bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Vibrational Entropy of a ½ 〈111〉 {110} Edge Dislocation in B.C.C. Iron
Authors: de Hosson J. Th. M. 
Published: July 2007

AbstractA computer simulation study is set up to obtain the vibrational entropy at low temperatures of an edge dislocation. The anharmonic correction to the vibrational entropy at 70 K appears to be about 10%. The contribution of the total entropy to the total free energy is at most 10% of the activation enthalpy for overcoming the Peierls‐Nabarro barrier in the low‐temperature region. A conclusion is made that the results presented here appear to be in reasonable agreement with the experimental data which demonstrate that there is at present no convincing evidence for any considerable activation entropy.
Dynamical Electrical Conductivity, Dielectric Function, and Plasma Oscillations of the Hubbard Model
Authors: Gasser W. 
Published: July 2007

AbstractExpressions are derived for the longitudinal dynamical conductivity, the dielectric function and the plasmon dispersion relation for the Hubbard model using approximations which are mainly based on the Hubbard‐I decoupling scheme for Green functions. In the limit of zero wave numbers a result is confirmed for the dc conductivity got by Kubo but later criticized by Lawson and Smith. The plasmon dispersion relation is determined up to the second order in the wave number.
Theory of Angle‐Resolved Photoemission. The Role of Electron Diffraction in the XPS Spectra
Authors: Paasch G. 
Published: July 2007

AbstractThe external photoelectron current can be expressed by the one‐electron Green's function for the crystal with surface. By calculating this GF with the matching formalism a general expression for the bulk contributions to the photoelectron spectra is obtained. As a consequence of the electron diffraction the transmission matrix of the surface enters this expression. The result is analyzed for the conditions of the angle‐resolved XPS measurements. Thereby it is shown what types of approximations or errors are contained in the two models which are used till now frequently for the calculation of angle‐resolved XPS spectra. Further a practicable approximate formula is given for these spectra which takes into account the electron diffraction in a simple manner.
Free Charges and Excitons in Stilbene Single Crystals Excited by Electron Pulses
Authors: Kostin A. K. , Savelev V. V. , Vannikov A. V. 
Published: July 2007

AbstractThe kinetics of relaxation currents, light absorption, and luminescence after excitation of stilbene single crystals by a pulse of accelerated electrons with τ = 40 × 10−9 s is measured. The excitation results in bulk generation of free charges and excitons. The microscopic mobilities are found to μp = 2.2 cm2 V−1 and μ, = 0.2 cm2 V−1 s−1. The radiation yield of the charges is G(p, e) = 0.25 ± 0.02, and of triplet excitons G(T) = 3.6. The optical absorption spectrum of triplet excitons is recorded, and it is found that vmax = 2.22 × 104 cm−1, the absorption coefficient Kvmax = 0.17 cm−1, and the oscillator strength of the T2 ← T1 optical transition band f = 0.20. The probability of creation of charges .
Colloid Centres in AgCl Induced by Heavy Ion Implantation
Authors: Diaine Ch. , Gisclon J. L. , Dupuy J. 
Published: July 2007

AbstractThe effects of ion implantation in AgCl produced mainly by the two types of interaction, electronic energy losses and nucleation energy losses, are essentially in the Ag+ lattice. Defects induced by the first one correspond to the photolysis mechanism and by the second perturbation are identified as Ag clusters. From the Lindhard diagram the conditions are given necessary to realize the two types of defects which are related to the mass and to the ion energy. The ions used are Li+, Na+, K+, Rb+, and Ar+ at RT and LNT. Due to the energy range available (50 to 500 keV) it is possible to produce significant variations of the nuclear energy loss ratio with Na+ ion and to observe seperately or simultaneously ionization defects and collision defects. It is found that the collision defects are colloidal silver connected to the nuclear energy losses.
Mössbauer Study of Dy3+ in CaF2
Authors: Kuo Ch. S. , Schroeer D. 
Published: July 2007

AbstractThe Mössbauer electric quadrupole interaction for Dy3+ in both oxygen‐free and oxygen‐injected CaF2 is measured between 90 and 630 K. Comparison of the experimental data with theoretical calculations confirms that in oxygen‐free CaF2 the stabilization occurs via an interstitial F− ion, while oxygen injection leads to stabilization by oxygen substitutionally replacing F− ions.
Ultrasonic Spectrum in a Multidomain Structure
Authors: Mitin A. V. , Tarasov V. A. 
Published: July 2007

