bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impurity Scattering in Weakly Compensated Gapless Semiconductors at Low Temperatures
Authors: Mikheev V. M. 
Published: July 2007

AbstractAn anomalous decrease in mobility with rising temperature is attributed to the contribution by scattering on acceptor–donor pairs. The change in the concentration of acceptor–donor pairs is related to the merging of pairs into large entities — “clusters”. In the case of “clusters” the scattering on charge fluctuations is essential which is more effective than that on individual pairs. An increase in cluster volume with rising temperature results in lower mobility. Within the framework of the model suggested, the electrical conductivity is calculated numerically for a material that has the parameters of HgCdTe. The results of numerical calculations agree well with experiment.
New Approach to the Theory of High‐Temperature Superconductivity
Authors: Fukuhara M. , Smith G. W. 
Published: July 2007

AbstractA new approach to the theory of high‐Tc superconductivity in cuprate oxides is proposed, based on the possibility of superelectrons derived from inner closed shells in shrunken atoms induced by a strong screened attractive interaction between an electron and an ion. An electrostatic fluctuation connected with an electronic polarizability halts the breaking‐up of the pre‐existing pairs of electrons with antiparallel spins in the shells. The transport of superelectrons can be explained by the virtual tunneling.
The Long‐Wavelength Limit of the Structure Factor of Liquid Alkali Metals Using a One‐Component Plasma System
Authors: Derouiche A. , Bretonnet J. L. 
Published: July 2007

AbstractThe one‐component plasma (OCP) is used as reference system to calculate the long‐wavelength limit S(0) of the structure factor of liquid alkali metals within the random phase approximation (RPA). It is found that the OCP system is suitable to describe S(0) when the plasma parameter corresponds to the minimum variational upper bound to the free energy.
Structure and Electrical Resistivity of Alkali–Alkali and Lithium‐Based Liquid Binary Alloys
Authors: Mishra A. K. , Sahay B. B. , Mukherjee K. K. 
Published: July 2007

AbstractHarmonic model potential, developed and used for simple metals is applied here to evaluate hardsphere diameters, which ensure minimum interionic pair potential for alkali–alkali (Na–K, Na–Rb, Na–Cs, K–Rb, K–Cs) and lithium‐based (Li–Na, Li–Mg, Li–In, Li–Tl) liquid binary alloys as a function of composition for use in the determination of their partial structure factors. These structure factors are then used to calculate electrical resistivities of alloys considered. The computed values of electrical resistivity as a function of composition agree both, in magnitude and gradient reasonably well with experimental values in all cases except in Cs systems, where the disagreement is appreciable.
Computation of Vacancy Formation Energy of Liquid Metals
Authors: Das T. , Nammalvar T. , Bhuiyan L. B. , Joarder R. N. 
Published: July 2007

AbstractA formulation of the vacancy formation energy involving pseudopotential and total pressure is utilized to calculate the vacancy formation energy for liquid alkali (monovalent) metals and liquid In, Al, and Pb (polyvalent). Both, the one component plasma and the charged hard sphere models are employed to simulate the systems studied. The calculated vacancy energies are in good agreement with experiment.
Orientational Effects Due to Traveling of Fast Neutrons and Hard γ‐Quanta through Crystals
Authors: Baryshevskii V. G. , Zaitseva A. M. 
Published: July 2007

AbstractThe paper presents orientational effects, which are observed during the passage of neutrons and γ‐quanta with an energy of the order of a few MeV through crystals. It is shown that for neutral particles channeling effects are also rather strong. Calculated results agree with the experiment.
A Contribution to DC Transport in Thin Bi Films
Authors: Gerlach E. 
Published: July 2007

AbstractA generalization of the energy‐loss transport concept, which includes carrier–carrier‐scattering, is applied to a thin (two‐dimensional) Bi‐film deposited on an e.g. CaF2‐substrate. In particular, scattering by ions is considered and by charge density fluctuations. An additional scattering channel is taken into account by a scattering frequency ωτ. If the concentrations of electrons and holes are about equal, the resulting resistance of the Bi‐film at not too low temperatures is governed by scattering by fluctuations.
Effect of Lattice Vibrations on the Change in Work Function
Authors: Patra S. , Kumar A. 
Published: July 2007

