bluuebunny/crossref_metadata_2025 huggingface dataset:
The Intersublattice Molecular Fields in the Rare Earth–Cobalt Intermetallics
Authors: Radwański R. J.
Published: July 2007

The value of 9.27 × 10−23 J for the exchange coupling parameter between the Ho and Co spins in Ho2Co17 has been derived. Some experimental evidence is given to show that the R–T spin coupling parameter is rather insensitive to the kind of the rare earth atom as well as on the cobalt composition. It allows to calculate the intersublattice molecular fields for the rare earth–cobalt intermetalic compounds. This field affects the R magnetic moment and originates from the Co sublattice in the R2Co17, RCo5, R2Co7, RCo3, and RCo2 compounds. The fields in the new magnetic materials of the R2Co14B type have also been evaluated.
Determination of Titanium CNDO Parameters and Application in Cluster Calculations of Different Titanium Compounds
Authors: Haberlandt H.
Published: July 2007

Electronic properties of the titanium clusters Ti4(Td) and Ti6(Oh) are calculated by means of the semiempirical quantum chemical CNDO method. The parameters are derived by adjusting the cluster electronic properties to the corresponding bulk data. Comparing the titanium cluster results with those of small nickel clusters calculated using Blyholder parameters, the same trends are observed as in comparing the bulk properties of both metals. An application of the titanium parameters to the calculation of the intermetallic compound Ni3Ti gives a further confirmation of their compatibility with the nickel parameters. Using the derived parameters in TiO2 cluster calculations leads to a satisfactory description of the electronic properties of this material.
Excitonic Absorption in Silicon in the Presence of Low Magnetic Fields
Authors: Donecker J. , Kluge J.
Published: July 2007

Magnetic circular dichroism (MCD) measurements are carried out on Si monocrystals in longitudinal magnetic fields up to 5.3 T. Near the indirect excitonic absorption many oscillations occur in the MCD spectra. In comparison with wavelength‐modulated absorption measurements it is shown that the MCD oscillations are due to strongly broadened steps in the absorption edge. The characteristic energies of the absorption steps behave like that of Landau levels with a phenomenological effective mass of m* = 0.38 ± 0.04 for B | [001], obtained also by cyclotron resonance experiments. The energies of the Landau‐like steps converge with B → 0 to energies near the series limit of the exciton. It seems to be the first time that Landau levels in the magnetoabsorption in Si are measured.
Dynamical Screening, Collective Excitations, and Electron–Phonon Interaction in Heterostructures and Semiconductor Quantum Wells. General Theory
Authors: Wendler L. , Pechstedt R.
Published: July 2007

A theory of dynamical screening in heterostructures and semiconductor quantum wells is developed which contains electron–electron interaction and electron–phonon interaction. In this theory both the types of long‐wave optical phonons, LO phonons and interface phonons, which occur in those layered structures are included. An expression is derived for the longitudinal screened interaction of subband electrons in heterostructures and quantum‐wells. The obtained screened interaction potential allows the derivation of the total longitudinal dielectric function and the dispersion relation of the coupled intra‐ and intersubband plasmon‐phonon modes. This screened interaction potential is used to develope a dynamically screened and finite‐temperature theory of the electron–phonon interaction in heterostructures and quantum wells. The leading‐order electron self‐energy is disscussed. An analytic expression of the polarization function of the quasi‐two‐dimensional electron gas is calculated within the random‐phase approximation. Further approximations, the plasmon pole approximation and the long‐wave approximation are discussed and the resulting analytic expressions of the polarization function are given.
The Pseudopotential Approach to the Shallow Donor Problem in II–VI Semiconductors
Authors: Grinberg M.
Published: July 2007

The problem of chemical shift of shallow donor states in compound semiconductors is investigated in the framework of pseudopotential theory. The “first principle” pseudo‐Hamiltonian including the electron–phonon interaction for shallow donor is obtained and the one‐band pseudo effective mass approximation is discussed. As an example the ionization energies for several donors in CdS and ZnSe are calculated. A good correspondence between the theory and experimental data for impurities in cation site is found.
Contribution of Medium Phonons to the Transition Probability of Reactive Processes on Solid/Solution Interfaces. Joint Treatment of Classical and Quantum Parts of the Medium
Authors: Engler C. , Rabe E.
Published: July 2007

Quantumstatistical calculations are made of transition probabilities for reactive processes on solid/liquid interfaces, which are assisted by multi‐phonon‐transitions of the surrounding medium. A joint treatment of a classical (solvent) and a quantal (lattice) part of the medium effect upon reactive transitions is given. Numerical calculations are carried out in different approximations.
Electron Spin Resonance Studies of Light Sensitive Centers with Tetragonal Symmetry in CaO
Authors: Boas J. F.
Published: July 2007

Two centers with tetragonal symmetry and principal axes along 〈100〉 are observed by ESR in single crystals of CaO. The ESR signal intensity of both the centers is affected by visible light illumination. One center (g∥ = 2.0048, g⟂ = 2.0007) occurs in highly colored crystals and may be associated with carbon impurities introduced during crystal growth. The other (g∥ = 1.99905, g⟂ = 1.99956) occurs in “clear” crystals after 1 MeV electron irradiation and has the characteristics of an anion–cation vacancy pair center containing one electron (i.e. a P− or F center). The g‐values do not agree with those found for the same center in polycrystalline CaO but are consistent with a simple model of a perturbed F+ center.
The Influence of External Effects on the Proton Conductivity of an Hydrogen‐Bonded Chain
Authors: Krasnogolovets V. V. , Tomchuk P. M.
Published: July 2007

