin A. N. , Evarestov R. A. 
Published: July 2007

AbstractThe results of the calculations of the electronic structure of the F‐centre and the impurity centre LiH(Mg) by means of the molecular orbital method in the framework of the so‐called cluster model are reported. An attempt is made to estimate the positions of the local defect levels relative to the crystal bands. The results of the calculations are in satisfactory agreement with the experimental data.
The Semiempirical LCAO Treatment of Co2+ in ZnS, ZnSe, and ZnTe
Authors: Biernacki S. W. 
Published: July 2007

AbstractThe Semiempirical LCAO method is used to describe the electronic 3d levels of the paramagnetic impurity Co2+ as well as the band states in II–VI compounds. The effective one‐electron Hamiltonian taken as a sum of the kinetic energy, the interaction energy with point nuclei, and the interaction energy with spatial distribution of the electrons contains one adjustable parameter. The cubic field splitting parameter Δ and the positions of impurity levels with respect to valence band are calculated and compared with experiments.
Zur Theorie der ½〈111〉‐Schraubenversetzung in Alkalimetallen
Authors: Hübner U. 
Published: July 2007

AbstractDie Energie der ½〈111〉‐Schraubenversetzung in den Alkalimetallen wurde mit Hilfe der linienweisen Summation für das Modell konstanter Ladungsdiehte gewonnen und minimalisiert. Die Gleichgewichtskonfigurationen stimmen mit Konfigurationen von Vitek et al. im wesentlichen überein. Eine metastabile Konfiguration konnte nicht ge‐funden werden. Die Winkelverteilung der kritischen Scherungen wurde für homogene Scherungen berechnet. Die Ergebnisse sind in guter Übereinstimmung mit aus experimen‐tellen Werten zu T =0 K extrapolierten Daten für Kalium.