bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the theory oi "heating" a cousto‐electric nonlinearity in semiconductors
Authors: Bugaev A. S. , Gulyaev Yu. V. 
Published: July 2007

AbstractA nonlinear theory of acousto‐electric effects for the sound waves of large amplitude is developed for semiconductors with small effective masses and large energy relaxation times of electrons whore the dominant type of acousto‐electric nonlinearity is due to the stationary heating of the electron gas by sound waves and to the dependence of the kinetic coefficients on the electron temperature. It is shown that the dependence of the electron absorption coefficient, acousto‐electric current, acousto‐electric field etc. on the sound intensity is quite different for various electron momentum and energy scattering mechanisms and is also different from corresponding dependencies for the case of the usual concentrational acousto‐electric nonlinearity. In particular, the dependence of the acousto‐electric current on the acousto‐elcctric field may be superlinear ‐ contrary to the case of the concentrational nonlinearity. It is also shown that the appearance of this "heating" nonlinearity moves off the onset of concentrational nonlinearity. The influence of a strong electric field on the nonlinear acousto‐electric phenomena is studied. It is shown that by heating the electron gas the electric field reduces both the concentrational and the "heating" nonlinear acousto‐electric effect and thus widens the dynamic range of the ultrasonic amplifier.
Electromodulation Spectroscopy of Excitons: Molybdenum Disulphide
Authors: Bordas J. , Davis E. A. 
Published: July 2007

AbstractIn order to clarify the role of excitons in electromodulation spectroscopy, detailed electroabsorption experiments on single crystals of 2H‐MoS2 have been undertaken. Measurements were made at 80 °K using a longitudinal field configuration, i.e. a sandwich cell, to which a square wave modulating voltage was applied. Simultaneous application of a dc bias voltage allowed the effects of incomplete field penetration to be elucidated. Modulation was obtained from the flat band condition. Detection of signals associated with both the discrete states of the exciton and the continuum has been achieved.
A Phase Shift Analysis of the Scattering of Carriers by Ionised Impurities in Non‐Degenerate Semiconductors
Authors: Boardman A. D. , Henry D. W. 
Published: July 2007

AbstractThe reliability of using the first Born approximation in the study of singly‐ionised electron‐impurity scattering has been investigated. A model, Brooks‐Herring, potential with a screening radius derived from the first Born approximation has been used in a partial wave analysis to determine violations of the Friedel sum rule. New screening radii and electron‐donor/acceptor cross‐sections, consistent with the sum rule, have been computed for a non‐degenerate system.
Optical Properties of Rhodium
Authors: Pierce D. T. , Spicer W. E. 
Published: July 2007

AbstractThe normal incidence reflectance of an electron‐gun‐evaporated Rh film measured over the photon energy range 0.5 ≦ ħ ω ≦ 11.7 eV is presented. The optical functions ϵ1(ω), ϵ2(ω), σ(ω), and the volume and surface loss functions have been calculated by a Kramers‐Kronig analysis of the appropriately extrapolated reflectance data. The structure in the optical conductivity σ(ω) at 1.1, 2.5, and 5.6 eV is compared to the predictions of a recent band structure calculation; the optical transitions giving rise to this structure are discussed. The volume and surface loss functions, which have peaks at 8.8 and 8.1 eV, respectively, are compared to characteristic electron energy loss measurements.
Vibration Spectra, Structure, and Angular Dispersion of Phonons in Crystalline Iodic Acid (α‐HIO3)
Authors: Krauzman M. , Le Postollec M. , Mathieu J. P. 
Published: July 2007

AbstractRaman and infrared spectra of oriented single crystals of α iodic acid allowed to determine the whole set of fundamental frequencies with their irreducible representations. Important static and correlation field effects did not allow to apply approximate methods to give a picture of the fundamental vibration modes. A study of the angular dispersion of polar Raman vibrations gave results in good agreement with the theoretical formulae.
Diffusion of Electron—Hole Drops and Excitons in Germanium
Authors: Martin R. W. 
Published: July 2007

AbstractThe diffusion of electron—hole drops and of excitons has been investigated in pure and doped germanium. It was found that the diffusion lengths depend on doping level, temperature, and excitation intensity. Qualitative explanations of the results based on simultaneous motion of excitons and electron—hole drops are presented.
Two‐Photon Photoconductivity Measurements in a Hexagonal ZnO Crystal
Authors: Koren G. 
Published: July 2007