A theoretical study is made of stimulation of hydrogen‐bonded‐chain‐proton conductivity in a constant longitudinal electric field by light‐and‐ultrasonic effects. The suggested mechanism of light effect is caused by nonactivated phonon transitions of charge carriers from the base level of one knot through an internal excited state to the base state of the neighbouring knot. The suggested mechanism of ultrasonic effect is caused by amplitude increase of acoustic fluctuations of the hydrogen bonded‐chain structure, that modulate the distance between knots, i.e. by increase of the resonance integral overlap of the carrier wave functions.
Plasmon Excitation in the Interaction of Fast Electrons with Metal Surfaces
Authors: Duy Bao Tran Thoai
Published: July 2007

The interaction of fast electrons with semi‐infinite metals is studied within the hydrodynamic model. Retardation effects, damping, and diffuseness of the electron density at the surface are included. The energy loss probability of surface plasmons is calculated for external electron beam travelling parallel to the metal surface. Numerical calculations are carried out for rs = 2 jellium.
Theoretical Analysis of the Oscillatory Diffusivity‐Mobility Ratio in Degenerate n‐InSb in the Presence of a Quantizing Magnetic Field
Authors: Ghatak K. P. , Mondal M.
Published: July 2007

An attempt is made to study theoretically the dependence of the Einstein relation for the diffusivity‐mobility ratio of the electrons on the reciprocal quantizing magnetic field in degenerate n‐InSb on the basis of the fourth order in effective mass theory and taking into account the interactions of the conduction, heavy‐hole, light‐hole and the split‐off bands. The results obtained are then compared to those derived on the basis of the well‐known three‐band Kane model since many authors have continued to use the three‐band Kane model for the same semiconductor. It is observed that the three‐band Kane model for n‐InSb exhibits smaller values of the diffusivity‐mobility ratio and the same ratio shows an oscillatory magnetic field dependence as expected in both the cases, since the origin of the oscillations in the Einstein relation is the same as that of the Shubnikov‐de Haas oscillations. Besides the corresponding results for isotropic parabolic energy bands, both, in the presence and absence of magnetic quantization, are also obtained from the expressions derived.
Many‐Exciton Theory for Multiple Quantum‐Well Structures
Authors: Manzke G. , Henneberger K. , May V.
Published: July 2007

The many‐exciton theory of highly excited semiconductors is reformulated in order to apply it to the case of a quasi two‐dimensional confinement of electrons and holes in a multiple quantum‐well structure. Using simple variational ansatzes for the exciton wave function in the low excitation limit density dependent exciton parameters are calculated for a GaAs‐GaAlAs multiple quantum‐well system. In contrast to bulk material but in agreement with experimental findings a blue shift of the excitonic resonance with increasing excitation intensity is obtained. The results are used to demonstrate nonlinear optical behaviour, especially bistabilities, for such systems.
Accuracy of the Transmission Coefficient across Parabolic Barriers as Obtained from a Generalized WKB Approach
Authors: Berz F. , Morice J. A.
Published: July 2007

A comparison is carried out in the case of parabolic potential barriers between the transmission coefficient T obtained from the solution of Schrödinger's equation and the approximate transmission coefficient T(WKB) which is derived from a generalised WKB approach. It is shown that T(WKB) is the first term of the asymptotic expansion of T in powers of 1/X2, with X2 ∼ s \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {U_B } $\end{document}UB, where s is the width of the barrier and UB is the barrier height. Expressions are obtained which give an upper limit \documentclass{article}\pagestyle{empty}\begin{document}$ |\overline {T - T(WKB)}| $\end{document}/T(WKB) of the relative error which occurs when using T(WKB) instead of T for the transmission coefficient. It is seen that in most practical cases this error is fairly small.
Changes in the 119Sn‐site hyperfine field of iron induced by substitutional vanadium and chromium
Authors: Dubiel S. M.
Published: July 2007

The effect of substitutional vanadium (up to 18 at%) and chromium (in the whole composition range) on the average 119Sn‐site hf field, HSn, in metallic iron is investigated using Mössbauer‐effect spectroscopy. From the room temperature measurements for both the impurities it is observed that HSn falls with increasing impurity content much faster than the corresponding 57Fe‐site hf field. For chromium HSn is a nonlinear function of impurity concentration and indicates the following four characteristic ranges: up to x ≈ 10 dHSn/dx ≈ 390 kOe; for 10 ≦ x ≦ 45 dHSn/dx ≈ ≈ 11 kOe; for 45 ≦ x ≦ 65 dHSn/dx ≈ 210 kOe; at x = 72 HSn ≈ 0 and for x ≧ 72 HSn increases with x in a nonlinear way. From the 4.2 K measurements for iron–chromium alloys it follows that HSn passes through a minimum of 27 kOe at x = 83, but it does not compensate completely. This concentration coincides with the spin‐glass state concentrations x = 81 to 84.
Magnetic and structural properties of rapidly quenched iron–boron metallic glasses
Authors: Hermann H. , Mattern N. , Matz W.
Published: July 2007

