bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dissociation of Frenkel Excitons at the Interface between a Molecular Crystal and a Metal
Authors: Killesreiter H. , Baessler H. 
Published: July 2007

AbstractThe first part of the paper deals with the non‐radiative decay modes of n π* triplet excitons at the interface between a p‐chloranil crystal and an aluminum contact studied by means of extrinsic photocurrents. Utilizing the technique of inserting fatty acid mono‐layers between crystal and metal, which allows variation of the interaction distance, it is shown (i) that the dominant exciton decay process is a fast charge transfer reaction and (ii) that its rate constant decreases exponentially with increasing reaction distance. In the second part of the paper a model is presented to treat exciton dissociation processes at a metal surface in general. It is based on the concept of configuration interaction between the bound molecular exciton state and a continuum of ionized states.
Spatial Charge Displaced by Impurity Scattering: T‐Matrix Approach
Authors: Brereton M. G. 
Published: July 2007

AbstractThe spatial charge displaced by an impurity is calculated using the T‐matrix formalism together with the aid of Green's function theory. For a certain class of T‐matrices an exact result, which explicitly obeys the Friedel sum rule is obtained. In other cases it represents an improved preasymptotic form.
Calculation of the Structural Energy of the Intermetallie Compound MgIn
Authors: Mrosan E. , John W. , Eschrig H. 
Published: July 2007

AbstractThe crystalline structure of the intermetallic compound MgIn is studied using pseudopotentials and perturbation theory. The potential is obtained from Shaw's non‐local model potential of the pure metals Mg and In recalculated for the changed model potential parameters and for the changed electron density of the compound. The c/a ratio for the L10 phase of MgIn is calculated. Conditions for the appearance of a long‐periodic superlattice like in the system CuAu are studied.
Formalism of the Rhombic Spin Hamiltonian with S = 2 and Its Application to EPR Spectra of Copper Aggregates in TGFB: Cu2+
Authors: Maćkowiak M. , Kurzyński M. 
Published: July 2007

AbstractThe properties of the spin Hamiltonian for S = 2 in a crystal field of rhombic symmetry are analysed up to terms with a, b, c proportional to the fourth power of spin operators, and a method for the determination of constants of this Hamiltonian is proposed. By perturbation calculation, the parameters a, b, c are shown to affect very strongly the anisotropy of the EPR spectrum; in certain directions, they can lead to new extrema in the graphs of EPR spectrum anisotropy. The results are applied to the description of the EPR spectrum of copper aggregates in TGFB. The spin Hamiltonian parameters are determined, and the spin level energies are given as function of the magnetic field strength. Full agreement with the experimental data is achieved showing, in conjunction with other data in reference [8], that in Cu2+‐ion‐admixtured TGFB there are present four‐ion copper complexes with spin S = 2 coupled by exchange interaction.
Experimental Study of Surface Optical Modes in Ionic Crystal Slabs
Authors: Bryksin V. V. , Gerbstein Yu. M. , Mirlin D. N. 
Published: July 2007

AbstractSurface optical vibrations have been revealed and investigated in slabs of a number of alkali halide crystals and crystals of CaF2 and CdF2. The measurements were carried out by the attenuated total reflection technique. The frequency dependence of reflection coefficient has been calculated in accordance with the experimental set‐up. For NaCl and CaF2 crystals dispersion curves of the surface modes have been measured at room and liquid nitrogen temperatures. The comparison of experimental and calculated data shows that the anharmonic term of the dielectric constant should be taken into account in the calculation of the surface modes.
Isotropic Limiting Behaviour of the Six‐Dimensional Formalism of Anisotropic Dislocation Theory and Anisotropic Green's Function Theory.ii. Perturbation Theory on the Isotropic N‐Matrix
Authors: Nishioka K. , Lothe J. 
Published: July 2007

AbstractPerturbation expansions in terms of the deviation from isotropy are developed for the eigenvalues and eigenvectors of the N‐matrix, which appears in the six‐dimensional formalism for anisotropic dislocation theory and anisotropic Green's function. The strongly degenerate behaviour in the limit of isotropy is elucidated. It is shown that divergent terms in fact cancel among themselves in certain sums to leave well‐behaved isotropic limits. It was necessary to develop a perturbation method applicable to a non‐semisimple matrix.
Optical Generation of Charge Carriers in Solid and Liquid Benzene (C6H6)
Authors: Hirth H. 
Published: July 2007

