bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantum Correction to the Classical Plasma Frequency in the Long‐Wavelength Limit
Authors: Pal R. K. , Tripathy D. N. , Mandal S. S. 
Published: July 2007

AbstractA negative frequency shift is observed to the classical plasma frequency ωpl in metals in the long‐wavelength limit (k = 0) by analysing the zeroes of the dielectric function of a degenerate many‐electron system evaluated beyond the random phase approximation (RPA). This is achieved by accounting for the non‐RPA contributions arising from the virtual plasmon effects of the effective interaction lines associated with the local field correction diagrams. Redefining the critical wave vector kc the experimentally observed frequency shift to ωpl is reproduced at k = 0 in Li, Al, and Na metals. The theory clearly indicates an extension of the plasmon modes to a momentum transfer region beyond kRPAc.
Analytical Theory of Crystal Growth of Two‐Component Systems II. Nonequilibrium Properties
Authors: Pfeiffer H. , Haubenreisser W. 
Published: July 2007

AbstractThe rate equations for two‐component crystal growth developed in part I of this paper are formulated on the basis of nonreactive interfacial elementary rates for attachment, detachment, and diffusional processes of species. For the attachment and detachment processes a symmetrical dynamics of interchange of species is assumed. An evaluation of the rate equations at small deviation from thermodynamic equilibrium is performed in continuous Bragg‐Williams approximation (CBWA) for a steady‐state growth. The in CBWA derived steady‐state nonequilibrium properties (interface profile, concentration profiles of the components, growth rate, kinetic, and distribution coefficient) are described analytically and discussed for ideal binary mixtures with atomically rough interfaces and normal crystal growth mechanism.
Study of the “Blocking Effect” for Fast Electrons in a Silicon Crystal
Authors: Popov D. E. , Plotnikov S. V. , Kaplin V. V. , Vorobiev S. A. 
Published: July 2007

AbstractThe effect of intensity inversion in the patterns of angular distribution of the electrons with energies up to 2.5 MeV scattered along the low‐index directions of a thin silicon crystal is studied. This phenomenon is observed when the angle of beam incidence relative to a low‐index axis of the crystal is large compared with the critical angle of channeling. The discussion is given in the scope of a model based upon bound states of channeled electrons, as a result of excitation of secondary bound states of electrons with atomic rows and planes.
The “Acoustic Local” Mode of H, D, and F in Amorphous Germanium and Silicon
Authors: Shen S. C. , Fang C. J. , Cardona M. 
Published: July 2007

AbstractThe quasi‐local mode of H in a‐Ge and a‐Si associated with the TA‐phonon branch is studied as a function of temperature of measurement and annealing. Isotopic substitution experiments are also performed. The results confirm the mass defect model recently proposed for this local mode. A similar local mode is observed for a‐Si:F, without hydrogen. It is much stronger than the corresponding mode of a‐Si:H for the same dopant concentration. Likewise in a‐Si:F the TO phonon band, as observed in ir absorption, is stronger than in pure and hydrogenated a‐Si and appears shifted to 510 cm−1. This shift, which is not seen in the Raman spectrum, is attributed to the strong polarity of the Si‐F bond.
EPR Spectra of Cr5+ Ions in KCl Crystals
Authors: Alybakov A. A. , Toichiev N. 
Published: July 2007

AbstractEPR, optical, and IR absorption spectra of X‐irradiated KCl crystals doped with K2CrO4 and K2Cr2O7 are studied. It is ascertained that the impurity enters as chromate in both cases and there are two centre types — isolated CrO ions and CrO ions coupled with divalent cation impurities. The X‐irradiation results in the formation of paramagnetic CrO3−4 centres with monoclinic local symmetry Cs whose excessive negative charge is compensated by an anion vacancy. The EPR spectrum due to these centres is described by a spin‐Hamiltonian for S = 1/2 with gx = 1.948, gy = 1.953, gz = 1.967. The x‐axis of the g‐tensor is oriented along 〈001〉 and two other principal axes along the directions of 〈110〉 type.
Micromagnetic Theory of Phase Transitions in Inhomogeneous Ferromagnets III. Non‐Local Landau‐Ginzburg Theory
Authors: Herzer G. , Fähnle M. , Egami T. , Kronmüller H. 
Published: July 2007

