bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of the elastic and inelastic scattering of light by magnetic crystals. II. Second‐order processes
Authors: Le Gall H. , Vien Tran Khanh , Desormière B. 
Published: July 2007

AbstractThe second quantization of the magneto‐optical interactions in ferromagnetic crystals is extended to second‐order processes. From the electric and magnetic dipole transitions induced by an incident radiation, the evolution of the electromagnetic field is analysed in the cases of bi‐gyrotropic and quadratic magneto‐optical materials. The physical and analytical relations between the elastic (linear magnetic birefringence) and inelastic (two‐magnon Raman effects) scatterings are derived from the second‐order magneto‐optical Hamiltonians. It is shown that the two‐magnon Raman susceptibility is proportional to the second power of the specific linear magnetic birefringence. In isotropic media the second‐order magneto‐optical interactions may be separated in an isotropic (or scalar) part and in an anisotropic (or tensorial) part. From the corresponding Hamiltonians the polarization rules are deduced for the second‐order inelastic scatterings. In ferrites and orthoferrites the first‐ and second‐order magneto‐optical constants may have equivalent values. As supported by experiments the influence of the quadratic magneto‐optical interactions on the first‐order inelastic scattering is shown from the magneto‐optical polarization and Hamiltonians. The one‐magnon Stokes component may be higher than the anti‐Stokes component when the polarization of the incident photons is parallel to the dc magnetization. The opposite result is obtained with light polarized perpendicular to the dc magnetization. The one‐magnon Raman Hamiltonians and susceptibilities modified by the quadratic effects are derived from the optical polarization and compared with experimental data.
Stabilization of aliovalent ions observed by Mössbauer emission spectroscopy in 57Co‐doped simple ligand compounds
Authors: Cruset A. , Friedt J. M. 
Published: July 2007

AbstractThe Mössbauer emission spectra of 57Co2+ in MgF2, CaF2, K2CoF4, and MgCl2 have been studied. Aliovalent charge states (Fe3+) have been observed in several of these salts. A general thermodynamic model, based on the correlation between the proportion of Fe3+ ions and the Madelung potential at the cation site in the host, is proposed to account for the stabilization of various iron species after 57Co electron capture in simple ligand compounds.
Inelastic impurity scattering of hot electrons in semiconductors
Authors: Kachlishvili Z. S. 
Published: July 2007

AbstractThe field and concentration dependences of the mobilities as well as the field dependences of the free carriers and conductivity have been calculated taking inelastic impurity scattering of hot electrons (the 1s‐2p excitation and the ionization of neutral impurities) into account. Besides the dependence of the breakdown field on the neutral impurity concentration has been estimated. The agreement with the experiment is satisfactory.
Numerical behaviour of transmission and derivative traces due to direct electronic transitions near van hove singularities
Authors: Doran N. J. , Harper P. G. 
Published: July 2007

AbstractAnalytical forms of the complex dielectric function ε(ω) near each of the singular (Van Hove) critical points are given for the allowed and forbidden transitions at arbitrary light polarizations. By numerically simulating ε(ω) the characteristic traces of the transmission T(ω) and its derivatives dT/dω, d2T/dω2 have been obtained over a range of refractive index n, k values. From these it has been found possible to tabulate the possible Van Hove singularities corresponding to a given characteristic trace.
Kinetics of self‐trapped exciton recombination in CsI
Authors: Lamatsch H. , Rossel J. , Saurer E. 
Published: July 2007

AbstractThe yield and decay lam of the intrinsic luminescence of CsI are studied. From the results obtained a configuration coordinate scheme for the relaxed exciton is suggested and the nature of the relaxed state is specified. The kinetics of electron‐hole recombination following an ionizing irradiation is reported.
Lifetimes of bound excitons in InP
Authors: Heim U. 
Published: July 2007

AbstractThe decay times of two bound exciton emission lines in InP have been measured at very low excitation levels and found to be of the order of 0.5 and 1.5 ns. These times agree within a factor of two with theoretical values, which were estimated using the model of Rashba and Gurgenishvili. The oscillator strength per molccule of the free exciton has been evaluated and found to be 8 × 10−5 The bound exciton oscillator strengths are larger by five orders of magnitude.
Exciton binding energies of layer‐type semiconductors GaSe and GaTe
Authors: Grandolfo M. , Gratton E. , Somma F. Anfosso , Vecchia P. 
Published: July 2007

