bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analytic treatment of stochastic models of crystal growth
Authors: Pfeiffer H. , Haubenreisser W. , Klupsch Th. 
Published: July 2007

AbstractThe kinetic properties of the solid‐fluid interfaces for one‐component systems are examined by means of the kinetic Ising model in “solid‐on‐solid” restriction. Two different dynamic models corresponding to two different possibilities of interpretation of the Ising model are studied which should be appropriate in describing the growth process from the melt and vapour, respectively. Considering rough interfaces, simple analytic expressions for the growth rate and interface thickness are obtained which are exact within the mean‐field and continuum approximation. The used method and its range of validity are discussed in comparison of available Monte‐Carlo results.
On born‐huang invariance conditions
Authors: Sarkar S. K. , Sengupta S. 
Published: July 2007

AbstractThe Born‐Huang (B‐H) invariance conditions have been criticised on the ground of insufficiency of rotational invariance by several workers who have obtained additional conditions. This point is examined and it is shown that the B‐H invariance conditions are complete. The equilibrium conditions for vanishing of stress should be separately considered. Then the additional conditions mentioned above are nothing new.
Positron Annihilation in Hydrides of Transition Metals
Authors: Dekhtyar I. Ya. , Shevchenko V. I. 
Published: July 2007

AbstractAn analysis of the degree of positron localization on alloy components is developed in application to palladium, tantalum, and yttrium hydrides. The method is based on the account of positron‐ionic core electron interaction. From the results a conclusion is made about a principal positron localization on metallic components. The degree of the localization depends on the nature of the transition metals. The electronic structure of a hydrogen ion can be changed from the partial “proton” state (PdH) up to nearly the complete “proton” state (YH). The anionic hydrogen state is excluded.
Far‐infrared absorption in small metallic particles
Authors: Maksimenko V. V. , Simokov A. J. , Lushnikov A. A. 
Published: July 2007

AbstractThe cross‐section for far‐infrared absorption of small metal particles are calculated in the dipole approximation. Considerable deviations are found from the corresponding classical results at small particle size a/l0⪅1 (a is the radius of the particle, l0 the mean free path of an electron in bulk metal). The results obtained give a possible explanation to the size dependence of the absorption coefficient of small metal particles observed in recent experiments.
Two‐photon resonance Raman scattering by excitons via an intermediate excitonie molecule. II Polarization properties and polarition effects
Authors: Henneberger F. , Hennererger K. , Voigt J. 
Published: July 2007

AbstractTaking into account the longitudinal and transverse character of the excitons as well as their strong coupling with the radiation field (polariton effect) the polarization and angle dependences of the two‐photon resonance Raman‐scattering spectrum of the excitonic molecule are investigated theoretically in cubic and uniaxial crystals. Numerical calculations are carried out for CuCl and CdS in different scattering configurations. Especially the different behaviour of scattering spectrum near the MT‐ and ML,‐band is studied. Well agreement with the experimental observations in CuCl can be stated.
The effective screening function in insulating solids
Authors: Duggan G. , Morgan G. J. , Shahtahmasebi N. , Lettington A. 
Published: July 2007

AbstractNumerical calculations are presented of an effective dielectric matrix which exactly defines a constituent screened ion in a perfect solid within the Hartree approximation. The accuracy of the numerical method is estimated using previous analytical calculations for a simple model. The nature of the screening charge is then considered in detail for Ge and reasonable values for the magnitude of the “forbidden reflections” are obtained. The behaviour of the screening function for a tight‐binding situation is also investigated.
A many‐body model of dielectric polarisation in solids. I. Experimental data and existing interpretations
Authors: Jonscher A. K. 
Published: July 2007

AbstractA detailed survey of the dielectric properties of a wide range of solids shows that their response functions in frequency or in time depart strongly from the Debye response and fall into a remarkably common or ‘universal’ pattern. The frequency response is similar for systems with permanent dipoles and with hopping charge carriers of electronic or ionic nature. It is also largely independent of the type of physical structure and chemical bonding in the materials. The existing approaches to the interpretation of this behaviour are shown to suffer from two basic drawbacks: they have to make rather arbitrary assumptions and they are unable to explain the essential similarity of the behaviour of many very different systems.
Emission spectra of NaBr: Tl+ excited in the A‐band
Authors: Casalboni M. , Grassano U. M. , Scacco A. , Tanga A. 
Published: July 2007

