bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mössbauer studies of low‐temperature radiation damage in α‐iron
Authors: Vogl G. , Schaefer A. , Mansel W. , Prechtel J. , Vogl W. 
Published: July 2007

AbstractThe Mössbauer effect has been used to study radiation damage in α‐iron, doped with 0.6 at% Os and 4 at% Pt. The samples were irradiated in a nuclear reactor at 4.6 K. The Mössbauer nuclei of Ir193 and Au197 were produced by capture of thermal neutrons in Os192 or Pt196, a process which simultaneously could lead to radiation damage. Compared with annealed samples, the average magnetic field was reduced after the irradiation by about 2% and the line width was increased by approximately 30%. Isochronal annealing processes were studied. The annealing of the irradiation effects took place primarily between 90 and 140 K with activation energies in the range between 0.30 and 0.40 eV. These effects are interpreted as mainly due to a vacancy as nearest or next nearest neighbour of the displaced Mössbauer atom combined with an interstitial several lattice sites away from the vacancy. The Mössbauer atom does not come to rest as an interstitial atom. These results are in good agreement with results from computer experiments of Vineyard's group.
X‐ray spectroscopic investigation of the electronic structure of diamond
Authors: Umeno M. , Wiech G. 
Published: July 2007

AbstractThe X‐ray K‐emission band and the so‐called self‐absorption spectrum of diamond have been measured with a concave grating spectrometer using primary excitation. The results are compared quantitatively with recent calculations of the energy band structure, and with the density of states of the valence and conduction bands of diamond. From the experiment the width of the valence band is determined to about 21 eV, while the calculated width varies from 19 up to 31 eV. It is found that structural features in the density‐of‐states curve to a high degree are reflected in the K‐band. X‐ray emission bands together with X‐ray photoelectron spectra seem to yield valuable information about the electronic structure of the valence band of second period elements.
The Jahn‐Teller effect in the 3000 Å Emission of KCl:Tl+: An investigation by time‐resolved emission spectroscopy
Authors: Gerhardt V. , Gebhardt W. 
Published: July 2007

AbstractThe 3000 Å emission of KCl:Tl+ which contains a fast and a slow decay process was investigated by time‐resolved emission spectroscopy. This technique permits sampling of photons which are emitted at a chosen delay time after excitation. Emission and excitation spectra and the polarization of emission were measured separately for both components with and without applied stress. The results give information about the Jahn‐Teller effect of the 3T1u, and 3A1u excited states. It is concluded that the 3A1u‐APES follows the 3A1u‐APES near the potential minima.
Far‐infrared absorption in amorphous III‐V compound semiconductors
Authors: Prettl W. , Shevchik N. J. , Cardona M. 
Published: July 2007

AbstractThe infrared spectra of amorphous films of GaP, GaAs, GaSb, InAs, and Ge prepared by sputtering have been measured from 10 to 4000 cm−1. The absorption spectra in the region of the “optical” phonon frequencies show similarities to the phonon density of states as deduced from Raman scattering but the absorption becomes much smaller at low frequencies. It is shown that while the coupling constant for Raman scattering by an amorphous material varies as the square of the wave vector, it varies in the case of infrared absorption as its fourth power. The results are compared with those of Raman scattering and with the predictions of a simple model.
Atomic structure of Cu3Au and Ni3Fe at temperatures above Tc
Authors: Golosov N. S. , Dudka B. V. 
Published: July 2007

AbstractAtomic configurations of Cu3Au and Ni3Fe which are in agreement with the experimental values of a short‐range order in the first and second coordination shells have been constructed by a Monte Carlo method on a model of 4000 atoms. By studying the atomic arrangement on the sites of the lattice it was established that in the model the short‐range order is not homogeneous. Three‐dimensional complexes of atoms are formed having short‐range order considerably exceeding the average value. The size of the complexes increases with decreasing temperature.
Two‐step excitation of photoluminescence in GaP
Authors: Schindler A. , Bindemann R. , Kreher K. 
Published: July 2007

AbstractDonor‐acceptor pair luminescence and radiation of bound excitons have been excited in GaP using radiation with photon energies lower than the band gap. This anti‐Stokes luminescence is explained by a two‐step excitation process via the deep donor oxygen. Excitation with radiation lower than the band gap results in a very low homogeneous excitation density throughout the bulk of the sample and enables the investigation of the phonon structure of the donor‐acceptor pair bands.
Determination of the domain wall energy from hysteresis loops in YIG
Authors: Guyot M. , Globus A. 
Published: July 2007

