bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of Anisotropic Electron–Phonon Interaction in Copper I. Electron–Phonon Matrix Elements
Authors: Schmidt H. , Mann E. 
Published: July 2007

AbstractThe electron–phonon interaction in copper is calculated on the basis of realistic wave functions and taking into account all anisotropies of the system. The electron wave functions are derived from a combined interpolation scheme, in which the wave functions are assumed to be composed of both, plane waves and Bloch sums of atomic d‐functions. Because of the “pseudo” character of the wave functions thus obtained, these have to be combined with a pseudopotential in order to render the correct electron–phonon matrix elements; this contrasts with an earlier paper in the literature. Taking a slightly modified Cohen‐Heine pseudopotential and the plane‐wave contributions only, leads to a satisfactory agreement between calculated and observed anisotropic quantities. The other contributions to the matrix elements are critically discussed. Applications will be considered in a subsequent paper.
Infrared Reflection and Raman Scattering Studies of the Vibrational Properties and Structure of As2S3Gex Glasses
Authors: Giehler M. , Pilz W. 
Published: July 2007

AbstractInfrared reflection and Raman spectra of As2S3Gex (0 ≦ x ≦ 35 at%) glasses are studied. The spectra are explained in terms of vibrational modes of atomic building blocks the investigated glasses are composed of. Particularly, the vibrational properties of the As2S3Gex (x < 4 at%) glasses are due to internal vibrations of AsS3/2 pyramidal and weakly As‐rich AsrSs (r/s ⪅ 1) building blocks. The number of GeS4/2 tetrahedral building blocks is very small, therefore, these structures do not noticeably affect the infrared reflection and Raman spectra of the considered glasses. The vibrational properties of the As2S3Gex. (4 ⪅ x ⪅ 14 at%) samples are dominantly affected by vibrations of As‐rich AsrSs (r/s ≈ 1), GeS4/2 tetrahedral, and AsS3/2 pyramidal building blocks. (The number of AsS3/2 pyramidal building blocks approaches zero in samples with Ge contents above about 10 at%.) Raman spectra indicate that samples with Ge contents between about 4 and 12.5 at% contain realgar‐like microcrystals. The vibrational properties of the As2S3Gex (x > 14 at%) glasses mainly are caused by vibrational modes of GeS4/2 tetrahedral and strongly As‐rich AsrSs (r/s ⪆ 1.3; including AsAs3/3) building blocks. Stretching vibrations of AsAs bonds of these strongly As‐rich AsrSs building blocks are indicated in the Raman spectra of the considered glasses. In glasses with x ⪆ 23 at% Ge content the number of AsS bonds becomes zero, therefore weakly Ge‐rich GeuSv (u/v ⪆ 0.67) building blocks are formed.
Spatial Dispersion Effects in the Transmission Spectra of Semiconductors in the Region of Exciton Resonances
Authors: Dietrich B. , Voigt J. 
Published: July 2007

AbstractThe influence of spatial dispersion on the transmittivity of a semiconductor platelet in the region of an exciton resonance is investigated theoretically. In detail the dependences on the exciton parameters such as translational mass, polarizability, and damping are discussed. It is found that all the peculiarities observed experimentally for the A ground state exciton in CdS can be explained quantitatively.
On the Homology of Lattice Vibrations of Rare‐Gas Solids
Authors: Ramamurthy V. , Rajendraprasad S. B. 
Published: July 2007

AbstractInvestigations of the dependence of phonon frequencies of rare‐gas solids on their interatomic distance, r, reveal that they satisfy an empirical relation, Mv2rα = δ(q), a constant which depends on q, with α = −2. 74 ± 0.14 at all wave vectors and he nce is homologous in the case of argon, krypton, and xenon. It is shown that the homology of lattice vibrations depends on the nature and strength of the interatomic forces, but not on the crystal structure of the solids. The influence of the zero‐point energy and the consequent differences in the behaviour of rare‐gas solids and alkali metals are discussed.
NQR Study of Phase Transitions in Proustite at High Pressure
Authors: Baisa D. , Bondar A. , Gordon A. , Maltsev S. 
Published: July 2007

AbstractThe 75As nuclear quadrupole resonance frequency and spin‐lattice relaxation (SLR) time are measured in proustite (Ag3AsS3) in the temperature range 4. 2 K < T < 77 K at the high hydrostatic pressure. The pressure shifts of the first‐ and second‐order phase transition (PT) temperatures are detected. The tricritical point is reached at T 55. 5 K and p = 3. 2 kbar. A theory explaining the behaviour of SLR times at the first‐order PT and in the environment of the tricritical point is developed.
Zero‐point effect in ferrimagnetic and antiquadrupolar biquadratic systems (S = 3/2)
Authors: Westwański B. 
Published: July 2007

