bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tunneling in k‐space. Application to degenerate valence band in the infinite spin–orbit interaction limit
Authors: Dargys A. , Rudolph A. F. 
Published: July 2007

AbstractHole tunneling between light and heavy mass bands in a homogeneous semiconductor due to a strong electric field is analyzed in the framework of spherical and at k = 0 degenerate bands when the spin–orbit interaction is infinite. Nonperturbative techniques are used to solve the problem. As in the case of zero spin–orbit interaction it is found that intervalence band tunneling takes place in a ring‐shaped volume whose symmetry axis is parallel to the electric field.
Influence of hydrogenation on the hyperfine interactions in (Y0.97Hf0.03)Fe2
Authors: Budzyński M. , Kochetov O. I. , Subotowicz M. , Niezgoda H. , Spustek H. , Tańska‐Krupa W. 
Published: July 2007

AbstractMeasurements of the parameters of the hyperfine interactions in (Y0.97Hf0.03)Fe2 before and after hydrogenation are performed by means of the time differential perturbed angular correlations (TDPAC) and Mössbauer effect (ME) methods. After hydrogenation of the intermetallic alloys superparamagnetic clusters are formed; they have equal anisotropy fields but their axes of easy magnetization are distributed randomly.
Quantum Theory of Channeling in Deformed Crystals
Authors: Kirilyuk A. P. 
Published: July 2007

AbstractA description of charged particle channeling in crystals with smooth strain fields of arbitrary nature and form is built within the framework of quantum mechanical approach based on the dynamical diffraction theory. General features of the solution obtained are discussed, and its particular applications to the studies of beam deflection by bent crystals and dechanneling on extended distortions are outlined, special attention is given to the influence of channel curvature variations. The effect of bulk retrapping into the channel is predicted and shown to play an important role for the case of alternating bending.
Stochastic Forces in Anharmonic Crystals and on Their Surfaces
Authors: Wiatrowski G. 
Published: July 2007

AbstractThe phonon theory for inhomogeneous thin films with fluctuation of equilibrium position is developed in the anharmonic approximation. The analytical relations describing the stochastic forces as a term of the system memory with fluctuating parameter, δ, the quasi‐exponential autocorrelation functions, and the asymptotic behaviour of the system at low temperatures are obtained. The present results concern the surface as well as the bulk, so that the spatial distribution of phonon excitations in the system with and without fluctuations, in dependence of the initial conditions, can be discussed. Moreover, some conclusions on the local and global melting points in thin films are presented.
Temperature Dependence of Second‐ and Third‐Order Elastic Constants of Rare Gas Solids
Authors: Lehri S. , Shanker J. 
Published: July 2007

AbstractThe three‐body interaction model recently developed by Lehri and Verma for rare gas solids is extended to include the effect of thermal contributions and zero‐point energy. The generalized expressions for second‐and third‐order elastic constants which are valid at any temperature are reported. These expressions are applied for evaluating the temperature dependence of second‐ and third‐order elastic contants for Ne, Ar, Kr, and Xe.
Quantum Interference in a Series of Metallic Rings in a Magnetic Field
Authors: Bulka B. R. 
Published: July 2007

AbstractThe role of quantum interference of free electrons in a one‐dimensional normal metal ring in a magnetic field is considered. Calculations of the transmission between two perfect wires connected to the ring through ideal splitters are presented. The transmission of the single ring is a symmetric function of the enclosed magnetic flux and oscillates with the basic period hc/e. However, in an infinite series of rings the interference conditions vary from ring to ring which leads to averaging of the transmission. The localization length shows oscillations with the period hc/2e. Recent resistance measurements on small metallic systems in a magnetic field are discussed in the framework of this model.
Quadrupole Scattering in PrNi5
Authors: Lippold B. , Müller H. , Mahmoud S. 
Published: July 2007

AbstractThe influence of the dipolar and quadrupolar scattering due to the 4f electrons on the temperature dependence of the electrical resistivity in PrNi5 is investigated. Using the experimental values of polycrystalline PrNi5 and the isostructural LaNi5 as well as the crystalline electric field splitting scheme it is found that the quadrupole scattering is the dominating one.
Stimulated Brillouin Scattering of EM Wave Propagating Obliquely in a Magnetoactive Solid State Plasma
Authors: Maheshwari K. P. , Tarey G. 
Published: July 2007

