bluuebunny/crossref_metadata_2025_split huggingface dataset:
Resonance energy shift for mössbauer impurity atoms trapped by vacancies
Authors: Tewari A. K. , Roy S. K. , Bhattacharya D. L. 
Published: July 2007

AbstractAn estimation of the second order Doppler shift is made for a simple lattice model containing impurities and vacancies by employing the double time Green's function technique at the high temperature limit. The changes in the force constants due to the presence of substitutional impurities and the vacancies near to the impurity are evaluated from the Debye relation and are used to estimate the contributions. It is found that the two contributions (one due to the impurity and the other due to the vacancy near to the impurity) arising from the last two terms of the lattice Hamiltonian yield a negative shift of the absorption line, which is expected to be significant for high concentrations of point defects.
Scattering of phonons by spherical defect aggregates
Authors: Joshi Y. P. 
Published: July 2007

AbstractThe phonon relaxation time due to defect aggregates in solids is studied by the perturbation method. The defect aggregates are assumed to have spherical shape and to be formed by the clustering of a large number of atoms that differ from the host crystal atoms in mass alone. The relaxation time τ obtained is found to be of the Rayleigh type with a frequency dependence of ω−4 type for wavelengths λ large compared with the diameter d of the defects, ω being the phonon frequency. However, its dependence on ω is observed to be approximately of ω−2 type for λ smaller than, and yet comparable in order of magnitude with d. This result is at variance with the geometrical scattering that is generally taken to be valid for shorter‐wavelength phonons. The transition of τ from ω−4 to ω−2 is found to be rather smooth.
Electromagnetic waves in an inhomogeneous semiconductor under electric and magnetic fields
Authors: Dykman I. M. , Prokhnitskii L. A. 
Published: July 2007

AbstractA theoretical investigation is made of the case of normal incidence of a linearly polarized electromagnetic wave upon a donor semiconductor to which a heating electric field F and a magnetic field H is applied. The impurity concentration is determined by the law N(z) = N0 + N1 cos qz. The wave inside the semiconductor splits into two waves with circular polarizations. Near the Bragg resonance, which can occur only for one of these two waves having the wave vector k ≈︁ q/2, some peculiarities appear in the reflection and the transmission of this wave. It is shown that the reflection and the transmission coefficients as well as polarization of the resulting wave can be considerably influenced by means of the magnetic and the electric fields.
The theory of magneto‐optical effects in shallow f‐centres
Authors: Gifeisman Sh. N. , Malkoch Yu. G. 
Published: July 2007

AbstractIn the framework of the path‐integral formalism of non‐relativistic quantum mechanics the Faraday effect theory of the local centres in ionic crystals with intermediate polaron coupling is developed. The dissipative properties of the phonon–impurity system are investigated by the non‐equilibrium density matrix method. In zeroth approximation the system is described by the trial Lagrangian, in which the Coulomb interactions of the impurity electrons with lattice defects and vibrations are imitated by elastic forces. In the first order on the difference between the exact and trial Lagrangians the expressions for the admittance tensor components of the system determining the Verdet and Cotton‐Mouton constants are obtained. At the absolute zero temperature the magnetic correction to the polaron effective mass is also calculated.
Impurity band in Hg1−xCdxTe alloys
Authors: Dugaev V. K. , Petrov P. P. 
Published: July 2007

AbstractThe problem of the acceptor impurity band formation in the Hg1−xCdxTe alloy with ϵg≦ 0.3 eV is discussed. Within the coherent potential approximation the density of states as a function of impurity concentration and alloy composition is calculated. The dependence of the impurity band centre location on alloy composition is obtained. The dependence of the acceptor impurity activation energy on the impurity concentration is determined.
Effects of controlled disorder on the phase transitions and charge density wave state in tetrathiofulvalene–tetracyanoquinodimethane
Authors: Gunning W. J. , Chiang C. K. , Heeger A. J. , Epstein A. J. 
Published: July 2007

AbstractTransport and magnetic studies of the phase transitions and low temperature charge density wave state in TTFTCNQ as a function of irradiation induced defect concentration are presented. The transport and magnetic results imply a suppression and broadening of the phase transition and incomplete 3d ordering for T < 34 K. Although the TCNQ susceptibility decreases toward zero at T = 0 in irradiated samples, the contribution from the TTF chains remains finite.
Pre‐asymptotic charge oscillations around 3d transition metal impurities in aluminium
Authors: Lautenschläger G. , Mrosan E. 
Published: July 2007

