bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic Correlation Effects (Exciton Manifestation) in the Singl—Particle Band Structure of Nonmetallic Crystals I. General Theory
Authors: Stolz H. , Zimmermann R. 
Published: July 2007

AbstractThe effect of electron correlation on the single‐particle spectrum of electrons in nonmetallic crystals is investigated starting from the full Hamiltonian of the interacting electron system. By these effects excitons become manifest in the single‐particle spectrum entering Dyson's equation of the corresponding Green's functions via the screeningof the Coulomb potential in the self‐energy. Dyson's equation is solved to render the spectral function by a systematic perturbative approach recently introduced in connection with the electron gas problem. The single‐particle spectrum exhibits modified main bands accompanied by exciton satellites contributing remarkably to the density of states. This picture appears not to be fully obtained by the electronic polaron theory starting from a model Hamiltonian which is also investigated in this study.
Cyclotron Resonance and Quantum Oscillations of p‐Type Semiconducting Bi1−xSbx Alloys
Authors: Oelgart G. , Herrmann R. 
Published: July 2007

AbstractMeasurements of magnetic‐field‐dependent microwave absorption at a p‐type semiconductor, Bi0.92Sb0.08 within the frequency ranges around 35, 70, and 135 GHz are reported. The resultsof the diamagnetic resonance and the quantum oscillations of the surface impedance are discussed. Diamagnetic resonance was measured both for light holes at the point L of the Brillouin zone and for heavy holes at thepoint Tof the Brillouin zone. The light holes define three ellipsoidal Fermi bodies of relatively large prolateness. For different models the Fermi energy isdetermined from the obtained cyclotron masses and extreme cross‐sections of the Fermi surface.
Microwave Faraday Effect in Heavily Doped n‐Type Germanium
Authors: Haller H. O. , Kahlert H. 
Published: July 2007

AbstractMeasurements are reported of the microwave Faraday effect at a frequency of 33 GHz in samples of n‐type Ge with carrier concentrations ranging from 5 × 1015 to 3 × 1017 cm−3. From these results the anisotropy of the momentum relaxation time for pure ionized impurity scattering is found to have a value of Kτ(i) = 11 ± 1. This value is comparedwith results from previous experimental investigations and is in good agreement with theoretical predictions.
Theory of Raman Scattering from Excitons
Authors: Peuker K. , Enderlein R. 
Published: July 2007

AbstractThe scattering cross section for Raman lines due to the creation of excitons in the final state of the crystal is calculated. According to the selection rules Raman scattering by p‐exciton is possible for allowed interband transitions, while in the case of forbidden transitions Raman scattering will occur between the ground state of the crystal and s‐ and d‐exciton levels. Analytical expressions for the Raman cross section are derived using a Green's function formulation. In discussing the experimental prospects for the observation of Raman scattering from excitons resonance and non‐resonance scattering are distinguished. The appropriate scattering efficiencies are estimated for CdS and the yellow exciton series of Cu2O.
X‐Ray Photoemission Measurements of the Valence‐Band Density of States of Sb and InSb
Authors: Vesely C. J. , Kingston D. L. 
Published: July 2007

AbstractThe valence‐band density of states has been measured for both crystalline Sb and InSb by X‐ray induced photoemission using 1253.6 eV Kα X‐rays of Mg. The results are compared with theoretically determined band structure and density‐of‐states calculations. A peak observed in the InSb curve at −6 eV is interpreted as being due mostly to s—p‐like bands of the Sb.
Electronic Correlation Effects (Exciton Manifestation) in the Single‐Particle Band Structure of Nonmetallic Crystals II. Investigation of a Model
Authors: Zimmermann R. 
Published: July 2007

AbstractThe appearance of excitonic satellites is the most pronounced feature due to electron correlation in the band structure of nonmetallic crystals. The general theory presented in a foregoing paper [1] is applied to a model of an insulator with parameter values appropriate to the alkali halide CsI. Only four bands with tight‐binding energies and one exciton line are taken into account. Numerical results are given for self‐energy, spectral function, and density of states in the main bands and the satellite bands.
Evaluation of Acoustoelectric Wave Vectors and Amplitudes from X‐Ray Diffraction Experiments
Authors: Köhler R. , Möhling W. , Peibst H. 
Published: July 2007

