bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deviations from Matthiessen's rule in silver containing low‐density defects
Authors: Goodarz M. , Barnard R. D. 
Published: July 2007

AbstractThe parameters obtained in an earlier paper by Barnard on the low field Hall effect in Ag alloys are used to calculate the contribution to the deviation from Matthiessen's rule (DMR) Δ1 due to anisotropy in the relaxation times in the systems AgAu, AgCd, and Ag + dislocations. Comparison is made with new experimental data of DMR on AgCd and Ag + dislocations between 4 and 300 K and pre‐existing data on AgAu. Whilst anisotropy in the relaxation times can account for most of the observed DMR in AgAu and Ag + dislocations, it makes only a minor contribution in Ag‐Cd (a charged impurity in Ag) because this impurity scattering is nearly isotropic. AgCd is discussed in terms of a second contribution Δ2 arising from inelastic coherent scattering (Kagan and Zhernov) and Δ3, a new contribution, developed in this paper arising from the energy dependence of the resistivity of the host metal and related to its diffusion thermopower. A discussion is also made of the applicability of Δ3 to the anomalous system MgAl where negative values of Δ exist at high temperatures.Die in einer früheren Arbeit von Barnard über den Halleffekt in niedrigen Feldern von Ag‐Legie‐rungen erhaltenen Parameter werden benutzt, um den durch die Anisotropie der Relaxationszeiten hervorgerufenen Beitrag zur Abweichung von derMatthiessen'schenRegel(DMR), Δ1 inden Systemen AgAu, AgCd und Ag + Versetzungen zu berechnen. Ein Vergleich mit den neuen experimentellen Werten der DMR an AgCd und Ag + Versetzungen zwischen 4 und 300 K und den vorher existierenden Werten an AgAu wird durchgeführt. Während die Anisotropie der Relaxationszeiten fast die gesamte beobachtete DMR in AgAu und Ag + Versetzungen erklären kann, wird für AgCd (eine geladene Störstelle in Ag) gefunden, daß sie nur einen kleinen Beitrag liefert, well diese Störstellenstreuung nahezu isotrop ist. AgCd wird mit einem zweiten Beitrag Δ2 diskutiert, der von der inelastischen kohärenten Streuung (Kagan und Zhernov) herrührt und mit Δ3 einem neuen Beitrag, der in der Arbeit entwickelt wird und aus der Energieabhängigkeit des Widerstands des Wirtsmetalls stammt und mit dessen Diffusions‐Thermospannung verknüpft ist. Die Anwendbarkeit von Δ3 auf das anomale System MgAl, wo negative Δ‐Werte bei hohen Temperaturen auftreten, wird ebenfalls diskutiert.
Triplet absorption of crystalline anthracene by high resolution photoconductivity spectroscopy
Authors: Fort A. , Coret A. 
Published: July 2007

AbstractThe photoconductivity spectrum of anthracene crystals at 4 K is studied with a cw dye laser in the spectral region corresponding to triplet exciton creation. Photocarriers are created by the detrapping of charges by excitons. This spectrum is complex but shows the different vibronic excitations which correspond to the purely electronic transition S0 → T1 coupled with different totally symmetrical vibration modes of the molecule. Lattice vibration modes also appear. The spectrum confirms the value of the Davydov splitting for the 0–0 transition and the broadening of the lines for the 0–1 and 0–2 transitions. The presence of satellite lines shows the formation of triplets on disturbed sites of the lattice.
On the dependence of light reflection from metals on adatom characteristics
Authors: Brodskii A. M. , Urbakh M. I. 
Published: July 2007

AbstractRelationships are derived to interrelate the experimentally observed variation in the reflection coefficient of light from metals during the adsorption and the microscopic characteristics of an adatom. A method is developed, similar to the introduction of pseudo‐potential in solid state physics and molecular physics, to describe the electron properties of adatoms. The theoretical relationships derived are suitable for treating experimental data. The theory proposed shows that optical methods are quite promising for the determination of important microscopic characteristics of adsorption.
Acoustic phonon scattering by electron‐hole droplets in Ge. Deformation potentialsz
Authors: Markiewicz R. S. 
Published: July 2007

