bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anharmonic Properties of the Ternary Semiconductor CuGe2P3
Authors: Prabhakar N. V. K. , Sanyal S. P. 
Published: July 2007

AbstractThe third order elastic constants and the pressure derivatives of second order elastic constants of ternary zinc blende semiconductor, CuGe2P3 are analysed using two theoretical approaches. The first model consists of Born‐Mayer type short‐range potential in addition to the long range many‐body interaction and Coulomb potentials, while the second model is derived from Martin's bond‐bending and stretching force model. It is shown that although the bond bending force model gives a reasonably good fitting to these properties, the present model including three body forces explains adequately the features of the anharmonic behaviour reasonably well.
Effective Potentials and Crystalline State Properties of Some Fluorite‐Structure Crystals
Authors: Dutt N. , Kaur A. J. , Shanker J. 
Published: July 2007

AbstractSeven different potential forms for the overlap repulsive energy proposed by various investigators as reported in the literature are examined for the fluorite‐structure crystals, viz. CaF2, SrF3, BaF2, PbF2, Sr(NO3)2, Ba(NO3), and Pb(NI3)2. A number of crystalline state properties such as cohesive energy, bulk modulus and its pressure derivatives, Grünesien und Anderson parameters, first and second order volume and pressure derivatives of dielectric constants are calculated using different potential functions. The results obtained are found to compare well with available experimental data, and also reveal the usefulness of the approach based on interionic potentials in predicting new results.
X K Edge Absorption of Titanium and L Edges of Tantalum in (Ti, Ta)O2 Rutile Solid Solutions
Authors: Poumellec B. , Marucco J. F. , Touzelin E. 
Published: July 2007

AbstractAn analysis of the Ti K edge and Ta L edges yields that the chemical shift amounts to 0.8 eV by a valence charge increase. An exciton line is resolved like in other rutiles. Exciton binding energy amounts to 1.1 eV and decreases to 0.6 eV for high tantalum content. The coordination polyhedron size of titanium increases to 11 × 10−3 nm with the tantalum content. This is essentially due to the increase of ionic radius of titanium by the valence charge increase. The crystal field splitting is found to be 3.1 eV for TiIV, 2.1 eV for TiIII, and (5.5 to 6.0) eV for TaV. It seems that the crystal field splitting is well correlated with the valence charge. Additionally a procedure is described to add several × absorption spectra recorded on several samples with the same composition but with different thicknesses.
Electronic Structure of the Ce Systems I. General Theory
Authors: López‐Aguilar F. , Costa‐Quintana J. 
Published: July 2007

AbstractA model is deduced for the electronic structure of the Ce systems. It includes a pseudopotential which considers the strong correlation effects due to the fluctuation of the number of f‐electrons in the Ce atoms. The pseudopotential affects the f‐symmetries according to their own occupations and is different from zero when the f‐states are spd/f hybridized. The APW method is modified in order to introduce the pseudopotential within the band structure Hamiltonian. Finally, the so‐called „three‐peak”︁ 4f structure which appears in the Ce systems is analyzed with our model.
Effect of Non‐Spherical Potential on the Band Structure of Metallic Dysprosium
Authors: Mukhopadhyay P. K. , Das K. C. 
Published: July 2007

AbstractThe effect of non‐spherical part of the crystal potential on the band structure of dysprosium metal in the warped muffin‐tin approximation has been studied using the augmented plane wave method. The band structure is not significantly affected by this factor in the present case. The maximum change in energy eigenvalues is 0.002 Ryd.
Dynamical Corrections to the Physical Characteristics of Solitons in Polyacetylene
Authors: Fedyanin V. K. , Osipov V. A. , Stoyanova I. S. 
Published: July 2007

AbstractThe soltion solutions to the continuum equations of motion of the trans‐(CH)x model in the limit of slowly moving solitons are obtained. The effects due to the soliton motion are considered. The main physical characteristics of moving solitons (the energy of creation, mass, charge, width, electrical moments) are calculated. In the case of the kink excitation the effects of motion are reduced by the small parameter ϵ ≈ 0.07, whereas for the polaron excitation the correction terms proportional to the polaron velocity are considerable.
Interaction of Crystal Impurity Centres with a Coherent Electromagnetic Field
Authors: Apanasevich P. A. , Kruglov V. I. , Tralle I. E. 
Published: July 2007