AbstractThe spectrum of sound vibrations excited by a rf field in a magneto‐acoustic resonator which is formed on the basis of the Landau‐Lifshits multidomain structure is investigated. The properties of magneto‐acoustic and acoustic resonators are compared. The numerical evaluation indicates that the spectrum may be observed experimentally.
Resonant Raman Scattering in As2S3 Amorphous Thin Films
Authors: Razzetti C. , Lottici P. P. 
Published: July 2007

AbstractThe RRS cross‐section and the optical constants are investigated in amorphous As2S3 thin films. The results indicate that the cross‐section relative to the 350 cm−1 band is simply related to the imaginary (dissipative, or resonant) part of the dielectric susceptibility. Also an enhancement is found of the width of the 350 cm−1 band, which seems to diverge with increasing exciting energy. An absorption–emission picture of the RRS process could account for the observed results.
Radiative Damping Effect for Ultrarelativistic Channelled Particles
Authors: Wedell R. 
Published: July 2007

AbstractA theoretical consideration is given to a possibility of focusing ultrarelativistic positrons and electrons under channelling conditions. The decrease of the transverse energy is mainly due to energy losses by a specific radiation considered recently by Kumakhov. This effect appears for electrons at energies of several GeV and for positrons of several dozens of GeV. The mechanism perturbing focusing is multiple scattering. The focusing effect decreases the divergence of the beam penetrating through the target. Target thicknesses which are necessary to exhibit this effect are estimated.
Optical Detection of Nuclear Magnetic Resonance with Distant F‐Centre Pairs in KCl
Authors: Jaccard C. , Ecabert M. 
Published: July 2007

AbstractIn quenched KCl crystals containing more than 1017 cm−3 F‐centres and excited by unpolarized light in the F‐band at 12 K, the NMR spectra of the neighbouring nuclei are detected at fields between 0.5 and 5 kG and radiofrequencies between 0.1 and 10 MHz as negative changes of the F‐luminescence (1%). This is explained by a non‐radiative disexcitation of F centre pairs through an F+F− state. Its probability is a function of the singlet admixture of the electronic triplet states, which is produced by non diagonal terms of the hyperfine coupling, and depends on the nuclear spin states. It is shown that the optical cycle produces a second order polarization of the nuclei, which is then decreased by applying a resonant rf field. The spin‐Hamiltonian parameters corresponding to the measured NMR spectra are the same as from single F‐centres ENDOR.
The Reduced Conductivity of Dielectrics when Both Boundary and Dislocation Scatterings are Important at Low Temperatures
Authors: Gupta I. J. , Trikha S. K. 
Published: July 2007

AbstractAn earlier theoretical result connecting the reduced thermal conductivity and reduced temperature of dielectrics is modified to deal with the cases where boundary as well as dislocation scattering simultaneously limit the phonon lifetime at low temperatures. Comparison with experimental data in case of solid argon and neon give satisfactory agreement for T* < 1.4.
Investigations on the Temperature‐Dependent TPA Linewidth of the Z3‐Exciton in CuCl
Authors: Kalm M. , Uihlein Ch. 
Published: July 2007

AbstractThe two‐photon absorption (TPA) line of the longitudinal Z3(1s) exciton in CuCl is studied in the temperature region between 4.6 and 185 K. The longitudinal exciton component has a Lorentzian‐like lineshape in the quoted temperature interval. The halfwidth of the narrow absorption line, which is approximately 0.14 meV below 10 K, increases rapidly for temperatures above 60 K (14 meV at 185 K). The steep increase is correlated with the number of thermally excited LO phonons. The temperature‐dependent halfwidth, which can be fitted by a Bose function with the energy of the LO phonon mode (26.3 meV), is found to be proportional to the LO phonon density. From this it is concluded that the lifetime of the Z3‐exciton is mainly determined by an intraband scattering process caused by the absorption of a longitudinal optical phonon.
On the Representation of the Non‐Stationary Density Matrix of an Electron–Phonon System by a Functional Integral
Authors: Fomin V. M. , Pokatilov E. P. 
Published: July 2007