The structure of rapidly quenched Fe1–xBx amorphous alloys (0.15 ≦ x < 0.25) is considered to be a stochastic arrangement of two kinds of clusters (α‐Fe and t‐Fe3B type short‐range order) and an interface region between them. The corresponding analytical structure model reproduces experimental results on density, small‐angle scattering, and radial distribution functions of atomic distances. Magnetically, each structural component is described by a certain magnetic moment of iron atoms. An expression for the average magnetic moment is derived from the structure model, and the moments of the structural components are determined by means of a least‐square fit to experimental values of the average magnetic moment. The theoretical curve agrees well with the experimental results on the concentration dependence of the average magnetic moment which deviates evidently from a linear behaviour. An extrapolation of structure and average magnetic moment to x = 0 (amorphous pure iron) is not possible at present.
Energy and Absorption Spectra of One‐Dimensional Exciton‐Phonon System
Authors: Sherman A. V.
Published: July 2007

Based on the recursion method of the calculation of the Green's function, the energy and absorption spectra of a one‐dimensional system of Frenkel excitons interacting with dispersionless optical phonons are investigated in a wide range of parameters. It is shown that there exist three regions of parameters, which correspond to qualitatively different spectra. In the first region, the spectra reveal the features peculiar to a vibronic exciton. The second region is characterized by the existence of a large number of exciton‐phonon complexes manifesting themselves in absorption. The appearance of such complexes can be regarded as a considerable softening of the chain around excitation. In the third region, coexistence of two types of states is observed throughout the Brillouin zone. The latter are the stable states of an intermediate coupling exciton and the decaying states of a nearly free exciton, the dispersion curve of which is strongly influenced by anticrossing with a peculiarity of a combined exciton‐phonon density of states.
Impurity Breakdown in Germanium at Low Lattice Temperatures
Authors: Pramanik T. K. , Bhattacharya D. P.
Published: July 2007

The kinetic processes which take part in the phenomenon of impurity breakdown in n‐Ge are known to be the impact ionisation of the neutral donor atoms by the relatively energised free electrons and the thermal recombination of the latter. The electric field dependence of the coefficients of these processes, AI(E) and BT(E) is calculated numerically. The calculations are carried out in the approximations of an effective electron temperature and a parabolic law of dispersion. The impurity breakdown characteristics of the material are then investigated. When compared with other calculations and with the available experimental data, the results obtained here show a better agreement in some of the characteristics with the experimental observations. The anomalous type behaviour obtained here in respect of some other characteristic is also discussed.
Sensitized Luminescence of Pure and Doped NaNO2 Single Crystals. II. Time‐Resolved Experiments and Preliminary Analysis
Authors: Pufahl H. , Köhler J. , Schmidt Th. , Schmid D. , Kenkre V. M.
Published: July 2007

The fluorescence decay times of pure NaNO2 and of NaNO2 doped with KNO2 are measured for varying temperature and dopant concentration. Both, time‐resolved and steady measurements are carried out and are found to be in agreement with each other. Energy transfer rates are deduced from the measurements and an attempt is made to interpret them with the help of a generalization of the standard sensitized luminescence theory which includes detrapping effects. The result of this attempt is a strong indication that the rates for trapping and detrapping in NaNO2 are not interrelated via detailed balance and the conclusion drawn is that a deeper theoretical investigation is necessary to analyze the experiment quantitatively. However, a rough estimate of the singlet exciton hopping rate can be made, and is found to be in agreement with the results of an interpretation of the lineshape asymmetry. For triplet excitons in NaNO2, it is shown that it is natural to conclude that energy transfer is motion‐limited and that the motion is one‐dimensional, in agreement with expectations based on the crystal structure of NaNO2.
On the Free Energy of the Hard Sphere Fluid
Authors: Edgal U. F.
Published: July 2007

The equilibrium properties of the hard sphere fluid are investigated in the low/medium density regime by finding upper and lower bounds for the free energy of the system. It is shown that the coincidence of the bounds in the low density limit justifies the Van der Waal's approximation at very low densities. A better approximation is obtained valid for moderately higher densities. Similarities and properties of the equilibrium packing and parking processes are employed, allowing a simple expression to be obtained for the partition function of the hard sphere fluid.
Thermodynamics of Superconductors with Charge‐ and Spin‐Density Waves
Authors: Gabovich A. M. , Gerber A. S. , Shpigel A. S.
Published: July 2007

Using thermal Green's function technique the thermodynamics of superconductors with charge‐ and spin‐density waves is considered. The Δ/Tc ratio and the paramagnetic limit Hp are calculated for various values of the dielectric gap σ and the parameter ν = Nnd(0)/Nd(0), where Nnd(0) and Nd(0) are the electron densities of states for non‐dielectrized and dielectrized Fermi surface sections, Δ(0) is the zero‐temperature value of the superconducting order parameters, and Tc is the critical temperature. It is shown that for the charge‐density wave‐superconductors the values Δ(0)/Tc are substantially less than in the conventional BCS theory. The theoretical conclusions are in a good agreement with the experiment.
Properties of Kinks in a Driven Damped Anisotropic Magnetic Chain
Authors: Costa B. V. , Pires A. S. T.
Published: July 2007

The motion of kinks in an anisotropic classical Heisenberg chain with magnetic field applied in the easy plane is studied, when a dissipative Gilbert‐like term is present.
Dispersion and Damping Properties of Plasmon Polaritons in Superlattice Structures. I. Infinite Superlattice
Authors: Haupt R. , Wendler L.
Published: July 2007

