bluuebunny/crossref_metadata_2025_split huggingface dataset:
Huang diffuse scattering from self‐interstitials in a trigonal lattice
Authors: Khanna Rita 
Published: July 2007

AbstractUsing the continuum theory of linear elasticity, the Huang diffuse scattering (HDS) is calculated from self‐interstitials in a trigonal lattice. Various defect configurations are represented according to the point group symmetry of the defect site and the contribution to HDS from all possible equivalent orientations of a defect configuration (assumed to be equally populated) is averaged It is possible to clearly distinguish between defects of different long‐range symmetry by measuring HDS about appropriately chosen reflections and directions.
Optical properties of inhomogeneous colloidal centres in alkali halides
Authors: Ekmanis Yu. A. , Radchenko I. S. 
Published: July 2007

AbstractCalculations are made of optical absorption spectra for the following inhomogeneous colloidal centers of sodium in NaCl: for metallic particles of sodium; particles with oxidized shell; particles with a dielectric unrelaxed shell, as well as the shell in the form of a transitional layer with a low concentration of free electrons acting in plasma oscillations, etc. The experimental observations of the position of the maximum of the absorption band enable the identification of a number of the models studied in irradiated as well as in additively coloured NaCl crystals.
Non‐radiative transitions: Fundamental difficulties of the adiabatic base approach
Authors: Wagner M. 
Published: July 2007

AbstractThe adiabatic base approach is extensively used in literature (“Condon” approximation, “non‐Condon” approximations). Two fundamental difficulties are indicated: (a) for large Huang‐Rhys factors it is not the non‐adiabaticity operator which governs the non‐radiative decay but tunneling; (b) for a small transitive coupling parameter Δ very high potential barriers (with divergent area) are built up as a non‐adiabatic consequence of non‐crossing. A possible way out is shown by suggesting a release of the non‐crossing requirement.
Modified Thomas‐Fermi approximation for systems with finite surface barriers
Authors: Bartoš I. , Kolář M. , Paasch G. 
Published: July 2007

AbstractIncorporation of a boundary condition into the Thomas‐Fermi approximation is generalized for systems with finite surface barriers. The standard and the modified procedures for the determination of the charge density are tested on the image‐type model potential corresponding to the bent bands at surfaces of semimetals or highly doped semiconductors. Substantial improvement of the description of the electron charge density is achieved in the modified Thomas‐Fermi approximation.
Vibronic and electron‐phonon coupling in spectra of substituted polyenes in rigid matrices
Authors: Nikitina A. N. , Osadko I. S. , Vasilieva I. A. , Yanovskaya L. A. 
Published: July 2007

AbstractIt is found that the electronic excited state 11Bu does not influence the intensity distribution in the electronic 11Ag → 21Ag transition though it is partially allowed. It is determined with the help of the electron‐vibrational interaction theory using the joint analysis of fluorescence spectra and fluorescence excitation spectra of three arylpolyenes in n‐paraffin matrices at 4.2 K. Elastic forces, binding the polyene molecules with the environment, are shown to change in the phototransition.
Consistency condition in the energy expression of the pseudopotential theory of metals and unified study of alkali metals
Authors: Sen D. , Sarkar S. K. , Sengupta S. , Roy D. 
Published: July 2007

AbstractFrom a careful analysis of the energy expression of the second‐order pseudopotential theory, the reason for the breakdown of the consistency condition is pointed out. The problem is resolved by introducing the concept of local volume strain which introduces some modifications in the dynamical matrix and leads to the equality of static and dynamic elastic constants. A unified study of the alkali metals with the Heine‐Abarenkov model pseudopotential in conjunction with Taylor's dielectric function, and taking proper care of the consistency condition, yields satisfactory results for both the static and dynamic properties of these metals. One interesting feature of the present investigation is that the theory satisfying the consistency condition reproduces the crossing of the longitudinal and transverse branches in the (100) direction for Li, while reproducing the normal behaviour for the dispersion curve of other metals.
Phonon‐assisted decay of excitons in anthracene crystals
Authors: Marisova S. V. , Myasnikov E. N. , Lipovchenko A. N. 
Published: July 2007