AbstractNew experimental results are given on the absorption coefficient of GaSe and GaTe single crystals near the fundamental edge. A new analysis of the direct exciton region due to Sell and Lawaetz has been used to assign the energy position of the exciton levels and of the energy gaps, and to determine the exciton binding energies.
Electronic and nuclear stopping cross sections in carbon for light mass ions of 4.5 to 46 keV energy
Authors: Höberg G. 
Published: July 2007

AbstractThe mean stopping cross section, S, of thin carbon foils has been determined for light mass particles with 3 ≦ Z1, ≦ 18. The dependence of stopping cross section on foil thickness and scattering angle is reported. The energy of the incident ions ranged from 4.5 to 46 ke V. The electronic, Se, and nuclear, Sn, stopping cross sections were deduced from the experimentally determined mean stopping cross section at zero output angle, \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {S(0)} \, = \,S_e \, + \,\overline {S_n \,(0)} $\end{document}, by putting \documentclass{article}\pagestyle{empty}\begin{document}$ S_e \, = \,\mathop {\lim}\limits_{t \to 0} \,\overline {S(0,\,t)} $\end{document} where t is the foil thickness. The reported values of Se, are in t → 0 good agreement with previously published results. The mean nuclear stopping cross section in the forward direction is found to reach a saturation value in foils thicker than about 8 μg/cm2. The increase of S with scattering angle is parabolic at small scattering angles and linear at large scattering angles.
Stress‐induced splitting of excitons due to exchange interaction in zinc telluride
Authors: Wardzyński W. , Giriat W. , Szymczak H. , Kowalczyk R. 
Published: July 2007

AbstractThe effect of uniaxial stress on the exciton reflection spectrum at 77 °K of ZnTe was studied by the wavelength modulation technique. The observed splitting is explained taking into account the exchange interaction between the spins of the electron and the hole composing the excition. From comparison of the experiment and the appropriate theory it is concluded that in ZnTe at 77 °K the second‐order term of exchange interaction being linear in strain and describing the variation of exchange interaction with stress plays the main role.
Magnetic dilution effects on morin phase transition in hematite
Authors: Srivastava J. K. , Sharma R. P. 
Published: July 2007

AbstractMössbauer investigations, in the range 10 to 1000 °K, in (1−x) Fe2O3‐x Al2O3 systems, have shown a nonlinear rapid decrease of the Morin temperature, TM, with the increasing magnetic dilution of the α‐Fe2O3 lattice. The phase transition is not sharp and becomes more and more diffused as the magnetic dilution increases. An anomalous variation of the angle, θ, between the spin direction and the c‐axis is seen for the 5.27 wt% diluted sample indicating the presence of three magnetic phases in this case. Unlike the case of undiluted α‐Fe2O3, for the 0.56 wt% diluted sample at low temperatures, outside the phase transition region, the Fe3+ spins do not lie along the c‐axis but are canted at an angle of about 30°. This angle, θ ≈ 30°, does not seem to change much with further increase in dilution. It is also seen that with dilution, the ratio TM/TN and the anisotropy energy, K, deduced from the temperature and concentration dependence of the hyperfine field, are decreased (TN Néel temperature). This supports the existing anisotropy theory.
High field transport in semiconductors. The drifted Maxwellian approach. I. general theory
Authors: Stokoe T. Y. , Cornwell J. F. 
Published: July 2007

AbstractThe rates of loss of energy and momentum by electrons to the polar optical, acoustic, and ionised impurity scattering mechanisms are calculated. They are averaged exactly over the drifted Maxwellian distribution function, from which the high field transport characteristics of semiconductors can be calculated. The formulae are expressed in terms of a generalised band structure, and the effect of the mixing of Bloch states with spin‐reversal scattering is included.
Structure factor and atomic distribution in liquid metals by X‐ray diffraction
Authors: Waseda Y. , Suzuki K. 
Published: July 2007