AbstractDeformation potentials are calculated for electron‐hole droplets in Ge and compared to the values for degenerate n‐ or p‐doped Ge. Due to the conduction band anisotropy and the presence of an equal number of electrons and holes, it is found that screening effects are substantially reduced, but that there are strong anisotropies in coupling to various phonon modes.
Electrical resistivity of antiferromagnetic alloys coherent potential approximation
Authors: Borodachev S. M. , Masharov S. I. , Volkov V. A. 
Published: July 2007

AbstractThe electrical resistivity of a binary antiferromagnetic alloy due to the scattering on spin disorder and on the static potential of a random distribution of different atoms over the lattice is calculated in the coherent potential approximation. The concentration dependences of the contributions to the resistivity due to the spin disorder and elastic scattering as well as of the interference term caused by differences of the atomic levels and exchange constants of the components are obtained. If the Fermi energy is far from the spectrum gap arising with the transition to the antiferromagnetic state, the resistivity of alloys decreases while the magnetization of the sublattices increases. A more complicated behaviour of the resistivity versus magnetization takes place in those alloys in which the Fermi energy is near the spectrum gap. In this case an increase of elastic and spin contributions to the resistivity is possible with antiferromagnetic ordering. This increase of some contributions to the resistivity may be a reason for such anomalies as the maximum or minimum of the total resistivity in the region of the Neel point.
Theory of radiation of charged particles channeled in a crystal
Authors: Kumakhov M. A. 
Published: July 2007

AbstractThe theory of a new effect is developed — spontaneous radiation of γ‐quanta in channeling relativistic particles. The radiation characteristics are different from the presently known types of radiation sources. At energies of the order of 1 GeV the radiation is characterized by wavelength ⪅ 10−3 Å. The radiation intensity is about 6 to 9 orders of magnitude higher than obtained from modern synchrotrons. Its monochromaticity is considerably better than bremsstrahlung or synchrotron radiation. The radiation is fairly well polarized. In the quantum treatment, the radiation is caused by transitions between levels, which are formed in channeling in the fields of atomic planes and rows. A classical and quantum calculation of the radiation intensity is presented. At a current of about 100 μA and a target thickness of ≈︁ 1000 μm, about 1018 to 1019 quanta/s are radiated. The spectral density of the radiation is considerably higher than that of any known kind of radiation. It is suggested that the radiation might be used to influence selectively nuclear transitions and to produce a γ‐laser. This radiation can be used to study the crystal lattice potentials, measure the particle energy, and so on. Dispersion is studied. The possibility of enhancing the induced radiation is shown. A number of studies on light channeled particles are analysed.
Coulomb gap in a disordered semiconductor
Authors: Bonch‐Bruevich V. L. 
Published: July 2007

AbstractConditions of the Coulomb gap to appear in the energy spectrum of a disordered semiconductor are studied avoiding assumptions too model‐like. In particular the form of the electron‐electron interaction potential is not specified, up to the assumption that it is screened in some way. Low temperature screening, absorption of low‐frequency electromagnetic waves, and some thermodynamic properties are considered for a system containing a “soft” density of states gap.
Image potential near a dielectric–plasma‐like medium interface
Authors: Kornyshev A. A. , Rubinshtein A. I. , Vorotyntsev M. A. 
Published: July 2007

AbstractThe effect of penetration of an electric field into the metal, electrolyte, solution, or other plasmalike medium (PLM) on the image‐potential energy in a dielectric adjacent to such a PLM is studied. The asymptotics of classical attraction of a test charge to an “impenetrable metal surface” at large distances and of effective interaction with “dielectric‐dielectric interface” at small distances are found. The latter results in a repulsion of a charge from the boundary, when the dielectric constant of the background medium, in which plasma particles are dissolved, is smaller than the permittivity of the dielectric. A minimum of the image‐potential curve is situated between the “repulsive” and “attractive” limiting branches. Thus an adsorption minimum is predicted within the scope of purely electrostatic considerations, the value of the “desorption energy” being estimated.
The critical voltage effect in transmission electron microscopy. IX. The Calculation of Critical Voltages and Experimental Extinction Distances in Complicated Many‐Beam Systems
Authors: David M. , Gevers R. 
Published: July 2007

