bluuebunny/crossref_metadata_2025_split huggingface dataset:
Partial densities of states and electron–phonon interaction in transition metals
Authors: John W. , Hamann D. , Urwank P. 
Published: July 2007

AbstractFor the 3d‐metals Ti, V, Fe, and Cu the electronic part η of the electron–phonon coupling constant is calculated in the rigid muffin‐tin approximation. Moreover for V and Cu the pressure dependence of this quantity is investigated. The results show that the correct evaluation of the angular momentum components of the electron density of states at the Fermi energy is important. Especially the density of p‐ and f‐states exhibit a strong energy dependence within the d‐bands and lead to a variation in η as one crosses the transition metal series. The non‐spherical corrections to the Gaspari‐Gyorffy formula are small.
Parametric excitation in Kane's semiconductors
Authors: Anh Vo Hong , Dat Nguyen Nhu 
Published: July 2007

AbstractThe parametric excitation of electromagnetic vibrations in narrow‐gap semiconductors with nonparabolic energy dispersion defined by Kane's model is investigated using the quantum formalism proposed previously. The numerical estimates performed for the typical sample of n‐InSb crystals in different cases show that the deviation from parabolicity lowers the instability threshold field values by about one order of magnitude.
Hyper‐rayleigh scattering in disordered sodium nitrate
Authors: Vogt H. , Neumann G. 
Published: July 2007

AbstractHyper‐Rayleigh scattering is observed in single crystals of NaNO3 when the order‐disorder phase transition point and the nearby melting temperature are approached. Besides the central line at twice the wavenumber of the exciting radiation a wing and a phonon band are found. All spectral features are due to the rotational mobility of the NO3− ions. The temperature dependence of the hyper‐Rayleigh intensity is interpreted in terms of an Ising model.
The phonon spectra of γ‐ and β‐CuBr
Authors: Haxton M. B. 
Published: July 2007

AbstractA previously paper on CuI, is repeated for CuBr. A rigid ion, second neighbor ionic model proposed by Banerjee and Varshni is used to fit the inelastic neutron scattering data of Prevot et al. for the γ phase of CuBr. The model consists of a long range Coulomb contribution calculated directly and short range parameters calculated for the best fit to the data. The dispersion curves of β‐CuBr are calculated using the same model. The long range Coulomb contributions are again calculated directly. The short range parameters for the ideal wurtzite structure are calculated by Euler transformations of the zinc blende short range interaction matrices. Because of the nonideal structure of β‐CuBr and because of the expansion of the lattice with the increase in temperature, some small corrections are necessary. With these long range and short range contributions, the dispersion curves for β‐CuBr are calculated.
Atomic magnetic moments of Fe, Co, Ni and hyperfine fields at impurities in ferromagnetic iron
Authors: Galperin F. M. 
Published: July 2007

AbstractMagnetic moments of free atoms of the elements Fe, Co, and Ni of Mendeleev's periodic table (MPT) are calculated. The calculated values are equal to the measured (fractional) ones of the atomic magnetic moments of Fe, Co, and Ni ferromagnetic metals. Further, a hyperfine field is calculated at the nucleus of the impurity atom of the transition 3d element in ferromagnetic iron. It is shown that this field depends on the own field at the nucleus of the impurity atom.
Strong coupling of electrons to black body radiation at high temperatures
Authors: Hora H. 
Published: July 2007

AbstractAn evaluation of the Richardson equations for electron emission leads to the most general formulation including the branches of degeneracy, classical statistics, and that of strong photon interaction. The photoelectric yield constant is derived in general form. For black body temperatures above mec2, strong coupling is found generally, while for lower temperatures all three branches exist, depending on the electron density. A confirmation of the consistency of the theory is given by the fact that the quantum process of photoemission does not take more than 5% of the energy density of the black body radiation.
Room temperature FF′ conversion in KCl crystals of various purity and method of coloration
Authors: Nierzewski K. D. , Todorov T. , Georgiev M. 
Published: July 2007

