bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Slow Vibrational Relaxation on Anomalous Stokes‐Shifted Luminescence and Energy Transfer in Solids
Authors: Dexter D. L. 
Published: July 2007

AbstractAn analysis is presented of the emission spectrum to be expected from model centers in vibrationally excited and electronically excited states. It is shown that for centers which normally exhibit a sizable Stokes' shift there will be, for a short time following excitation, a large component of emission at approximately twice the usual Stokes' shift. This anomalous emission would be detectable by ultra‐fast (pico‐second) excitation and detection, and in selected systems by conventional means. Its measurement would provide an estimate of the vibrational relaxation time of the center. The implications of the relaxation rate on electronic energy transfer between like species are briefly discussed.
A Model for the Phase Diagram of Fe(PdαxPt1−x)3 Showing a Quadruple Point
Authors: Wissel Ch. 
Published: July 2007

AbstractThe pseudo‐binary Cu3Au type ordered alloys Fe(PdxPt1−x)3 are described using a Heisenberg Hamiltonian. The free energy and the sublattice magnetization are calculated in the molecular field approximation at T = 0 and near the transition to the paramagnetic state for all values of x (0 ≦ x ≦ 1). For special values of the parameters full agreement is obtained with the experimental results including the quadruple point. In other cases some other interesting results are obtained.
Electron and Hole Mobilities in Solid and Liquid Benzene C6H6
Authors: Hirth H. , Stöckmann F. 
Published: July 2007

AbstractThe mobility of electrons and holes has been deduced in the temperature range −100 to 60 °C from transit time measurements. The electron mobility in solid benzene can be described by μ ∝ T−2, which may be explained by interaction with acoustic phonons. The hole mobility in solid benzene rises exponentially with increasing temperature. The mobility is controlled by interaction with traps depending on the purity of the samples. Approaching the melting point there is a reduction of the electron and hole mobility. This may be explained by thermally produced lattice defects which show up already some ten degrees below the melting point. In liquid benzene the mobilities are three orders of magnitude smaller rising slightly upon temperature. In the liquid polaron‐like states are formed, where the charge carriers propagate by an intermolecular hopping mechanism.
Hot Electron Kerr Effect in Semiconductors with Non‐Parabolic Dispersion Law of Energy
Authors: Almasov L. A. , Dykman I. M. 
Published: July 2007

AbstractThe phenomena of birefringence and plasma frequency splitting in semiconductors with isotropic non‐parabolic dispersion law of carrier energy in the presence of a dc electric field have been considered on the basis of expressions obtained in a previous work [l]. n‐InSb is taken as an example for the numerical calculations. It is shown that the phase shift due to the birefringence can attain a considerable value. The effect can, in principle, be used for creation of modulators, shutters, and circulators of electromagnetic radiation in the infrared range.
Thermal Conductivity of Ni++ Doped AgCl
Authors: Donecker J. 
Published: July 2007

AbstractThe thermal conductivity of quenched AgCl crystals doped with 190 to 3300 ppm Ni++ has been measured between 2 and 70 °K. The values have been analysed within the framework of the relaxation‐time approximation. It was not possible to describe the temperature dependence of each of the experimental curves or their concentration dependence solely with a Rayleigh‐type phonon scattering mechanism. A perturbation treatment of the scattering by a mass‐defect complex yields deviations from the Rayleigh behaviour at high frequencies. But these theoretical deviations cannot explain the experimental data. It is suggested that resonance scattering of the vacancy is the additional scattering mechanism. The values of the Rayleigh‐scattering parameters of the complex are discussed.
On the Spin Wave and Exciton Density of States in an Antiferrornagnet
Authors: Baryakhtar V. G. , Petrov E. G. 
Published: July 2007

AbstractThe singularities in the spin wave and exciton density of states are considered. It is shown that the strongest singularity in the magnon density of states g(ω) has the form g(ω) ∼ |ω – ωc|−½. This singularity is due to the constant‐energy surface. The strongest singularities in the exciton state density are observed for wave vectors which lie on the straight lines directed from the centre of the first Brillouin zone to the centres of its hexagonal faces.
Study of Colour Centres in BaCl2 and BaBr2
Authors: Houlier B. , Yuste M. , Chapelle J. P. , Taurel L. 
Published: July 2007