AbstractA non‐stationary density matrix depending on the coordinates of both electron and phonons is obtained for an ensemble of electron–phonon systems with an arbitrary initial distribution. This density matrix is used to describe the non‐linear optical properties of a semiconductor in the presence of a flow of electrons. A generalized non‐linear dielectric permeability tensor and a generation tensor are found for this case. The anisotropy of absorption, the birefrigence, the transformation of type, and change of parameters of the laser wave polarization and the second harmonic generation due to the flow of electrons are discussed.
Effect of Correlation on the X‐Ray Diffuse Scattering
Authors: Semenovskaya S. V. 
Published: July 2007

AbstractThe contribution of the correlation in X‐ray diffuse scattering caused by short‐range order in disordered binary alloys is considered. This consideration results in the development of the Krivoglaz‐Clapp‐Moss theory for the X‐ray diffuse scattering. It is based on the equation for the free energy of a disordered alloy which takes into account the correlation terms as well as arbitrary‐range interaction. The derived equation looks like the Krivoglaz‐Clapp‐Moss equation. However, it contains some effective value Veff (k) instead of the Fourier transforms of interchange energies V(k). It means that the value V(k) found from X‐ray data by means of Krivoglaz‐Clapp‐Moss equation is really Veff(k). Some experimental data for Fe–Al and Fe–Si alloys reveal large difference between Veff(k) and real value of Fourier transforms of interchange energies V(k).
Auger Neutralization of Slow Protons at Solid Surfaces
Authors: Horiguchi S. , Koyama K. , Ohtsuki Y. H. 
Published: July 2007

AbstractAuger neutralization of slow protons (⪅ a few keV) scattered from solid surfaces is considered. The neutralïzation probability per unit time P(s) is calculated as a function of the proton distance s from the surface to P(s) = A{e−2xs + (Bs + C) e + (Ds2 + Es + F) e}, where a0 is the Bohr radius and A, B, C, D, E, F, and x proper constants depending on the target. At large distances from the surface, the second and third terms of P(s) can be neglected. As the proton approaches the surface, however, P(s) deviates from the simple exponential dependence of s. The neutral fraction φ0 is also calculated. From the obtained φ0, it is shown that Auger neutralization is important, at least in the low energy region.
Neutron Scattering on Anomalous Fluctuations of Phonons
Authors: van Trong Nguyen 
Published: July 2007

AbstractThe process of inelastic neutron scattering in crystal is investigated in the case, where the crystal is suggested to be an electron–phonon system placed in an external radiation field. The cross‐section of one‐phonon scattering process is calculated by using the two‐particle correlation function of phonon. It is shown that near the borderline of parametric instability region the correlation function of phonon and the cross‐section of neutron consequently take anomalously large values.
The Excitonic Surface Potential in Semiconductors
Authors: Balslev I. 
Published: July 2007

AbstractA perfect semiconductor surface produces a potential associated with the translational motion of excitons. This potential is calculated including contributions from both short and long range forces. The relative motion of electron and hole is studied by a variational method and by asymptotic estimates. The potential is used for a detailed description of the exciton free layer and the macroscopic boundary condition relevant for explaining spectra of dispersive resonances. The agreement with previously reported experiments encourages to further studies of the influence of clean surfaces on excitonic phenomena.
Theory of Second‐Order Resonance Raman Scattering in the Case of Strong Excitonic Effects
Authors: Bechstedt F. , Haus D. 
Published: July 2007

AbstractCalculations of the integral and differential cross‐section of the two‐phonon resonance Raman scattering are presented. Both the cases of Q‐independent deformation and Q‐dependent Fröhlich electron–one‐phonon coupling are considered. The electronic intermediate states are described in the Wannier‐Mott approximation. The large binding energy limit is assumed. It is shown that the intensity of combination tones are negligible small compared to that of pure overtones if the exciton binding energy is large enough. In contrast to the case of uncorrelated electron‐hole pairs for both the allowed and forbidden scattering a pronounced double peak structure is found in the resonance behaviour of the integral cross‐section. Analogously to the case without electron‐hole Coulomb interaction the lineshape of the two‐phonon scattering depends strongly on the incident photon energy. Only far from electronic transition energies the second‐order Raman spectra can be interpreted in terms of the two‐phonon density of states. Results obtained here are in qualitative agreement with experimental observations in CdS.
Functional Integral Approach for the Hubbard Model with Arbitrary Electron Density
Authors: Richter A. , Röpke G. , Goedsche F. 
Published: July 2007

