bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stimulated Brillouin scattering of transversely polarized electromagnetic waves in magnetoactive moderately piezoelectric semiconductor plasmas
Authors: Ghosh S. , Khan S. 
Published: July 2007

AbstractAn analytical investigation is made of the stimulated Brillouin scattering of a large amplitude, transversely polarized, electromagnetic pump wave produced by both, an electron‐plasma wave and acoustical phonon vibrations in a magnetoactive n‐type moderately piezoelectric semiconductor. Using the hydrodynamical model of plasma, the general dispersion relation is obtained in the presence of a large magnetostatic field applied at an arbitrary angle θ to the direction of propagation of the pump wave. The analysis is applied to both the cases of isotropic (B0 = 0) and magnetoactive (B0 ± 0) plasmas. The threshold electric field necessary for the onset of Brillouin instability and the growth rate of the unstable Brillouin mode well above the threshold are studied. It is concluded that the threshold pump amplitude as well as the growth rate are strongly dependent on the orientation of the magnetostatic field with respect to the directions and magnitudes of the wave vectors k and k1 of the acoustic and scattered electromagnetic waves, respectively.
Theory of interimpurity transitions in condensed medium
Authors: Christophorov L. N. , Kharkyanen V. N. 
Published: July 2007

AbstractThe problem is investigated of the quantum particle transfer between impurities imbedded in a condensed medium via the states of the latter. The kinetic equation containing explicitly no medium indices (the role of medium is taken into account by effective constants found from “free” medium properties) is obtained. The two‐impurity case (the donor‐acceptor transfer) is considered in detail for an one‐dimensional model of a crystal.
Peculiarities of phase transitions and physical properties in (NH4)2SbF5
Authors: Avkhutskii L. M. , Davidovich R. L. , Zemnukhova L. A. , Gordienko P. S. , Urbonavičius V. , Grigas J. 
Published: July 2007

AbstractThe dynamics of the (NH4)2SbF5 crystal lattice showing the superionic phase transition is studied in a broad temperature interval by NMR and NQR methods, together with electrophysical and calorimetrical properties. The investigations establish the ionic state of the axial fluorine atom in relation to equatorial atoms in the [SbF5]2− complex. The successive phase transitions are revealed and the mechanism of phase transitions is elucidated. The phase transitions are caused by the reorientation movements of NH4 and [SbF5]2− groups. The paper also describes the influence of water solution inclusions in the crystal on the superionic phase transition.
Local partial DOS and experimental Al K spectra of transition metal aluminides charge transfer trend
Authors: Müller Ch. , Blau W. , Ziesche P. 
Published: July 2007

AbstractFor the B2‐type compounds VAl, CrAl, MnAl, FeAl, CoAl, and NiAl the local partial DOS (densities of states) and the corresponding integrated DOS are determined on the basis of a linear KKR‐method. The calculated local partial DOS are directly compared to experimental SXE (soft X‐ray emission)‐spectra. The integrated local partial DOS provide the valence charge distributions per unit cell. The latter are used to estimate the charge transfer in the intermetallic compounds. The calculated results are in good agreement with the experimental observed trend.
Energy losses in crystalline and amorphous solids in the intermediate energy region
Authors: Kührt E. , Wedell R. 
Published: July 2007

AbstractUsing the classical theory for two moving charged particles the electronic stopping power of amorphous and random oriented crystalline solids is calculated. It is shown that in the intermediate energy region, where the stopping is maximized, motion of the target electrons must be considered. The specific problems of energy losses in crystals are discussed and directional effects are taken into account. Calculated values of the stopping power agree well with experimental results for protons in the random as well as in the channeling regime.
Charged‐particle stopping in crystals
Authors: Khodyrev V. A. , Sirotinin E. I. 
Published: July 2007

AbstractThe energy loss by a charged particle moving along a given path in the crystal lattice is calculated in terms of quantum perturbation theory. In calculating the contribution of excitations with lowenergy transfer, the sum rule is used. The highly‐excited states are described in a quasi‐classical approximation. The results obtained with these approximations coincide in the intermediate region of excitation energy. The results obtained allow the electrons of the core and the valence electrons to be treated from a unified standpoint. The averaging of the obtained expression for ΔE(b) over the random impact‐parameteri distribution leads to the Lindhard‐Scharff formula. The calculated dependence of the mean relatve proton‐energy loss upon the dechanneling depth is compared with available experimental data.
Volume dependence of the melting temperature for alkali metals with Debye's model
Authors: Soma T. , Kagaya H.‐Matsuo , Nishigaki M. 
Published: July 2007