AbstractEmission spectra of NaBr:Tl+ excited in the A‐band are measured at various temperatures. The main emission band, called AT, shows a well resolved doublet, whose splitting increases as T1/2. The time resolved emission spectroscopy indicates the presence of a slow emission in the region of the high energy component of the AT doublet. This behaviour is somewhat different from that of the typical thallium phosphors and may be tentatively explained with a Jahn‐Teller splitting of the emission level.
The EPR linewidth of triplet excitons in single‐crystal anthracene: A re‐examination
Authors: Bizzaro W. , Rosenthal J. , Berk N. F. , Yarmus L. 
Published: July 2007

AbstractThe magnetic resonance linewidths of triplet excitions in single‐crystal anthracene are measured in room temperature experiments performed at 24 GHz. The motivations for this study are the recent appearance of Reineker's linewidth theory, which is based on an extension of the Haken‐Strobl model of exciton transport, and the inability of this theory to account satisfactorily for earlier published results on anthracene. The data presented here, which differ distinctly from the previous work, are fit in both magnitude and angular dependence by the theory. This supports the theoretical assumption that hopping between differently oriented molecules in the unit cell is the dominant spin relaxation mechanism for triplet excitons in molecular crystals similar to anthracene.
Specific heat of TbPO4
Authors: Schwab M. , Kahle H. G. 
Published: July 2007

AbstractThe specific heat of TbPO4 single crystals is measured in the temperature range from 1.2 to 6 K. To avoid any effect of strain, the sample is mounted completely free from external stress. The thermal contact inside the sample holder is established by 3He exchange gas. In contrast to earlier measurements the experiment yields two anomalies close together at T = (2.15 ± 0.02) and (2.28 ± 0.02) K.
Investigation of the highest valence band in (Bi1‐xSbx)2Te3 crystals
Authors: Köhler H. , Freudenberger A. 
Published: July 2007

AbstractMaking use of the Shubnikov‐de Haas effect an investigation is made of the electronic parameters of p‐type (Bi1−xSbx)2Te3 crystals (0 < x < 1) prepared by a vertical Bridgman technique. Magnetic fields up to 10 T flux density are available, the crystal temperature at experiment is between 1.6 to 4.2 K. In the whole range, up to 90% antmony content, p‐type crystals can be prepared, allowing the observation of magnetoresistance oscillations in quantizing magnetic fields at least for B ∥︁ c (c trigonal axis). Up to x = 0.6 the results may be explained in the Bi2Te3 ellipsoidal non‐parabolic model for the constant energy surfaces, where the tilt angle of the principal axes increases monotonously with Sb content while the principal mass parameters remain constant. Simultaneously the g‐tensor components vary monotonously with the composition. For x > 0.6 the obtained data on highly doped samples are no longer complete in order to draw reliable conclusions, thouth it is obvious that the Fermi surfaces change their shape. The energy gap between both different valence band maxima, which are occupied at high hole concentrations, is approx imately constant in the whole range of the mixed crystal system.
Theory of the influence of exciton motion on proton relaxation in orgaic solids
Authors: Schwarzer E. , Haken H. 
Published: July 2007

AbstractThe influence of the motion of triplet excitons on the relaxation of protons in organic solids is investigated. The dependence of the longitudinal relaxation rate T1−1 on the Larmor frequency, i.e. on the external magnetic field, is strongly different for different dimensionalities and types of exciton motion. The latter may be coherent (Bloch wave type) or incoherent (diffusive) or in a manner in between as described by the Haken‐Strobl model which is used in this paper. Using this theory the components of the exciton diffusion tensor and the exciton band width can easily be obtained from proton relaxation time measurements.
Elastic response of the fluxoid lattice with planar pinning forces
Authors: Brandt E. H. 
Published: July 2007

