bluuebunny/crossref_metadata_2025_split huggingface dataset:
Generalized huggins‐mayer potentials and properties of alkali halides under the effect of high pressure
Authors: Shiromany A. , Srivastava G. M. S. , Shanker J. 
Published: July 2007

AbstractEquation of state and dielectric properties of alkali halides under the effect of high pressure are investigated using the generalized Huggins‐Mayer potential form. Values of potential parameters derived from ultrasonic data and recent van der Waals interactions by taking proper account of thermodynamic contribution are used in the present calculations of the equation of state and the volume derivatives of dielectric constants. It is found that the inclusion of thermodynamic contribution based on recent data improves significantly the agreement between theoretical and experimental results. The present investigation is superior to other previous studies in respect of using a thermodynamically consistent set of potential parameters.
Optical study of the defect stability in Tl‐doped potassium iodide
Authors: Rzepka E. , Lefrant S. , Taurel L. 
Published: July 2007

AbstractThe thermal stability of the centres created in KI : Tl crystals submitted to an ionizing radiation at room temperature is studied. It is observed that F centres are transformed at room temperature, giving rise to more complex centres, unidentified either by EPR or Raman spectroscopy. The complementary hole centres consist of polyiodides in a low concentration and other complexes implying thallium and iodine interstitials. A recombination between some of these centres occurs at 127 °C. A quenching at LNT of a coloured sample annealed at 127 °C < T < 170 °C shows, by means of Raman experiments, that interstitials are still present since I−3 ions are observed in large concentration.
Coupled waves in conducting spin glasses
Authors: Sultanov K. M. , Kuliev Sh. A. , Abdullaev N. G. 
Published: July 2007

AbstractThe energy spectrum of semiconducting and metallic spin glasses is studied. It is shown that at resonance between the electromagnetic branches of the spectrum and spin waves there exist coupled spin‐spiral, spin‐Alfven, and other coupled spin‐magnetohydrodynamical waves. For all the cases a detuning of the resonances is found.
Heisenberg‐type and double exchange in mixed‐valence clusters
Authors: Belinskii M. I. , Ya. Gamurar V. , Tsukerblat B. S. 
Published: July 2007

AbstractThe theory of double exchange is generalized to be applicable for the degenerate states of d‐electrons in crystal fields. A two‐centre three d‐electron system is studied, Coulomb and exchange intercentre interaction and resonance splitting of exchange multiplets are taken into account. A group‐theoretical classification method for resonance‐exchange multiplets in crystal fields is developed. A dependence of the electron transfer parameters on orbital symmetry and the spin of resonant states is found. The energy spectrum of a binuclear cluster is studied. The resonance interactions are assumed to be relatively weak in comparison with intera‐atomic interactions. It is shown that the Heisenberg‐type exchange parameter is redetermined as long as the transfer is taken into account. The results are compared to the conclusions of the Anderson‐Hasegawa theory.
Anomalous composition dependence of the dielectric constant in bismuth‐antimony alloys due to disorder‐induced indirect interband polarization processes
Authors: Enders P. , Schuchardt R. 
Published: July 2007

AbstractThe strong increase of the dielectric constant observed at a critical antimony concentration in semiconducting bismuth‐antimony alloys is interpreted in terms of a purely electronic interband polarization enhanced by vanishing of the thermal energy gap. The dominant indirect transitions between conduction and valence band states near the L‐ and T‐points of the Brillouin zone are considered as induced by the short‐range scattering potential due to the chemical disorder of the alloy. Reasonable system parameters allow for a satisfactory fit to the experimental data.
Nonlinear optical effects studied by time‐resolved reflection measurements
Authors: Hönerlage B. , Tomasini F. , Bigot J. Y. , Frindi M. , Grun J. B. 
Published: July 2007

AbstractAt very low temperature, the reflection properties of CuCl samples under high pulsed light excitation conditions are investigated by a “pump and probe” technique. The non‐linear reflection changes are shown to have different origins and different time scales: excitonic effects lead to a new reflection structure near the energy of the longitudinal exciton (∼ 1 ns time scale) and interaction with non‐thermalized acoustical phonons to a decrease of the exciton reflection maximum (∼ 60 ns).
On the force between high‐density jellium‐metal surfaces at small separation
Authors: Streitenberger P. 
Published: July 2007