AbstractThe FF′ conversion is initiated by flash‐light excitation at room temperature with the aim of obtaining data on the electron trapping and transition characteristics in KCl crystals of various purity and coloured in different ways. The purest, γ‐irradiated sample exhibits a relatively short F' lifetime and a proportionally large F centre‐to‐anion vacancy cross‐section ratio presumably resulting from an enhanced trapping ability of the F centre. In contrast, Na‐containing irradiated samples show unusually long F' lifetimes, not correlated to the corresponding cross‐section ratios. The F' yield in the pure samples is found to drop on repeated flashing which presumably reflects the drop in F centre ionization quantum efficiency as a result of clustering processes. Electrolytically coloured samples doped with divalent cations are also investigated.
Raman scattering of HgCr2Se4
Authors: Iliev M. N. , Anastassakis E. , Arai T. 
Published: July 2007

AbstractThe Raman spectrum of the ferromagnetic semiconductor HgCr2Se4 (TC = 106 K) and its dependence on temperature and incident photon energy is measured. Five Raman‐active modes are found at 65, 157, 168, 210, and 237 cm−1 and are assigned to certain ionic vibrations in the spinel unit cell. The temperature variations of the scattering cross‐section for different modes show no pronounced anomalies near the magnetic phase transition at TC but depend significantly on the wavelength of the exciting radiation. The resonance curve at 300 K exhibits two peaks at 1.9 and 2.35 eV superimposed by a broad structure which increases toward low energies.
Carrier mobility in ferromagnetic semiconductors
Authors: Patil C. G. , Krishnamurthy B. S. 
Published: July 2007

AbstractThe electron mobility in ferromagnetic semiconductors below the Curie temperature incorporating electron–two‐magnon scattering is calculated besides the usual non‐magnetic scattering using the variational procedure. It is found that the mobility due to two‐magnon process is proportional to T−1/2 (T lattice temperature). The calculation is compared with the experimental Hall mobility data in CdCr2Se4 (In doped) accepting ionized impurity scattering as the non‐magnetic scattering. The calculated mobility variation with temperature is in close agreement with the experimental data indicating the importance of electron–two‐magnon scattering mechanism.
Vacancy‐induced splitting of excited states and the structure of Sn2+V centres in alkali halides
Authors: Hizhnyakov V. , Zazubovich S. 
Published: July 2007

AbstractThe polarization characteristics are calculated for the A and C emissions of Sn2+V centres in alkali halides, taking into account the rearrangement in the electronic level system of the excited sp states in the course of relaxation. The light absorption processes are considered in the approximation of a weak crystal field. The emission processes are described by a model in which the interaction of the optical electrons of impurity ions with Eg lattice vibrations (JTE) is assumed to be the principal, and the spin–orbit interaction and the interaction with T2g vibrations are taken into account as additive corrections. It is also assumed that in Sn2+V centres the influence of the cation vacancy V is small as compared with JTE. Comparing the results of the calculation with the experimental data, the order of three tetragonal minima on the adiabatic potential energy surface (APES) of the 3P state of Sn2+V centres is established which is consistent with the order of the corresponding minima of 1P state. It is shown that in both excited states Z minima are the lowest ones. The vacancy‐induced splitting of the relaxed excited A state is found to be about 10−2 eV. The limit values are determined for the polarization degrees of A and C emissions at various temperatures, the parameters are found and the structure is discussed for the Sn2+V centres in alkali halides.
Long optical vibrations and elastic constants of hexagonal boron nitride
Authors: Ramani R. , Mani K. K. , Singh R. P. 
Published: July 2007

AbstractThe long optical vibrations of hexagonal BN are studied using the valence force constants of the borazine molecule. It is shown that the in‐plane interactions are adequately described by the transferred molecular force constants. The elastic constant (c11 + c12), calculated from the above model compares well with the experimentally deduced value. It is argued that the interplanar forces cannot be satisfactorily described by a simple Lennard‐Jones potential.
Impurity scattering of electrons in quantizing magnetic fields
Authors: Baranskii P. I. , Demidenko L. S. , Korolyuk S. L. , Samoilovich A. G. 
Published: July 2007

AbstractThe isotropic scattering of current carriers is investigated in quantizing magnetic fields at arbitrary value of the action radius of the scattering centre. A variational method is suggested allowing to obtain the phase functions of scattered electron, by means of which the electroconductivity is calculated. A comparison is made with earlier works, which are valid for the short‐range forces. In semiconductors, as a rule, the case of an intermediate action radius of scattering centre is found. It is shown, that in the case of short‐range forces the known results are received in first approximation. Numerical calculations are made for the parameters of GaAs.
Theory of Stark‐Ladder Currents
Authors: Kümmel R. , Rauh H. , Bangert E. 
Published: July 2007