AbstractA change in work function is calculated by extending previous calculations beyond Hartree‐Fock approximation. The chemisorption energy and the change in the work function are also found to depend on the strength of adatom–electron interaction by including the effects of lattice vibrations on adatoms on a metal surface.
Auger Recombination in Disordered Semiconductors. Effect of the Band‐Gap Fluctuation
Authors: Quang Doan Nhat 
Published: July 2007

AbstractThe Auger recombination coefficient is calculated for disordered semiconductors with fluctuating band gap which can be described by the smooth random Gaussian field model. The effect of different random bending of the conduction and valence bands on Auger transitions is investigated for the case of non‐degenerate carrier statistics. An integral relationship for the Auger coefficient is derived which is analogous to the Dexter representation for the optical absorption. For various recombination processes general analytic expressions of the Auger coefficients are obtained, which exhibit simple linearly exponential functions of the random‐field parameters, and the Auger recombination might be strongly enhanced as compared to that in the appropriate fluctuationless system. In contrast to the case of case of uniform random band bending, the influence of the band gap fluctuation is shown to depend on the type of recombination process and the effective masses of the material as well. Moreover, this effect is especially sensitive to the kind of relative band bending. Numerical estimates indicate that the Auger transition might still remain as one of the most effective recombination mechanisms for non‐crystalline semiconductors.
Dependence of the Line Strength of f–f Transitions on the Manifold Energy. I. Projector on the Basis of Nonorthogonal Functions
Authors: Kornienko A. A. , Kaminskii A. A. , Dunina E. B. 
Published: July 2007

AbstractThe method of construction of effective operators in nonorthogonal basis states with the help of projection operators is suggested. According to this method the localization of the ground and excited states are preserved. The expressions for the effective operator are given in third order of perturbation theory.
The Electronic Structure of Copper Oxide Crystalline Compounds. I. LUC‐CNDO Approach to the Electronic Structure of Cu2O and CuO Crystals
Authors: Evarestov R. A. , Veryazov V. A. 
Published: July 2007

AbstractLUC‐CNDO computation scheme and its valence theory applications are discussed. Electronic structure calculations of well‐known semiconductors Cu2O are reviewed. The parameters of CNDO scheme for copper–oxygen compounds are calibrated using the results of Cu2O band theory calculations and experimental data.
Effect of Fluctuations in Delta‐Doping Superlattices on Donor–Acceptor Pair Luminescence
Authors: Zehe A. , de la Cruz D. 
Published: July 2007

AbstractDonor–acceptor pair luminescence represents a recombination channel depending on the crystal site separation of donors and acceptors in semiconductors. This fact turns out prolific when doping superlattice structures are concerned. The donor–acceptor‐pair distribution function is very sensitive in respect to the mutual positions of doped layers in superlattice structures. Effects of disorder or non‐ideal arrangement of doped layers in the one‐atomic length scale are thus accessible to luminescence experiments.
First‐Order Quantum Corrections to the Current Driven by a Force and Einstein Equivalence
Authors: Lenk R. 
Published: July 2007

AbstractEmploying a superposition representation of the density matrix for a fixed energy the first order quantum corrections to the current driven by a weak constant force are calculated for independent charge carriers scattered by uncorrelated point‐like scatterers. This complements a preceding treatment of the corresponding diffusion problem and demonstrates the Einstein equivalence as a property of the density matrix itself. The changes in kinetic energy caused by the force field lead to a reformulation of the correction terms which resemble now the known vertex structure of the Bethe‐Salpeter equation. The influence of the force is considered explicitly in the propagator construction.
The Magnetic Field Influence on a Superconducting Bisoliton Condensate
Authors: Brizhik L. S. , Davydov A. S. , Ermakov V. N. 
Published: July 2007

AbstractIt is shown that in terms of the bisoliton model the effect of a magnetic field on ceramic high‐temperature superconductors is qualitatively different from that on superconductors that satisfy BCS theory. The energy gap and the critical temperature change little with increasing field and sharply become zero in fields exceeding the critical value.
Mean‐Field Theory for Spin Glasses with Many Macroscopic States
Authors: Janiš V. 
Published: July 2007

AbstractAssuming from the beginning that there may be many macroscopic states in the Sherrington‐Kirkpatrick model, a new many‐state free energy is derived for one configuration of spin‐spin couplings and a new technique for averaging it. It is shown that the free energy of Thouless et al. must be extended to define the averaging scheme or the thermodynamic limit with many macroscopic states.
Magnetic Properties of Single Crystals of Bismuth Doped with Lead and Tin
Authors: Banerjee D. , Bhattacharya R. 
Published: July 2007