AbstractAfter additive or electrolytic coloration, BaCl2, and BaBr2, single crystals exhibit F‐centres, whose proper symmetry is C3. The hyperfine spectrum in BaCl2 can be accounted for with the assumption that there exist two types, FI and FII, of F‐centres, and that each hyperfine constant referring to a Ba2+ ion (k) is given by an empirical expression ak = gN A/d, where dk is the distance between the ion k and the F‐centre. The two types of F‐centres have the same g‐tensor with principal values, in the case of BaCl2, gXX = 1.966; gYY = 1.976; gZZ = 1.986. The F‐centres can be optically bleached at room temperature, and then regenerated by heating above 100 °C.
Mössbauer Effect Studies of 57Co and 57Fe in β‐Rhombohedral Boron
Authors: Stanke F. , Parak F. 
Published: July 2007

AbstractThe behavior of 57Fe and 57Co doped β‐rhombohedral boron was investigated by means of Mössbauer spectroscopy. Samples prepared by diffusing 57Fe at temperatures above 1000 °C and 57Co at temperatures of 1500 °C or higher showed a reproducible quadrupole interaction and a strongly anisotropic ƒ‐factor. Using combinations of the different parameters obtained from the spectra it was attempted to determine the position of the impurities. There is some evidence for an incorporation within the 28 atom subgroup. It was shown that the sites occupied by Co and Fe do not have a C5 v point symmetry.
X‐Ray Spectra of Disordered Alloys
Authors: Babanov Yu. A. , Sokolov O. B. , Sorokina M. F. 
Published: July 2007

AbstractA formula for the X‐ray spectrum intensity is derived taking “cross‐over” transitions into account. The “cross‐over” transition is shown to be only one of possible mechanisms explaining the additional maximum in the X‐ray spectra of disordered binary alloys. The results of the calculation of the intensity by the Green's function method are used for the qualitative interpretation of the Lβ2‐emission bands of Ag and Pd in a set of disordered alloys.
Light Scattering and Infrared Absorption in Cuprous Oxide
Authors: Reydellet J. , Balkanski M. , Trivich D. 
Published: July 2007

AbstractA great number of bands have been observed by light scattering and infrared absorption in Cu2O crystals corresponding to transitions most of which are normally forbidden in the perfect crystal. An analysis of the symmetry properties of the lattice modes in the presence of defects is given. In particular the role of each symmetry site for the defects is investigated and the observed modes interpreted as being due to actived band modes and localized modes. Double phonon processes are observed as well as the normally allowed optical transtions for the perfect crystal.
Reflectivity and Magnetoreflectivity Measurement on n‐Type PbSe
Authors: Mycielski A. , Aziza A. , Balkanski M. , Moulin M. Y. , Mycielski J. 
Published: July 2007

AbstractInfrared refectivity and magnetoreflectivity measurement were performed at 30 °K on‐type PbSe samples with electron concentrations rangingfrom 4.5 × 1017 to 4.3 × 1018cm−3. From the best fit of experimental and theoretical curves the electron effective mass and relaxation time were determined as functions of electron concentration. The dependence of the effective mass on electron concentration is in good agreement with Kane's model of the conduction band.
Higher Anharmonic Contributions to Diffuse X‐Ray Scattering
Authors: Reid J. S. 
Published: July 2007

AbstractAn investigation has been made into the importance of higher‐order anharmonic interference terms between the one‐phonon and multiphonon scattering. The second‐order terms are discussed in detail and an exact expression is also given for the general term involving the direct coupling of the one‐phonon and n‐phonon scattering processes. The most interesting second‐order process has been evaluated directly for the alkali halides NaF, NaCl, NaBr, NaI, KCl, and KBr with the scattering vector lying along [100]. It is concluded that the first‐order term is dominant most of the way to the zone boundary at temperatures up to at least 600 °K. This rapid convergence appears to continue for the third and higher‐order diagrams and these are not expected to contribute significantly to experimental intensities. However, near the zone boundary the second‐order term can be a few percent of the total scattering and hence should be considered.
Remarks on Screening of Positive Particles in an Electron Gas
Authors: Stachowiak H. 
Published: July 2007

AbstractThe March‐Murray formalism is used in the first approximation to study two effects which are neglected by the static RPA approximation. These are the exchange Hartree‐Fock correction and the effect of the small mass of the positive particle in the case of a positron and their influence on the screened potential of the positive particle is investigated. The results are of interest for the theory of positron annihilation in metals.
Magnetic and Excitonic Instabilities in a Two‐Band Model
Authors: Teleman E. , Ciobanu G. , Fazakas A. B. 
Published: July 2007

