bluuebunny/crossref_metadata_2025_split huggingface dataset:
Theory of photoemission from molecular crystals
Authors: Belkind A. I. , Brodskii, V.V.Grechov A. M. 
Published: July 2007

AbstractOn the basis of previous approach and considering non‐direct transitions an expression is obtained for calculating photoemission (PE) current from molecular crystals. The model used for treating optical transitions contains the concept f quasi‐particle (hole) formation simultaneously with generation of an electron. The band, corresponding to this quasi‐particle, has a width approximately equal to polarization energy. For the limiting case of high energies a relationship is obtained by means of which it is possible to find energy dependence of density of states in the hole band, using experimental results. The cubic law is deduced for the near‐threshold region using the above‐mentioned relationship based on the experiment. The general expression for photocurrent is also used to obtain the spectral dependences of photoconductivity in the threshold region.
Many‐body lattice theory of elastic dielectric and its application to solids with NaCl structure
Authors: Goyal S. C. , Prakash R. , Tripathi S. P. 
Published: July 2007

AbstractA phenomenological lattice theory of elastic dielectric based on the Lundqvist potential of ionic cohesion is developed. In this theory the lattice is considered to be initially in the deformed and polarised state. The theory yields the expressions for the second order elastic constant, third order elastic constants, dielectric constants, and its strain derivatives. The many body lattice theory (MLT) of elastic dielectric so developed is applied to calculate the strain derivatives of the high and low frequency dielectric constants of the alkali halide solids. The calculated values of these constants are better than those obtained in all earlier models and are in excellent agreement with the experimental values.
Temperature dependence of the electrical resistivity and Hall coefficient in a model of concentrated alloy
Authors: Brauwers M. , Bhattachrya A. K. 
Published: July 2007

AbstractThe effect of temperature on the electrical resistivity and Hall coefficient of a two s‐d hybridized band model representing concentrated transition and noble metal alloys is investigated. Depending on the location of the Fermi level, the electrical resistivity and Hall coefficient are found to increse or decrease with temperature; such a behaviour is observed in various concentrated transition and noble metal alloys.
Thermal conductivity of NbTi alloy in the low‐temperature range
Authors: Flachbart K. , Feher A. , Jánoš Š. , Málek Z. , Ryska A. 
Published: July 2007

AbstractThe temperature dependence of the thermal conductivity of a NbTi (50/50) superconductor is measured in the temperature range from 1.3 to 300 K in two different laboratories. From the analysis of the experimental results it follows that the electron processes provide the main contribution to the thermal transport in the range above 0.3Tc while phonon contribution is decisive, due to the defect structure, only below this temperature. The values of energy gap 2Δ = (2.15 to 2.3) kTc are found by three independent methods. Further, the temperature dependence of the thermal diffusivity is presented in the temperature range above 4 K.
Disorder scattering in CdxHg1−xTe mixed crystals
Authors: Dubowski J. J. 
Published: July 2007

AbstractAn experimental and theoretical analysis is given of the electron mobility at 4.2 K and the longitudinal Nernst‐Ettingshausen effect at 30 K of highly‐doped (n ≈ 9 × 1017 cm−3) CdxHg1−xTe crystals. The molar composition x of measured samples ranged from 0.03 to 0.33. In the theoretical analysis of the experimental data the band structure is described by the full Kane equation. The dielectric function anomaly is also taken into account in the semimetallic region. In order to explain the experimental data it is necessary to consider both the charged centre and disorder scattering as the compensation effect.
Analysis of charge—orbital ordering in compounds with mixed valence
Authors: Ionova G. V. , Makarov E. F. , Pachev O. M. , Ionov S. P. 
Published: July 2007

AbstractOrbital and charge ordering in transition element compounds are considered and a theoretical model is established. Special emphasis is given to the divalent compounds of Cu2+, Ag2+, Au2+ and the trivalent compounds of Pd3+ and Pt3+. It is shown that spatial orbital ordering takes place in compounds with strong intracentre correlation (Cu2+, Cr2+, Mn3+) and that strong intercentre correlation results in charge ordering on orbitals or centres (Ag2+, Au2+, Pd3+, and Pt3+). Real systems and lattice distortions caused by spatial and charge ordering are discussed.
Internal strain and piezoelectricity in zincblende crystals
Authors: Varshney S. C. , Gundjian A. A. 
Published: July 2007