AbstractCurrent and relaxation time of electrons are calculated for a lattice where a sufficiently strong applied electric field forms a Stark ladder. The population of states with momenta ℏk⟂ normal to the applied field is described by a function which is either uniform or a Maxwellian distribution. Various temperatures between 0 and 300 K are considered. The current‐voltage characteristic exhibits negative differential conductivity. Current peaks due to resonant phonon transitions between Stark‐ladder levels do not appear except in the case, when all electrons occupy states very close to k⟂ = o, which is not a stationary Stark‐ladder situation. Therefore and because of the smallness of the relaxation time of Stark‐ladder electrons interacting with LO phonons in ZnS, the previously observed resonant‐type current anomalies in ZnS should not yet be considered as the final experimental proof of the existence of Stark ladders.
Effects of Core and Correlation Corrections on the Electrical Resistivity of Lithium
Authors: Ball M. A. , Islam M. M. 
Published: July 2007

AbstractThe effects of correlation and core corrections on the electrical resistivity of lithium are investigated; the form factor is evaluated using the modified screened uniform charge model. The calculation of the screening is discussed, and a new form for the correction factor G(q) in the dielectric function ϵ(p) valid for q ≦ 2kF is suggested. The improvement of the calculated resistivity due to the core corrections are more significant than due to the changing the form of G(q).
The “Quasidirect” Radiative Recombination of Free Holes at Neutral Shallow Donors in GaP
Authors: Bindemann R. , Schwabe R. , Hänsel T. 
Published: July 2007

AbstractThe luminescence band at 2.24 eV in n‐type GaP is investigated in the temperature range of T = 27 to 120 K. It consists of a no‐phonon line and several phonon replicas (TAX, LAX, TOX), which overlap with the donor–acceptor pair band. According to the analysis of the line shape and the energetic position of the intensity maximum in dependence of the temperature, the excitation intensity, and the time after excitation this band can be interpreted as being caused by free (hole)‐to‐bound (electron bound at the sulfur donor) transition. Taking into account the consequences of the GaP band structure on the symmetry properties of the bound electron states the free‐to‐bound transition is described as ‘quasidirect’. The calculated line shape is in good agreement with experiment using an indirect gap value which is 11 meV higher than accepted hitherto. The obtained indirect gap energy and free exciton binding energy are determined to Eg(T = 4.2 K) = (2.350 ± 0.002) eV and EFE = (22 ± 2) meV, respectively.
Study of Linewidth and Exciton–Impurity Scattering in Cu2O
Authors: Nikitine S. , Elkomoss S. G. , Schwab C. 
Published: July 2007

AbstractThe profile of the n = 1 line of the yellow exciton series in Cu2O, which was studied experimentally as a function of the concentration of silver impurity, is calculated by the Lorentz theory used in atomic spectroscopy. According to this theory, the broadening of the line as a function of the impurity concentration is due to exciton–impurity elastic scattering. The theory depends of two parameters, namely the maximum absorption Kmax and the width of the line Δv1s, the values of which are taken from experiment. The line in the perfect crystal is assumed to have a pure Gaussian profile with an extrapolated width ΔvG = 0.57 cm−1. The calculations are also carried out for the values ΔvG = 0.4 and 1 cm−1. In silver doped crystals, the n = 1 lineshape is a contribution of a Gaussian and a Lorentzian component. The width of the Lorentzian ΔvL increases monotonically with impurity concentration. A good agreement between the calculated and observed profiles is obtained. The mean value of the exciton‐impurity scattering cross‐section σ, calculated from ΔvL, is of the order of 10−14 cm2. Further discussion of these results leads to useful information.
Magnetic‐Resonant Modulation of Photoconductivity of Crystalline Charge Transfer Complexes. Anthracene‐Tettacyanbenzene
Authors: Frankevich E. L. , Tribel M. M. , Sokolik I. A. , Pristupa A. I. 
Published: July 2007