AbstractA two‐hand model with short range interactions between electrons is studied in order to find magnetic and excitonic instabilities. Using the vertex part equation method, some general conditions for the appearance of instabilities leading to phase transitions are derived. Due to the existence of different coupling constants and the possibility of various band shapes, many cases appear and are discussed.
Debye Theory of Dislocations
Authors: Mihály L. G. , Tichy G. G. 
Published: July 2007

AbstractContinuum models of dislocation lead to divergencies in the core. Using the Debye model, i. e. a cutoff at the wave vector kD, the divergency, inherent to the continuum approximation, disappears and an explicit expression for the cutoff radius in the coordinate space is obtained. The static Green's function of the elasticity and the stress field of a screw dislocation are calculated and shown that in the classical elasticity theory a singularity appears on the surface along which the dislocation is introduced. This stress however can be neglected because of the atomic structure of the crystal.
The Hindered Rotation in Various Fields of Cubic Symmetry
Authors: Beyeler H. U. 
Published: July 2007

AbstractThe hindered rotation in cubic fields of various shapes and intensities is studied. The “Devonshire Model” is extended to include cubic fields being linear combinations of spherical harmonics of order four and six. In contrast to Devonshire's potential, this two parameter manifold of potentials contains some with the energy minima at the 〈110〉 directions. Agreement is found between the low‐lying rotator levels in a large hindering potential and these of harmonic oscillators localized in the minimum wells of the potential.
Thermomodulation of Optical Parameters in Tellurium
Authors: Herrmann Kabin , Dumröse H. 
Published: July 2007

AbstractA temprature modulation of the optical absorption, x, and the reflection coefficient, R, in tellurium is made for the first time by a periodicallyi haeating CO2 ‐laser beam. For highlyi doped tellukrium the thermoreflection spectra show a stong temperature and polarisation dependence and are discussed as far as fpossible in terms of xisting energy band models. Thermoabsorption in the optical band‐gap region may be interpreted by indirect transitions and show that the temperature dependence of the band gap is not the dominating process.
Binding Energy and Compressibility of Alkali Metals
Authors: Kachhava C. M. 
Published: July 2007

AbstractThe binding energy and compressibility of alkali metals are calaulated from the Ashcroft's empty core model potential on the basis of core radii obained by the fittings to the phonon data. The importance of overlap exchange repulsion and the correct dielectric screening theory is discussed. On the whole, a very satisfactory agreement between theoretical results and experimental data is obtained from these considerations.
Spectre d'absorption et champ cristallin agissant sur I'ion Nd3+ dans I'oxysulfure de neodyme
Authors: Souillat J. C. , Rossat‐Mignod J. , Linares C. 
Published: July 2007

AbstractDes spectres d'absorption nous ont permis de préciser la structure électronique de l'ion Nd3+ dans le composé Nd2O2S. Les paramètres de Slater F2 = 326,3 F4 = 47,95, F6 = 5,26 cm−1 et la constante de couplage spin‐orbite ζ = 855,5 cm−1 rendent compte de la structure de l'ion “libre” avec une déviation quadratique moyenne de 67 cm−1. Dans le cadre du couplage intermédiaire les niveaux de champ cristallin issus de 4I9/2, 4F5/2, 4F5/2, 4F7/2 et 4F9/2 nous ont permis de déterminer les paramètres de champ cristallin.
The Raman Spectrum of Amorphous Tellurium
Authors: Brodsky M. H. , Gambino R. J. , Smith J. E. , Yacoby Y. 
Published: July 2007

AbstractThe reduced Raman spectrum of amorphous Te consists of broad maxima at 90 and 157 cm−1. The spectrum reflects the vibrational density of states and is interpretable in terms of disordered chains. The highest vibrational energies of the disordered chains are higher than the corresponding energies of the ordered chains in crystalline Te. The higher vibrational energies in the amorphous form are due to the reduced effectiveness of long range forces which tend to depress vibrational energies in the crystalline form.
Investigation of Hf Interaction of 181Ta Dissolved in the Ni Lattice
Authors: Bożek E. , Hrynkiewicz A. Z. , Goloczewski J. , Goss R. , Styczeń J. 
Published: July 2007

AbstractThe hyperfine field at Ta nuclei diffused into a nickel foil was studied by the PAC method both with and without and external polarizing magnetic field. The value Hhf = (−82.6 ± 1.1) KG is smaller than the reported one of 90 kG, which could be explained by the large field distribution observed. For assumed Lorentzian shape of the field distribution FWHM (δ) = 22%.
Galvanomagnetic Properties of HgTe in High Magnetic Field
Authors: Zakrzewski T. , Dziuba E. Z. 
Published: July 2007