AbstractThe reflection spectra, R(ω), are investigated from the (201) face of anthracene single crystals at low temperatures (4.2 to 60 K). Absence of surface effects makes possible to judge from the reflection curve on the spectral dependence of the decay parameter, γ, due to exciton‐phonon interaction. The calculation of γ(ω) is made by use of a nomogram graphically representing the functional relation between the values R, ω, and γ. It is shown that the decay parameter is essentially frequency dependent at low temperatures. On the basis of the calculated γ(ω) the mean value is estimated of the interaction energy of excitons with acoustic and optical phonons in anthracene crystals.
Spin‐phonon interactions in the ising model with a transverse field
Authors: Wesselinowa Julia M. 
Published: July 2007

AbstractA Green function technique is used to study the effects of spin–phonon interactions in the Ising model with a transverse field. The renormalized energy of the coupled mode, the damping of the spin waves, and the phonon damping are evaluated. The transverse dynamic structure factor exhibits three peaks due to the coupling of the transverse soft‐mode and the acoustic phonon mode. The width of the central peak is proportional to the phonon damping.
Comparison of different approaches to the study of local defects in crystals. I. Theoretical considerations and computational schemes
Authors: Pisani C. , Dovesi R. , Ugliengo P. 
Published: July 2007

AbstractThe standard way of treating local defects in crystals is to correct the Green function of the perfect periodic host system so as to account for the defect. This approach, which is termed here as “perturbed crystal”, is compared with a “perturbed cluster” approach where instead the molecular solution for a cluster of atoms around and including the defect is corrected in order to account for the presence of the infinite surrounding medium. It is first shown that when a unique basis set is used to describe the crystal both, before and after the defect is created, the perturbed crystal approach is essentially simpler. When however the defect is complicated and the use of different basis sets is practically compulsory, then the other approach is more natural and the corresponding computational scheme is more easily implementable. New explicit formulae for the perturbed cluster approach are derived which are more powerful and general than those used in previous works.
Effect of uniaxial long‐range exchange interaction on the properties of surface spin waves in a Heisenberg ferromagnet
Authors: Petrova T. G. , Syrkin E. S. 
Published: July 2007

AbstractThe low‐ and high‐frequency surface states in a single‐magnon spectrum of the Heisenberg ferromagnet with uniaxial exchange interaction of the long‐range type are studied. The energies and damping decrements of surface spin waves and the surface projected spectral densities of magnon states are obtained. It is found that the considered anisotropic interaction results in new formation conditions of the surface spin waves and essentially affects their characteristics.
Comparison of different approaches to the study of local defects in crystals. II. Substitutional impurities in the tight‐binding approximation
Authors: Pisani C. , Dovesi R. , Ugliengo P. 
Published: July 2007

AbstractDifferent approaches to the study of local defects in perfect crystals are compared as applied to the classical problem of substitutional impurities in tight binding (TB) cubic metals. The standard embedding procedure proposed by Koster and Slater (KS) is perfectly suited for this problem and its results are taken as a reference. It is so possible to evaluate the performance of isolated cluster (IC) calculations, and of those “perturbed cluster” approaches which correct the cluster molecular solution by a suitable coupling operator (MLEC schemes). It is shown that while IC results are affected by enormous relative errors at small perturbations even with large clusters, the MLEC approach is very effective in accounting for the presence of the surrounding media and reproducing the correct electronic structure within the cluster.
Positron–annihilation measurements of the Fermi surface of copper‐base solid solutions with gallium, germanium, and nickel
Authors: Steinmetz K.‐H. , Fischer H.‐P. , Martin M. , Nembach E. 
Published: July 2007

AbstractThe {011} cross‐section of the Fermi surface of Cu‐rich solid solutions with Ga, Ge, and Ni is measured by positron annihilation. The “rotating specimen” method is used. The concentrations of Ga and Ge cover the whole range of primary solid solutions; cNi extends up to 22 at%. For all three solutes investigated, the neck radius of the Fermi surface increases monotonously with solute concentration. For a given electron per atom ratio e/a, Ga widens the neck 32% more than Ge does. All three solutes decrease the ratio of maximum to minimum diameter of the Fermi surface. The electronic structure of these solid solutions is not exclusively determined by the e/a ratio, but depends on the specific properties of the solute. The present experimental results do not support the view that the extent of primary solid solutions is mainly governed by the electron structure.
Thermoluminescence and optical absorption studies rubidium bromide doped with barium
Authors: Sastry S. B. S. , Nagarajan S. 
Published: July 2007