AbstractTwo negative branches of the spectrum in the antiquadrupolar phase and a negative one in the ferrimagnetic phase for Heisenberg‐biquadratic interactions with S = 3/2 lead to the zero‐point motion in energy and order parameters in the (1/z)1 approximation.
Electron‐hole drops in uniaxially stressed silicon
Authors: Wagner J. , Sauer R. 
Published: July 2007

AbstractThe photoluminescence of electron‐hole drops (EHD) in silicon is studied under uniaxial stress P ≦ 5 × 103 kp/cm2. The infinite stress limit is virtually reached, and characteristic EHD parameters are derived from lineshape fits including lifetime broadening effects. For P ∥ [100] and [110] “hot” EHD luminescence is observed due to electrons in the up‐shifted conduction bands. Thermalization with the “cold” electrons in the down‐shifted conduction bands only occurs for large band splittings above ≈︁ 20 meV and is suggested to be initiated by TA‐phonon assisted intervalley scattering. An extra line ≈︁ 1.3 meV below the cold free exciton emission for P ∥ [100] is attributed to the radiative decay of biexcitons.
Electronic polarization (relaxation) effects in the core level spectra of semiconductors. I. General theory of electronic polarization (relaxation) in semiconductors
Authors: Bechstedt F. , Enderlein R. 
Published: July 2007

AbstractThe core electron binding energies of semiconductors cannot correctly be described without taking into account of polarization (relaxation) energies due to the core hole. A formula is developed which relates the polarization energy to the dielectric function ϵ(q, ω) of the semiconductor. Band structure effects and the dynamics of polarization are considered. An approximate expression for ϵ(q, ω) is derived which can be shown to give a reasonable description for the relevant q‐ and ω‐regions. The theory represents the basis for the calculation of polarization energies in terms of only a few experimental parameters. The numerical results are given in the forthcoming paper (II).
Positron annihilation studies of the electronic structure of B.C.C. Fe
Authors: Szuszkiewicz S. , Rozenfeld B. , Szuszkiewicz M. 
Published: July 2007

AbstractAngular distributions of annihilation quanta are measured for monocrystalline b.c.c. Fe samples oriented along the following five crystallographic directions: [100], [110], [111] [210], and [211]. Based on experimental data, the distributions of momentum density of annihilation quanta are calculated for the principal directions. The results obtained are analyzed on the basis of electronic band structure and following from this the shape of the Fermi surface.
On the theory of a natural (orientational) superlattice in a two‐dimensional electron gas
Authors: Volkov V. A. , Sandomirskii V. B. 
Published: July 2007

AbstractThe energy spectrum of electrons in the inversion layer on a high‐indexed surface of Si is considered The natural superlattice due to such surface orientation mixes the states with wave vectors differing by a reciprocal surface lattice vector. The classification of minigaps obtained is given for the various combinations of quantum numbers (the valley and subband numbers) of the states in question. The position of all types of minigaps in the k‐space is found.
Volume dependent lattice dynamics of solid argon A pseudo‐harmonic approach
Authors: Massa N. E. , Mitra S. S. , Vetelino J. F. 
Published: July 2007

AbstractThe volume dependent lattice dynamics of solid argon is calculated using a pseudo‐harmonic approach. The volume dependence of the elastic constants, from which the lattice dynamical model parameters are deduced, is obtained by relating the elastic constants to a m‐n pair potential of the Mie‐Lennard‐Jones type. The volume dependence of the phonon states is used to obtain the first and second Grüneisen parameters and constants. The thermal expansion coefficient is then calculated from the Grüneisen parameters in the quasi‐harmonic approximation. Finally, the Mie‐Grüneisen equation of state and the Lindemann melting criterion are combined to predict the melting curve of argon. Reasonable agreement is obtained between the calculated and experimental results.
On the nature of dielectric permittivity of PbTiO3 single crystals
Authors: Turik A. V. , Shevchenko N. B. , Gavrilyachenko V. G. , Fesenko E. G. 
Published: July 2007

