bluuebunny/crossref_metadata_2025 huggingface dataset:
Local field effects and a model dielectric response matrix ϵG,G′(q) for a covalent semiconductor
Authors: Oliveira L. E.
Published: July 2007

A model for the microscopic dielectric response ϵG,G′(q) of a covalent semiconductor is proposed in which the effects of the localized and plane wave features of the band structure on the polarizability are separated. Within this model for diamond a calculation is performed of the static longitudinal wave vector dependent macroscopic dielectric function ϵM(q), including local field corrections, together with an analysis in real space of the microscopic local field E(r) and polarization charge density ϱindr) induced by a uniform externally applied electric field. The results indicate that although the macroscopic dielectric function is essentially insensitive with respect to small changes in the effective charge model parameter Z, microscopic quantities such as the induced charge density and microscopic local field can be fairly sensitive to variations in Z. This suggests that careful tests on model based dielectric responses ϵG,G′(q) are probably necessary before one calculates, for instance, phonon frequencies.
Temperature dependence of ESR spectra of doped a‐Si:H
Authors: Dersch H. , Stuke J. , Beichler J.
Published: July 2007

The temperature dependence of the ESR lines with g = 2.01 for boron‐doped and with g = 2.0043 for phosphorus‐doped a–Si:H, associated with singly occupied tail states of the valence and conduction band, respectively, is investigated. Both resonances broaden considerably with increasing temperature, and the broadening δHpp(T) is related with the electrical conductivity σ(T) as δHpp(T) = c[σ(T]n with 0.64 < n < 1. The g‐values of both lines decrease with rising temperature. The spin density N8 is for weakly boron‐doped samples constant at low temperatures, for phosphorus‐doped a‐Si: H, however, an increase of N8 with rising temperature is observed. These results are explained in a model with a small correlation energy ( U < kT) for the conduction band tail and a large one (U ≫ kT ) for the valence band tail. The temperature variation of the g‐value is ascribed to its energy dependence. Electrons in localized states near the mobility edges are assumed to have smaller g‐values than those in states with a larger energy distance from the edges. The relation between the line broadening δHpp(T) and the conductivity can be understood by spin relaxation of the localized electrons due to exchange coupling with rapidly relaxing carriers in extended states.
A hierarchy of equations for finite temperature Green functions
Authors: Lambert C. J.
Published: July 2007

Employing a new theorem on time ordered products of operators, an infinite hierarchy of equations for the finite temperature Green functions of a many particle system is obtained. The analysis provides a basis for the extension to finite temperatures of recent results from ground state perturbation theory. The connection between the present analysis and the corresponding ground state formalism is briefly discussed.
Substitutional and interstitial hydrogen impurities in alkali halide crystals
Authors: Augst G. R. , Bakhshetsyan L. G.
Published: July 2007

An expression for the energy of an alkali halide crystal with a charged point defect is obtained using the Ewald method. The lattice relaxation is taken into account by the lattice static method. The repulsive overlap interaction between ions is approximated by the Hnggins‐Mayer potential. The Van der Waals interaction plays a very important part. Numerical calculations are done for KCI and KBr crystals containing interstitial and substitutional hydrogen ions with a view of obtaining the energy of formation of an impurity Frenkel pair. The activation energy of atomic hydrogen diffusion is calculated in the same crystals.
Temperature and concentration dependence of the electric field gradient in the cadmium‐magnesium alloy system
Authors: De U. , Hoph S. , Witthuhn W.
Published: July 2007

The quadrupole coupling constant, eQVzz/h, for 111Cd probe nuclei in CdxMg1−x, alloys (x = 0.0 to 1.0) is measured as a function of temperature and composition, using the time differential perturbed angular correlation technique. The observed temperature dependence of the electric field gradient (EFG), Vzz can be described by a T3/2‐relation for each of the compositions studied, except in the cases where phase transformations take place. From the measured concentration dependence of the EFG in the disordered h.c.p. phase of the alloy with lattice constants c and a, plots for the variation of a3(eQVzz/h) with c/a are made at different temperatures. These experimental results are discussed, using a theory of the EFG in metals, which predicts such a plot to belinear.
Planar channeling trajectories in diamond and silicon
Authors: Roosendaal H. E. , Schmiedeskamp B. , Hubbes H. H. , Lutz H. O.
Published: July 2007

Planar channeling backscattering spectra of 230 keV protons in silicon and diamond, and of 350keV He ions in silicon have been measured. The half wavelengths and the average stopping power of ions oscillating between the crystal planes with an amplitude of half the planar spacing are determined. For the half wavelengths agreement is obtained with theoretical calculations. The average stopping power of the ions considered turns out to be roughly 50% larger than the random stopping power.
Excitation mechanisms and excited states of the I1 bound exciton in CdS
Authors: Baumert R. , Gutowski J.
Published: July 2007

For the neutral‐acceptor‐bound exciton emission (I1) of CdS three new excitation lines with light E ⟂ c are found at 1.2, 2.5, and 3.7 meV on the high energy side of the I1 line. The nearest one is interpreted as due to the simultaneous excitation of the bound exciton and a transverse‐acoustic phonon. The other two are understood as the direct creation of the I1 bound exciton in excited states with one of the equal holes belonging to a higher configuration. With light E ‖ c the excitation mechanisms via the free exciton states AL and AF and the bound exciton states I1B and I1B are discussed. An excitation intensity dependent energy shift of the long wavelength tail of the band edge is reported for the first time.
Fonctions optiques d'une couche mince de sulfure de mercure
Authors: Debiais G.
Published: July 2007