AbstractBy the projection operator technique the non‐Markovian kinetic equation for the density matrix of a crystal impurity centre in an external electromagnetic field is derived, taking into account the electron–phonon interaction. The analytical solutions of this equation are obtained for the external field as an ultrashort pulse and in the case of a monochromatic wave.
Photon Recycling in Double Heterostructures II. The Case of Non‐Perfect Optical Confinement
Authors: Enders P. 
Published: July 2007

AbstractThe influence of photon recycling (PR) onto the minority carrier distribution in double heterostructures is investigated. For non‐perfect optical confinement of the luminescence radiation in the active zone, the corresponding integro‐differential equation (without drift term) of the diffusion model cannot longer be solved exactly. The enlargement of the radiative lifetime, as measured in photoluminescence experiments, e.g., is calculated approximatively by means of perturbational methods. Particular attention is devoted to the dependence of this enlargement due to PR upon the thickness of the active zone. In very thin active zones, PR should play a minor role due to the loss of luminescence radiation.
The Generalized Curie‐Weiss Law
Authors: Fähnle M. , Souletie J. 
Published: July 2007

AbstractIt is shown that the zero‐field suscetpibility χ of many ferromagnets may be described with high accuracy by a modified power law (generalized Curie‐Weiss law) χT ∼ [(T – TC)/T]−γc in the whole paramagnetic regime, where γc is the critical susceptibility exponent. In contrast, the conventional power law χTC ∼ [(T – TC)/TC]−γc holds only for the very small critical regime. Application of the scaling variable (T – TC)/T, which is non‐linear in T, to other physical situations (spin glasses, percolation) is discussed. Altogether the temperature range where scaling ideas are useful appears to be much wider than generally expected.
Quantum Theory of Free‐Carrier Absorption in Quasi‐Two‐Dimensional Semiconducting Structures. Degenerate Carrier Case
Authors: Comas F. , Giner C. Trallero , León H. 
Published: July 2007

AbstractFree‐carrier absorption coefficient of light is calculated for the case of quasi‐two‐dimensional (Q‐2D) semiconducting systems (of the kind of “quantum well” structures) assuming the conditions for highly degenerate carrier statistics are fulfilled. A comparison with recent results for the case of non‐degenerate carrier statistics is made: higher absorption coefficient for lower values of the quantum‐well width is predicted (as in the non‐degenerate case), but the absorption coefficient is lower for the degenerate carrier case.
Electronic Structure of PbTe–Pb1−xSnxTe Superlattices
Authors: de Dios Leyva M. , López‐Gondar J. 
Published: July 2007

AbstractIn the framework of the envelope function approximation a simplified effective Hamiltonian for each valley in the PbTe–Pb1−xSnxTe superlattice is obtained. Analytical expressions are given for the dispersion relations connected with different valleys as a function of the kx, ky transverse wave vector components.
Time‐Resolved Degenerate Four‐Wave Mixing in CuCl under Nanosecond Pulsed Excitation
Authors: Frindi M. , Hönerlage B. , Levy R. 
Published: July 2007

AbstractUsing nanosecond laser pulses the time behaviour is investigated of degenerate four‐wave mixing close to the biexcitonic resonance in CuCl. The signal emission presents different time evolutions depending on excitation conditions. Its generation rate shows intensity changes and retardation effects. These effects are explained by an attenuation of the pump pulse through a time‐dependent nonlinear absorption and, at the resonance, by a loss of coherence related to collisions with bi‐excitons.
Modelling of Angle Resolved Photoemission Spectra at Low Energy
Authors: Beckmann A. 
Published: July 2007

AbstractThe calculation of low‐energy angular resolved photoemission spectra is based on the method of surface Green's function. This approach enables excitations from bulk and surface states to be treated uniformly, thus elucidating the connection between peak characteristics and lifetimes of electrons and holes better than before. Furthermore, the method is suitable to describe surface disorder. Experimental results obtained by Gartland and Slagsvold for Cu(111) are used for discussion.
Diffusion of Non‐Interacting Quantum Particles in a Disordered System. The Transport Length in the Classical Limit
Authors: Lenk R. 
Published: July 2007

AbstractWithin the model of uncorrelated scatterers and a long mean free path the recently proposed structure of the density matrix in a current‐carrying state is shown to be produced and reproduced by the superposition of all scattered waves. The corresponding transport length corresponds to its classical value, but the physical picture is a new one.
Reconstructed Structures of Symmetrical 〈011〉 Tilt Grain Boundaries in Silicon
Authors: Kohyama M. , Yamamoto R. , Doyama M. 
Published: July 2007

