bluuebunny/crossref_metadata_2025_split huggingface dataset:
Remarks on the Ferromagnetic Solutions of the Extended Hubbard Model
Authors: El‐Jaick Léa J. , Troper A. , Gomes A. A. 
Published: July 2007

AbstractThe extended Hubbard Hamiltonian is studied using the method of the equations of motion. The decoupling approximations, suitable for the strong intra‐atomic repulsion limit are discussed. One of the approximations (mean field approach to deal with next neighbour interactions) is worked out numerically. The magnetization is obtained as a function of the strength of the next neighbour couplings and of the number of electrons per atom.
Mutual Annihilation of Triplet Excitons in 4,4′‐Dichlorobenzophenone Single Crystals at Low Temperatures
Authors: Avdeenko A. A. , Dobrovolskaya T. L. , Kultchitskii V. A. , Naboikin Yu. V. 
Published: July 2007

AbstractRelative quantum yields and decay kinetics of exciton phosphorescence (O–O band at 412.46 nm) and those of X1‐traps (O–O band at 413.54 nm) are measured versus the exciting light intensity in 4,4′‐dichlorobenzophenone single crystals at 1.5 and 4.2 K. The phenomena observed are treated from the point of view of mutual annihilation of triplet excitons, whose rate constant, equal to (4.2 ± 2.0) < 10−13 cm3 s−1, is unchangeable in the temperature range studied. Equivalent free excitons are shown to be responsible for mutual annihilation. The decay kinetics of X1‐trap phosphorescence is explained by optical spin alignment in the excited triplet state.
Mixing of Frenkel Excitons and Ionic Excited States in a Linear Crystal of Donor‐Acceptor Complex. II. ADA‐Type Complexes
Authors: Petelenz P. 
Published: July 2007

AbstractThe previously proposed Merrifield‐type model of the coupling between neutral and ionic excited states of a linear crystal of a weak AD‐type donor‐acceptor complex is generalized for ADA‐type complexes. It is demonstrated that CT interactions involving the locally excited Frenkel states can be adequately described in terms of a Hamiltonian entirely analogous to that used for AD‐type complexes but with renormalized parameters. The spectrum of ADA‐type complexes is however richer due to the appearance of a new system of absorption bands due to the (–) CT states which do not couple with the Frenkel states.
Theoretical Investigation of the Critical Josephson Current of Niobium‐Lead Tunnel Junctions
Authors: Seidel P. , Richter J. 
Published: July 2007

AbstractIn order to calculate the critical Josephson current Ic of niobium‐lead tunnel junctions the proximity‐effect model previously presented by the authors is used to describe the niobium electrodes. The resulting Ic.‐dependence on temperature differs from the commonly used Ambegaokar‐Baratoff result in accordance with many experimental observations. The theoretical model allows to explain these differences and offers good possibilities to describe the experiments.
Variational Approach for the Anderson Model: Impurity Pair
Authors: Oleś A. M. , Chao K. A. 
Published: July 2007

AbstractWith a Variational method the effect is studied of impurity‐impurity interaction on the formation of local moments within the framework of the Anderson model. Compared to the similar calculation on. a single impurity, the local moment is enhanced, especially when the two impurities are nearest neighbours of each other with a ferromagnetic direct coupling.
Lattice Vibrations of MnxCdi1‐xTe Mixed Crystals through Raman Scattering Measurements
Authors: Picquart M. , Amzallag E. , Balkanski M. , Julien Ch. , Gębicki W. , Nazaeewicz W. 
Published: July 2007

AbstractRaman scattering measurements are performed on Mn‐xCd1‐xTe mixed crystals, in the concentration range x = 0 to x = 0.5. The first‐order spectra show a “two‐mode” behaviour for the long‐wavelength optical phonons, which can be explained using the theoretical REI model. The rest of the spectra, confirmed by infrared absorption measurements, is tentatively interpreted in terms of two‐phonon processes and presumably one‐acoustic‐phonon disorder‐induced modes, resulting from mass disorder.
Electrical Resistivity in a System of Coupled Donor and Acceptor Chains
Authors: Bulka B. R. 
Published: July 2007

AbstractA system of weakly coupled donor and acceptor chains possesses a sink‐type energy band structure. The resistivity due to the inside sink and between sinks electron scattering is calculated. For acoustic phonon scattering the resistivity is described by Q = ATλ where λ. > 2. A case of electron scattering against optical phonons is considered as well.
d‐Electrons and Dispersion Relations in B.C.C. Zirconium
Authors: Rathore R. P. S. 
Published: July 2007