AbstractThe elastic displacements of the hexagonal flux line lattice in a type II superconductor are calculated for planar pinning forces. The nonlocal elastic behaviour, derived in a previous paper from the Ginzburg‐Landau theory, leads to strains which may become larger than the homogeneous strain of the local theory by factors up to 2x2b2/(1 − b)2, where b = B/Bc2 is the reduced induction and x is the GL parameter. At b > 0.5 the displacement of the n‐th lattice plane due to a pair of planar forces at n = 0 and at n ≫ 1 is proportional to (1 − b)−2 (−0.7)|n|. This means that the displacements are oscillatory and diverge as b → 1. The elastic response is extremely anisotropic: the maximum strain caused by the same planar force applied in two different directions may differ by a factor of 23. This result is in conflict with the homogeneous and isotropic response predicted by local elasticity theory.
NMR investigations of the melting behaviour of mesogen compounds
Authors: Limmer S. , Grande S. , Lösche A. 
Published: July 2007

AbstractProton NMR spectra of mesogen compounds in the solid phase are recorded. Between 20 and 40 K and 4 and 12 K below the melting point they exhibit a very narrow central line with a structure caused by the chemical shift, which is superimposed to the broad structureless line normally expected from polycrystalline solid phases. It is conclulded that it originates from “quasi‐liquid” molecules whose intensity grows drastically with increasing temperature and involves a maximum of about 2.5% of the whole intensity of the spectrum. In the region close to the melting point appears another lineshape, the so‐called “suprer‐Lorentzian” line, whose intensity increases still stronger than that of the narrow line. It can be shown that it is due to the existence of mesomorphic clusters the directors of which are statistically distributed in the sample. The impurity dependence of these effects is investigated and and an attempt is made to explain them.
Interaction of atomic order with itinerant ferromagnetism
Authors: Billard L. , Villemain P. , Chamberod A. 
Published: July 2007

AbstractThe simultaneous occuring of atomic ordering and ferromagnetic ordering is described in a mean field approximation for an alloy where magnetic properties are due to the itinerant character of electrons: thus a generalization of the Stoner‐Wohlfarth model is proposed for the case of nondisordered ferromagnetic alloys. Treating first the non‐magnetic case, when the intra‐atomic correlation parameter U is not too high, a higher ordering temperature is obtained than in the Bragg‐Williams case; considering then the (weak) ferromagnetic case, also an increase of the Curie temperature is found. However, different situations can occur, according to the choice of the model density of states.
The effect of internal strain and electrical field of an impurity on electron–phonon interaction in n‐type germanium and silicon
Authors: Singh M. Dhwaj 
Published: July 2007

AbstractConsidering the effect of internal strains on bound electron‐phonon interaction, one can get an excellent agreement between theory and experiment for n‐type germanium. It is also established that the large decrease in low‐temperature conductivity on n‐type germanium and silicon, caused by an introduction of impurities with concentration ≦ 1017, cm−3, may be explained be explained by scattering of phonons by charge carriers in the effective electric field of the impurity centres for q < 2kF and by a more consistent consideration of the screening of the phonon‐electron interaction in the region of the long‐wavelength phonons for Ziman scattering for q ≦ 2kF.
Energy bands and electron correlation effects in manganese pnictides
Authors: Bärner K. 
Published: July 2007

AbstractThe optical spectra of MnV compounds (V = P, As, Sb, Bi) do not yield unambiguous evidence on the absorption mechanisms beyond that expected from one‐electron excitations in a spin‐polarized energy band description, although the scattering of the conduction electrons indicates strong d‐electron correlations; in particular, since the scattering is comparable to that of s‐electrons on open 3d and 4f shells a decomposition of the 3d4 cation state into extended and quasi‐localized electron states is suggested.
CPA treatment of the extended Hubbard model
Authors: Mizia J. 
Published: July 2007

AbstractThe Hamiltonian for a completely degenerate d‐band including intra‐atomic Coulomb and exchange interactions is studied using the two‐sublattice alloy analogy method. The density of states and the criterion for the appearance of antiferromagnetism are calculated by this method. At the transition from paramagnetism to antiferromagnetism the energy gap appears. The interaction constant required to produce antiferromagnetism tends to zero at the maxima of the state density function.
Chemical binding and energy band structure of vanadium monocarbide
Authors: Mokhracheva L. P. , Tskhai V. A. , Geld P. V. 
Published: July 2007