AbstractThe internal strain parameter is calculated from lattice dynamics for zinc blende crystals utilizing the modified rigid ion model. The piezoelectric coefficient is then obtained in terms of the internal strain parameter and the deformation dipole moment in the crystal. A simple form of this dipole moment is proposed and is found to predict the piezoelectric coefficient in II–VI and I–VII zinc blende crystals in very good agreement with the measured values.
Effect of nonlocal potential on the Fermi surface of metals and the phase shift parametrization scheme
Authors: Wang J. Shy‐Yih , Rasolt M. 
Published: July 2007

AbstractThe intrinsic problem of treating a nonlocal potential within the muffin‐tin approximation is studied. Specific attent on is given to the effect of the nonlocal nature of the self‐energy (or quasi‐particle potential) on the Fermi surface of free electron like metals.
Relativistic one‐particle equation for electron states of heavy metals
Authors: Gollisch H. , Fritsche L. 
Published: July 2007

AbstractA scalar relativistic one‐particle equation for a spherically symmetric potential is derived by approximately solving the associated Dirac equation. In contrast to the so‐called Pauli equation this approximation remains valid if the electron is very close to the nucleus. Results obtained for W demonstrate the improvement over the Pauli approximation.
Magnetothermal oscillation and spin splitting of electrons in dilute Bismuth‐antimony alloys
Authors: Matsuo S. , Nishimoto T. , Hayashi S. , Noguchi S. 
Published: July 2007

AbstractMagnetothermal oscillations in dilute BiSb alloys are measured with dc methods in fields up to 22 kOe. The period of the oscillation agrees with that one obtained from the de Haas‐van Alphen effect. A splitting of the peak is observed around 15 kOe and considered as the spin splitting of electrons. The spin‐splitting factor 2Δ calculated from the present results shows some deviations from unity. The deviations are interpreted by assuming the effect of the other bands after Baraff. The variation of 2Δ with increasing Sb concentration seems to imply that the relative energies of the other bands at the point L in the Brillouin zone „shrink”︁ with regard to the centre of the gap.
Coherent potential approximation for the electrical resistivity of partially ordered binary magnetic alloys
Authors: Goedsche F. , Richter R. , Vojta G. 
Published: July 2007

AbstractThe dc electrical resistivity is calculated for a b.c.c. based random binary substitutional magnetic alloy with partial long‐range order for a single‐band tight‐binding model with diagonal disorder, two kinds of localized spins, arbitrary concentrations and arbitrary order parameter. The spin‐disorder contribution to the resistivity is treated by means of the sd exchange model. Within the framework of the CPA up to second order in the scattering potential a general closed resistivity formula is given in terms of alloy parameters and spin parameters. The resitivity is discussed for various special cases in dependence on the long‐range order parameter.
Phase transition in the mixed crystals TbpY1−pAsO4
Authors: Schwab M. 
Published: July 2007

AbstractThe energy of the four lowest crystal field levels of Tb3+ in the mixed crystals TbpY1−pAsO4 is investigated in the range of the crystallographic and magnetic phase transition as a function of temperature and Tb‐concentration (0.2 < p ≦ 1). The results show that, in contrast to the magnetic ordering, the interaction causing the crystallographic transition is of long range and hence a simple molecular field theory fits the experimental data. For small Tb‐concentrations, the feature of this system are superimposed by effects of internal strains caused by the substitution of Tb3+ by Y3+ ions.
Raman‐induced Kerr effect with elliptical polarization in optically active and anisotropic crystals
Authors: Bergmann J. , Kneipp K. , Ponath H. E. 
Published: July 2007

AbstractThe Raman‐induced Kerr effect (RIKE) with an elliptically polarized pump laser beam in optically active and anisotropic crystals is discussed theoretically, taking into account the phonon‐photon‐interaction. It is shown that also in more complicated cases in crystals the RIKE spectrum can give information about the relative value of the non‐resonant term of the non‐linear susceptibility. General theoretical results are specified for the 817 cm−1 A(LO) mode in the uniaxial crystal LiIO3 and experimentally tested. The relative value v of the non‐resonant term of the fourth‐rank tensor is found to v≦ 0.1.
Electrical properties of TlTe single crystals
Authors: Ikari T. , Hashimoto K. 
Published: July 2007