AbstractAn exact relation is derived yielding the force constant of a bimetallic interface described by the jellium model in terms of the corresponding density‐potential response function. This relation in conjunction with a step‐density model and Thomas‐Fermi screening is used to derive an approximate formula for the force constant of a bimetallic interface in the limit of high densities. For identical metals it is demonstrated that the relation obtained satisfies the surface virial theorem and how the force between the two metal surfaces can be decomposed into the kinetic and interaction contributions. Starting from the small and large‐separation limiting behaviour of the force an attempt is made to estimate the adhesive energy of high density bimetallic contacts using the force constant calculated for the jellium model. For dissimilar metals it is found that the adhesive energy tend to a limit proportional to r1—5/4 r2—9/4 as r1, r2→ 0 and r1/r2→ 0, where r1 and r2 are the mean interelectronic distances of the two metals.
Flux spiral instability in a transport current carrying type‐II superconductor
Authors: Shehata L. N. , Saif A. G. 
Published: July 2007

AbstractThe nucleation of vortex flux lines on a surface of a transport current carrying type II superconductor in the presence of an external magnetic field He occurs at He ˜ Hcl, the first critical field. A spiral flux line in a long cylinder and in a long thin ellipsoid is investigated. In the latter case the force‐free magnetic fields are also considered.
Electric field gradient in Ag alloys
Authors: Ponnambalam M. J. 
Published: July 2007

AbstractIn Ag the impurity‐induced electric field gradient (efg) q and the asymmetry parameter η at the nearest neighbor due to Cd, In, Sn, and Sb are calculated. The valence efg qV is evaluated using an exact expression, valid at all distances from the impurity. The size effect efg qs is calculated using an oscillatory form for the displacement. Without the use of floating parameters, good agreement is obtained with the experiment for all the systems.
S‐Polarized nonlinear surface polaritons effects of a transition layer
Authors: Wendler L. 
Published: July 2007

AbstractThe dispersion relation of s‐polarized nonlinear surface polaritons is derived for a system consisting of an optical nonlinear and an optical linear semi‐infinite medium which are seperated by a dipoleactive transition layer. With the power flow of the nonlinear surface polaritons an additional physical parameter enters the dispersion relation. The various resulting forms of the dispersion relation are analyzed and presented in graphical form. It is shown that in the case of resonance of the s‐polarized nonlinear surface polaritons with the transverse optical vibrations of the transition layer the dispersion curves are altered dramatically. The electromagnetic fields, the Poynting vector, and the energy flow of the s‐polarized nonlinear surface polaritons are calculated and presented in graphical form.
A Kinetic Theory for the Motion of Accelerated Particles in Solids. I. Derivation of Basic Equations
Authors: Urmanov A. R. , Linetskaya A. M. , Puzanov A. A. 
Published: July 2007

AbstractAn approach to the derivation of kinetic equations describing the motion of accelerated particles in solids is suggested based on the microscopic phase density method. It is shown that the unified approach suggested makes possible to obtain all the known kinetic equations used for describing the interaction of accelerated particles with condensed medium as well as more exact expressions for the coefficients of these equations. A new type of the kinetic equation is obtained describing, in particular, ion channeling in complex single crystals.
Investigation of Nonequilibrium Phonons in GaAs
Authors: Danilchenko B. A. , Poroshin V. N. , Slutskii M. I. , Asche M. 
Published: July 2007

AbstractThe propagation of acoustic phonons in GaAs generated by laser radiation of a clean as well as Au coated surface are experimentally investigated in dependence on the crystallographic orientation. The angular dependence of the T1 phonon spectrum is confirmed by comparison with the calculated focussing factor. Besides the ballistic motion of modes of L, T1, and T2 polarization a further peak is observed in the time of flight spectra, which is interpreted by repeated conversion and decay processes of high‐frequency phonons leading to T2 modes with a frequency low enough for ballistic motion.
Self‐Consistent CPA Treatment of the Conduction Electron Spin Polarization of Degenerate Ferromagnetic Semiconductors
Authors: Borgieł W. , Nolting W. , Borstel G. 
Published: July 2007

AbstractA theory for the temperature and charge carrier concentration dependence of the electronic quasiparticle spectrum, of a ferromagnetic 4f‐system is presented. The s‐f model is used with inclusion of a Coulomb interaction between the conduction electrons. The full analytical solution of the zero band width limit of this model is used to formulate an alloy analogy, which is then treated by a conventional CPA‐procedure. In this way in a selfconsistent manner basic quantities are determined like the quasiparticle density of states and the conduction electron spin polarization. The quasiparticle spectrum is shown to be composed of three subbands which can be interpreted as consequence of different simple elementary processes. The spin polarization is almost complete for small band occupations n and temperatures below the Curie‐temperature. It drops down quite abruptly at a certain critical concentration, reaching again a relative maximum for the exactly half‐filled conduction band. The temperature dependence of the spin polarization for fixed n explains recently performed field emission experiments.
Exchange Potential and Plasma Modes in Coupled Two‐Dimensional Electron Systems
Authors: Sy H. K. , Song L. M. 
Published: July 2007