AbstractThe energy lost by the continuous pinning and depinning of the domain wall as it moves and the energy lost by the formation and destruction of a fraction of the wall surface may be the origin of the losses which find their expression in the hysteresis loop. This new hypothesis, based on Globus' model, allows to calculate the wall energy γ and the pinning force/Experimentally, only a simple measurement of the loop areas is needful to calculate the γ value, which is in very good agreement with theoretical values deduced from the theory of Landau and Lifshits. In addition, the γ values measured are proportional to the global anisotropy of polycrystals K (K = K1 + σn λs), that results in a very small wall thickness (0.07 μm) which is almost constant as a function of T. The connection between the natural stresses σn and the intrinsic properties is confirmed by revealing a relationship between K, K1, and A.
Solitary excitons in one‐dimensional molecular chains
Authors: Davydov A. S. , Kislukha N. I. 
Published: July 2007

AbstractThe change in time of the state of intramolecular excitation in an one‐dimensional molecular chain is investigated, where its deformability is taken into account. It is shown that the excitation which is accompanied by a local deformation of the chain, can move uniformly along the chain, the size of the region under excitation remaining constant. These excitations in one‐dimensional molecular chains can be called particle‐like excitons or solitary excitons.
Propriétés des alliages InSb1‐xBix. III. Estimation théorique de la bande interdite
Authors: Jean‐Louis A. M. , Duraffourg G. 
Published: July 2007

AbstractLa bande interdite d'un composé hypothétique InBi cristallisant dans la structure de la blende est estimée en utilisant trois méthodes indépendantes basées respectivement sur la règle d'évaluation des effets relativistes de Herman, sur une extension de la méthode des pseudootentiels empiriques de Cohen et Bergstresser et sur le modèle “ssemiconduteur” de Van Vechten. La variation de la bande interdite des alliages InSb1−xBix avec la concentration x est ensuit déduite: dans le domaine des faibles concentrations le calcul conduit à und diminution de al bande interdite de 2,4 eV par mole InBi à comparer avec la valeur expérimentale (3,6V/mole).
Effect of internal excitations of polarons on magneto‐optical absorption and cyclotron resonance in polar crystals
Authors: Devreese J. T. , Kartheuser E. P. , Ward R. , Baldereschi A. 
Published: July 2007

AbstractThe energy spectrum of Fröhlich polarons in a magnetic field is investigated theoretically. The constants of the motion of the system are studied and a “Feynman model” serves as B guide in this study. A crucial difference between the energy spectra of polarons and rigid particles is predicted at rather strong coupling strengthsor large magnetic fields. It is due to the internal structure of the polaron system. When the electron‐LO‐phonon coupling constant becomes large enough to allow internal excitations, a resonance may appear in the one‐phonon continuum. This resonance is split by Zeeman effect at small field values and the components of the multiplet tend asymptotically to the Landau levels with increasing field strengths. The stability of one component at least is enhanced by the magnetic field, so that magnetic fields could be used to reveal internal excitations of polarons, in cyclotron resonance or magneto‐optical absorption experiments. Recent experimental results on magneto‐absorption by excitons are discussed in the light of the present work.
The density of states of the anderson model of cellular disorder with random diagonal and random off‐diagonal elements in CPA
Authors: Braeter H. , Eifrig Th. , Kirsten E. 
Published: July 2007

AbstractUsing a generalized version of the single‐site coherent potential approximation (CPA) the electronic density of states is calculated for the Anderson model of cellular disorder with random diagonal and random off‐diagonal elements. An elliptical probability distribution for the site energies is assumed. The off‐diagonal matrix elements are assumed to be linearly dependent on the site energy. In dependence on the fluctuation widths the electronic density of states in this model can have an appreciably different shape compared to models with non‐fluctuating off‐diagonal elements.
High‐field conduction mechanism in amorphous germanium
Authors: Telnic M. , Vescan L. , Croitoru N. , Popescu C. 
Published: July 2007