AbstractSingle crystals of TlTe are grown from Te‐rich melt at 280°C. Resistivity, Hall coefficient, magnetoresistance, and thermoelectric power are measured. The experimental results are explained by the assumption of an uncompensated semimetal model, where the band overlapping energy between conduction and valence bands E0 is 0.20 eV in the high‐temperature phase above 172 K and 0.10 eV in the low‐temperature phase. The effective masses of electrons and holes are m = 1.0m0 and m = 1.5m0, respectively, in both the temperature phases.
Multiple scattering theory for magnetoresistance of localized impurities in metals
Authors: Mrosan E. , Schober Ch. , Lehmann G. 
Published: July 2007

AbstractIt is shown that starting from a multiple scattering formalism for localized impurities in metals the linearized Boltzmann equation can be solved by the degenerate kernel technique. In this case the Boltzmann equation reduces to an algebraic set of linear equations of finite rank. An expression for the magneto‐resistance, valid for arbitrary strength of external magnetic fields is derived. In the limit of a nearly‐free‐electron‐like host band structure the well‐known results for magnetoresistance and impurity resistivity are reproduced.
ESR From boron in silicon at zero and small external stress I. Line positions and line structure
Authors: Neubrand H. 
Published: July 2007

AbstractESR observations at zero external stress of the shallow acceptor centre boron in silicon are reported for the first time. These observations have become possible by the high degree of crystal perfection attainable today in Si‐crystal growth. The spectrum, its angular and uniaxial pressure dependence are interpreted in terms of a spin Hamiltonian given by Bir. Additional terms in this spin Hamiltonian are shown to be necessary to account for the experimental result and to explain the differences between the spin Hamiltonian constants derived by different authors.
Site ordering and magnetostriction in garnet II. Iron
Authors: Muller M. W. 
Published: July 2007

AbstractThe crystal field model of Akselrad and Callen is used to estimate the contribution of Fe ions to the growth‐induced non‐cubic magnetostriction of rare‐earth iron garnets. The effect is predicted to be significantly smaller than the previously calculated non‐cubic magnetostriction due to rare‐earth‐site ordering. The estimate uses a feature of the model which renders the local magnetoelastic tensor symmetric in strain and spin components. A plausible argument is adduced to support the conclusion independently of the model.
Singularities in the paramagnetic susceptibility of random Hubbard alloys
Authors: Kolley E. , Kolley W. 
Published: July 2007

AbstractThe paramagnetic susceptibility of disordered alloys is derived from a microscopic Fermi liquid approach for tightly bound electrons at zero temperature. Particle–particle and particle–hole effective vertices are calculated within the coherent local ladder approximation. The correlationenhanced expressions for component and alloy susceptibilities refer to paramagnetic instabilities. Numerical results are presented for partial and total CPA averages of static susceptibilities, magnetizations, and spin‐dependent densities of states.
Ionized impurity scattering in semiconductors
Authors: Gerlach E. , Rautenberg M. 
Published: July 2007

AbstractIn the Brooks‐Herring‐formula the scattering centres are assumed to be independent. The range of validity of this assumption is investigated. For this purpose the scattering of electrons by a pair of impurities is considered as a function of its internal separation and its orientation with respect to the electronic current. For a separation larger than about the Debye‐Hückel screening length the ionized impurities are found to act as independent scattering centres. For smaller separations the interaction of the scattering centres cannot be neglected.
Two‐phonon infrared absorption in In1−xGaxP mixed crystals
Authors: Ulrici B. , Jahne E. 
Published: July 2007

AbstractThe transmission spectra of In1−xGaxP mixed crystals (0 ≦ x ≦ 1) are measured between 20 and 550 K in the spectral range from 400 to 800 cm−1 in which the optical absorption is due to two‐phonon summation processes. The spectra of the end‐member crystals and that of the mixed crystals consist of two main band groups in which up to seventeen structures are observed and pursued over the entire composition range. As an effect of disorder a broadening of the structures and an increase of absorption in the structureless region of the spectra are observed. The structures in the spectra are assigned to particulart two‐phonon combinations or overtones of the various phonon branches — exploiting existing neutron and Raman data of the end‐member crystals as well as the measured temperature dependence of the infrared spectra of mixed crystals. The compositional dependence of the LO, LA, TO, TA phonons at the × and L point and the LO, TO phonons at the T point are derived. It turns out that all phonon modes assigned display one‐mode behaviour.
Manifestation of k‐linear term effects on the Zeeman splitting of the A1‐exciton emission lines in ZnO
Authors: Hümmer K. , Helbig R. , Baumgärtner M. 
Published: July 2007

