bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of Secondary Electron Emission. I. General Theory for Nearly‐Free‐Electron Metals
Authors: Rösler M. , Brauer W. 
Published: July 2007

AbstractA detailed theory of secondary electron emission (SEE) for nearly‐free‐electron (NFE) metals is developed. The creation of secondary electrons (SE) by primary electron (PE) collisions with metal electrons in core states and in the Fermi sphere is considered. Especially a calculation is given of SE production by plasmon decay on the basis of a general model potential. Both, elastic and inelastic collisions of internal secondaries are taken into account. Primary energies are limited to 1 to 2 keV. General formulas regarding excitation functions, mean free paths, and scattering functions, necessary for the computation of the energy angular distribution of SE and secondary yield, are derived.
The Electron–Hole Plasma in a Strong Electromagnetic Field. Optical Properties in a Simplified Model
Authors: Harbich Th. , Mahler G. 
Published: July 2007

AbstractAn electron–hole plasma in the presence of a high‐intensity laser field is considered in the quasienergy picture. Using a two‐band model it is shown that the gain spectrum depends on the strength of the laser field in a characteristic way, provided the frequency of transitions between the conduction and the valence band is at least of the order of the inverse collision time.
Nearest‐Neighbour Poisson Approximation to a Functional Approach for the Hubbard Model
Authors: Behn U. 
Published: July 2007

AbstractIn the framework of the Poisson approximation to a functional scheme for the Hubbard model the effect of the spatial correlation of the discrete stochastic potential Uvi(t) simulating the spin‐↓ subsystem is considered. For a half‐filled band in the paramagnetic case at zero temperature the density of states is calculated in a nearest‐neighbour approximation. For strong Coulomb repulsion the subbands occur sharper and the minimum in between is deeper compared with the single‐site approximation. The influence of the spatial correlation on the possible appearance of a gap within a dynamic approximation is discussed.
Composition Dependence of the Maximum Cyclotron Mass m in n‐Type Semiconducting Bi1–xSbx
Authors: Fellmuth B. , Krüger H. , Rudolph R. , Herrmann R. 
Published: July 2007

AbstractThe propagation of magnetoplasma waves in the configuration B‖C2‖k is measured for a number of n‐type semiconducting Bi1–xSbx alloys (0.07 < x < 0.14) at frequencies of 41 and 70 GHz and helium temperatures. The attenuation behaviour and a comparison between the experimental and the theoretical dispersion of the waves yield a rapid increase of the maximum cyclotron mass m1c with increasing x, which by far exceeds the variation of the low cyclotron mass m2c. Under the given conditions, the results obtained are largely independent of the dispersion relation of the electrons, which is used in the description of the wave dispersion in a quantizing magnetic field.
Polarized TiKβ Valence Band Spectra of TiO2 (Rutile)
Authors: Dräger G. , Brümmer O. , Heera V. , Seifert G. , Ziesche P. 
Published: July 2007

AbstractThe TiKβ valence band spectra of a TiO2 (rutile) single crystal are measured polarized parallel and perpendicular to the tetragonal c‐axis. The shape of the spectra shows a strong anisotropy giving more information on the electronic structure of this substance than the corresponding unpolarized spectrum of a polycrystalline sample. Theoretical spectra are calculated for a TiO6 cluster with D2h symmetry on the basis of the results of a SW Xα cluster calculation. The agreement between the theoretical and experimental spectra is very good with respect to the calculated orbital energies and measured peak positions and is qualitatively satisfying regarding the intensities. For the last case, however, a cluster–cluster interaction along the c‐direction of rutile must be taken into consideration.
The Influence of Far‐Band k · p Interaction on Carrier States in Lead Chalcogenides
Authors: Mironov A. G. , Ziep O. 
Published: July 2007

AbstractStatements of the Dimmock model with respect to dispersion relation und wave functions are discussed within the framework of the k·‐matrix of Mitchell and Wallis. The eigenvalues obtained are compared with the exact secular equation of a six‐band model which neglects the interaction between far bands. With respect to the dependence on the Fermi energy of carrier concentration and density of states predictions of the Kane model, of a recent developed multiband model, and of the Dimmock model are compared.
The Luminescence Properties of Alkaline‐Earth Oxides Activated with 6s2 Ions
Authors: van der Steen A. C. , Dijcks L. T. F. 
Published: July 2007