AbstractFree electrons and holes have been generated optically near one electrode via exciton states. At high excitation strengths the charge is proportional to the square of the illumination. At low excitation levels it is proportional to the illumination. In solid benzene the quadratic process dominates. Approaching the melting point this process decreases. At the melting point and in the liquid only the linear process remains. The dependence of these two processes has been investigated as a function of the electric field and the temperature. The quadratic process can be explained by a mutual annihilation of two excitons in the bulk of the material and the linear process by an Auger type recombination of an exeiton at the surface.
Crystal Field Theory of Magnetic Anisotropy of RbNiF3
Authors: Jäger E. 
Published: July 2007

AbstractBasing on crystal field theory the constants K1 and K2 of the magnetocrystalline anisotropy and the anisotropy of magnetization of RbNiF3 are calculated. The coupling of the spins to the crystal field via spin‐orbit coupling is responsible for the magnetic anisotropy, the interaction of the spins is treated in the molecular field approximation. Using experimental values of the splitting in cubic crystal fields, 10 Dq, of the spin‐orbit coupling constant λ, and of the molecular field Hex the calculated values of K1 and K2 at T = 0 K agree with the experimental ones up to a factor two. The influence of the parameters 10 Dq, λ, Hex, and the splitting in the trigonal crystal field, 3 r, on K1 and K2 is discussed.
On the Dispersion Relation of Holes in Bismuth
Authors: Dittmann H. , Herrmann R. 
Published: July 2007

AbstractFrom the known change of energy band structure of bismuth and bismuth‐antimony alloys Bi1−xSbx under hydrostatic pressure the dependence of carrier concentration on the Fermi energy of holes is calculated. This dependece points to a non‐parabolic dispersion relation of holes.
LCAO Energies and Wave Functions in a Covalent Semiconductor with Topological Disorder
Authors: Hulin M. 
Published: July 2007

AbstractThe free electron model is used as a guide for an algebraic transformation of the LCAO Hamiltonian for a semiconducting material which exhibits topological disorder. The energies and wave functions are obtained in terms of the eigenvalues and eigenvectors of the “connectivity matrix” previously introduced.
Compression‐Induced Magnetic Anisotropy and Superlattice Dislocation in Long‐Range‐Ordered Iron‐Aluminium Alloys
Authors: Takahashi S. 
Published: July 2007

AbstractMagnetic anisotropy induced by plastic deformation in Fe3Al is calculated for various types of dislocations in the DO3 and B2 superlattices on the basis of the slip‐induced directional order. It is found that the induced magnetic anisotropy depends largely upon the dislocation density, its configuration, and state of order; also, it is found that the direction of easy magnetization in the DO3 long ‐ range ‐ordered superlattice is that of hard magnetization in the B2 long‐range‐ordered superlattice for the same slip systems. Further, it is shown that the magnitude of the induced magnetic anisotropy is about 105 to 105 erg/cm3 for usual deformation when the individual dislocation distributes independently.
Hyperfine Field at Rh Nuclei in Fe‐Rh Alloys
Authors: Keszthelyi L. , Demeter I. , Szőkefalvi‐nagy Z. , Varga L. , Mezei G. 
Published: July 2007

AbstractThe concentration dependence of the hyperfine field at Rhnuclei in Fe‐Rh alloys measured after Coulomb excitation deviates from the concentration dependence measured by NMR method. In the case of Fe51.5Rh48.5 alloy the field was observed to decrease exponentially with the irradiation dose. Both effects may be understood in terms of radiation damage theory.
Hartree‐Fock Band Structure of Alkali Fluorides and Chlorides
Authors: Perrot F. 
Published: July 2007

AbstractThe APWHF method, previously described and used in solid neon and argon is applied to the calculation of the Hartree‐Fock band structure of alkali fluorides (LiF, NaF, and KF) and chlorides (LiCI, NaCl, and KCl). The important polarization effects are then taken into account and the calculations are repeated for the conduction band, including an additional potential which is an extension to solid of Mittleman's polarization potential. The correlation effects lead to a constant shift of the valence band. The optical gaps obtained from these energy band calculations are in good agreement with experiment. Some other band‐to‐band transitions are compared with previous theoretical results and experimental data.
The Strak Effect of M and N Color Centers in Alkali Halides
Authors: Dewerd L. A. 
Published: July 2007

AbstractThe Stark effect of the M center in LiF, KCl, and NaCl and of the N centers in KCl and NaCl was measured with an alternating electric field along the 〈100〉 direction. The data for the Stark effect of the M band were analyzed to find the difference in energy of two mixing nondegenerate energy levels of opposite parity and to find the matrix element between these two energy levels when the electric field was applied. Measurements of the Stark effect for the N centers in KCl and NaCl were resolved into two components representing contributions from the N1 and N2 centers.
Symmetrische verallgemeinerte Wannierfunktione. I. Definition und Grundlagen
Authors: Krüger E. 
Published: July 2007

