bluuebunny/crossref_metadata_2025 huggingface dataset:
Soliton Excitations in Terms of Pseudo‐Riemannian Manifolds
Authors: Wiatrowski G.
Published: July 2007

Advantages are shown of description of one‐dimensional ferromagnetic soliton excitations in an anisotropic medium in terms of a pseudo‐Riemannian manifold. The soliton appears then as a solution of a linear equation of motion of the Schrödinger type in an isotropic curved space of observations equipped with a pseudo‐Riemannian metric. Physically this describes, in particular, the temporal fluctuations of the system, and the change of the exchange interactions as well as predicts the superposition of solitons. The approach enables a consistent explanation of the decay of soliton and space deformation as well.
Optical Properties of NiAl Intermetallic Compounds during Concentration and Temperature B.C.C.–F.C.T. Transitions
Authors: Sasovskaya I. I. , Korabel V. P. , Shreder E. I.
Published: July 2007

Optical constants in the spectral interval ħω = 0.07 to 4.7 eV are measured to investigate the electronic structure of the b.c.c. β′‐phase (type B2) of NiAl compounds over the entire range of the β′‐phase and especially at the boundary of the β′‐phase, when the latter changes into a lowersymmetry f.c.t. (type LI0) phase. The behaviour of the special features of the optical absorption can be explained, if it is assumed that with the growth of Ni content the Ni d‐band terminates on EF, so that EF is at the small density‐of‐states peak. This is the cause of the structural instability of NiAl compounds in the vicinity of 60 at% Ni. Following the b.c.c.‐f.c.t. martensite transformation the higher‐energy (ħω > 3.5 eV) optical absorption structures due to electron transitions not including EF, are conserved, while the low‐energy structures (ħω < 3.5 eV) disappear and a new absorption band emerges in their place in the infrared region of the spectrum at ≈ 0.8 eV. These changes are analyzed using a Jahn‐Teller type effect model for the suppression of degeneracy of some electron energy bands at EF. Optical data are in agreement with the similar model of peak N (EF) in the b.c.c. phase and N (EF) minimum in the f.c.t. phase, proposed earlier.
A Comparison of the C KVV Auger Spectra of NbC and NbN0.7C0.3
Authors: Shitlga Yu. M. , Gutsev G. L. , Rubtsov V. I.
Published: July 2007

The C KVV Auger spectra of NbC and NbN0.7C0.3 are obtained and compared with each other. It is concluded that essential local redistributions of the electronic density may occur under alloying of NbC and NbN. In particular, the negative charge on carbon atoms in the alloy NbN0.7C0.3 increases as compared to that of NbC.
Theory of Vibrational Relaxation of R 2★ Centres in Rare‐Gas Solids. Application to Ne 2★
Authors: Selg M.
Published: July 2007

A tunnel mechanism of vibrational relaxation is proposed for a class of emission centres which are characterized by a weak coupling to the crystalline environment and have vibrational quanta considerably exceeding phonon energies. For such kind of centres, e.g. for R centres in solidified rare gases, a new relaxation channel, connected with the anharmonicity of vibrations, appears. The theory is applied to the centre Ne in solid Ne: a direct calculation of the probabilities of vibrational transitions is carried out.
The Non‐Equilibrium Electron Distribution Function in the Electrical Resistance Problem for Potassium Metal Influence of N‐ and U‐Processes
Authors: Zhernov A. P. , Pashaev Kh. M. , Aliev A. M.
Published: July 2007

The angular and energy structures of the nonequilibrium electron distribution function for potassium at low temperatures are investigated. It is shown that the peculiarities in the δfk structure due to U‐processes are largely suppressed by interference between normal and U‐processes. Hence at the umklapp process freezing temperatures the value of resistivity is affected not only by U‐transitions from “hot spots” but equally by diffuse N‐transitions. The solution of Boltzmann equation by quadrature formulas is discussed.
Cadmium Concentration Dependence of Mobility in Cadmium‐Doped Lead Telluride
Authors: Rustom‐Dalouche R. , Rolland S. , Granger R. , Pelletier C. M.
Published: July 2007

Lead telluride doped with cadmium is grown in a two temperature furnace. The cadmium content is controlled through cadmium vapor pressure. Electronic concentration and Hall mobility are measured for cadmium concentrations up to 1.65 × 1021 cm−3 at 77 and 300 K. Mobility variations are fairly explained by a model taking into account dispersion on acoustic and optical phonons, and neutral impurities.
Pressure‐Induced Phase Transition in RbH
Authors: Bashkin I. O. , Ponyatovskii E. G. , Dergachev Yu. M.
Published: July 2007

Measurements of the RbH volume in dependence on pressure up to 35 kbar are carried out in the temperature range 290 to 525 K. The bulk modulus of the initial RbH phase is equal to 136 kbar at room temperature. A phase transition with a jump of volume of 8.5% is found in RbH at about 17 kbar. The T–P phase diagram of RbH is plotted. The results obtained are in accord with the previously stated idea of the crystallochemical similarity of alkali hydrides and alkali halides.
Vibrational Modes in Bi12GeO20 and Bi12SiO20 Crystals
Authors: Wojdowski W.
Published: July 2007

An interpretation of the Raman and infrared phonon spectra in Bi12GeO20 and Bi12SiO20 crystals is proposed. Some quasi‐molecular units are distinguished due to the presence of heavy bismuth atoms in the crystal lattice. The frequencies of motion and the force constants of the tetrahedral GeO4 and SiO4 units are determined. Moreover, the frequencies of the stretching modes of A and F symmetry of the BiO bonds are considered and the stretching force constants for the BiO bonds are calculated. The results are in good agreement with the Raman and infrared data obtained in the recent works.
A Parametric Study of Crystal Stability and Surface Energy for Diamond Cubic Structures
Authors: Takai T. , Halicioğ;lu T. , Tiller W. A.
Published: July 2007

