bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Motion of Solute Atoms in Cages and Loops in Metal Lattices Studied with Nuclear Methods
Authors: Vogl G. 
Published: July 2007

AbstractInterstitial cages in metals are found with the Mössbauer effect on 57Fe in aluminium, silver, and α‐zirconium after trapping of irradiation‐induced interstitials and recently after implantation. Cage motion manifests itself in a strong decay of the apparent line intensity due to quasielastic effects and — in suitable systems — in a relaxation of the quadrupole splitting. The results are compared to the results of internal friction methods. Correlation effects in solute diffusion via vacancies can be described in terms of vacancy caging and looping. Analogies between interstitial and vacancy caging are discussed. The possibilities to observe and study these effects with nuclear methods are considered.
Theory of Nucleation Fields in Inhomogeneous Ferromagnets
Authors: Kronmüller H. 
Published: July 2007

AbstractThe effect of the microstructure on the coercive field of sintermagnets is investigated on the basis of the theory of micromagnetism. From the linearized micromagnetic equations nucleation fields are determinded for magnetic inhomogeneities with quasi‐harmonic spatial variations of the magnetocrystalline anisotropy energy. For one‐ and two‐dimensional nucleation modes the eigenvalues of the nucleation fields are derived as a function of the width and the strength of planar magnetic inhomogeneities.
Specific Heat Experiments at the Cooperative Jahn‐Teller Transition in the Mixed Crystal Systems (Tbx, Tm1−x)AsO4 and (Tbx, Tm1−x)VO4
Authors: Kasten A. , Kahle H. G. , Klöfer P. , Schäfer‐Siebert D. 
Published: July 2007

AbstractSingle crystals of the systems (Tbx, Tm1−x)AsO4 and (Tbx, Tm1−x)VO4 are investigated by means of specific heat measurements in the temperature region 1 to 40 K. Whereas for the arsenate a cooperative Jahn‐Teller distortion is observed over the whole concentration range x, in the vanadate the phase transition is missing for 0.1 ≦ x ≦ 0.4. This can be understood in mean field theory taking into account the effect of local strains which are assumed to have a random (Gaussian) distribution.
Dynamical Deceleration of a Dislocation by Surface Defects
Authors: Malashenko V. V. , Sobolev V. L. , Khudik B. I. 
Published: July 2007

AbstractThe influence of surface defects on dynamical deceleration of a dislocation is studied. It is shown that the deceleration force acting on the dislocation through surface defects is essentially different from the deceleration force due to volume defects.
Dynamics of Bjerrum Faults and Protonic Ice Conductivity
Authors: Sergienko A. I. 
Published: July 2007

AbstractThe exact solution describing the motion of D‐ and L‐faults in water molecule chains — the Bernal‐Fowler filaments — under the influence of an electric field is obtained. It is shown that at a certain critical field value the fault mobility determines the proton current but not the mobility of protons themselves. That's why the current‐voltage characteristic exhibits the break.
Molecular‐Type Motion of Relativistic Electrons at Planar Channeling in Crystals
Authors: Vyatkin E. G. , Vorobiev S. A. 
Published: July 2007

AbstractChanneling of relativistic electrons in (111) planar direction in a diamond crystal and the channeling radiation spectra are investigated using computer simulation by the binary collisions model and using the model of a continuum potential of the atomic planes. The calculations are performed for electrons with the energy E0 = 900 MeV. The peculiarities revealed of the angular distributions and radiation spectra of electrons in the atomic‐ and molecular‐type states allow to discern these channeling states in the experiment.
Chemical Bond Formation Processes on Semiconductor Interfaces at Electronic Equilibrium or Nonequilibrium
Authors: Lorenz W. 
Published: July 2007

AbstractThe quantum theoretical treatment of chemical bond formation and partial charge transfer in condensed systems is extended recently to charge injection processes in electronic nonequilibrium. An exposition of the theoretical fundamentals is given, which apply particularly to electrochemical and photoelectrochemical processes on semiconductors. Related problems in semiconductor electronics are likewise included in the discussion.
Relativistic Theory of Photoemission from Solids. III. Bulk and Surface Transition Matrix Elements
Authors: Braun J. , Thörner G. , Borstel G. 
Published: July 2007

