bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of optical constants: Derivative spectra from ellipsometric data
Authors: Jungk G. 
Published: July 2007

AbstractDerivative spectra calculated from the ellipsometrically determined dielectric function are discussed. The line‐shape analysis enables the determination of type, energetic position, and broadening parameter of van Hove singularities. The procedure is demonstrated for the E1structures in Ge and GaP. For Ge critical points are found near 2.0 eV (M0‐type); 2.1 eV (Mo‐type), and 2.3 eV (M1‐type). The optical structure near 3.7 eV in GaP consists mainly of a M1‐transition. The influence of final‐state interactions is discussed.
Second‐order effects in the anisotropic elastic field of a straight edge dislocation
Authors: Seeger A. , Teodosiu C. , Petrasch P. 
Published: July 2007

AbstractA method is described for the calculation of the non‐linear anisotropic elastic field of a straight edge dislocation lying along a two‐fold axis of material symmetry taking into account the continuity conditions at the boundary of the dislocation core. The results may be applied to improve the study of the dislocation core by using semi‐discrete techniques.
Extension of the coherent potential approximation for disordered alloys with random transfer integrals
Authors: Eifrig Th. , Kolley E. , Kolley W. 
Published: July 2007

AbstractThe one‐electron Hamiltonian which takes into account the diagonal and off‐diagonal randomness is used to describe disordered binary alloys. The k‐dependent self‐energy is calculated in an extended single‐site coherent potential approximation based on the cluster concept. The behaviour is found to be correct in the dilute alloy limit. The formalism is quite tractable for numerical calculations and yields continuous self‐energies. The difference to the method proposed by Brouers is demonstrated by a numerical example.
The critical voltage effect in transmission electron microscopy. II. A theoretical study neglecting absorption effects
Authors: Gevers R. , Serneels R. , David M. 
Published: July 2007

AbstractUsing degenerate perturbation theory a study is made of the critical voltage effect in electron microscopy. In particular the dependence on the accelerating electron voltage of the profile of the second order bend contour for centrosymmetric crystals is considered. The case of non‐centrosymmetric crystals is included in the formulae. It is found for centro‐symmetrical crystals that the more the critical voltage is approached, the second order bend contour appears as a kinematical like bend contour which disappears completely in a small interval around the critical voltage. Also the symmetry properties are discussed of the Bloch waves corresponding to the branches of the dispersion surface which touch at the critical voltage. It is shown that away from the critical voltage and when the second order reflection is not exactly satisfied the Bloch waves are nearly symmetric or antisymmetric. When the voltage is varied towards the critical voltage a continuous change appears of the Bloch wave symmetry in a given interval around the critical voltage. The smaller the mis‐orientation the smaller is the voltage interval. For non‐centrosymmetric crystals a similar effect is observed.
Galvanothermomagnetic effects in anisotropic media
Authors: B1Abanskii P. I. , Buda I. S. , Dakhovskii I. V. , Samoilovich A. G. 
Published: July 2007

AbstractFrom a uniform point of view the possible transverse (with respect to J or ▽) and longitudinal (directed along J or ▽) galvanomagnetic and thermomagnetic effects arising in anisotropic media are considered. Presenting the tensors magnified image as sums of the symmetrical and antisymmetrical parts a classification is supposed which is convenient for the experimental investigations of the galvanomagnetic and thermomagnetic effects (transverse and longitudinal, even and odd with respect to H) arising in anisotropic media. The classification of the galvano‐ and thermomagnetic effects based on the physical considerations shows that effects which have not been investigated formely should arise in anisotropic media together with the known phenomena. The phenomenological considerations developed in the work are valid for any anisotropic medium. Detailed calculations of the kinetic coefficients describing the effects considered in the work can be made (for such crystals as germanium, silicon et al.) on the basis of the anisotropic scattering theory.
Experimental and theoretical study of Raman scattering in Co++‐ and Fe++‐doped magnesium oxide
Authors: Billat A. , Mon J. P. , Voisin M. 
Published: July 2007

AbstractRaman spectra of iron or cobalt doped MgO single crystals have been obtained. A strong band which lies between 250 and 330 cm−1 for the cobalt doped crystal and between 100 and 350 cm−1 for the iron doped sample appears in the spectrum and has been assigned to resonance modes. Using experimental frequencies, the central and shear force constant changes βr. and γr have been calculated.
Radiative and non‐radiative transitions of electrons in local centers involving hot phonons
Authors: Kovaeskii V. A. , Popov E. A. , Chaikovskii I. A. 
Published: July 2007