AbstractBy means of an algorithm based on perturbation theory, the illumination conditions under which a given many‐beam system has a twofold degeneracy, can be calculated quickly and to arbitrary accuracy, provided a good estimate of the critical values is available. The same technique can be used, conversely, to calculate corrections on theoretical extinction distances so as to fit critical voltage measurements.
A many‐body model of dieletric polarisation in solids. II. The universal model
Authors: Jonscher A. K. 
Published: July 2007

AbstractOn the basis of the experimental data previously presented, the case is made for a unifying approach to the interpretation of the common dielectrie response of most solids. This approach starts from the unique property of this response tht the ratio to the energy lost per cycle to the energy stored in the system is independent of frequency. A “screened hopping” model involving many‐body interactions is proposed which has the requied generality and which should account for the commonly observed behaviour. The physical nature of the loss peaks is also interpreted in terms ofthe new model as the result of sequential interplay of the different types of decay processes in the time domain. The relation of the new model to the classical Debye picture is briefly discussed.
Polarizabilities of donors in elemental semiconductors
Authors: Palaniyandi E. , Balasubramanian S. 
Published: July 2007

AbstractUsing the multivalley effective‐mass theory and the variational method the following expression is obtained for the polarizability α of donors in elemental semiconductors: α = 4a4/[(−a/K) + + (1/m*) + 2EDa2], where a is the effective Bohr radius for the donor, K the static dielectric constant of the host semiconductor, m* the conduction electronic effective mass, and ED the donor ionization energy. The estimates of α for various donors in Si and Ge are discussed.
Temperature dependence of knight shift and susceptibility of single crystal molybdenum
Authors: Karcher R. , Köbler U. , Lüders K. , Szücs Z. 
Published: July 2007

AbstractThe temperature dependences of the Knight shift (for 95Mo and 97Mo) and the magnetic susceptibility of single crystals of molybdenum are measured in the temperature region 10 to 300 K. Furthermore the relaxation rates are determined on the same samples. A complete separation of the quantities into the s‐, d‐, and orbital contributions is made using some additional assumptions. For the temperature dependence it results that the orbital contribution predominates.
Influence of an electric field on the Jahn‐Teller split absorption band 4A2g → 4T1g(P) of Co2+ in CdF2 and CaF2
Authors: Krylov V. A. , Ulrici W. 
Published: July 2007

AbstractThe change of the optical absorption of the Jahn‐Teller split and vibration‐induced 4A2g → → 4T1g(P) band of Co2+ in CaF2 and CdF2 induced by external electric fields up to 160 kV cm−1 applied in the three main crystallographic directions is measured with polarized light at 78 K. In all cases an enhancement of the oscillator strength is found increasing quadratically with the electric field. The field‐induced changes of the moments of the absorption band are calculated up to the third moment. However, both the line shape of the electromodulated spectra and the dependence on field direction and polarization cannot be explained within the approximation of the linear interaction with even and odd lattice modes. From the experiments arguments are derived that higher‐order interactions with even and odd modes determine the electromodulated spectra.
Thermopower and the transverse nernst‐ettingshausen effect in semiconductors in a strong electric field
Authors: Babaev M. M. , Gasymov T. M. 
Published: July 2007

AbstractThe thermopower and the transverse Nernst‐Ettingshausen effect of semiconductors in strong (heating) electric and nonquantisized magnetic fields are investigated regarding the phonon darg of electrons and the heating of the phonons. The dependences are obtained of the thermopower and Nernst‐Ettingshausen voltage on the electric field strength E0. It is shown that in the case of strong electron and phonon heating and impurity scattering of the nondegenerate electrons the electronic part of the thermopower increases α E04/3, whereas the phonon part α E010/3, if the phonons are scattered by electrons. But if the phonons are scattered by crystal boundaries the electronic part of the Nernst‐Ettingshausen voltage in weak magnetic fields is α E010/3, whereas the phonon part is α E04.
On the properties of cobalt impurities in zinc selenide crystals. I. Effect of in‐band position of states on photoelectric properties
Authors: Radlinski A. P. 
Published: July 2007