AbstractCurrent‐voltage measurements on a‐Ge in the temperature range 77 to 143 °K and the field range 10 to 5 × 104 V/cm are analysed in the frame of the conduction model used to explain low‐field conduction in the T−1/4 region. In this model the conduction is due to non‐degenerate carriers tunnelling without thermal activation between localized states in two linear tails. Assuming that the high field effects concentrate essentially upon the distribution function quantitative expressions are obtained for the current which ensured a good fit to the normalized experimental data for unannealed and annealed a‐Ge.
Hyperfine quadrupole splitting and mössbauer spectra for an orbital doublet
Authors: Bersuker I. B. , Borshch S. A. , Ogurtsov I. Ya. 
Published: July 2007

AbstractA theoretical investigation is made of the effect of vibronic coupling on the line shapes of Mössbauer spectra in an orbital degenerated E‐term system including relaxation transitions among the vibronic states and magnetic hyperfine interaction. The vibronic interaction is taken into account in the limiting case of strong linear coupling and arbitrary second‐order contribution. The quadrupole splitting of the energy levels for a nuclear spin I = 3/2 and the transition probabilities for I = 1/2 → I = 3/2 transitions were obtained. The effect of relaxation transitions on the line shape is studied on the basis of a generalized Kubo‐Andersen model. For a set of actual relaxation and vibronic parameter values the Mössbauer spectra are calculated numerically with a computer. The possibilities of comparison with experiment are discussed.
Fine structure of shallow wannier‐mott exciton levels in a polarizable field
Authors: Fedoseev V. G. 
Published: July 2007

AbstractA theory of the fine structure of Wannier‐Mott excitons, due to the interaction of the electron and hole with the polarizable vibrations of the lattice, is developed. The “non‐hydrogen‐like” corrections to the exciton energy, and also the corrections to the effective mass of the exciton, depending on the internal state of the exciton, are calculated.
Interband faraday rotation in silicon
Authors: Kessler F. R. , Metzdorf J. 
Published: July 2007

AbstractThe nonresonant interband Faraday rotation in silicon single crystals was measured in the spectral region 0.55 to 3.1 eV. A new modulation method is developed for measuring rotations of the plane of polarization of linearly polarized radiation to an accuracy of better than 0.001° in normal cases. The range of measurements was extended up to 2 eV above the indirect energy gap with sample thicknesses between 1 mm and 1 μm, at temperatures between 100 and 350 K, and in a magnetic field of 2 T. The Faraday rotation increases monotonously in the whole range up to a photon energy of 3.1 eV. As the analysis by means of theoretical dispersion functions, of the dispersion relation known as Becquerel equation, and the temperature dependence shows, the interband Faraday rotation in silicon is only associated with direct transitions, the band gap of which should be between 3.2 and 3.4 eV and is not below 3.1 eV.
On the mobility of holes in deformed semiconductors
Authors: Düster F. , Labusch R. 
Published: July 2007

AbstractThe scattering of free holes at dislocations is calculated by a Born approximation. The scattering potential is composed of a coulomb interaction with the charged dislocation core and an interaction with the strain field via the deformation potential. Combination of these two mechanisms with phonon scattering in the transport equation leads to a modification of Matthiessen's rule for the total mobility. Comparison with mobility data on deformed p‐Ge shows that the modifications are essential for a quantitative agreement between theory and experiment. A sharp peak in the second derivative of the mobility with respect to temperature is predicted, when the charge in the dislocation core goes through zero. This may turn out to be an accurate means to determine the “neutrality temperature” independent of other methods.
High‐field transport and low‐field mobility in tellurium single crystals
Authors: Hoerstel W. , Kusnick D. , Spitzer M. 
Published: July 2007

AbstractThe Hall effect and the conductivity in a low electric field and the conductivity in a pulsed high electric de‐field were investigated on carefully prepared and long‐time annealed samples. The reproducible experimental findings obtained at largely undistorted crystals were compared with calculated values. The calculations were carried out for a simple isotropic but non‐parabolic energy band model and for different scattering mechanisms. The result, which states that the temperature dependence of the mobility within the range extending from 65 to 180 K as well as the field dependence of drift velocity up to approximately 1.5 kV/cm, can be explained only by means of polar optical scattering for a parabolic energy band structure, can serve as a starting point for more detailed analyses.
Comments on the evidence for sharp and gradual optical absorption edges in amorphous germanium
Authors: Connell G. A. N. , Lewis A. 
Published: July 2007