Une méthode de calcul des constantes optiques relative aux couches minces est analysée et appliquée à une couche de sulfure de mercure renfermant 50% de cinabre (α‐HgS) et 50% de méta cinabre (β‐HgS). Nous calculons les fonctions optiques et les frbquences des modes dans l'infrarouge entre 4000 et 250 cm−1 et observons l'influence respective des deux formes sur ces résultats.
The electronic theory of the alloy systems composed of alkali metal elements. I. Bulk properties of CsK, CsRb, and RbK solid solutions
Authors: Soma T. , Matsuo H. , Kohbu Y.
Published: July 2007

A local Heine‐Abarenkov model potential of the pseudo alloy atom is proposed for the CsK, CsRb, and RbK alloy systems. Two parameters are determined by satisfying the zero pressure condition and Vegard's law for the pseudo ion core radius. The total binding energies and bulk modulus are calculated as a function of alloy compositions.
133Cs Quadrupole Perturbed NMR Study of Jahn‐Teller Phase Transitions in CsCuCl32)
Authors: Corti M. , Rigamonti A. , Magistris A.
Published: July 2007

133Cs nuclear spin‐lattice relaxation measurements in CsCuCl3, in the temperature range 100 to 700 K, and an analysis of the first‐order static quadrupole effects on the NMR levels, are reported. Some data regarding the dc conductivity and the dielectric constant are mentioned and briefly discussed. Interesting insights in the static and dynamical properties of CsCuCI3, around the 418 K phase transition to the helical electric dipole structure driven by the cooperative Jahn‐Teller effect are obtained. The 133Cs spin‐lattice relaxation is driven by the fluctuations of the dipolar magnetic field from the Cu2+ ion and its temperature dependence is interpreted in the light of the properties of the electronic spin dynamics in presence of crystalline field effects.
The Influence of the Electric Field on the Electron Capture Coefficient of Screened Coulomb Centres
Authors: Olejníkoná B.
Published: July 2007

The method of Abakumov et al. who dealt with the evaluation of the lifetime of carriers in the field of Coulomb attractive centres in a strong electric field is applied here for a calculation of the field‐induced change of the capture coefficient of screened Coulomb centres. The use of a computer enables to study the field dependence in a broad interval of electric fields without restriction to weak or strong ones. The calculated values are compared with results of previous paper obtained by the method of Dussel and Boer. Results given by these two different approaches differ considerably in both the magnitude and the shape of functional dependence.
The Pseudopotential Method and Thermodynamics of Eutectic Systems
Authors: Landa A. I. , Panin V. E. , Zhorovkov M. F.
Published: July 2007

The pseudopotential method and the thermodynamic perturbation theory are applied to construct the phase diagram of the eutectic system Cd‐Zn. The Einstein model approximation in the solid phase and the hard sphere approximation in the liquid phase are chosen as reference systems. Satisfactory agreement of the calculated phase separation curves with experimental data is observed. A correlation between the position of the phase separation curves and the thermodynamic characteristics of the components is found. An analysis of the contributions to the mixing energy is made, and the correlation between the mixing energy and the mixing volume is established.
Infrared and Raman Spectra of Germanium Dichaleogenides(II). GeSe2
Authors: Popoviá Z. V. , Stolz H. J.
Published: July 2007

Polarised Raman spectra at 300 and 4.2 K as well as IR reflectivity and transmission spectra of single crystal GeSe2 are obtained and analysed with the help of a factor group analysis. The IR reflectivity data are analysed with a Kramers‐Kronig analysis and by means of an oscillator fitting procedure. The results obtained are discussed in terms of the analogy between the vibrational spectra of GeS2 (Part I) and GeSe2.
Luminescence et résonance paramagnétique de l'ion Mn2+ dans le luminophore MgS
Authors: Asano S. , Yamashita N. , Nakao Y. , Matsushima Y.
Published: July 2007

ESR spectra and emission and excitation spectra of the MgS:Mn2+ phosphor are measured at 6, 80, and 300 K. From ESR spectra the values of the parameters g and A are obtained: g = 2.0019 and A = −74.8 × 10−4 cm−1 at 300 K. Furthermore, the analysis of the excitation spectra leads to the values B = 631 cm−1, C = 3345 cm−1, and Dq = 817 cm−1 with covalency parameter ϵ = 0.044. The value of the cubic field parameter a estimated from the shape of ESR spectra is much smaller than that theoretically deduced from the observed value of the parameter Dq.
Investigation of the XPS Valence Band Structure from Sn Chalcogenides
Authors: Berg U. , Chassé T. , Brümmer O.
Published: July 2007

XPS valence band spectra reflect the electronic density of states weighted with cross‐sections. The spectra will give additional information about the symmetry of the electron wave function, if they are measured in dependence on the electron emission angles. Valence band spectra of SnS, SnSe, SnTe, and SnS2 are measured partly in dependence on the polar angle θ. These measurements allow an identification of the symmetry of valence orbitals from intensity variations of the valence band maxima.
Shift in the Binding Energy of the Inner Electrons Due to Chemical Combination
Authors: Srivastava K. S. , Husain M. , Gupta P. , Srivastava A. K. , Sinha K. , Singh S. , Kumar V.
Published: July 2007

The numerical order of the chemical shift of an X‐ray absorption edge of a metal when it undergoes a chemical combination and forms a compound is calculated by calculating the binding energy shift of the core electrons. It is found that the shift in the binding energy corresponds well with the chemical shift.
Theory of the Auger Spectra of Narrow‐Band Metals with Impurities
Authors: Drchal V. , Kudrnovský J.
Published: July 2007