AbstractA magnetic‐resonant modulation of the photoconductivity of polycrystalline samples of CT complex anthracene–TCNB is observed. The modulation is due to microwave induced transitions between Zeeman sublevels of the excited triplet CT state. The magnetic resonance spectrum of the CT triplet state is registered, the lifetime of the latter is estimated to be about 10−9 s. Switching‐on the resonant microwave field decreases the photoconductivity. The nonresonant effect of the permanent magnetic field on photocurrent and fluorescence of anthracene–TCNB crystals is investigated. A scheme is given representing the processes of the electronic excitation energy conversion in the anthracene–TCNB CT complex.
Critical Behaviour near the Intersection of Second‐Order Phase Transition Lines in a Random System
Authors: Izyumov Yu. A. , Skryabin Yu. N. , Laptev V. M. 
Published: July 2007

AbstractThe critical behaviour of inhomogeneous systems with the coupled order parameters is studied by means of Wilson's renormalization group theory. A disordered binary magnet, which is characterized by the mixed exchange interactions, is the example of those systems. It is shown that there is no stable fixed point in the system corresponding to the intersection of phase transition lines, and, hence, the second‐order phase transition cannot take place in it.
Lundqvist Three‐Body Interaction and Lattice Dynamics of Ionic Crystals
Authors: Sarkar S. K. , Sengupta S. 
Published: July 2007

AbstractThe Lundqvist three‐body interaction which was originally deduced for rigid ions is rederived in the framework of a shell model. Some discrepancies in a previous interpretation are pointed out. Application is considered for NaCl crystal. If the parameter of the three‐body interaction is determined from the overlap integrals it is found that the calculated dispersion curves, in general, deviate more from the experimental ones. Some static properties are also calculated.
Electronic Absorption of SrCl2:Fe2+ and SrCl2:Co2+
Authors: Droste R. , Gmeiner R. , Geick R. 
Published: July 2007

AbstractSrCl2 single crystals doped with Fe2+ and Co2+ are grown and the absorption spectra in the far infrared (5 to 100 cm−1) and middle infrared (400 to 4000 cm−1) spectral ranges are investigated. Several lines are observed which are assigned to electronic transitions of the impurity ions based on their dependence on the impurity concentration and on the temperature. The crystal field Hamiltonian appropriate for Fe2+ and Co2+ in SrCl2 is diagonalized. The crystal field parameter Dq and the spin–orbit coupling parameter λ are obtained from an optimum fit of the calculated level spacing to the experimentally observed transitions. Application of a magnetic field yields for both kinds of impurity ions the g‐factor of the ground state.
Jahn‐Teller Coupling of Cr2+ Ion in ZnS, ZnSe, and ZnTe
Authors: Biernacki S. W. 
Published: July 2007

AbstractCalculations for the T–e‐problem of Cr2+ ion in ZnS, ZnSe, and ZnTe are performed. The coupling with acoustical and optical phonons of the entire phonon spectrum is taken into consideration. The Jahn‐Teller energy and the displacements of the neighbors nearest to the impurity which result from the Jahn‐Teller interaction are estimated. Attention is paid to the estimation of the Jahn‐Teller coupling constant on the basis of the simple crystal field theory.
Validity Range of the Maxwell‐Garnett Theory
Authors: Ruppin R. 
Published: July 2007

AbstractThe various restrictions which have to be imposed on the particle size in order for the Maxwell‐Garnett theory to be valid are discussed. It is shown that the requirement that the particle size must be much smaller than the wavelength of the light in the surrounding medium is insufficient near resonances of the dielectric constant of the particles. The relative merits of the various validity criteria are illustrated by some numerical examples.
EPR Spectrum of the Oxygen Vacancy in Single Crystals V2O5
Authors: Vanhaelst M. , Clauws P. 
Published: July 2007

AbstractA new EPR spectrum of V2O5 is reported which is related to the non‐stoichiometry of the crystals. Its intensity increases on reduction and decreases on reoxidation. The spectrum is labelled El. El can be described by an S = 1 spin Hamiltonian with parameters gx = 1.33, gy = 2.51, gz = 1.01 (y ‖ b, x and z at angles of 25° to c and a), and D = 200 × 10−20 erg, E = −40 × 10−20 erg. E1 and the near‐infrared spectrum F1 (absorption bands at 1.25 and 1.52 eV with E ‖ a) are assigned to the two donor electrons from the oxygen vacancy in V2O5. The electrons are localized on nearest vanadium neighbours of the vacancy.
Electronic Structure of Silicon with Non‐Spherical Potentials for the Two Basis Atoms
Authors: Kim C. K. , Kunz A. B. 
Published: July 2007