AbstractAn investigation is made of two 2‐D electron systems, separated spatially but coupled by Coulomb interaction. The acoustic and the optical plasma modes are studied using coupled Boltzmann equations. An effective exchange potential calculated using the formalism of Kohn and Sham is included. The dispersion relation is obtained numerically for different densities and separations.
Intermediate‐Valence and Kondo Impurities. Approximate Analytic Results within NCA
Authors: Kozabzewski B. 
Published: July 2007

AbstractAn approximate analytic solution of the NCA integral equations for an impurity system at arbitrary temperature is given. Renormalized energies of ionic states are found. It is also shown that the ion can change its state from magnetic to nonmagnetic one at some temperature corresponding roughly to the Kondo temperature.
Electron‐Phonon Interaction and Structure of Molecular Luminescence Center in Crystals
Authors: Reznik L. E. 
Published: July 2007

AbstractThe spectral features of the lowest 1B1 ⇄ 1A1 and 3B1 molecular ion in the crystalline state at low temperatures are studied, using single crystals of MNO2 nitrites and MN03 nitrates (M is a metal) in polarized light. It is shown that the electron‐phonon interaction broadens the spectra; the crystal microscopic characteristics mostly affecting the electron‐phonon coupling are deduced.
Phonon Dispersion of Disordered FeAl Alloy
Authors: Garg S. , Gupta H. C. 
Published: July 2007

AbstractPhonon dispersion curves for disordered state (b.c.c.) of Fe‐22.5% Al alloy are calculated using the deLauney angular force model and compared with the experimental one. It is found that the force constants of the alloy system are related to the force constants of Fe and Al in the b.c.c. and f.c.c. phase, respectively. Good agreement is obtained between theory and experiment.
On the Temperature Variation of the Anderson‐Grüneisen Parameters of NaCl
Authors: Dhoble Aruna , Verma M. P. 
Published: July 2007

AbstractIt is shown thermodynamically that the isothermal Anderson parameter δTcan be expressed in terms of the constant pressure and constant volume temperature derivatives of the thermal expansion coefficient α. This result is used to study the temperature variation of δTfor NaCl. The study suggests that δT should present a sharply rising temperature variation particularly at temperatures approaching the melting temperature.
Vibrational Properties of Metastable Phases of Si and Ge
Authors: Winer K. , Wooten F. 
Published: July 2007

AbstractThe phonon dispersion curves and density of states for BC8 Si and ST12 Ge are calculated using a generalization of Weber's adiabatic bond charge model. Variations in the vibrational properties are related to the different types of structural distortions present in the two phases.
Surface Migration of Adsorbed Particles
Authors: Kozhushner M. A. , Prostnev A. S. , Rozovskii M. O. , Shub B. R. 
Published: July 2007

AbstractA relaxation model of single adsorbed particle migration on the surface of solids is proposed. It is shown that the jump length is determined completely by an energy relaxation time for a continuous spectrum of the surface periodic potential. The jump length is found to exceed the lattice period appreciably if the adatom motion velocity is smaller than the sound speed in the solid. For this case an analytic expression for the diffusion coefficient is obtained which does not contain any fitting parameters.
L‐Holes and Their Effect on the Band Parameters of Bismuth
Authors: Mikhail I. F. I. 
Published: July 2007

AbstractThe effect of L‐holes on the temperature dependence of the band structure parameters of bismuth is investigated. Modified expressions for the weak‐field galvanomagnetic coefficients are derived. These expressions are used in a re‐evaluation of mobilities and band parameters in the temperature range 77 K ≦ T ≦ 300 K.
Exciton Absorption Spectrum in a ZnSiP2 Crystal
Authors: Madelon R. , Hurel J. , Paumier E. 
Published: July 2007