The intraatomic CVV Auger spectrum for a single impurity in a perfect crystal with an initially filled band is investigated. The impurity is characterized by its atomic level Δ and the contact pair interaction U of electrons (Wolff‐Clogston model). The exact solution of the problem is found. The spectrum may consist of three parts: (i) band of the two‐hole extended states, (ii) isolated localized two‐hole states, and (iii) band of mixed two‐hole states, in which one hole is localized, and the other one is in an extended state. The band of extended states is present in all cases, the localized and mixed states appear simultaneously for a certain value of |Δ|. The condition for the existence of bound states is derived, and the theory is numerically illustrated for a simple bandstructure model.
EPR Observation of an Au–Fe Complex in Silicon. II. Electronic Structure
Authors: Sieverts E. G. , Muller S. H. , Ammerlaan C. A. J. , Kleinhenz R. L. , Corbett J. W.
Published: July 2007

For a description of the Au–Fe complex which is discussed in Part I of this article, a model by Ludwig and Woodbury is adopted. This model does not allow for an analysis of the observed hyperfine interactions in a simple LCAO description. Instead a model of exchange coupled spins is proposed. The calculated actual hyperfine interactions are compared with data of atomic wave functions for Au and Fe. Due to covalency and/or hybridization effects the quantities 〈r−3〉d which characterize the d‐orbitals on the Fe and Au atoms are considerably reduced in silicon with respect to the free atoms. As a result, the s‐core polarization effects which determine the isotropic hyperfine interactions are found to be weaker in a silicon matrix than in most other materials.
Change in Electron Mass and Collision Frequency Due to Acoustic Wave Propagation in Piezoelectric Semiconductors
Authors: Palanichamy P. , Singh S. P.
Published: July 2007

A phenomenological theory is developed to study the relative change in electron mass and collision frequency when an acoustic wave propagates through piezoelectric semiconductors. The results show that the change in collision frequency is more than that in electron mass for all acoustic wave frequencies in n‐CdS, and is more appreciable at lower temperatures.
Inverse Problem in Mössbauer Spectroscopy in Case of Low‐Frequency Modulation
Authors: Nadjaryan G. N. , Gabrielyan R. G. , Nkrtchyan A. R. , Khanamiryan R. M.
Published: July 2007

Investigations are made to determine the type (time dependence) and parameters of external low frequency excitations on the basis of Mössbauer absorption spectra (inverse problem). On the basis of the performed analysis the paper suggests a numerical method for solving this problem. The type of velocity and extreme values of oscillations of two types are determined by this method.
A Refined Equation of State for Monovalent Metals
Authors: Goel S. C. , Nanda V. S.
Published: July 2007

A refined equation of state for monovalent metals based on a quantum mechanical version of the cell model is given. Here not only the contribution of free electrons to the equation of state is taken into account but also to a first approximation the effect of anharmonicity of the cell potential is included. The latter refinement results in a considerably improved agreement between theory and experiment.
Redistribution on Impurities in the Field of a Strong Electromagnetic Wave
Authors: Litvnov V. I. , Valuev K. A. , Tovstyuk K. D.
Published: July 2007

A model in which donor‐acceptor electronic transitions under illumination induce impurity redistribution among non‐equivalent positions in semiconductor lattice is considered.
Model Hamiltonian Wannier Functions
Authors: Craig B. I. , Smith P. V.
Published: July 2007

Many theoretical approaches to the problem of defects and impurities in an otherwise perfect lattice require the existence of well localized basis functions on each lattice site, the so‐called Wannier functions. The construction of such Wannier functions from a model Hamiltonian representation of the host metal bandstructure is discussed and the dependence of the degree of localization of these functions on both the choice of phase factors and the constraints of orthogonality examined. The value of such functions in providing an adequate set of basis functions is also critically examined for several systems of physical interest.
On a New Photogalvanic Effect Due to Free‐Carrier Absorption
Authors: Henneberger F. , Averkiev N. S. , Rasulov R. J.
Published: July 2007

A new photocurrent induced by optical orientation of free carriers under intraband absorption is theoretically investigated. Using a one‐band model it is shown that this current originates from interferences between harmonic and anharmonic processes of the electron–phonon interaction. A general expression for the current is derived for both, linear and circular polarized light. As an example the temperature dependence of the current is calculated for tellurium.
Electronic Properties of the TI–AgTITe2 System in the Liquid State
Authors: Uemura O. , Itoh M. , Satow T.
Published: July 2007

The electrical conductivity, the magnetic susceptibility, and the thermoelectric power of the liquid TI–AgTITe2 system are measured as a function of temperature and composition. The temperature coefficient of electrical conductivity and magnetic susceptibility in the concentration range from pure AgTITe2 to 66.7 mol% TI decreases gradually with increasing TI concentration. The alloys in the vicinity of 66.7 mol% TI have a weak temperature‐dependent conductivity and diamagnetism at low temperature but above 700°C both quantities of these alloys vary strongly with temperature. The electrical conductivity indicates a deep minimum and the diamagnetic susceptibility gives a sharp maximum at 66.7 mol% TI, while the thermoelectric power changes its sign around this composition. These results suggest that the state density of electrons has a minimum at the composition corresponding to AgTI3Te2 (66.7 mol% TI) and a metal–semiconductor transition as found for the liquid TI‐Te system also occurs in this system. The electronic properties obtained are discussed in terms of the current diffusive transport model for liquid semiconductors.
Infrared Absorption Spectra of Eu‐Rich EuO. Excitations of the Bound Magnetic Polaron
Authors: Lascaray J. P. , Diouri J. , Nadai J. P. , Ferre J.
Published: July 2007