AbstractA new scheme, comprising of all the possible interactions coupling various constituents of the b.c.c. transition metal is developed. It is inferred that the electrons partially filling the d‐levels (called d‐electrons) of these metals contribute significantly towards the Cauchy discrepancy. The crystal equilibrium is considered under the combined influence of cores d‐electrons and s‐electrons. Deformation parameters associated with these electrons are evaluated on the consideration of their respective energies. The dispersion relations, thus derived, are employed to predict the phonon frequencies in b.c.c. zirconium. Recently reported data on the phonon‐energy of this metal are compared and a promising good agreement is obtained.
Concept of Force Variation Due to Charged Defects in Elemental and Compound Semiconductors
Authors: Vandevyver M. , Talwar D. N. , Plumelle P. , Kunc K. , Zigone M. 
Published: July 2007

AbstractGreen's function calculations of force variation due to charged impurities in elemental and compound semiconductors are analysed on the basis of simple physical arguments. It is strongly suggested that the trends of force variation may not be related with the long range Coulomb interactions, however, the important criteria should be the effect of electric field of charged impurity on its nearest neighbour bonds that mainly affects the short range couplings. Some new experimental results by i.r. method due to Si and Cl impurities in CdTe are also included that lend additional justification to the arguments.
Impurity Effects on Adatom Density of States
Authors: Ueba H. 
Published: July 2007

AbstractThe influence of both, impurity and surface states on the adatom electronic properties is studied using the Dyson equation approach. The surface Green function of a semi‐infinite crystal contaminated by a single impurity atom is calculated. It is found that the surface state energy depends on the location of the impurity atom. A similar calculation is performed for the case where an adatom interacts with the contaminated substrate and the energy Ea of an electron localized on the adatom is determined as a function of the impurity atom location and potential. The adatom density of states is also calculated to discuss the significant effect of the impurity near the surface.
Optical Orientation of the Carriers in an Electron—Hole Plasma in CdS Crystals
Authors: Gubarev S. 
Published: July 2007

AbstractThe degree of circular polarization of the electron—hole plasma recombination radiation is measured under high power excitation with circular polarized light. Depolarization of the radiation on the high‐energy edge of the spectrum is observed in the transverse magnetic field. The experimental results are explained in terms of different populations in the electron and hole spin subbands. The spin disorientation times for electron Tsc and hole Tsh systems and the life time of the carriers τ in the electron—hole plasma are defined from the Hanle effect and are equal to Tse = (3 to 5) × × 10−12 s, Tsh = (10 to 15) × 10−12 s and τ = (80 to 120) × 10−12 s.
Phenomenological Behaviour and Phase Transition Mechanism of the Layered Antiferroelectric Squaric Acid
Authors: Maier H. D. , Petersson J. 
Published: July 2007

AbstractUsually it is assumed that the interactions between the protons within the molecular layers drive the phase transition of the antiferroelectric squaric acid. In the present work it is proposed that besides these interactions also the interlayer interactions play a central role for the phase transition mechanism. This assumption is discussed in relation to some well‐known properties of squaric acid above Tc. On these conditions a potential is developed describing the behaviour of the order parameter, and of the dielectric and elastic constants above and below Tc. Finally the dynamics is discussed on the assumption of a flipping motion of the protons.
First Plasmon Satellite in the (e, 2e) Process in Metals Temperature Dependent Theory
Authors: Zhivopistsev F. A. , Comas F. E. 
Published: July 2007

AbstractFirstly, the plasmon satellite structure is discussed in the (e, 2e) reaction in metals when a core electron is excited from a localized state. Finitely temperature effects are considered by means of a certain generalization of Nozières‐de Dominicis' theory. A Gaussian broadening is predicted for (e, 2e) spectra. FWHM is computed for Li and Na. The results are compared with other theoretical data and with the data from photoemission experiments.
Polarizabilities of Donors in Elemental Semiconductors (II)
Authors: Palaniyandi E. 
Published: July 2007

AbstractUsing the multivalley effective mass equation and a variational method, an expression for the polarizability of donors in semiconductors is derived including the electron mass anisotropy in the Hamiltonian and using an improved trial function. Polarizability estimates of shallow donors in Si are made and these are compared with experimental results and the results of earlier calculations. The electron mass anisotropy contributes significantly to the polarizability values. Estimates of the polarizabilities of shallow donors in Ge are also presented.
The Theory of Paraelectric Induction and Echo Formation under Conditions of a Strong Inhomogeneous Broadening
Authors: Vagapova F. S. , Saburova R. V. 
Published: July 2007