AbstractSeveral investigators have analyzed optical data on amorphous Ge films prepared by evaporation on room‐temperature substrates to derive a sharp absorption edge near 0.5 eV. A re‐examination of their work shows that the sharp edges, found hitherto, may be artifacts resulting from either experimental or calculational errors and that the preponderance of the current evidence favors a gradual absorption edge.
Investigation of k = 0 phonons in Bi, Cd, Mg, and Zn by Raman scattering
Authors: Grant W. B. , Schulz H. , HÜfner S. , Pelzl J. 
Published: July 2007

AbstractMeasurements are reported for optical phonons (k = 0) by Raman scattering at 300, 80, and 2 K for Bi, Cd, Mg, and Zn. The linewidths are found to increase, and the frequencies to decrease, as the temperature is raised. The temperature dependent portion of the linewidth is attributed to a two‐phonon decay process. In addition, the contributions to the line‐width from the isotope effect, the electron‐phonon interaction, and strains are discussed.
Magnetoresistivity of n‐Si at High Magnetic and Strong Electric Fields
Authors: Asche M. , Bondar V. M. , Kurtenok L. F. , Martynchenko V. I. 
Published: July 2007

AbstractThe magnetoconductivity of n‐Si at a strong but not quantizing magnetic field is presented for 77 °K. In contrast to weak magnetic fields a superlinearity of the current‐voltage characteristics is obtained. This agrees with theoretical predictions of the inversion of the ratio of the mean carrier energies and repopulation of electrons between the valleys.
Contribution of Excitons to the Optical Properties of GaSe
Authors: Bianchi D. , Emiliani U. , Podini P. , Paorici C. 
Published: July 2007

AbstractFaraday effect measurements were performed on excitons in GaSe using a pulsed magnetic field up to 80 kG in synchronous operation. The interpretation of the experimental data showed the necessity of Zeeman splitting, magnetoabsorption and dichroism measurements. The analysis of the results suggested an analytical model taking into account the contribution of excitons to the optical constants of GaSe. Using this model the experimental data were successfully fitted. Such an approach is quite general and can be used every time one has well isolated resonances for which Nƒ ≪ (ϵ0 μ γ ω0)/(2 π e2). It is shown that this condition is satisfied for GaSe, for Nƒ = 1.06 × 1017 cm−3, g+ = −3.5 is obtained while the damping factor γ changes from sample to sample between 3.6 × 1012 and 4.5 × 1012 s−1.
Brillouin Scattering by Phonons Renormalized by Two‐Magnon Excitations in Ferromagnetic Dielectrics
Authors: Krishnasamy L. , Kumar N. 
Published: July 2007

AbstractBrillouin scattering by one‐phonon‐two‐magnon interacting excitations in ferromagnetic dielectrics is discussed. The basic light scattering mechanism is taken to be the modulation of the density‐dependent optical dielectric polarizability of the medium by the dynamic strain field generated by the longitudinal acoustic (LA) phonons. The renormalization effects arising from the scattering of phonons by the two‐magnon creation‐annihilation processes have, however, been taken into account. Via these interactions, the Brillouin components corresponding to the two‐magnon excitations are reflected indirectly in the spectrum of the phonon scattered light as line‐broadening of the otherwise relatively sharp Brillouin doublet. The present mechanism is shown to be dominant in a clean saturated ferromagnetic dielectric with large magneto‐strictive coupling constant, and with the magnetic ions in the orbitally quenched states. Following the linear response theory, an expression has been derived for the spectral density of the scattered light as a function of temperature, scattering angle, and the strength of the externally applied magnetic field. Some estimates are given for the line‐width and line‐shift of the Brillouin components for certain typical choice of parameters involved. The results are discussed in relation to some available calculations on the ultrasonic attenuation in ferromagnetic insulators at low temperatures.
On Green's Tensor Funktion for a Hexagonal Crystal with Applications to Dislocation Theory
Authors: Chou Y. T. , Yang H. C. 
Published: July 2007

AbstractExplicit expressions for the planar Green's tensor function defined on the basal plane of a hexagonal crystal are given. These expressions are functionally identical to those for an isotropic medium. Applications to the stress fields and energies of dislocation segments and curved dislocations are shown.
Radiative Decay of Electron‐Induced Surface Plasmons in Rough Surfaces
Authors: Sauerbrey G. , Woeckel E. , Dobberstein P. 
Published: July 2007