AbstractThe dependence of the Hall coefficient and conductivity of mercury telluride crystals on the magnetic field has been investigated at temperatures 4.2, 77, and 300 K. The results are explained with the assumption that the transport phenomena are caused not only by electrons and holes but also by additional low mobility carriers. These additional low mobility carriers are assigned to an impurity band.
Anomalous Spin‐Lattice Relaxation by Quasi–Spin Waves in K4Fe(CN)6·3H2O
Authors: Kubarev Yu. G. , Moskvich Yu. N. , Zeer E. P. 
Published: July 2007

AbstractThe influence of quasi‐spin waves on the spin‐lattice relaxation time, T1, in ferroelectric K4Fe(CN)6·3H2O crystals is considered. It is shown that the quasi‐spin waves theory explaines the anomalous behaviour of T1 near the ferroelectric transition temperature Tc. The calculated value of the critical shortening of T1 at Tc and the angular dependences of T1 near Curie temperature agree well with experimental data.
On the Bi‐Exciton Formation in Crystals
Authors: Bobrysheva A. I. , Miglei M. F. , Shmiglyuk M. I. 
Published: July 2007

AbstractThe binding of two free excitons into a bi‐exciton due to direct exciton‐exciton interaction is studied. The process of bi‐exciton formation via exciton–phonon interaction is not taken into account. By group theory methods the wave functions of two interacting excitons are constructed for a model applicable to CuCl and Cu2O crystals. Making use of these functions, the Fourier transform of exciton‐exciton interaction energy is calculated. By the Green's function method the dissociation energy of the bi‐exciton is obtained in the adiabatic approximation (the exciton‐exciton interaction energy is much smaller than the ionization energy of the exciton). A numerical estimate and comparison with experimental values is made for CuCl crystals.
Akustische Kernresonanz an Na23 im NaF‐Einkristall
Authors: Grande S. , Shutilov V. A. , Fershtat L. N. 
Published: July 2007

AbstractBei Zimmertemperatur wurde die akustische Sättigung der magnetischen Kernresonanz von Na23 mit Hilfe von Impulsverfahren im NaF‐Einkristall beobachtet. Die T2‐Werte sind anisotrop und werden hauptsächlich durch Dipol‐Wechselwirkung bedingt. Die Spin–Gitter‐Relaxationszeit T1 ≈ 5 s wird überwiegend durch Quadrupoleffekte verursacht, zeigt jedoch eine Winkelabhängigkeit. Die Ultraschall‐Sättigung der Übergänge Δm = ±2 erfolgt mit akustischen Längswellen über die Quadrupol‐Spin–Phonon‐Kopplung. Es wird die Frequenz–Amplitudencharakteristik der Sättigung und daraus die Linienbreite der akustischen Sättigung bestimmt. Die Spin–Phonon‐Kopplungskonstante und γ∞ werden errechnet. Aus dem experimentellen Abfall der Sättigung bei Einstrahlung am Rand der Linie wird die Rolle des Dipol‐Reservoirs bei der akustischen Sättigung behandelt.
Optical and Magnetooptical Absorption in Pure HgTe
Authors: Saleh A. S. , Fan H. Y. 
Published: July 2007

AbstractInfrared absorption in pure, n‐type HgTe has been studied in the wavelength range 3.5 to 35 μm. At ≈ 12 °K, the absorption continues to decrease with decreasing photon energy showing that the energy gap is < 40 meV. The absorption at 300 °K rises with decreasing photon energy after passing a minimum at ≈ 55 meV, due to effect of free carriers. Under an applied magnetic field, up to 30 kG, the absorption at a fixed wavelength shows oscillatory variation with the field strength. These oscillations give a determination of the effective mass and the g‐factor of conduction electrons, and show that the energy gap is close to zero.
Propagation of Surface Spin Waves in the Inhomogeneous Field of Rectangular YIG Samples
Authors: Schilz W. 
Published: July 2007

AbstractThe propagation velocity and the coupling of surface spin waves to the outside rf field in rectangular YIG samples is strongly influenced by the local variation of the internal magnetic field. An experimental study of these effects is made and a clarification of the reflection mechanism of surface modes near the ends of the sample is presented.
Field Dependence of Exciton‐Induced, Contact‐Limited Photocurrents in Molecular Crystals
Authors: Killesreiter H. , Baessler H. 
Published: July 2007