AbstractAn investigation is made of stimulated Brillouin scattering of an electromagnetic wave propagating obliquely with the external magnetic field in n‐InSb. As the pump wave propagates in the semiconductor, the electrons acquire oscillatory drift velocity. The oscillatory drift velocity and the magnetic field of the pump interact with low frequency acoustic perturbation to produce high frequency side band which further interact with the pump to produce low frequency ponderomotive force responsible for driving the original density perturbation. The nonlinear dispersion relation is obtained for the coupled mode. The results show that the growth rate for SBS increases with the obliquity of the pump. The growth rate is found to decrease with the angle of scattering. In the weak magnetic field regime (0 ⪅ ωc/ωa ⪅ 0.7) the growth rate decreases with the magnetic field whereas in the strong magnetic field regime (0.7 ⪅ ωc/ωa ⪅ 0.9) the growth rate increases with the magnetic field.
Etude par RMN de la mobilité de l'ion flour au sein de la solution solide Pb1−xBixOxF2−x
Authors: Laborde P. , Villeneuve G. , Reau J. M. 
Published: July 2007

AbstractL'étude par RMN de 19F de la solution solide Pb1−x, BixOxF2−x (0 ≦ x ≦ 0,67) a montré que les anions oxygéne se placent préférentiellement dans les sites normanx (et relaxés), ronfirmant ainsi les hypothbses émises lors de l'étude de Pb1−xBixOxF2−x par diffraction de neutrons. Les mouvements des ions fluor détectés par RMN peuvent être considérés comme non‐diffusifs.
Measurement of Oscillator Strengths of “F2A” Centres in MeF2:A+ (Me = Ca, Sr; A+ = Li+, Na+, K+)
Authors: Hamaïdia A. , Margerie J. 
Published: July 2007

AbstractFrom combined EPR and optical measurements, the oscillator strengths f are determined of absorption bands of “F2A” centres in CaF2,:Li+ CaF2:Na+ SrF2:Na+ and SrF2:K+. The results are compared with f‐values obtained from the observed lifetimes of the first excited level of the same centres.
On the Interband Absorption in Size‐Quantized Bi Films
Authors: Zalużny M. , Okulski W. 
Published: July 2007

AbstractThe influence of the size‐quantization on the interband absorption spectrum of Bi films with normal along the trigonal or binary axis is investigated. The optical conductivity is evaluated on the basis of the two‐band model, taking into account the k‐dependence of optical matrix elements.
Photostimulated Reorientations of PO2− Centers in Alkali Halides
Authors: Lohmeier F. J. 
Published: July 2007

AbstractReorientations of molecular PO2− centers following an electronic transition are investigated in different alkali halides. Photoinduced reorientations which occur during the vibrational relaxation, as well as thermal reorientations are studied. The results are compared with an earlier study of the isoelectronic AsO2− center.
Reorientation of Hole Centers in CaWO4 Monitored by EPR and Optical Absorption
Authors: Herget M. , Hofstaetter A. , Nickel T. , Scharmann A. 
Published: July 2007

AbstractIn CaWO4 intrinsic hole centers are created by X‐irradiation and localized at one oxygen of the WO4 tetrahedron at temperatures below 150 K. More information about this trapping mechanism can be obtained by EPR measurements with applied uniaxial pressure and by optical absorption measurements. The results point to a Jahn‐Teller instability as the main part of this mechanism leading to a trigonal distortion of the tetrahedron.
Detailed Study of IR Absorption Spectra of Manganese–Zinc Ferrites
Authors: Katsnelson E. Z. , Karoza A. G. , Meleshchenko L. A. , Pankov V. V. , Khavkin B. G. 
Published: July 2007

AbstractIR absorption spectra of the Mn1−xZnxFe2O4 ferrite‐spinel system are investigated in the frequency range ν = 800 to 40 cm−1. The spectra of the second derivative d2T/dν2 are obtained from the computer processed experimental transmission spectra (T). On their basis the two complex bands ν1 and ν2 of the IR spectra are resolved into three and four components, respectively (for zinc ferrite — into three) and for the band ν3 — into two components. From the concentration dependences of the bands νm(n) (m, n = 1, 2, 3, 4) it is concluded that the vibrations, the frequencies of which are independent of zinc ferrite concentration in certain ranges x, correspond to those of separate bonds MnO, ZnO, FeO i.e. they are characteristic with respect to frequency. The spectra of the spinels investigated are analyzed in accord with the irreducible representations of the point group F43 m(Td2). Small tetrahedral structure distortions due to higher covalency of the ZnO bonds and the availability of the Jahn‐Teller ions are considered.
Temperature Dependence of the Static Structure Factor for Liquid Bi, Ga, Sb, and Sn
Authors: Zou Xian‐Wu , Jin Zhun‐Zhi , Tang Sheng‐Qun 
Published: July 2007