AbstractThe absorption and photoconductivity spectra of ZnSe:Co in the spectral region of the 4A2(4F) → → 4T1(4F) and 4A2(4F) → 4T1(4P) crystal field transitions within the 3d7 shell of the Co2+ ion are presented. The structure of the photocurrent observed here is associated with the degeneracy of the 4T1(4P) and 4T1(4F) excited states of the Co2+ ion with the conduction band of ZnSe. The autoionization times of Co2+ ion via those states to the conduction band are estimated to lie within the range of 10−9 to 10−4 s.
The influence of fast neutron irradiation on the critical current densities in Nb3Sn. II. High neutron doses (Φ > 2 × 1018 neutrons/cm2)
Authors: Fähnle M. 
Published: July 2007

AbstractBy a model calculation within the framework of the Labbé‐Friedel‐van Reuth theory of A15‐superconductors the influence is investigated of radiation induced atomic disorder on the critical temperature Tc, the Fermi level EF, the Ginzburg‐Landau parameter x, the coherence length ξ, the penetration depth λ, the critical fields Hc and Hc2, and the critical current density Jc. The theory describe successfully the experimentally observed depressions of Tc, Hc2, and Jc after high dose neutron irradiation. The assumption of statistically distributed atomic defects turns out to be more appropriate to explain the experimental results than the assumption of a strongly inhomogeneous defect distribution.
Theory of radiation of relativistic channelled particles
Authors: Kumakhov M. A. , Wedell R. 
Published: July 2007

AbstractA quantum theory of spontaneous γ‐quantum radiation by relativistic channelled particles is developed. Planar channelling of positrons and axial channelling of electrons are considered. The calculation results are in a good agreement with classical estimates. Population of the levels is studied and the conditions of spontaneous radiation are analyzed in detail. It is shown that, when the transitions between the lower levels are considered, one may limit oneself to the solution of the problem for a single potential well since in this case the neighbouring wells fail practically to affect the calculation results. The effect of the potential unharmonism on spectral distribution is estimated.
Instability of the flux‐line lattice in a type‐II superconductor containing planar imperfections
Authors: Brandt E. H. 
Published: July 2007

AbstractThe pinning forces exerte dby a planar imperfection on the flux lines in a type‐II superconductor are calculated from the Ginzburg‐Landau theory. The elastic strains caused by this imperfection in the flux line lattice are found to diverge at large inductions. As a consequence, even rather thin planar inclusions or grain boundaries lead to a breakdown of elastic linearity and to a trapping of flux lines by the imperfection as the induction is increased. This result does not require a vanishing shear modulus of the flux‐line lattice but is due entirely to the nonlocal character of the elastic behaviour of the lattice. It may explain in certain cases the observed peak in the volume pinning force at large inductions.
Polariton effects on the recombination of cold biexcitons
Authors: Ostertag E. , Bivas A. , Grun J. B. 
Published: July 2007

AbstractIf one assumes that, when the biexcitions are created directly by two‐photon absorption, a cold gas of biexcitons with virtually no interaction is formed, the position and shape of the narrow emission lines due to their recombination should be influenced by some salient features of the final state. By adopting a special geometrical configuration, the magnitude of the wave vector of the exciton left in the final state is varied in a range such that this exciton penetrates deeply into the polariton region of its dispersion curve when it is of transverse type. The resulting observations of a shift and broadening of the narrow emission line associated with that final state, as well as of the change in the ratio of the intensities of the two narrow lines, are in good agreement with the theoretical predictions derived from that model.
Thermal conductivity of irradiated RbMgF3
Authors: Hartmann J. B. , Martin J. J. 
Published: July 2007

AbstractThe thermal conductivity of RbMgF3 has been measured from 2.5 to 80 K as a function of radiation damage. When RbMgF3 is irradiated at room temperature with 1.5 MeV electrons, F centers and complementary fluorine interstitials are produced. Irradiation to an F‐center concentration of 4 × 1017 cm−3 causes a reduction in the thermal conductivity at all temperatures below 25 K. No change in thermal conductivity is observed when the F centers are converted to R centers by a 673 K anneal. This result shows that the radiation‐induced phonon scattering is caused by the interstitials. This additional scattering can be described by the sum of frequency‐independent and point defect scattering terms. The observed increase in the frequencyindependent term is consistent with the formation of interstitial clusters during irradiation. Both contributions to the scattering grow linearly with F‐center concentration.
Temperature‐dependent multi‐ion interactions in simple metals
Authors: Takanaka K. , Yamamoto R. 
Published: July 2007