AbstractThe band structure of vanadium monocarbide is calculated by the tight‐binding method. A set of ten Boch of the 3d, 4s and 2s, 2p states of the free V and C atoms is used as the basis functions. The secular equation is solved at the 89 points of the 1/48th of the Brillouin zone. The denisty of states and partial density of states histograms are obtained. The populations of the orbitals show that about 0.5 electrons transfer from the carbon to the vanadium, orbitals. However, the distribution of the electron charge density points out that there are strong directional metalnon‐mental bonds, in which carbon cannot be considered as a positive ion.
Anisotropic emission of the X‐ray K‐emission band of nitrogen in hexagonal boron nitride
Authors: Tegeler E. , Kosuch N. , Wiech G. , Faessler A. 
Published: July 2007

AbstractThe intensity distribution of the N K‐emission band of hexagonal boron nitride samples with partially oriented crystallites is found to be strongly dependent upon the take‐off angle of the emitted radiation. The obserbed emission bands can be separated unambiguously into a σ‐ and a ‐subband. On the basis of the directional characteristic of radiating dipoles within the layers (σ‐bondings) and perpendicular to the layers (π‐bonding) the angular dependence of the intensity of the subbands is quantitatively explained. In addition, the degree of orientation of the crystallites in the sample can be determined. The intensity distributions of the emission bands to be expected for single crystals and for samples without any texture are determined; in the latter case the results are found to be in good agreement with experiment.
Jahn‐Teller effect on the 3T1(3F) state and resonance of the 3T1(3P) state with the conduction band in CdTe:Ti2+
Authors: Gardavský J. , Barvík I. , Zvára M. 
Published: July 2007

AbstractOptical absorption spectra of CdTe:Ti2+ with shallow acceptor levels due to cadmium vacancies, exhibit a well resolved triplet structure of the 3T1(3F) band with temperature behaviour suggesting a dynamical Jahn‐Teller effect in the presence of spin–orbit coupling. The photoionization background and the antiresonance band shape of the 3T1(3P) band provide evidence for its location with in the conduction band.
Direct evidence for the singlet‐triplet exciton annihilation in anthracene crystals
Authors: Michel‐Beyerle M. E. , Haberkorn R. , Kinder J. , Seidlitz H. 
Published: July 2007

AbstractTwo‐photon excited singlet excitons are quenched by triplet excitons generated via the monophoton absorption of ruby laser emission. This causes a linear increase of the first‐order decay rate of the fluorescence yielding a singlet—triplet annihilation rate equal to 3 × 10−8 cm3s−1.
Theoretical study of the forbidden ESR transitions of Cr3+ and Fe3+ in alums
Authors: Fårcaş S. I. , Darabont A. , Nicula A. 
Published: July 2007

AbstractThe forbidden fine structure transitions of Cr3+ and Fe3+ ions in alum is explained, using the general theory of the ESR transitions. The calculated transition probabilities are in good agreement with the previously communicated experimental data. The theoretical angular dependence of both, the allowed and forbidden transition probabilities are also presented.
Effects of correlation interaction of electrons with deep holes in X‐ray spectra of metals
Authors: Grebennikov V. I. , Sokolov O. B. , Turov E. A. 
Published: July 2007

AbstractAbsorption spectra and spectra of emission excited by the secondary method are calculated. Two modes of emission excitation are considered: (i) the energy of exciting quanta is great with respect to the inner‐level ionization threshold, (ii) the energy of exciting quanta is continuously filling a small interval (about the width of the valence band) near the threshold. The calculations are carried out for a simple metal model by a one‐site approximation using the formalism of an effective non‐hermitian Hamiltonian which enables one to involve in a natural way into the theory the readjustment effects of a valence system in the field of the emerging hole as well as the finite lifetime of that hole. In the whole frequency interval of the observed values of the spectra the calculation results obtained by the non‐hermitian Hamiltonian method are compared with those obtained on the basis of other methods known earlier. The effect of overlap of the absorption and emission spectra for the threshold mode of excitation is made depending on the relation between the hole lifetime and the conduction electron relaxation time.
Electron localization and statistical mechanics of a zero‐component classical field
Authors: Kumar N. , Heinrichs J. 
Published: July 2007