AbstractMeasurements made of magnetic susceptibility of single crystals of bismuth doped with tin and lead (two each) are reported in the temperature range 100 to 300 K. Both, tin and lead have marked effect in changing the band structure of bismuth. The temperature variation of χ∥ shows that in one region there is an increase in observed diamagnetism followed by a region of decrease of diamagnetism. This is shown to be due to the decrease of both, the dia‐ and paramagnetic contribution of excited free carriers residing in different bands.
Field Influence on the Parameters of Ferromagnetic Semiconductor Superlattices Formed by Coherent Light Beams
Authors: Grechko L. G. , Ogenko V. M. , Semchuk A. Yu. 
Published: July 2007

AbstractThe behaviour is studied of the electron–magnon system of a ferromagnetic semiconductor in an external constant electric field and a high‐frequency field of coherent light beams. It is shown that in a field of coherent light beams the system of nonequilibrium electrons and magnons of a ferromagnetic semiconductor forms several superlattices differing in their parameters. The superlattice parameters are found to depend on the electron density, sample temperature, heating field strength, and on the amplitude and frequency of the coherent light beam field.
Moment Expansion of the Optical Second‐Harmonic Response Tensor of Condensed Media
Authors: Keller O. 
Published: July 2007

AbstractWith main emphasis on studies of optical second‐harmonic generation in centrosymmetric media new expressions for the local and near‐local parts of the nonlinear conductivity response tensor are derived. The expressions are obtained via a moment expansion of the fully nonlocal response. The new results allow a direct comparison between the multipole expansion formulation used in studies on dielectrics and the delocalized approach often adopted in works on the metals. Contact is made to recent investigations of the nonlinear response of a flat surface.
Investigation of Electron Mobility in a Two‐Dimensional Electron Gas. GaAs–AlxGa1−xAs Heterostructures, Application of the Hydrostatic Pressure Method
Authors: Kończewicz L. , Litwin‐Staszewska E. , Maslowska A. , Piotrzkowski R. , Robert J. L. , André J. P. 
Published: July 2007

AbstractHydrostatic pressure experiments are a very useful tool for 2D electron transport effect investigations as they allow the electronic properties of the heterojunction to be precisely modified without changing the intrinsic properties of the material. The hydrostatic pressure technique is applied in 2D gas mobility investigations in GaAlAs/GaAs heterojunctions in liquid helium temperature range. The experimental mobility versus 2D electron concentration and temperature dependences are compared with the theoretical predictions and it is shown that the mobility variations are generally described by the scattering by charged centers in the GaAlAs layer.
Optical Behaviour of Lead Selenide Films
Authors: El‐Ocker M. M. , Sharaf F. , Yossef S. M. , Metawe F. , El‐Desouki M. 
Published: July 2007

AbstractLead selenide thin films of thicknesses between 80 to 250 nm, are prepared by thermal evaporation under vacuum of ≈ 1.3 × 10−3 Pa. X‐ray diffraction studies reveal the formation of polycrystalline films. The optical gap is determined as a function of film thickness. It is observed that the width of the optical gap lies between 0.3 to 0.4 eV, additionally it shows the tendency to decrease with increasing film thickness. Ellipsometry is used to estimate the optical constants and the absorption coefficient. Two well defined peaks are observed at energies of about 1.8 and 2.9 eV. The data are analysed in the frame of the band structure of PbSe2.
Transfer Matrix Method to Compute Energy Levels of Superlattices
Authors: Pavesi L. , Reinhart F.‐K. 
Published: July 2007

AbstractUsing the transfer matrix method the Kronig‐Penney model is generalized to superlattices formed by whatever successions of layers. Imposing the boundary conditions, the miniband structure as well as the envelope wave functions are obtained. As examples, the “enlarged well in a superlattice” problem and the Fibonacci superlattices are discussed. The Lyapunov coefficients as a function of energy are calculated to determine the localization properties of the eigenstates in the entire superlattice spectrum. The single channel Landauer formula is used to get the conductance spectrum. Results are presented for random disordered superlattices.
Magnetisation and ESR Studies of Gd(Ni1−xRhx)5 Compounds
Authors: Tari A. , Hwang J. S. 
Published: July 2007