In computer simulation calculations, a necessary and sufficient condition for the prediction of relative stability between various crystal structures is a potential energy function that includes a three‐body contribution as well as the usual two‐body contribution. The order of structural stability with increasing three‐body strength parameter, Z*, is h.c.p. → is h.c.p. → f.c.c. → β‐tin → diamond → graphite and structural transformations from diamond → β‐tin and from graphite → diamond are predicted to occur at high pressure. For the diamond structure, marked contraction of the first surface layer spacing is predicted for the (100), (110), and (111) planes with dimer formation on the (100). The reduced surface tension, σ*, decreases with increase of Z* for all three planes and falls in the expected experimental range.
Annihilation of Frenkel Pairs in B.C.C. Metals (α‐Iron). III. The Case of a Hydrostatically Compressed Lattice
Authors: Ratishvili I. G.
Published: July 2007

A model describing the Frenkel pair annihilation process in a free b.c.c. lattice is extended to the case of the lattice subjected to external stresses. It is assumed that new conditions of the annealing can be considered in the calculations by a relevant modification of the field of potential barriers dividing the different positions of the Frenkel pair components.
ESR and Optical Absorption Study of the Tl0 (1) Center in NaCl. A Stable Laser‐Active Type Defect
Authors: Nistor S. V. , Heynderickx I. , Goovaerts E. , Bouwen A. , Schoemaker D.
Published: July 2007

The properties are given of the laser‐active type Tl0(l) center in NaCl as derived from an ESR and optical study. The higher thermal and optical stability of this center in NaCl compared to KCl, RbCl, and KBr suggests that it could be a candidate for a viable laser‐active system. The procedure for optimal production of Tl0(l) in NaCl is distinctly different from that known for this center in the other hosts. Optical absorption bands at 470 and 1060 nm, both possessing σ‐character, are attributed to the Tl0(l) center in NaCl and correspond to the so‐called “F‐like” and the pump laser transitions, respectively, of Tl0(l) in the other hosts.
Free Carrier Dynamics and Energy Transfer to the Si Lattice during Pico and Nanosecond Nd Laser Pulse Irradiation
Authors: Baeri P. , Harith M. A. , Russo G. , Rimini E. , Giulietti A. , Vaselli M.
Published: July 2007

Transmission experiments of Nd: YAG laser pulse of 25 ps and 30 ns duration through 100 μm thick silicon single crystal allow the determination of the free carrier absorption cross section, σFC = 5 × 10−18 cm2, and of the Auger decay constant, γ3 = 8 × 10−31 cm6 s−1. These two parameters are used in the numerical solution of a set of coupled differential equations which describe the space and time evolution of carrier concentration, carrier energy, and lattice temperature. A comparison with time resolved reflectivity data reported in literature, allows the determination of the energy relaxation time constant, τe ≈︁ 1 ps. The validity of the thermal model used to describe laser annealing in the nanosecond regime is also discussed and justified.
A Model for Band‐Gap Shrinkage in Semiconductors with Application to Silicon
Authors: Landsberg P. T. , Neugroschel A. , Lindholm F. A. , Sah C. T.
Published: July 2007

A model for band‐gap shrinkage in semiconductors is developed and applied to silicon. A survey of earlier experiments, and of new ones obtained by the authors, gives agreement between the model and experiments on n‐ and p‐type silicon which is good as far as transport measurements in the ≈︁ 300 K range by various authors are concerned. In fact, the discrepancies between theory and experiment are no worse than the discrepancies between the experimental results of various authors. It also gives a good account of recent optical determinations of the band‐gap shrinkage at 5 K. The model is based on Debye screening and, apart from effective masses, temperature, dielectric constant, and carrier concentrations, which must enter any theory of gap shrinkage in some form, it is parameter‐free. The model gives in Gaussian units ΔEg =126,6(m*/m)1/2 ×(ϵ/10)−3/2(n/1018)1/6 meV in the degenerate limit.
New Experimental Evidence Concerning the Nature of L, M, and N Lines in ZnSe:Co
Authors: Sokolov V. I. , Surkova T. P. , Kulakov M. P. , Fadeev A. V.
Published: July 2007

The absorption and electroabsorption spectra of ZnSe:Co in the region of the L, M, and N lines are investigated. The experimental data indicate that these lines arise from transitions to excited states of d7 configuration. The electroabsorption spectrum exhibits new α°, β°, γ°, δ°, and ϵ° lines that have intense LO phonon replicas. These lines result from the formation of donor excitons according to the scheme d7 + hω → [d6e]. The d7 configuration ground state 4A2 is separated from the bottom of the conduction band by 2.565 eV assuming a hydrogen‐like electron binding energy.
Direct Observation of Bound Excitons in the Spectra of Resonance Secondary Emission of LiH:Mg Crystals
Authors: Pilipenko G. I. , Plekhanov V. G. , Tyutyunnik V. I. , Tyutyunnik O. I. , Gavrilov F. F.
Published: July 2007

An experimental study is made of resonant secondary emission, reflection, and excitation spectra which indicate the existence of bound excitons in LiHMg crystals. The spectroscopic properties of the bound exciton are studied by selectively excited luminescence and resonant Raman scattering. The resonance energy of the bound exciton is estimated to be 4.842 eV. For the first time, the transformation of resonant Raman scattering into luminescence is found when the incident photon energy is above the resonance.
ESR of Isolated Mn2+ Centers in Alkali Chlorides
Authors: De Keersgieter A. , Callens F. , Baroen M. , Matthys P. , Boesman E.
Published: July 2007