AbstractTwo specific aspects of a fully dynamical relativistic one‐step model of photoemission from solid surfaces are discussed which turn out to be crucial for the development of an explicit calculational scheme: (i) The evaluation of the single‐ and double‐contributions to the bulk transition matrix elements is demonstrated and (ii) it is shown how a realistic effective one‐dimensional image‐potential surface barrier can be taken into account within the relativistic formalism.
Cylindrical Quantum Well with Position Dependent Mass
Authors: Pérez‐Alvarez R. , Parra‐Santiago J. L. , Pajón‐Suárez P. 
Published: July 2007

AbstractUsing the envelope function approximation and a one band model, the cylindrical quantum well with position dependent mass problem is studied. The boundary conditions to be fulfilled by the radial wave functions are deduced. The transcendental equation for the energy levels, the normalised wave functions, and the confinement are obtained in the flat band approximation considering a sectionally constant mass profile. Also numerical results are given for the GaAsAl0.32Ga0.68As cylindrical quantum well.
Nitrogen Bound Electrons, Excitons, and Multiexcitons in GaP
Authors: Haufe A. 
Published: July 2007

AbstractBy means of a simple effective mass model the density functional theory is used to calculate the ground state energy of the exciton at the isolate N impurity. For this purpose, the N potential is adjusted and provides the value known from experiment. This potential offers the basis for the computations of the bound multiexciton complexes at the isolated N impurity and of the electron binding energy at the N pairs. The results so obtained are in good qualitative agreement with the experimental ones.
Quantum Theory of Thermopower in Quantum Well Wires
Authors: Jali V. M. , Kubakaddi S. S. , Mulimani B. G. 
Published: July 2007

AbstractA quantum theory for thermopower in quantum well wires is presented. Expressions for thermopower are obtained, both, in the longitudinal and transverse configurations where the temperature gradient is parallel and perpendicular to the wire, respectively. The expression obtained in the longitudinal configuration agrees with that obtained from the conventional Boltzmann transport equation in the relaxation time approximation.
Mott‐Insulation, High Frequencies, and the High Transition Temperatures of the New Ceramic Superconductors
Authors: Hyland G. J. 
Published: July 2007

AbstractA recent proposal of Fröhlich concerning the origin of the high transition temperatures, Tc, which characterize the newly discovered ceramic superconductors, is examined for the case of materials based on La2CuO4. Whilst one of the conditions specified by Fröhlich — namely the existence of a narrow energy band based on incomplete inner shells of certain metal atoms is indeed realized in terms of a quasi two‐dimensional lower Hubbard band of Cu d‐orbitals — it is noted that certain ionic (Cu–O) vibrational breathing modes exist whose frequency is already high enough (≈ 10 × 1013 Hz) to account, via BCS theory, for the high Tc's, without having to invoke the higher frequency excitonic‐like modes envisaged by Fröhlich. Evidence is adduced that the carriers responsible for the superconductivity are essentially Cu 3d holes introduced into the lower Hubbard band by divalent dopants, and/or deviations from La stoichiometry; their density, n, is thus rather low, which could well account for the low critical currents, Jc, found experimentally. It is noted that n is most probably less than the degree of doping, x, on account of the possible contributions of oxygen vacancies to the maintenance of charge neutrality; this, in turn, imposes a lower limit on x if n is to be > 0.
A New Effective Ensemble Approach for the Free Energy
Authors: Ferreira J. R. Faleiro , Silva N. P. 
Published: July 2007

AbstractIt is shown that the effective ensemble utilized in Bogolyubov principle may be replaced by new effective ensembles more complete than the former one. That brings some improvements on the approximate thermodynamic function calculations and preserves short range order effects above the critical temperature even if one particle trial Hamiltonian is used.
Influence of Dipolar Interactions on the Dynamical Dielectric Response
Authors: de la Fuente M. R. , Jubindo M. A. Pérez , Balda R. , Tello M. J. 
Published: July 2007

AbstractAn analysis is made of the modifications produced in the complex susceptibility with regard to the complex polarisability, when one takes into account the dipolar interactions in the molecular field approximation. The analysis is carried out for both, exponential and non‐exponential responses and covering the weak interaction limit as well as the strong one.
Luminescence Due to Radiative Transitions between Valence Band and Upper Core Band in Ionic Crystals (Crossluminescence)
Authors: Jansons J. L. , Krumins V. J. , Rachko Z. A. , Valbis J. A. 
Published: July 2007