AbstractThe luminescence spectra of CaO and SrO activated with Pb2+ or Bi3+ ions show vibrational structure. The features in the spectra are discussed by considering the PbO (BiO) octahedron as an isolated unit in the rocksalt lattice. The luminescence spectra of Tl+‐activated CaO and SrO do not show vibrational structure. Comparisons are made with other s2 ion‐activated systems.
Pressure Derivatives of Elastic Stiffness Constants under Pressure of Si and Ge
Authors: Soma T. 
Published: July 2007

AbstractThe bulk modulus B, the shear elastic constants C44 and C′ = (C11 – C12)/2 under pressure of Si and Ge are studied theoretically using the presented local Heine‐Abarenkov model potential and the higher order perturbational formalism. The pressure‐derivatives dB/dP, dC44/dP, and dC′/dP decrease under compression from the experimental data at low pressures, and dC44/dP and dC′/dP tend to become negative below about 100 kbar.
On the Magnetism in Narrow‐Band Conductors
Authors: Karpenko B. V. 
Published: July 2007

AbstractThe problem of the double exchange interaction mechanism in narrow‐band magnetic conducting crystals in terms of the Vonsovskii s‐f exchange model is considered taking into account the Coulomb interaction between conduction electrons, using Hubbard approximation. The values of the Néel paramagnetic temperature and of effective paramagnetic moment, as function of concentration of current carriers, are determined. A comparison of the theoretical expressions with the experimentally found Gd concentration dependence of the Curie paramagnetic temperature of solid solutions Eu1–xGdxSe helps to obtain a correlation between the conduction band width, the magnitude of the intraatomic exchange integral, and the value of the Coulomb interaction of electrons on a site. The variation of the effective magnetic moment value in the Eu1–xLaxS series, as a function of La concentration is discussed.
Temperature Dependence of the Baric Magnetization Coefficient of a Band Ferromagnet
Authors: Ponomarev B. K. , Thiessen V. G. 
Published: July 2007

AbstractAn expression for the temperature dependence of the baric magnetization coefficient (1/σs) × (∂σs/∂p)T is obtained in the framework of Wohlfarth's model for a very weak band ferromagnetism. Good agreement is obtained between calculated and experimental values for nickel and iron‐nickel alloys of invar composition. The derivative of the effective exchange interaction parameter with respect to pressure, dI/dp, is estimated for nickel and iron‐nickel invar Fe0.66Ni0.34. It is shown that anomalously high values of the quantity dI/dp in a band ferromagnet are not the necessary condition to obtain great values of the quantity (1/Tc) (dTc/dp) specific for invars.
Band Structure Calculation of Electronic Properties in CuIn1–xGaxSe2
Authors: Chizhikov V. I. , Panyutin V. L. 
Published: July 2007

AbstractThe energy band structure of CuIn1–xGaxSe2 solid solution is calculated in the center of the Brillouin zone by empirical pseudopotential method, using the model of average statistical substitution. The results of calculations are in good agreement with experimental data. An estimation of the acoustic deformation potential and temperature deviation coefficients of lattice parameters is also made.
The Phenomenon of Self‐Induced Transparency in the Range of the Proper Lattice Absorption
Authors: Kiselyova E. S. 
Published: July 2007

AbstractSoliton wave pulses are investigated in the phonon range of the spectrum. The phenomenon of self‐induced transparency (SIT) is considered taking into account both, the amplitude and the phase modulations of the soliton wave packets. In essence new dispersion laws and the wave vector dependence of the soliton velocity are obtained. Criteria of SIT theory application are given, and also new possibilities of observing non‐linear optical phenomena in the phonon range of the spectrum are pointed out.
Effect of Electron–Phonon Interaction on the Optical Conductivity of Alloys
Authors: Taranko R. , Taranko E. , Wysokińaski K. I. 
Published: July 2007

AbstractThe effect of electron‐phonon interaction on the optical conductivity γ(ω) of disordered alloys is investigated in the framework of coherent potential approximation. The formalism is used for the case in which the one‐particle Hamiltonian includes thermal diagonal and compositional diagonal and off‐diagonal disorder. The results of numerical calculations of γ(ω) are presented in the case of the model binary alloy AxB1–x for various temperatures.
Impurity Vibrational Properties of Ga in InP Crystals
Authors: Jahne E. , Kleinert P. , Kh. Bairamov B. , Topoprov V. V. 
Published: July 2007