AbstractOn the basis of a theory presented earlier [1] diffraction phenomena in CdS crystals with acoustoelectrically generated lattice vibrations are analyzed. Evidence for the generation of a second harmonic is given. Wave vectors and amplitudes of first and second harmonics are calculated from measured changes of reflection curves. The increase of the integrated intensities in dependence on the vibration amplitudes is evaluated, and a model for the transition from dynamical to kinematical diffraction behaviour is discussed.
Nernst‐Ettingshausen and Seebeck Effect of Pure and Electron‐Irradiated Tellurium at Low Temperatures
Authors: Saffert R. , Schapawalow J. , Landwehr G. , Gmelin E. 
Published: July 2007

AbstractFor the first time experimental data of the Nernst‐Ettingshausen effect at low temperatures in tellurium are reported. Measurements of resistivity, Hall coefficient, Seebeck coefficient, and Nernst‐Ettingshausen coefficient on the same sample allow to deduce directly the scattering exponent r, which characterizes the energy dependence of the relaxation time τ. The results clearly reveal a strong anisotropy in the scattering factor r. This is explained by the presence of dislocations. Irradiations with 1 MeV electrons at low temperatures confirm earlier results on the recovery stages I and II in tellurium. It is demonstrated that the Nernst‐Ettingshausen effect is a very useful tool to decide whether recombination or only rearrangement of radiation induced defects occurs during sample recovery.
On Variable Range Hopping near the Fermi Energy One‐Dimensional Systems
Authors: Maschke K. , Overhof H. , Thomas P. 
Published: July 2007

AbstractModel calculations on variable range hopping conduction in quasi‐one‐dimensional systems are presented. It is shown that the temperature behaviour of the conductivity depends strongly on the geometry of the sample consisting of 1D strands. Comparison with an analytical theory is made. Careful numerical evaluation of an integral in the latter approach is necessary to obtain reasonable agreement with the results of the model calculation.
Nuclear Magnetic Resonance in IB–III–VI2 Semiconductors
Authors: Spiess H. W. , Haeberlen U. , Brandt G. , Räuber A. , Schneider J. 
Published: July 2007

AbstractNuclear magnetic resonance spectra of Cu63 and Al27, Ga69 and In115 have been recorded in ternary IB–III–VI2 semiconductors, which crystallize in the tetragonal chalcopyrite structure. Nuclear electric quadrupole coupling constants have been determined and are discussed in connection with the structural parameters of these compounds, which were determined by X‐ray diffraction.
Electron and Mössbauer Spectra of M2SbxSn1−xCI6 Mixed Crystals
Authors: Ionova G. V. , Makarov E. F. , Ionov S. P. , Aleksandrov A. Yu. 
Published: July 2007

AbstractOn the basis of MSössbauer spectra, a packing and nearest neighbour arrangement model is proposed in M2SbxSn1−x Cl6 mixed crystals. The electron spectra of the pure (x = 1) and mixed crystals are discussed in terms of this model.
Core Transitions from the Al 2p Level in Amorphous and Crystalline Al2O3
Authors: Balzarotti A. , Bianconi A. , Burattini E. , Grandolfo M. , Habel R. , Piacentini M. 
Published: July 2007

AbstractThe soft‐X‐ray spectra of aluminium oxide in the polycrystalline γ and amorphous forms have been investigated in detail with improved resolution using the synchrotron radiation of the Frascati electron synchrotron. In contrast to a previous measurement, it is found that the L2,3 threshold starts at almost the same energy in both forms. The sharp peaks observed at the absorption edge are interpreted as excitons. This picture fits well both with ESCA results and with the optical spectra at the fundamental edge in the ultraviolet. It is suggested that metastable excitons are responsible for the intense structure observed at (82.6 ± 0.3) eV in the ordered phase and lacking in the amorphous phase. The spectral features of crystalline alumina are analyzed on the basis of the band structure. The modifications induced by the lack of long‐range order in the amorphous samples are discussed thoroughly.
Isotope Effect in Self‐Diffusion of Cs in Single Crystals of CsI
Authors: Klotsman S. M. , Polikarpova I. P. , Tatarinova G. N. , Timofeev A. N. 
Published: July 2007