AbstractA simple approach is presented to calculate the temperature dependence of the static structure factor for non‐simple liquid metals, based on the hard sphere cluster model and considering the temperature dependence of the hard sphere diameters and atomic percentage of the second type of clusters. The structure factors of liquid metals are calculated for Bi (T = 300, 500, 550, 800, and 950 °C), Ga (T = 50, 200, 550, 800, and 1000 °C), Sb (T = 660 and 800 °C), and Sn (T = 250, 300, 700, 900, and 1100 °C). The calculated results are in good agreement with experiments.
Group‐Theoretical Analysis of the Symmetry Changes in R2MX4 Compounds
Authors: Abdi S. , Mlik Y. , Ben Ghozlen M. H. 
Published: July 2007

AbstractCommensurate subgroups of Pnma are obtained by a group‐theoretical method started from the Landau theory of continuous phase transitions. The investigated high symmetry points are Γ, X, Y, Z, R, T, S, U, Σ, Δ, and A. These points belonging to the first Brillouin zone, are the most involved ones according to literature experimental data. The selected order parameter is defined in the basis associated with the corresponding irreducible representation of Pnma, so it may represent any physical property. The results are given in table form together with some useful information concerning the low symmetry structure. A particular interest is devoted to R2MX4 compounds (R = organic cation; M = Cu, Cd, Hg, Zn,…; X = Cl, Br) where the parent structure has Pnma symmetry.
Lattice Vibrations in Mixed Alkali Halide Crystals
Authors: Gupta B. R. K. 
Published: July 2007

AbstractThe phonon dispersion curves of two mixed alkali crystals KCl0.5Br0.5 and K0.5Rb0.5Cl are calculated using the extended three‐body force shell model (ETSM). The ETSM developed in the present study consists of two short‐range overlap potential parameters (A, B), two long‐range three‐body interaction parameters (f0, r0f′0), two distortion polarizabilities (d1, d2), and two modified shell charge parameters (Y1, Y2). The results on phonon dispersion curves are found to agree reasonably well with the experimental curves of Beg and Kobbelt.
Mode Grüneisen Parameters and Pressure‐Induced Phase Transition of Tetrahedral Compounds
Authors: Kagaya H.‐Matsuo , Soma T. 
Published: July 2007

AbstractThe pressure effect on the phonon frequency, i.e. the mode Grüneisen parameter of AIP, AlAs, and AlSb is studied from the electronic theory of solids. Then, a linear correlation by Weinstein between the TA‐mode Grüneisen parameter γ at the point X and the phase transition pressure Pt, is not necessarily satisfied for all of tetrahedral covalent crystals.
Effective‐Atom Fluctuations and the Representative Effective Atom in Liquid Nickel. A Cluster Study within the Muffin‐Tin Concept
Authors: Solbrig H. 
Published: July 2007

AbstractSuperposition potentials are calculated for 50 atomic spheres in a big relaxed cluster. Two conclusions can be drawn: (i) Effective‐atom fluctuations contribute less than 10% to the observed d‐band broadening. (ii) There are two straightforward approaches to a representative effective atom. The first one attempts approximating highly probable cases whereas the second one accounts for fluctuations, too.
LO‐Phonon Modes Bound to Neutral Impurities in Polar Semiconductors. II. Special Cases and Experimental Results
Authors: Monecke J. , Cordts W. , Irmer G. , Bairamov B. H. , Toporov V. V. 
Published: July 2007

AbstractIn a previous paper the Fröhlich interaction between charge carriers bound at impurities and LO‐phonons in polar semiconductors is considered within second‐order perturbation theory. Here special cases including the possibilities of degenerate electronic ground and excited states are discussed. Jahn‐Teller like splittings of degenerate ground states as well as Lamb‐Retherford like splittings of degenerate excited states are obtained. Besides renormalized electronic excitations the solution of the eigenvalue problem yields phonons bound to neutral imuprities (dielectric modes). Results of Raman spectroscopic determinations of these modes in GaP:S, Te, Si, and Sn are presented and their experimental binding energies are compared with theoretical results.
Auger Neutralization of Fast Ions at Surfaces
Authors: Taute Elke 
Published: July 2007