AbstractThe energies of reconstructed structures of symmetrical 〈011〉 tilt grain boundaries with θ > 70.53° in silicon are calculated using the tight‐binding type electronic theory (bond orbital model). The energies of the most stable reconstructed boundary structures are in the same range or a little larger than those with θ ≦ 70.53°. These reconstructed structures are more stable than those with dangling bonds. There exists the continuity of boundary structure in the range 70.53° ≦ θ ≦ 148.41° (Σ = 27). Shallow cusps in the energy against θ curve can be found at special boundaries of type Σ = 3 (θ = 109.47°), Σ = 11 (θ = 129.52°), and Σ = 27 (θ = 148.41°), all of which are composed of one kind of original patterns. For θ > 148.41°, boundary structures are composed of an array of a0[100] edge dislocations.
Damping of a Kinked Dislocation by Electrons in Metals at Low Temperatures
Authors: Das Amal K. 
Published: July 2007

AbstractThe mobility of a dislocation in metals at low temperatures is limited by the damping due to conduction electrons. The kink model of a dislocation is pursued in order to study this damping force and hence the mobility. Calculations are presented for one, two and three dimensions. The dependence of the mobility and electron density is exhibited for different dimensions. New results are derived.
The Effect of Higher‐Order Cumulants in the Random‐Field Ising Model
Authors: Janiš V. 
Published: July 2007

AbstractIt is shown that below a critical dimension dc = 4 higher‐order random‐field cumulants contribute to the divergent part of the free energy. They renormalize the standard diagrammatic expansion into the most divergent terms in weak random fields in such a way that the perturbative effective dimensionality in the scaling region of the d < 4 model is two. It is argued that any dimensional reduction based on a diagrammatic expansion is doubtful in lower dimensions.
Adiabatic Method for Excitonic Molecules
Authors: Vukajlović F. R. , Vinitskii S. I. 
Published: July 2007

AbstractThe binding energy for excitonic molecules, four‐body systems with Coulomb interactions, is investigated using the adiabatic method usually applied to three‐body Coulomb systems. The infinite system of coupled Schrödinger‐type equations obtained, is approximated by a finite system of twenty‐one coupled equations and solved. The investigation gives an increase in binding of these systems practically in the whole region 0 < σ = me/mh ≦ 1, compared to previous varational results.
Dissociation and Thermodynamic Properties of Bipolarons
Authors: Li Yan‐Min , Chao K. A. 
Published: July 2007

AbstractThe degenerate perturbation theory is used to calculate the bipolaronic energy bands in various one‐, two‐, and three‐dimensional crystal structures. The dissociation energy of bipolaron is calculated, from which the stability of the bipolaron is investigated. Higher stability is found in lower‐dimensional systems. The triplet bipolaron state is almost as stable as the singlet bipolaron state, and so plays a very important role in determining the thermodynamic properties of bipolaronic systems.
Low‐Temperature Reflectivity Spectra of AgGaS2 and AgGaSe2 Compounds
Authors: Artus L. , Bertrand Y. , Ance C. , Lopez‐Soler A. 
Published: July 2007

AbstractReflectance measurements are made at 5 K on the ternary compounds AgGaS2 and AgGaSe2 in the energy range located above the fundamental gap of each compound up to 5.5 eV. Reflectivity spectra are interpreted according to a model previously proposed by the authors to interpret the reflectivity spectra of these compounds at room temperature in a wider energy range. According to this model, the reflectivity spectra of AgGaS2 and AgGaSe2 are found to be principally dominated by the existence of structures of type E1, E′0, E2, and E′1, as occuring in the binary analogues of zincblende type. Using this model, the structures are identified of Ei type which take place in the energy range in which the 5 K reflectivity spectra have been taken. Also, structures which may be due to pseudodirect transitions are observed.
Density of States and Photoconductivity of Hydrogenated Amorphous Silicon
Authors: Terekhov V. A. , Trostyanskii S. N. , Domashevskaya E. P. , Golikova O. A. , Mezdrogina M. M. , Sorokina K. L. , Kazanin M. M. 
Published: July 2007