AbstractA theoretical and experimental study is undertaken on the vibrational mode frequencies, infrared and Raman response functions of isolated substitutional Ga impurities in InP. The calculations are based on the existing rigid‐ion and defect models for isolated impurities in zincblende lattices. They yield an impurity‐induced infrared absorption and Raman scattering in the regions a few cm−1 above the maximum TA, LA, and optical phonon frequencies. Experimentally the infrared reflection and Raman scattering are measured of InP containing 1% Ga impurities. A local mode is observed 4.5 cm−1 above the LO(Γ) frequency of InP. From these experimental data the relative force constant change around the Ga impurity is estimated to Δf/f ≈ 0.14.
Model Pair Distribution Functions for Amorphous Binary Metal–Metalloid Alloys Based on Crystal‐Like Short‐Range Order
Authors: Mattern N. , Hermann H. 
Published: July 2007

AbstractA model is introduced for the description of the atomic structure of amorphous metal–metalloid alloys. The model is based on the assumption that the local arrangement of the atoms in the amorphous state is similar to that in the corresponding crystalline phase. Short‐range order of the Fe3C and Ni3P structure types is used for modelling amorphous metal–metalloid alloys. The partial and the total pair distribution functions are calculated and compared with experimental values. The Ni3P unit cell is suitable as a structural unit for modelling the amorphous atomic structure. The Fe3C unit cell is not realized as a structural unit in amorphous metal–metalloid alloys in general.
Local Quasiparticles in the Anderson Model
Authors: Nolting W. , Oleś A. M. 
Published: July 2007

AbstractWith a new spectral density approach it is shown firstly that the ground state of the Anderson model is nonmagnetic. Local quasiparticles corresponding to transitions between different occupancies of the impurity orbital are shown to be well defined and well separated for realistic values of the parameters of the Anderson model. Lifetimes of the quasiparticles strongly depend on the hybridization coupling constant Vdk and are almost independent of temperature. The maxima of the spectral density Adσ(ω) are in qualitative agreement with the results of the optical absorption experiments performed on noble metal alloys containing 3d magnetic impurities.
Acoustic Wave Scattering by Mixing Modes in Piezoelectric Media
Authors: Albuquerque E. L. 
Published: July 2007

AbstractThe scattering process for waves propagating in piezoelectric media is presented and its features are discussed. The coupling between the acoustic and electromagnetic field, for the geometry presented in this paper, allows these waves to be polarized in the xz plane showing a new aspect of the scattering process. Some limiting cases are presented and they are in agreement with the general treatment.
Negative Volume Plasmon Dispersion in Be for k > kF
Authors: Priftis G. D. , Boviatsis J. 
Published: July 2007

AbstractMeasurements of volume plasmon dispersion in beryllium excited by X‐rays are reported for k up to 1.5kF. The dispersion curve shows a flattening for k near kF and for k ≈ 1.2kF its slope becomes negative. These results are consistent with previous X‐ray scattering experiments and with some electron scattering experiments. However they cannot be explained in the context of the existing RPA theories.
Effects of Microstructure Scale on the Temperature Coefficient of Electrical Resistivity
Authors: Aubauer H. P. , Rossiter P. L. 
Published: July 2007

AbstractThe temperature coefficient of resistivity dϱ/dT is shown to contain a component which depends upon the microstructure scale R0 and the conduction electron mean free path Λ. The size of this contribution depends upon the rate of change of Λ with temperature but in general dϱ/dT will be larger when R0 < Λ. The general predictions of the theory are shown to be in agreement with the limited experimental data available.
Stability Region of the Two‐Dimensional Electron Crystal in Strong Magnetic Fields
Authors: Lozovik Yu. E. , Musin D. R. 
Published: July 2007

AbstractIn the self‐consistent harmonic approximation equations are obtained for the frequency spectrum of a two‐dimensional electron crystal in a magnetic field H. From the condition of the existence of “soft” mode peculiar for the crystal at H ≠ 0 the absolute stability curve of the crystal is analyzed. The stability region increases with H. In the H‐n phase diagram at temperature T = 0 (n is the electron density) along the stability curve obtained the phenomenological Lindemann‐type rule 〈u2〉/b2  γ = const. is fulfilled for strong H with γ ≈ 0.06 (〈u2〉 is the mean square amplitude in the harmonic approximation, b is the lattice period). At H → 0 the Lindemann‐type constant γ decreases. The phase diagram of the two‐dimensional electron system and effects of H on the electronic crystal‐isotropic liquid and liquid‐electronic crystal‐isotropic liquid transitions are discussed.
Effective One‐Particle Crystal Field Potentials in the Point Charge Approximation
Authors: Adam S. , Adam Gh. , Corciovei A. 
Published: July 2007