The dispersion and damping properties of plasmon polaritons in infinite superlattices are analyzed using a local theory with retardation. The band structure and the zone folding of the plasmon polaritons are discussed. It is shown that in a definite range of the thickness ratio of the single‐layers of the superlattice a degeneracy point of the two interface‐like plasmon‐polariton bands occurs. An analytic expression for the damping function is derived by means of a perturbative method. The different behaviour of the damping of plasmon polaritons in various infinite superlattice structures is discussed. The dispersion curves and the damping function are calculated and presented in graphical form.
Spectrum of Excitations of an Easy‐Plane Ferromagnet (S = 3/2) in a Magnetic Field
Authors: Valkov V. V. , Valkova T. A. , Ovchinnikov S. G.
Published: July 2007

The quantum spectrum of elementary excitations of easy‐plane ferromagnet with S = 3/2 in a magnetic field is calculated by the diagram technique for Hubbard operators. It is established that the collective excitation spectrum in the low‐temperature region consists of one longitudinal and two transverse branches. The limiting cases of strong and weak anisotropy are analysed in detail. In the region of small values of quasimomentum the intervals are determined in whose limits the ω(q) dependence is quadratic and linear in quasimomentum modulus.
Transport Properties of Ferrous Oxide Fe1−yO at High Temperature
Authors: Molenda J. , Stokłosa A. , Znamirowski W.
Published: July 2007

Electrical conductivity and thermoelectric power of ferrous oxide are measured as a function of temperature (1090 to 1580 K) and oxygen pressure in the whole range of its stability. The results are analysed with reference to the measurements of its deviation from stoichiometry. It is shown that at temperatures exceeding 1070 K the total electrical conductivity of Fe1−yO is a sum of intrinsic and extrinsic conductivity related to the ionic defect concentration. It is shown that a simple band model is insufficient to describe the electrical properties of Fe1−yO. A semiconductor–metal transition is revealed in Fe1−yO. The semiconductor–metal transition corresponds to the stability limits of wustite pseudophases (w1, w2). A qualitative model of electronic structure of Fe1−yO is proposed.
Investigation of p‐CdTe and p‐ZnxCd1−xTe Single Crystals by ps‐Laser‐Induced Gratings and by Photoluminescence
Authors: Rückmann I. , Petrauskas M. , Netikšis V. , Tamulaitis G. , Halfpap J.
Published: July 2007

From the measured erasure times of transient gratings created in the volume and on the surface of non‐intentionally doped p‐type CdTe and ZnxCd1−xTe (x ≦ 0.11) single crystals the free‐carrier lifetime and the surface recombination velocity at room temperature are determined, respectively. The erasure time of the surface grating in CdTe is found to be 130 ps, which is one order smaller than that of the volume grating. A lifetime shortening is observed in mixed crystal. Moreover, using cw‐laser excitation the samples are characterized additionally by photoluminescence investigation at low temperatures to test the quality, to determine the mole fraction, and to identify impurities. The A0X‐line observed is interpreted as due to a single acceptor on Te site. In the mixed crystals at x ≧ 0.09 the two‐mode behaviour of LO‐phonons and an up to now not observed splitting of the A0X‐line are found.
X‐Ray Dynamical Diffraction in Crystals Being Subjected to the Action of Ultrasonic Waves
Authors: Polikarpov I. V. , Skadorov V. V.
Published: July 2007

A dynamical theory is given of X‐ray diffraction in crystals being subjected to the action of longitudinal or transversal ultrasonic waves. Analytical expressions for the X‐ray field diffracted on nonstationary crystals in Bragg and Laue geometry are obtained.
Aggregation Kinetics of Divalent Impurity–Vacancy Dipoles in Alkali‐Halide Matrix. II. KCl:Eu2+ System
Authors: Berg G. , Poźniak J. , Macalik B.
Published: July 2007

The decay curves of the Eu2+–cation vacancy dipole concentration in KCl crystals isothermally annealed at 75, 100, 140, and 240 °C are presented. On the basis of a theoretical model discussed in Part I, the rate constants of association and dissociation of the dimers and trimers as well as the enthalpy of these reactions are evaluated.
Intramolecular Excitation Dynamics in a Thermalized Chain. I. Formation of Autolocalized States in a Cyclic Chain
Authors: Kadantsev V. N. , Lupichov L. N. , Savin A. V.
Published: July 2007

A numerical study of the Davydov soliton dynamics in a thermalized cyclic molecular chain is performed. Account is taken of the effect of thermalized molecular vibrations within the scope of the quantum‐mechanical theory. It is shown in contrast to results of a number of works, where account of the thermal vibration effect is taken within the framework of the classical model, that using the quantum‐mechanical description the thermal vibrations not only don't prevent but also favour autolocalization of intramolecular excitation.
The Influence of Next‐Nearest‐Neighbour Exchange Coupling on the Spin‐Wave Resonance Spectrum in Uniaxial Ferromagnetic Thin Films
Authors: Duda A.
Published: July 2007

The spin‐wave resonance spectrum is calculated for a uniaxial ferromagnetic thin film with both' nearest‐neighbour and next‐nearest‐neighbour exchange coupling. The profiles of the resonance modes, the positions of the absorption lines, and their intensities are analysed for various values of the nnn coupling parameter. It is found that the spectrum is strongly affected by the nnn coupling, especially by the coupling of antiferromagnetic type.
Conduction in Metals
Authors: Mott Nevill
Published: July 2007

An account is given of some recent and unexpected developments in the theory and observation of the conduction of electricity in metals, for materials in which the mean free path is small.
Application of Dimensional Method to Superconductivity
Authors: Chapnik I. M.
Published: July 2007

