bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of Resonant Brillouin Scattering in GaAs
Authors: Itoh Y. , Adachi S. , Hamaguchi C. 
Published: July 2007

AbstractThe dispersion curves of the resonant Brillouin scattering cross sections in GaAs measured by Garrod and Bray are analyzed on the basis of the resonant Brillouin scattering theory and piezobirefringence theory. The resonant enhancement and cancellation are found to be well interpreted in terms of the sign reversal of the Brillouin amplitude (or photoelastic constant). A good agreement is found between the experimental data and the present analysis. In addition the present analysis predicts a cancellation of the Brillouin scattering at Λ = 0.976 μm for the scattering by the slow transverse (Tl) acoustic phonons. This prediction is supported by the analysis of the photoelastic constant made by using piezobirefringence theory.
Precision Investigations of the Fermi Surface of Molybdenum
Authors: Gasparov V. A. , Harutunian M. H. 
Published: July 2007

AbstractThe Fermi surface (FS) of molybdenum is investigated with high precision ±;(0.2 to 0.5%) by means of the radio‐frequency size effect (RFSE) on thick samples. The anisotropy of extremal dimensions of all sheets of the FS of molybdenum in the {100} and {110} planes is measured. High precision of the measurements allows to separate effectively RFSE lines stipulated by the FS sheets with close dimensions, and to measure reliably the gaps between the tightly situated FS pieces of molybdenum. With the aid of computer calculations the analytical description of the FS is obtained in form of a series in spheric and cubic harmonics. The derivatives ∂S/∂kz for various directions kz are calculated with a computer according to these data. The extreme values of these derivatives are in good agreement with the RFSE experiments in the inclined magnetic field and with dopplerons experiment. The comparison is done of the analytical model with theoretical calculations and other experiments.
Electron Scattering by a Layer of Dislocation Lines in a Semiconductor
Authors: Gerlach E. , Kluttig H. 
Published: July 2007

AbstractIf dislocation lines are arranged periodically in a plane, the dc and the dynamical transport properties may become anisotropic around a single dislocation. The ratio of the resistivities for transport parallel and perpendicular to the plane are calculated using the energy loss method. Geometrical resonances appearing in the plasmon and in the power law regime are explained in terms of Bragg reflections by the periodic arrangement.
Use of the Symmetry‐Adapted Atomic Orbitals in the Large Unit Cell Approach to Solids
Authors: Evarestov R. A. , Lovchikov V. A. 
Published: July 2007

AbstractThe use of symmetry‐adapted linear combinations (SALC) of atomic orbitals in large unit cell (LUC) calculations of solids is considered. A procedure is proposed of SALC generation being convenient for the automation in computer calculations. It is shown that the use of the SALC in the semiempirical LUC calculations has advantages in essential computer time and memory savings and in simple distinction of the infinite crystal band states from the molecular orbitals obtained. The results of complete neglect of differential overlap (CNDO) calculations of LiF crystal LUC's in Li8F8 and Li32F32 are discussed.
A Phonon Dispersion Calculation of Silicon in the Dielectric Screening Theory a Closure Approximation
Authors: van Camp P. E. , van Doren V. E. , Devreese J. T. 
Published: July 2007

AbstractThe phonon dispersion curves of silicon are calculated based on the dielectric screening approach. Electron wave functions and energies are obtained from a Hamiltonian matrix with a pseudo‐potential which is self‐consistent with the electron‐ion potential. A direct summation of up to 40 conduction bands in the polarizability matrix yields a negative square of the TA mode. Positive frequencies are obtained if closure over all conduction states is used by treating the energy denominator as a constant. The results are in reasonable agreement with experiment.
Calculation of Soft X‐Ray Emission Spectra by the Relativistic APW Method: Lutetium
Authors: Nemoshkalenko V. V. , Antonov Vl. N. , Antonov V. N. , John W. 
Published: July 2007

AbstractStarting from the Dirac equation an expression for the intensity of the X‐ray emission spectra is derived in the one‐electron approximation. As an example the OIII‐emission spectrum of lutetium is calculated by the relativistic APW method. The numerical results, which are obtained by using alternative dipole matrix elements are in reasonable agreement with the measured X‐ray emission spectrum.
Influence of Dislocations on the Cyclotron Resonance Absorption in Tellurium
Authors: Gerstenhauer E. , Bauer G. , Grosse P. , Doukhan J. C. 
Published: July 2007