AbstractIn some wide band gap halides of heavy alkali and alkaline‐earth metals (BaF2, CsCl, RbF etc.) the energy separation between the valence band involving mainly the halogen electronic states and the upper cation core band is smaller than the band gap. Under the excitation generating holes in the core band radiative electronic transitions from the valence band to the core band take place giving rise to a specific kind of intrinsic emission which is proposed to call crossluminescence. Its decay time is about 1 ns and the thermal quenching starts at temperatures well above room temperature. The width of the emission spectrum practically coincides with the width of the valence band deduced from ultraviolet photoelectron spectroscopy and the shape of the spectrum depicts the electronic structure of the valence band.
Comparative Raman Study of Phonon Linewidths in Pure and Lead‐Doped CsCdBr3
Authors: Pilla O. , Cazzanelli E. , Blanzat B. , Andraud C. , Pelle F. 
Published: July 2007

AbstractRaman spectra of CsCdBr3 are reported in the temperature range 4.2 to 300 K. The symmetry assignation is performed for all the observed peaks; besides the five expected Raman active first‐order modes, a weak structure is observed and attributed to a second‐order process. The temperature dependence of frequencies and linewidths is studied. An anomalous effect of Pb doping on the low temperature linewidths is discussed.
Additional Results on SERS from Ag Colloids in Alkali Halide Crystals
Authors: Abel H.‐B. , Fischer F. 
Published: July 2007

AbstractThe size of thermally or photochemically produced colloids is controlled by their Mie absorption band. Excitation in this band shows strong resonant SERS. Vibrational contributions contain one‐phonon scattering of the host and localized (or resonant) modes due to a cation‐silver bonding. The continuous background only extends to the Stokes side with a cut‐off frequency influenced by the exciting photon energy. The anti‐Stokes side has its cut‐off at ṽ = 0 with a temperature‐dependent shape given by the Fermi factor of the metal electrons.
Effect of Metal Substitution in ZrS3 and TiS3 Compounds. Electronic, Raman, and Resonance Raman Study of Zr1−xTixS3 Ternary Phases, 0 < x < 1
Authors: Gard P. , Sourisseau C. , Gorochov O. 
Published: July 2007

AbstractThe effects of metal substitution on the electronic and vibrational properties of ZrS3 and TiS3 are studied through UV–visible absorption, Raman and resonance Raman scattering experiments on various Zr1‐xTixS3 ternary phases, 0 < x < 1. All these broad band semiconductors display excitonic type transitions on their absorption edge whose maxima vary monotonously from 500.0 to 960.0 nm as the titanium content increases. These excitons consist of d‐like conduction electrons and the existence of higher‐energy transitions due to 3p*(SS) orbitals is confirmed by resonance Raman results in Zr0.6Ti0.4S3. The polarized Raman spectra of the solid solutions present variations in band‐wavenumbers as a function of the compositional parameter x and three different types of mode‐behavior are observed depending on the nature of the vibrations. All the Raman results are sustained on force field calculations in ZrS3 and TiS3 and on the estimations of short‐, medium‐, and long‐range interactions within each vibrational state.
Enhancement of 3d‐Electron Transitions in Neutron‐Irradiated MgO:Mn2+ Crystals
Authors: Okada M. , Kawakubo T. , Seiyama T. , Nakagawa M. 
Published: July 2007

AbstractA study of optical absorption of 3d‐electrons in neutron‐irradiated MgO:Mn2+ crystals is made. Intensity enhancements and energy shifts of spin‐forbidden optical transitions of Mn2+ ions are observed in samples as‐irradiated and after heat treatments. An investigation of thermal properties of optical absorption for Mn2+ ions and F centres in the irradiated MgO:Mn2+ indicates the presence of two types of defects associated with F centres. These defects are accounted for as an interstitial‐Mn2+–F center complex and a Mn2+–F centre complex. The origin of the optical transition enhancement and energy shifts are attributed to both, an exchange interaction of Mn2+ ions with F‐center electrons and a parity‐forbidden removal caused from symmetry changes due to the formation of above described complexes.
Pressure Dependence of the EPR Parameters of Cs3CoCl5 Crystal
Authors: Yu Wan‐Lun , Rao J. L. 
Published: July 2007