Two typical absorption bands of Eu‐rich EuO, located around 0.56 and 0.67 eV are studied in the temperature range 20 to 270 K. The results and previous data cannot be explained satisfactorily by the two models reported in the literature: i) excitations of electrons localized into F+ centers, ii) optical transition involving a spin‐flip process of the electron of the bound magnetic polaron. An improved, more refined description of the previous interpretation is proposed for which absorption bands are due to optical transitions inside the 5d (t2g) levels split by the spin–orbit coupling and the exchange interaction.
Random Site Ising Model in Self‐Avoiding Walk Approximation
Authors: Medvedev M. V. , Sadovskii M. V.
Published: July 2007

The free energy of random site Ising model with competing exchange interactions of nearest neighbours is studied with the use of high‐temperature expansions in the self‐avoiding walk approximation. Conditions for the instability of the paramagnetic state are determined by the convergence criterion of the random high‐temperature series. The possibility of a concentration interval with the absence of the long‐range magnetic order is studied for different 2d and 3d lattices.
Lattice Constant Fluctuations in Anharmonic Crystals
Authors: Wojtczak L. , Siklós T. , Mrygon B. , Mielnicki J.
Published: July 2007

A model of lattice constant fluctuations in crystals is discussed in self‐consistent phonon theory. The influence of fluctuations on the mean square displacement of atoms from their equilibrium position is considered. The fluctuation effects connected with correlations are also included.
Photoemission Study of Oxygen Adsorbed on Sputtered a‐Si(H) and a‐Si
Authors: Cháb V. , Zemek J. , Koc S. , Mikušík P.
Published: July 2007

The electronic structure of natural oxide layers and of oxygen adsorbed on the surface of sputtered a‐Si and a‐Si(H) thin films are investigated by combining ultraviolet photoemission spectroscopy and X‐ray photoemission spectroscopy. The emission structure in the valence band region which is derived from the oxygen and silicon orbitals, is found to represent the nondissociative adsorption of oxygen on a‐Si(H) surface independently of hydrogen content. XPS study of Si2s and Si2p core levels shows a minimally 0.3 eV smaller value of the chemical shift in the case of naturally oxidized a‐Si(H) and a‐Si films than the value measured on c‐Si oxidized under the same conditions. The ion‐beam effect on oxide layers is briefly discussed.
The Heat Capacity of Nb3SnHxin Dependence on the Hydrogen Content
Authors: Shamrai V. , Bohmhammel K. , Wolf G.
Published: July 2007

Investigations of the heat capacity on Nb3SnHxsamples (0 ≦x≦ 1.0) in the temperature range from 2 to 30 K are communicated. A strong decrease ofTcand γ is observed experimentally with risingxvalue. The change of the density of states near the Fermi level and the electron‐phonon interaction parameter in dependence onxare determined. The discussion of the change in the properties considers the possibility of the formation of H–Nb bonding states and the position of the H‐atoms near to the crossing point of the Nb‐chains in the A15‐structure.
Spin–Orbit Interaction in Superexchange with Orbital Degeneracy II. Effective Tensor Hamiltonian
Authors: Blaszak M.
Published: July 2007

Methods of irreducible tensor algebra for a chain SU2 → O* are applied to determine the effective tensor Hamiltonian of superexchange with orbital degeneracy with the spin–orbit interaction on magnetic ions assumed. The parameters of each Hamiltonian are calculated in quasi‐diagonal approximation.
Dynamics of Two‐Spin Cluster in Spin Glass II. The Magnetization Process at T = 0
Authors: Nara S. , Heber G.
Published: July 2007

Based on the simple two‐spin cluster model of spin glass, the magnetization process at T = 0 is investigated. An ensemble of clusters is considered consisting of two Heisenberg spins in the external field and two kinds of molecular field which are called “homogeneous molecular field” and “inhomogeneous molecular field” created by inter‐cluster interactions. The spin quantum number is taken as S1 = S2 = 1/2 for conveniency. It is shown that this model qualitatively can well describe the S‐shape like magnetization process and hysteresis loops of several substances which are measured at very low temperature (T ⩽ Tf). Also special cases are found of unstable magnetization changes which in reality will be smeared out.
Photoconductivity of Lead(II)‐ and Cadmium (II)‐Doped Silver Bromide
Authors: Deri R. J. , Haynam Ch. , Spoonhower J. P.
Published: July 2007

The photoresponse of AgBr binderless powder precipitates doped with Pb2+ and Cd2+ ions is studied near liquid‐nitrogen temperature by using microwave cavity techniques. Pb2+‐ and Cd2+‐doped samples have much longer photoelectron lifetimes and higher peak photoelectron signals than undoped samples. The decay kinetics of the doped samples appears to consist of the superposition of two first‐order processes. The temperature dependence of the kinetics is established to follow the Arrhenius model, and activation energies are deduced. The data are interpreted in terms of “impurity conductivity” caused by photoelectrons trapped by the Pb2+/Cd2+ dopants and the migration of silver‐ion interstitials.
Thermal Noise, Diffusion, and the Mobility of Hot Holes in Silicon
Authors: Bosman G. , Zijlstra R. J. J.
Published: July 2007