AbstractTwo‐photon‐photoconductivity (TPPC) measurements in ZnO, using two different dye lasers as sources, are reported. Photocurrents produced by each laser beam separately were determined and subtracted. Linear dependencies of TPPC as a function of the intensity of one source while the other source intensity was kept constant, were found forvarious source frequencies. The spectral measurements of TPPC as a function of the frequency of one source while the other source frequency is constant show a square root dependent rise of TPPC at the crystal energy gap, at 3.38 eV, and a second very strong and approximately linear rise at 4.25 eV. This second rise is due to a forbidden one‐photonbut allowed two‐photon transition from a deeper valence band to the first conduction band in the ZnO crystal, and was also seen in ZnO crystals. A theoretical calculation, predicting qualitatively the behaviours of TPPC as a function of the sum of the energy ofthe two photons, is also given.
Calculation of Binding Energy and Elastic Constants of Simple Metals
Authors: Shimada K. 
Published: July 2007

AbstractBy use of the simple model potential which is a smooth function and whose parameters depend on the lattice constant, the total energy expression is obtained by the second order perturbation theory. One calculates the binding energy, the lattice constant, and elastic constants of simple metal with cubic structure and finds the numerical values of parameters which give good agreement with the experiment in the case of alkali metals except Li.
Localized Magnetic Vibrations of Quadrupole Impurity Strongly Coupled with the Matrix
Authors: Ivanov M. A. , Mitrofanov V. Ya. , Fishman V. Ya. 
Published: July 2007

AbstractThe spectrum of localized magnetic vibrations of an impurity atom situated symmetrically with respect to the magnetic sublattices of an antiferromagnetic crystal is considered. For an arbitrary exchange interaction of the impurity atom with the matrix the effective Hamiltonian of a spin cluster containing the impurity atom and its nearest neighbours is found. The spectrum of the low‐lying excited states for a weakly and strongly coupled impurity has quadrupole character (with Kramers degeneracy) and lies in the spin‐wave zone of the unperturbed crystal. In the case of a weakly coupled impurity the obtained results coincide with the data of exact calculation. The removal of the Kramers degeneracy in an external magnetic field and the angular dependence of the g‐factor are investigated.
Absorption, Photoluminescence, and Resonant Raman Scattering in Bil3
Authors: Petroff Y. , Yu P. Y. , Shen Y. R. 
Published: July 2007

AbstractAbsorption, photoluminescence, and resonant Raman scattering have been measured in BiI3 at low temperatures with a tunable dye laser. The results do not support the “bielectron” model of Gross et al.
On the Theory of the Interband Conductivity for Forbidden Transitions and Indirect Transitions
Authors: Henneberger K. , Strehlow R. , Wünsche H.‐J. 
Published: July 2007

AbstractFollowing an approach of Enderlein and Peuker Kubo's formula serves to calculate the differential tunneling conductivity in the cases of direct forbidden transitions and indirect (phonon‐assisted) allowed transitions. Whereas the forbidden transitions lead to a conductivity roughly hundred times smaller than for allowed transitions the contribution from the indirect transitions depends on the coupling constant of the electron‐phonon interaction and may have the same order of magnitude as for the direct allowed transitions.
Optically Active Lattice Vibrations in Bi2Se3
Authors: Köhler H. , Becker C. R. 
Published: July 2007

AbstractThe preparation of Bi2Se3 single crystals with low free carrier densities allowed an investigation of the lattice vibrations to be carried out from the reflectivity of cleavage planes at nearly normal incidence of the radiation (E ⟂ c). The experimental results can be explained with two classical oscillators, whose eigenfrequencies occur at 92 and 69.5 cm−1. The static dielectric constant was determined to be 100 ± 10 for E ⟂ c.
Theory of the Residual Resistivity of Bloch Walls I. Paramagnetic Effects
Authors: Cabrera G. G. , Falicov L. M. 
Published: July 2007