AbstractMeasurements of absorption coefficients near the pseudodirect band edge in ZnSiP2 are performed using polarized light from 4.2 K to room temperature. By fitting a theoretical curve with the measurements at several temperatures values of the band gaps As′, B′, and C′, as well as the binding energies of the first exciton level are obtained for the three transitions A′, B′, and C′. The last values are temperature independent. Other results are the broadening parameters of the three excitons. Also obtained are the spin‐orbit splitting, the crystal field splitting, and the exciton reduced mass.
Vibrational Spectra of TlInS2, TlIn0.95Ga0.05S2, and TlIn(S0.8Se0.2)2 Crystals in the Vicinity of Phase Transitions
Authors: Nurov Sh. , Burlakov V. M. , Vinogradov E. A. , Gasanly N. M. , Dzhavadov B. M. 
Published: July 2007

AbstractStructural phase transitions in TlInS2, TlIn0.95Ga0.05S2, and TlIn(S0.8Se0.2)2 crystals are investigated by infrared reflection spectroscopy. An attempt is made to affect the parameters of the vibrational spectrum and the phase transition temperatures of a TlInS2 crystal by introducing impurities into it in order to obtain additional data necessary to construct phase transitions mechanisms.
EPR of Colour Centres in Alkaline Metal Doped Calcium and Strontium Fluorides
Authors: Hamaïdia A. , Hachimi A. , Margerie J. , Hémidy J. F. 
Published: July 2007

AbstractThe EPR is studied of FA centres in CaF2:Li+, CaF2:Na+, and SrF2:Na+. In CaF2:Li+, the spectrum is very similar to that of F centres in pure CaF2: the superhyperfine coupling constant with lithium is unmeasurable. On the other hand, in CaF2:Na+ and SrF2:Na+, the superhyperfine coupling with a sodium nucleus is noticeable. The EPR of so‐called “F2A” centres in the same matrices is also observed, which corroborates our previous magnetic circular dichroism conclusions: “F2A” centres do not correspond to two electrons in two adjoining anion vacancies with a substitutional sodium in close vicinity. From the observed superhyperfine structure, it is not yet found what is the genuine microscopic structure of these “F2A” centres.
Effect of the Temperature and Concentration of Magnetic Atoms on Phase Diagrams and Order Parameters in Ferromagnetic Superconductors
Authors: Kopeć T. K. , Klamut J. 
Published: July 2007

AbstractUsing the free energy functional with two coupled order parameters the model of a rare earth ferromagnetic superconductor is considered by means of the Landau theory of phase transitions. By making the experimentally verified assumption about the dependence of critical temperatures for magnetic and superconducting subsystems on the concentration of magnetic rare earth atoms, the resulting phase diagrams are analysed in the temperature—concentration plane. It turns out that for weak coupling between magnetic and superconducting subsystems the uniform coexistence state of ferromagnetism and superconductivity sets in, while for strong coupling a spatially non‐uniform metastable state exhibiting hysteretic behaviour for ferromagnetic and superconducting phase appears. The explicit dependence of the order parameters on the temperature and concentration of magnetic atoms is also given.
On the Influence of Noise on the Density of States and Absorption in Disordered Molecular Systems
Authors: Esser B. , Marlow F. 
Published: July 2007

AbstractA disordered excitonic system perturbed by the Gauss‐Markov noise approximating the exciton‐phonon interaction is investigated. The structure of the mass operator is discussed in dependence on the eigenfunctions of the excitonic Hamiltonian. Explicit calculations of the density of states and the imaginary part of the DF ϵ2(ω) are performed for Lorentzian static disorder. The influence of the breaking of the k‐selection rule or of fluctuations in the transition matrix elements on the frequency dependence of ϵ2(ω) is considered.
The Multimode Jahn‐Teller Effect in the Luminescence Spectrum of the Tetrahedral 2T2 ⊗ (e + t2 + t2) Impurity System ZnS:Cu2+
Authors: Polinger V. Z. , Boldyrev S. I. 
Published: July 2007

AbstractThe multimode Jahn‐Teller effect for the tetrahedral 2T2 term coupled with E and T2 vibrations is discussed taking into account the spin—orbit interaction. Harmonic vibrations are considered at the trigonal minimum point of the lowest sheet of the adiabatic potential. Using the Green's function method the redetermined projected densities of states are obtained. The one‐phonon sideband of the 2E → 2T2 transition is expressed in terms of projected densities and compared with the experimental data for 2E → 2T2 luminescence of ZnS:Cu2+.
Lattice Thermal Conductivity of Gadolinium Monosulphide above Room Temperature in the Frame of Two‐Mode Conduction of Phonons
Authors: Al‐Edani M. C. , Dubey K. S. 
Published: July 2007

