bluuebunny/crossref_metadata_2025_split huggingface dataset:
Laser modulation of photochromic effect in crystals with sillenite‐type structure
Authors: Efendiev Sh. , Gavryushin V. , Raciukaitis C. , Bagiev V. , Kazlauskas V. , Puzonas G. , Aliev R. , Mustafaev E. 
Published: July 2007

AbstractIn sillenite‐type crystals at low temperatures the phenomena of effective laser modulation of the photochromic effect (LM PCE) previously investigated in steady‐state conditions are found. The lack of effects of spatial excitation transfer during PCE is shown from the kinetics of PCE laser “switching”. Conclusions about intracentre behaviour of the above processes are made. The IR laser illumination is found to lead to anomalous LM PCE (optical obscurity of crystals) relative to the previously known steady‐state IR effect on PCE (crystal brightening). Based on the LM PCE data, a new model of intracentre optical processes and PCE centers with anomalously strong electron—phonon interaction (EPI) near the centers with a number of excited states is proposed. The idea of the above model is the assumption of non‐photoactivity of the ground states of PCE due to strong EPI from which the centers remove at IR illumination. The main regularities of PCE previously known are also explained by the microscopic model proposed with regard to Stokes losses of lattice relaxation.
A model for describing dielectric breakdown in vitreous solids based on the concept of low‐energy excitations
Authors: Danziger M. , Bernhardt A. 
Published: July 2007

AbstractThe anomalous behaviour of different physical characteristics in vitreous solids compared to the behaviour in the crystalline phase, in particular their dielectric behaviour, can be described by the concept of a system of low‐energy excitations in these solids. This concept is also applicable for amorphous SiO2 layers in MOS structures. Thus, a model of breakdown behaviour based on the assumption of the existence of fluctuations of correlated local internal electrical fields and low‐energy excitations within these layers is elaborated.
Phonons in Some H.C.P. Solids
Authors: Rathore R. P. S. , Singh A. , Agrawal R. M. 
Published: July 2007

AbstractThe phonon dispersion along the directions [0001] and [0110] in Hf, Ti, and Cd is determined by employing the combined form of a pairwise and non‐pairwise potential, which derive their forms from the generalised exponential nature of repulsive and attractive interactions.
Coherent Potential Method in the Electronic Theory of Disordered Alloys
Authors: Kulish N. P. , Petrenko P. V. , Repetskii S. P. , Shatnii T. D. 
Published: July 2007

AbstractA general solution of the problem of multiple scattering on a localized random potential is achieved in a single‐band model of diagonal disorder for a binary substitutional alloy. A configurationally averaged 〈T〉‐matrix is presented as a cluster‐type expansion. The short‐range order effect on the electronic spectrum, specific heat capacity, and residual electrical conductivity is studied with regard to the multiple scattering on a two‐particle cluster (on pairs of atoms) for the coherent potential satisfying the condition of the single‐site approximation. Expressions for the electronic density of states and electrical conductivity (allowing for the scattering on pairs) are presented in an analytical form.
Low‐Temperature Heat Conductivity of a Crystal Lattice with Nondiagonal Disorder
Authors: Zhernov A. P. , Salamatov E. I. , Chulkin E. P. 
Published: July 2007

AbstractA theory is developed which allows investigation of the phonon‐transfer processes in a harmonic crystal lattice with nondiagonal disorder taking into consideration the weak localization phenomenon. In the expressions obtained for the heat conductivity coefficients the phonon and impurity modes are taken into account.
The Electronic Structure of Crystalline Lead Oxides. I. Crystal Structure and LUC‐CNDO Calculations
Authors: Evarestov R. A. , Veryazov V. A. 
Published: July 2007

AbstractThe crystalline structure of lead oxides is rewieved. In the framework of LUC‐CNDO computational scheme the electronic structure of PbO, PbO2, Pb2O3, and Pb3O4 crystals is investigated. The results obtained are compared with experimental data.
The Electronic Structure of Crystalline Lead Oxides. II. Chemical Bonding in the Crystalline Lead Oxides
Authors: Evarestov R. A. , Veryazov V. A. 
Published: July 2007

AbstractA quantum‐chemical definition is proposed of the full atomic valence taking into account both, covalent and ionic components of chemical bonds formed by an atom in molecules or crystals. Atomic charges, covalent bond orders, and full atomic valencies of lead and oxygen atoms in the crystalline lead oxides are calculated in the framework of the LUC‐CNDO approach.
Exciton Trapping at Au and Ag Atoms in Rare Gas Matrices
Authors: Schrimpf A. , Herkert B. , Manceron L. , Schriever U. , Stöckmann H.‐J. 
Published: July 2007