AbstractIn tellurium a‐glide dislocation systems are activated by uniaxial compression experiments at T = 300 and 77 K. The dislocation substructures, chosen with respect to their elastic strain field, are characterized by etch pit counting and X‐ray topography. Optical transmission experiments performed under cyclotron resonance conditions in the submillimeter wavelength region (Λ = 337 and 311 μm) show a considerable effect of the dislocation density and configuration on the observed spectra. The appearance of CRI mode absorption is accounted by a change of the dielectric tensor in the basal plane, as caused by the dislocation strain field.
X‐Ray Spectra and Electronic Structure of Some CsCl‐Type Transition Metal‐Aluminium Alloys
Authors: Blau W. , Weisbach J. , Merz G. , Kleinstück K. 
Published: July 2007

AbstractThe aluminium Kβx emission spectra and transition metal L2,3 emission and self‐absorption spectra of the alloys VAl, FeAl, CoAl, and NiAl are measured by the use of a primary Bragg‐Soller spectrometer. Emission spectra and absorption spectra are converted into differential emission probabilities. Therefore, their height relations are significant. The spectra and the integral intensities are discussed in terms of free electron‐d‐resonance and charge transfer. A detailed comparison with bandstructure calculations will be presented in a second paper.
Luminescence of KBr:In+
Authors: Casalboni M. , Crisanti F. , Grassano U. M. , Manfroncelli C. , Scacco A. , Tanga A. 
Published: July 2007

AbstractThe temperature dependence of the luminescence spectra and of the emission lifetimes are measured in KBr:In+. From these results detailed information is obtained on the adiabatic potential energy surface of the relaxed excited state.
Thermoreflectance of CdCr2S4 near the Curie Point
Authors: Iliev M. , Pink H. 
Published: July 2007

AbstractThe thermoreflectance (TR) spectrum of the ferromagnetic semiconductor CdCr2S4 (Tc = 86 K) is measured between 24 and 330 K at photon energies ranging from 1. 5 to 3. 2 eV. A magneticorder‐induced band splitting associated with the earlier observed anomalous C‐band (Ec = = 1. 87 eV at 4. 2 K) is found below the Curie‐Weiss temperature as well as an additional “red shifting” structure at higher photon energies. The results support the assumption of a strong coupling between the electron and spin subsystems in ferromagnetic spinels. The mechanism of the spin‐dependent electronic processes seems to be more complex than predicted by the simplest models.
On the Renormalization of Collective Excitations in Intermediate Valence Metals
Authors: Barabnov A. F. , Tsvelik A. M. 
Published: July 2007

AbstractThe experimentally known minimum of the longitudinal sound velocity in the vicinity of the electronic phase transition is explained for metals with intermediate valence. It is shown that the density of states on the Fermi surface increases due to s‐fhybridization. This increase givesrise to screening of the electron‐ion interaction and hence the longitudinal sound velocity is reduced. The theoretical calculation is compared with experimental data for the γ‐α transition in Ce. It is also shown that the hybridization does not reproduce the existence of the recently proposed acoustic plasmon branch in intermediate valence metals.
Electron‐phonon and electron Raman scattering in polar semiconductors in high magnetic fields
Authors: Goltsev A. V. , Lang I. G. , Pavlov S. T. 
Published: July 2007

AbstractResonant electron‐phonon and electron Raman scattering are investigated in direct‐band polar semiconductors in high magnetic fields. The secondary radiation cross‐section is calculated as a function of the incident and emitted light frequencies ω1 and ωs, the magnetic field H and the direction of the emitted light. It is shown that for arbitrarily high magnetic fields, the appearance of sharp peaks in the cross‐section as a function of ω1 and ωs is due to electron and hole transitions into states kz = 0, kz being the projection of the electron or hole wave vector on the direction of H. Sharp maxima are also found at the cyclotron frequencies of electrons and holes. A study of the secondary radiation polarization suggests that the polarization is determined by the energy of the secondary radiation quantum and its direction of propagation as well as by the electron‐hole effective mass ratio.
Correlated pairs and a mass action law in two‐component Fermi systems excitons in an electron‐hole plasma
Authors: Stolz H. , Zimmermann R. 
Published: July 2007