AbstractThe lattice thermal conductivity of gadolinium monosulphide is studied by estimating the separate contributions due to transverse and longitudinal phonons in the temperature range 300 to 800 K and a very good agreement is found between calculated and experimental values. It is also reported that the transverse phonons are mainly responsible for the heat conduction in the present sample. The temperature exponents for the three phonon scattering relaxation rates is also reported for gadolinium monosulphide for the first time.
Calculation of the Electronic Structure! of Disordered Hydrogen Adsorption on the Si(111) Surface
Authors: Gadiyak G. V. , Karpushin A. A. , Korolenko I. V. , Morokov Yu. N. , Yu. Semenova I. , Sorokin A. N. , Tomášek M. 
Published: July 2007

AbstractThe local density of electronic states is calculated on the (111) surface of silicon with disordered adsorption of atomary hydrogen with an arbitrary degree of coverage. Computations are made by the recursion method and the method of generalized Bethe lattices. The dependence of the electronic density of states on the degree of coverage of the surface by hydrogen is investigated. The results obtained by the recursion method and the generalized Bethe lattice method are compared with those obtained by other methods and by the experiment and a good overall agreement is found. The contribution of hydrogen and silicon atomic states into the electronic structure of the Si(111) surface is analyzed.
On the Theory of Crystal Excitation of Electric Discharges II. Ionization of Defects
Authors: Voitikov S. V. , Gribkovskii V. P. 
Published: July 2007

AbstractThe theory of point defect ionization in semiconductors by the streamer discharge electric field is developed. It is shown that due to high streamer velocity and sharp spatial inhomogeneity of the electric field defect ionization is a fast quantum process with a large energy uncertainty of particles involved and, hence, it does not occur by tunneling. Localized wavefunctions are described by the quantum defect method. The ionization probability is calculated and its straightforward dependence on the velocity and the form of the streamer field and the defect parameters is determined. As in the case of interband transitions considered in the first work the ionization probability is an increasing function of the streamer velocity and the field steepness.
Localization in Random Systems I. Effect of Off‐Diagonal Disorder
Authors: Brezini A. , Sebbani M. , Dahmani L. 
Published: July 2007

AbstractThe question of localization is examined in a tight‐binding Hamiltonian. The present method is based on a self‐consistent theory reproducing correctly the band edge in the limit of zero disorder. Randomness is introduced also in the off‐diagonal elements. In a purely diagonal disorder it is found that the results for the critical disorder Wc for which the Anderson transition appears are in good agreement with other theories while for a purely off‐diagonal disorder the states around the middle of the band remain extended.
Variable‐Range Hopping in Neutron‐Transmutation‐Doped Gallium Arsenide
Authors: Rentzsch R. , Friedland K. J. , Ionov A. N. , Matveev M. N. , Shlimak I. S. , Gladun C. , Vinzelberg H. 
Published: July 2007

AbstractFirst investigations are reported on the temperature dependence of the dc‐conductivity at T = = 0.05 to 300 K on neutron‐transmutation‐doped (NTD) n‐GaAs in the vicinity of the metalinsulator transition (MIT). At a medium compensation of K = 0.60 to 0.77 the MIT takes place at the critical electron concentration of nc = 2.3 × 1016 cm−3. On the dielectric side of the MIT in the variable‐range hopping regime (VRH) at T ≦ 10 K the conductivity obeys the equation σ(T) = σ0exp [— (T1/T)1/2] and not the Mottlaw. The experimental values T1 are for all samples much smaller than T1theor for isolated shallow impurities and scale down according to T1 = = T1*(1 ‐ n/nc)1.6±0.4 with T1* = 5.9 K by approaching the MIT. This behaviour is due to the divergency of the localization radius a and the static DK ϵ0 at the MIT. The obtained linear In σ — T−1/2 law over about 2.5 orders of magnitude in temperature variation and more than three orders of magnitude of variation in conductivity is interpreted in the frame of a Coulomb gap with vanishing density of states at the Fermi level, as predicted by Efros and Shklovskii. The pre‐exponential factor ϱ0 = σ0−1 shows also scaling behaviour according to ϱ0 = ϱ0*(1 ‐ n/nc)1.2±0.4 and a value of ϱ0* = 2.2 Ω cm. At n → nc σ0 = ϱ0−1 reaches the value of Mott's minimal metallic conductivity of σMM = (Ce2/h) nc1/3, with 0.025 ≦ C ≦ 0.05.