bluuebunny/crossref_metadata_2025_split huggingface dataset:
Semi‐Empirical LCAO Band Structures for Different Crystalline Phases of Tellurium
Authors: Weigel C. , Messmer R. P. , Corbett J. W. 
Published: July 2007

AbstractThe electronic band structure of trigonal tellurium is calculated by the extended Hückel theory using parameters adjusted to match known features of the band structure as determined by experiment. These same parameters then are employed to predict the band structures of arsenic‐type, rhombohedral, and hypothetical simple cubic tellurium. All predicted band structures turn out to be metallic.
Some Properties of Type‐II Superconductors Derived from a Non‐Local Theory
Authors: Brandt E. H. 
Published: July 2007

AbstractSome properties of flux lines and of the flux‐line lattice are derived from the non‐local theory for type‐II superconductors given in a previous article. The curvature of the magnetic field increases with decreasing temperature (even in reduced units), resulting in a sharp cusp at zero temperature and B = Hc2 (clean limit). At large distances from the vortex core the magnetic field reverses its sign for small x and T < 0.78 Tc′, whereas the gap parameter increases monotonically to the BCS‐value. Both effects can separately explain the attraction of flux lines observed in experiment for small x and T.
Microscopic Magnetic Field Distribution in Superconducting Niobium Single Crystals in the “Dirty Limit”
Authors: Weber H. W. , Schelten J. , Lippmann G. 
Published: July 2007

AbstractNeutron diffraction experiments on the flux lines in superconducting niobium single crys‐ tals varying in their Ginzburg‐Landau parameter x1 between 1.8 and 3.0 are reported. In all cases the flux line lattice was found to be single crystalline. Using the analysis of the integral reflectivities described previously [ l ] the local magnetic field distribution is obtained as a function of the flux densitny. Comparing the results for different x a systematic variation of the magnetic microstructure is observed: with increasing x the attractive inter‐action between individual flux lines disappears, the maximum field decreases, and the mni‐mum and saddle point fields increase; the linear superposition of the fields of single flux lines observed with x ≈ 4 changes systematically into a nonlinear one a t x ≈ 1. Finally, the results on the “isolated” flux line are compared with theory.
Electrical and Optical Properties of Amorphous and Monoclinic Selenium under Very High Pressure
Authors: Fuhs W. , Schlotter P. , Stuke J. 
Published: July 2007

AbstractThe conductivity of amorphous, monoclinic, and trigonal selenium has been measured at 300°K as a function of quasihydrostatic pressure up to 150 kbar. Amorphous and monoclinic samples after exposure to pressure above 120 kbar are transformed irreversibly to the trigonal modification. This result is confirmed by the direct observation of the corresponding shift of the absorption edge. Besides conductivity, for amorphous selenium the shift of absorption edge with pressure is investigated. The resulting pressure coefficient of the band gap is in good accordance with the value obtained from the pressure dependence of the conductivity with the assumption that intrinsic conduction predominates in amorphous selenium.
Metal–Insulator Transition and Lifshits Instability in the Hubbard Model. II. Stationary Point Approximation for the Functional Integral
Authors: Gobsch G. , Weller W. 
Published: July 2007

AbstractThe self‐consistent approximation scheme developed in an earlier paper [1] was evaluated numerically in the stationary point approximation (SPA) and in Hubbard's alloy analogy (AA). The results confirm the occurrence of a Lifshits instability leading to a discontinuous metal‐insulator transition.
Role of Singlet and Triplet Excitons in Extrinsic Photocurrent Production in the Anthracene–Gold System
Authors: Chance R. R. , Prock A. 
Published: July 2007

AbstractExtrinsic hole photocurrents in a gold coated anthracene crystal are measured as a function of the absorption depth of the exciting light. Charge pairs are formed at the gold‐anthracene interface as a result of exciton–gold interactions. It is found that both singlet and triplet excitons are involved as precursors to charge formation. The contributions of singlets and triplets to the observed photocurrent quantum yields are determined for 394 nm excitation light (a and b polarized) and 340 nm excitation light (a and b polarized). Since reabsorption is known to have a significant effect on the distribution of excitons and on the effective singlet lifetime, a steady state numerical solution for the reabsorption problem is offered for this system. The inclusion of the reabsorption effect allows the calculation of a “reabsorption free” singlet diffusion length (316 Å) and an evaluation of the electron transfer efficiency ratio (ηT/ηS ≈ 3.5) where ηS is the probability of electron injection per singlet exciton quenched by the surface and ηT is the corresponding probability for a triplet exciton. The magnitude of the ratio ηT/ηS is interpreted in terms of singlet energy transfer to the gold layer.
EPR Spectra of Transition Element Impurities with 3d2 Configuration in Hexagonal CdS and CdSe Single Crystals
Authors: Böttcher R. , Dziesiaty J. 
Published: July 2007