AbstractThe contribution of Bloch‐wall electron‐scattering to the electrical resistivity of a ferromagnetic metal is calculated. Calculations are carried out for various cases which include small as well as large exchange splittings. In all cases, spherical Fermi surfaces are considered, the wall width is assumed to be small compared to the intrinsic electron mean‐free‐path and diamagnetic effects are neglected. It is found that the experimental results (large negative magnetoresistance between 0 and 100 G) could be explained, even when diamagnetic effects are not included, if the majority and minority spins have sizeably different density‐of‐states at the Fermi level.
Microscopic Theory of Lattice Dynamics in Nonconducting Crystals
Authors: Mitskevich V. 
Published: July 2007

AbstractA consistent quantum‐mechanical theory of lattice dynamics in nonconducting crystals is proposed. Using the density matrix a general expression for the energy of the molecular system is derived. Taking into account the dipole moments of the electron clouds of atoms the equations of motion for the crystal lattice are obtained and the contributions in the dynamical matrix from the long‐ and short‐range interactions are derived. The influence of the overlap of the electron clouds on the terms in the dynamical matrix expression is considered.
On the Usability of Debye Theory in Mössbauer Spectroscopic Studies
Authors: Mahesh K. 
Published: July 2007

AbstractThe usability of the Debye theory of vibrational frequency spectra of solids for evaluating the Mössbauer recoilless fraction is discussed. Mössbauer effect in solid krypton is particularly considered for this purpose. The study of the effect of pressure on recoilless fraction of the Fe57 impurity in vanadium supports the Debye model. Further improvement is outlined using the concept of centro‐frequency of the vibrational spectra.
ENDOR Investigation of Cu++ Centres in NH4Cl. II. Theoretical Interpretation
Authors: Boettcher F. , Spaeth J. M. 
Published: July 2007

AbstractA theoretical interpretation is given of the superhyperfine (shf) interactions of two Cu++ centres in NH4Cl described in Part I. In the approximation of an orthogonalised envelope function including covalency admixtures and using free ion and free molecule wave functions the centres can be understood as complex centres: [CuCl2(H2O)2] (centre I) and [CuCl4(NH3)2]2− (centre II). The shf data of the NH3 and H2O molecules are understood only qualitatively in this approximation, whereas the higher shell lattice nuclei are quantitatively understood as well as those in simple impurity defects in alkali halides. The analysis gives further support for the models proposed for the two centres in Part I.
Infrared Studies of Hydrogenated SrCl2:RE3+ Crystals
Authors: Sinnema S. G. , Den Hartog H. W. 
Published: July 2007

AbstractLocalized vibrations of hydride ions in hydrogenated SrCl2:RE3+ single crystals are studied with IR spectroscopy. In moderately hydrogenated crystals doped with La3+, Ce3+, or Pr3+ two doublets are observed at about 1050 and 700 cm−1. The position and the splitting of the high frequency doublet depend upon the dopant whereas only the position of the low frequency doublet is RE‐dependent. The high frequency doublet is ascribed to a complex consisting of a substitutional trivalent lanthanide ion and a substitutional hydride ion in nearest neighbor positions (C3v oscillator). The low frequency pair is due to a localized vibration of an interstitial hydride ion neighboring a substitutional RE3+ ion (C4v oscillator). The positions of the individual lines in the C4v doublet are calculated for SrCl2:La, H and are in good agreement with experiment.
Theory of Exciton Dissociation in Molecular Crystals at the Interface of a Metal
Authors: Singh J. , Baessler H. 
Published: July 2007

AbstractThe phenomenon of dissociation of anthracene singlet excitons at the interface of the crystal and an aluminium metal layer has been treated quantitatively applying the configuration interaction scheme. HMOs are used as the wave functions of anthracene molecule. Calculated values of the rate constants are two orders of magnitude lower than the experimental ones. This discrepancy has mainly been attributed to the use of HMOs in the calculations. It has been suggested, on the basis of the results obtained for a different set of MOs, that the agreement between theory and experiment would improve by using proper molecular wave functions.
Optical Properties and Collective Excitations in GaSe in the 2 to 80 eV Range
Authors: Mamy R. , Martix L. , Leveque G. , Raisin C. 
Published: July 2007