AbstractThe method of the functional integral is applied to the conventional Hubbard model with an arbitrary filled band. A relation between the number of electrons per atom, n, and the chemical potential μ at T = 0 is calculated. The static magnetic susceptibility and the local magnetic moments are studied. Looking for the dependence of magnetic properties on the electron correlation U and the number of electrons per atom n, a phase diagram is obtained at zero temperature. Besides the paramagnetic phase ferromagnetic and antiferromagnetic phases exist within this diagram.
Band Theory of Size‐Quantised Electron States in Thin Crystalline Films
Authors: Cottey A. A. 
Published: July 2007

AbstractThe discrete electron states in a thin film with an arbitrary three‐dimensional periodic crystal potential are analysed. First the quantum size effect states of a symmetric film are found exactly for Dirichlet (ψ = 0) and Neumann (ψ′ = 0) boundary conditions, and the interpolation between these extremes is studied. Then a surface scattering matrix formalism is set up in the general (unsymmetric) case. This treats the general situation when there may be M up‐ and M down‐travelling Bloch waves with a given energy and surface‐parallel component of crystal momentum modulo surface reciprocal lattice. The equations are solved in the general 1 × 1 and symmetric 2 × 2 cases. The QSE solutions approximate gently undulating parallel surfaces in k‐space. Usually the separation of these surfaces is roughly uniform. An exception occurs in the 2 × 2 case near a band edge which is not at the centre or edge of the Brillouin zone; the solutions are then in nearly degenerate pairs. The results agree with available experimental data.
Hot Electrons in Zero‐Gap Semiconductors with Non‐Parabolic Electronic Band Structure
Authors: Beneslavskii S. D. , Ziep O. 
Published: July 2007

AbstractMobility μ and concentration n of electric‐field‐induced hot electrons are investigated in zero‐gap HgCdTe with linear band structure at liquid helium temperatures. Taking into account the admixture of s‐like wave functions, dielectric anomalies, and the renormalization of the heavy‐hole spectrum it is shown that Coulomb scattering is the dominant mechanism for relaxation of momentum and energy at 4.2 K. Using rate equations and an electron temperature model the behaviour of μ and n is calculated up to electric field strength of 1.5 V/cm.
Positron Annihilation Rates in the Metals of Ag and Au Series
Authors: Shrivastava S. B. , Bonde H. P. 
Published: July 2007

AbstractThe effect of electron–electron and electron–positron correlations on the positron annihilation rates in the metals of the Ag and Au series are investigated and discussed with the help of positron annihilation angular correlation results. The correlation effects are found to have little variation for the metals in the same series. However, they decrease for the higher Z series metals. The calculated annihilation rates obtained using the simple proposed model are found to be in good agreement with those observed experimentally.
Faraday Rotation in Presence of Attractive Traps
Authors: Bhattacharya D. P. , Kachlishvili Z. S. 
Published: July 2007

AbstractThe Faraday rotation is investigated in the general case for any mechanism of energy and momentum scattering of hot electrons in the presence of a strong or weak transverse magnetic field, when the free carriers are captured by oppositely charged impurity centres. For some definite scattering mechanisms the investigations are carried out in the presence of any finite magnetic field. It is shown that the capture parameters for deep traps and the dominant scattering mechanism of the hot carriers can be determined from a comparison of the theoretical results with experiments. Calculations are carried out assuming a parabolic dispersion law and a scalar effective mass.
Diffraction of Radiation from Channelled Charged Particles
Authors: Baryshevskii V. G. , Grubich A. O. , Dubovskaya I. Ya. 
Published: July 2007

AbstractAn explicit expression for cross‐section and radiation spectrum at diffraction is calculated. It is shown that photons emitted by channelled particles form a typical diffraction pattern which contains information about the crystal structure. It is also shown that the change of the longitudinal energy of the particle caused by the radiation braking becomes important when the particle energy is increased.
Hot Electrons in Semiconductors with Quasi‐Relativistic Band Structure
Authors: Dykman I. M. , Rosenbaum V. M. , Vasko F. T. 
Published: July 2007

AbstractA kinetic equation for hot electrons in semiconductors of the lead chalcogenide type is obtained. The effects of heating‐up with a dc or microwave electric field are discussed. A function of the electron distribution at quasielastic scattering of acoustic phonons with equiparted energy is derived in the diffusion approximation. Such parameters as current—voltage characteristics, effective high‐frequency conductivity (depending on the intensity of incoming radiation) and μ‐photoconductivity of the electron gas are examined. The kinetic coefficients are calculated for a highly degenerate gas with accurate estimation of the quasi relativistic band spectrum; for non‐degenerate electrons kinetic coefficients are calculated to first corrections by ϵ/ϵg (ϵ average electron energy in the conductivity band; ϵg width of forbidden gap).
On the Non‐Adiabatic Properties of Tunneling Centres
Authors: Wagner M. 
Published: July 2007