AbstractThe current–field dependence of contact‐limited photocurrents resulting from dissociation of Frenkel excitons at the interface between molecular crystals and a metal or a fatty acid layer is investigated. In the field range 3 × 103 Vcm−1 < F < 105 Vcm−1 both photocurrent and dark current follow a j = j0 (1 + bF) relationship with no indication of a field‐independent limiting current. An explanation is given in terms of the Onsager model for thermally activated diffusional escape of a carrier inside the crystal from the attractive Coulombic potential of its countercharge. At higher fields the Frenkel‐Poole effect becomes operative. It is concluded that exciton dissociation initially produces a thermalized carrier inside the crystal.
The Korringa‐Kohn‐Rostoker and Augmented Plane Wave Method for Non‐Spherically Symmetric Muffin‐Tin Potentials
Authors: John W. , Lehmann G. , Ziesche P. 
Published: July 2007

AbstractBy means of an appropriate description of the scattering states of non‐spherically symmetric potentials a generalized KKR method is derived. As an example a lattice with several atoms per unit cell is considered. Also a generalized APW method is derived.
Zur Ultrarot‐Absorption in Ionenkristallen
Authors: Knohl U. 
Published: July 2007

AbstractDie ultrarote Absorption und Reflexion von Lithiumfluorid wurden bei 7,5, 70 und 300 °K in einem Schalenmodell mit deformierbaren Schalen [4,5] berechnet, wobei Anharmonizität dritter Ordnung berücksichtigt wurde. Es zeigte sich, daß die anharmonischen Beiträge der Coulomb‐Kräfte von gleicher Bedeutung sind wie diejenigen der Kräfte kurzer Reichweite. Der Einfluß des nicht‐linearen Dipol‐Moments zweiter Ordnung stellte sich als vernachlässigbar heraus bei Frequenzen unterhalb der zweieinhalbfachen Resonanzfrequenz. Die Übereinstimmung zwischen Experiment und Theorie mit einem anpaßbaren Parameter ist sehr gut bei tiefen Temperaturen, wird jedoch schlechter bei höheren Temperaturen wegen der Vernachlässigung biquadratischer Glieder in der Anharmonizität.
Exciton Interaction in CdSe
Authors: Bille J. , Liebing H. , Mengel P. 
Published: July 2007

AbstractThe emission spectrum of CdSe platelets has been observed at 2 K under laser excitation from 0.1 to 10 MW/cm2. By light pulses from a frequency‐doubled Nd:YAG laser (531 nm) hot electrons are created in CdSe, which thermalize into the exciton bands within 10−13 s and decay radiatively within 10−9 s. The spectra, obtained by this excitation, show a considerable increase of the temperature of the crystals. By resonant excitation, i.e. direct excitation of the valence band electrons into the exciton bands by a tunable laser, this temperature increase could be avoided. A Bose condensation of the excitons, as expected by Gross et al., was not observed. Instead, results have been obtained which seem to indicate the formation of exciton molecules and the condensation of the excitons into drops with an electron‐hole pair density of about 2 × 1017 cm−3.
Hartree‐Fock Calculation of Electron States in Small Aggregates of Lithium and Beryllium Atoms
Authors: Stoll H. , Preuss H. 
Published: July 2007

AbstractSCF‐MO‐LCGO calculations, which have been performed on small periodic aggregates of Li and Be atoms, are reported. It is shown that properties which are characteristic of solids can be found already in comparatively small systems. The variation of these properties with shape and size of the systems is discussed. In addition effects which are attributed to the influence of the surface are treated, e.g. the fluctuation of charge density and the distortion of lattice in the zone near the boundaries.
A Method for Calculating Signals of NMR‐Pulse Experiments in Solids
Authors: Ernst H. , Schmiedel H. , Schneider H. 
Published: July 2007

AbstractA method for calculating signals of NMR pulse experiments in solids is given which allows to calculate the detailed form of signals between pulses. Applying this method to a multiple pulse cycle given by Mansfield and Waugh‐Huber one is able to discuss the detailed form of the first few echoes. Considering a great number of pulses this method diverges, however.
Spectra of Electronic Excitations in CaF2, SrF2, and BaF2 in the 8 to 150 eV Range
Authors: Frandon J. , Lahaye B. , Pradal F. 
Published: July 2007

AbstractThe characteristic energy losses suffered by a 20 keV electron beam through CaF2, SrF2, and BaF2 films have been measured with a magnetic spectrograph. From the energy loss function — Im ε−1, optical constants are calculated by means of Kramers‐Kronig analysis in the 8 to 40 eV range and are compared with the available reflectance data, especially those obtained with synchrotron radiation. The observed structure is tentatively explained for the three compounds, following a band model based upon symmetry considerations. The origin of the energy losses corresponding to the soft X‐ray range is also briefly discussed.