AbstractOptical functions of GaSc are derived from the Kramers‐Kronig analysis of reflectivity data performed at quasi‐normal incidence and at room temperature in the 2 to 80 eV range. Attempts of interpretation are suggested according to recent band structure calculations. In the experimental range, all the valence electrons are excited. On the high energy side, some structure corresponds to the excitation of 3d‐electrons of Ga and Se, respectively. The calculated position of the plasmon peak is in good agreement with energy loss experiments.
Multiphonon Processes in the Spin–Lattice Relaxation of Paramagnetic Ion Nuclei
Authors: Vaisfeld M. P. 
Published: July 2007

AbstractIt is shown on the example of paramagnetic ions with a triplet ground electronic state that alongside with the two‐step Orbach‐Aminov processes multiphonon processes of the resonant type, in particular three‐ and four‐step ones, can contribute greatly to the relaxation of paramagnetic ion nuclei. 141Pr3+ ions in yttrium ethyl sulphate have been taken as an example.
On the Theory of an Impurity Molecule. I. Kinetic Energy Operator
Authors: Kiselev A. A. , Liapzev A. V. 
Published: July 2007

AbstractFor an impurity molecule the translational, rotational, and vibrational coordinates are introduced by means of the Eckart conditions. The kinetic energy operator is transformed from Cartesian to new coordinates mentioned with the help of the Frobenius theorem and the Gaussian algorithm of matrix algebra.
Dispersion Relations of Mode Grüneisen Parameters in Rubidium Halides
Authors: Jex H. 
Published: July 2007

AbstractDispersion relations of microscopic mode Grüneisen parameters have been calculated from an evaluation of a shell model to third order. Leading terms such as the anharmonic shell‐shell interaction between first and second neighbours and Coulomb contributions are taken into account. In the phonon dispersion curves breathing terms are included. The thermal expansion and mean Grüneisen constants of RbF, RbCl. RbBr, and RbI are analysed with this model.
Reconstructed Three‐Dimensional Valence Electron Momentum Density of Si from Compton Profile Measurements
Authors: Schülke W. 
Published: July 2007

AbstractRecently measured anisotropies of Si valence electron Compton profiles with the scattering vector in the [100], [110], and [111] direction are analyzed together with calculated anisotropies of the corresponding Compton profiles from a modified free electron model. From both sets of profiles the momentum density ϱ(p) is reconstructed. In comparison with the modified free electron model the experimental momentum density is strongly reduced in the vicinity of p =0.6 to 1.0 at. units along the [100] direction and enhanced mainly in the vicinity of p =1.1 at. units along the [110] direction. These main features of the reconstructed experimental momentum density are well reproduced by a pseudopotential band calculation of valence electron momentum densities along the [100], [110], and [111] directions. Also the influence of the orthogonalization term on the momentum density is estimated.
Raman Spectra of BaZnF4
Authors: Quilichini M. , Poulet H. 
Published: July 2007

AbstractRaman spectra of a single crystal of BaZnF4 have been obtained. Frequencies and symmetries of the Raman active optical phonons are given. The temperature dependence of the spectra have been examined. The directional dispersion of each of the oblique optical phonons has been measured from the Raman data and calculated. The dimensionless oscillator strengths are calculated.
Spin–Lattice Coupling Constants of Divalent Manganese in a Tetragonal Lattice
Authors: Owens F. J. 
Published: July 2007

AbstractThe shift of the fine structure resonances of Mn2+ in KN3 due to uniaxial stress are measured and the spin‐lattice Coefficients, C13 and C33 are measured t o be 3.53 × 10−13 and ‐7.06 × 10−13 cm/dyn respectively. The Blume‐Orbach model and the point ion representation of the lattice potential are used to calculate the zero‐field splitting yielding a value of +395.8 G compared to the experimental value of 534 G measured at room temperature. The theory is also used to calculate the zero‐field splitting as a function of uniaxial stress and spin‐lattice coefficients in excellent agreement with the measured values are obtained. A calculation of the implicit temperature dependence of the zero‐field splitting predicts a linear dependence on temperature with a slope of ‐0.14 G/deg which is markedly smaller than the measured value of ‐0.76 G/deg. The difference is attributed to the fact that the dominant influence in the temperature dependence is a coupling to the lattice vibrations. The effect of the relaxation of the nearest neighbor azide ions about the Mn2+ on the calculated zero‐field splitting is also considered.
Burstein Shift of the Absorption Edge of nBi2Se3
Authors: Köhler H. , Hartmann J. 
Published: July 2007