AbstractThermoluminescence (TL) and optical absorption studies are made on RbBr:Ba2+. An absorption band due to Z1‐centres appears at 1.58 eV on F‐light bleaching subsequent to γ‐irradiation. A TL glow peak attributable to Z1‐centres is identified. TL emission under the main glow peak shows a broad emission at 2.65 eV with a shoulder at 1.95 eV. This 1.95 eV emission is attributed to VM2‐centres which give rise to an absorption band around 4.1 eV. A tentative energy band scheme is suggested explaining the various TL processes.
EPR and luminescence of Mn2+ in distorted tetrahedral symmetry in CaZnF4 crystals
Authors: Heming M. , Lehmann G. , Recker K. , Wallrafen F. 
Published: July 2007

AbstractSmall crystals of CaZnF4 with scheelite‐type structure, doped with about 1% Mn are obtained from the melt by the Bridgman method with subsequent annealing at 725 °C, 50 K below a reversible phase transformation detected by DTA. Mn2+ exclusively occupies Zn sites as evident from the size of the hyperfine splitting constant. The intrinsic zero field splitting parameter of second order obtained from superposition analysis is in the same range as that for [MnF6]4− units. The luminescence spectra do not serve as a critical test for distinction between four‐ and eightfold coordination.
Magnetization and 161Dy mössbauer effect study of DyMn2 and Dy6Mn23 and their ternary hydrides
Authors: Gubbens P. C. M. , Ras W. , Van Der Kraan A. M. , Buschow K. H. J. 
Published: July 2007

AbstractThe compounds DyMn2 and Dy6Mn23 and their ternary hydrides are investigated by means of magnetic measurements and 161Dy Mössbauer spectroscopy. In DyMn2 magnetic ordering disappears after charging with hydrogen gas. In Dy6Mn23 the absorption of hydrogen gas leads to a strong reduction of the bulk magnetization even though the Dy sublattice remains magnetically ordered at low temperatures, with magnetic moments on the Dy atoms close to the free ion values.
Study of the 3D5 Shell Deformation of Fe3+ Ions in Znfe2O4 by High‐Field Mössbauer Spectroscopy
Authors: Ligenza S. , Lukasia M. , Kucharski Z. , Suwalski J. 
Published: July 2007

AbstractThe deformation of the 3d5 electron shell of Fe3+ ions in ZnFe2O4 is investigated by Mössbauer spectroscopy without and with an external magnetic field of 6 T at 4.2 K. It is found that 3d5 shell deformation observed by neutron spectroscopy brings about a quadrupole shift equal to ϵ3d = −0.030 mm/s. The magnitude of all other hyperfine interaction parameters of 57Fe nuclei are also reported. Noncollinear arrangements of Fe3+ spins, inside clusters as well as in their local environments, are observed. Among the Fe3+ ions in the octahedral B‐sites five different magnetic configurations are distinguished.
Low‐Temperature Fluctuational Motion of Dislocations in Crystals II. Manifestations Of Dissipative and Quantum Effects in the Low‐Temperature Plasticity
Authors: Osetskii A. I. 
Published: July 2007

AbstractThe temperature behaviour of the fluctuation‐dissipative effects is analysed. At sufficiently low temperatures it is controlled by variations in the viscosity coefficients of the phonon and electron gas. Some experimental data are quoted which can be regarded as evidence for the influence of fluctuation‐dissipative effects upon the low temperature plasticity of materials, i.e. change in the activation energy during NS transition, correlation between the activation energy and the phonon gas viscosity, etc. The temperature dependence of such values as the flow stress, activation energy and activation volume, work hardening coefficients, and the relaxation depth of effective stresses are analysed for the range of temperatures where fluctuation‐dissipative effects are essential. The dependences are calculated both, in the framework of the classical approximation and in the fluctuation‐dissipative model, and compared with the data measured with single crystals of lead and zinc at temperatures below the Debye point. As found, many anomalies observed at low temperatures in the temperature behaviour of the plasticity parameters can be satisfactorily explained as manifestations of the impact of dissipation on the velocity of activated dislocation motion through the crystal.
Tight‐Binding Cluster Model for C, Si, and Ge. I. Analytic Solution for s‐States in Diamond Lattice
Authors: Bílek O. , Skála L. , Künne L. 
Published: July 2007

AbstractUsing the tight‐binding approximation an analytic solution of the Schrödinger equation for the s‐states of C, Si, and Ge clusters in the form of a rectangular parallelepiped is found and discussed.
Local Heine‐Abarenkov Potential with Volume‐Dependent Parameters of Al
Authors: Soma T. , Konno Y. , Kagaya H.‐B. 
Published: July 2007