AbstractUsing the volume‐dependence of the Grüneisen constant at higher temperatures, the volume effect on the melting temperature of alkali metals is studied by Lindeman's melting law and Debye's model. The obtained melting curve increases as function of the compressed volume and shows the maximum of the melting point at the characteristic volume. The resultant data are qualitatively in agreement with the observed tendency for alkali metals.
On the theory of singlet and triplet charge‐transfer excitons
Authors: Schmid B. J. , Reineker P. P. 
Published: July 2007

AbstractA many‐particle Hamiltonian for electrons which takes into account their energy in a periodic potential and in an external magnetic field, as well as their Coulomb and spin—spin interaction energies is specialized for charge‐transfer excitons on a linear chain with one donor and one acceptor molecule in the unit cell. The Hamiltonian decomposes into a part for singlet excitons, which is diagonalized exactly, and a part for triplet excitons, whose diagonalization is reduced to wave vector dependent eigenvalue problems of the dimension of the unit cell. The fine‐structure tensor is expressed explicitly in terms of electronic matrix elements.
Observation of dispersion on magnetic polaritons
Authors: Häussler K. M. , Brandmüller J. , Merten L. , Finsterhölzl H. , Lehmeyer A. 
Published: July 2007

AbstractFar‐infrared reflectivity measurements on uniaxial antiferromagnetic CoF2 display a characteristic dispersion of the magnetic reststrahlenbands if the wave vector components of the radiation are varied by choosing different angles of incidence. Thus the expected dispersion behaviour of the socalled magnetic polaritons is demonstrated experimentally in a direct manner for the first time. The simulation of the infrared reflectivity spectra based on a generalized formula for anisotropic magnetically ordered insulators shows good agreement with the experimental results and can be used to predict even weak polariton dispersion effects.
Photoinduced absorption spectra of ZnS:Fe crystals
Authors: Zimmermann H. , Boyn R. , Nagel N. 
Published: July 2007

AbstractPhotoinduced absorption (PA) spectra of ZnS:Fe crystals are measured between 0.3 and 3.6 eV by means of a modulation technique. Transitions related to the charge states Fe3+ and Fe+, which have been detected by EPR a long time ago, are believed to be seen in these spectra. In particular, the processes Fe3+ → Fe2+ + h and Fe2+ + Fe3+ + e are identified, the latter manifesting itself most clearly in the excitation spectrum of the PA band due to the former transition. The shapes of the photoneutralization and photoionization spectra are discussed, and the position of the Fe+ ground state in the forbidden gap is estimated.
Emission of free and bound excitons in layered gase crystals
Authors: Gnatenko Yu. P. , Kovalyuk Z. D. , Skubenko P. A. , Zhirko Yu. I. 
Published: July 2007

AbstractThe emission spectra of GaSe single crystals of ϵ‐modification doped with Co of 0.001 to 0.5 wt% concentration are investigated at different temperatures (T = 4.2 to 35 K) using polarized light. It is shown that the wide emission band with energy 2.031 eV is due to structural defects while the other wide bands of 2.039 and 2.008 eV are due to indirect exciton transitions with radiation of TO‐phonons. The narrow emission lines correspond to the decay of direct excitons bound on different defects and to their phonon sattelites involving phonons of (14.5 ± 0.5) meV. The temperature dependence of a doublet structure of the free exciton emission line, which is thought to be due to the peculiarities of the GaSe crystal band structure, namely the splitting of the valence band by inter‐layer interaction is investigated.
Temperature dependence of the wannier‐stark level width in a semiconductor in a strong electric field
Authors: Berezhkovskii A. M. , Ovchinnikov A. A. 
Published: July 2007

AbstractAnalytical expressions for the level width of the Wannier‐Stark ladder caused by an electron‐phonon interaction are derived. They allow to investigate the dependence of the width on temperature, external field, and semiconductor band parameters. It turns out that with increase in temperature the width associated with acoustic phonons is drastically increased whereas the width associated with optical phonons rises much more slowly. It seems that almost all experiments for finding the Wannier‐Stark ladder had been carried out at too high temperatures when the interaction of an electron with acoustic phonons eliminates the ladder.
Optical conductivity in the impurity band of doped semiconductors
Authors: Gryko J. 
Published: July 2007