AbstractThe magneto‐luminescence spectra of the fourfold n = 1 A‐exciton in ZnO up to H = 5 T are reported. The Zeeman splitting in the configuration H ∥ c, k ⊥ c, E ⊥ c clearly demonstrates the influence of the k‐linear energy terms allowed for the k‐components perpendicular to the c‐axis for T7 valence bands of the wurtzite structure. The appropriate exciton coupling matrix is calculated. From the comparison with the experimental results the A‐valence band slope C = = 2 × 10−10 eV cm is calculated.
Many‐exciton effects in the theory of biexcitons
Authors: Ekardt W. , Sheboul M. I. 
Published: July 2007

AbstractStarting from a previously derived many‐particle equation describing biexciton states, dynamical screening effects in the irreducible exciton‐exciton interaction are taken into account. As a result, density‐dependent biexciton binding energies are obtained. Numerical results are given for CuCl and CuBr in the region of free‐exciton density from 10−5 ≦ nexa ≦ 5 × 10−2. In qualitative agreement with experimental data only a small shift of the biexciton luminescence line should be observed.
On the RKKY interaction in spin glass systems
Authors: Freudenhammer A. 
Published: July 2007

AbstractThe dependence of the critical temperature Tg of a spin glass on the Fermi‐momentum kF is calculated numerically. A strong dependence of Tg on kF is found. A proposal is made that this dependence should be measured experimentally in order to obtain information about the basic interaction in spin glass systems.
The disorder scattering in zincblende narrow‐gap semiconducting mixed crystals
Authors: Kossut J. 
Published: July 2007

AbstractA formula for the relaxation time for the disorder scattering mechanism is derived taking into account the complexities of the narrow‐gap zincblende semiconductor band structure. The main features of this formula are discussed showing the importance of the actual form of the electron wave functions appropriate for narrow‐gap semiconductors. Other theoretical approaches to the problem of disorder scattering are reviewed briefly.
The Singularities of the Small Polaron Effective Mass
Authors: Mańka R. 
Published: July 2007

AbstractUsing the Bogolyubov inequality, a more general polaron dispersion relation than known up to now is obtained. The effective polaron mass derived from it for high temperatures and for a strong electron–phonon coupling is the same, but for semiconductors with a suitable wide electron band, the effective mass is discontinuous as a function of the temperature and the electron–phonon coupling constant.
Neutron and Light Scattering from Ferroelectric Fluctuations and Domain Walls of Strontium Barium Niobate
Authors: Prokert F. , Schalge R. 
Published: July 2007

AbstractThe mixed crystal SrxBa1−xNb2O6 (x = 0.70) is investigated in the phase transition region by inelastic neutron scattering. Softening of TO modes is not found but an additional quasi‐elastic neutron scattering (QNS) is detected, which arises mainly from a narrow central peak. This peak is also studied by Rayleigh scattering. Both methods show that the central peak consists of two parts. One part has a broad maximum at the diffuse phase transition (PT) and probably arises from phase fluctuations. The other part below the PT increases with decreasing temperature. It depends on static domain structure and the neutron scattering data can be interpreted by scattering from domain walls.
Photoconductivity in a‐GeSe
Authors: Vescan L. , Stötzel H. , Stoica T. , Kottwitz A. 
Published: July 2007

AbstractThe temperature, illumination, frequency, and photon energy dependences of the photoconductivity in a‐GeSe films are investigated. The conduction activation energy is 0.95 eV, the photoconductivity edge lies at 1.4 eV. The photoconductivity is field‐independent up to 3 × 104 V/cm and independent of the frequency of the chopping light up to at least 103 Hz. The activation energy of the photoconductivity decreases with decreasing temperature from 0.3 eV to almost zero. The experimental curves are consistent with activated mobilities for electrons and holes and recombination by both a direct and an indirect mechanism. A value of 4 × 1013 cm−3 for the density of localized states at the Fermi level is obtained.
Electrical Resistivity of Chromium–Gold Alloys between 77 and 700 K
Authors: Eroglu A. , Arajs S. , Moyer C. A. , Rao K. V. 
Published: July 2007