AbstractMagnetisation and electron spin resonance measurements are performed on Gd(Ni1−xRhx)5 compounds with x = 0, 0.1, 0.2, 0.3, 0.5, and 1.0. In the ordered state the value of the spontaneous moments is 6.5 μB/f.u. in GdNi5, rising to 6.7 μB/f.u. at the GdRh5 end of the series. Both θp and Tc show rapid variation with Rh substitution, particularly at the GdNi5 end of the series where dθp/dc ≈ 1.1 K/at% Rh. The ESR measurements indicate that the system is bottlenecked. The substitution of Rh for Ni reduces the slope of the linewidth from 7 × 10−4T/K in GdNi5 to 4 × 10−4T/K in GdRh5 and raises the g‐value from 1.923 in GdNi5 to about 2.000 at the GdRh5 end of the series; both indicative of a change in the character of the conduction electrons from predominantly d‐like in GdNi5 to predominantly s‐like in GdRh5. From the g‐shift a value of J = −0.005 eV is obtained for the effective exchange integral. Both, ESR and magnetic data indicate that the density of d‐states goes through a minimum close to the GdNi5 end of the series.
Reflection Spectra of Some Garnet and Orthoferrite Single Crystals in Vacuum Ultraviolet
Authors: Kučera M. , Kolobanov V. N. , Mikhailin V. V. , Orekhanov P. A. , Makhov V. N. 
Published: July 2007

AbstractThe near normal reflectivity of single crystal garnets (Y3Fe5O12, Y3Fe4GaO12, Ca3Fe2Ge3O12, Y3Al5O12, Gd3Ga5O12), and yttrium orthoferrite (YFeO3) are studied over the energy range from 5 to 30 eV using synchrotron radiation. The spectra of complex permittivity ε1, ε2, the optical constants n, k, α, and the energy loss function Im(1/ε) are obtained by means of Kramers‐Kronig analysis. The optical spectra are very similar in this region and are only slightly affected by the different chemical composition of the samples. An interpretation of basic features of the spectra is proposed in terms of a simple energy band model.
Diffusion in Crystals with Competing Interactions of Migrating Ions
Authors: Zubkus V. , Kundrotas P. , Lapinskas S. , Kashcheev V. 
Published: July 2007

AbstractTransport processes are investigated by means of the lattice gas model with nearest and nextnearest neighbour attractive and repulsive interactions. The temperature and concentration dependences of self‐diffusion coefficient and electroconductivity in the disordered homogeneous phase of these systems are calculated by the cluster approximation. The regions of deviation from the Arrhenius law are determined. The spatial‐time distributions of migrating particles are obtained. The influence of strong short‐range interactions on the relaxation time of the diffusion process is investigated. Several experimental results of diffusion in systems with strong shortrange correlations are discussed by the theory proposed.
Calculation of Energy Loss Characteristics of Accelerated Ions Passing through Thin Targets
Authors: Akkerman A. F. , Fain V. E. 
Published: July 2007

AbstractThe possibility is discussed of checking the formula for the impact parameter dependence of energy losses in an inelastic collision, comparing calculated and experimental mean energy losses and straggling of ions passing a thin foil. Some results of Monte‐Carlo calculations are presented.
Equations of Order–Disorder Kinetics in Alloys with B. C. C. and F. C. C. Lattices. Tetrahedron Approximation
Authors: Bakai A. S. , Fateev M. P. 
Published: July 2007

AbstractThe kinetic equations describing the order‐disorder in alloys with b. c. c. and f. c. c. lattices are derived taking into account atom correlation. The consideration is based on the master equation using a superposition approximation. It is supposed that atom movements are controlled by a vacancy mechanism. For the first time, the closed kinetic equations describing the kinetics of ordered alloys with b. c. c. and f. c. c. lattices in four‐particle tetrahedron approximation are obtained. As clusters the tetrahedron atom configuration is chosen. For the system in a stationary state the equations obtained give the same results as a variation cluster method.
Crystal Growth, Raman and Infrared Spectra of BaFI Single Crystals
Authors: Sieskind M. , Ayachour D. , Merle J.‐C. , Boulou J.‐C. 
Published: July 2007