AbstractIn an electron‐hole (or electron‐proton) plasma the density of either species is calculated from the single particle Green's function including ladder type diagrams. The density can be decomposed into contributions of uncorrelated quasiparticles and particles in correlated pairs, the latter referring to both, bound and scattering states. No discontinuity occurs at the Mott criterion. In the non‐degenerate limit a mass action law is obtained which is illustrated by a simple model calculation.
Nonlinear transport in Qn(TCNQ)2
Authors: Mihály G. , Jánossy A. , Kürti J. , Forrö L. , Grüner G. 
Published: July 2007

AbstractA nonlinear electric field dependence is found in the quasi‐one‐dimensional organic conductor Qn(TCNQ)2. The non‐Ohmic behaviour sets in at electric fields as low as 2 V/cm and it is observed to temperatures above 100 K. Results obtained on a series of crystals with different lengths show that in defect‐free crystals the nonlinearity is intrinsic. Microscopic breaks enhance while chemical impurities depress the nonlinearities. The observations are in contradiction with a simple band semiconductor model and also with models where transport properties are assumed to be determined by short localization lengths.
Quantum‐limit magnetoresistance for impurity scattering
Authors: Arora V. K. , Spector H. N. 
Published: July 2007

AbstractThe theoretical formalism for calculating the magnetotransport effects developed by Arora and Peterson is extended to include the effects of anisotropic screened ionized impurity scattering in nondegenerate semiconductors in the quantum limit when ħωc ≫ kBT. Screening is found to be negligible at high magnetic fields for the transverse magnetoresistance. It is found that for point defect scattering, both the longitudinal and transverse magnetoresistance are linear in the magnetic field, whereas the Hall coefficient differs from its high field value 1/encc by a temperature dependent factor which is found to be close to unity. For ionized impurity scattering, the longitudinal magnetoresistance is found to be independent of the magnetic field, whereas the transverse magnetoresistance and the Hall coefficient decrease with magnetic field, the former as B−1, where B is the magnetic field. For combined acoustic phonon and ionized impurity scattering, the acoustic phonon scattering is found to dominate at very high magnetic fields giving rise to the ex‐perimentally observed linear magnetoresistance. The combination of acoustic phonon and point defect scattering also yields similar results.
Investigation of n‐Pb1−xSnxSe absorption spectra
Authors: Luchytskii B. M. , Manzhara V. S. , Staryk P. M. 
Published: July 2007

AbstractThe long‐wavelength edge of fundamental absorption and absorption by free carriers of Pb1−xSnxSe (x = 0.06) single crystals with free electron concentration 1.0 × 1017 ≦ N ≦ 5.0 × 1018 cm−3 is investigated. The absorption coefficient within 10 to 1500 cm−1 is shown to be exponentially dependent on photon energy. In samples with N > 5.0 × 1017 cm−3 the absorption edge is described by the Urbach rule only at high temperatures. At T < TU the Burstein‐Moss effect dominates the shape of the absorption edge. A correlation between the calculated electron‐phonon coupling parameters γ and the experimental (2/3) σ values is found. The temperature dependence of light absorption at λ = 14 μ by free carriers is investigated. Manifestation of the conduction band non‐parabolicity in the considered phenomena as well as the scattering mechanism of free electrons are discussed.
Iterative EHT calculations for the positive divacancy in silicon
Authors: Weigel C. , Ammerlaan C. A. J. 
Published: July 2007

AbstractIterative EHT calculations are carried out for the positive divacancy in silicon with an improved set of EHT parameters for silicon. The nearest neighbours of the divacancy are systematically displaced in the symmetry‐allowed distortion modes until an acceptable agreement between calculated and experimentally derived wave function coefficients is reached for the nearest neighbours. At this particular distortion, the agreement for several shells of next‐nearest neighbours also appears reasonable.
On the theory of absorption and luminescence spectra in amorphous semiconductors
Authors: Sprenger D. 
Published: July 2007

AbstractOptical transitions in a system of randomly distributed localized electron states coupled to the phonon system are considered. A general expression for the spectral dependence of the absorption coefficient and the luminescence intensity is derived. This expression is applied to the uncorrelated case where the spectral dependences are determined by a density‐of‐states model. Various types of optical transitions within a density‐of‐states model are considered and the corresponding spectral dependences discussed. The derived spectral representation allows the direct calculation of the temperature dependent moments for the various bands.
Fast radiationless recombination in amorphous silicon
Authors: Rehm W. , Fischer R. 
Published: July 2007