AbstractCoupling between fast electron‐induced surface plasma waves in metals and an electromagnetic field was calculated for surfaces with statistical roughness. Measurements of electron‐induced surface plasmon radiation from evaporated silver targets (3.54 eV ≙ ≙ 350 nm peak wavelength) showed that a non Gaussian surface autocorrelation function must be assumed, which prefers medium spatial frequencies, and that the assumption of a plane surface for the surface plasmon excitation process is allowed if the surface is not too rough. With increasing roughness additionally lower frequency excitations take place. Agreement with the measured spectral distributions only could be obtained, if the optical constants of Philipp and Taft were used; from the optical constants of evaporated silver targets follows the peak intensity at 3.62 eV (λ = 342 nm), retardation taken into account.
Theory of Coupled Nuclear and Electronic Spin‐Wave Modes I. The Linear Approximation
Authors: Tucker J. W. 
Published: July 2007

AbstractA quantum field theoretical perturbation method is employed in a study of the coupled nuclear and electronic spin‐wave modes that exist in magnetically ordered materials due to the hyperfine interaction. The calculation makes use of a diagrammatic technique in which the evaluation of the thermal averages of products of spin operators is facilitated by the use of the drone‐fermion representation. The dispersion relation for the undamped coupled nuclear and electronic spin‐wave modes is derived in linear theory and the contribution to the free energy from the spin‐flip part of the hyperfine interaction is found.
On the Quantum Theory of Spin Waves in an Electron Liquid
Authors: Okulov V. I. , Pamyatnykh E. A. 
Published: July 2007

AbstractThe basic relations of the quantum theory of the electron liquid of a metal in a magnetic field are formulated. On the basic of a proposed approximation for the kernel of the Fermi‐liquid interaction the quantum oscillations of the effective magnetic moment of the quasi‐particles are considered. Taking into account two constants of the Fermi‐liquid interaction and assuming them to be small, the frequencies of spin waves propagating across the direction of a magnetic field are obtained. The quantum oscillations of the frequencies and the spin magnetic susceptibility are discussed.
Characteristic Surfaces of Fluctuations and Critical Index for the Phase Transition in Uniaxial Ferromagnets
Authors: Klamut J. , Sznajd J. 
Published: July 2007

AbstractBasing on Landau's theory which admits spatial inhomogeneities of the magnetization, the fluctuations near the ferro‐paramagnetic phase transition have been calculated. The magnetic anisotropy is shown to lead to anisotropic correlation functions which for a uniaxial ferromagnet lead to ellipsoidal isocorrelation surfaces with rotational symmetry, instead of the spherical symmetry assumed in the conventional Orstein‐Zernike theory. For the phase transition in the presence of an external magnetic field, the field and temperature dependence of the anisotropic correlation radii has been determined.
Valence Bands of Solid Hydrogen in H.C.P. Lattice
Authors: Parravicini G. Pastori , Piccini F. , Resca L. 
Published: July 2007

AbstractThe valence electronic states of ortho‐hydrogen crystals in h.c.p. lattice are calculated assuming space group Pca21 for the orientation of the molecules. The maximum and the minimum of the valence bands, whose width is found to be 0.080 Ryd, occur at the points X and Γ of the Brillouin zone. A detailed comparison with the energy bands of solid ortho‐hydrogen in f.c.c. lattice is considered. The modifications of the energy levels in the case of a h.c.p. disordered structure arc also discussed.
Variational Calculation of Electron‐Phonon Scattering in Heavily Doped n‐Ge
Authors: Singh D. P. , Verma G. S. 
Published: July 2007

AbstractThe simplified variational method has been extended to Ziman's electron‐phonon scattering and the results are applied to explain the phonon conductivity results of heavily doped n‐Ge, for which donor‐electron states merge with conduction states and phonons are scattered by donor electrons in the conduction state. The expressions for the scattering matrix elements for the electron‐phonon scattering are obtained and its contribution to the thermal resistivity is considered in the temperature range 2 to 10 °K in the presence of boundary scattering and isotopic scattering of phonons. The analysis of the thermal resistivity data reveals that the effective mass of the donor electron in the conduction state varies from 0.25 to 0.45 in the temperature range 2 to 10 °K.