AbstractA formula for the optical conductivity is derived from the Kubo relation in a framework of tightbinding approximation using a method due to Matsubara and Toyozawa. The derived formula is applied to the calculation of the optical conductivity and optical absorption in the far IR of doped semiconductors at low temperatures. The calculated values of the optical absorption obtained using different approximated Green's functions are compared with the experimental data for Sb doped germanium.
Hartree‐fock exchange and LCAO approximation in the band structure calculations of solids
Authors: Evarestov R. A. , Lovchikov V. A. , Tupitsin I. I. 
Published: July 2007

AbstractIt is shown that the use of the simple cubature formula for the approximate calculation of the density matrix Qrr in the non‐local Hartree‐Fock exchange for crystals leads to a non‐physical divergence of the lattice sums. To overcome this difficulty it is proposed to introduce a weight function in the cubature formula for the numerical integration over the Brillouin zone in calculating non‐local exchange. It is discussed the simple way to choose the nodes of the numerical integration which is based on the large unit cell transformation in the direct and reciprocal lattices. This choice allows to extend the special point technique of the Brillouin zone integration to the non‐local exchange calculation.
Phase Segregation in Tellurium‐Saturated GeTe
Authors: Vengalis B. , Valatska K. 
Published: July 2007

AbstractRegions with different free hole concentrations and different lattice distortions are assumed to explain the specific heat, electrical resistivity, and IR reflectivity data for annealed GeTe crystals with 50.4 to 50.8 at% Te. The phase segregation is explained taking into account free hole redistribution between the twelve Σ‐valleys of the material.
Dispersion of Optical Constants in Cdp2
Authors: Babonas G. , Korets N. S. , Marcinkevičius S. 
Published: July 2007

AbstractSpectral dependences of the gyration tensor components g11, g33, refraction indices and birefringence of tetragonal CdP2 are investigated at 300 K. The optical activity of the crystal is found to be determined by both the crystal and the molecular contributions, the latter being due to the distortion of the tetrahedral symmetry of the structural elements. The dispersion of the refractive indices is discussed on the basis of a single‐effective‐oscillator model. The ionicity of CdP2 is equal to 0.56 and is close to the values of AIIBVI compounds and the ionicity of CdP bond in AIIBIVC semiconductors. The dispersion of the spectroscopic properties of CdP2 is concluded to be mainly determined by the CdP bound.
Band‐Gap Narrowing in n‐Type Moderately Doped Silicon at 300 K
Authors: Vancong H. 
Published: July 2007

AbstractThe band‐gap narrowing at 300 K in n‐type moderately doped silicon is investigated, basing on a second‐order Thomas‐Fermi model which was first developed by Friedel and recently by Van Cong et al. There are three contributions to band‐gap narrowing: (1) Δg,opt (rigid‐band effect), (2) Γn (non‐rigid band effect), and (3) ΔEg,FD (Fermi‐Dirac statistics effect), where ΔEg,FD is negligible because of large negative values of the Fermi energy. ΔEg,opt is a major contribution, while Γn only takes an effect at sufficiently high donor concentrations; they increase with increasing doping. It is suggested that the numerical results of ΔEg, opt and ΔEg, elec ≈︁ (ΔEg, opt + Γn) are in good agreement with optical measurements of Balkanski et al., and with electrical measurements of Mertens et al., respectively. Finally, the present results of ΔEg,opt and Γn are also compared with a recent theory of Lanyon and Tuft, and with that of Dhariwal and Ojha, respectively.
Comparative Studies of Fast Recombination Processes in Amorphous Silicon Films
Authors: Bergner H. , Brückner V. , Kerstan F. , Nowick W. 
Published: July 2007

AbstractComparative studies of recombination processes of laser‐induced charge carriers in the picosecond range are performed in amorphous silicon films prepared by glow discharge technique, UHV evaporation, and sputtering. By means of time‐resolved reflectivity and conductivity measurements a two‐step relaxation process is obtained, where the time of the fast recombination process decreases with increasing defect density. Some semiconductor parameters (recombination constant, capture cross‐section, carrier mobility) are estimated using experimental results.
Experimental Investigations of Electron‐Hole Plasma in Tellurium‐Doped Gap
Authors: Schwabe R. , Streit I. , Thuselt F. , Unger K. 
Published: July 2007