AbstractIn amorphous ferromagnets spatially fluctuating exchange interactions give rise to a critical behaviour substantially different from crystalline magnets. Within the framework of a molecular field theoretical approach, a non‐local Landau‐Ginzburg equation is formulated for phase transitions in amorphous ferromagnets taking into account cooperative spin fluctuations. This is done by introducing a correlated molecular field, which can only vary on larger scale than the spin correlation length. Therefore, the manner how the structural disorder affects the critical behaviour changes with temperature. To some extent, the theory interpolates between the so‐called homogeneous and inhomogeneous versions of the molecular field theory so far used in the literature. The theory is capable of reproducing satisfactorily the experimentally observed curvatures of the Arrott plots and the temperature dependence of the paramagnetic susceptibility in disordered ferromagnets.
Perturbation‐Theoretical Model Calculation of the Lattice Mechanics of Ionic Crystals in the Point‐Dipole Approximation
Authors: Basu A. N. , Sengupta S. 
Published: July 2007

AbstractA perturbation‐theoretic model calculation is developed in the point‐dipole approximation for the study of ionic crystals from a knowledge of the Hartree‐Fock wave functions of the free ions that constitute the solid. The salient features of the present calculation are that it a) provides a method for calculating the different lattice static and dynamic properties of a crystal directly from the free ion wave functions without using any crystal property; b) clearly gives an empirical justification for the major assumption of the phenomenological shell model; c) develops a new method for evaluating the Coulomb overlap interaction; d) suggests a modified short‐range polarisation mechanism; and lastly e) shows how far actually the free ion wave functions are realistic as a starting point. The method is applied to calculate a number of lattice mechanical properties of the two ionic crystals namely, NaCl and KCl. Despite the simplicity of the approach the agreement, with observation for both the crystals is quite impressive. The source of the remaining discrepancy is discussed.
Resonance Scattering of Hard Synchrotron Radiation and Neutrons by Nuclei in Crystals
Authors: Haas M. A. , Hizhnyakov V. V. 
Published: July 2007

AbstractA resonant scattering of hard synchrotron radiation and neutrons by nuclei in a crystal is considered at a recoil energy of R≫ ℏ\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \omega \limits^ \sim $\end{document} and the lifetime of the compound nucleus τ0 ≈︁ 2π/\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \omega \limits^ \sim $\end{document}, with \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \omega \limits^ \sim $\end{document} being the characteristic phonon frequency. In these cases the main contribution to the scattering is made by the secondary particles emitted in the relaxation process of the recoil energy of the compound nucleus. This emission is called hot nuclear fluorescence (hot emission of neutrons). Numerical calculations are performed to show the strong dependence of this type of resonant scattering spectra on the parameters R/ℏ\documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \omega \limits^ \sim $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \omega \limits^ \sim $\end{document}τ0, and local lattice dynamics. The requirements for the corresponding experiments, following from this study are considered. A possible set‐up for an experiment is proposed which allows to study the hot nuclear fluorescence without spectrometer.
Polarized Electronic Absorption, Emission, and Excitation Spectra of Cs2CdCl4:Ni2+ Single Crystals
Authors: Ghosh B. , Mukherjee R. K. 
Published: July 2007

AbstractThe polarized absorption spectra are reported of Ni2+ doped in Cs2CdCl4 single crystals at 295 and 77 K in the range 5000 to 25000 cm−1. Emission and excitation spectra are also reported in the range 11000 to 25000 cm−l. The Ni2+ ions occupy the Cd2+ sites in octahedral geometry and the spectra are satisfactorily interpreted in terms of a cubic ligand field model including spin‐orbit coupling. The ligand field parameters evaluated to best fit the observed spectra are Dq = 600 cm−1, F2 = 1260 cm−1, F4 = 87 cm−l, und λ = 290 cm−l. No strong spectral evidence for tetragonal distortion is observed.
Reduction of the Energy Splitting of an E‐State by Jahn‐Teller Coupling and by Covalency
Authors: Biernacki S. W. 
Published: July 2007

AbstractA semiempirical LCAO method is used for the calculation of the spin‐orbit and spin‐spin splitting parameter K of the 5E state of Fe2+ in ZnS. The estimated reduction due to covalency effect of the spin‐orbit parameter is 15% and the reduction of the angular orbital momentum is 20%. The calculated value of the Jahn‐Teller energy on the base of the multimode model of coupling is 7.0 em−1.
ESR and NMR Study of Mixed Yttrium–Lutetium–Aluminum Garnets
Authors: Asatryan H. R. , Petrosian A. G. , Sharoyan E. G. , Wósjcik M. , Zbieranowski W. T. 
Published: July 2007