AbstractThe charge density oscillations around 3d transition metal impurities in aluminium are discussed. Comparing the asymptotic and pre‐asymptotic results, in the pre‐asymptotic case a reduction of the amplitude of the charge density oscillations is found. This reduction reflects the energy dependence of the impurity scattering phase shifts.
On the susceptibility of strongly correlated electrons
Authors: Elk K. 
Published: July 2007

AbstractThe isothermal longitudinal susceptibility of the Hubbard model is calculated. It is shown that in strongly correlated electron systems the susceptibility is proportional to the reciprocal temperature in the low temperature region as well as at high temperatures. Therefore the particular experimental results of some quasi‐one‐dimensional systems cannot be explained by the influence of the electron correlation.
Flux redistribution of channeled fast electrons
Authors: Popov D. E. , Kaplin V. V. , Vorobiev S. A. 
Published: July 2007

AbstractThe orientation dependence of planar channeling for 0.5 to 2.5 MeV electron transmission through crystalline Si is experimentally observed. The phenomenon of spatial flux redistribution results from the formation of bound states of the channeled electrons with atomic planes. Application of electron channeling is considered for the control of irradiation effects in crystals and the study of perfection of the crystalline structure.
Appearance potential spectroscopy in metals and alloys multiple scattering approach
Authors: Donato E. , Giuliano E. S. , Ruggeri R. , Stancanelli A. 
Published: July 2007

AbstractA multiple scattering approach is used to deal with the excitation of core electrons in metals and alloys within the one‐electron approximation. By assuming the crystal potential in the nonoverlapping muffin‐tin form the excitation probability is written as a product of atomic‐like and the scattering path operator matrix elements. It is also shown how this way of factorizing the excitation probability is particularly suitable for describing the scattering process in random alloys, too.
Calculation of the interband absorption in lead chalcogenides using a multiband model
Authors: Ziep O. , Genzow D. 
Published: July 2007

AbstractThe optical absorption coefficient for direct allowed interband transitions between states L+6 and L−6 is calculated within the framework of a multiband model, including six bands in a k · p treatment. Due to the enhanced joint density of states at higher energies in the multiband model as compared with the Dimmock‐model a good agreement is obtained between calculated and experimental absorption spectrum also at photon energies hw > 2EG.
Mean component approximation for the correlation energy of multicomponent electron–hole plasmas
Authors: Wünsche H.‐J. 
Published: July 2007

AbstractElectron–hole plasmas are considered that may involve several components, i.e., particles of different types with equal isotropic masses but different densities. The RPA energy of the correlation between any two components is expressed by that of an electron gas by finding an equivalent auxiliary plasma that is composed of an effective number of components equally occupied with a mean density (“mean components”) and that has the same correlation energy. Finally using an interpolation formula for the correlation energy of the electron gas, an analytic expression is obtained which is shown to yield good results for the spin‐polarized electron gas as well as for neutral and non‐neutral electro–hole plasmas.
Theory of dechanneling
Authors: Rozhkov V. V. 
Published: July 2007

AbstractA theory of dechanneling is proposed. It is based on the solution of the boundary problem for the kinetic equation describing the evolution of channeled particles. The expressions for the dechanneled fraction, distribution function of the lifetime of the channeled particles, and half‐thickness are obtained in a general form. The theory permits to take into account in a simple manner the simultaneous action of many dechanneling factors as well as incomplete dechanneling on channel borders and rechanneling.
Surface modes in piezoelectric crystals
Authors: Albuquerque E. L. 
Published: July 2007

AbstractThe dispersion relation and the surface mode are discussed for acoustic waves propagating in a piezoelectric semi‐infinite medium. The polarizations of these acoustic waves are chosen to allow coupling between the acoustic and electromagnetic field. Two physically different situations are considered for the piezoelectric medium and found that, while in one case propagation of surface waves occurs, there is no propagation of such waves in the other case.
Stimulated brillouin scattering in a magnetised semiconductor plasma
Authors: Guha S. , Apte N. 
Published: July 2007