AbstractEiner beliebigen abgeschlossenen Bandgruppe, die aus v miteinander entarteten Bändern bestehe, werden v verallgemeinerte Wannierfunktionen zugeordnet, die nach einer Darstellung der Punktgruppe des Kristalls transformiert werden und optimal lokalisiert sind. Es wird untersucht, wie weit die Struktur der verallgemeinerten Wannierfunktionen durch die Symmetrie des Kristalls und das Symmetrieverhalten der Blochfuktionen, die zu der betrachteten Bandgruppe gehören, bestimmt wird. Insbesondere wird gezeigt, daß durch den Symmetrietyp der Bandgruppe das Symmetrieverhalten der verallgemeinerten Wannierfunktionen und ihr Symmetriemittelpunkt festgelegt wird.
Thermal Conductivity and Poiseuille Flow of Phonons in Dielectric Films and Plates
Authors: Bausch W. 
Published: July 2007

AbstractBy an extension of the Callaway ansatz for the solution of the Boltzmann equation it is possible to calculate the phonon thermal conductivity of thin layers and plates for all values of combined relaxation time to thickness, in particular also for the region of Poiseuille flow of phonons. The integral equation for λ, the parameter that describes the drifting phonon distribution that results from the normal processes, is solved approximately. The model is applied to NaF and 7LiF of various thicknesses, impurity concentrations, and dislocation densities and it can be shown that the phonon interaction in NaF is probably too weak to make the observation of Poiseuille flow possible. In plates of LiF there is a distinct maximum for thicknesses greater 0.5 cm which is suppressed by 6Li concentrations > 0.1% or dislocation densities > 5 × 105cm−2. Measurements on thin plates allow the investigation of scattering processes at such temperatures where boundary scattering prevails for quadratic samples.
Exact Treatment of the Coupled Coherent and Incoherent Motion of Triplet Excitons and Its Influence on the Lineshape of ESR
Authors: Reineker P. 
Published: July 2007

AbstractThe motion of excitons is considered by a stochastic model comprising both its coherent and incoherent motion. The coherent motion is determined by the exchange interaction integral J whereas the incoherent motion is described by the strengths of local (γ0) and non‐local (γ1) fluctuations. The spin motion is described by the usual spin Hamiltonian of two differently oriented molecules. The equation of motion of the density matrix of the system is solved and the lineshapes of ESR are calculated for several sets of the above parameters by computer calculation. Especially, it is shown that the coherent motion too may lead to a single absorption line as previously obtained for incoherent exciton motion. Furtheron, it is inferred that the transition from coherent to incoherent exciton motion is determined mainly by the ratio of γ0 and J and that γ1 is a decisive quantity in the transition from the broadening of one or several ESR lines to the narrowing of a single line.
Hole Transport in Polar Semiconductors
Authors: Costato M. , Jacoboni C. , Reggiani L. 
Published: July 2007

AbstractThe transport properties of holes in cubic semiconductors have been studied with a Monte Carlo technique taking into account polar scattering within and between the two valence bands degenerate at K = 0. The predominant p‐like symmetry of the valence band wave functions has been found to enhunce the polar ohmic mobility of about a factor two with respect to the case in which it is neglected. The comparison between theoretical results and experimental data evidences the dominant importance of polar scattering mechanism for a typical II‐VI compound (CdTe)in the region of temperatures between 100 and 400 °K. On the contrary, this scattering mechanism alone cannot explain the low field transport of a typical III‐V compound (GaAs) in the same temperature range, according to its lower ionicity.
Pair Interaction and Magnetic Relaxation of Yb3+ ion YasO4
Authors: Kalbfleisch H. , Kumberg H. , Müller‐vogt G. , Stengel M. 
Published: July 2007

AbstractUsing an EFP absorption spectrometer the pair interaction of Yb3+ ions was stukdied in YAsO4 crystals. Also an investigation of the relaxation behaviour was performed concerning with the temperature and angular dependence of hte relaxation times of the isolated ions. The relaxation is partially affected by cross relaxation between the single ions and the Yb3+ ion pairs. The direct process at the lowest temperatures is bottlenecked.
Symmetrische verallgemeinerte Wannierfunktionen. II. Eigenschaften und Beispiele ‐ Bandstruktur des Germaniums
Authors: Krüger E. 
Published: July 2007