On the basis of dimensional analysis a relationship is derived between the superconducting transition temperature (Tc) and material parameters effective electron mass and permittivity Experimental data in support of the obtained relationship are presented and analysed.
On the Motion of Solute Atoms in Cages and Loops in Metal Lattices Studied with Nuclear Methods
Authors: Vogl G.
Published: July 2007

Interstitial cages in metals are found with the Mössbauer effect on 57Fe in aluminium, silver, and α‐zirconium after trapping of irradiation‐induced interstitials and recently after implantation. Cage motion manifests itself in a strong decay of the apparent line intensity due to quasielastic effects and — in suitable systems — in a relaxation of the quadrupole splitting. The results are compared to the results of internal friction methods. Correlation effects in solute diffusion via vacancies can be described in terms of vacancy caging and looping. Analogies between interstitial and vacancy caging are discussed. The possibilities to observe and study these effects with nuclear methods are considered.
Theory of Nucleation Fields in Inhomogeneous Ferromagnets
Authors: Kronmüller H.
Published: July 2007

The effect of the microstructure on the coercive field of sintermagnets is investigated on the basis of the theory of micromagnetism. From the linearized micromagnetic equations nucleation fields are determinded for magnetic inhomogeneities with quasi‐harmonic spatial variations of the magnetocrystalline anisotropy energy. For one‐ and two‐dimensional nucleation modes the eigenvalues of the nucleation fields are derived as a function of the width and the strength of planar magnetic inhomogeneities.
Specific Heat Experiments at the Cooperative Jahn‐Teller Transition in the Mixed Crystal Systems (Tbx, Tm1−x)AsO4 and (Tbx, Tm1−x)VO4
Authors: Kasten A. , Kahle H. G. , Klöfer P. , Schäfer‐Siebert D.
Published: July 2007

Single crystals of the systems (Tbx, Tm1−x)AsO4 and (Tbx, Tm1−x)VO4 are investigated by means of specific heat measurements in the temperature region 1 to 40 K. Whereas for the arsenate a cooperative Jahn‐Teller distortion is observed over the whole concentration range x, in the vanadate the phase transition is missing for 0.1 ≦ x ≦ 0.4. This can be understood in mean field theory taking into account the effect of local strains which are assumed to have a random (Gaussian) distribution.
Dynamical Deceleration of a Dislocation by Surface Defects
Authors: Malashenko V. V. , Sobolev V. L. , Khudik B. I.
Published: July 2007

The influence of surface defects on dynamical deceleration of a dislocation is studied. It is shown that the deceleration force acting on the dislocation through surface defects is essentially different from the deceleration force due to volume defects.
Dynamics of Bjerrum Faults and Protonic Ice Conductivity
Authors: Sergienko A. I.
Published: July 2007

The exact solution describing the motion of D‐ and L‐faults in water molecule chains — the Bernal‐Fowler filaments — under the influence of an electric field is obtained. It is shown that at a certain critical field value the fault mobility determines the proton current but not the mobility of protons themselves. That's why the current‐voltage characteristic exhibits the break.
Molecular‐Type Motion of Relativistic Electrons at Planar Channeling in Crystals
Authors: Vyatkin E. G. , Vorobiev S. A.
Published: July 2007

Channeling of relativistic electrons in (111) planar direction in a diamond crystal and the channeling radiation spectra are investigated using computer simulation by the binary collisions model and using the model of a continuum potential of the atomic planes. The calculations are performed for electrons with the energy E0 = 900 MeV. The peculiarities revealed of the angular distributions and radiation spectra of electrons in the atomic‐ and molecular‐type states allow to discern these channeling states in the experiment.
Chemical Bond Formation Processes on Semiconductor Interfaces at Electronic Equilibrium or Nonequilibrium
Authors: Lorenz W.
Published: July 2007

The quantum theoretical treatment of chemical bond formation and partial charge transfer in condensed systems is extended recently to charge injection processes in electronic nonequilibrium. An exposition of the theoretical fundamentals is given, which apply particularly to electrochemical and photoelectrochemical processes on semiconductors. Related problems in semiconductor electronics are likewise included in the discussion.
Relativistic Theory of Photoemission from Solids. III. Bulk and Surface Transition Matrix Elements
Authors: Braun J. , Thörner G. , Borstel G.
Published: July 2007

Two specific aspects of a fully dynamical relativistic one‐step model of photoemission from solid surfaces are discussed which turn out to be crucial for the development of an explicit calculational scheme: (i) The evaluation of the single‐ and double‐contributions to the bulk transition matrix elements is demonstrated and (ii) it is shown how a realistic effective one‐dimensional image‐potential surface barrier can be taken into account within the relativistic formalism.
Cylindrical Quantum Well with Position Dependent Mass
Authors: Pérez‐Alvarez R. , Parra‐Santiago J. L. , Pajón‐Suárez P.
Published: July 2007

Using the envelope function approximation and a one band model, the cylindrical quantum well with position dependent mass problem is studied. The boundary conditions to be fulfilled by the radial wave functions are deduced. The transcendental equation for the energy levels, the normalised wave functions, and the confinement are obtained in the flat band approximation considering a sectionally constant mass profile. Also numerical results are given for the GaAsAl0.32Ga0.68As cylindrical quantum well.
Nitrogen Bound Electrons, Excitons, and Multiexcitons in GaP
Authors: Haufe A.
Published: July 2007