AbstractAn investigation of the frequency dependence of dielectric permittivities ϵ11 and ϵ33 in single‐domain tetragonal PbTiO3 crystals enables one to determine all the permittivity tensor components and shows the presence of only the piezoelectric dispersion. Comparing the dielectric measurements with the Raman data, it may be concluded that, in contrast to many other oxygen‐octahedra ferroelectrics, ψ and ϵ of PbTiO3 are entirely determined by the resonance mechanisms of electronic and ionic polarizations.
Photoelectron spectra of core electrons from palladium—silver alloys
Authors: Berndt K. , Marx U. , Brümmer O. 
Published: July 2007

AbstractFor a number of PdAg alloys the photoelectron spectra of the core electrons are studied in a systematical way. The role of the so‐called extrinsic and intrinsic losses, satellite structures, and line‐shapes is to be discussed for 3p and 3d lines. Existing theories are discussed for the given cases. A multi‐electron mechanism for explaining satellite structures is proposed. Asymmetry of the Pd 3d lines is studied and a strong dependence on the density of states at the Fermi energy is found.
Luminescence du centre dimère des ions Sn2+ dans le phosphore CaSe
Authors: Asano S. , Yamashita N. 
Published: July 2007

AbstractEmission and excitation spectra of the dimer center of Sn2+ ions in the CaSe phosphor are measured at 6 K. The temperature quenching of the luminescence of the dimer and monomer centers is also measured. Eight excitation bands originating from the dimer center are found. The values of the spectroscopic parameters appearing in the energy matrices of the dimer center are determined so that the electronic levels obtained experimentally and theoretically may coincide with each other.
The effective screening function in Si, Ge, and GaAs and the effects of exchange
Authors: Duggan G. , Morgan G. J. , Lettington A. 
Published: July 2007

AbstractCalculations are reported of the effective dielectric function for screening a pseudopotential in Si, Ge, and GaAs. The effects of exchange are also investigated by numerical calculations and an interpolation formula is given which fits the computed values. Screening the exchange interaction results in very small corrections to the effective dielectric function.
Nonradiative multiphonon carrier capture by deep neutral traps
Authors: Bhattacharya D. P. , Kachlishvili Z. S. 
Published: July 2007

AbstractThe galvanomagnetic effects and the Faraday rotation are investigated in the general case for any mechanism of the energy and momentum scattering of hot electrons in the strong and weak magnetic field limits and under the condition when the free carriers are captured in a nonradiative way by deep neutral traps described by a δ‐like attractive potential. For some definte scattering mechanisms the investigations are carried out in the presence of any finite magnetic field. The possibility of using the results for the estimation of some semiconductor parameters and for the determination of the dominant scattering mechanism is discussed. The calculations are carried out assuming spherical constant energy surfaces in the κ space.
Electronic states for the Al overlayer on the Si (111) surface
Authors: Nishida M. 
Published: July 2007

AbstractCalculations are iteratively carried out for the overlayer of Al chemisorbed on the Si (111) surface using extended Hückel theory. The total, local, and orbital densities of states are presented for threefold‐coordinated substitutional and interstitial site chemisorption geometries. It is found that the electronic structure for Al on the Si(111) surface depends strongly on the chemisorption geometries and that the interstitial site geometry presents better agreements with existing spectroscopic experiments.
Anharmonic effects in ferroelectric Pb5Ge3O11
Authors: Suski T. , Müller‐Lierheim W. 
Published: July 2007

AbstractRaman spectroscopic studies of Pb5Ge3O11 at various temperatures (300 to 400 K) and pressures (up to 6 kbar) are performed to obtain the variation of the frequency, width, and intensity of the ferroelectric and other low frequency symmetric modes. The results of the measurements allow separation of the measured temperature dependent frequency shift into the pure volume and the pure temperature parts. It shows that the higher order anharmonicities determine the temperature evolution of the modes Raman active only in the ferroelectric phase. Additional examination of the temperature and pressure dependency of the intensities and the self‐energy contribution of the lowest frequency modes leads to the conclusion that modes observed in the Raman experiment behave as uncoupled oscillators. The measured specific heat as well as the calculated Debye temperature (θ ≈︁ 230 K) are almost temperature independent and exhibit only weak anomaly in the phase transition region. To correlate the ferroelectric mode behavior with variation of the thermodynamic properties the calculation of the thermodynamic mode and Debye Grüneisen functions are performed.
Electron paramagnetic resonance of Er localized electron magnetic states in thorium hydrides
Authors: Drulis H. , Suleimanov N. M. 
Published: July 2007