AbstractESR of Mo3+ ions and NMR of 27Al nuclei is investigated in mixed single crystals of yttrium‐lutetium‐aluminum garnets (Y1−xLux)3Al5O12, where O ≦ x ≦ 1. Several new centres of Mo3+ and 27Al compared with Y3Al5O12 and Lu3Al5O12 single crystals are revealed associated with symmetry and crystalline field parameter changes at isomorphous substitution of Y3+ ions in the rare‐earth sublattice of the garnet by those of Lu3+. Symmetry, nearest coordination, and parameters of spin‐Hamiltonians are estimated concerning all of Mo3+ and 27Al centres in (Y1−xLux)3Al5O12, at x < 0.15.
Quadratic Response of the Electron Gas. Inclusion of Local Field Corrections
Authors: Paasch G. , Heinrich A. 
Published: July 2007

AbstractFor the description of the static quadratic response of the electron gas several quadratic response functions are defined in analogy to the linear response theory. These response functions can be determined self‐consistently using the known quadratic response function for non‐interacting electrons. Local field corrections describe the influence of exchange and correlation beyond the random phase approximation. They are included in the self‐consistent procedure in the framework of the Hubbard‐Singwi approach.
Comments on Many‐Body Dielectric Relaxation in Solids
Authors: Jonscher A. K. , Dissado L. A. , Hill R. M. 
Published: July 2007

AbstractA discussion is given elaborating some salient features of a recently proposed many‐body theory of dielectric relaxation in solids. It is pointed out that orientational polarisation involves disorder as an essential element and this leads to important conclusions regarding the relaxation processes. Three types of transitions, outlined in the original theory, are discussed in some detail and distinctions are made between “large” and “small” transitions. The physical nature of correlated states is discussed and some comments are made about energy loss processes involved in the many‐body model of dielectric relaxation, with particular reference to the frequency‐independent ratio of energy lost per cycle to energy stored in polarisation.
Scattering of Phonons by Charge Carriers and Peripheral Phonons and Lattice Thermal Conductivity of a Metal act Low Temperatures. Application to Sb
Authors: Dubey K. S. 
Published: July 2007

AbstractThe role of the scattering of phonons by charge carriers (electrons and holes) and peripheral phonons in the calculation of the lattice thermal conductivity of a metal at low temperatures is studied. The entire study is made in the frame of the Callaway integral using the Ziman expression for the scattering relaxation rate of phonons by the charge carriers, Sb is taken as an example. The percent contributions due to non‐peripheral and peripheral phonons are also calculated and it is found that the percent contribution due to peripheral phonons increases with increasing temperature. The separate contributions due to each scattering process to the total lattice thermal resistivity are studied and it is found that at low temperatures, the lattice thermal resistivity of Sb is mainly due to the charge carriers. The effect of the characteristic temperature θ* which differentiates the peripheral phonons from non‐peripheral phonons, on the lattice thermal conductivity is also studied by calculating the total lattice thermal conductivity of Sb for different values of θ*. The contribution of the correction term due to the three‐phonon normal processes to the total phonon conductivity of Sb is studied and it is reported that the contribution due to the correction term is very small compared to the total lattice thermal conductivity, so one can neglect its contribution.
Orientational Population of Quantum States for Fast Electrons in Planar Channeling
Authors: Plotnikov S. V. , Popov D. E. , Rozum E. I. , Kostareva O. G. , Vorobiev S. A. 
Published: July 2007

AbstractThe strong orientation dependence of angular distributions for 4.9 MeV electrons channeled along the (110) atomic planes through crystalline Si is observed and investigated in detail. For electron transmission along the 〈111〉 axis and (110) planes a considerable increase of the X‐ray yield is observed. These experimental results are explained by the orientation population of the different quantum states for channeled electrons.
Decay of Magnetic Fluctuations in Thin Films
Authors: Duszewski J. 
Published: July 2007