AbstractAusgehend von der Symmetrie des Kristalls und dem Symmetrieverhalten der Blochfunktionen einer beliebigen abgeschlossenen Bandgruppe werden die Eigenschaften der zugehörigen verallgemeinerten Wannierfunktionen untersucht. An einigen Beispielen in einem Kristall mit kubisch‐flächenzentriertem Gitter ‐ insbesondere an der Bandstruktur des Germaniums ‐ wird gezeigt, wie man ihr Symmetrieverhalten und ihren Symmetrie‐mittelpunkt bestimmen kann.
Thermal Expansion of a Linear Lattice
Authors: Ninio F. , Oitmaa J. 
Published: July 2007

AbstractIf the thermal expansion of a lattice with periodic boundary conditions is calculated exactly, the result is zero. An expression is derived for the thermal expansion is of a monatomic linear chain with free ends using the exact normal modes and it is shown that this result may be reproduced to thermodynamic accuracy by using at some stage of the calculation, normal modes appropriste to a periodic chain.
Ginzburg‐Landau‐Parameter x1(T) und x2 (T) in der Nähe von 1/√2
Authors: Kumpf U. 
Published: July 2007

AbstractAnhand von Magnetisierungsmessungen an Pb‐TI‐Einkristallen mit 0,572 ≦ x ≦ 0,948 wurde die Temperaturabhängigkeit der verallgemeinerten Ginzburg‐Landau‐Parameter x1 (T) und x2 (T) untersucht. Dabei ergibt sich beim Übergang vom Supraleiter I. Art zum Supraleiter 2. Art für T < Tc eine Diskrepanz zwischen x1 (T). Die Temperatur abhängigkeit von x1 (T) und x2 (T) in der Nähe der Übergangstemperatur Tc wird mit den Beziehungen aus der Neumann‐Tewordt‐Theorie verglichen.
Jahn‐Teller Theory of the Ti3+ Ion in Corundum
Authors: Rai R. 
Published: July 2007

AbstractThe apparent reductions in the trigonal field and spin‐orbit interactions in Ti3+ ion doped in Al2O3 is explained to be due to the presence of a moderate Jahn‐Teller effect. The spin‐orbit, trigonal field, and a part of the Jahn‐Teller interaction which causes three equivalent oscillations along the three pseudo‐fourfold axes of the complex, are treated on equal footing. The effect of the tunnelling through the potential barriers between these equivalent oscillations is considered as a perturbation. The resulting ground wave functions are used to calculate the EPR g‐values. The theoretical values are compared with the experimental magnetic and spectroscopic results.
Non‐Even Dependence of Conductivity of Hot Electrons on Magnetic Field Strength in Many‐Valley Semiconductors
Authors: Asche M. , Sarbei O. G. , Savyalov Yu. G. 
Published: July 2007

AbstractThe transverse magnetoresistivity of n‐Si with different impurity densities was investigated theoretically and experimentally for a nonsymmetrical orientation of the current in strong electric fields. The experimental results for the linear change of conductivity with respect to the magnetic field are compared with numerical data and qualitative agreement is shown.
The Modulation of Light by Non‐Equilibrium Optical Phonons in n‐Ge
Authors: Vorobev L. E. , Stafeev V. I. , Shturbin A. V. 
Published: July 2007

AbstractThe modulation of light near the edge of the direct transitions in Ge in strong pulsed electric fields was investigated. High‐resistance n‐Ge (ϱ = 40 Ωcm) and low‐resistance p‐Ge (ϱ = 1.0 Ωcm) exhibit the Franz‐Keldysh effect only. The low‐resistance samples of n‐Ge (ϱ = 1.0 and 0.3 Ωcm) exhibit Franz‐Keldysh effect together with a variation of the absorption coefficient ΔαDE which is proportional to the free carrier concentration and has a threshold approximately at the photon energy deficit equal to the energy of the longwave optical phonon (0.037 eV). The additional absorption ΔαDE is caused by the indirect band‐to‐band transitions with participation of non‐equilibrium optical phonons, emitted by hot electrons. From a comparison of the experimental and calculated results for ΔαDE the lifetime is estimated to be 5 × 10−11 s at T0 = 90 °K for the long‐wave optical phonons. This value is in satisfactory agreement with Klemens' theory and also with the results of Raman scattering in Ge.
Free Carrier Absorption in CdSxSe1−x Single Crystals
Authors: Lisitsa M. P. , Demidenko Z. A. , Malinko V. N. , Pidlisnyi E. V. , Valakh M. Ya. , Vitrikhovskii N. I. 
Published: July 2007