AbstractX‐ray diffraction patterns have been obtained from liquid metals (Al, Ga, In, Tl, Pb, Sn, Bi) near the melting point. After calculating the structure factor (Fourier analysis), the atomic radial distribution function was evaluated from which interatomic distance and coordination number were obtained. It has been shown that the ratio (K2/K1) of the position of the first peak (K1) to that of the second peak (K2) in the structure factor is a very useful parameter to represent the structure of liquid metals.
Charged particle energy loss to electron gas
Authors: Pathak A. P. , Yussouff M. 
Published: July 2007

AbstractThe contribution of the conduction electrons to the stopping power (– dE/dx) of fast charged particles in a crystal has been calculated using different forms of the dielectric function. The various approximate forms of dielectic functions used are: 1. random phase approximation (RPA), 2. Hubbard approximation (both, screened and unscreened), 3. Kleinman approximation, and 4. the dielectric function obtained by variational calculation of Langreth. The intermediate velocity range for the incident particles, namely 2 VF<V<10 VF was investigated and it has been found that in this region the stopping power varies inversely to the particle velocity. Moreover the velocity dependence is found to be insensitive to the form of the dielectric function used in the calculation.
The effects of sample imperfections on optical spectra
Authors: Filiński I. 
Published: July 2007

AbstractThe results of the theory of light reflection from rough surfaces have been extended to cover the case of light transmission through a sample with rough surfaces, as well as reflection and transmission for inhomogeneous samples. A concept of “Inhomogeneity Induced Roughness” of the constant phase plane has been introduced to describe the specular reflection from inhomogeneous media. The drastic influence of the multiple scattering effect on the optical spectra has been demonstrated for a simple model. The generalized formulae for reflection and transmission of light for imperfect samples are given. Finally, several peculiar experimental observations concerning exciton spectra in II–VI compounds, light scattering at the plasma frequency in metals, electroreflection, and other effects are discussed.
Perturbation theory in transmission electron diffraction I. The perturbing matrix is constant and hermitian
Authors: Serneels R. , Gevers R. 
Published: July 2007

AbstractInstead of using the usual Schrodinger equation perturbation theory is directly applied to the system of Howie and Whelan. According to the nature of the perturbing dynamical matrix generally three different types of perturbation are distinguished. The perturbing dynamical matrix may be a) constant and hermitian, b) constant but not hermitian, c) not constant but depth dependent. The perturbing dynamical matrix is supposed to be constant and hermitian. Applying perturbation theory series expmsions for the eigenvalues and eigenvectors of the dynamical matrix are derived. Furthermore these series expansions are used to obtain series expansions for the amplitudes and intensities of the different beams. Two practical examples are discussed. First the influence of weak beams is studied by this method. As a particular result the kinematical expression for the amplitude of the weak beam formed by scattering out of N + 1 strong beams is given. Secondly it is suggested that the method can be applied to study the influence of slightly tilting the crystal around an orientation for which the problem was solved.
Optical phonon drag effect in single crystals of CdSe
Authors: Kubalkovl S. , Sakalas A. 
Published: July 2007

AbstractAn investigation is made of the optical phonon drag effect. In contrast to [1] where all calculations were performed for low carrier densities and the change of sign of phonon drag effect at low temperatures was obtained, it is shown in this paper that for high carrier densities no change of sign takes place. The phonon drag effect is found to be inversely proportional to the carrier density. These conclusions were checked experimentally on CdSe single crystals.
Local approximations in the theory of hot electrons in spatially inhomogeneous systems
Authors: Zviagin I. P. 
Published: July 2007

AbstractThe distribution function of hot electrons in a static, slowly in space varying electric field is calculated. This distribution function is used to obtain a phenomenological expression for the current density. The transport coefficients are presented as local functions of the field strength, drift velocity, or power absorption. The connection of different local approximations is discussed.
Low temperature thermomagnetic effects in n‐type PbS
Authors: Chan Y. C. , Finlayson D. M. 
Published: July 2007