AbstractThe dynamic behaviour of fluctuations in magnetization is considered in inhomogeneous systems represented by thin films. The presented approach is a generalization of Oguchi's method's for the description of the spin correlation decay. The time‐dependent correlation function is obtained for thin films. In the case of infinite sample it is reduced to the Ornstein‐Zernike form. The damping and the diffusion coefficients are evaluated. The spin correlation time is of a local character and may be treated as a parameter for the determination of the surface fluctuations observed in experiments.
Galvanomagnetische und thermoelektrische Transportuntersuchungen an Sb2Te3
Authors: Simon G. , Eichler W. 
Published: July 2007

AbstractEs werden erstmalig alle zwölf galvanomagnetischen Schwachfeldtransportkoeffizienten sowie die beiden Seebeck‐Koeffizienten von Sb2Te3 im Temperaturbereich von 100 bis 360 K angegeben. Ferner wird die Änderung einiger dieser Effekte bei Pb‐Dotierung beobachtet. Ausgehend von qualitativen Unterschieden im Transportverhalten von Sb2Te3 und der Analogiesubstanz Bi2Te3 werden Modelle zur konsistenten Beschreibung der Transporteigenschaften von Sb2Te3 diskutiert.
An Ising Model Analysis of Dielectric Polarization. I. Analysis for the Dielectric Response of Infinite and Finite Dipolar Chains in Dielectrics
Authors: Bozdemir S. 
Published: July 2007

AbstractAn analysis of the dielectric polarization for a model system consisting of a one‐dimensional chain of dipoles with nearest neighbour interaction only is presented. In this model, each dipole is assumed to have two components: One is normally oriented between two localized states in a plane perpendicular to the chain axis, while the other is oriented along the chain. The model further presumes that the reorientation probability of any dipole located on the site chain has a time‐dependent parameter, depending at any instant upon the momentary orientation of neighbouring dipoles. Glauber's time‐dependent Ising model formalism is applied to this situation. It is shown that the decay function of a single dipole located in either an infinite or a finite chain results in a non‐Debye‐type form, due to the many‐body nature of the induced molecular moments.
Three‐Body Interaction in the Fluorite Structure Ionic Crystals
Authors: Basu A. , Sengupta S. , Basu A. N. 
Published: July 2007

AbstractThe importance of the three‐body interaction in the study of simple ionic solids with centrosymmetric structure is both, theoretically and empirically well established. But so far there is no attempt to investigate its significance in the properties of ionic crystals belonging to fluorite and antifluorite structures. In contrast to said alkali halides the absence of the centre of symmetry for this structure implies complications which make a direct estimate of this effect quite difficult. From an analysis of the elastic data the inadequacy of a two‐body central interaction to describe the elastic constants of such crystals is demonstrated. An order of estimate is made of the three‐body interaction in the elastic properties of the calcium fluorite crystal from the HF wavefunctions of the ions. For the other crystals where the Clementi wavefunctions for the ions are not available the estimate is done directly from the elastic constants. The order of magnitude of this interaction obtained for the different crystals is comparable and lies in the range observed for other ionic solids. Further this investigation apart from indicating the importance of the three‐body interaction also accounts for the anomalies in the previous calculations. Finally some of the limitations of the present calculation are pointed out.
Electrical Conductivity Mechanism in Zinc and Copper Substituted Magnetite
Authors: Srinivasan G. , Srivastava C. M. 
Published: July 2007

AbstractThe electrical transport properties in polycrystalline ferrous zinc ferrites, ZnxFe3−xO4 (x = 0, 0.2, 0.4, 0.6) and ferrous zinc–copper ferrites, ZnxCu0.1Fe2.9‐xO4 (x = 0, 0.1, 0.2, 0.3, 0.4), are studied by measuring the conductivity and the Seebeck coefficient. The conductivity is shown to arise from the phonon‐induced tunneling of electrons from one B site to another in the cubic phase of these ferrites.
Anisotropy of Exciton Polaritons and Polariton‐Phonon Interaction in 2H‐PbI2 Crystals. II. Anisotropy of the Photoluminescence of 2H‐PbI2
Authors: Biellimann J. , Gubanov V. , Meyer B. , Schwab C. 
Published: July 2007

AbstractA detailed investigation of the anisotropy of the photoluminescence spectra of 2H–PbI2 as a function of the orientation of the electrical and propagation vectors of the emitted light is reported. The results are analysed in terms of exciton polariton emission and polaron mass anisotropy.
The Incommensurate Peierls Phase of the Quasi‐One‐Dimensional Fröhlich Model with a Nearly Half‐Filled Band
Authors: Mertsching J. , Fischbeck H. J. 
Published: July 2007