AbstractThe luminescence of armorphous silicon is excited by intense dye laser pulses of different energies. The variation of luminescence intensity with excitation intensity follows a square‐root law at high intensities. This indicates that here the recombination kinetics is governed by a bimolecular non‐radiative recombination process.
Stimulated brillouin scattering of helicon waves in a semiconductor
Authors: Sodha M. S. , Sharma R. R. 
Published: July 2007

AbstractA right‐handed circularly polarised helicon wave decays resonantly into a low‐frequency acoustic wave and a scattered helicon wave in a piezoelectric semiconductor. The low‐frequency nonlinearity arises through the parallel ponderomotive force on electrons whereas the high‐frequency nonlinearity arises through the equation of continuity. The growth rate of instability turns out to be ≈︁ 103 s−1 for 1 to 10 MHz acoustic perturbations when a microwave of 20 kW/cm2 propagates through n‐InSb.
Central peak in ising model with transverse field
Authors: Kashcheev V. N. 
Published: July 2007

AbstractThe momentum and temperature dependence of the central peak (CP) width is found for the Ising model with a transverse field in the right neighbourhood of the Curie point. The width of CP in the critical and hydrodynamic limits is described by a scaling‐type relation. During deuteration the width of CP diminishes as a squared tunneling frequency.
Pb2+ and Bi3+ impurity centres in alkali‐earth oxides vibronic spectra, lattice dynamics, and electron‐phonon interaction
Authors: Zavt G. S. , Ellervee A. F. 
Published: July 2007

AbstractThe vibrational structure in the emission spectra of Pb2+‐ and Bi3+‐doped CaO and SrO single crystal is studied at 4.2 K. The emission spectra are caused by the forbidden 3A1u → 1A1g transition which is initiated by the mixing of 3A1u and 3T1u states by T1g lattice vibrations. A theory is given which takes into account, within the Cochran‐Cowley shell model, a linear vibronic coupling to A1g modes and a change of force constants in the final electronic state. In most cases the main source of the electron‐phonon interaction is found to be the coupling of the transition with the electronic polarization of the nearest anions. The T1g‐symmetry‐projected phonon density of states is shown to be concentrated within a narrow interval of the order of 10 cm−1. An estimate is presented showing that the hyperfine interaction can be responsible for the appearance of the weak zero‐phonon lines observed in the emission spectra.
Energy band structure of Cd3P2 for real D symmetry II. Symmetry properties
Authors: Plenkiewicz P. , Dowgiallo‐Plenkiewicz B. 
Published: July 2007

AbstractThe fundamental symmetry properties of the D space group, necessary in determining the band structure of Cd3P2 are studied in detail. The SCPW for all points and axes of high symmetry, and the compatibility relations for this group are constructed. The selection rules for double‐valued representations are calculated. Finally, the consequences of including spin to the calculated band structure of Cd2P2 are discussed.
Pressure dependent conductivity in InSb
Authors: Lam H. Y. , Jones R. E. , Keeler W. J. , Paranjape V. V. 
Published: July 2007

AbstractThe pressure dependent conductivity of n‐type InSb at 81 K is investigated theoretically and experimentally up to 10 kbar. In the calculations, the mobility is assumed to be dominated by ionized impurity scattering. An expression for the pressure dependent conductivity is obtained by considering the pressure dependence of the non‐parabolic conduction band, the dielectric constant, and the effective mass. The theoretical analysis, in spite of its simplicity, does explain the variation of conductivity with pressure up to 5 kbar although some deviation occurs at higher pressures.
Magnetic susceptibility of the A‐15 compound system (V1−xCrx)3Si
Authors: Handstein A. , Pietrass B. , Behr G. 
Published: July 2007

AbstractThe magnetic susceptibility of single and polycrystalline samples of the A‐15 compounds (V1−xCrx)3Si (0 ≦ x ≦ 1) is measured at temperatures between 4.2 and 320 K. The magnitude and the temperature dependence of the susceptibility diminish with increasing Cr concentration. Applying a peak model for the density of electronic states it is found that the change of the temperature dependence of the susceptibility with increasing Cr concentration is caused mainly by broadening of the peak in the density of electronic states.
Optical‐acoustic two‐phonon relaxation in spin systems
Authors: Singh A. , Shrivastava K. N. 
Published: July 2007