AbstractUsing the superposition model of a crystal field, a relationship is established between the crystal structure and the EPR parameters of d7‐ions in weak D2d fields. The analysis shows that the zerofield splitting parameter D is positive for a compressed structure and negative for elongated‐type crystals. With the help of Zhao and Zhang's approximate SCF d‐orbital of the Co2+ ion, the relationship is used to investigate the pressure dependence of D of Cs3CoCl5 crystal and the theoretical values are reasonable. The origin of the pressure variation of D is explained and the pressure dependence of the g‐factor is predicted theoretically.
Temperature Dependence of Exciton Absorption Spectra. A Calculation Based on the Recursion Method
Authors: Sherman A. V. 
Published: July 2007

AbstractBased on the recursion method of calculating correlation functions, the absorption spectra of a model of a three‐dimensional dielectric crystal containing a band of Frenkel excitons interacting with a branch of dispersionless optical phonons, are investigated in a wide range of material parameters and temperatures. The cases of a weak exciton—phonon coupling, vibronic exciton, coexistence of nearly free and self‐trapped excitons as well as intermediate situations are considered. It is shown that in a definite region of parameters the character of exciton—phonon coupling is changed with the growth of temperature so that the weak‐coupling‐type spectrum acquires some features of the vibronic exciton spectrum. In addition, in a definite temperature range, a change in the physical meaning of the observed peculiarities occurs. In the case of the coexistence of nearly free and self‐trapped states the temperature behaviour of the related peculiarities are shown to be different, a fine structure caused by self‐trapped states is manifested in the vicinity of the main peak only in the low‐temperature spectra. At higher temperatures the spectral shape can essentially differ from the asymmetric Lorentzian due to a sideband in a short‐wave side of a maximum. A long‐wave absorption tail at high temperatures and the considered sets of parameters satisfies the Urbach rule. With the lowering of temperature in the case of weak coupling a structure with a step approximately equal to the phonon frequency stands out in this tail.
Resonance Tunneling with Dissipation Taken into Account
Authors: Ermakov V. N. , Ponezha E. A. 
Published: July 2007

AbstractThe effect of interbarrier‐space dissipation on the resonance electron tunneling through a system of two identical potential barriers is investigated. It is shown that the dissipation leads to a general decrease in barrier transparency, but the qualitative features of nonlinear resonance tunneling remain unchanged. The influences of dissipation on the autovibratory tunneling regime are discussed.
Construction of Bond‐Centered Wannier Functions for Silicon Valence Bands
Authors: Satpathy S. , Pawlowska Z. 
Published: July 2007

AbstractBond‐centered Wannier functions are constructed for the valence bands of silicon by a direct superposition of the Bloch functions whose phases are chosen on physical grounds. The Bloch functions are calculated using the linear muffin‐tin orbitals method within the local density approximation. The resulting four Wannier functions per unit cell are equivalent to one another. Each is localized on a bond‐center, has the Γ1 symmetry of the D3d group, and falls off exponentially.
Estimation of the Crystal Field at R Sites in R2Fe14B Compounds
Authors: Zhao Tiesong , Zhu Yong , Jin Hanmin 
Published: July 2007

AbstractThe mean values of some crystal field parameters at f and g sites in R2Fe14B (R = Pr, Nd, Sm, Dy, Ho, Er, Tm, and Yb) compounds are estimated from magnetization curves of single crystals along the major crystal axes at 4.2 K and room temperature and from spin reorientation temperatures.
The Influence of Manganese on Magnetic Properties of RE2(Co1−xMnx)17, RE = Y, Gd Compounds
Authors: Kąkol Z. , Figiel H. , Chmist J. , Kołodziejczyk A. 
Published: July 2007

AbstractThe pulse field measurements of magnetisation for Y2(Co1−xMnx)17 and Gd2(Co1−xMnx)17 series with x ≦ 0.3 in the 78 to 300 K temperature range are reported. In contrast to anisotropy changes different behaviours of saturation magnetisation for the Y and Gd based series are observed. The presented results are analysed and explained by preferential substitution and reorientation of Mn moments, where dipolar interactions with Gd are considered.
Soliton Energy in a Quantum Ferromagnet with Two Anisotropies
Authors: Talim S. L. , Pires A. S. T. 
Published: July 2007