AbstractThe formation of paraelectric induction and echo is shown to be associated with the inhomogeneously broadened resonant line and excited pulse parameters. The exact times of coherent responses are calculated. The effects of the induction‐decay and echo retardation are predicted. To determine the form of the echo a numerical integration is made. It is shown that the interaction of the electric dipole moment of the paraelectric centers with external oscillating fields creates new signals with other conditions for the excitation wave vector and the generated pulses.
On Stochastic Models of the Excitation Transfer in Molecular Crystals The Lineshape of the Phononless Exciton Band
Authors: Rips I. B. , Čápek V. 
Published: July 2007

AbstractIn the Sumi model describing the effect of the exciton—phonon coupling on excitons in molecular crystals by a stochastic Markoff‐Gauss process with a site‐diagonal potential with a time‐dependent exponentially decaying correlation function, the phononless exciton lineshape is investigated. It is proved that in general, cumulants of all even orders contribute to the optical lineshape function due to non‐commutativity of relevant operators at different times. So the recent result by Blumen and Silbey is shown to be just an approximation neglecting all but second‐order cumulants. The fourth‐order correction is calculated and it is proved that starting from this order of approximation, the free‐exciton density of states does not give a sufficient information necessary to deduce the optical lineshape function.
Charge Density Fluctuations and the Dielectric Matrix in a Quasi‐One‐Dimensional CDW Distorted Solid
Authors: Heiner E. , Gasser W. 
Published: July 2007

AbstractUsing an extended RPA procedure and symmetry properties of the system, the macroscopic dielectric function, plasmon frequencies, and the dielectric matrix are calculated for an one‐dimensional CDW‐distorted electron system in the condensed phase. Thereby the Peierls charge‐density wave potential is treated for a general case. Real and imaginary parts of the macroscopic dielectric function are discussed in the limit of vanishing wave numbers for different values of the dynamical parameters.
Neutron Spectroscopic Study of Lattice Vibrations in NaClO3 and Specific Heat
Authors: Haugstuen W. , Grip J. , Fjaer E. , Samuelsen E. J. 
Published: July 2007

AbstractThe acoustic branches and one optic branch of phonons in cubic NaClO3 are studied at room temperature by inelastic neutron scattering. Sound velocities are deduced, and specific heat versus temperature calculated by incorporating also high energy branches from Raman scattering. Connection between the specific heat and a suggested order—disorder process in NaClO3 is discussed.
An Assessment of the Scattered‐Wave Cluster Technique by Considering the Internal Conversion of 99mTc in the Metal
Authors: Hartmann E. , Seifert G. 
Published: July 2007

AbstractThe electronic structure of a 13‐atom Tc cluster is obtained from Xα‐SW calculation. Comparing the data derived for the internal conversion (IC) of 99mTc in the metallic state with recent experimental findings an assessment is made of the scattered‐wave cluster technique for the study of short‐range phenomena in metals.
Polar Kerr Effect of Magnetite in the Visible and Near Infrared Spectral Regions
Authors: Šimša Z. , Legall H. , Široký P. 
Published: July 2007

AbstractPolar Kerr rotation and ellipticity of the synthetic single crystal magnetite are measured at room temperature in the 400 to 2400 nm spectral region. Using these magnetooptical measurements together with the earlier optical data the diagonal and the off‐diagonal tensor elements of the dielectric function are deduced. In the infrared region the dependences are dominated by the presence of the charge carriers while the behaviour in the visible part of the spectra is mainly due to the 3d crystal field transitions of the tetrahedral and octahedral iron ions.
Partial Pressure Contributions to the Equation of State of Alkali Metals
Authors: López J. M. , In̄guez M. P. , Alonso J. A. 
Published: July 2007

AbstractThe density functional formalism is combined with the concept of ionic pseudopotential in the form proposed by Meyer, Umar, and Young, and the different contributions to the equation of state of alkali metals are analyzed. The inhomogeneity of the electron density is shown to play a major role. The theoretical compressibility shows good agreement with experiment.
Optical Properties of Ni+ Centres in CaF2:Ni and SrF2:Ni
Authors: Alonso P. J. , González J. Casas , Den Hartog H. W. , Alcalá R. 
Published: July 2007