AbstractAuger neutralization of fast He++ moving parallel to a solid surface at constant distance s is discussed. Results for the transition rate as a function of s and the impact energy of the ions are presented. The orientation for the He+2p‐states is also calculated leading to the conclusion that orientation effects due to Auger neutralization cannot be neglected a priori compared to those due to charge exchange.
Cluster Identities for the Ising Model as a Basis for Simple Effective Field Approximations Discerning between Various Lattices with the Same Coordination Number
Authors: Tomczak P. , Sarmento E. F. , Siqueira A. F. , Ferchmin A. R. 
Published: July 2007

AbstractIdentities are proposed for clusters of N interacting Ising spins. For a single spin they reduce to Callen identity, for a spin pair to that of Bobák and Jaščur. It is shown that effective field approximations for spin correlations lead to different Curie temperatures for lattices of the same coordination number but different dimension.
Magnetic Field Dependences of Two Kinds of Structural Transition Temperatures of CeAg1−xInx
Authors: Kurisu M. , Kadomatsu H. , Fujiwara H. 
Published: July 2007

AbstractThe magnetic field H dependence of the cubic‐tetragonal transition temperature, TM1, of the CeAg and TM2 of the CeAg1−xInx system with x = 0.01 and 0.02, are determined from resistivity measurements. TM1 is increased with H, while TM2 is decreased with H. These differences between the magnetic field dependences of TM1 and TM2 are attributed to their origins: 4f quadrupole ordering for TM1 and d‐band Jahn‐Teller effect for TM2, respectively.
On Some Optical Properties of NaF Single Crystals X‐Ray Irradiated under DC Fields
Authors: Veeraiah N. 
Published: July 2007

AbstractResults of the following measurements on NaF single crystals X‐ray irradiated at room temperature under different de fields (0 to 20 kV/cm) are reported: (i) growth of absorption bands (F‐ and M‐bands) with de field, (ii) thermal bleaching characteristics of the absorption bands, (iii) thermo‐luminescence in the temperature range 30 to 300 °C, and (iv) the optical absorption of NaF samples X‐ray irradiated at elevated temperatures (100 and 190 °C) under de fields. These results are explained as due to the generation of negative ion vacancies near the dislocations by the de field and the formation of F‐centres on X‐ray irradiation. From these results it is also possible to establish a correlation between colour centre destruction and thermoluminescence peaks.
On the Screening Length of Disclinations in Amorphous Structures
Authors: Richter A. , Romanov A. E. , Pompe W. , Vladimirov V. I. 
Published: July 2007

AbstractDisclinations represent the main defects beside dislocations in topologically disordered structures. The stress field and the energy of a disclination depend strongly on the boundary conditions, mostly the presence of a free surface. Stress field, self‐energy, and pair interactions of disclinations in a finite cylinder are calculated pointing out the relevance of additional interactions of disclinations with the surface, if the disclination is not positioned in the center of the cylinder. The energy of the model system is always diminished by such surface effects. Numerical calculations of the screening length in a disclination network for an amorphous structure show that a cut‐off radius only exists because of the interaction between defects. The screening length is about three times larger than the average distance between disclinations and depends on the disclination density. The cut‐off radius corresponds to the creation of internal surfaces resulting in an additional screening of defects.
Self‐Consistent Calculations of the Melting Criterion Based on Lattice Instability
Authors: Malinowska‐Adamska C. 
Published: July 2007

AbstractMelting criterion as a function of the external pressure for cubic crystals is examined using Plakida and Siklòs's model for the lattice dynamics of crystals by computing the ratio, xm, of the rootmean‐square relative displacement of neighbouring atoms and the interatomic spacing at the instability temperature for a number of cubic metals belonging to different groups of the periodic table. This ratio has nearly the same value for elements of one particular group but exhibits wide variation from one group to another. The variation is in accordance with the nature of binding in metals.
Invariant Harmonic Oscillator Functions. IV. The Thirty Two Point Groups
Authors: Schöpp J. , Wöhlecke M. , Scherz U. 
Published: July 2007

AbstractA method is given to calculate symmetry adapted harmonic oscillator functions for all 32 point groups. Due to reduction theorems between the various groups all functions can be found from those of the cubic groups and D4. The cubic groups are dealt with in the foregoing papers and here explicitely the oscillator functions for the group D4 are given.
Thermal Conductivity and Thermoelectric Figure of Merit of Bi1−xSbx Films With 0 < x ≦ 0.3
Authors: Völklein F. , Kessler E. 
Published: July 2007