AbstractTransverse and longitudinal Nernst effects have been measured over the temperature range 1 to 80°K. Acoustical and optical phonons are confirmed as the main scattering mechanisms at liquid air temperatures. At low temperatures neither ionised nor neutral impurity scattering provide an explanation of the measurements. The results are tentatively explained in terms of localised spin scattering.
Piezobirefringence in the vacuum ultraviolet: Alkali halides and alkaline‐earth fluorides
Authors: Sánchez C. , Cardona M. 
Published: July 2007

AbstractThe spectral dependence of the piezobirefringence coefficients of NaCl, KCl, LiF, CaF2, SrF2, and BaF2, at room temperature is measured. From these results values for the shear deformation potentials of the energy bands are obtained. The LiF data suggest that the lowest interband edge occurs along [lll], a situation unique among the alkali halides. The data for the alkaline‐earth fluorides indicate a rather complicated structure for the lowest absorption edge.
The mechanical interaction of a point defect with a surface layer
Authors: Bacon D. J. 
Published: July 2007

AbstractA relationship is derived which expresses the interaction energy between a source of internal stress and a surface in terms of the elastic field. This is used to consider the mechanical interaction energy between a point defect and a layer of finite thickness on the surface of body. For convenience, the body is taken to be semi‐infinite and isotropic, and the layer is also isotropic but with different elastic constants. The point defect is approximated by a dilatation centre. A transform method is used to obtain the elastic field, and this gives analytic expressions for the interaction energy in the limiting case corresponding to a bicrystal. For situations of finite layer thickness, the energy has been determined numerically for a wide range of values of elastic constants, layer thickness and defect to layer‐matrix interface distance. The conditions which give rise to attraction or repulsion of the defect from the interface have been studied, not only for the case in which the defect is in the matrix but also when it is in the layer.
The low temperature magnetic susceptibility of semiconductors in strong magnetic fields
Authors: Wallace P. R. , Gupta O. P. 
Published: July 2007

AbstractWe calculate the magnetic susceptibility of Kane‐type semiconductors in the ultra‐quantum limit, taking account of spin splitting. It is shown that, when the bottom of the upper spin branch of the n = 0 Landau band passes through the Fermi surface, there is a strong minimum in the diamagnetic susceptibility as the spins of all free carriers align. The conditions are considered for transition to a conduction electron paramagnetism. Calculations are carried out for InSb with carrier concentrations of 2 × 1016 and 2 × 1017 cm−3.
No‐phonon and phonon‐assisted exciton absorption in GaAs1 − x, Px with indirect energy gap
Authors: Pikhtin A. N. , Razbegaev V. N. , Yaskov D. A. 
Published: July 2007

AbstractInvestigating the fine structure of intrinsic absorption of GaAs1 − x, Px at 4.2°K, the influence of composition x and band structure on the no‐phonon and phonon‐assisted processes of light absorption by excitons has been determined.
The modified convolution approximation model for neutron scattering from short range ordered paramagnets
Authors: Rao L. Madhav 
Published: July 2007

AbstractA modified convolution approximation model is developed to explain neutron scattering from short range ordered paramagnets, employing the concepts used in understanding neutron scattering of simple liquids. Calculations based on this model are compared with the following experimental results in paramagnetic MnO: (1) scattered neutron energy spectra at room temperature, using the triple‐axis spectrometer, (2) scattered neutron time‐of‐flight spectra at 124, 143, and 298 °K. The model explains satisfactorily the narrowing of the line shape observed in (1) and also explains qualitatively the observed energy shifts in (2), at all the three temperatures without assuming spin‐wave like excitations. These apparent energy shifts are explained to arise essentially from the “non‐constant Q” nature of the measurements.
On the many‐beam dynamical theory of electron diffraction in faulted crystals
Authors: Schapink F. W. 
Published: July 2007

AbstractThe dynamical theory of electron diffraction in a thin foil with a stacking fault is reconsidered from the point of view of Bloch wave scattering at the stacking fault. A formalism for many‐beam systematic diffraction is developed from which a close relationship between the stacking‐fault‐induced transformation of the various Bloch waves and the corresponding transformation of the excitation amplitudes of the Bloch waves emerges. It is suggested that the present formulation shows more clearly the nature of the scattering process involved.
Luminescence due to trapping of holes by In+ and In+v centres in KCl:In
Authors: Zazubovich S. 
Published: July 2007