AbstractThe optical properties of X‐irradiated CaF2:Ni and SrF2:Ni are studied. An absorption band at 255 nm in CaF2 and 270 nm in SrF2 is created by X‐irradiation. It is concluded from optical bleaching experiments in low‐temperature X‐irradiated samples that those absorption bands are due to Ni+ ions. Optical dichroism experiments indicate that these Ni+ centres are oriented along the <100> directions. A comparison with previous EPR experiments of X‐irradiated CaF2:Ni indicates that the centres responsible for the 255 nm band in CaF2:Ni and the 270 nm band in SrF2:Ni are Ni+ ions displaced from the centre of the cube of fluorines toward one of the faces of that cube.
X‐Ray Spectroscopic Investigation of the Electronic Structure of AIIBIVCV2‐Type Semiconducting Phosphides
Authors: Gusatinskii A. N. , Bunin M. A. , Blokhin M. A. , Minin V. I. , Prochukhan V. D. , Averkieva G. K. 
Published: July 2007

AbstractK‐bands and absorption spectra of phosphorus and emission L2, 3‐bands of silicon and phosphorus in MgSiP2, ZnSiP2, and CdSiP2 are obtained. From a comparison of the spectra of different series and components in these compounds the influence of metal d‐states on the valence band structure is studied. The admixture of phosphorus and zinc states to a metal d‐state is estimated from the ZnSiP2 spectra. Its smallness and the similarity of shape, position, and relative intensity of details of the corresponding spectra of all compounds are indicative of the fact that all metal d‐states are only slightly hybridized with other states and only weakly affect the valence band structure. A sufficiently fair correspondence is revealed between the calculated spatial charge density distribution of valence electrons and the data about the localization and symmetry of electron states obtained from X‐ray spectra. Good agreement between ΔE and Eg is found (ΔE is the energy gap between the emission ending and the onset of absorption of corrected P K‐spectra, Eg is the energy gap obtained by other physical methods).
Electrical Properties of Some TCNQ Complexes
Authors: Shaikh M. A. , Fleming R. J. 
Published: July 2007

AbstractIn order to have some insight into the conduction mechanism of TCNQ complexes, electrical resistivity and thermoelectric power of four TCNQ complexes, namely, methyltriphenylphosphonium (TCNQ)2, ethyltriphenylphosphonium (TCNQ)2, dibenzotetrathiofulvalinium (TCNA), and 1,2‐di (N‐ethyl‐4‐pyridinium) ethylene (TCNQ)4 are investigated in the temperature range 77 to 370 K. The results are presented and discussed on the basis of three models: a) metallic conduction, b) Hubbard model, and c) simple semiconductor band model.
Electrical Resistivity of Antiferromagnetic Chromium–Rhenium Alloys
Authors: Arajs S. , Moyer C. A. , Abukay D. 
Published: July 2007

AbstractElectrical resistivity (ϱ) of Cr‐Re alloys containing 0.56, 2.45, 5.05, 6.57, 10.7, and 13.1 at% Re is studied as a function of temperature (T). The ϱ vs. T curves exhibit large anomalies at the Néel temperature (TN). The TN vs. at% Re curve has a maximum near 7 at% Re. The data of ϱ near TN and the behavior of TN with Re concentration are discussed from the viewpoint of Fermi surface nesting within the two‐band model.
Monte‐Carlo Calculation of the Electron Transmission, Reflection, and Absorption in Solids in the Energy Range up to 10 keV
Authors: Akkerman A. F. , Chernov G. Ya. 
Published: July 2007

AbstractThe Monte‐Carlo model of individual collisions is applied for low energy electron transport calculations. The applicability of this model is analyzed in detail with theoretically calculated cross sections. Some semiempirical relations for the most important characteristics of the transmission, backscattering, and absorbed energy distributions for C, Mg, Al, Si, Ge, Bi solid targets are obtained.
Peculiarities of the Magnetoresistance of Hg1−xMnxTe
Authors: Davydov A. B. , Ponikarov B. B. , Tsidilkovskii I. M. 
Published: July 2007

AbstractOn semimetallic Hg1−xMnx Te samples with 0.02 ≦ x ≦ 0.06 the dependences of the Hall constant‐RH and longitudinal, ϱZZ, and transverse, ϱxx, magnetoresistances are investigated on the induction of magnetic field B in the region of 0 ≦ B ≦ 50 kG at temperatures 1.6 ≦ T ≦ 40 K. A maximum of ϱxx(B) observed in 5 to 7 kG fields at helium temperatures is accounted for by the contributions which both, conduction band electrons and impurity acceptor band holes, make to the transport processes. The decrease in magnetoresistance in fields B > 7 kG is attributed to the increase of the mobility of carriers in the impurity band due to the ordering of magnetic moments of manganese ions in the magnetic field. It is proved that the maximum ϱxx(T) at 7 ≦ B ≦ 12 kG occurring at temperatures between 2.5 and 5 K is not a thermooscillation peak.
Optical Transitions at Ag Centers in ZnS Crystals
Authors: Schwenkenbecher K. , Boyn R. , Resagk H. 
Published: July 2007