AbstractA theory of multi‐quantum radiative and non‐radiative (NRT) transitions in local centers under a high power laser radiation is presented. A model of local center having local phonons (LP) is used. When the interaction between the LP and the thermostat (crystal vibrations) is weak, the quantum transitions of electrons involving hot phonons result in a heating of the LP to an effective temperature Tv well above the equilibrium one. An explicit expression for Tv based on the method of nonequilibrium statistical operator is derived. The latter is determined self‐consistently in terms of quantum correlation functions, which contain standard multiphonon structures. This allows the shape function of absorption and NRT involving hot phonons to be found. In particular one displays the LP heating by means of a sharp asymmetry (flattening) of the absorption band and an essential activation of NRT.
Non‐conservation of frenkel excitons and bound states
Authors: Maeinković M. M. , Tošarić B. S. 
Published: July 2007

AbstractA new method which is characterized by a clean approach and high efficiency is proposed for the analysis of bound states in systems that do not conserve the number of quasiparticles. This approach observes fully the specific commutation relation belonging to Pauli operators. Its efficiency made it possible to calculate the energy spectrum of biexcitons in a higher order of approximation than in previous papers and avoids some of their errors. The calculations are performed using the Dyson‐Maleev Bose representation of Pauli operators as well, in order to settle a fair estimate of the fitness of this representation for the analysis of non‐conservative systems of Prenkel excitons. In the linear approximation a full agreement is found with the Dyson‐Maleev approach. In higher approximation, as could be expected, Dyson‐Maleev representation does not yield correct results. Finally the critic is directed to the uncritical application of some previous approaches and the possible cause of errors to which such applications led is discussed.
Multiple inelastic scatterings in electron diffraction
Authors: Ohtsuki Y. H. 
Published: July 2007

AbstractA multiple inelastic‐scattering theory for electron diffraction is developed in terms of the transport equation formed from the Bloch waves. The diffusion of the Bragg spot due to inelastic scattering is represented by a coupled diffusion equation with a generalized diffusion coefficient which is the Fourier component of the position‐dependent diffusion‐coefficient function appearing in dechanneling theory. The two‐wave case is studied in detail, in which the coupled diffusion equation may be separated into two single diffusion equations with two modified diffusion coefficients. The modified diffusion coefficients are calculated for many‐phonon and single‐electron excitations.
Electron‐hole drops in Ge: Correlation effects in the emission line shape
Authors: Rösler M. , Zimmermann R. 
Published: July 2007

AbstractThe effect of exchange and correlation on the density of states and the emission intensity of highly excited Ge is investigated. The self‐energy is calculated using the single‐plasmon pole approximation for the dielectric function. At the equilibrium density rS = 0.58 an enhancement factor of about three and a line narrowing of 5% are found for the emission line shape.
Electric field effects on anisotropic excitons in lead iodide
Authors: Bordas J. , Ricco B. 
Published: July 2007

AbstractThe electric field dependence of the ground state of the exciton at the fundamental absorption edge of PbI2 is interpreted by means of a theoretical approach including anisotropy. As a result of the theoretical fit to the experimental curves the following exciton parameters are obtained: R = 16 meV, ε⟂ = 36, ε‖ = 24, a⟂ = 20 Ǎ, a‖ = 13 Ǎ. These estimates are used to explain satisfactorily the behaviour of the electroabsorption spectrum as well as the temperature dependence of the width of the exciton line which previous published values failed to do.
Resonant tunnelling into a size‐quantised metal film
Authors: Cottey A. A. 
Published: July 2007

AbstractThe theory of resonant tunneling through a thin oxide layer into a size‐quantised metal film has hitherto been given only by modelling the metal film as a free‐electron well with infinite potential barriers at the surface. It Is shown that the essential feature of the theory, namely the “bunching of commensurate energy levels near the middle of the Brillouin zone”, is retained if allowance is made for the lattice potential, for a finite surface potential, and for relaxation of the surface layers of atoms. There is, however, a uniform displacement of the energy levels, and this has an influence on the phase of the observed oscillations of conductance versus bias.
The kinetics of dislocation pinning at low temperatures
Authors: Thompson D. O. , Buck O. 
Published: July 2007