AbstractA local Heine‐Abarenkov model potential with volume‐dependent parameters is proposed for Al. Two parameters are determined by satisfying the zero pressure condition and the first zero of the empirical pseudopotential interpolated from band calculations. Calculated values of cohesive energy and the equation of state are in good agreement with the experimental data.
Resonant Coherent Energy Transfer. Role of Initial Conditions
Authors: Agabekyan A. S. 
Published: July 2007

AbstractThe dependence of dynamics of coherent resonant energy transfer of electronic excitation between impurity ions in condensed media on the initial conditions of the donor excitation is investigated. Their crucial role in the coherence of the energy transfer process is shown. Validity criteria of different limiting cases of the energy resonant transfer are specified taking into account initial conditions of excitation. The “excitation trapping” effect at the coherent energy transfer is also shown to be present.
Density of States and Optical Conductivity of Ferromagnetic Nickel
Authors: Ahuja A. K. , Auluck S. , Joshi S. K. 
Published: July 2007

AbstractThe density of states and the interband optical conductivity of ferromagnetic nickel are calculated using the energy eigenvalues and the eigenfunctions from the interpolation scheme band structure where the parameters are adjusted to fit the Fermi surface data. The Brillouin‐zone integrations are performed using the special‐direction method. The effects of including optical matrix elements and a phenomenological lifetime broadening are studied. The calculations are in good agreement with the optical data. A comparison is made with the recent angle resolved photoemission data.
The Biexciton Levels and Nonlinear Optical Transitions in ZnO
Authors: Hvam J. M. , Blattner G. , Reuscher M. , Klingshirn C. 
Published: July 2007

AbstractThe controversy about the level scheme of the biexcitons in ZnO is solved by two‐photon reabsorption spectroscopy. Three levels are detected, corresponding to the possible combinations of A and B valence band holes. The diamagnetic shift of these states is below 2 × 10−6 eV T−2 in agreement with the small exciton and biexciton radii. In forward two‐photon Raman scattering, two excitation induced renormalizations of the polariton dispersion are observed, partly involving transitions to the biexciton level. The M‐band luminescence and the resonance structure observed in backward two‐photon Raman scattering are reconsidered in terms of the new level scheme.
Effects of a Transition Layer on Nonlinear Surface Polaritons
Authors: Wendler L. 
Published: July 2007

AbstractThe dispersion relation for nonlinear surface polaritons is derived, for both, p‐ and s‐polarization, which propagate in a system consisting of two semiinfinite media. One of them is characterized by a nonlinear diagonal dielectric tensor. Moreover a transition layer (thickness 20 to 150 Å) between the two media is taken into account.
Impurity Band Conduction in HgTe. II. Theoretical Analysis
Authors: Dziuba Z. 
Published: July 2007

AbstractThe impurity band conduction in HgTe is analysed. The electrical conduction in low magnetic field is described in short mean free path approximation. The impurity concentration is estimated by the analysis of the electrical conduction versus magnetic field. The electrons and holes in the impurity band are qualitatively described as carriers from different parts of the impurity band.
Electronic Relaxation Effects in Core Level Spectra of Surfaces and Interfaces
Authors: Bechstedt F. , Enderlein R. , Reichardt D. 
Published: July 2007

AbstractThe electronic relaxation energy of core hole excitations is calculated for the spatial inhomogeneous system of a solid with a surface or interface. The most important approximations involved in the calculations are the linear expansion of the relaxation energy with respect to the difference of the shielded and bare core hole potentials and, for the treatment of the surface or interface, the neglect of quantum mechanicals interference terms in the polarization function of the system. At a given distance from the interface the relaxation energy of the excited core hole can be expressed in terms of the bulk dielectric function. The general theoretical results are applied to calculate relaxation energies as functions of the distance from the surface or interface for the clean Si surface and for abrupt interfaces of Si with SiO2, GaAs, and metallic Pd. The relaxation energy exhibits notable spatial variations only within a thin layer of about 2 at. units thickness whereas it remains practically constant and shows only small deviations from the bulk value outside of this layer. The conclusion is drawn that core electron binding energies from first layer atoms at a surface or interface are shifted because of spatial changes of relaxation energies by tenths of an eV compared to bulk binding energies. For chemisorbed atoms the relaxation of the electrons in the underlying solid changes core electron binding energies compared to those of free atoms much stronger (several eV).
The Luminescence of K4Bi2Br10 · 4 H2O and Rb3BiBr6 Single Crystals
Authors: Timmermans C. W. M. , Blasse G. 
Published: July 2007