AbstractA generał method is developed for the derivation of the one‐particle crystal field potential characteristic of a given crystallographic symmetry, for arbitrary effective interatomic forces. Calculations performed for cubic and hexagonal structures lead to the standard representations in spherical harmonics with the coefficients given, however, by power series of rn rather than by single rn terms as obtained within the usual hypothesis of Coulombian interatomic forces. This result is found to have implications on the interpretation of some recently published theoretical and experimental data.
A Study in the Homology of Lattice Mechanical Properties of Alkali Metals
Authors: Sarkar S. K. , Sen D. , Sengupta S. 
Published: July 2007

AbstractThe nature of the dependence of the Heine‐Abarenkov model pseudopotential parameters rc and u for different alkali metals, obtained through a comprehensive unified study of the metals, on the atomic number, Z, is investigated, leading to simple empirical relations between Z and the parameters. The product of Z1/2 and the dynamical matrix, D, calculated using the parameters yielded by these relations is found to satisfy a relation of the form DZ1/2 = C1(q, e) for various Z‐values, C1(q, e) being a constant depending on the phonon wave vector q and the polarization e. This at once leads to the relation m1/2Z1/4v = C2(q, e) which is verified empirically and thus implies that the lattice vibrations of alkali metals are homologous. The relations obtained are used for a comprehensive unified study of Cs and for predicting its dispersion relation. The importance of the approach lies in the fact that knowing only Z, a unified study of a large number of lattice static, dynamic, and electronic properties of any alkali metal can be carried out within the framework of the pseudopotential theory.
Magnetic Configurations in Anhydrous Sulphates and Selenates of the 3d Transition Metals
Authors: Hautecler S. , Wegener W. 
Published: July 2007

AbstractThe various magnetic structures compatible with the crystallographic symmetry in the anhydrous sulphates and selenates of the 3d transition metals are determined using the matrix method of Bertaut. The stability conditions and the minimum range of the magnetic interactions needed to stabilize the different configurations are derived.
Electron Paramagnetic Resonance Studies of Cu2+ in NH4Cl1−xBrx Single Crystals
Authors: Aruna B. , Ramakrishna Y. V. S. , Narayana P. A. 
Published: July 2007

AbstractElectron paramagnetic resonance studies of Cu2+ in mixed single crystals of NH4Cl1−xBrx (0 ≦ x ≦ 0.2) are carried out in the temperature range of 100 K ≦ T ≦ 290 K. The variation of the spin Hamiltonian parameters with temperature and the dependence of the linewidth on the nuclear magnetic quantum number MI indicate that Cu2+ is coordinated only by Cl− for x ≦ 0.08. In the range of 0.08 ≦ x ≦ 0.2 Cu2+ is coordinated by both, Cl− and Br−.
Peculiarities of an Electromotive Force Arising in a Scemionductor in a Non‐Homogeneous Magnetic Field (II)
Authors: Gulamov Sh. A. , Katulevskii Yu. A. , Muminov R. A. 
Published: July 2007

AbstractThe spatial distributions of current carriers and the electric field as well as the expression for the electromotive force are found for the homogeneous semiconductor placed only into a non‐homogeneous magnetic field for the case when the semiconductor length in the direction of the magnetic fields gradient far exceeds the bipolar diffusion length of current carriers. The magnetic field is supposed to be non‐quantized. It is shown that these characteristics strongly depend on the spatial structure of the magnetic field. The special case of linear coordinate dependence of the magnetic field is considered.
A New‐Type V Centre in SrO
Authors: Seeman V. , Reifman S. , Lehto T. 
Published: July 2007

AbstractA new type of V centre with orthorhombic symmetry is observed in SrO crystals. An investigation of the superhyperfine structure of the ESR spectra shows that this centre consists of an O− ion near a cation vacancy surrounded by two OH− groups. The values of the superhyperfine structure constants are used for the calculation of the distance between the O− ion and the OH− groups.
Nonlocality of Carrier Multiplication in Semiconductor Depletion Layers
Authors: Gribnikov Z. S. , Ivastchenko V. M. , Mitin V. V. 
Published: July 2007