AbstractAn experimental study is made of transitions occuring at the centers responsible for the blue emission band of Ag‐doped ZnS crystals. Excitation and infrared quenching spectra of this emission and of photoconductivity are measured. The results are consistent with the pair‐transition model proposed by Shionoya and coworkers. A discussion is given of the transition energies in this system, taking account of lattice relaxation and using data on electron‐lattice coupling which are deduced from the temperature dependence of the emission band width.
Application of ENDOR‐Induced Electron Spin Resonance to the Study of Point Defects in Solids
Authors: Niklas J. R. , Spaeth J. M. 
Published: July 2007

AbstractThe technique of ENDOR‐induced ESR (EI‐ESR) is applied to the investigation of several point defects in insulating crystals. It is shown that the lineshape of the EI‐ESR spectrum depends on the ENDOR line used for the experiment. The EI‐ESR technique allows the separation of overlapping ESR spectra in the presence of several defects. New applications are the selection of spin states and the determination of relative signs of spin‐Hamiltonian parameters, the selection of centre orientations and the assignment of nuclei in complex ENDOR spectra, and the determination of quadrupole interactions which are not resolved in the ENDOR spectrum.
Recalculations of Madelung Potentials and Polarisabilities of Ions in Stoichiometric Rutile (TiO2)
Authors: Iguchi E. , Sawatari H. , Tilley R. J. D. 
Published: July 2007

AbstractThe Madelung potentials in stoichiometric rutile (TiO2) are calculated and found to be 29.53 eV at the Ti4+ site and −41.20 eV at the O2‐ site. These potentials lead to the value of 141.5 eV for the Madelung energy per TiO2 “molecule” and also the value of 4.810 for the Madelung constant. Using the Madelung potential at the Ti4+ ion, the electronic polarisability of the Ti4+ ion is estimated to be 0.368 Å3. This result is used to determine the ionic polarisability of the Ti4+ ion and the electronic and ionic polarisabilities of the O2‐ ion. The electronic polarisability of the O2‐ ion is found to be large in value compared with that in other oxides. The possible connection between polarisability and defect structure formation in nonstoichiometric rutile is discussed.
Theory of Optical Bistability of Excitons
Authors: Goll J. , Haken H. 
Published: July 2007

AbstractThe saturation behaviour of excitons driven by an impinging electromagnetic plane wave is investigated. The nonlinear absorption coefficient and the nonlinear refractive index are determined. Taking care of the boundary conditions at the end faces of the crystal, the nonlinear transmissivity of the crystal is determined. The phenomenon of optical bistability is investigated taking into account standing wave effects and the influence of the detuning is discussed.
A First‐Principles Model of Energetical Trap Distributions in Solids II. The Finite Defect Chain of Uniform Curvature
Authors: Hamann C. 
Published: July 2007

AbstractThe model of the finite defect chain is used to calculate the trap distributions caused by a defect chain with a uniform curvature. For spherical potentials not belonging to the Coulomb‐type analytical solutions are obtained. This paper shows that any spatial defect chain causes essentially trap distributions with exponential characteristics in the solid.
Short‐Range Order Modelling and Bonding in Metal–a‐Ge Systems
Authors: Manaila R. , Devenyi A. 
Published: July 2007

AbstractA structural model is proposed for the metal‐amorphous Ge systems, based on the filling of the inner voids by the metal in a tetrahedral CRN. This starting model is relaxed under a set of bond‐stretching, bond‐bending, and Me‐Ge interaction potentials, for the specific case of the Cux(a‐Ge)1−x alloys (x = 0.22 and 0.40). A good agreement between the calculated and an experimental interference function is obtained by assuming an alteration of the bonding character in the a‐Ge matrix towards a more metallic one.
On the SD Model for Coexistence of Ferromagnetism and Superconductivity
Authors: Tonchev N. S. , Brankov I. G. 
Published: July 2007

AbstractThe Vonsovskii‐Zener model for a superconductor with regularly positioned magnetic impurities is considered. Two theorems are given which prove the exact solubility of the thermodynamic problem by the approximating Hamiltonian method. Exact analytical solutions for the zero‐temperature order parameters and the ground state energy of the mixed phase are derived. A comparison of the energies of the different phases confirms the known result that ferromagnetism and superconductivity cannot coexist in the ground state of the model.