AbstractElectron paramagnetic resonance has been studied for divalent titanium with 3d2 configuration substituting for Cd in hexagonal single crystals of cadmium sulphide and cadmium selenide. The parameters of the spin‐Hamiltonian have been determined at T = 27 and 77 K. It is found that the symmetry of the centre is axial, corresponding to the C3V symmetry of an isolated impurity on normal lattice sites in wurtzite.
The Paraelastic Interaction between Lattice Defects and Flux Lines
Authors: Kronmülleb H. , Schmucker R. 
Published: July 2007

AbstractWithin the framework of the micromagnetic theory of superconductivity explicit expressions for the elastic stresses of flux lines are derived. The dependence of the stress tensor on the superconducting parameters λ, ξ, and χ is discussed. It is shown that the magnetic pressure associated with the magnetic field gives rise to elastic stresses of the same order of magnitude as the contribution from the Δ V/V effect of the order parameter. Explicit expressions are derived for the pinning forces exerted by dislocations on flux, lines. They are found to be approximately proportional to the condensation energy H/8π.
Model Pseudopotential and Lattice Vibrations of Alkaline Earth Metals
Authors: Prasad B. , Srivastava R. S. 
Published: July 2007

AbstractThe phonon frequencies and the binding energies of alkaline earth metals Ba, Sr, and Ca have been computed using the two parameter model pseudopotential proposed by Krasko and Gurskii. The exchange and correlation effects in the Hartree dielectric function have been adequately considered in the manner of Singwi et al. The calculated results are compared with experimental data. Reasonable agreement is found between experiment and theory.
Electric Field Gradients in Charge‐Perturbed Lattices
Authors: Pustówka A. J. , Sawicka B. D. , Sawicki J. A. 
Published: July 2007

AbstractComputer experiments were performed to find the electric field gradients at nuclei in randomly charge perturbed cubic and hexagonal lattices up to 50% defect concentration. Possible modifications of Mössbauer spectra and TDPAC attenuation factors are discussed.
The Optical Properties of Silicon Ditelluride
Authors: Lambros A. P. , Economou N. A. 
Published: July 2007

AbstractThe optical properties of SiTe2 have been studied in the region 2.5 to 0.5 μm and in the temperature range 300 to 100°K. In the absorption spectrum three distinct regions have been observed which have been attributed to Te vacancies, indirect, and direct transitions, respectively. The fine structure in the vicinity of the indirect transitions indicates the participation of four phonons and a two‐dimensional exciton. The absorption in the vicinity of the direct transitions follows Urbach's rule. The main parameters characterising the indirect and direct transitions are determined.
Elastic Energy and Shape of New Phase Coherent Inclusions
Authors: Khachatubyan A. G. , Hairapetyan V. N. 
Published: July 2007

AbstractAn analysis is made of the shape of coherent inclusions of a new phase in an elastic an‐isotropic medium in dependence on the surface tension energy, the elastic medium anisetropy, and the crystal lattice rearrangement. It is shown that the internal stress energy consists of two terms if the inclusions are of plate‐like shape. The first term is proportional to the inclusion volume and the second to the length of the closed contour, which encircles the inclusion along its periphery in the habit plane. Formally the second term gives the dislocation loop energy, where the Burgers vector is the product of the plate thickness and the characteristic deformation produced by the phase transition. The minimum of this term defines the shape of the inclusion in the habit plane. A detailed analysis of the shapes in the extreme case of a small plate thickness with respect to the length is made.
Screw Instability in a Three‐Component Electron‐Hole Plasma
Authors: Meilikhov E. Z. 
Published: July 2007