The longitudinal diffusion coefficient and the mobility of holes in silicon are calculated as a function of electric field strength from noise and conduction measurements on p+ πp+ planar silicon devices at T = 100, 145, and 210 K. The electric field is oriented along the 〈100〉 direction. The results obtained for the longitudinal diffusion coefficient at T = 100 and 145 K show that both light and heavy holes contribute to charge transport. The values found for the mobility agree very well with those which Ottaviani et al. obtained using the time‐of‐flight technique.
On the Phonon Contribution to the Electrical Resistivity of Intermediate Valence Systems
Authors: Christoph V.
Published: July 2007

The electrical resistivity of an electron–phonon system with two hybridized tight‐binding electron bands is calculated. The electron–electron interaction is taken into account in the Hartree‐Fock approximation leading to an occupation dependent narrowing of the bands. The influence of the effective band width on the resistivity is discussed.
Mössbauer Isomer Shifts of 40K+ in KF, KCl, and KBr Lattices
Authors: Bansal C. , Shrivastava K. N.
Published: July 2007

Charge densities at 40K+ in KF, KCl, and KBr lattices are calculated from Hartree‐Fock wavefunctions including the effect of overlap of core orbitals with the neighboring atoms. From the calculation of KF and KCl and the experimental measurements of Mössbauer centre of gravity shifts we estimate the relative change in nuclear charge radius upon emission of 29.4 keV γ‐radiation to be in the limits of −6 × 10−4 ≦δ/ ≦ 31 × 10−4.
Magnetic States of a Quenched Random Site Heisenberg Magnet with Competitive Exchange Interactions. I. High‐Temperature Magnetic States in Simple and Body‐Centered Cubic Lattices
Authors: Medvedev M. V. , Zaborov A. V.
Published: July 2007

For a quenched random site Heisenberg system with competitive nearest‐neighbour exchange interactions (IAA > 0, IAB ≶0, and IBB < 0) the molecular field distribution functions of various random magnetic structures are derived in the approximation of large nearest‐neighbour number z (z >> 1). The obtained distribution functions are utilized to discuss magnets with simple (s.c.) and body‐centered cubic (b.c.c.) lattices. It is shown that at high temperatures random collinear ferromagnetic and antiferromagnetic states (and a canted structure as well) can occur at the transition from the paramagnetic state. The occurrence of a spin‐glass state in s.c. and b.c.c. lattices at high temperatures is scarcely probable even in the framework of the molecular field approximation (MFA).
Investigation of the Charge Carrier Scattering in Bi under High Hydrostatic Pressure
Authors: Kraak W. , Herrmann R. , Haupt H.
Published: July 2007

A detailed and precise measurement is given of the temperature dependence of the electrical resistivity of bismuth in the temperature range 2 K < T < 77 K. Under high hydrostatic pressure the Fermi energy is varied over a wide range. From the obtained temperature dependence of the electrical resistivity – a linear dependence for temperatures > 20 K and a T2 dependence at lower temperatures – as well as the characteristic dependence of the strength of the linear and quadratic terms from the electron Fermi energy, it is suggested that at temperatures > 20 K the resistivity is dominated by electron–phonon scattering, however, at lower temperatures a contribution due to carrier–carrier scattering may be significant.
Long‐Wave Secondary Radiation in Polar Semiconductors as a Function of Temperature
Authors: Giner C. Trallero
Published: July 2007

The long‐wave secondary radiation in direct‐band polar semiconductors is investigated. The secondary radiation cross‐section is calculated as a function of the incident, ω1, and emitted, ωs, light frequencies and the temperature T. It is shown that for arbitrary temperature values the cross‐section is of a step‐like shape and new thresholds appear relative to T = 0 K.
Simple Exciton in Intermediate Magnetic Field Application to Cdx−1MnxTe Mixed Crystals
Authors: Twardowski A. , Ginter J.
Published: July 2007

The energy levels, both discrete and resonant of a simple, anisotropic exciton in external magnetic field are calculated. Obtained results are used to describe excitonic spectra of CdMnTe mixed crystals reported earlier, for which giant spin splittings offer on exceptional possibility to observe simple excitons.
Localization in a Random System of N Coupled Chains I. Microscopic Model, General Scheme
Authors: Weller W. , Prigodin V. N. , Firsov Yu. A.
Published: July 2007

On the basis of a microscopic model describing the motion of an electron under the influence of a weak random potential in a system of N weakly coupled chains localization of all eigenstates for finite N is proved. Using Berezinskii's idea of ordering the diagrams along the chain the diagram analysis for this system with N states in each cross section and an effective method for treating this N2‐variable problem are developed. The localization length is shown to be equal to Nl2 (l2 mean free path for backward scattering at one chain). In the limit N → ∞ diffusion is obtained for d = 3.
The Excitation Map of Surface Barrier Resonances I. The Excitation Map for Ni(001) in the (10) Azimuth
Authors: Solbrig H.
Published: July 2007

A map of ∣det (I – RphS+−)∣ as a function of the energy E and the surface‐parallel momentum k∥ is called an excitation map (Rph substrate reflection matrix, S+− matrix of inner reflection by the barrier). The information content of such an excitation map is analyzed. An example is given (Ni(001), (10) azimuth) and discussed with emphasize on the ground resonance which yields most of the information on the saturation of the barrier potential.
Infrared Spectra of NiO Microcrystals at High Temperatures
Authors: Mochizuki S.
Published: July 2007

The infrared spectra of NiO microcrystals are measured at various temperatures from 300 to 1273 K in the spectral region from 250 to 700 cm−1 by the thermal‐emission and reflection methods. The results are discussed in the light of the theory of anharmonic crystals. The anharmonic phonon frequency shift of the microscrystals is seen to be larger than that of the infinite single crystal.
Cluster Calculations of Alkaline‐Earth Fluorides by the MSXα Method
Authors: Bielschowsky C. E. , Maffeo B.
Published: July 2007