AbstractThe spectral position of the absorption edge of n‐type Bi2Se3, single crystals was determined from reflectivity measurements on cleavage planes at nearly normal incidence of the radiation (E ⊥ c). A small reflectivity peak yields a maximum of the real part n2 ‐ k2 of the dielectric constant, which is correlated to the critical photon energy of the direct absorption edge. A direct optical gap of 160 me V at 77 K is extrapolated for an empty conduction band. The temperature coefficient between 77 and 300 K is ‐2 × 10−4 eV/K. Assuming a linear temperature dependence down to T = 0 a gap of 175 me V at T = 0 and of 115 me V at 300 K is derived. For E ⊥ c a parabolic ϵ(k) relation of the valence band of Bi2Se3 is deduced with m = 0.125 m0 ± 10%.
Bloch Electrons in Irrational Magnetic Fields
Authors: Rauh A. , Wannier G. H. , Obermair G. 
Published: July 2007

AbstractA group‐theoretical analysis is given of the eigenstates of a charged particle when a magnetic field and a periodic potential are simultaneously present. The field is assumed totally or partially irrational with respect to the crystalline structure. The representations of the magnetic translation group are generated from free electron Landau states for convenience, but no discrepancies with the Frobenius method arise. The results are as follows: if H is parallel to a lattice direction, k · H is a good quantum number; otherwise, k · H may be assigned a fixed value for all members of a representation but is not numerically unique. According to group theory, there is a fixed finite δk⊥ which separates members of the same representation, and hence, equal energy. However, consideration of the energy matrix shows that there is complete degeneracy in ky for totally irrational fields; this case is thus close to the case of free electrons. In the cases intermediate between zero and totally irrational field boundary conditions may be crucial for the energy spectrum, as illustrated by an example.
Influence of Clusters on the Thermal Conductivity of GaAs
Authors: Vuillermoz P. L. , Laugier A. , Pinard P. 
Published: July 2007

AbstractThe influence of a heat treatment on the thermal conductivity of GaAs in the range 5 to 77°K has been investigated. Below 20 °K the results are interpreted on the basis of scattering of phonons by extended defects (clusters). Using Callaway's analysis the size and the number of precipitates after each quenching are calculated. In the low temperature region the effects appear also in virgin crystals and give following typical values: diameter 30 Å, concentration 1015 cm−3.
Normal Electromagnetic Waves and the Propagation of Light through Crystals
Authors: Davydov A. S. , Myasnikov E. N. 
Published: July 2007

AbstractThe conditions under which monochromatic light propagates through a crystal in the region of exciton absorption frequencies are investigated. It is shown that the plane electromagnetic wave passing through a crystal with a broad exciton band is, in the general case, a superposition of two normal waves with different refractive indices and absorption coefficients. The relative contribution of these waves is defined by the crystal temperature and the frequency of light passing through a crystal. At temperatures above a critical one only one of the normal waves gives an essential contribution. At temperatures below a critical one both the waves play a comparable role. At frequencies less the resonance one the dominant contribution is made by one of the waves, and at frequencies greater than the resonance one by the other wave. In the resonance region both the waves with different refractive indices make comparable contributions. Therefore, the attenuation of the intensity of a plane wave is different from the exponential one and the concept of a refractive index in this frequency range gives no sense.
Les spectres RPE des ions V4+ dans les monocristaux VO2
Authors: Grunin V. S. , Ioffe V. A. , Patrina I. B. 
Published: July 2007

AbstractLes spectres de la RPE des monocristaux VO2, étaient étudiés dans les diapasons X et Q à la température 77°K. Dans tous les échantillons on a observé le spectre des ions V4+ qui se décrit par le spin‐Hamiltonian avec les constantes: gx, = 1,895 ± 0,002, Ax, = 47 × 10−4 cm−1, gy, = 1,930 ± 0,005, Ay, = 44 × 10−4 cm−1, gz, = 1,925 ± 0,001, Az = 147 × × 10−4 cm−1. L'état des ions isolé V4+ dans VO2, est analogue à celui dans les structures de type routile. L'apparitions des electrons célibataires est probablement due à la présence des ions M4+ n'ayant pas des électrons 3d dans les sites de V du réseau de VO2.