AbstractThe luminescence properties of K4Bi2Br10 · 4 H2O and Rb3BiBr6 are reported. Both compounds show blue luminescence at low temperatures. For Rb3BiBr6 the luminescence is ascribed to the 3P0 → 1S0 transition on the isolated Bi3+ centre, while in K4Bi2Br10 · 4 H2O the luminescence originates from the [Bi2Br10]4− dimers. The energy level diagram of the dimer centre is approached by using simple MO‐theory. The compound K4Bi2Br10 · 4 H2O shows also an emission band in the red, which is ascribed to a charge‐transfer transition. The quenching of the luminescence is caused by energy migration among the dimers in K4Bi2Br10 · 4 H2O, while in Rb3BiBr6 the luminescence is quenched via the charge‐transfer state.
Channeling of Ultrarelativistic Electrons in Crystals
Authors: Muralev V. A. 
Published: July 2007

AbstractThe kinetic equation for axially channeled ultrarelativistic electrons in the energy range of 1 to 55 GeV for Si and W is solved. The results show that the dechanneling lengths for different targets are close. Yet, the Kumakhov radiation power in W is higher than in Si. Therefore, the Kumakhov radiation efficiency in heavy crystals, such as tungsten, can be very high. The present method permits to study the contribution provided to the dechanneling function by electron scattering, thermal vibrations, the density effect etc. It is shown that electron scattering provides the main contributions. The results can be useful in planning experiments on charged‐particle radiation in channeling and in the data analysis, in particular in obtaining the optimal crystal thickness.
Radiation Damage Studies of Co2+ and Ni2+ Doped NH4Cl Crystals
Authors: Rambau B. , Ramasastry C. , Chowdari B. V. R. 
Published: July 2007

AbstractResults from the radiation damage studies of NH4Cl:Co2+ and NH4Cl:Ni2+ crystals are presented. On X‐irradiation at room temperature the NH4Cl:Co2+ crystals are found to absorb at 270, 345, 585, 900, and 1000 nm. These absorption bands are attributed to the charge transfer transitions between radiation induced hydrazine‐like defect, N2H, and ligands H2O or NH3 which are made available in the crystal along with the divalent impurity. If not all the absorption bands but similar absorption is found on irradiation in Ni2+ doped NH4Cl crystals also. ESR studies of X‐rayed Ni2+ doped NH4Cl crystals reveal the formation of both, Ni+ and Ni3+. Spin‐Hamiltonian parameters for these centers are given.
Central Peak in Ising Model with Transverse Field (II)
Authors: Kashcheev V. N. 
Published: July 2007

AbstractIt is shown that in the hydrodynamic limit the central peak, traced back to the interaction of the pseudospin critical fluctuations with thermal diffusion mode in the Ising model with a transverse field, has the Lorentz form. The critical exponent of the width of this peak is calculated.
Splitting of the 3d Levels of Iron Group Impurities in Crystals with Zincblende Structure
Authors: Biernacki S. W. 
Published: July 2007

AbstractA new parametrization scheme is presented of the crystal term energies for 3d impurities in ZnS‐ structure crystals. This allows a practical analysis of the optical spectra in these structures. This scheme, unlike the Tanabe‐Sugano scheme, accounts for the different deformations of e‐ and t2‐ orbitals in the tetrahedral crystal field. To avoid the complexity caused by the many unknown parameters which appear when the e‐ and t2‐Orbitale are considered deformed to different degrees, the point charge model of the crystal field and the Slater form of the d‐orbitals are employed. This provides two adjustable parameters for describing the crystal term energies. The results indicate that the energy separation between the crystal terms depends not only on the Racah parameters B and C but also on the Racah parameter A, and it is shown how the Racah parameters for a given impurity depend on the crystal field. The energy separation Δ between the crystal terms A2 and T2 is interpreted to be the sum of two terms: Δcryst the contribution due to the crystal field splitting and Δrep the contribution due to different repulsion energies between the electrons in the two states. As an example of the application of this parametrization scheme, the impurities Ti2+, V2+, Co2+, and Ni2+ in ZnSe are considered.