AbstractThe simultaneous diffusion of Cs‐131 and Cs‐137 has been measured over the temperature range 470 to 600°C. The isotope effect was measured by the method of separation of the radiations of the two isotopes. The strength of the isotope effect is E = ∫ δK = (0.54 ± 0.02) and is independent of temperature within the experimental error. This indicates that the contribution of divacancies (cation‐anion vacancy pairs) to the selfdiffusion in CsI is small and the predominant mechanism of self‐diffusion in these crystals s the diffusion via free monovacancies.
The Magneto‐Seebeck Coefficient of Bismuth Single Crystals
Authors: Uher C. , Goldsmid H. J. 
Published: July 2007

AbstractThe magneto‐Seebeck Coefficients α11 (B3) and α33 (B1) have been measured for pure bismuth crystals between about 20 K and room temperature in magnetic fields of up to 5.5 T. The observed behaviour has been compared with a theory due to Korenblit. It appears that a phonon‐drag component of the Seebeck coefficient at very high fields persists up to well above liquid nitrogen temperature. However, some features of the results are not in accordance with theory.
The Fermi Surface of White Tin from RF Size Effect Measurements
Authors: Matthey M. M. M. P. , Devillers M. A. C. , de Vroomen A. R. 
Published: July 2007

AbstractExtensive results of RF size effect measurements on the Fermi surface of white tin are presented. The data are interpreted for the larger part and a set of unambiguously determined points on the Fermi surface is given.
Optical Pumping and Transverse Magnetic Field Effect for Excitation above the Band Edge in p‐Type Semiconductors
Authors: Fishman G. , Hermann C. 
Published: July 2007

AbstractThe polarization of the luminescence light shows the importance of the thermalization time for electrons, excited in the conduction band by circularly polarized light of energy larger than the band gap. The influence of the thermalization time on the oscillations of the light polarization as a function of the excitation energy is discussed and applied to GaSb and GaAs. Besides, the effect of a transverse magnetic field (”︁Hanle effect„) in a three level atomic system is extended to a semiconductor. This allows to explain the Hanle effect that had not yet been interpreted for such an energy of excitation in a semiconductor. A new form of Hanle line is predicted and the experimental conditions to observe it are specified.
An Exact Solution of a New Superconducting State
Authors: Fink H. J. , Poulsen R. S. 
Published: July 2007

AbstractAn exact solution of a new superconducting state is obtained which exists for DC currents larger than the critical current in thin wires. The order‐parameter is zero at all times at certain points in the whisker, thereby permitting the phase to slip at a constant rate, a consequence of which is a de potential difference between the separate singly‐connected superconducting regions. These solutions are periodic in space and lead to voltage steps in the do voltage‐current characteristic. It is proven in the limit when the zeros of the order‐parameter are far apart that these solutions are stable.
State Equation of the Ising Model in the Ladder Approximation
Authors: Sadreev A. F. 
Published: July 2007

AbstractThe three‐dimensional Ising model for the case S = ½ in an external magnetic field is considered by the diagram expansion of the Green temperature function. The state equation of the Ising model is proposed in the ladder approximation. The calculation of the state equation is given as magnetization curves for the temperature region T ⪆ Te and for magnetic fields H = 18 and 5 kOe. Also the Tyablikov equation is solved for the same temperatures and magnetic fields. The comparison shows a better agreement of the ladder approximation with the experimental data than the molecular field approximation or the Tyablikov equation.
The Influence of “Rotational” Lattice Deformation States on the F Center Emission
Authors: Ascarell G. 
Published: July 2007