AbstractThe results of the investigation of hydrogenated amorphous silicon films by ultrasoft X‐ray spectroscopy are compared with the measurements of photoconductivity on the same samples. It is shown that the saturation of amorphous silicon by hydrogen causes a decrease of the localized states density just above the valence band top which leads to the rise in photoconductivity. As a result, a maximum in the density of localized states clearly reveals itself at 1 eV above the top of the valence band providing n‐type conductivity.
An Unconventional Jahn‐Teller Phenomenon in a Valency‐Mixing Surrounding
Authors: Weber C. , Sigmund E. , Wagner M. 
Published: July 2007

AbstractStimulated by ESR measurements in SmB6:Er3+ the unusual g‐factor behaviour of the Er3+ ground state, which is extraordinarily isotropic, is ascribed to a new kind of Jahn‐Teller‐type phenomenon. The 4f–5d hybridization deformations of the Sm neighbourhood adopt the role which in conventional Jahn‐Teller systems is played by nuclear distortions. Arguments for this proposition and numerical results are given. These show that the “minimal” model constitutes a good starting point for refined theories. Several options of refinement are indicated.
Resonant Brillouin Scattering at Bound‐Exciton States in CdS
Authors: Gutowski J. , Schott J. , Broser I. 
Published: July 2007

AbstractStrong resonant Brillouin scattering (RBS) is studied occurring under high excitation densities in the bound‐exciton energy range in CdS. RBS shows pronounced resonance enhancement not only at well‐known bound‐exciton ground state energies but also for energies of various excited states of these complexes. In this energy range, RBS has not been observed under low‐excitation‐density conditions. The phonon coupling determining the Stokes or anti‐Stokes shift of the RBS line maxima allows to calculate the spatial dimensions of the excited bound‐exciton levels acting as intermediate resonance states of the scattering process. In general, high‐density RBS spectroscopy is shown to yield important information on ground and excited states of bound exciton complexes.
Electron Spin–Lattice Relaxation in Fractals
Authors: Shrivastava K. N. 
Published: July 2007

AbstractA theory of the spin–fracton interaction for paramagnetic ions in fractal structures is developed The interaction is exponentially damped by the self‐similarity length of the fractal and by the range dimensionality dphiv;. The relaxation time of the spin due to the absorption and emission of the fracton is calculated for a general dimensionality called the Raman dimensionality dR, which for the fractons differs from the Hausdorff (fractal) dimensionality, D, as well as from the Euclidean dimensionality, d. The exponent of the energy level separation in the relaxation rate varies with dRdphiv;/D. Also the spin relaxation rate due to a new type of Raman process is calculated in which one fracton is absorbed to affect a spin transition from one electronic level to another and later another fracton is emitted along with a spin transition such that the difference in the energies of the two fractons is equal to the electronic energy level separation. The temperature and the dimensionality dependence of such a process is found in several approximations. In one of the approximations where the van Vleck relaxation rate for a spin in a crystal is known to vary with temperature as T9, the calculated variation for fractals turns out to be T6.6 whereas the experimental value for Fe3+ in frozen solutions of myoglobin azide is T6.3. Since dR = 4/3 is used and the fracton range dimensionality dphiv; = D/1.8, it is expected to measure the dimensionalities of the problem by measuring the temperature dependence of the relaxation times. Also calculated is the shift of the paramagnetic resonance transition for a spin in a fractal for general dimensionalities.
Exact Solutions for Homogeneous Linear Biased Correlated Walks. A Case of the Boltzmann Entropy Decreasing in Time
Authors: Godoy S. V. , Fujita S. , Rodriguez R. 
Published: July 2007

AbstractThe probabilities of arrival with directions for a linear biased correlated walk satisfy a set of coupled linear difference equations. An exact analytic solution to the equations subject to a periodic‐boundary and homogeneous‐initial condition is obtained. The Boltzmann entropy (the negative of the Boltzmann constant kB times the Boltzmann H‐function) computed in terms of the solution may decrease (or increase) in time, depending on the chosen initial condition. The physical meaning of this striking behavior is discussed by taking diatomic impurities (CO) in liquid solution (Ar) under external electric fields. It is concluded that in the presence of a bias the sense of the time‐development of a general physical system cannot be given by the conventional Boltzmann H‐function.
Surface Phonon Polaritons in Semi‐Infinite Semiconductor Superlattices
Authors: Nkoma J. S. 
Published: July 2007