AbstractAnalytical and numerical calculations of multiplication coefficients in the Schottky junctions are performed with inhomogeneity of the electric field taken into account. It is shown that in the thin depletion layers distribution functions of electrons and holes and their impact ionization (II) coefficients is nonlocal, i.e. they depend not only upon the electric field strength at a certain point but also on the fields in the vicinity of the point. In such nonlocal cases the introduction of the II coefficients is justified only for small multiplication coefficients, for the large ones they make no sence. If one assumes that the carriers — holes and electrons — differ from each other by the sign of the charge only, the nonlocality effect does not change just the values of the II coefficients obtained in the local approximation, but provides as well the difference between the electron and hole multiplication coefficients. This is due to the electric field asymmetry in the depletion layer.
Theory of Second‐Harmonic Generation by Soft Ultrasonic Shear Waves in Transforming A‐15 Compounds
Authors: Agyei A. K. 
Published: July 2007

AbstractA theory of second‐harmonic generation by pulsed “soft” ultrasonic shear waves in a transforming A‐15 compound, A3B, is presented which accounts for the generation observed in V3Si by Testardi. It is shown that this phenomenon, which is forbidden on the basis of static symmetry considerations, is possible under conditions of quasi‐static distortion of the crystal by the free A‐atom oscillations excited by the front of the driving‐wave pulse. Under these conditions not only should the driving‐wave‐amplitude dependence of the second‐harmonic waves be cubic at low drive levels and linear at high drive levels, as observed by Testardi, but the generated waves should also be amplitude modulated by a sine curve (in the absence of damping) of a period equal to the free‐oscillation period of the A atoms. This latter effect can thus be used to measure the soft‐phonon frequency as a function of temperature and the phonon dispersion at very low wave numbers.
On the Electrical Conductivity of the Periodic Anderson Model
Authors: Elk K. 
Published: July 2007

AbstractThe periodic Anderson model is used as a simple model describing intermediate valence compounds. In that model a strong electron—electron correlation is taken into account. The correlation term is decoupled using the alloy analogy approximation, which yields a two‐peak structure of the density of states of the f‐electrons. Then the electrical conductivity can be obtained using the Kubo‐Greenwood formula. By numerical methods the density of states and the temperature dependence of the conductivity are calculated. The density of states shows an interesting structure in the centre of the hybridized f‐band. For the conductivity σ an increase with increasing temperature is found. A remarkable pressure dependence of σ is not observed in the model used.
The Exponential Shape of the Optical Absorption Edge Tail
Authors: Szczyrbowski J. 
Published: July 2007

AbstractA simple model of light absorption for photon energy smaller than the width of the forbidden band‐gap Eg is proposed. Assuming that the shape of the fundamental absorption edge is influenced by elastic fluctuations in Eg caused by both, permanent and temperature lattice disorder, a general expression for the exponential shape of the optical tail is obtained, which is valid for both, amorphous and crystalline solids. The so‐called Urbach rule (exponential dependence on energy and temperature) represents an asymptotic relation of this formula when the permanent disorder is neglected. The proposed model also predicts quantitatively the values of the steepness parameter for several materials which show the Urbach shape of the absorption edge tail.
Spectral Density Method for the Spinless Fermion Model
Authors: Ihle D. , Lorenz B. 
Published: July 2007

AbstractA self‐consistent approximation scheme for the spectral densities of the one‐dimensional spinless fermion model is developed, where the one‐particle spectral density fulfils the first four moments. At T = 0 the one‐particle excitation spectrum is calculated in dependence on the Coulomb and band energy parameters. The exact results for the atomic and band limits and the gas—liquid like phase transition are reproduced.
Correlated Hartree‐Fock Theory of the Electron—Hole Plasma Containing Exciton Bound States
Authors: Stolz H. , Zimmermann R. , Röpke G. 
Published: July 2007

AbstractFor the electron—hole plasma the Hartree‐Fock scheme is extended to include those pair correlations leading to excitonic bound states. Thus an effective single‐exciton Schrödinger equation is obtained systematically accounting for the interaction of an exciton with others in a mean‐field approximation valid to linear order in the density. This single‐exciton equation may also be derived from a many‐exciton Hamiltonian subject to Hartree‐Fock decoupling. The excitons are represented by Boson operators, the Pauli principle for the electrons and holes being maintained by a proper antisymmetrization of the interaction matrix element.