AbstractPhotoluminescence spectra are measured for GaP doped with tellurium in the density range of 2 × 1017 to 5 × 1018 cm−3 at low temperatures. At low doping concentrations and high excitation an electron‐hole liquid is observed only weakly influenced by the impurities. An obvious feature that emerges in intermediately doped samples is the coexistence of two plasma‐like phases, in qualitative agreement with theoretical expectations. The results obtained from the spectra are supported by decay measurements. Further, from the decay times also Auger coefficients are determined.
Effective Debye Temperature of the (110) Ni Face for Different Azimuths
Authors: Mróz S. , Mróz A. , Grudniewski A. , Bąk E. 
Published: July 2007

AbstractThe effective Debye temperature θeff for directions normal to the (110) Ni face and with an angle of about 54° to the normal is measured by LEED for different azimuths, for electron energies of 70 to 100 and 130 to 160 eV, respectively, and for the incidence angle of a primary beam of about 60°. Under such conditions the primary electron beam is diffracted mainly on the first layer of atoms and averaging over an azimuth angle should eliminate the multiple scattering effects. Therefore, the averaged effective Debye temperature θ should describe the vibrations of atoms in the first layer. Values of θ⟂ = (218 ± 20) K and θ54° = (287 ± 20) K are obtained. A dependence of θeff,54° on the azimuth angle is not found, in contradiction to the theoretical prediction for the face investigated. The ratio 〈u2⟂〉 / 〈u〉 calculated by applying our results is equal to 3.37, in good agreement with calculations based on quasi‐harmonic and anharmonic approximations.
Electronic Spectrum of the Co(II) Ion in the Columbite CoNb2O6 Host Lattice at 4.2 K
Authors: Borromei R. , Cavalli E. , Ingletto G. 
Published: July 2007

AbstractThe polarized absorption spectrum of the Co(II) ion in CoNb2O6 at 4.2 K in the range 5000 to 28000 cm−1 with the electric vector E parallel to all three crystallographic axes is reported. After a careful examination of the excited states and of the site symmetry, the bands are assigned as “ligand field bands”. As far as the intensity is concerned, the most contribution is due to the effect of the local distortion, but the effects of the spin–orbit coupling and vibronic interaction are also taken into consideration. The assignments are confirmed from the behaviour of the intensity of the polarized bands and from a ligand field calculation that fits the band energies very well.
Influence of a Strong Electric Field on the Carrier Capture by Nonradiative Deep‐Level Centers in GaAs
Authors: Prinz V. Ya. , Rechkunov S. N. 
Published: July 2007

AbstractThe techniques of capacitance spectroscopy are used to measure directly electron and hole capture cross‐sections of deep levels in a neutral material at zero electric field and in the depletion layer with a strong electric field. The data show that if at zero electric field the electron capture cross‐sections onto the centers are thermally activated and described by the theory of nonradiative multiphonon capture, then in a strong electric field (F ≈ 104 V/cm) the capture cross‐sections increase to the limiting large value (σ ≈ 10−14 to 10−12 cm2) and are only little dependent on temperature. It is shown that an electric field causes a simultaneous increase of the electron and hole capture cross‐sections of the level EL2 by five orders of magnitude at low temperatures (T ≈ 90 K).
Thermally Stimulated Depolarization of AsO Centres in Alkali Halide Crystals
Authors: Pilatus U. , Fischer F. 
Published: July 2007

AbstractA TSD band below LNT attributed to the AsO centre is observed in several alkali halide crystals. In KI:AsO by annealing at 150 °C the 60 K band can be decreased while a 19 K band appears. NaI:AsO has a band at 11 K. Measured dipole moments of the AsO centre are between 0.9 and 1.2eÅ depending on the off‐centre displacement of the ionic charge.
The Metallic and Ionic Contributions to Lattice Vibrations of III–V Covalent Crystals
Authors: Soma T. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractThe binding force, which includes partially ionic contributions in addition to covalent interactions based on the pseudopotential formalism, is proposed for III–V tetrahedral compounds. Numerical calculations on the phonon dispersion curves are performed for GaAs, GaSb, InAs, and InSb. The resulting ones are qualitatively in good agreement with the observed data in spite of no introducing of adjustable parameters except for the optical phonon‐frequency splitting in the long wavelength limit.
Statistics and Transport Behaviour of Electrons in SiO2
Authors: Köster H. , Hübner K. 
Published: July 2007