AbstractThe one‐dimensional Fröhlich model with a nearly half‐filled band is solved in the mean‐field approximation for finite temperatures, extending a recent ground‐state calculation by Brazovski et al. The commensurate–incommensurate phase transition is shown to be continuous, and the corresponding transition temperature is calculated as a function of the chemical potential or the electron density.
Phonon Dispersion Relations in the Bi0.95Sb0.05 Alloy
Authors: Sosnowski J. , Bednarski S. , Bührer W. , Czachor A. , Maliszewski E. 
Published: July 2007

AbstractNeutron inelastic scattering experiments are made using triple‐axis spectrometers at the EWA and DIORIT reactors to determine the phonon dispersion relations in dilute Bi0.95Sb0.05 alloy at room and liquid nitrogen temperatures. The shifts of phonon frequencies for the Γ–T, Γ–X, and Γ–L directions are determined.
Vk Center in Cesium Halides by the MSXα Method
Authors: Oliveira P. M. , Maffeo B. 
Published: July 2007

AbstractThe electronic structures of the Vk center in CsCl, CsBr, and CsI are calculated using the MSXα method. Comparison with two experimental energy values is made, and very good agreement is found. The internuclear distances in the halogen molecular ion are estimated and the results compared to those obtained by other workers.
Optical and Thermal Stability of Ag Centres in RT X‐Irradiated KCl:Ag Crystals
Authors: Sridaran P. , Bhuniya R. C. , Ratnam V. V. 
Published: July 2007

AbstractThe optical absorption, thermoluminescence (TL), monochromatic TL, and TL spectra of potassium chloride crystals doped heavily with silver are measured after X‐irradiation at RT. The effect of optical bleaching on X‐irradiated crystals with light in the F, E, and B bands both, separately and together, as well as thermal annealing effects of the defect centres are studied. It is found that in the heavily doped crystals the role of holes in the form of doubly charged impurity ions (Ag++) is predominant compared to holes of the host lattice in the form of Cletc. The Ag ions stabilised only at cation sites in different valence states are involved in the recombination‐luminescence process. From the TL spectral data of the glow peaks preferential redistribution of the excess electron centres on optical bleaching is evident. The results support that tunnelling of electrons is responsible for the observed TL and TL spectral data.
Vacancy Formation Enthalpy in Cadmium by Positron Lifetime Measurements
Authors: Mascher P. , Breitenhuber L. , Puff W. 
Published: July 2007

AbstractBecause of a strong prevacancy effect in cadmium the assumptions of the trapping model seem to be fulfilled rather badly. Therefore the formation enthalpy of monovacancies is also determined by methods using the trapping model only to some extent or not at all. H is obtained as (0.39 ± 0.04) eV (from the trapping model), H = (0.42 ± 0.02) eV (from the inflection point), and H = (0.45 ± 0.08) eV (from the threshold temperature).
Liquid Metal Pair‐Correlation Functions from Empirical Pair Potentials
Authors: McGurn A. R. , Esterling D. M. 
Published: July 2007

AbstractThe pair‐correlation functions of liquid Fe, Cu, Ag, Au, and V are calculated from empirically determined potentials obtained from the solid state of these substances. The calculations use Percus‐Yevick theory, and comparison is made between the results using the empirical potentials obtained by Esterling‐Swaroop and those of Johnson and Wilson. Reasonable agreement with the experimentally determined pair‐correlation functions is obtained for Fe, Cu, and Ag with both sets of potentials. However, the results for Au and V with the Esterling‐Swaroop potentials are not satisfactory. It is noted independent evidence suggests that the pair potential approximation is inadequate for these two metals. In addition, the pair‐correlation function serves as a discriminator between two pair potentials for iron derived from the same phonon data.
Temperature Dependence of Electrical Resistivity of Zn, Cd, Hg, Al, In, Tl, and pb by Nonlocal Harmonic Model Potential
Authors: Sahay B. B. , Srivastava P. L. , Mitra N. R. 
Published: July 2007

AbstractThe harmonic model potential is used in its nonlocal form to study the temperature variation of the electrical resistivity of liquid Zn, Cd, Hg, Al, In, Tl, and Pb. The variation of the electrical resistivity with temperature is well demonstrated by the model and the numerical values are consistent with the experimental measurements in all the cases, except Hg.