By means of a simple effective mass model the density functional theory is used to calculate the ground state energy of the exciton at the isolate N impurity. For this purpose, the N potential is adjusted and provides the value known from experiment. This potential offers the basis for the computations of the bound multiexciton complexes at the isolated N impurity and of the electron binding energy at the N pairs. The results so obtained are in good qualitative agreement with the experimental ones.
Quantum Theory of Thermopower in Quantum Well Wires
Authors: Jali V. M. , Kubakaddi S. S. , Mulimani B. G.
Published: July 2007

A quantum theory for thermopower in quantum well wires is presented. Expressions for thermopower are obtained, both, in the longitudinal and transverse configurations where the temperature gradient is parallel and perpendicular to the wire, respectively. The expression obtained in the longitudinal configuration agrees with that obtained from the conventional Boltzmann transport equation in the relaxation time approximation.
Mott‐Insulation, High Frequencies, and the High Transition Temperatures of the New Ceramic Superconductors
Authors: Hyland G. J.
Published: July 2007

A recent proposal of Fröhlich concerning the origin of the high transition temperatures, Tc, which characterize the newly discovered ceramic superconductors, is examined for the case of materials based on La2CuO4. Whilst one of the conditions specified by Fröhlich — namely the existence of a narrow energy band based on incomplete inner shells of certain metal atoms is indeed realized in terms of a quasi two‐dimensional lower Hubbard band of Cu d‐orbitals — it is noted that certain ionic (Cu–O) vibrational breathing modes exist whose frequency is already high enough (≈ 10 × 1013 Hz) to account, via BCS theory, for the high Tc's, without having to invoke the higher frequency excitonic‐like modes envisaged by Fröhlich. Evidence is adduced that the carriers responsible for the superconductivity are essentially Cu 3d holes introduced into the lower Hubbard band by divalent dopants, and/or deviations from La stoichiometry; their density, n, is thus rather low, which could well account for the low critical currents, Jc, found experimentally. It is noted that n is most probably less than the degree of doping, x, on account of the possible contributions of oxygen vacancies to the maintenance of charge neutrality; this, in turn, imposes a lower limit on x if n is to be > 0.
A New Effective Ensemble Approach for the Free Energy
Authors: Ferreira J. R. Faleiro , Silva N. P.
Published: July 2007

It is shown that the effective ensemble utilized in Bogolyubov principle may be replaced by new effective ensembles more complete than the former one. That brings some improvements on the approximate thermodynamic function calculations and preserves short range order effects above the critical temperature even if one particle trial Hamiltonian is used.
Influence of Dipolar Interactions on the Dynamical Dielectric Response
Authors: de la Fuente M. R. , Jubindo M. A. Pérez , Balda R. , Tello M. J.
Published: July 2007

An analysis is made of the modifications produced in the complex susceptibility with regard to the complex polarisability, when one takes into account the dipolar interactions in the molecular field approximation. The analysis is carried out for both, exponential and non‐exponential responses and covering the weak interaction limit as well as the strong one.
Luminescence Due to Radiative Transitions between Valence Band and Upper Core Band in Ionic Crystals (Crossluminescence)
Authors: Jansons J. L. , Krumins V. J. , Rachko Z. A. , Valbis J. A.
Published: July 2007

In some wide band gap halides of heavy alkali and alkaline‐earth metals (BaF2, CsCl, RbF etc.) the energy separation between the valence band involving mainly the halogen electronic states and the upper cation core band is smaller than the band gap. Under the excitation generating holes in the core band radiative electronic transitions from the valence band to the core band take place giving rise to a specific kind of intrinsic emission which is proposed to call crossluminescence. Its decay time is about 1 ns and the thermal quenching starts at temperatures well above room temperature. The width of the emission spectrum practically coincides with the width of the valence band deduced from ultraviolet photoelectron spectroscopy and the shape of the spectrum depicts the electronic structure of the valence band.
Comparative Raman Study of Phonon Linewidths in Pure and Lead‐Doped CsCdBr3
Authors: Pilla O. , Cazzanelli E. , Blanzat B. , Andraud C. , Pelle F.
Published: July 2007

Raman spectra of CsCdBr3 are reported in the temperature range 4.2 to 300 K. The symmetry assignation is performed for all the observed peaks; besides the five expected Raman active first‐order modes, a weak structure is observed and attributed to a second‐order process. The temperature dependence of frequencies and linewidths is studied. An anomalous effect of Pb doping on the low temperature linewidths is discussed.
Additional Results on SERS from Ag Colloids in Alkali Halide Crystals
Authors: Abel H.‐B. , Fischer F.
Published: July 2007

The size of thermally or photochemically produced colloids is controlled by their Mie absorption band. Excitation in this band shows strong resonant SERS. Vibrational contributions contain one‐phonon scattering of the host and localized (or resonant) modes due to a cation‐silver bonding. The continuous background only extends to the Stokes side with a cut‐off frequency influenced by the exciting photon energy. The anti‐Stokes side has its cut‐off at ṽ = 0 with a temperature‐dependent shape given by the Fermi factor of the metal electrons.
Effect of Metal Substitution in ZrS3 and TiS3 Compounds. Electronic, Raman, and Resonance Raman Study of Zr1−xTixS3 Ternary Phases, 0 < x < 1
Authors: Gard P. , Sourisseau C. , Gorochov O.
Published: July 2007