AbstractA theory of the screw instability in a three‐component electron‐hole plasma of semiconductors in a weak magnetic field is formulated. At these conditions the screw instability has two modifications (monopolar and bipolar modes). The role of intervalley (interband) scattering in developing of the monopolar screw instability is estimated. It is supposed that the observation of the latter is possible in GaSb. The results of numerical calculations of threshold electric fields and oscillation frequencies are given for both modes of the screw instability in p‐ and n‐GaSb.
Optical Absorption of Tellurium in the Region between 39 and 250 eV
Authors: Sonntag B. , Tuomi T. , Zimmerer G. 
Published: July 2007

AbstractThe absorption spectrum of evaporated thin films of crystalline and amorphous tellurium was measured in the region between 39 and 250 eV. The electron synchrotron DESY was used as a light source. A sharp doublet around 42 eV and a weak structure on its high energy side associated with transitions from the spin—orbit split 4d core levels to the conduction band were observed and compared with the density of conduction states of crystalline tellurium and with the calculated multiplet splitting of the 4d95p5 configuration of atomic Te. The doublet was also observed in the amorphous phase. At higher energies the absorption spectrum is dominated by a broad, large maximum at 87 eV. After a minimum at 165 eV the absorption increases again with increasing photon energy. This behavior is very similar to the absorption spectrum of solid and gaseous xenon. It can be explained by quasi‐atomic d–f transitions.
Raman Scattering by α‐HgS (Cinnabar)
Authors: Nusimovici M. A. , Meskaoui A. 
Published: July 2007

AbstractRaman scattering is observed in first and second order by optically active phonons in mercury sulphide HgS having the cinnabar structure (α‐HgS). For the first time these spectra could be obtained in polarised light and interpreted using selection rules derived by group theoretical considerations. The experiments have been performed both at room temperature and at low temperatures (90 °K).
Phonon‐Assisted Interband Absorption and Electroabsorption in Disordered Semiconductors
Authors: Esser B. 
Published: July 2007

AbstractThe phonon assisted interband absorption coefficient is calculated for a disordered semiconductor having a random field of impurities with high concentration (compensation). The frequency dependence of the contributions to the absorption coefficient due to the emission and absorption of phonons is obtained. The corresponding optical tail may be described approximately by an exponential dependence with the same characteristic energy as that obtained in case of direct transitions. Several cases are considered where the total optical tail coincides with that given by the contributions in question. The phonon‐assisted interband electroabsorption coefficients are calculated for the random field of impurities and for a smooth random field. In case of the impurity field the graphs are plotted. In case of the smooth field the asymptotic tail of the electroabsorption coefficient is calculated explicitly. The shifted band edge representation is discussed.
Cyclotron Resonance of n‐Type Semiconducting Bi1‐XSbx Alloys
Authors: Oelgart G. , Herrmann R. 
Published: July 2007

AbstractMeasurements are presented of cyclotron resonance on n‐type semiconducting Bi1‐xSbx alloys within the wavelength range of 4 mm and a temperature of 4.2 K. The anisotropy of cyclotron masses can be explained by means of an ellipsoid as a model of the iso‐energy surface. This model resembles that of electrons in pure Bi except of the stretching of the ellipsoids. It is found that the mass values strongly depend on the antimony concentration.
Photoelectric Properties of Mg2Si, Mg2Ge, and Mg2Sn I. X‐Ray Excitation
Authors: Tejeda J. , Cardona M. , Shevchik N. J. , Langer D. W. , Schönherr E. 
Published: July 2007

AbstractThe energy distribution spectra of photoelectrons (XPS) and Auger electrons (AES) excited with AlKα radiation in Mg2Si, Mg2Ge, and Mg2Sn are reported. For the purpose of determining core shifts, measurements were also performed on the elemental constituents. These measurements yield information about the density of valence states, the position and the chemical shifts of the core levels. The energy of the valence plasmons is also obtained. This paper (I) is followed by a second one (II) in which similar results obtained with far UV excitation are reported and discussed in the context of the present work.
Magnetoresistance Anisotropy in Bismuth and Bismuth—Antimony Crystals
Authors: Jacobson D. M. 
Published: July 2007