AbstractThe stimulated Brillouin scattering of a large amplitude electromagnetic wave due to the excitation of an acoustic wave is investigated analytically in a piezoelectric semiconductor plasma in the presence of a homogeneous static magnetic field parallel to the direction of propagation. A dispersion relation is obtained using the coupled mode theory and the threshold electric field of the pump necessary for the onset of instability as well as the initial growth rate of the unstable mode are obtained analytically for the two cases: 1. without magnetic field, 2. with magnetic field. The threshold electric field and the growth rate for these two cases are compared and it is found that the magnetic field reduces the threshold electric field considerably but increases the growth rate.
Optical properties of charge carriers in magnetite and Mn ferrites
Authors: Šimša Z. 
Published: July 2007

AbstractThe optical properties of magnetite and iron‐excess manganese ferrites are analyzed in terms of both, the Drude‐Zener model of the free electron gas and the small polaron theory applied to the hopping of the electrons (Fe2+ ions) in the octahedral positions of the spinel lattice. Several characteristic parameters of the charge carriers are deduced and a comparison with the dc electrical conductivities is made.
Far‐infrared absorption of BaF2:Dy3+ versus concentration
Authors: Villermain‐lecolier G. , Morlot G. , Roger A. , Hadni A. 
Published: July 2007

AbstractIn the BaF2:Dy3+ FIR spectrum the vibration frequencies of the interstitial compensation ion Fi is observed and the presence of some cluster types is revealed for concentrations equal to or higher than 0.4 mol%. A 125 cm−1 line is observed for the first time with Dy3+. In BaF2:Nd3+ and BaF2:Ho3+ studies it is previously ascribed to the Fi vibration longitudinal mode in a trigonal site. Calculation gives 135 cm−1 for the transversal mode vibration; experimentally it is observed for the first time. The 42 cm−1 line previously ascribed to an electronic transition of Dy3+ in trigonal site disappears when the concentration increases.
Infrared spectra of calcium hydride fluoride CaF2−xHx
Authors: Vergnat‐grandjean D. , Vergnat P. , Brice J.‐F. , Leveque R. 
Published: July 2007

AbstractThe existence of solid solutions of composition CaF2−xHx (0 < x ≦ 1.24) is recently established, crystallizing in CaF2‐type cubic symmetry. There is a statistical substitution of fluoride ions by hydride ions in the CaF2 unit cell. The infrared spectroscopy gives informations on these compounds by the behaviour of the H− ions localized vibration and that of the fundamental TO mode when x varies.
A boltzmann equation for phonons and electrons
Authors: Nonnenmacher Th. F. , Zweifel P. F. 
Published: July 2007

AbstractA Boltzmann equation is derived for electron and phonon transport in bounded systems, which is more reliable than the relaxation time approximate version of the transport equation. The corresponding cros‐sections have non‐azimuthal symmetry. This requires basically new solution techniques which will also be discussed.
Disorder effects on free excitons in CdS1−xSex mixed crystals
Authors: Goede O. , Hennig D. , John L. 
Published: July 2007

AbstractIn CdS1−xSex mixed crystals the energies and transition probability ratios for free A, B, and C excitons are obtained as a function of the composition x by reflection and emission measurements at 77 K. The observation of the disorder‐allowed A(Γ6) exciton transition, the bowing of the energy difference between A and C exciton, and the broadening of the exciton lines clearly demonstrate the importance of disorder effects in these mixed crystals. This conclusion is further supported by the stress‐induced enhancement of the A(Γ6) exciton transition probability by uniaxial stress parallel to the c‐axis of the mixed crystals. The experimental results are discussed on the basis of an effective exciton Hamiltonian consisting of a quasi‐cubic VCA‐Hamiltonian for wurtzite‐type mixed crystals and an additional lower‐symmetric term which describes the disorder effects phenomenologically by two fluctuating crystal fields parallel and perpendicular to the c‐axis, respectively.
Pseudoharmonic effect of phonons in electrical resistivity
Authors: Malinowska‐Adamska C. , Wojtczak L. 
Published: July 2007