AbstractThe potential difference of two basis atoms, which arises from the tetrahedral bonding, is included in the calculation of the silicon band structure using the local empirical pseudopotential method (EPM). It is shown that the small antisymmetric form factor due to the potential distortion gives substantial contribution to high lying conduction bands.
Thermal Properties and Grüneisen Parameters of Alkali Metals Employing the Model Potential of Krasko and Gurskii
Authors: Prasad B. , Srivastava R. S. 
Published: July 2007

AbstractA new form of the local model potential proposed by Krasko and Gurskii is used for computation of phonon frequencies, specific heat, and Grüneisen parameters for the two alkali metals, potassium and sodium. The Brillouin zone is divided into 1000 miniature cells. Corresponding to the centre of each miniature cell, phonon frequencies and Grüneisen parameters are computed and used for studying the variation of the mean value of the Grüneisen parameter with temperature. Variation of the thermal expansion coefficient with temperature is also studied in the manner of Wallace. The computed results are discussed in the light of available experimental and theoretical results. There is over all qualitative agreement between theory and experiment.
Interpretation of Compositional Modulation Spectra to Determine Some Optical Properties of Alloys
Authors: Enderlein R. , Hummel R. E. , Andrews J. B. , Nastasi‐Andrews R. J. , Shanley C. W. 
Published: July 2007

AbstractA theory is developed for the line shape of compositional modulation spectra of alloys. Inter‐band transitions between d‐ and s‐band states just above the Fermi level are assumed. Rigid band shifts and changes of the Fermi energy with composition are considered. The calculated line shape reproduces remarkably well the experimental modulation spectra of copper based alloys in the vicinity of the fundamental absorption edge. From a line shape analysis of the experimental spectra the threshold energy for interband transitions and the lifetime broadening parameter can be obtained.
First‐Order Mott Transition of the Exciton Gas in GaP
Authors: Maaref H. , Barrau J. , Brousseau M. , Collet J. , Mazzaschi J. , Pugnet M. 
Published: July 2007

AbstractThe high‐density electron‐hole system in GaP is investigated. The luminescence spectra are discussed as function of the excitation level and temperature. The Mott transition of the exciton gas is observed and the conditions are found for the separation into two phases between 40 and 70 K. A low‐density phase is an insulator: a high‐density phase (np = 5 × 1018 cm−3) is a conductor.
Phonon Dispersion in Red HgI2
Authors: Prevot B. , Schwab C. , Dorner B. 
Published: July 2007

AbstractPhonon dispersion curves of red HgI2 are measured by inelastic neutron scattering up to a frequency of 1.5 THz for waves propagating in the [100] and [001] symmetry directions. Indications of a two‐dimensional character are found through a slight anisotropy in the sound velocities and through the comparison between inter‐ and intralayer stretching forces. Further, the unusual low c66 value suggests that strong directional anisotropy may exist within the layer planes. A new assignment of the optical phonon frequencies is proposed on the basis of the observations.
Role of Electron—Phonon Interaction and Peripheral Phonons in the Lattice Thermal Conductivity of Doped Semiconductor at Low Temperatures. Application to Phosphorus‐Doped Germanium
Authors: Boghosian H. H. , Dubey K. S. 
Published: July 2007

AbstractThe role of the electron—phonon scattering and the peripheral phonons are studied by calculating the lattice thermal conductivity of phosphorous doped Ge in the temperature range 1 to 5 K. The temperature and the carrier concentration dependences of the reduced Fermi potential (η*) and of the density of states effective mass (m*) of electrons are also studied at low temperatures. The entire study is made using the Ziman expression of the electron—phonon scattering relaxation rate and the Callaway integral of the lattice thermal conductivity. The contribution of the peripheral phonons in the total phonon conductivity of the P‐doped Ge is also studied. A good agreement is found between the calculated and experimental value of the phonon conductivity for five different samples of P‐doped Ge having different carrier concentrations of 1.2 × 1017 to 1.1 × × 1018 cm−3 in the entire temperature range 1 to 5 K. The analytical expressions are also obtained for the phonon conductivity of the doped semiconductor in the low temperature approximation.