The MSXα method is employed to calculate the electronic structure of clusters representing CaF2, SrF2, and BaF2 perfect crystals. Interband energy intervals are calculated and compared with experimental data, when two different boundary conditions are employed. It is shown that the commonly used “Watson model” produces results in systematically poorer agreement with experiment.
Secondary Electron Radiation from Different Targets Exposed to Photons with Energy 0.1 to 3 MeV
Authors: Akkerman A. F. , Botvin V. A. , Grudskii M. Ya. , Smirnov V. V. , Chernov G. Ya. , Shilenkova M. V.
Published: July 2007

Differential and integral yields of secondary electrons from different targets bombarded by monoenergetic photon beams are calculated using the Monte Carlo method. The results are compared to experimental data and values calculated by other authors. The discovered 20 to 30% decrease of calculated backward yields according to experimental data for heavy elements is explained by the limited applicability of Sauter's formula for the description of photoelectron angular distribution.
Magnetic States of a Quenched Random Site Heisenberg Magnet with Competitive Exchange Interactions II. Magnetic States with Partial Spin‐Glass Freezing in Simple and Body‐Centered Cubic Latticess
Authors: Medvedev M. V. , Zabrovo A. V.
Published: July 2007

The typical magnetic phase diagrams of a random site Heisenberg magnet with competitive exchange interactions of the nearest neighbours are investigated. It is emphasized that there appear magnetic states which are superpositions of the long‐range magnetic ordering of some spin vector components and the spin‐glass freezing‐in of other components, namely, the asperomagnetic (random noncollinear ferromagnetic) state, the antiasperomagnetic (random noncollinear antiferromagnetic) one, and the noncoplanar canted one.
Influence of Semiconductor Dielectric Function Spatial Dispersion on Charge Electrostatic Energy near the Semiconductor/Vacuum Interface and Field Emission Current
Authors: Gabovich A. M. , Voitenko A. I.
Published: July 2007

The electrostatic charge energy W near the semiconductor/vacuum interface is calculated for a variety of models describing the semiconductor static dielectric function ε(k) dependent on a momentum transferred k. It is shown that the correct account of this dependence leads to the finiteness of the energy W and the image force electrostatic field – σW/σz, when z → O, where z is the distance from the interface. The potential barrier shape for the field emission from semiconductors is found and the dependences of the tunnel current density j on the applied field F, the temperature T and the doping impurity concentration n0 are calculated. It is shown that the spatial dispersion effects of ε(k) essentially affect the magnitude of j, but do not change the dependence j(F) which follows from the Fowler‐Nordheim classical formula.
The F+ Center in Lithium Tantalate
Authors: Ho Fat Duen
Published: July 2007

A study of the electronic states associated with an oxygen vacancy in lithium tantalate (LiTaO3) is reported. The F+ center (one oxygen ion vacancy with one trapped electron) is treated by the similar model used in the study of the isomorphous crystal, LiNbO3, by the author. Treating the crystal as an array of point charges the potential of the lattice of 810 ions is computed. The convergence of the lattice sums is demonstrated. The potentials resulting from polarization of the medium are also taken into account. Using a variational method the Schrödinger equation is solved in a self‐consistent manner. The calculations show that one of the absorption bands (450 nm) observed may be ascribed to the presence of the F+ center.
Magnetic After‐Effects in Single‐ and Poly‐Crystalline Magnetite
Authors: Walz F. , Brabers V. A. M. , Chikazumi S. , Kronmüller H. , Rigo M. O.
Published: July 2007

The magnetic relaxation spectra of different types of single crystalline magnetite are investigated in the temperature range 4 K < T < 450 K and compared with corresponding spectra obtained on stoichiometric (Fe3O4) and vacancy‐doped polycrystals (Fe3−ΔO4). Three basic relaxation mechanisms are revealed within the following temperature ranges 4 K < TI < 35 K, 40 K < < TII < 130 K and 200 K < TIII < 450 K, which may be associated to either electronic (TI, TII) or ionic (TIII) hopping processes. In crystals with systematically reduced stoichiometry characteristic modifications in the structure of these spectra are observed from which additional information for a theoretical understanding may be obtained.
Electron‐Energy‐Loss Spectroscopy of Different Al2O3 Modifications II. Lineshape‐Analysis of Energy Derived Dielectric Function
Authors: Tews W. , Zimmermann R.
Published: July 2007

The dielectric function ε(E) = ε1(E) + iε2(E) deduced from electron‐energy‐loss measurements of amorphous and polycrystalline γ‐ and α‐Al2O3 is investigated in the spectral range from 5 to 30 eV. A lineshape analysis applied to the energy derivative of the dielectric function gives parameters of an exciton and an M0‐singularity in the band‐edge region. At higher energies, a set of critical points is identified. The data are interpreted in terms of the electronic structure of Al2O3 with special emphasis on a comparison between amorphous and polycrystalline films.
Study of Relaxation Processes in Antiferromagnets Using Sound Absorption Measurements
Authors: Tarasenko S. V. , Chepurnykh G. K.
Published: July 2007

For antiferromagnets of easy‐plane type outside nuclear magnetoacoustic resonance conditions at different temperatures the interaction of nuclear spins with lattice vibrations via electron spin waves is studied at conditions when between spin and sound waves a strong coupling takes place (the linear coupling parameter is of the order of unity). Simple relations (nuclear spin subsystem considered) are obtained for spin wave and additional sound attenuation due to coupled magnetoelastic waves. They are necessary for studies of relaxation processes in a magnon subsystem using sound absorption.
The E Centre in SiO2 MO Calculation of the 17O, 20Si, and 1H Hyperfine Splittings
Authors: Haberlandt H.
Published: July 2007