AbstractThe temperature behaviour of the electrical resistivity of metals is investigated in the case when the anharmonic properties of phonons are taken into account in the pseudoharmonic approximation. The results show that the pseudoharmonic effects of lattice vibrations are not negligible in calculations concerning the high temperature region. A comparison with experimental data is given for copper, silver, and gold theoretically described by various potential functions.
EPR of Mn2+ doped single crystals of Ni(NH42) (SO4)2 · 6 H2O and NiSO4 · 7 H2O
Authors: Misra S. K. , Mikolajczak B. 
Published: July 2007

AbstractX‐band EPR measurements are reported on single crystals of Ni(NH4)2(SO4)2 · 6 H2O and NiSO4n · 7 H2O doped by Mn2+ ions at various temperatures. The absolute sings of the spin Hamiltonia parameters are determined from liquid helium temperature data. A study is made of the variation of linewidths with temperature, as well as with the magnitude of the static magnetic field. The spin Hamiltonian parameters are evaluated rigorously from a simultaneous fitting of the data obtained for several orientations of the static magnetic field, using the method of least‐squares fitting and numerical diagonalization of the spin Hamiltonian matrix appropriate to electronnuclear spin coupled systems.
Spectral density of phonons in alkali metals
Authors: Vaks V. G. , Zein N. E. , Kravchuk S. P. , Trefilov A. V. 
Published: July 2007

AbstractThe phonon spectral density g(ω) is calculated for five alkali metals. The previously described pseudopotential model giving a rather accurate description of these metal dynamics is used for the phonon frequencies computation. The calculated g(ω) are similar for all the alkali metals and have the characteristic three‐peak form with a high and narrow high‐frequency peak. The volume dependence of g(ω) is investigated and is found to be rather sharp. It is shown that g(ω) is very sensitive to the choice of the theoretical model so that its measurements can provide an effective method for the proof of the accuracy of these models.
Band‐edge discontinuities and interface potential step in the two‐band narrow‐gap approach
Authors: Detcheva V. , Kandilarov B. D. 
Published: July 2007

AbstractRelations between band‐edge discontinuities and interface potential step are derived in the framework of the two‐band narrow‐gap approach and in terms of gap‐attached bulk properties of the two semiconductors in epitaxial contact. The expressions, initially deduced for energy gaps opened at the centre or edges of the corresponding Brillouin zones, are subsequently extended to include the more general case of gaps opened in other points inside the Brillouin zones.
Coherent States and Bloch Functions
Authors: Krivoshlykov S. G. , Manko V. I. 
Published: July 2007

AbstractA quasi‐momentum representation for an arbitrary quantum system is constructed by the integrals‐of‐motion method and by the coherent‐states method. Explicit expressions in terms of the Jakobi ϑ‐functions are obtained for the Bloch functions of the following dynamical systems: a relativistic and non‐relativistic electron moving in a constant uniform magnetic field and a non‐relativistic electron moving in both, time‐dependent and constant crossed electromagnetic fields. New mathematical relations between the Jacobi ϑ‐functions are obtained.
Generation of Free Excitons and Exciton—Impurity Complexes by Fast Electrons in Extremely Anisotropic Crystals
Authors: Kozitskii S. V. , Rack M. 
Published: July 2007

AbstractThe generation of free and bound excitons by fast electrons is calculated within the framework of an extremely anisotropic model of a layer crystal. Selection rules are discussed. The oscillator strength of the exciton—impurity complex is two or three orders of magnitude higher than that for free excitons in the case of direct transition and greatly decreases with increasing distance between the extrema in the case of indirect transition. For small scattering angles θ ≈ 10−3 rad the probability of generation of excitons as well as exciton—impurity complexes by fast electrons does not depend on θ.
Non‐Linear Transport Properties of Band Electrons at Arbitrary Electron—Phonon Coupling
Authors: Fomin V. M. , Pokatilov E. P. 
Published: July 2007

AbstractThe equations of motion for the electronic density matrix represented by functional integrals are obtained at arbitrary electron—phonon coupling strengths. The method of a self‐consistent calculation of the functional integrals is generalized to the varying strong electric fields. This approach is applied to the problem of a stationary non‐linear response of band electrons to a constant electric field and strong electromagnetic fields. The relations are found which determine an immediate dependence of these fields on the given average response. The effects connected with the polarization due to a non‐linear electron response are described.
Calculation of the Electron Momentum Distribution in Zinc in Connection with Positron Annihilation
Authors: Pawłowska Z. 
Published: July 2007