AbstractSurface phonon polaritons in a semi‐infinite semiconductor superlattice bounded by vacuum are studied. The modes associated with the polaritons are obtained and used to obtain the dispersion relation. Numerical results show that polariton bands exist between the TO and LO phonon frequencies, and are found to approach two surface mode frequencies in the limit of large tangential wave vector. The dependency of frequencies on the ratio of layer thicknessses is shown. The results are illustrated by a GaAs—GaP superlattice bounded by vacuum.
A Contribution to the Theoretical Interpretation of the UPS Spectra of Monoatomic Adsorption of Oxygen on the Si (111) Surface
Authors: Karpushin A. A. , Sorokin A. N. , Semenova I. Yu. , Tomášek M. 
Published: July 2007

AbstractA calculation is performed of the early stage of adsorption of atomary oxygen on the Si (111) surface in the on‐atom (top) position, saturating the dangling bond of the surface silicon atom. By considering the possible presence of a vacancy in the adsorbed oxygen monolayer, it is shown that the basic features of the experimental energy spectrum can be obtained without resorting to the idea of the existence of SiOSi bridge structures on the surface. Nevertheless, the results obtained do not contradict such an idea, nor the idea that the early stage of adsorption corresponds to a molecular form with a peroxide bridge formation. They merely suggest the possibility of an alternative early stage adsorption model. The method of calculation is the recently introduced generalized cluster Bethe‐lattice method.
The Electronic Heterogeneous States in Ferroelectric Semiconductors
Authors: Egorov B. V. , Egorova I. B. , Krivoglaz M. A. 
Published: July 2007

AbstractThe thermodynamically stable heterogeneous states (HS) are considered in ferroelectric semiconductors in which polarization and carrier concentration are self‐consistently dependent on the coordinates. These HS are shown to be thermodynamically favoured at carrier concentrations n being larger than the critical one and especially in a temperature range close to the Curie point of the second order phase transition. An investigation is made of the conditions for the formation of these HS, the phase diagram in variables T, n, and the characteristics: the values of periods (connected with the screennig length), the amplitudes of the carrier concentration and the polarization variations, and the coordinate dependence of the polarization. Depending on the parameters two types of the HS are possible: one with domains separated by sharp walls and the other with smooth wavelike polarization.
Energy Gap and Valence Band Structure of Cd1−zMnzTe1−ySey Alloys
Authors: Chehab S. F. , Woolley J. C. 
Published: July 2007

AbstractMeasurements of wavelength modulated reflectance are made as a function of temperature on Cd1−zMnzTe1−ySey alloys for both zinc blende and wurtzite fields. The room temperature energy gap E0 is found to show a square law variation with y independent of the change in crystal structure and the relation proposed by Moon et al. for E0 values at a general composition (z, y) is found to be satisfied. At low temperatures for the Cd1−zMnzSe alloys, the E0 values show an increase ΔE0 due to magnetic effects and the values of ΔE0 agree with the theoretical predictions of Alexander et al. Also for Cd1−zMnzSe, the values of valence band splittings are used to show that the fractional d‐like character of the valence band increases linearly with z and has a value of ∼0.26 at z = 0.2.
Recursive Scattered‐Wave Approach to the Electronic Density of States of Topologically Disordered Systems
Authors: Solbrig H. 
Published: July 2007

AbstractThe electronic density of states is calculated from the incident‐field amplitudes of a multiple scattering problem based on a muffin‐tin model. Using the idea of Haydock's LCAO recursion method, the multiple scattering between atomic angular‐momenturn channels is replaced by multiple scattering between incident‐field distributions of decreasing local relevance. The proposed method is tested numerically for a cluster of 13 nickel atoms.
The Influence of Carbon Vacancies and Local Atomic Displacements on the Electronic Structure of Niobium Carbides
Authors: Novikov D. L. , Ivanovskii A. L. , Gubanov V. A. 
Published: July 2007

AbstractA nonempirical Xα discrete variational method is used to calculate clusters that with respect to the carbon sublattice simulate complete and nonstoichiometric niobium carbides. The presence of carbon vacancies is found to lead to the formation of an extra peak near the low energy edge of metallic band. A discussion is presented of the effect of niobium atom local displacements near the anion vacancies on electronic structure, chemical bond, and charge distribution in NbCx. Data obtained are compared with the results of X‐ray photoelectron spectroscopic studies of niobium carbides.