AbstractA further analysis is made of earlier, low‐amplitude internal friction results (εmax ≈≈ 1.2 × 10−7) for a γ‐irradiated copper single crystal. It is shown that the minimum in the rate at which irradiation produced defects arrive at dislocations in Cu at 170 to 180 K is obtained not only from measurements at the irradiation temperature, but also from measurements made at lower temperatures following irradiation. This is in direct contrast to the results obtained by Lücke et al. The unusual temperature–internal‐friction relation of the crystals used by Lücke et al. suggests that dislocation pinning by impurities affected the results of the Aachen group.
Excitation spectra of exciton luminescence in CdTe
Authors: Hiesinger P. , Suga S. , Willmann F. , Dreybrodt W. 
Published: July 2007

AbstractMeasurements of the excitation spectra of the photoluminescence lines below the band gap of CdTe led to the identification of emissions originating from excitons bound to neutral donors, to ionized donors, and to neutral acceptors, as well as from two‐electron transitions. Oscillatory variations of the free and bound exciton emission intensity with the energy change of the exciting light above the band gap and their changes with temperature indicated details of the exciton relaxation mechanisms.
The stress‐induced anisotropy of the dielectric function in α‐Sn
Authors: Blinowski J. 
Published: July 2007

AbstractThe interband Γ8‐Γ8 part of the dielectric function and its anisotropy for α‐Sn samples under [001] compressional stress have been calculated by the BPA method. In the high stress region, the anisotropy of the dielectric function in the long‐wavelength limit depends neither on stress nor on material parameters and results entirely from the p‐character of the Γ8 Bloch functions and the breakdown of the cubic symmetry. The result obtained: εvc⟂/εvc ‖ = 57/46 should therefore remain valid also for HgTe and HgSe. The wave‐vector, electron concentration, and frequency dependence of the dielectric function in stressed a‐Sn also has been investigated.
Uniaxial stress dependence of the EPR spectrum of Ir4+ in Y3Ga5012
Authors: Hodges J. A. 
Published: July 2007

AbstractMeasurements have been made by EPR techniques of the stress dependence of the lowest Ir4+ (5d5; 2Ta2g) levels in yttrium gallium garnet. The results confirm the comparable behaviour of Ir4+ arid Ru3+ (4d5; 2T2g) ions at the octahedral sites in garnets in contrast to recent results obtained by ferrimagnetic resonance. On a simple molecular field model the Ir4+ energy levels in YIG: Ir4+ introduce a negative contribution to λ100and a smaller positive contribution to.λ111.
Effect of potential scattering on the spin disorder resistivity
Authors: Troper A. , Gomes A. A. 
Published: July 2007

AbstractAn extension of the calculation of the temperature‐independent resistivity performed by Blackmann and Elliott is prrsented. in order to describe transition metal‐like hosts. An integral Dyson‐like equation is derived for the one eleetron s‐s propagator using the Green's function formalism. The integral equation is solved to second order in the exchange parameters. in the absense of magnetic order. Out of this solution an expression for the temperature‐independent resistivity is obtained in terms of phase shifts and exchange copulings.
Spectral distribution of nonlinear oscillators with nonlinear friction due to a medium
Authors: Dykman M. I. , Krivoglaz M. A. 
Published: July 2007

AbstractThe analog of a quantum kinetic equation for the description of time correlation functions of singled out nonlinear oscillators interacting with a medium (e.g. local or quasi‐local vibrations in crystals) is obtained. Both the frictions, the linear and nonlinear one (the latter is due to decays with participation of two quanta of singled out oscillators), were taken into account. Spectral distributions of the correlation functions of the coordinates are found as well as those of occupation numbers. The essentially non‐Lorentzian shape of the spectral distribution and its dependence on interaction parameters and temperature are analysed.
Determination of the crystal field parameters for Pr3+ in LaF3 from least‐squares fits
Authors: Matthies S. , Welsch D. 
Published: July 2007