AbstractThe transverse magnetoresistance anisotropy along the bisectrix axes of Bi and Bi (98)Sb(2) single crystals at 4.2 and 89 K is compared with the theory for magnetic fields applied in two symmetry directions. It is found that the changes in shape of the magnetoresistivity anisotropy curves are consistent with expressions derived from Aubrey's magnetoconductivity tensor for bismuth.
Thermodynamics of the Hot Electron System I. Gradient of the Phonon Temperature
Authors: Alvarez‐Torres J. , Negrete P. 
Published: July 2007

AbstractThe effects of electron‐phonon interaction in a system of hot electrons are discussed. Particular consideration is given to the effect associated with the generation of a temperature gradient in the phonon system. An expression for this gradient as a function of the electric field is obtained and some experimental implications are discussed.
Reversible Photochemical Reactions in Additively Coloured CaF2 Crystals
Authors: Görlich P. , Ullmann P. 
Published: July 2007

AbstractThe influence of selective light irradiation on the absorption behaviour of additively coloured CaF2 crystals at 84, 300, and 500 °K is investigated. It was found that reversible photochromic reactions occur especially at 500 °K. Irradiation into the F band gives rise to an absorption increase of the long‐wavelength absorption peaks. A complete reconversion is possible, so that the formation of colloids can be ruled out.
Interaction of Exciton‐Polaritons with Charged Impurities in Semiconductors
Authors: Skaistys E. , Sugakov V. I. , Zinets O. S. 
Published: July 2007

AbstractThe retarded exciton Green's function G(ω) is calculated for semiconductors with randomly distributed impurities. The expression of the exciton absorption band shape due to polariton scattering by charged impurities is obtained using a relation between the complex conductivity tensor σα β (ω) and G(ω). The band shape is of Lorentz type with Γ depending on the frequency, Γ(ω) = (h/2) v nc (σ + σ), where v is the velocity of the light generated exciton, σ and σ are the cross sections of elastic and inelastic S‐scattering by an isolated charged impurity, nc the charged impurity concentration. Numerical calculations concerning CdS and GaAs have been made. This band broadening mechanism may be dominant at high impurity concentrations.
Photoelectric Properties of Mg2Si, Mg2Ge, and Mg2Sn II. UV Excitation
Authors: Cardona M. , Tejeda J. , Shevchik N. J. , Langer D. W. 
Published: July 2007

AbstractIn the previous paper (I) the energy distribution spectra of photoelectrons (XPS) and Auger electrons (AES) excited with AlKα radiation in Mg2Si, Mg2Ge, and Mg2Sn were presented. Here similar measurements are reported performed with He resonant radiation (48.4, 40.8, and 21.2 eV). The effect of surface contamination by O2 or H2O is shown to be very important in these UPS spectra and results meaningful of the material under study can only be obtained if such contamination is kept to less than 0.2 monolayers. The strong structure which appears in less clean samples has been identified as related to the compounds MgO and Mg(OH)2. The UPS spectra of the clean materials yield information about the densities of valence states and about the outermost d electrons of the Ge and Sn core. Very accurate values for the corresponding spin‐orbit splittings and chemical shifts are obtained.
A Scanning Electron Diffraction Study of Vapor‐Deposited and Ion Implanted Thin Films of Ge (II)
Authors: Graczyk J. F. , Chaudhari P. 
Published: July 2007

AbstractThe reduced intensity function and the structure factor for several models of amorphous Ge have been calculated. These include the diamond cubic, the amorphon, and a random network model. It is found that the data on amorphous Ge is best described by the random network models. Also the effect of interparticle interference function in evaluating the models is taken into account.
A Low‐Temperature Phase Transition in the One‐Dimensional Conductor K2Pt(CN)4Br0.30 ·x H2O
Authors: Comes R. , Lambert M. , Zeller H. R. 
Published: July 2007

AbstractIt is shown that the linear superlattice distorsion of periodicity 6 × 2.88 Å, which was recently observed by X‐ray diffuse scattering in the one dimensional conductors of the type K2Pt(CN)4Br0.30 · x H2O, looses progressively its one‐dimensional character for temperatures lower than 120 °K. This seems to announce a phase transition at a temperature lower than 77 °K leading to a unit cell 3 c × 2 a × 2 a, referring to the room temperature parameters. It is suggested that this phase transition arises from the condensation of the lowest frequency longitudinal soft modes due to a giant “Kohn anomaly”.
Quenching of Benzophenone Phosphorescence in the Vitreous Phase by Long‐Lived Guest Triplet States
Authors: Peter L. M. , Vaubel G. 
Published: July 2007