The ESR spectra of isolated Mn2+ centers in NaCl and KCl single crystals, formed by a high uniaxial stress, are observed at room temperature. The formation mechanism of these impurity centers with cubic symmetry is discussed. From the analysis of the spectra it is concluded that these Mn2+ centers are identical with centers, formed by heating unstressed NaCl:Mn2+ and KCl:Mn2+. Similarities and differences with uniaxially stressed alkali chlorides, doped with V2+ ions, are also analysed.
Site Selective Spectroscopy of ZnS:Tm3+ Crystals
Authors: Zimmermann H. , Boyn R.
Published: July 2007

The method of site selective excitation spectroscopy is applied to Tm3+ ions in ZnS crystals containing various codopants. By dye‐laser 4f–4f excitation at helium and neon temperatures it is possible to separate three different sites, for which 4f–4f emission, excitation, and absorption spectra are determined in the range of several free‐ion transitions. Energy spectra are deduced from these data, and some considerations are made about the nature of the sites observed.
MNDO Calculation on Molecular Clusters Chosen to Model the Bonding of Oxygen in Silicon
Authors: Ying Xie , Snyder L. , Sahu S. N. , Corbett J. W.
Published: July 2007

MNDO (Modified Neglect of Diatomic Overlap) method cluster computations are carried out in studies of the bonding state and behavior of oxygen in a silicon lattice. These studies are compared with similar ab‐initio work. The MNDO studies find the most stable bonding state for oxygen to be a pyramidal ylid structure. The mixing of 3s with 3p orbitals in the lone pair of the trivalent silicon in the pyramidal ylid is believed to stabilize this structure. This point remains to be explored in ab‐initio computations where C2v symmetry is assumed. Since these MNDO calculations find the observed puckered bond‐centered interstitial oxygen configuration to be less stable than the pyramidal ylid structure, it is concluded that the present MNDO parameters may not be optimum for silicon.
Pairs of F‐Centres and F− Impurities in KCl Studied by ENDOR
Authors: Söthe H. , Studzinski P. , Spaeth J.‐M.
Published: July 2007

By optical bleaching of F‐centres in KCl doped with KF at −60 °C about half of the F‐centres can be converted into room temperature stable pairs of F‐centres and F− impurity ions, which have a single optical absorption band peaking at a 5% lower energy than the F‐centre. With electron nuclear double resonance (ENDOR) could be shown that the F− impurity resides in a [200] next‐nearest position and not in a [110] nearest halogen position. The K+ ion between the anion vacancy and the F− ion is displaced by ≈︁ 11% towards F−. Its superhyperfine constants show a strong temperature dependence.
Induction of Superconductivity by the Inner Contact Potential
Authors: Shapiro B. Ya.
Published: July 2007

The inner contact potential changes the density of electron states and increases the value of the electron–electron interaction. A theory of the inhomogeneous superconducting state in these systems is presented. The critical temperature and magnetic field are calculated.
Theory of the Ferroelectric Superconductors
Authors: Mańka R. , Molak A.
Published: July 2007

The behaviour of the ferroelectric superconductors described by a BCS Hamiltonian and interband electron‐phonon interaction is studied.
Electron–Electron Interaction and Isotope Effects in Superconducting Metal–Hydrogen (Deuterium) Systems Like PdHx(Dx)
Authors: Drechsler S.‐L. , Zhernov A. P.
Published: July 2007

Using various experimental and theoretical data the origin of the inverse isotope effect (IIE) for the superconducting transition temperature Tc of the PdH(D) system is analyzed on the basis of a solution of the Berk‐Schrieffer equations. It is found that the IIE can be described at weak or intermediate anharmonicity of the electron–optical phonon interaction β = (λ/ −1≈︁to 0.14, standard or slightly enhanced values of Coulomb pseudopotential μ', and weak spin fluctuations λsp ≈︁ 0.05 to 0.1. The importance of the electron‐electron interaction in determining the superconducting properties of non‐stoichiometric PdHx(Dx) and some other hydrides (deuterides) is emphasized.
Phonon Structure (α2F(Ω)) of Superconducting V3Si Monocrystals by Tunneling Measurements
Authors: Schumann J. , Otschik P.
Published: July 2007

On the surface of single phase V3Si single crystals, tunnel junctions with different superconducting electrodes are prepared, which have reproducible and stable characteristics. In the second derivative of the (U)‐characteristics well defined extrema in the energy range of phonon excitations 15 meV ≦ E ≦ 50 meV may be detected. The general capability of the tunnel element on V3Si for phonon investigations is proved by the detection of phonon structures of the Pb and In top electrodes. By detailed investigations in the temperature range of T ≦ Tc (V3Si) and T ≦ Tc (V3Si) it is verified, that the structures found in tunnel characteristics are caused by phonon induced effects in V3Si. The solution of the Eliashberg equation, obtained by means of experimental tunneling data, yielded for the electron‐phonon coupling constant λ = 2 ∫ α2(Ω) F(Ω) dΩ/Ω ≈ 1. This allows the conclusion to classify V3Si as a superconductor with strong electron‐phonon interaction.
Calculation of Potential Energy Parameters for the Silicon—Carbon System
Authors: Takai T. , Halicioǧlu T. , Tiller W. A.
Published: July 2007