AbstractThe trapping of holes by In+ and In+v centres in KCl:In is found to be accompanied by luminescence of the same spectral composition as the emission spectra of In++ and In++v centres, respectively. The processes of migration and trapping are investigated for holes thermally or optically released from In++, Vk, VF and other hole centres.
Temperature Shift, Recoil‐Free Fraction, and Force Constant in Mössbauer Studies
Authors: Gupta G. P. , Lal K. C. 
Published: July 2007

AbstractA simple relation connecting the temperature shift, the recoil‐free fraction, and the force constant has been derived. The force constants for host–host and for impurity–host atoms and their ratios have been calculated from this relation. The values thus obtained are compared with the values obtained by other authors. The agreement has been found to be satisfactory and confirms the applicability of the derived relation. The results also indicate the change in the force constant for an impurity atom in a host lattice.
Magneto‐Reflectance of the First Exciton in KI and RbI
Authors: Ahrenkiel R. K. , Teegarden K. J. 
Published: July 2007

AbstractThe Zeeman effect of the first exciton in KI and RbI has been measured by a technique which senses the magneto‐reflectance dichroism. The analysis indicates an excited‐state g‐factor of about 0.9. This result cannot be interpreted in terms of either a Wannier or Frenkel model.
Comparison of Lattice Parameter and Resistivity Change in Electron‐Irradiated Copper
Authors: Dworschak F. , Wagner H. , Wombacher P. 
Published: July 2007

AbstractLattice parameter and residual resistivity measurements were performed on high‐purity copper samples irradiated simultaneously with 2.6 MeV electrons at 6 K up to defect concentrations of about 0.1%. Lattice parameter changes could be measured with a resolution of Δa/a = 5 × 10−6. In six irradiations the ration η = (Δa/a)/Δϱ was determined as a function of defect concentration and thermal recovery. During defect production the ratio η amounts to (1.75 ± 0.10) × 103 (Ωcm)−1 and is independent of the defect concentration. Furthermore, the ratio η stays constant throughout the recovery stages I, II, and III.
Electrical and Optical Properties of Crystals with “nipi‐Superstructure”
Authors: Döhler G. H. 
Published: July 2007

AbstractThe zigzag‐shaped potontial in crystals with “nipi‐Superstructure” (a periodic array of n‐ and p‐doped layers, separated from each other by zones of the intrinsic material) splits the bands into subbands. As a consequence the electronic properties as a function of photon frequency or of external fields should show oscillations reflecting the subband structure. Furthermore these crystals should show interesting features, which are based on the weak interaction between carriers of different impurity layers, and on the change of the amplitude of the superstructure potential with the degree of excitation. Thus, the absorption coefficient, as well as the recombination radiation shows a strong red shift, which depends on the degree of excitation. The efficiency for light storage is high. The application of external fields has drastic effects on the absorption coefficient and on the intensity and frequency of luminescence. At high fields electroluminescence with high efficeincy eventually may be observed.
The Mechanism of F‐Center Aggregation
Authors: Paul J. L. , Scott A. B. 
Published: July 2007

AbstractThe rate of formation of M centers from F centers by thermal aggregation was studied in nominally pure KCl and in KCl containing oxide and sulfide ions. The process was initially about 3/2 order with respect to F‐center concetration, becoming approximately first order later. The order with respect to O2 ‐ion concentration was 0.64 ± 0.10. The activation energy was (1.06 ± 0.05) and (1.07 ± 0.05) eV in oxide‐ and sulfide‐containing crystals respectively, nearly the same as the reported jump activation energy for negative‐ion vacancies (ǒ centers) which compensate the divalent ions. The results support the two‐step mechanism F + α = F, F + F = M α, with the first step being rate‐determining. The order should be unity with respect to F‐center concentration, but deviates intially, it is believed, because of a non‐random spatial distribution of F centers at the start. Since oxide ions and α centers are strongly associated, the order should be one‐half, or somewhat greater, with respect to oxide‐ion concentration.