AbstractThe results of least‐squares fits of the energy levels of Pr3+ in crystalline LaF3, are reported. Especially, by carrying out a 23‐variable fit involving the crystal field parameters as well as the free‐ion parameters, second‐order effects due to J‐mixing are taken into account. From testing the resulting energies and eigenfunctions by inelastic neutron scattering experiments the reported crystal field parameters are expected to describe the physics of Pr3+ in LaF3 sufficiently well.
Raman‐active phonons in α‐boron
Authors: Richter W. , Ploog K. 
Published: July 2007

AbstractSingle crystals of the α‐rhombohedral boron modification, prepared by chemical vapor deposition, were investigated by Raman scattering. Twelve quite strong peaks were observed in the Raman spectrum. The results are compared with group theoretical predictions and a lattice dynamical model, recently developed for α‐boron.
Bond charge model for the transverse dynamic effective charge and the piezoelectric constant of zincblende‐type crystals
Authors: Hübwer K. 
Published: July 2007

AbstractA bond charge model for the transverse dynamic effective charge and the piezoelectric constant of the zincblende structure is presented. It works with analytical pseudopotentials and leads to simple analytical results, which yield numerical agreement with experimental data. The transverse dynamic effective charge is obtained from ionic and electronic polarizations arising in an optic‐mode sublattice displacement. The piezoelectric constant is calculated regarding additionally the effects of a macroscopic strain in a deformable‐ion model. It consists of an internal‐displacement term and a charge redistribution term, the latter comes from the bond charge. Both are of the same order of magnitude but of opposite sign and confirm quantitatively Lawaetz' qualitative local‐field analysis of Martin's theory of the piezoelectric effect.
ESR investigations of Tl2+‐ and Pb3+‐centres in alkali halides
Authors: Frey W. , Huss R. , Seidel H. , Werkmann E. 
Published: July 2007

AbstractThe results of ESR investigations of Tl2+‐centres in NaCl, KCl, RbCl, KBr and of Pb3+‐centres in KCl are reported. The g‐factor and the heavy‐metal hyperfine (hf) constant as well as superhyperfine (shf) constants for the six nearest neighbour halogen nuclei are determined. The quadrupole interaction is analyzed in KBr:Tl2+. An interpretation of the shf‐ and the hf‐interaction is presented. Model calculations show that the complex formed by the centre ion and the six halogen ligands is strongly determined by covalent bonding.
On the theory of interband ε(ω) and External Electric Field Modulated Δε(ω) in Disordered Semiconductors
Authors: Esser B. , Kleinert P. 
Published: July 2007

AbstractThe interband dielectric function ε(ω) and its external field induced change Δε(ω) are calculated in the one‐electron approximation for a semiconductor with fluctuating band edges presented by smooth random Gaussian fields. The influence of different random bending of the valence and conduction band edges onε(ω) and Δε(ω) is investigated. The corresponding plots are presented. A broadening of the line shape Δε(ω) is obtained if the band bending becomes different. This broadening might be obtained in electromodulation experiments of crystals propagated by an internal acoustic noise flux. Application of the model to amorphous semiconductors is discussed.
An analysis of the fine structure in the main band of a disordered chain with dilute light impurity concentrations
Authors: Wu Shi‐Yu , Chao M. 
Published: July 2007

AbstractThe main band of a disordered binary chain is studied, using Dean's method of negative mode counting, Schmidt's method of functional equation and an approximate theory of Wu. It is found that even for dilute light impurity concentrations, the main band is not smooth as previously believed, but has fine structure. By comparing the results of these calculations, the nature of the construction of the frequency spectrum in the form of a histogram is discussed. The truncation scheme in the approximate theory of Wu is also examined.
EPR of Gd ions in Jahn‐Teller‐distorted rare‐earth crystals TbAsO4, TmAsO4, and TmVO4
Authors: Schwab G. 
Published: July 2007

AbstractEPR measurements on TbAsO4, TmAsO4, and TmVO4 doped with 1 to 2% Gd ions were carried out at temperatures below TD, the critical temperature for the Jahn‐Teller phase transition. A spin‐Hamiltonian allowing for lower symmetry and magnetic interaction is fitted to the spectra of the Gd ions. Low symmetry parameters B are determined. The parameters of the magnetic interaction for Gd ions in the Tb and Tm host crystals are extremly different.
On the theory of hyper Raman scattering in molecular crystals
Authors: Zavorotnev Yu. D. , Ovander L. N. 
Published: July 2007