The effects of metal substitution on the electronic and vibrational properties of ZrS3 and TiS3 are studied through UV–visible absorption, Raman and resonance Raman scattering experiments on various Zr1‐xTixS3 ternary phases, 0 < x < 1. All these broad band semiconductors display excitonic type transitions on their absorption edge whose maxima vary monotonously from 500.0 to 960.0 nm as the titanium content increases. These excitons consist of d‐like conduction electrons and the existence of higher‐energy transitions due to 3p*(SS) orbitals is confirmed by resonance Raman results in Zr0.6Ti0.4S3. The polarized Raman spectra of the solid solutions present variations in band‐wavenumbers as a function of the compositional parameter x and three different types of mode‐behavior are observed depending on the nature of the vibrations. All the Raman results are sustained on force field calculations in ZrS3 and TiS3 and on the estimations of short‐, medium‐, and long‐range interactions within each vibrational state.
Enhancement of 3d‐Electron Transitions in Neutron‐Irradiated MgO:Mn2+ Crystals
Authors: Okada M. , Kawakubo T. , Seiyama T. , Nakagawa M.
Published: July 2007

A study of optical absorption of 3d‐electrons in neutron‐irradiated MgO:Mn2+ crystals is made. Intensity enhancements and energy shifts of spin‐forbidden optical transitions of Mn2+ ions are observed in samples as‐irradiated and after heat treatments. An investigation of thermal properties of optical absorption for Mn2+ ions and F centres in the irradiated MgO:Mn2+ indicates the presence of two types of defects associated with F centres. These defects are accounted for as an interstitial‐Mn2+–F center complex and a Mn2+–F centre complex. The origin of the optical transition enhancement and energy shifts are attributed to both, an exchange interaction of Mn2+ ions with F‐center electrons and a parity‐forbidden removal caused from symmetry changes due to the formation of above described complexes.
Ion Interaction in Simple Metals
Authors: Alfred L. C. R.
Published: July 2007

Analytic expressions are obtained for the ion interaction potentials in simple metals in the pseudopotential formulation by utilizing an approximation scheme. The technique is applicable with most of the model pseudopotential form factors in common use. The analytic potentials are found to be in reasonable agreement with the exact ones obtained by numerical integration.
Pressure Dependence of the EPR Parameters of Cs3CoCl5 Crystal
Authors: Yu Wan‐Lun , Rao J. L.
Published: July 2007

Using the superposition model of a crystal field, a relationship is established between the crystal structure and the EPR parameters of d7‐ions in weak D2d fields. The analysis shows that the zerofield splitting parameter D is positive for a compressed structure and negative for elongated‐type crystals. With the help of Zhao and Zhang's approximate SCF d‐orbital of the Co2+ ion, the relationship is used to investigate the pressure dependence of D of Cs3CoCl5 crystal and the theoretical values are reasonable. The origin of the pressure variation of D is explained and the pressure dependence of the g‐factor is predicted theoretically.
Temperature Dependence of Exciton Absorption Spectra. A Calculation Based on the Recursion Method
Authors: Sherman A. V.
Published: July 2007

Based on the recursion method of calculating correlation functions, the absorption spectra of a model of a three‐dimensional dielectric crystal containing a band of Frenkel excitons interacting with a branch of dispersionless optical phonons, are investigated in a wide range of material parameters and temperatures. The cases of a weak exciton—phonon coupling, vibronic exciton, coexistence of nearly free and self‐trapped excitons as well as intermediate situations are considered. It is shown that in a definite region of parameters the character of exciton—phonon coupling is changed with the growth of temperature so that the weak‐coupling‐type spectrum acquires some features of the vibronic exciton spectrum. In addition, in a definite temperature range, a change in the physical meaning of the observed peculiarities occurs. In the case of the coexistence of nearly free and self‐trapped states the temperature behaviour of the related peculiarities are shown to be different, a fine structure caused by self‐trapped states is manifested in the vicinity of the main peak only in the low‐temperature spectra. At higher temperatures the spectral shape can essentially differ from the asymmetric Lorentzian due to a sideband in a short‐wave side of a maximum. A long‐wave absorption tail at high temperatures and the considered sets of parameters satisfies the Urbach rule. With the lowering of temperature in the case of weak coupling a structure with a step approximately equal to the phonon frequency stands out in this tail.
Resonance Tunneling with Dissipation Taken into Account
Authors: Ermakov V. N. , Ponezha E. A.
Published: July 2007

The effect of interbarrier‐space dissipation on the resonance electron tunneling through a system of two identical potential barriers is investigated. It is shown that the dissipation leads to a general decrease in barrier transparency, but the qualitative features of nonlinear resonance tunneling remain unchanged. The influences of dissipation on the autovibratory tunneling regime are discussed.
Construction of Bond‐Centered Wannier Functions for Silicon Valence Bands
Authors: Satpathy S. , Pawlowska Z.
Published: July 2007

Bond‐centered Wannier functions are constructed for the valence bands of silicon by a direct superposition of the Bloch functions whose phases are chosen on physical grounds. The Bloch functions are calculated using the linear muffin‐tin orbitals method within the local density approximation. The resulting four Wannier functions per unit cell are equivalent to one another. Each is localized on a bond‐center, has the Γ1 symmetry of the D3d group, and falls off exponentially.
Estimation of the Crystal Field at R Sites in R2Fe14B Compounds
Authors: Zhao Tiesong , Zhu Yong , Jin Hanmin
Published: July 2007

The mean values of some crystal field parameters at f and g sites in R2Fe14B (R = Pr, Nd, Sm, Dy, Ho, Er, Tm, and Yb) compounds are estimated from magnetization curves of single crystals along the major crystal axes at 4.2 K and room temperature and from spin reorientation temperatures.
The Influence of Manganese on Magnetic Properties of RE2(Co1−xMnx)17, RE = Y, Gd Compounds
Authors: Kąkol Z. , Figiel H. , Chmist J. , Kołodziejczyk A.
Published: July 2007