Starting from the relaxed O− vacancy model the 29Si, 17O, and 1H hyperfine splitting (hfs) parameters are calculated by means of the extended Hückel theory (EHT) within the cluster approach for different models of the E'1 centre in SiO2. The 29Si hyperfine splittings strongly depend on the lattice relaxation. The accordance of calculated and experimental hfs data, recently observed by Griscom, is checked. Two modified O− vacancy models are proposed to explain the E centre: one for the centre exhibiting “weak” hfs and the other for the centre exhibiting no “weak” hfs.
Electron Emission from Gold Island Films
Authors: Blessing R. , Pagnia H.
Published: July 2007

The electron energy distribution from Au island films shows field emission and hot‐electron emission in two different regions of the applied voltage. The two processes can be determined by their relative energetic position compared with UV photoelectrons and their dependence on the voltage applied. There are field emission in the high‐voltage region (Up > 8 V) following the Fowler‐Nordheim equation and electron excitation at low voltages (Up < 8 V).
The Excitation Map of Surface Barrier Resonances. II. Some Qualitative Arguments Concerning the 2D NFE Behaviour of Surface Barrier Resonances
Authors: Solbrig H.
Published: July 2007

Using the example of the {10} emergences for normal incidence on the Ni(001) surface the levels of the Rydberg series are demonstrated to depend on the speculiar reflection by the substrate rather than on the reflection by the corresponding laterally averaged potential of the substrate.
Effets des pièges sur la fusion triplet–triplet dans les cristaux de naphtalètne
Authors: Bonno B. , Laporte J. L. , Rousset Y.
Published: July 2007

L'étude de 300 à 77 K des fluorescences retardées de polycristaux de naphtalène purs ou dopés à l'anthracène permet de préciser l'effet de l'introduction dans le cristal de petites quantités de cette impureté. Lorsque la température décroǐt, l'intensité des fluorescences retardées varie de façons très différentes pour le cristal pur et les cristaux mixtes. Ces comportements sont interprétés à partir de la présence d'un piège pour l'exciton triplet (ΔE = 1575 cm−1, τ = 3,6 × 10−2 s) liè à l'introduction de l'anthracène au sein du cristal. La concentration de ce piège varie comme celle de l'impureté.
Anisotropy of the Free Carrier Piezoelectric Scattering by Dislocations in III–V Compounds
Authors: Vignaud D. , Farvacque J. L. , Ferre D.
Published: July 2007

Calculations of the piezoelectric potential associated with dislocations of sphalerite structure are made, i) by taking into account the elastic anisotropy of the materials, ii) by neglecting it. The results show a large similarity in the behaviour of the induced resistivity calculated in both cases. These results allow to make use of the isotropic approximation for the elastical medium for any calculation of the electrical properties associated with dislocations.
On the Anomalies in the Temperature Dependence of Conductivity in Hg1−xCdxTe
Authors: Arapov Yu. G. , Davydov A. B. , Tsidilkovskii I. M. , Shelushinina N. G.
Published: July 2007

The temperature (1.8 K ≦ T ≦ 77 K) and magnetic field (0 ≦ H ≦ 22 kOe) dependence of the conductivity σ, longitudinal magnetoconductivity σzz, and of the Hall coefficient R for gapless Hg1−xCdxTe crystals are measured. At temperatures Tmin = 6 to 11 K there occur deep minima of conductivity σ(T). It is shown that the origin of these minima cannot be accounted for by the resonance scattering of electrons by acceptors. The minima in σ(T) arise from the decrease in electron mobility caused by the increase of the number of charged centres with increasing temperature when T < Tmin and by the increase of the concentration of electron‐hole pairs when T > > Tmin. The anomalies in the conductivity (plateau) and the Hall effect (double inversion of sign) observed in the temperature range 20 K < T < 40 K are due to the contribution of three types of carriers, viz. light conduction band electrons, heavy acceptor band electrons, and valence band holes.
Band Structure, High Temperature Electrical Resistiviy, and Exchange‐Induced Magnetic Moment of the Itinerant Electrons in Gd‐La Alloys
Authors: Beznosov A. B. , Nikolskii G. S. , Feher A.
Published: July 2007

The electrical resistivity ϱ of the Gd‐La alloy system containing up to 12 at% of La is measured in the temperature range from 300 to 1000 K. Above the magnetic transition temperature a deviation of the dependence ϱ(T) from the linear behaviour is found for all alloys investigated. The analysis of the dependence ϱ(T) in the temperature range 500 to 1000 K shows a negative contribution to the electrical resistivity due to the temperature dependence of the Fermi distribution. The posibility of using the information obtained in the study of the magnetic properties of rare earth metals in discussed.
Exchange Contributions and Plasmon Spectra of One‐Dimensional Systems
Authors: Brosens F. , Devreese J. T. , Kahn L. M. , Ruvalds J.
Published: July 2007

The dynamical exchange decoupling method for including exchange in the dielectric function of the electron gas is applied to one‐dimensional systems with a tight‐binding energy band. Depending on the bandwidth and the position of the Fermi energy in the band, dynamical exchange effects are shown to have appreciable effects on the plasmon dispersion. For propagation of the plasmon along the strand axis, and in the long‐wavelength limit, exchange effects drastically lower the slope of the plasmon dispersion. For non‐parallel incidence, the exchange effects are less pronounced, and extended over a smaller wave vector region.
Optical Absorption in PbSe1‐‐xTex Due to Transitions between Band States and Localized Energy Levels
Authors: Finkenrath H. , Franz G. , Uhle N.
Published: July 2007