AbstractA non‐adiabatic formulation of the Hamiltonian for tunneling centres is given. A modified Born‐Oppenheimer basis is employed, which attaches the tunneling particle to a central reference coordinate. The non‐adiabatic dynamical lattice disturbance near the defect is established. New phonon assisted relaxation paths of a direct nature are exhibited. In Li+‐like centres these seem to be dominant, since the conventional ones are of pure non‐adiabatic origin (and of second order).
From Small to Infinite F.C.C. Clusters
Authors: Kadura P. , Künne L. 
Published: July 2007

AbstractThe size and shape dependence of some properties of finite f.c.c. clusters is investigated using the tight binding approximation. Three different sequences of rectangular prismatic f.c.c. crystallites with (100) surfaces (edge length A, B, C) are taken into account, namely cubes (A = B = C), plates (A = B ≫C) and rods (A = B≪ C). Numerical results for the s‐like band structure, binding energy per atom, and Fermi level are presented in dependence on the number of atoms, up to some millions of atoms. The results visualize the convergence of the cluster properties and indicate their shape specifity.
Electronic Transport in Doped a‐Ge and a‐Si Prepared by DC Cathodic Sputtering
Authors: van Dong Nguyen , Hai Tran Quoc 
Published: July 2007

AbstractDoped a‐Ge and a‐Si films are prepared by the cathodic sputtering technique with Sb and In impurities for a‐Ge, P and B impurities for a‐Si. The electrical conductivity σ and thermopower S of different samples are measured as a function of absolute temperature between 150 and 500 K. The effect of doping is to change not only the activation energies Eσ and Es but also other parameters in the expression of σ and S. The considerable reduction in the pre‐exponential term of σ is found to be much larger for a‐Si than for a‐Ge. The temperature shift of the Fermi level is taken into account to explain the variations of these parameters. The activation energy of conductivity is higher than that of thermopower by about 0.10 eV for a‐Ge and 0.15 eV for a‐Si. Experimental data analysis suggests that in both, a‐Ge and a‐Si, for high doping concentrations the hopping conduction through an impurity band makes a dominant contribution to the current flow below room temperature.
Modulation Spectroscopy on the Group IV and VI Transition‐Metal Dichalcogenides
Authors: Saiki K. , Yoshimi M. , Tanaka S. 
Published: July 2007

AbstractPiezoreflectance, thermoreflectance, and wavelength modulated reflectance are measured on the group IV and VI compounds of transition‐metal dichalcogenides. From the evaluation of the spectra by different modulation techniques, from the alloying effect which is first investigated, and from the comparison with the band structure calculations, it is most likely that the A and B excitons observed in the absorption edge of the group VI compounds correspond to the d—d transitions, while the A′ and B′ excitons observed in the higher‐energy side correspond to the p—d transitions. For the group IV compounds the modulated reflectance is first measured and new peaks are found. The comparison with the band structure calculations is also carried out.
On the Ward Identities for the Hubbard Model. Particle‐Number Conservation and the Analytical Structure of the Self‐Energy
Authors: Behn U. 
Published: July 2007

AbstractThe Ward identities for the Hubbard model connected with the spin‐rotational invariance and the particle‐number conservation are derived considering the equation of motion for 4‐point Green functions. Exploiting the generalized Ward identity connected with the particle‐number conservation, the self‐energy splits into a static part and a dynamic part. The latter describes the effects due to the hopping of the electrons of the opposite spin. The analytical structure which guarantees the particle‐number conservation and the reproduction of the atomic limit, can explicitely be seen so that approximations may be performed conserving this structure.
Spin‐Wave Resonance Spectrum in Thin Films with Internal Isotropically Coupled Impurity Layer
Authors: Duda A. , Maciejewski W. 
Published: July 2007

AbstractThe spin‐wave energies, amplitudes, and resonance line intensities in thin films with an internal impurity layer are analysed. The influence of the ferromagnetic and antiferromagnetic impurity coupling both on bulk and localized states is discussed. It is shown that the impurity coupling can be calculated from the resonance measurements.