Specific parameters involved in two‐body plus three‐body semi‐empirical potential energy functions for the silicon, carbon, and silicon carbide systems are calculated. Excellent reproduction for various energetic and structural quantities is found.
161Dy Mössbauer Effect in Dy2Fe14B
Authors: Gubbens P. C. M. , Van Der Kraan A. M. , Buschow K. H. J.
Published: July 2007

The 161Dy Mössbauer effect is measured in the tetragonal compound Dy2Fe14B at various temperatures between 4.2 and 300 K. The spectra are analysed in terms of two subspectra associated with the two crystallographic Dy sites in the structure of Dy2Fe14B. It is found that the crystal field split ground state corresponds to Jz = −15/2 for both the types of sites. The results of bulk magnetization measurements and the temperature variation of hyperfine field and quadrupole splitting are used to derive values of the magnetic coupling constant between the Fe moments (JFeFe) and the rare earth and iron moments (JFeR).
Wannier‐Mott Exciton States in Two‐Layer Periodic Structures
Authors: Pokatilov E. P. , Beril S. I. , Fomin V. M. , Pogorilko G. A.
Published: July 2007

A theoretical research of Wannier‐Mott exciton states in two‐layers periodic structures is carried out. The potentials of the electron‐hole interaction and the self‐action are found on the basis of exact solution of the Poisson equation with account of the anisotropy of dielectric constants of these structures. It is shown that the self‐action effect influences essentially the exciton energy spectra, leading to the renormalization of the energy band gap. Analytical results are obtained for the limiting case of thin‐layer period structures.
Planar Channeling Radiation of Positrons and Electrons at Moderate Energies in Simple Crystals
Authors: Dedkov G. V. , Shidov E. Kh.
Published: July 2007

A theoretical calculation of the positron and electron Kumakhov radiation peak energies at planar channeling in simple crystals (diamond, silicon, and germanium) is made. The particle energies are in the range 28 to 56 MeV. The calculation is based on a potential model, proposed earlier. A detailed comparison with experiments and other theoretical models is given.
Optically Detected Cyclotron Resonance in AgBr
Authors: Booth I. J. , Schwerdtfeger C. F.
Published: July 2007

Optically detected magnetic resonance (ODMR) studies reveal cyclotron resonance of electrons and holes in AgBr as well as a number of paramagnetic resonances already observed by other workers. Cyclotron resonance signals are observed in the recombination radiation from excitons bound to iodine isoelectronic impurities. Asymmetry of the electron‐cyclotron resonance gives a measure of the nonparabolicity of the conduction band which results in an energy dependent effective mass. The enhanced trapping of electrons on iodine centres by interaction with LO phonons is discussed.
Order Parameter Functional Method in the Theory of Atomic Ordering
Authors: Gusev A. I. , Rempel A. A.
Published: July 2007

An order parameter functional method is proposed which permits the description of structural order‐disorder‐type phase transitions and combines features of the cluster variation method and static concentration waves method. The method proposed is employed to describe the atomic ordering in a nonstoichiometric niobium carbide.
Semiclassical Theory of Dechanneling and the Diffusion Coefficients
Authors: Nitta H.
Published: July 2007

A new expression of the “local diffusion coefficient” for dechanneling theory is derived within a framework of the semiclassical approximation. By making use of the present result, the diffusion coefficient for nuclear contribution is calculated in detail. It is shown that the nuclear diffusion coefficient can be approximately represented in the form Dn=DK‐o+DL where Dk‐o and DL are the Kitagawa‐Ohtsuki's formula and the Lindhard's formula, respectively. These conclusions correspond to Matsunami‐Howe's proposal and Fuschini‐Uguzzoni's computer simulation.
Dynamical Nature of Superexchange Interaction in Y3Fe5O12 Studied by Neutron Spectroscopy
Authors: Ligenza S.
Published: July 2007

Inelastic neutron scattering is used to investigate spin interactions in polycrystalline Y3Fe5O12. Neutron spectra due to local spin interaction are observed and interpreted by the 6S5/2‐term splitting of Fe3+ ions located in octahedral (a)‐sites and tetrahedral (d)‐sites of the garnet structure. The observed neutron spectra are analyzed using a phenomenological spin Hamiltonian assuming combined interaction of magnetic and quadrupole electric moments of the 3d5 electron shell with a static magnetic molecular field and a static electric field gradient, respectively. The neutron energy peaks connected with various magnetic coordination numbers at (a)‐sites and (d)‐sites are obtained. This phenomenon is interpreted as due to the dynamical nature of superexchange interaction of Fe3+ ions in YIG. The dynamical interactions bring about fluctuations of the magnetic moments with a relaxation rate between 10−8 s > τm > 10−13 s. The quadrupole and superexchange interaction parameters are determined to D = −0.508 meV and Es = 3.00 meV, respectively. The effect of lowering of magnetic moments of Fe3+ ions situated on (a)‐ and (d)‐sites is discussed.
Commensurate‐Incommensurate Transition in a Quasi‐One‐Dimensional Conductor with a Nearly 1/3‐Filled Band
Authors: Fischbeck H. J. , Mertsching J.
Published: July 2007

The commensurate‐incommensurate transition in a quasi‐one‐dimensional system with commensurability three is studied using the continuum, the mean‐field, and the one‐kink‐band approximaions. Except for special cases, the commensurate‐incommensurate transition is discontinuous in general. The lattice distortion, the chemical potential, and the spectrum of the electrons at the transition are calculated and related to known results from alternative approximations.
Electronic Structure of Perfect Chemisorbed Monolayers and of Disordered Surfaces
Authors: Beckmann A.
Published: July 2007