AbstractFree electron absorption in single crystals of CdS and CdSe, as well as in CdSxSe1−x solid solutions (x = 0.80, 0.58, 0.43, 0.36, 0.31, 0.21), has been investigated at Hall concentrations N = 2 × 1016 to 2 × 1019 cm−3 in the temperature interval T = 80 to 450 °K. For all the samples investigated, absorption coefficients K ∼ λn, where n = f(N, T), and a mixed mechanism of scattering by optical phonons and charged impurities is found, whereas for N of the order of 1016 cm−3 scattering occurs practically only by optical phonons. An interpretation of the wavelength and concentration dependences of the measured absorption coefficients is given.
Attractive Interactions between Flux Lines as Derived from a Generalized Neumann‐Tewordt Functional
Authors: Hubert A. 
Published: July 2007

AbstractA generalized Ginzburg‐Landau (GL) functional is derived which is equivalent to the functional of Neumann and Tewordt (NT) if used to calculate first order corrections to known GL solutions, but which avoids the instabilities formerly encountered in a direct evaluation of the NT functional. Flux lines in superconductors near Tc are calculated using the circular cell approximation of Marcus. In contrast to the GL case we find a first order transition at Hc 1 which results from an attractive interaction between flux lines. The initial induction, the lower critical field, the magnetization curves and some flux line profiles are given as functions of the GL parameter ϰ, the temperature and the impurity parameter α. The results are consistent with former results of Jacobs and with experimental observations of Kumpf.
Neutron and Mössbauer Studies of the Planar Antiferromagnet KFeF4 in the Critical Region
Authors: Heger G. , Geller R. 
Published: July 2007

AbstractResults obtained from diffuse neutron scattering investigations and those derived from magnetic Bragg peaks on single crystals of the planar antiferromagnet KFeF4 in the critical region reveal that the temperature dependence of the two‐dimensional short range magnetic order and of the sublattice magnetization follow (T – TN)−νv and (1 – T/TN)β laws, respectively, where v = 0.60, β = 0.20, and TN = 148 K. Mössbauer measurements at 300K showed that for KFeF4 the isomer shift is (+ 0.138 ± 0.002) mm/ssee page 232.
and the quadrupole splitting is (1.460 ± 0.005) mm/ssee page 232.
. In the temperature range 0.96 < T/TN < 0.998 the internal magnetic field follows the power law Hin(T) = H(0) D (1 – T/TN)β, where H(0) = H (4.2 K) = (540 ± 4) kOe, TN = (141.51 ± 0.05) K, D = 1.12 ± 0.03, and β = 0.209 ± 0.008.
Piezoemission Study of Free Excitons in CdS
Authors: Goede O. , Büchtemann A. 
Published: July 2007

AbstractThe free exciton emission bands in CdS are investigated with static uniaxial stress, σ, applied to the crystal. The measured peak shifts and intensity ratios as function of stress σ ∥ c and σ ⟂ c are interpreted on the basis of first order perturbation theory and lead to quantitative information on the stress‐induced mixing of exciton states. In particular, the A(Γ6)‐exciton, stress‐allowed for σ ⟂ c, is studied and the corresponding mixing matrix element is determined. For both stress directions a Boltzmann distribution of the exciton concentrations is found.
Evidence of Anomalous Z1‐Dependence of Interaction Potential by Multiple Scattering Experiments
Authors: Krygel P. , Lippold J. , Schwabe S. 
Published: July 2007

AbstractOn the basis of Meyer's theory of multiple scattering, the collision parameters are estimated, which substantially influence the scattering distribution. For reduced thicknesses of τ ≦ 2 higher values of collision parameters around p ≧ 2 a (a screening parameter) have an influence on the scattering distribution. Experiments with various ions at carbon targets seems to show deviations of the half‐width from the theoretical dependence on the atomic number. These deviations are interpreted by means of periodic fluctuations in the interaction potential, which have been shown experimentally by Nelson [2], and theoretically by Cheshire and Poate [1].
On Creep Strain Delay at the Superconducting Transition
Authors: Soldatov V. P. , Startsev V. I. , Vainblat T. I. , Danilenko L. A. 
Published: July 2007

AbstractThe kinetics of the jump‐like process of creep strain increase during the crystal transition from the normal to the superconducting state was studied. It is shown that the crystal transition from the N (normal) to the S (superconducting) state in the creep process is characterized by a certain delay time during which the creep rate remains constant after the transition to the S state. The delay time dependence on temperature and stress was studied. The delay time decreased exponentially with the increase of stress on the crystal at the normal state and displays a sharp decrease with the lowering of temperature. The obtained results are accounted for on the basis of the model of a thermally activated unpinning of dislocations from obstacles taking into consideration the peculiarities of the model in the low‐temperature region.