AbstractHyper Raman scattering in crystals with an inversion centre is investigated using polariton theory. I n the Hamiltonian of a crystal, terms are taken into account, which are responsible for the intermolecular, kinematic interactions and the interaction of charges with the transverse photon field. The explicit form of the hyper Raman scattering tensor is calculated. For groups with an inversion centre the way of identification of the contribution of the intermolecular interaction to this effect is shown.
Effects of high pressure on the optical absorption spectra of colloid centers in KCl and NaCl
Authors: Mamola K. C. 
Published: July 2007

AbstractThe spectral behavior of colloid centers in additively colored KCl and NaCl has been studied at room temperature over the pressure range 1 to 10 kbar. The optical absorption bands associated with non‐scattering colloidal particles in these salts are found to exhibit blue shifts with increasing pressure. A plasma resonance model is used to account for the pressure shifts. The increase with pressure in the density of conduction electrons in the colloidal particles is the dominant effect. Pressure shifts of the peaks of the optical absorption bands are calculated using available compressibility data and the known pressure dependences of the refractive indices of the two salts. Agreement with the measured data is good.
Die rolle des drucks bei der untersuchung der zwischenbandstreuung in n‐GaAs
Authors: Sviridov I. F. , Presnov V. A. , Sonnenburg K. 
Published: July 2007

AbstractDie Druckabhängigkeit der elektrischen Leitfähigkeit von n‐GaAs wird theoretisch untersucht. Es wird gezeigt, daß bei geringen Drücken der Größenordnung 2,5 kbar und Zimmertemperatur die Zwischenbandstreuung im n‐GaAs nicht in Erscheinung tritt. Für beste Übereinstimmung von Theorie und Experiment muß angenommen werden, daß das Matrixelement der Zwischenbandstreuung 10 bis 28% des Matrixelementes des „intravalley”︁‐ Effekts im Minimum (000) ausmacht.
Formation of substitutional hydrogen centers in LiF:OH crystals
Authors: Kamikawa T. 
Published: July 2007

AbstractESR and infrared absorption are measured on neutron‐irradiated LiF:OH crystals. In unirradiated specimens an sharp absorption at 2.8 μ;m is observed and attributed to OH− ions coupled to a Mg impurity. After neutron irradiation the 2.8 μm band disappears and a broad band appears at 1930 cm−1. When the irradiated crystal is annealed at higher temperatures, the 1930 cm−1 band increases a little and then decreases. In parallel with the decay of the 1930 cm−1 band, another absorption band grows peaking at 1013 cm−1, which is attributed to U centers in LiF. H0 centers are observed by ESR in neutron‐irradiated crystals. On annealing at higher temperatures the H0 centers increase as the 1013 cm−1 band grows. While the 1013 cm−1 band increases monotonously with temperature, the H0 centers decrease above 270 °C. It is concluded that hydrogen centres are produced by dissociation of OH‐ ions in neutron‐irradiated LiF:OH crystals and that immediately after irradiation U centers do not exist, which are formed in the course of annealing from the precursor suggested to be U1 centers and afterwards from H0 centers.
Exchange and correlation in nearly free‐electron metals
Authors: Brosens F. 
Published: July 2007

AbstractOn the basis of the Hohenberg‐Kohn theorem, an effective exchange and correlation potential is derived for nearly free electron metals. Using the one particle approach, derived by Kohn and Sham, on variational grounds, an expansion of the total energy with respect to deviations from the uniform density allows for calculating the effective potential.
Experimental and theoretical study of Pr3+ in CaF2
Authors: Bhola V. P. 
Published: July 2007

AbstractCalculations of Pr3+ ion in CaF2 crystal were performed for octahedral symmetry. Tensor operator technique was used to calculate the matrix elements of the crystal field. The crystal field parameters are found to be B = −397 cm−1; B = −799 cm−1. The values of F2, F4, F6, and ζ are found to be 309, 55.4, 6.8, and 716 cm−1, respectively. The r.m.s. deviation for 25 Stark split components is 13 cm−1; if one of the components 1Γ1(3F4) is neglected, the r.m.s. deviation reduces to 10 cm−1. Due to agreement between experimental and theoretical results, it is suggested that the symmetry surrounding the Pr3+ ion in the matrix of CaF2 is octahedral, but the presence of another symmetry is not excluded.