On the basis of a simple tight‐binding model, the local spectrum of a semiinfinite crystal is discussed on the surface layer of which both the local energy levels and the transfer integrals are changed with respect to the bulk. The two cases of an ordered and a substitutionally disordered surface are considered. For the transfer integrals the multiplicative type of Shiba is generally presumed. It is shown that for considerable deviation of the surface transfer integrals from those of the bulk (i) the local density of states shows a quasi two‐dimensional behaviour, and (ii) surface state bands may split into two separate parts.
Ionicity and Static Ionic Charge
Authors: Enders P.
Published: July 2007

Recently, Falter et al. have proposed an ionicity scale basing on the longitudinal effective charge eL (that is wrongly identified with the static ionic charge q). It is shown that ionicities that vary linearly with q or eL are, however, not appropriate to construct structural maps, and it is concluded that nor q, nor eL is very relevant or even a measure for structural properties.
Measurements of Proton Channeling Energy Losses in Silicon in the Intermediate Energy Region
Authors: Gehrmann P. , Lenkeit K. , Stolle R.
Published: July 2007

The energy loss of protons in the energy region from 40 to 350 keV is measured for (110), (100), and (111) planar channeling, for 〈110〉, 〈111〉, 〈112〉 axial channeling, and for random directions in silicon. The investigations are carried out by means of the transmission experiment using silicon targets of several thicknesses. Stopping power values are derived from the peak and the leading edge of energy spectra for channeled particles. Special procedures are applied to correct the obtained stopping power data with respect to the target thickness. In the case of leading edge the stopping power data depend strongly on the target thickness. It is shown that only the extrapolation to zero thickness leads to correct stopping power values for best channeled particles. It is found that the ratio of channeled to random stopping power shows a maximum in the energy region at about 70 keV. Here the stopping power for channeling and random directions reach their largest value, too.
Electronic Contribution to the Ordering Energy of a Binary Alloy
Authors: Bortel K.
Published: July 2007

The band theory of the phase transitions in the binary alloy of transition metals is investigated by means of the Landau theory and coherent potential approximation, CPA. The investigation of the mechanisms responsible for the transition from disordered to ordered phase of an alloy is the main purpose of the considerations. It is shown that the asymmetry of interactions and energy transfer are the primary causes of the ordering process in a binary alloy.
Low Energy Electron Exchange Excitation of 4f Transitions and Location of 4f Levels in Rare Earths
Authors: Bauer E. , Kołaczkiewicz J.
Published: July 2007

Eu, Gd, and Tb single crystal films and atomically dispersed layers adsorbed on W(110) surfaces are studied by low energy electron loss spectroscopy. A very sharp dominant loss peak at about 4 eV is analyzed in detail and attributed to spin exchange excitation of the 4f level. This interpretation agrees very well with self‐consistent spin‐polarized free atom and band structure calculations. The results are compared with XPS and other experimentel data which leads to a reconsideration of the interpretation of the 4f XPS binding energies.
Bound Phonons
Authors: Balkanski M. , Jouanne M. , Kanehisa M.
Published: July 2007

The strong electron‐phonon coupling, occurring when the energy of the electronic excitation is comparable to that of the LO mode, is treated in two cases: (i) the electronic state is a localized impurity level and (ii) the electronic excitation is an interband transition continuum between valence or conduction bands in degenerate n‐ and p‐type silicon. In the first case the mixed bound electron‐phonon state has as many bound‐phonon levels as electronic excitation energies, deduced from detailed band structure, coming in close coincidence with the LO‐phonon energy. In the second case the electron‐phonon coupling results in frequency shifts and phonon line deformations due to phonon binding to the electronic states.
Optically Induced Nernst‐Ettinghausen Effect in the Far Infrared and Strong Magnetic Fields in HgTe and InSb
Authors: Knap W. , Stȩpniewski R. , Fantner E.
Published: July 2007

Voltage generation in strong magnetic fields (0 to 6 T) in HgTe and n‐InSb under far‐infrared illumination is observed. The fine structure of the observed voltage versus the magnetic field is interpreted as being due to transitions between Landau sublevels. A new method of experimental determination of the nature of the observed voltage is presented. It is shown that for both the materials investigated, the observed phenomenon is due to the optically‐induced Nernst‐Etting‐ hausen effect. From the qualitative analysis it is concluded that at low temperatures and in quantisizing magnetic fields, the phonon drag is the main process responsible for the observed voltage in both, InSb and HgTe.
Light Transmission at the 1s‐Exciton Resonance of CdS in the Presence of a Density Profile of Excitons
Authors: May V.
Published: July 2007

The pumped transmission spectrum of a CdS platelet at the 1s‐exciton resonance is calculated for the case of high exciton densities and spatial inhomogeneous distribution of excitons. The lowering of the Is level and the increase of damping due to high excitations are considered linear in the exciton density. The corresponding wave equation for the electric field strength with spatial varying dielectric function is solved approximately. A remarkable dependence of the transmission coefficient on the density profile in the platelet is obtained.
A Localized Orbital Description of Ge‐Si Alloy
Authors: Erbarut E. , Tomak M.
Published: July 2007

The simplest Gaussian orbitals of S and P symmetry are employed for the study of electronic band structure of Ge‐Si alloy. A reasonably good description of the valence and conduction band is obtained.
On the Conductivity Mechanism of Weakly Doped Polyacetylene
Authors: Frankevich E. L. , Kadyrov D. I. , Sokolik I. A. , Pristupa A. I. , Kobryanskii V. M. , Zurabyan N. Y.
Published: July 2007