AbstractRecent ENDOR measurements of the relaxed excited state of the F center indicate that this state is p like. Previous theories of the temperature dependence of the radiative lifetime of the F center and of the Stark effect in emission are based on the assumption that the excited state is s like with an admixture of the p like states produced by the interaction with Γ modes. The present model supposes instead an extended p like excited state and a large lattice relaxation of Γ symmetry. The electronic state and the associated lattice are described by an appropriate vibronic state. It is assumed that a series of rigid rotator “rotational” states can be associated with each of the forementioned vibronic states. These “rotational” states are interpreted as describing the rotation of the center of mass of the nearest neighbour ions around the geometrical center of the vacancy. The Stark effect can be explained as having both an electronic and an ionic component. The latter is very much enhanced by the local electric field produced by the change of the electronic charge distribution resulting from the applied field. The ionic contribution to the Stark effect is larger than the electronic one. The changes of lifetime produced by the applied field do not depend on the direction of polarization of the emitted light in agreement with the experimental result. The major difficulty of the model is that it predicts no polarization of the emission. This is contrary to the experimental result. To explain the observed effect a selective population of some of the pi states must be assumed during lattice relaxation in a crystal subject to an external electric field.
Temperature Dependence of the Nuclear Spin Relaxation Rate of Liquid l15In
Authors: Halder N. C. 
Published: July 2007

AbstractTemperature dependence of the atomic structure and self diffusion coefficient have been considered to predict the temperature dependence of the nuclear magnetic relaxation rate W1m and the nuclear quadrupolar relaxation rate W1q. The present calculation indicates that substantical a mount of the relaxation rate comes from the nuclear quadrupolar interaction. While Wlm increased from 3.677 to 6.894 ms−l, W1q, decreased from 0.276 to 0.070 ms−1 in the temperature range 170 to 650 °C.
On the Theory of Rate Processes in Condensed Media
Authors: Fain V. M. 
Published: July 2007

AbstractA general theory of electronic transitions in condensed media is developed which describes in particular various possible chemical reactions in condensed media. The approximations used are: the Born‐Oppenheimer adiabatic approximation, the Condon approximation to describe the dependence of the matrix elements of the electron transition, and the harmonic approximation to describe the nuclear motion in the initial and final electronic states. In the framework of these approximations general expressions are obtained for the rate constants of the corresponding reactions. In a certain approximation these constants can be reduced to the form given by the Eyring theory of rate processes. In the other region the expressions for the rate constants are obtained which are of an essentially different character and are interpreted in terms of the theory of the multiphonon transitions. Reactions are considered which occur only with a conformation transition of the system as well as those which are accompanied by conformation transitions and by breaking of a chemical bond.
Far‐Infrared and Raman Studies on (NH4)Cl1−xBrx Mixed Crystals in the Cubic Phases β and δ
Authors: Bauhoper W. , Genzel L. , Jahn I. R. 
Published: July 2007

AbstractThe lattice modes in the cubic phases β and δ of the mixed crystal system (NH4)Cl1−xBrx are investigated by far ir and Raman spectroscopy. The system (NH4)Cl1−xBrx shows an optical one‐mode behavior. Therc is sonie evidence for a two‐mode behavior in the acoustical frequency region.
Atomistic Formulation for the Melting Point of Metallic Elements
Authors: Plendl J. N. 
Published: July 2007

AbstractThe formulation for the melting point of metallic elements, derived from relations recently deduced from an analysis of the infrared spectra of solids, involves three atomic characteristics which decisively determine the melting point. They are: the critical amplitude of the thermal vibrations, the atomic coordination valency and a structural parameter, the reciprocal of which is proportional to the atomic packing density. The higher the bond strength of the atonis within the atomic coordination in the lattice (atomic coordination valency) and the lower the collision frequency of the vibrating atoms (proportional to the atomic packing density and to the eigen frequencies), the higher a temperature is required to produce the critical amplitude of the atomic vibrations, which eventually causes the breakdown of the lattice bonds, and so starts the melting process. The formulation has been verified by the agreement obtained between experimental and calculated data of 20 metallic elements with strong bondings. In relating the critical amplitude of the atomic vibrations with the data of full‐range thermal expansion up to the melting point, an atomistic explanation of the phenomenon of thermal expansion has been developed, without recourse to asymmetrical vibrations, nonexistent in metallic elements with cnbic structures.
Polarization of the Luminescence of Cubic ZnS:Mn Single Crystals
Authors: Scharmann A. , Schwabe D. 
Published: July 2007