AbstractAn expression for the temperature‐dependent multi‐ion interactions in simple metals is obtained using the temperature Green's function. This expression gives a damping factor, exp (−πTr/vF) for the two‐body interaction, where T, vF, and r are the temperature, Fermi velocity, and the distance between two ions, respectively.
Lattice heat capacity and thermal vibrations in alkali metals
Authors: Vaks V. G. , Zarochentsev E. V. , Kravchuk S. P. , Safronov V. P. , Trefilov A. V. 
Published: July 2007

AbstractThe lattice heat capacity cv(T) and mean‐square displacement of the ion, \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {x^2 } $\end{document}(T) in alkali metals are calculated on the basis of the pseudopotential model described earlier. Agreement with experiment is in general quite good for Debye temperatures θ and not bad for the dependences cv(T). Some conclusions on the phonon spectrum of Cs are drawn from the data on heat capacity. The pseudopotentials giving a good description of the phonon spectra of Na, K, Rb are proposed. Values of \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {x^2 } $\end{document}(T) are discussed in detail and compared with experiment. The sensitivity of all the results to the approximations for the dielectric function ε(q) and for the pseudopotential V(q) and for the pseudopotential V(q) is also discussed.
Polarization effects in mössbauer absorption of a FeCl2 · 4 H2O single crystal in an external magnetic field
Authors: Spiering H. , Hösl S. , Vogel H. 
Published: July 2007

AbstractAn unusual Mössbauer spectrum of a single crystal in external magnetic field is discussed concerning the line positions and the intensity of the transitions. A method is described to attach the line positions to the appropriate transitions. The intensity is in contradiction to a simple intensity sum rule as a result of polarization effects. It is shown that the thickness effect provides additional information of the orientation of the electric field gradient.
Symmetry and analytical expressions of matrix components in the tight‐binding method
Authors: Kuznetsov V. N. , Men A. N. 
Published: July 2007

AbstractThe method of summing over lattice sites in the tight‐binding method which systematically deals with the point symmetry of crystals is taken into consideration. General expressions of matrix components via independent parameters by summing over an arbitrary number of neighbours in arbitrary crystals are deduced. Group‐theoretical calculations are done and simple formulas are obtained for cubic crystals. As an example, the structures of NaCl, zincblende, diamond, and CaF2 are considered.
A computational study of the correlation of attenuated total reflection minima with surface polariton modes
Authors: Aers G. C. , Boardman A. D. , Clark P. 
Published: July 2007

AbstractA computational study is made of the variation of θmin, the coordinate of the minimum in Rp, the p‐polarised reflected intensity of typical ATR systems, with d i.e. the air/vacuum spacer thickness (GAM system) or the metal film thickness (GMA system). θmin is correlated to detailed numerical solutions of the dispersion equations of these coupled systems using both a free‐electron model of sodium and some experimental magneto‐optical nickel data. For many frequencies the minimum in the sodium GAM reflectivity agrees well with actual solutions of the coupled system dispersion curves but cut‐offs occur below which a minimum in Rp cannot be associated with such solutions. For the sodium GMA reflectivity, θB, the pseudo‐Brewster angle, shifts to smaller values as Ω is increased and when θB is in the neighbourhood of θp, the plasmon angle, somewhat indistinct results can occur as d is decreased. Nevertheless there is a fair correlation of the minima in Rp with surface mode existence for all frequency branches of a (θmin, d) curve which progress towards the origin without a break. Finally, some experimental data for nickel is used to produce (θmin, d) curves over a range of d for which a significant departure from free‐surface behaviour is expected. For GAM the qualitative behaviour for nickel is, in fact, similar to that of sodium but the maximum value of θmin falls well below the 90° region as the frequency increases. For GMA the picture is much more complicated with only the curve for the lowest frequency resembling that obtained for the free‐electron sodium metal.