The decrease of the electrical conductivity of pristine and weakly iodine‐doped polyacetylene, (CH)x, films under the action of an external magnetic field has been revealed. The dependence of the relative decrease of the (CHx) electrical conductivity in the external dc magnetic field is typical for magnetic field spin effects with participation of pairs of paramagnetic species with spin 1/2. The magnetic electron spin resonance signal detected via the (CH)x electrical conductivity change has been revealed. The dependence of the magnetic field effect on the ac magnetic field frequency (up to 9 kHz) has been measured. A model of the observed phenomenon has been proposed based on the magnetic field effect on the probability of the charge carrier hop in pairs of paramagnetic species “polaron‐defect” in the conjugated chain.
On the Suppression of X‐Ray Anomalous Transmission by Acoustic Oscillations
Authors: Entin I. R.
Published: July 2007

It is shown that the Debye‐Waller factor describes correctly the Borrmann effect acoustic suppression only within the short‐wave range (λs ≪ τ, λs ultrasonic wavelength, τ extinction length). The suppression factor is expressed both, for long‐wave (λs ≫ τ) and intermediate (λs ≈ τ) cases. An analysis of the published experimental data establishes that an incorrect description of the suppression effect by the Debye‐Waller factor can cause an error of several orders when determining displacements by the measured attenenuation of anomalous transmission. In some cases experimental results demonstrate the main contribution of X‐ray acoustic resonance to be suppression effect.
Dynamic and Static Aspects in the Theory of Itinerant Spin Glasses
Authors: Kolley E. , Kolley W.
Published: July 2007

A superfield formulation of the Langevin dynamics for itinerant‐electron spin glasses is developed. Before taking the quenched configuration average the field‐theoretical scheme involves the supersymmetry. For comparison the standard replica method combined with Bogolyubov's variational principle is used to get the statics. The spin‐glass transition temperature is calculated in the presence of spatial fluctuations as well as in the mean‐field limit.
Magnetic Properties of Amorphous Fe90.6Zr9.4
Authors: Beck W. , Kronmuller H.
Published: July 2007

The temperature dependence of the spontaneous magnetization, Ms, and the magnetization curve of melt‐spun amorphous Fe90.6Zr9.4 alloys are investigated by means of a SQUID magnetometer in the temperature range 4.2 K < T < 150 K, and for magnetic fields 1 mT < μ0H < 4 T. At low magnetic fields, μ0H < 80 mT, Ms is found to obey a T2 law whereas for μ0H >0.27 T Bloch's T3/2‐law is obtained. No evidence for a spin‐glass transition at low temperatures can be detected. The high‐field susceptibility points to the presence of circular quasidislocation loops.
Chemical Shifts and EXAFS of the LIII Absorption Discontinuity of Dysprosium in Some of Its Compounds
Authors: Islam M. S.
Published: July 2007

The LIII X‐ray absorption discontinuity of dysprosium is studied in the pure element and in some of its binary and ternary compounds. A graph of the chemical shift ΔE in binary compounds against the effective charge q on the absorbing atoms is plotted. This plot is helpful in determining the effective charges in ternary compounds in which they cannot be calculated theoretically. The EXAFS (extended X‐ray absorption fine structure) in the vicinity of discontinuities is also recorded and interpreted with the help of the graphical method given by Lytle et al.
Green Function, Local Density of States, and Statistical Equilibrium in Muffin‐Tin Systems
Authors: Lenk R. , Solbrig H.
Published: July 2007

For a muffin‐tin potential a multiple scattering problem where all scatterers act only aS black‐box entities is separated in general form from those relations which yield the wave field within a, given muffin‐tin sphere. This separation renders possible the construction of the Green function. In comparison with other formulations the role of the fields incident at the individual scatterers is emphasized. In a second step the close connection is employed between the Green function and the density matrix in a statistical equilibrium state. This yields an explicit and exact formula for the statistical mean values of all intensity‐like quantities which are bilinear in the angular momentum projections of the incident fields. Reciprocity properties are treated, too.
Optical Switching Behaviour in Two‐Beam Experiments with CuCl
Authors: Levy R. , Bigot J. Y. , Frindi M. , Hönerlage B.
Published: July 2007

An investigation is made of the transmission properties of a test beam through CuCl samples and through Fabry‐Perot etalons containing CuCl under simultaneous excitation of a pump beam. For appropriately chosen photon energies of the two beams, the transmission of the test beam through the sample decreases due to nonlinear absorption, or increases when the sample is in a F.P. resonator. The switching behaviour indicates that the nonlinear absorption and dispersion properties of CuCl depend on the exciton and biexciton population dynamics.
Optical Absorption Studies on Colored KCl:Na:Pb Crystals
Authors: Dalal M. L. , Sivaraman S. , Murti V. Y. G. S.
Published: July 2007

The nature of the Pb‐centers in colored KCI:Na:Pb crystals is studied by optical absorption spectroscopy. The crystals are colored by exposure to X‐rays and y‐rays as well as by electolysis and nonstoichiometry. A large number of absorption bands are observed most of which are attributed to either the Pb centers or the Pb° centers.
Study of the Sensitization Effect of Eu2+ Ions on the Trivalent Rare‐Earth Fluorescence in CdF2 Crystals
Authors: Jouart J. P. , Bissieux C. , Mary G. , Egée M.
Published: July 2007