AbstractElectrical resistivity is measured as a function of temperature of binary chromium alloys containing 0.27, 0.54, and 0.60 at% gold. Gold decreases the Néel temperature linearly at a rate of 32 K/at% gold. Such a decrease is contrary to the predictions of conventional models for the antiferromagnetism in dilute chromium alloys, but can be explained if the excess nuclear charge on gold impurities is totally screened by the band electrons. Total screening also is consistent with the observed temperature variation of resistivity well above the transition temperature if, as seems reasonable, the scattering of electrons from gold impurities reduces the electronic density of states of the alloy at the Fermi energy.
Spin–Orbit and Crystal Field Splittings of the Valence Band in II3V2 Semiconducting Compounds
Authors: Dowgiałło‐Plenkiewicz B. , Plenkiewicz P. 
Published: July 2007

AbstractThe pseudopotential method is used to calculate the spin–orbit and crystal field splittings of tetragonal II3V2 compounds at the Γ point of the Brillouin Zone. The computed splittings are compared to experimental data of other authors. The resulting structure of the valence bands in these compounds at the Γ point is presented.
Lattice Dynamics of Group IV Elements with the Local Heine‐Abarenkov Model Potential
Authors: Soma T. 
Published: July 2007

AbstractThe lattice dynamics of group IV elements is investigated using the local Heine‐Abarenkov model potential. The phonon curves obtained for Si, Ge, and α‐Sn are in good agreement with the observed data of the neutron scattering, contrary to those using the Ashcroft type.
A Cluster‐Bethe Lattice Treatment for the F‐Center in Alkali Halides
Authors: de Queiroz S. L. A. , Koiller B. , Maffeo B. , Brandi H. S. 
Published: July 2007

AbstractThe electronic structure of the F‐center in alkali halides with the NaCl structure is studied using the cluster‐Bethe lattice method. The central cluster is taken as constituted by the vacancy and the nearest and second neighbours to it, respectively cations and anions. The optical transitions are calculated and compared to experimental data on the location of the peak of the F‐absorption band. The agreement obtained indicates that this method may be used to study properties of this defect in alkali halides.
Interface States in One‐Dimensional Models of Deformed Heterojunctions
Authors: Kandilarov B. D. , Tashkova M. G. , Petrova P. C. 
Published: July 2007

AbstractThe existence of interface states in deformed heterojunctions is discussed on the basis of one‐dimensional models and in terms of the scattering matrix approach. Necessary and sufficient conditions for the existence of interface states are derived and numerical results are obtained in a form which makes possible a comparison with the earlier results for ideal heterojunctions without any deformations.
Nuclear Spin Relaxation by Quadrupolar Interactions. The Diffusion of Substitutional Impurities in Ionic Crystals
Authors: Becker K. D. 
Published: July 2007

AbstractSpectral densities are calculated for nuclear spin relaxation via quadrupolar interactions caused by the vacancy diffusion of impurities in NaCl‐type ionic crystals. The treatment, which takes correlation effects into account, is based on the encounter model. NMR cw‐studies on the diffusion of Na+ ions in AgBr are analysed in the framework of this model. The impurity diffusion coefficients derived are found to be in good agreement with tracer diffusion data.
Electrical Resistivity and Magnetoresistivity of Amorphous CrxPd82−xGe18 Alloys
Authors: Ilonca Gh. 
Published: July 2007

AbstractElectrical resistivity and magnetoresistivity measurements are made of amorphous alloys obtained by radio frequency sputtering using argon on fused quartz substrates to thicknesses of about 20 μm. The compositions of these alloys are CrxPd82−xGe18, in which x is the atomic concentration and ranges between 0 to 8. A well‐defined minimum in the resistivity versus temperature curve is observed for these alloys. Below the resistivity‐minimum temperature Tm, the resistivity difference Δ∂ varies as — ln T in agreement with Kondo's theory and tends to level off at lower temperatures. The resistivity‐minimum anomaly is always accompanied by a negative magnetoresistivity.