The optical absorption of thin PbSe1‐xTex films prepared by hot‐wall epitaxy in the frequency range 80 to 660 cm−1. The maximum of a broad absorption band changes its spectral position in a characteristic manner when the composition parameter x is varied. Some possible absorption mechanisms are discussed. The experimental results are mostly understandable by the assumption of electronic transitions between valence band states and localized energy levels within the valence band.
Is the Electronic Structure of Liquid Metals Free‐Electron‐Like or Bloch‐Electron‐Like?
Authors: Halder N. C. , Phillips K. C.
Published: July 2007

The electronic density of states (EDS) are calculated for liquid Na, Hg, Ga, Pb, Sn, and Bi. Calculations are performed using two formalisms: (i) second‐order perturbationtheory and (ii) the Green function theory. The EDS plots resulting from these two sets of calculations reveal that the perturbation calculations give consistently more structure than the Green function calculations. However, the general features of the two sets of calculations are the same and agree within their respective theoretical limitations and basic approximations. It is concluded that the electronic structure of liquid metals is neither free‐electron‐like nor Bloch‐electron‐like.
Microwave Measurements of the Thermal Expansion of Organic Metals
Authors: Miane J. L. , Carmona F. , Delhaes P.
Published: July 2007

The thermal expansion of organic metals is measured by the Buravov‐Shchegolev method (microwave cavity at 9.5 GHz). A relation is found between the frequency shift of the cavity and the length of the sample, independent of the skin depth in the sample. The linear thermal expansion coefficients αb are measured along the organic chains in charge transfer complexes (TTF–TCNQ, HMTTF–TCNQ) and ion radical salts (TMTTF2–I, TMTSeF2–ClO4, TTT2–I3 and TSeT2–I). Organic metals with TTF and its selenium analog TSeF show large coefficients for bi‐chain compounds (like TTF–TCNQ) as well as for monochain compounds (like TMTSeF2–ClO4). These metals are found to exhibit strong anharmonic effects leading to a T2 law for the electrical resistivity (Weger's model). On the contrary metals with TTT or TSeT have weak coefficients αb and their electric properties are more similar to those of inorganic metals (their resistivity follows a Bloch‐Grüneisen law with ϱ ∝ T).
Propagation of Strong Electromagnetic Waves in Kane Semiconductors under Conditions of Electron and Phonon Heating
Authors: Gasymov T. M. , Katanov A. A. , Kocharli F. K.
Published: July 2007

The propagation of a strong electromagnetic wave (EMW) is studied in nondegenerate semiconductors with a Kane spectrum taking into account the heating of electrons and acoustic phonons‐In the limiting cases of a parabolic and strongly nonparabolic spectra it is shown that if the cyclotron frequecy ω is high enough compared to that of the incident wave ω the refraction index of the medium n is independent of the amplitude of the incident wave E0. At ω ≫ ωn depends on E0 if the spectrum is nonparabolic. In the case of a strongly nonparabolic spectrum n increases with the electron temperature θe. The field and temperature penetration lengths LE and Lθe are calculated. In the strongly nonparabolic case where a “thermal reservoir” is present and the electron scattering is due to the piezoacoustic phonons these lengths as well as the dissipative part of the conductivity σRe are found to be independent of E0. In the strong damping region the semiconductor impedance ζ grows with E0. In all the cases considered the field and temperature damping functions are obtained. In absence of a “thermal reservoir” and in a strong magnetic field the thermoelectric and Nernst‐Ettingshausen fields reverse their signs when passing from the parabolic to the strongly nonparabolic spectrum.
Electron Paramagnetic Resonance Studies of Cu2+ Impurities in Ferroelectric LiH3(SeO3)2
Authors: Hefni M. A. , Grecu N. M. , Grecu V. V. , Popescu F. F.
Published: July 2007

The electron paramagnetic resonance spectra of Cu2+ doped in LiH3(SeO3)2 single crystals are studied. The ions reside in different chemically distinct sites. For two of them, the strongest in the EPR spectra, the g and A matrices and the Q tensor are determined. Within the limit of experimental errors, the EPR spectra of one site exhibits an orthorhombic symmetry with a pronounced axial character, while the other site exhibits a monoclinic symmetry. In the last case low symmetry effects such as asymmetries of g and A matrices are evidenced.
Unsymmetrized Self‐Consistent Field Approximation for Imperfect Strongly Anharmonic Crystals
Authors: Zubov V. I.
Published: July 2007

The nonlinear integral equations of the unsymmetrized self‐consistent field method for imperfect strongly anharmonic crystals are treated. These equations are reduced to a set of transcendental ones. More emphasis is placed on the cubic strongly anharmonic crystals with taking into account the surfaces and monovacancies.
Crystal Structure and Raman Spectra of InSe
Authors: Ikari T. , Shigetomi S. , Hashimoto K.
Published: July 2007

A polytype of InSe single crystals is determined to be of γ‐type by means of X‐ray Laue and diffractometer measurements. Polarized Raman scattering studies are carried out at room temperature and the spectra are analysed by using the normal modes of γ‐InSe. Two Raman lines of the A1 mode (118, 228 cm−1) and two of the E mode (43, 180 cm−1) are observed. An additional Raman line at 214 cm−1 is attributed to an LO phonon with E symmetry.