It is shown that, under visible or near infrared excitation, the Eu2+ ion sensitizes the [RE3+, F] fluorescence in as‐grown and annealed CdF2 crystals (RE  Sm, Eu, Er) cooled at 77 K and previously irradiated with UV light. Non‐radiative energy transfer from Eu2+ in cubic surroundings to minor [RE3+, F] complexes, via the conduction band of the host lattice, is identified. The sensitization mechanism is based on the photoionization of Eu2+ ions and requires the simultaeous presence of neutral interstitial fluoride ions (F), each associated with a RE3+ ion. This study demonstrates the existence of three kinds of interstitial fluoride ions in CdF2. From the excitation spectrum of the RE3+ fluorescence, a value (1.1 eV) is deduced for the photoionization threshold of Eu2+ ions in CdF2, close to the theoretical value obtained from the Pedrini et al. model. Besides, the Eu3+ fluorescence spectroscopy is used to determine the symmetry of the site occupied by Eu2+.
On the pressure dependence of grüneisen parameter in solids
Authors: Kumari M. , Dass N.
Published: July 2007

A simple theory is developed to study the pressure dependence of Grüneisen parameter, γ. The final results show that γ varies linearly with the pressure, that is, γ(p, T) = γ(0, T) – ηp where η is found to be a pressure‐independent but temperature‐dependent parameter. Moreover, it is shown that η is related to some other thermodynamic parameters and hence can have positive or negative magnitude which in turn will decide whether γ(p, T) decreases or increases with pressure. The calculated values of γ(p, T) in the whole range of pressure and temperature are found in very good agreement with the experimental results in case of all the solids studied like NaCl, CaF2, MgO, quartz, Na, K, and Li. Further, it is shown that the second Grüneisen parameter, q, and the Debye temperature, θ, can also be calculated as a function of pressure with the help of the present theory.
Electron potential energy near the ferromagnetic metal– vacuum interface
Authors: Gabovich A. M. , Voitenko A. I.
Published: July 2007

The charge electrostatic energy W(z) near the surface of a metal with an arbitrary spontaneous magnetization 0 ≦ ζ ≦ 1 is calculated using the random‐phase approximation for the metal dielectric function. It is shown that the variation of the surface value W(0) under the ferromagnetic transition amounts up to 12% of its original value and depends on free‐electron concentration. Such a variation can be observed in LEED experiments.
Density functional pseudopotential calculation of the cohesive properties of Ordered (CsCl‐Type) compounds of nontransition metals
Authors: González D. J.
Published: July 2007

The density functional formalism is used to calculate the electron density, equilibrium volume, and heat of formation of ordered (CsCl‐type) alloys of nontransition metals. A cellular method is employed to separate the alloy in atomic cells with appropriate matching conditions at the cell boundaries. The ion cores are substituted by empty core pseudopotentials. The results are compared with other theoretical results and with the experiment.
Time‐resolved luminescence of CdGaInS4 under pulsed laser excitation at 30 K
Authors: Colocci M. , Fermi F. , Querzoli R. , Vinattieri A.
Published: July 2007

A detailed study of the time‐resolved luminescence of CdGaInS4, after pulsed laser excitation at T = 30 K is presented. Results are given on the time‐resolved spectra in the range 50 ns to 10 ms of delay time with respect to excitation, on the time decay of the luminescence intensity at 610 nm, and on the time evolution of the integrated luminescence intensity for different emission wavelengths. Finally a simple model is presented for the recombination processes at low temperatures yielding good agreement with the experimental data.
Spectial features of lattice dynamics and electron‐phonon interaction in Re
Authors: Shitikov Yu. L. , Tulina N. A. , Zemlyanov M. G.
Published: July 2007

The dynamic properties of the rhenium lattice are investigated using the methods of neutron and point‐contact spectroscopy. Based on the double differential cross‐sections of inelastic neutron scattering measured at 300 and 500 K the phonon spectra of rhenium are reconstructed with regard to the coherence effects. From the results of measurements of the second derivative of the current–voltage characteristic made in various Re point‐contact, a mean point‐contact function of electron‐phonon interaction is obtained. The features of electron–phonon interaction function coincide within the experimental error with those of Re phonon spectrum on one and the same energy interval. Thus, the phonon spectrum participates entirely in the formation of the electron–phonon interaction function.
Thermal expansion coefficients of ternary AIIIBV solid solutions
Authors: Pietsch U.
Published: July 2007

As experimentally established recently the atoms of a particular sublattice of ternary AIIIBV solid solutions are elongated out systematically of their regular positions. Using a Keating like approach for the strain energy of the relevant binary compounds the thermal expansion coefficient of some ternary solid solutions are calculated by means of a perturbation treatment relative to the values which are interpolated linearly between these ones of binary end components. The calculated bowing parameters coincide with the experimental findings published till now.
Theoretical analysis of the chemical activivity of noble gas atoms in silicon
Authors: Gagarin S. G. , Mudryi A. V. , Pushkarchuk A. L. , Ulyashin A. G. , Teterin Yu. A.
Published: July 2007

The possibility of formation of a chemical bond between noble gas atoms (Ne, Ar), ion‐implanted into silicon, and matrix atoms is treated theoretically in a cluster representation using both, the scattered‐wave Xα (SW‐Xα) and complete, neglect of differential overlap (CNDO/2) electronic structure methods. It is shown that the presence of noble gas atoms in the silicon lattice results in formation of inner valence molecular orbitals (MO) when Ar and Ne atoms interact with Si atoms. A theoretical analysis is made of the results of possible investigations of these structures by photo‐electron spectroscopy measurements.
Radiation yield of high‐energy electrons in thick crystals
Authors: Baier V. N. , Katkov V. M. , Strakhovenko V. M.
Published: July 2007

The radiation of high‐energy electrons moving near the crystalline axes in thick crystals is analysed. The radiation brightness and yield are discussed. The results obtained are compared with experiment.
Electron states in periodic dislocation networks in semiconductors
Authors: Nabutovskii V. M. , Romanov D. A.
Published: July 2007