AbstractEPR of Er3+ ions in polycrystalline ThH2 and Th4H15 is studied and the possibility of the Kondo effect in ThH2 is discussed. In Th4H15 electron bottleneck is observed. The lineshape calculation is made for a metallic system in the case of an axial crystalline field. It is shown that in the point charge approximation a proton model is realized in Th4H15.
Raman scattering and phase transformations of TlGaSe2 and TlGaS2 under pressure
Authors: Vinogradov E. A. , Zhizhin G. N. , Melnik N. N. , Subbotin S. I. , Panfilov V. V. , Allakhverdiev K. R. , Salaev E. Yu. , Nani R. Kh. 
Published: July 2007

AbstractRaman spectra of single crystals TlGaS2 and TlGaSe2 are investigated in equilibrium conditions at room temperature under various hydrostatic pressures up to 7.25 and 9.27 kbar, respectively. Phase transitions at about 5 kbar are shown to occur in both the single crystals. Mode parameters γi = (1/vi) (dvi/dP) are determined for most of the Raman bands observed. The different values of these parameters are used to find out which frequencies have to be assigned to interlayer vibrations. It is shown that Raman spectra can be explained best when the unit cell of TlGaS2 and TlGaSe2 is supposed to contain two layers and the structure of the layer is supposed to be similar to that of TlSe.
On the spin‐disorder resistivity of amorphous ferromagnets
Authors: Richter R. , Wolf M. , Goedsche F. 
Published: July 2007

AbstractThe spin‐disorder resistivity of amorphous ferromagnets is investigated in the temperature regimes 0 ≦ T ≫ TC and T ≫ TC. The resistivity is calculated within the force–force correlation function method up to the second order in the sd‐exchange constant. A simple structural model for a structurally disordered Heisenberg ferromagnet is presented. At lowest temperatures the spin‐disorder resistivity varies as T3/2 for a sufficient high degree of disorder. It is concluded that the experimentally observed T2‐dependence at these temperatures is of non magnetic origin. This dependence can be qualitatively understood if the thermal smearing of the structure factor is taken into account.
Optical studies of alkali trihalogeno‐plumbate mixed crystals
Authors: Heidrich K. , Trendel G. 
Published: July 2007

AbstractOptical measurements on pseudoternary alloys of the alkalitrihalogeno‐plumbates (AHPs), CsPbCl3 and CsPbBr3 are reported for the whole range of mixing. With these results it is demonstrated that an empirical LCAO band scheme is suitable for a description of optical and electronic properties of plumbates. The mixed crystal behaviour of the AHPs is compared to that of thallous halides, their binary III–VII analogs.
A comparative study of phonons in polycrystalline and single‐crystalline LiF films by electron spectroscopy
Authors: Jakobs R.‐H. , Geiger J. 
Published: July 2007

AbstractThe electron energy loss spectra of thin polycrystalline and single‐crystalline LiF films are measured by means of a high‐resolution electron spectrometer (resolution 5 to 8 meV for 30 keV electrons) in the range from 30 to 100 meV. Theoretical spectra are calculated by using the dielectric theory of inelastic electron scattering and expressing the relevant frequency‐dependent dielectric constant analytically by a dispersion formula. The over‐all agreement between experiment and theory is good. Noticeable differences are found between the spectra of polycrystalline films and of thin single crystals: an excess of energy loss intensity is observed for polycrystalline films between 60 and 80 meV. The interpretation is, that the interfaces between the microcrystals give rise to the development of additional surface modes near 72 meV, which may be related to certain normal modes of isolated cubes.
Reflectance spectra of CdSiP2 and ZnSiP2
Authors: Ambrazevičius G. , Babonas G. , Šileika A. 
Published: July 2007

AbstractReflectance spectra of CdSiP2 and ZnSiP2 are measured at 300 K in the range 1 to 12 eV. These ternary compounds are electronic analogs of AlP and have the shortest bond SiP among the AIIBIVC2V semiconductors. The peculiarity of the investigated optical spectra is a close proximity and possible overlap of peaks which correspond to the structures E1 and E2 in AIIIBV compounds. The mean energies of the characteristic peak groups in the AIISiC2V compounds are shown to scale linearly with the average energy gap calculated by the dielectric theory.
Effective medium theory for the hopping conductivity in high electrical fields
Authors: Böttger H. , Bryksin V. V. 
Published: July 2007