AbstractAn analytical expression for the statistical distribution function of conduction electrons in SiO2 is derived by taking into account static electric fields of different strengths and various types of electron‐phonon interaction (i.e. scattering of electrons due to longitudinal‐optical, transversaloptical, and acoustic modes). Electronic energy balances and critical electric field strengths as well as the threshold and runaway behaviour of conduction electrons are derived from their distribution function, the time and field dependence of which is analysed quantitatively.
Covalency as Source of Intensity for d‐d Transitions in Octahedral Complexes
Authors: Malakhovskii A. V. , Vasilev G. G. 
Published: July 2007

AbstractA pair‐vibrational mechanism is suggested for inducing of spin‐forbidden d‐d transitions in centrosymmetric complexes. Only the vibrational part of this mechanism appeared to be sufficient to account for the observed strong difference in intensity of the corresponding d‐d transitions (spinforbidden included) in different crystals with analogous magnetic properties. This phenomenon is proved to be due to the difference in the degree of covalency of the metal‐ligand bonds and not to the difference in the value of crystal fields in the compounds. Experimental results obtained on the crystals RbMnF3, CsMnF3, and RbMnCl3, (in hexagonal and cubic modifications) are in agreement with the drawn deductions.
Magnetic Properties of the Ising Model with a Free Surface
Authors: Tamura I. , Sarmento E. F. , Fittipaldi I. P. , Kaneyoshi T. 
Published: July 2007

AbstractThe magnetic properties in a semi‐infinite ferromagnetic Ising model with enhanced surface couplings are studied by means of a new type of correlated effective field theory. For suitably enhanced surface exchange couplings Js = J(1 + Δ) there are surface orderings. A phase diagram, magnetization curves for surface and bulk, and short‐range order parameters are calculated.
Thermal Conductivity of LiF Containing Dislocations at Low Temperatures
Authors: Kumar A. , Sinha A. K. , Ansari M. A. 
Published: July 2007

AbstractThe thermal conductivity at very low temperatures of LiF crystals containing dislocations are analysed by using the Callaway model, Callaway's approximations, and approximations suggested by Kumar and Joshi. It is found that the contribution of the effective phonon‐dislocation scattering processes to the lattice thermal conductivity can be calculated by suitably combining the static and the dynamic phonon‐dislocation scattering processes.
Dynamics and Thermodynamics of Anharmonic Crystals near the Instability Point
Authors: Malinowska‐Adamska C. 
Published: July 2007

AbstractUsing the self‐consistent phonon theory based on the thermodynamic double‐time Green's function method the dynamics of crystal lattice and the thermodynamics of the anharmonic cubic crystals in the vicinity of the instability point are investigated. The results of calculations for the instability temperature Ts, relative displacements of atoms, anharmonic contributions to the free energy, and free Gibbs energy as well as the isothermal elastic constants are given and compared with experimental and other theoretical data for potassium, sodium, and rubidium.
Phonon Polaritons in the Presence of a Magnetic Field
Authors: Regiński K. 
Published: July 2007

AbstractThe problem of propagation of phonon polaritons in the presence of an external magnetic field is investigated on the basis of equations of motion derived previously. First the dispersion relations for diatomic ionic crystals in the absence of a magnetic field are derived. Then the indices of refraction of right and left circularly polarized waves are found in the case of the Faraday configuration of the system. The Faraday rotation as a function of frequency is determined. Numerical calculations are performed for NaI.
Effect of Crystal‐Field Splitting on the Einstein Relation in Tetragonal Semiconductors
Authors: Chakravarti A. N. , Ghatak K. P. , Ghosh K. K. , Mukherjee H. M. 
Published: July 2007

AbstractAn attempt is made to study the effect of crystal‐field splitting on the Einstein relation for the diffusivity‐mobility ratio of the carriers in tetragonal semiconductors, taking inherently degenerate n‐Cd3As2 as an example. It is found on the basis of the Bodnar model, which has recently been demonstrated in the literature to be the most valid model for Cd3As2, that the above ratio increases with increasing carrier concentration as expected for degenerate semiconductors. It is also shown that the tetragonal crystal‐field effectively reduces the ratio with increasing amount of reduction with increasing carrier concentration.