AbstractThe quantum corrections are calculated to the energy of the soliton in the easy‐plane ferromagnetic spin chain with two anisotropies. A semiclassical continuum approximation is used which allows to treat the leading order deviations from idealized classical behavior. The soliton density at finite temperatures is also calculated.
The Periodic LUC‐MINDO Method and its Application to Diamond
Authors: Craig B. I. , Smith P. V. 
Published: July 2007

AbstractIn previous work it is shown that neither the periodic LUC‐CNDO nor LUC‐INDO formalisms are accurate enough to yield reliable values for the bulk properties of the homopolar covalent solids. Calculations based on the more sophisticated MINDO molecular orbital method appears more successful, however. In this paper the periodic LUC‐MINDO method is outlined and its application to diamond is considered. The predicted one‐electron eigenvalues, bulk elastic constants, and phonon frequencies are now found to be in very satisfactory agreement with experiment.
Calculation of Dipole Transition Matrix Elements in Muffin‐Tin Models
Authors: Shilkova N. A. , Shirokovskii V. P. 
Published: July 2007

AbstractMatrix elements of momentum and of gradient of the potential for electronic states in solids are calculated by the Green's function method. Their absolute identity is shown if the integral over the elementary cell volume is correctly reduced to integrals over the space restricted by the muffin‐tin sphere, and through the surface of this sphere. It is ascertained that the surface term gives the main contribution in momentum matrix element values. It is proved that the commutation relationship connecting both the types of matrix elements is exactly valid for the muffin‐tin function irrespective of the variational series length. The influence of high‐angular‐momentum terms in the expansion of the wave function on the matrix element values is discussed.
Carrier Kinetics in a Semiconductor with Light‐Induced Gaps
Authors: Hartmann M. , Zimmermann R. , Stolz H. 
Published: July 2007

AbstractDue to the influence of a strong electromagnetic field an induced gap is expected to occur in the band structure of a semiconductor. In this paper the influence of the damping by electron–phonon collisions and by recombination on the new band structure is investigated. Taking into account damping kinetic equations for the electrons are derived and discussed with the help of calculations.
Green's Function Approach to Nonequilibrium Charge Carriers in Direct Gap Semiconductors Generated by Short Light Pulses
Authors: Glaeske H. , Schubert M. 
Published: July 2007

AbstractIn the present paper the Green's function approach to nonequilibrium quasi‐free charge carriers in highly excited semiconductors is applied. In doing this a system of kinetic equations for generalized Wigner distributions of renormalized quasi‐electrons and holes is obtained, that takes into account (additionally to well‐known published results) the interaction of the longitudinal optical phonons and the intraband interaction of the radiation field with the electron–hole plasma. Thus, utilizing the corresponding field equations and the suitable boundary conditions, relaxation processes in the semiconductor after excitation by a short laser pulse and a laser probe beam experiment may be described.
A New Electronic Pinning Mechanism for Sliding Charge Density Waves
Authors: Fischebeck H. J. 
Published: July 2007

AbstractIt is shown that the time component of the chiral Noether current is a constant of motion in a quasi‐one‐dimensional charge density wave (CDW) system in the absence of a disordered potential. Therefore this system possesses a current‐carrying equilibrium state which is characterized as the minimum of an accordingly generalized thermodynamic potential. A random impurity potential breaks the chiral invariance so that a current‐carrying equilibrium state in the strict sense does not exist in this case. It is assumed, however, that the sliding CDW state can approximately be described as a quasi‐equlibrium in the coordinate frame co‐moving with the velocity ν. It is shown that the density of states in the co‐moving frame exhibits tails in the Peierls gap which enhance the thermodynamic potential of the quasi‐equilibrium proportional to |ν| so that the current‐driving Lagrange parameter in this potential must exceed some threshold value before the sliding CDW state is thermodynamically favoured against the resting one. This is an electronic pinning mechanism which acts independently of the conventional phase pinning.
Cation Vacancy Migration Entropy in Alkali Halides
Authors: Eftaxias K. , Varotsos C. , Hadjicontis V. 
Published: July 2007

AbstractVaraksin and Shipitsin have recently presented a method for the calculation of the migration entropy (sm) of defects in solids. By applying this method to the case of a cation vacancy migration in NaCl and KCl values are obtained that significantly differ from the experimental data. On the other hand a model is suggested which leads to reliable sm‐values for both materials i.e. NaCl and KCl. This model is based on a reasonable assumption stating that the absolute value of the “constant volume” migration entropy is appreciably smaller than that corresponding to “constant pressure”.