AbstractThe two phonon Raman process of spin–lattice relaxation is investigated in spin systems having electronic properties appropriate to both optical and acoustic branches of phonon spectrum. Apart from exponential temperature dependence of relaxation times for resonance processes, T−3‐, T−4‐, T−5, and T−6‐processes are found for both branches under several conditions. However, when the Debye energy is very high, the T−2‐dependence dominates with corrections of T−3 and T−4. The level structure of the spin system is found to be important for the temperature dependence of relaxation times.
Self‐trapped exciton and F centre formation by picosecond laser pulses in alkali bromides and iodides
Authors: D'Hertoghe J. , Jacobs G. 
Published: July 2007

AbstractSingle crystals of NaBr, RbBr, KBr, CsBr, NaI, KI, RbI, CsI are excited by two‐photon absorption of the second harmonic of a mode‐locked ruby laser at room temperature and/or below. Induced absorption is measured at the wavelength of the first harmonic. The measured absorption is interpreted in terms of the formation of the lowest triplet state of the STE or of F centre formation depending on the case and the temperature.
Energy levels at Γ‐point in Hg1−xMnxTe in intense magnetic fields
Authors: Byszewski P. , Szlenk K. , Kossut J. , Gała̧zka R. R. 
Published: July 2007

AbstractMeasurements of Shubnikov‐de Haas effect in Hg1−x, MnxTe for x = 0, 0.02, 0.04, 0.09 in magnetic fields up to 30 T are reported. The experiments are interpreted within a model which takes into account the exchange interaction of mobile electrons and 3d localized electrons of Mn. At very low temperatures the freeze‐out effect is also observed.
Theory of nonradiative multiphonon transitions in impurity centers with extremely weak electron‐phonon coupling
Authors: Pukhov K. K. , Sakun V. P. 
Published: July 2007

AbstractThe nonradiative multiphonon (NMP) electron transition rate in impurity centers in ionic crystals is calculated taking into account high‐order anharmonicity terms in expansion of the electronphonon (EP) interaction in atomic displacements. In the extremely weak coupling limit the traditional potential energy surface displacement relaxational mechanism is shown to be inefficient and NMP relaxation is caused mainly by high anharmonicity of the EP interaction. For this limit a new formula is obtained, which may be applied, e.g., in analysing the NMP relaxation of RE ions in ionic crystals.
Multimode Jahn‐Teller effect for an E term with strong vibronic coupling I. Local and resonant states
Authors: Polinger V. Z. , Bersuker G. I. 
Published: July 2007

AbstractThe multimode Jahn‐Teller (JT) effect problem for an impurity orbital doublet strongly linearly interacting with lattice vibrations is solved. Within the adiabatic approximation the behaviour of the system is reduced to its collective rotation along and to small harmonic vibrations near the bottom of the circular trough of the potential surface. The JT interaction induces JT local and resonant states essential in the interpretation of the fine structure of vibronic spectra. The conditions of their occurrence are discussed.
The electronic theory of SiGe solid solutions
Authors: Soma T. 
Published: July 2007

AbstractThe pseudopotential theory of covalent crystals is applied to Si1−xGex systems using the virtual crystal approximation, the pseudo alloy atom model, and the ordered zinc‐blende‐type lattice (Si0.5Ge0.5). Calculated values of the equilibrium point are in good agreement with the experimental lattice constants. But, at the low temperatures, the phase mixture Si1−x + Gex is favourable compared with the disordered solid solution.
Isotope effect on the Verwey transition temperature of magnetite
Authors: Terukov E. I. , Reichelt W. , Ihle D. , Oppermann H. 
Published: July 2007

AbstractElectrical resistance and DTA measurements on single crystals of Fe3O4, in which the oxygen is partially replaced by the stable isotope 18O, show a positive isotope shift in the Verwey transition temperature TV of δTV = (6.1 ± 0.05) K for the 18O concentration of 43%. This result can be qualitatively explained by a theory which is based on the concept of the condensation of a coupled charge density–phonon mode at TV and takes into account both the electron–phonon and the electron–electron interactions.
Spontaneous polarization of NH4Cl at the order–disorder phase transition
Authors: Kessler A. , Koreng B. 
Published: July 2007

AbstractMeasurements of the spontaneous polarization of doped and undoped NH4Cl at the order‐disorder phase transition are carried out. It is found that the cause of the polarization is an off‐centre position of divalent impurities. The transition into the polarized state is of first order and is most probably caused by a coupling between aligned dipole moments of the centers and a distortion of the lattice due to the reverse piezoeffect.