The misfit dislocation electron propagation is studied as an example of quantum particle behavior in a periodic network. Transitions in the net sites are described by the S‐matrix formalism. The energy band structure for a rectangular network cell is investigated. Particularly, the analytical form of the dispersion law is obtained in the quadratic cell case. It is shown that the incommensurability of lattice periods leads to an intrinsic stochasticity of the electron spectrum. Anomalies of conductivity, galvanomagnetic, and high‐frequency properties as functions of band occupation and applied electric and magnetic fields are discussed.
EPR of Nd3+ ions in Y‐type zeolites
Authors: Trif Eleonora , Nicula Al.
Published: July 2007

An analysis is made of the EPR spectrum of Nd3+ ions entered by ion exchange (1%) in Y‐type zeolite. The hydrated samples show an isotropic EPR signal at geff ≈︁ 2.73. This resonance arises from ions located in sites of C3 symmetry. The experimental EPR signal is identified with the theoretical isotropic EPR transitions at g = 2.62. The isotropy of the EPR signal advocates the pathology of the zeolite crystals, i.e. the absence of the complete long‐range order in Y‐type zeolites.
Fractional moments. New source of information in radiospectroscopy
Authors: Nigmatullin R. R.
Published: July 2007

A new fractional moments method for the absorption and dispersion curves in radiospectroscopy is suggested. The fractional moments solve the problem of moments existing in the mathematical statistics and enable one to restore the complex susceptibility ξ(ω) and the relaxation function Φ(t) completely. The bond between the fractional moments of the ξ(ω) and the function Φ(t) is found. The possible applications of this method for experimental measurements are shown.
Conductivity tensor of a two‐dimensional electron gas in a strong magnetic field in higher orders of perturbation theory. Quantum hall effect
Authors: Balev O. G. , Boiko I. I.
Published: July 2007

The components of the conductivity tensor σ are considered for the case of a strong magnetic field H. The investigation of the higher orders in perturbation theory up to the fourth order in static scattering potential shows that for an electric field E under the condition E ≪ E0  [heH3/2m2c3]1/2 the Hall conductivity magnified image and the transverse conductivity σyy ∼ exp (−E/E2here Ne, is the carrier concentration. In virtue of the extreme small collisional contribution to the conductivity the picture of the quantum Hall effect is similar to that for an ideal noninteracting two‐dimensional electron gas.
Off‐diagonal conductivity and magnetization of PdFe, PdCo, and PdNi alloys in coherent potential approximation calculated on the basis of realistic models of component densities of states
Authors: Voloshinskii A. N. , Ryzhanova N. V. , Vishnekov L. Yu. , Obukhov A. G.
Published: July 2007

The concentration dependence of the off‐diagonal component of the electroconductivity tensor and that of the average magnetic moment are calculated for PdFe, PdCo, and PdNi alloys in the coherent potential approximation (CPA). These calculations are based on realistic models of the component densities of states (DOS's). Experimental and theoretical results are compared.
The influence of nonparabolieity on self‐consistent treatment for GaAsAlxGa1–xAs heterojunction
Authors: Milanović V. , Tjapkin D. , Šašić R.
Published: July 2007

The self‐consistent determination is analysed of the relevant parameters of a GaAsAlxGa1–xAs heterojunction in the presence of nonparabolicity of bands. Starting from Kane's theory, a suitable form of the Schrödinger equation for electrons is given. It is shown that there are, generally, two different energy spectra. The notion of an extended effective mass is introduced, which are depending on the potential, the energy gap, and subband index. The numerical analysis of results is performed on GaAsAl0.4Ga0.6As heterojunction. These numerical results confirm theoretical conclusions exposed in the first part of the paper.
Raman scattering studies of mobile ions in superionic conductor hollandites
Authors: Shibata Y. , Suemoto T. , Ishigame M.
Published: July 2007

The Raman spectra of the superionic conductors K1.6Mg0.8Ti7.2O16, Cs1.2Mg0.6Ti7.4O1.6, and (KTI)1.6Mg0.8Ti7.2O16 are measured in the frequency range from 5 to 1000 cm−1. In the range from 100 to 1000 cm−1 Raman spectra hardly show alkali ion dependence. On the contrary, in the frequency range from 5 to 100 cm−1, an additional Raman band is observed. This Raman band shows alkali ion dependence. By using the Frenkel‐Kontorova model for the hollandite crystal with the given configuration of the mobile ions, it is found that the dependence of vibrational frequency of mobile ions with kinds of alkali ion is well explained and that the concept of “super unit cell” that is introduced by Beyeler is very useful to explain the Raman bands which are observed below 100 cm−1 in hollandite crystals.
Dislocation core models and their positron annihilation effects
Authors: Shen J. Q. , Lung C. W. , Wang K. L.
Published: July 2007

Positron annihilation parameters with three simplified dislocation core models are calculated. The positron annihilation effect at a dislocation line is mainly contributed by the dislocation core. The positron annihilation effects at pure dislocation lines are large enough to be measurable though they are much weaker than at vacancies.
Low‐temperature properties of antiferromagnetic GdRhxSny, compound
Authors: Rojek A. , Sulkowski C. , Zygmunt A. , Kozlowski G.
Published: July 2007

Magnetic and electric resistivity measurements on single crystals of GdRh1.07Sn4.21 compound are performed. The compound is antiferromagnetic with a Néel temperature TN = 11.6 K. The temperature dependence of resistivity has four temperature regions: T3/2, T2, T, and ln T. The data are considered in terms of coexistence of local moment antiferromagnetism of the Gd atoms and localized spin fluctuations (lsf) or itinerant electron ferromagnetism of the Rh atoms.