The pulse field measurements of magnetisation for Y2(Co1−xMnx)17 and Gd2(Co1−xMnx)17 series with x ≦ 0.3 in the 78 to 300 K temperature range are reported. In contrast to anisotropy changes different behaviours of saturation magnetisation for the Y and Gd based series are observed. The presented results are analysed and explained by preferential substitution and reorientation of Mn moments, where dipolar interactions with Gd are considered.
Soliton Energy in a Quantum Ferromagnet with Two Anisotropies
Authors: Talim S. L. , Pires A. S. T.
Published: July 2007

The quantum corrections are calculated to the energy of the soliton in the easy‐plane ferromagnetic spin chain with two anisotropies. A semiclassical continuum approximation is used which allows to treat the leading order deviations from idealized classical behavior. The soliton density at finite temperatures is also calculated.
Image Potential of an Electron in a Gap Between Two Metals
Authors: Thoai D. B. Tran , Zeitler E.
Published: July 2007

The image potential of an electron located in the vacuum gap between two metals is calculated including the spatial dispersion. Numerical results show deviations from the classical image potential.
The Periodic LUC‐MINDO Method and its Application to Diamond
Authors: Craig B. I. , Smith P. V.
Published: July 2007

In previous work it is shown that neither the periodic LUC‐CNDO nor LUC‐INDO formalisms are accurate enough to yield reliable values for the bulk properties of the homopolar covalent solids. Calculations based on the more sophisticated MINDO molecular orbital method appears more successful, however. In this paper the periodic LUC‐MINDO method is outlined and its application to diamond is considered. The predicted one‐electron eigenvalues, bulk elastic constants, and phonon frequencies are now found to be in very satisfactory agreement with experiment.
Calculation of Dipole Transition Matrix Elements in Muffin‐Tin Models
Authors: Shilkova N. A. , Shirokovskii V. P.
Published: July 2007

Matrix elements of momentum and of gradient of the potential for electronic states in solids are calculated by the Green's function method. Their absolute identity is shown if the integral over the elementary cell volume is correctly reduced to integrals over the space restricted by the muffin‐tin sphere, and through the surface of this sphere. It is ascertained that the surface term gives the main contribution in momentum matrix element values. It is proved that the commutation relationship connecting both the types of matrix elements is exactly valid for the muffin‐tin function irrespective of the variational series length. The influence of high‐angular‐momentum terms in the expansion of the wave function on the matrix element values is discussed.
Carrier Kinetics in a Semiconductor with Light‐Induced Gaps
Authors: Hartmann M. , Zimmermann R. , Stolz H.
Published: July 2007

Due to the influence of a strong electromagnetic field an induced gap is expected to occur in the band structure of a semiconductor. In this paper the influence of the damping by electron–phonon collisions and by recombination on the new band structure is investigated. Taking into account damping kinetic equations for the electrons are derived and discussed with the help of calculations.
Green's Function Approach to Nonequilibrium Charge Carriers in Direct Gap Semiconductors Generated by Short Light Pulses
Authors: Glaeske H. , Schubert M.
Published: July 2007

In the present paper the Green's function approach to nonequilibrium quasi‐free charge carriers in highly excited semiconductors is applied. In doing this a system of kinetic equations for generalized Wigner distributions of renormalized quasi‐electrons and holes is obtained, that takes into account (additionally to well‐known published results) the interaction of the longitudinal optical phonons and the intraband interaction of the radiation field with the electron–hole plasma. Thus, utilizing the corresponding field equations and the suitable boundary conditions, relaxation processes in the semiconductor after excitation by a short laser pulse and a laser probe beam experiment may be described.
A New Electronic Pinning Mechanism for Sliding Charge Density Waves
Authors: Fischebeck H. J.
Published: July 2007

It is shown that the time component of the chiral Noether current is a constant of motion in a quasi‐one‐dimensional charge density wave (CDW) system in the absence of a disordered potential. Therefore this system possesses a current‐carrying equilibrium state which is characterized as the minimum of an accordingly generalized thermodynamic potential. A random impurity potential breaks the chiral invariance so that a current‐carrying equilibrium state in the strict sense does not exist in this case. It is assumed, however, that the sliding CDW state can approximately be described as a quasi‐equlibrium in the coordinate frame co‐moving with the velocity ν. It is shown that the density of states in the co‐moving frame exhibits tails in the Peierls gap which enhance the thermodynamic potential of the quasi‐equilibrium proportional to |ν| so that the current‐driving Lagrange parameter in this potential must exceed some threshold value before the sliding CDW state is thermodynamically favoured against the resting one. This is an electronic pinning mechanism which acts independently of the conventional phase pinning.
Cation Vacancy Migration Entropy in Alkali Halides
Authors: Eftaxias K. , Varotsos C. , Hadjicontis V.
Published: July 2007

Varaksin and Shipitsin have recently presented a method for the calculation of the migration entropy (sm) of defects in solids. By applying this method to the case of a cation vacancy migration in NaCl and KCl values are obtained that significantly differ from the experimental data. On the other hand a model is suggested which leads to reliable sm‐values for both materials i.e. NaCl and KCl. This model is based on a reasonable assumption stating that the absolute value of the “constant volume” migration entropy is appreciably smaller than that corresponding to “constant pressure”.