AbstractThe thermal conductivity λ and thermoelectric figure of merit z of Bi1−xSbx films with 0 < x ≦ 0.3 and thicknesses from 30 to 400 nm are measured in the temperature range 80 to 400 K. The lattice thermal conductivity λϱ is determined from the measured total thermal conductivity λ and the calculated charge carrier contribution λe. The results are discussed in the framework of earlier proposed models for the charge carrier and phonon heat transport in polycrystalline films. The Sb‐concentrations for maximum z‐values of the films are established.
Collective Excitations in the Extended Hubbard Model with Intrasite Attraction
Authors: Kostyrko T. 
Published: July 2007

AbstractCollective excitations in the superconducting state of an extended Hubbard model with an intrasite attraction are investigated using the random phase approximation method. The results for the energy of gapless excitations are consistent with the well known result of Anderson in the limit of weak attraction and the result of the perturbation theory (with respect to the band term) in the limit of strong attraction. Investigating the dependence of the excitation energy on the density of electrons in the band conditions are found of instability of the singlet superconducting state with respect to the disordered state (for attractive intersite interactions) and to the charge ordered superconducting state (for intersite repulsion).
Mixed Valence Properties of CeM2Si2 (M  Mn, Fe, Co, Ni, Cu)
Authors: Ammarguellat C. , Escorne M. , Mauger A. , Beaurepaire E. , Ravet M. F. , Krill G. , Lapierre F. , Haen P. , Godart C. 
Published: July 2007

AbstractLattice parameter measurements in the temperature range 12 to 300 K and LIII edge measurements in the range 4.2 to 300 K are performed on the compounds CeM2Si2 (M  Mn, Fe, Co, Ni, Cu) to study the valence changes. Magnetic measurements (1.6 to 600 K) for fields up to 1 T confirm antiferromagnetism of CeMn2Si2 (TN ≈ 370 K) and show enhanced Pauli paramagnetism of mixed valence compounds with M  Fe, Co, Ni with spin fluctuation temperatures around 150 K with Co, Ni. Transport properties measurements show that the compounds with M  Co, Ni, Fe do not become superconducting down at 18 mK and that a Fermi liquid behaviour exists in the range 40 to 70 K.
On the Effective Mass of Pekar's Polaron
Authors: Davydov A. S. , Enolskii V. Z. 
Published: July 2007

AbstractThe polaron motion in Pecar's model is shown to be possible only in ionic crystals with positive dispersion Ω2(κ)  Ω + νκ2, at the velocity ν ≦ ν0. The expression for the polaron effective mass up to v20 is obtained.
Selfconsistent Discrete Equations for Nonlinear Defects in Peierls Systems with Broken Electron–Hole Symmetry
Authors: Drechsler S. L. , Heiner E. , Malek J. 
Published: July 2007

AbstractThe SSH‐Hamiltonian extended by long‐range hopping parameters and long‐range interatomic elastic forces is investigated. A discrete system of electron eigenvalue equations together with self‐consistency conditions for atomic displacements is derived and numerically solved for soliton states in polyacetylene. As a novel feature it is found that (1) the soliton level is slightly shifted from the exact midgap position and (2) a weak internal charge structure appears for neutral solitons and antisolitons and gives rise to a long‐range repulsive interaction between them.
Non‐Stationary Stimulated Acousto‐Optical Interactions in Solid Dielectrics
Authors: Bukowski R. , Kleszczewski Z. 
Published: July 2007

AbstractA theoretical analysis of non‐stationary interactions of intensive laser light and a bulk acoustic wave in dielectric crystals is made. The time dependence of the source of both, light waves and acoustic wave is considered. All fundamentals kinds of acousto‐optics interactions, viz. Stokes and anti‐Stokes processes, as well as the generation of acoustic waves by “mixing” two light beams are discussed.
The Memory Effect in Empirical Descriptions of Dielectric Relaxation
Authors: De La Fuente M. R. , Jubindo M. A. Pérez , Solier J. D. , Tello M. J. 
Published: July 2007

AbstractAn analysis of the memory effect in some empirical descriptions which account for the dynamical dielectric response of a great number of real systems is presented. The study is carried out considering the relaxations as stochastic processes. The involved time‐dependent transition rates are directly related with the memory effect. A comparison among underlying dipolar dynamics for the most usual empirical descriptions is made.
Self‐Consistent Description of the Effect of Point Defects on Spectrum and Dynamic Deceleration of Dislocations
Authors: Malashenko V. V. , Sobolev V. L. , Khudik B. I. 
Published: July 2007

AbstractA self‐consistent equation of dislocation motion in elastic fields created by defects is obtained. The deceleration force value is calculated due to defect collisions and it is shown to have a quasiviscous character under low velocities.