AbstractThe formal similarity between the exact analytical expressions for the configuration‐averaged propagator for an electron in a random lattice with a Gaussian site energy distribution, and the statistical‐mechanical two point correlation function for a zero component classical field with a quartic self‐interaction is investigated. This enables one to identify the critical point with the mobility edge and thus to obtain the latter as a function of disorder from the recursion relations of the renormalization group. Two distinct situations corresponding to the random potential being real, or imaginary arise naturally in the treatment. The latter case describes the possibility of random absorption or emission of the particle, e.g., by recombination—generation processes. Explicit calculations for the case of an imaginary potential show that the mobility edge moves inward from the ordered band edge and that an Anderson‐like transition occurs when the disorder exceeds a certain value. When the random site potential is real, the mobility edge is not displayed by the treatment, which leads instead to an unphysical fixed point.
Superconductivity originating from quasi‐orbital electrons I. The model of quasi‐orbital conduction electrons
Authors: Krüger E. 
Published: July 2007

AbstractIt will be shown that an adequate description of superconductivity can be given, similar to ferromagnetism, in terms of „quasi‐orbital”︁ conduction electrons, i.e., of conduction electrons occupying repeatedly for a short time localized orbitals and so performing a kind of hopping motion through the crystal. The present theory is based on the observation that the bands of superconducting metals, and only these, yield a distinct type of localized functions. It is shown that quasi‐orbital electrons cannot be described in the framework of the adiabatic approximation when they are assigned to the narrowest bands of the metals. The non‐adiabatic system requires an extension of the operator of the Coulomb interaction. This non‐adiabatic interaction leads to a spin‐phonon interaction for the bands existing in superconductors.
Surface polariton effects in spontaneous Emission II. Effects of spatial dispersion
Authors: Agarwal G. S. , Vollmer H. D. 
Published: July 2007

AbstractThe radiation characteristics of atoms or molecules placed close to the dielectric surface are studied with full account of the spatial dispersion of the dielectric. Both the cases of plasmon polariton and the exciton polaritons are treated. The appropriate response functions are calculated and used to derive an analytic expression for the widtn of the excited state. The numerical results show that spatial dispersion reduces considerably the width from that one in the absence of spatial dispersion. It is found that spatial dispersion effects become more pronounced as the distance of the atom from the surface decreases.
Inelastic incoherent neutron scattering spectra at different temperatures and computer experiment for external phonon modes of naphthalene crystals
Authors: Bokhenkov E. L. , Rodina E. M. , Sheka E. F. , Natkaniec I. 
Published: July 2007

AbstractInelastic incoherent neutron scattering spectra are given from naphthalene crystals at 4.7, 80, and 296 K in the region of external phonon modes. The formulation of a computer experiment to obtain information involved in experimental spectra is analyzed and the advantages of the direct spectral problem as a method of solution are shown. The solving of the problem is carried out in the harmonic and quasi‐harmonic approximations. The results are used to explain the observed temperature changes in the scattering spectra. Computer calculation sensitivity to structural data and parameters of interatomic potential is revealed. Parameter dependence of the crystal phonon density of states on temperature is established.
A new concept of the model for the paramagnetic E′‐centre in the SiO2−x system
Authors: Shendrik A. V. , Yudin D. M. 
Published: July 2007

AbstractThe main paramagnetic centres radiation‐induced in vitreous and crystalline silica are the E′‐centres. Essential basis for this model is the assumption that the unpaired spin is located on the sp3 hybrid orbital of a silicon atom oriented to the O‐vacancy. This assumption is based on the detection of hyperfine structure line doublet with a splitting of 400 G. The intense spectrum of this doublet is observed on samples of silica unenriched with isotope 29Si, but containing hydrogen. From the dependence of the E′signal on the preparation conditions and the samples treatment an association of the doublet not with the 29Si nuclei but with protons is suggested. A model for the E′‐centre is proposed, where the unpaired spin is located on the molecular orbital bonding three ligand oxygens, but not on the sp3 hybrid orbital of silicon.