AbstractThe polarization of the visible luminescence of cubic ZnS:Mn single crystals under excitation with light has been investigated. The influence of birefringence of faulted ZnS on the polarization results has been calculated. The 585 nm emission band, attributed to Mn as impurity, is never polarized, whereas other emission bands at 700, 475, 410, and 385 nm show polarization under polarized excitation. The experimental results exclude band‐models. The 585 nm emission probably originates from a Mn‐center with symmetry Td. The other emission bands can only originate from centers having symmetry C3v, C2v or Cs.
Contribution of Plasmon and Quasi‐Elastic Scattering to the Kikuchi Structures of Si Measurement and Comparison with the Dynamical Theory
Authors: Meyer‐Ehmsen G. , Siems A. 
Published: July 2007

AbstractAbsolute intensity measurements of the Kikuchi structures in the electron diffraction diagram (75 keV) of a thin Si single crystal have been carried out. The contributions of plasmon and quasielastic scattering have been measured separately by energy analysis. The measured line profiles and band edges are compared with the theory. From the intensity distribution due to plasmon scattering the structure potential V220 and the absorption potentials P000 and P220 could be determined. From the shape of the band edges it can be deduced that the contribution of Umklapp processes to the plasmon scattering is less than 5%. The intensity profile of the quasielastic scattering can mainly be interpreted by phonon scattering.
Luminescence and Optically Detected EPR of Close F‐Center Pairs in KCl
Authors: Schnegg P. A. , Jaccard C. , Aegerter M. 
Published: July 2007

AbstractBy an appropriate optical treatment at RT the distance separating the members of F‐center pairs can be decreased, giving rise to different optical and magnetic properties, revealed by the existence of a spin dependent non‐radiative disexcitation mechanism. A model with an exchange spin‐spin interaction is analyzed and compared with experiments at LHeT (variation of the luminescence with an applied magnetic field, optical detection of the EPR, and relaxation processes). The observed effects are related with population changes in the ground state caused by optical pumping and they are sensitive to the mixing of the states produced by the different interactions. The average exchange energy is found to range between the hyperfine and the Zeeman energy depending of the state of aggregation. The paramagnetic resonance occurs in the ground state (g = 1.998, linewidth 52 G) and the relaxation times range between 25 and 250 ms, depending of the optical pumping rate. The relation predicted by the model between the luminescence variation and the relaxation rate agrees with the experiments.
Phonon Dispersion Relations in Copper and Silver by a Modified Sharma‐Joshi Model
Authors: Goel C. M. , Pandey B. P. , Dayal B. 
Published: July 2007

AbstractThe Sharma and Joshi model has been modified by substituting an exact expression for Bardeen's G‐function in the electron‐ion interaction term and to include angular forces, in addition to usual central forces, proposed by Clark, Gazis, and Wallis, up to the second neighbours. The modified model has been applied to study the phonon dispersion relations in copper and silver. The results obtained show an excellent agreement with experimental data.
Optical Modulation Spectra of CdP2 Crystals and Ni‐CdP2 Schottky Barriers
Authors: Radautsan S. I. , Syrbu N. N. , Kiosev V. K. 
Published: July 2007

AbstractThe relative photosensitivity spectra of Ni‐CdP2 Schottky barriers have been investigated experimentally; in these spectra a structure consisting of nine maxima has been observed in the intrinsic absorption region. The anisotropy of the observed transitions has been investigated using electroabsorption or spectral distribution of the photoelectromotive force or photoconductivity. The splittings of the bands responsible for the observed transitions have been determined. The fine structure of photoelectromotive force caused by high‐frequency phonons involved in the transitions at K = 0 is considered.
On a Self‐Consistent Approximation Procedure with Application to the Hubbard Model
Authors: Elk K. 
Published: July 2007

AbstractConsidering a very general derivation of Dyson's equation an approximation procedure is discussed, which exhibits a summary of different known methods. Concerning the Hubbard model a generalization of Roth's procedure follows. In particular it is possible to obtain a self‐consistent method.
Inelastic Neutron Scattering by Cerium Hydrides I. Experimental
Authors: Vorderwisch P. , Hautecler S. 
Published: July 2007

AbstractInelastic neutron scattering measurements have been performed on polycrystalline samples of the cerium hydrides CeH1.98and CeH2.72at 70 °C in order to study their lattice dynamics. For the data analysis the spectrometer resolution has been carefully taken into account. A qualitative interpretation of the results clearly shows the importance of hydrogen‐hydrogen interactions. A diffusive motion of hydrogen could not be observed for both samples.