AbstractStarting from the rate equation in presence of an electrical field with arbitrary strength the hopping conductivity in a system with nearest neighbour hopping is investigated by using an effective medium approximation. At not too high fields the differential conductivity is shown to decrease with increasing field. This behaviour is qualitatively in agreement with experimental results on doped semiconductors.
Generation of dichroic h centres in KCl by polarized optical bleaching of interstitial atomic hydrogen
Authors: Reuter G. , Lohse F. , Spaeth J. M. 
Published: July 2007

AbstractUpon optical bleaching of interstitial atomic hydrogen (H or U2 centres) with polarized light U and H centres (H and Cl) are produced, the latter in an unbalanced distribution which is measured by optical absorption and ESR. Similar results are obtained for bleaching of U2 centres in a mixed configuration with one Br− as nearest neighbour (H(Br)). In the H centre formation Clo is ejected to form a Cl−2 crowdion only into those [110] directions which appear perpendicular to the [111] optical transition moment of the U2 charge transfer transition. It is concluded that H centres are formed in an excited π‐state.
Exciton states in semi‐infinite molecular crystals with a point defect near the surface
Authors: Sugakov V. I. , Tovstenko V. I. 
Published: July 2007

AbstractThe energy spectrum of a semi‐infinite molecular crystal with a point defect on the surface is studied. It is shown that the criterion of uncoupling and the position of the impurity level depend on the distance of the impurity to a crystal boundary. In the case when a level of a surface exciton exists in the system, the uncoupling of the impurity term from the surface exciton band occurs at any slightest distortion of the molecule term. The data obtained can be used to investigate a number of phenomena such as the phonon spectrum and the electron spectrum in the approximation of tight coupling and in some other cases.
Readily computable expressions for LCAO two‐centre integrals over slater‐type orbitals with arbitrarily high quantum numbers
Authors: Eschrig H. 
Published: July 2007

AbstractReadily programmable formulas for the LCAO two‐centre integrals over Slater‐type orbitals are derived which have numerically proved to give correct results in any practical case even for very high quantum numbers and which due to very simple recursion formulas require a minimum numerical effort. Also formulas for the LCAO electron–phonon matrix elements are given, and the way to use the given formulas to calculate the electron–electron interaction two‐centre integrals is described.
The influence of spatial dispersion and of the angle of incidence on thermomodulation spectra of the An=1‐exciton in CdS
Authors: Stössel W. , Wagner H. J. 
Published: July 2007

AbstractRelflectance (R) and thermomodulated reflectance spectra (ΔR/R) of CdS in the region of the An=1‐exciton are measured at 8 K for angles of incidence between 5° and 85°. Because of the higher resolution obtained with the thermomodulation technique, a different behaviour of the “spike”, i.e. the additional reflection structure due to spatial dispersion, is detected than that previously derived from reflectance measurements alone. Measurements of its temperature dependence show that the spike is not very sensitive to thermal broadening. Fitting calculations, made with Pekar's additional boundary condition and allowing for an exciton‐free surface layer, show that the underlying models describe very well the experimental data, namely the behaviour of the transverse and the longitudinal exciton modes as well as that of the longitudinal‐transverse mixed mode.
Calculation of the electronic energy spectrum of a thin disordered solid film
Authors: Leipold W. C. , Feuchtwang T. E. 
Published: July 2007

AbstractThe effects of positional disorder on the electronic energy spectrum of a model finite insulating barrier are considered. The spectrum is studied for two different sets of boundary conditions imposed at the film surfaces: 1) traveling wave boundary conditions, leading to transmission resonances, and 2) periodic boundary conditions. Ledermann's theorem relates the transmission resonances to the corresponding discrete spectrum obtained using periodic boundary conditions. Halpern's reduced Green function technique for the calculation of approximate spectra of infinite systems is extended from a single to a multiband formulation and applied to the thin film problem. A quantitative estimate of the effect of the loss of short range order on the integrated density of states in a thin film is presented. The spectrum is discussed and related to the elastic tunneling transmission coefficient of a metal–insulator–metal heterojunction in which the insulating film is the tunneling barrier.
Balance equation for non‐equilibrium electrons in the mobility gap of a disordered semiconductor in the presence of light
Authors: Sulimov V. B. 
Published: July 2007

AbstractUsing non‐equilibrium Green's functions a balance equation is obtained describing the light induced stationary non‐equilibrium distribution of electrons over the localized states in a disordered semiconductor. The light is assumed to be monochromatic and in the final results only the terms linear in and independent of the light intensity are retained. Electron–phonon interaction is accounted for by perturbation theory.