AbstractThe electron momentum distribution in zine is computed on the base of band structure calculations in three directions: [001], [100], [110]. The group‐theoretical treatment resulting in a selection rule for the h.c.p. structure shows that some bands cannot contribute to the photon‐pair momentum density along symmetry lines in momentum space. Results of the application of the selection rule to the h.c.p. structure are given in the paper.
Many‐Body Effects on the Third‐Order Elastic Constants of Alkaline Earth Fluorides
Authors: Bedi S. S. , Verma M. P. 
Published: July 2007

AbstractExpressions for the third‐order elastic (TOE) constants are derived from the Lundqvist potential for the non‐centrosymmetric solids crystallizing in the fluorite structure. The values of the TOE constants determined from these expressions agree fairly well with the measured values for CaF2, SrF2, and BaF2 and show significant improvements over the values obtained in other theoretical studies.
Electronic Structure of the Ferromagnetic Semiconductor s—d Model from the Lowest Six Momenta
Authors: Čápek V. , Chvosta P. 
Published: July 2007

AbstractThe lowest six momenta of the spectral function of the ferromagnetic semiconductor s—d model are expressed in terms of the spin correlation functions. This information is used to fit the unknown spectral function by a physically acceptable model function preserving the lowest six momenta. Using that, a model electronic quasiparticle energy structure is calculated and discussed for all relevant areas of parameters involved. Throughout the work, the rotational symmetry of the original Hamiltonian is preserved.
Magnetoplasma Effects in Bi and Semimetallic BiSb Alloys at 300 GHz
Authors: Braune W. , Lebech J. , Saermark K. 
Published: July 2007

AbstractExperimental results on magnetoplasma phenomena in Bi and semimetallic BiSb alloys with Sb concentrations up to 6.8 at% are presented. The Voigt configuration and trigonal sample planes are used. The field configurations B ‖ C2 ⟂ Erf and B ‖ C1 ⟂ Erf are considered. The field positions for the dielectric anomaly and cyclotron masses are determined as functions of the Sb concentration.
On the Composition Dependence of the Lattice Dielectric Constant in Bismuth—Antimony Alloy Systems
Authors: Schuchardt R. , Rudolph R. , Keiper R. , Krüger2 H. 
Published: July 2007

AbstractThe strong increase of the lattice dielectric constant observed at a critical antimony concentration in semiconducting bismuth—antimony alloy systems can be interpreted in terms of an electronic interband polarization enhanced by vanishing thermal energy gap. In particular, the indirect transitions between the T‐point valence and the L‐point conduction bands assisted by elastic short‐range scattering mechanisms play a dominant role. The direct transitions within the quasidegenerate L‐point band complex lead only to a nearly composition independent “background” dielectric constant when the available information on the composition dependence of the relevant band structure parameters is taken into account.
Calculations of the Properties of Superconducting Alloys via the Average T‐Matrix Approximation. An Application to the Binary Substitutional NbMo Alloy System
Authors: Chatterjee P. 
Published: July 2007

AbstractThe theoretical formula of McMillan, modified via the multiple‐scattering theory by Gomersall and Gyorffy, has been very successful in computing the electron—phonon coupling constant (λ) and the transition temperature (Tc) of many superconducting elements and compounds. For disordered solids, such as substitutional alloys, however, this theory fails because of the breakdown of the translational symmetry used in the multiple‐scattering theory. Under these conditions the problem can still be solved if the t‐matrix is averaged in the random phase approximation (average T‐matrix approximation). Gomersall and Gyorffy's expression is reformulated for λ in the random phase approximation. This theory is applied to calculate λ and Tc of the binary substitutional NbMo alloy system at different concentrations. The results appear to be in fair agreement with experiments.
Structural Studies of Thermal Vibrations in Ferroelectric SbSI
Authors: Itoh K. , Matsunaga H. , Nakamura E. 
Published: July 2007

AbstractThe anharmonic atomic potential at 1.3 °C and the temperature dependence of thermal amplitudes in SbSI are calculated from crystal structures previously reported. The contribution of the soft mode to the thermal amplitude is found along the c‐axis for the Sb atom over a wide temperature range around the transition temperature. The temperature dependence of the frequency of the soft transverse optic mode is estimated in the paraelectric phase up to 100 °C.