AbstractTriplet (host)‐triplet (guest) annihilation has been observed and characterised in vitreous benzophenone. The quenching of the benzophenone phosphorescence by long‐lived guest triplet states was measured and the bimolecular annihilation rate constant γhg determined using naphthalene, pyrene, and coronene as guest materials. γhg is found to be independent of the nature of the guest, being of the order of 10−16 cm3s−1. This low value is related to the slow rates of exciton migration in the vitreous phase.
Elastic Field of a Shear Dislocation Loop in an Anisotropic Hexagonal Crystal by the Green's Function Method
Authors: Ohr S. M. 
Published: July 2007

AbstractAnalytical expressions for the components of displacement and stress around a circular shear dislocation loop in the basal plane of an anisotropic hexagonal crystal are derived by the Green's function method. The components of displacement are obtained in terms of surface integrals over the area of the loop of the partial derivatives of the Green's function. It is shown that the surface integrals can be expressed in terms of Lipschitz‐Hankel integrals for a shear, as well as for a prismatic, dislocation loop. Calculations have been carried out in the case of graphite and the results are presented graphically by means of contour plots. In agreement with previous results on the prismatic dislocation loop, the most noticeable effect of crystal anisotropy is to reduce the magnitude of stresses and the displacement components parallel to the basal plane around a shear dislocation loop. The method can be extended to problems of anisotropic elasticity of non‐basal dislocation loops.
Calculation of the Surface Energy of Solid Metals from Work Function Values and Electron Configuration Data
Authors: Missol W. 
Published: July 2007

AbstractA formula for surface energy, ω, in terms of electron work function, φ, and the effective number of free electrons per atom, z, is given. The basis for its derivation were the known equations of the free electron theory of metals and the known advanced Frenkel's relation between electron work function and heat of sublimation. Furthermore in the formula (M atomic mass, γ density) \documentclass{article}\pagestyle{empty}\begin{document}$ \omega = \frac{{1530}}{q}\,\frac{\varphi }{{(M/\gamma)^{2/3} }}z^{2/3} $\end{document} details of the crystal structure of metals were taken into account by introducing the structural coefficient q. The calculated values of surface energy were compared with experimental data.
Hot Electron Faraday Rotation and Birefringence in Semiconductors with Non‐Parabolic Energy Bands
Authors: Almazov L. A. 
Published: July 2007

AbstractThe phenomenon of Faraday rotation arising in semiconductors with isotropic dispersion law of carrier energy in the presence of dc electric and magnetic fields has been considered on the basis of expressions for the dielectric tensor obtained in a previous work [1]. It is shown that in the case of non‐parabolic energy bands the free‐carrier Faraday rotation is accompanied by birefringence. n‐type InSb is taken as an example for numerical calculations.
A Study of the Effect of Deformation on Optical Absorption of MgO Single Crystals
Authors: Turner T. J. , Murphy C. , Schultheiss T. 
Published: July 2007

AbstractThe concentration of V centers, produced by a hole trapped at a magnesium vacancy, has been found to increase linearly with deformation in single crystals of magnesium oxide, When one slip system is operative in the deformation process an anisotropic defect is produced whose axis is 〈100〉 perpendicular to both the {110} slip plane and 〈110〉 slip direction. This defect produces optical absorption bands at 4.07 and 5.17 eV when the deformed crystal is X‐irradiated. These bands are attributed to vacancy complexes which have trapped one or more electrons. Bleaching experiments are reported in which these bands are annihilated by electron release or the capture of holes released from the V band.
Temperature dependence of the hyperfine interaction of trivalent gadolinium in single crystal thorium oxide
Authors: Marshall S. A. , Nistor S. V. , Huang Chao‐Yuan , Marshall T. 
Published: July 2007

AbstractHyperfine structure splittings for the M = − ½ → ½ transition of trivalent gadolinium in single crystal thorium oxide have been measured from 1.25 to 350 K. The temperature dependence of these splittings is interpreted in terms of a modified Šimánek‐Orbach theory.