AbstractSingle crystals of BaFI are synthetized and their Raman and infrared properties are investigated at room temperature. The reflectivity is measured between 50 and 4000 cm−1 using a Fourier transform infrared spectrometer. The experimental reflection spectra are analysed by means of the classical oscillator model and the Kramers‐Kronig transformation to obtain the TO and LO frequencies and the optical constants. The position of the Raman and infrared modes of the matlockite series (PbFCl) are qualitatively discussed. The most significant force constants of the dynamical matrix are estimated from the high frequency Raman modes.
Lattice Dynamics of Alkali Metals
Authors: Mishra S. K. , Singh T. N. 
Published: July 2007

AbstractThe lattice dynamics of alkali metals is investigated on the basis of a phenomenological model which is consistent with the translational symmetry of a lattice. The potential energy is considered due to (1) ion‐ion and (2) ion‐electron interactions. The contribution to ion‐ion interaction is evaluated applying the valence force field. The contribution to the potential energy from ion‐electron interaction is considered through the screened Coulomb potential. The theoretical model developed is employed to compute the phonon dispersion curves of Na, K, Li, Rb, and Cs. Computed phonon frequencies are used to interpret the Debye characteristic temperatures at different temperatures. The calculated results for phonon dispersion curves and Debye characteristic temperatures compare well with the experimental ones.
Charge Carrier Energy Spectrum in Multilayer Structures and Superlattices in the Field of the Self‐Action Potential
Authors: Pokatilov E. P. , Beril S. I. , Semenovskaya N. N. , Fahood M. 
Published: July 2007

AbstractThe manifestation of the self‐action potential in spatially heterogeneous structures is investigated theoretically. The expressions for the self‐action potential energy of a test charge placed in a central layer of the three‐layer structure or in either of the superlattice layers are obtained. The numerical results which correspond to the exact formulae are compared with the approximate ones which correspond to the analytical expressions, for which the criteria of validity are deduced from this comparison. The electron energy spectra are obtained from both, numerical and analytical calculations accounting for the self‐action potential energy. The applicability range of analytical results is established.
A Tight‐Binding Calculation of Band Discontinuities in the AlxGa1−xAs/GaAs(AlAs) Heterostructures
Authors: Gushchina N. A. , Nikulin V. K. 
Published: July 2007

AbstractValence (ΔEv) and conduction (ΔEc) band discontinuities at the AlxGa1−x As alloy‐GaAs(AlAs) crystal interface are calculated within the tight‐binding approximation basing on the bulk electron properties of the individual components and taking into account the presence of a dipole layer at the interface. The alloy is considered in the virtual crystal approximation using the self‐consistent parameters of the sp3s* Hamiltonian obtained for the GaAs and AlAs crstals. The calculated value of the ratio of Qv = ΔEv/ΔE to Qc = ΔEc/ΔE, where ΔE is the difference between the direct band‐gap widths for the crystal and the alloy, is found to be 0.33:0.67 for all values of the Al concentration which is in good agreement with recent optical measurements. These parameters permit to obtain within the tight binding approximation the values of concentration x at which a direct‐indirect crossover occurs in the alloy (xc = 0.38) and a transition occurs from the first to the second type of heterojunction in the AlxGa1−xAs/AlAs structure (xc2 = 0.25), values being close to the experimental data.
The One‐Dimensional Plasma Model
Authors: Yanetka I. 
Published: July 2007

AbstractThe Hamiltonian of the one‐dimensional electron‐ion system is proposed. The relevant forces between electrons and ions are of the Coulomb‐type. Besides, the repulsive pseudopotential in the form of the delta‐function is included in the electron‐ion interaction. The stability of the system against lattice distortion is examined. The effects of the periodicity appear to strengthen the transition to the state with lattice distortion. The region of the parameter values describing the stable system against lattice distortion is defined.
Magnetic Field Splitting and Dispersion of the Lower 1S‐Exciton Polariton in KI and RbI
Authors: Fröhlich D. , Kirchhoff St. , Köhler P. , Nieswand W. 
Published: July 2007

AbstractResonances on the lower polariton branch of KI and RbI are measured by the use of three‐photon difference‐frequency generation (TP‐DFG). From these data the energy of the lowest transverse exciton state is derived. Due to the small linewidth of the resonances it is possible to measure the k‐dependent magnetic field splitting of the lower branch for the first time. The results allow to determine the exchange energy, the longitudinal‐transverse splitting and the g‐values of the uppermost valence band (Γ‐symmetry) and the lowest conduction band (Γ‐symmetry) with much higher accuracy than before.