AbstractThe fluorescence of Au and Ag atoms in Ar and Kr matrices is investigated as a function of the excitation wavelength in the UV and VUV range. The occurrence of a fluorescence of the dopants during excitation into the exciton bands of the matrices demonstrates the existence of energy transfer from the solid host to the embedded metal atoms. The emission spectra after exciton and inner‐shell excitation, respectively, as well as the temperature dependence of the emission yield show striking similarities. From this it is concluded that the exciton trapping leads to an excitation of the same inner‐shell states that are also populated by direct inner‐shell excitation of the metal atoms.
A Functional‐Integral Study of the t̃pp‐Jpd‐Jdd Model for CuO2‐Based Superconductors
Authors: Bryja L. , Kolley E. , Kolley W. 
Published: July 2007

AbstractA functional‐integral representation of the ˜pp‐Jpd‐Jdd model for a CuO2 layer in high‐Tc superconductors is exploited in the saddle‐point approximation. The self‐consistent mean‐field scheme resulting from the static and homogeneous approximation of the saddle‐point equations is solved numerically at T = 0. The O‐hole pairing connected with the superconductivity is investigated as a function of the doping concentration of O holes. The interplay between the Cu–O Kondo‐type and the Cu–Cu superexchange interactions is illustrated.
Transfer Matrix Formalism for Retarded Waves in Layered Magnetic Structures. Bulk and Surface Modes
Authors: Barnaś J. 
Published: July 2007

AbstractThe retarded modes of layered magnetic structures are considered theoretically for arbitrary direction of wave propagation. A 4 × 4 transfer matrix formalism is used to derive the dispersion equations for bulk and surface modes of semi‐infinite superlattices.
Magnetic Susceptibility Calculation of Zn1‐xMnxS by the Nearest‐Neighbour Isolated Cluster Model
Authors: Spasojevic V. , Bajorek A. , Szytula A. , Giriat W. , Mitic D. 
Published: July 2007

AbstractMagnetic susceptibility of semimagnetic semiconductor Zn1‐xMnxS (x = 0.05, 0.10) is measured by the Faraday method. Starting from the isolated cluster model in the nearest‐neighbour approximation, and from the random distribution of Mn2+ ions, the temperature dependence is calculated of the magnetic susceptibility of Zn1‐xMnxS. By comparing these results with experimental χ (T) data, good agreement is obtained only for lower concentration x = 0.05. Treating the probabilities of finding the Mn2+ ions as singles, pairs, or triplets as adjustable parameters (modified distribution), quantitative agreement is obtained for both concentrations. Probabilities for every type of cluster, in both distributions, are given. The results show an enhancement of the clusterisation when the concentration x increases.
Analysis of Electronic Polarizabilities in Ionic Crystals
Authors: Dikshit U. C. , Kumar M. 
Published: July 2007

AbstractThe existing sets of additive electronic polarizabilities for alkali halides and alkaline earth chalcogenides are examined by evaluating the high frequency electronic dielectric constants and presenting a comparison with experimental data. The crystalline state values of polarizabilities are also compared with free ion values. Various physical effects responsible for changing the values of polarizabilities in the crystalline state are discussed. The differences in free state and crystalline state polarizabilities are investigated in terms of the classical model due to Havinga and quantum mechanical model due to Yamashita and Kurosawa.
Blue and Violet Emission of PbCl2
Authors: Nikl M. , Birch D. J. S. , Polak K. 
Published: July 2007

AbstractThe blue and violet emission of undoped PbCl2, is investigated in the temperature region from 4.2 up to 200 or 60 K, respectively. Two subbands are resolved in the blue emission and the energy transfer between them is revealed at temperatures above 80 K. The origin of blue emission and the influence of oxygen are discussed. The decay of violet emission is reported and the activation energy of its thermal quenching is calculated from the lifetime‐temperature dependence. The influence of diffusion of bromide ions into PbCl2 surface layer on the violet emission is tested.
Defect Production and Annealing Due to Relaxation of Electron Excitations in Fast Ion Tracks
Authors: Urmanov A. R. 
Published: July 2007

AbstractA mechanism of defect production and annealing due to irradiation with high‐energy ions is proposed. It is shown that the degree of damage on the subsurface region of a crystal is determined by competition of two processes: migration of defects from the depth to the crystal surface and their recombination due to an increase in the mobility of defect‐forming atoms and vacancies.
Model Calculations of Nonlinear Optical Effects in Molecular Aggregates
Authors: Voigt J. , Bittner Th. , Kehrberg G. 
Published: July 2007

AbstractBasing on new experimental results on nonlinear transmission of photosynthetic particles measured with the pump‐ and probe‐beam technique a reaction kinetic three‐level model involving one‐ and two‐particle excitations is developed to describe the observed phenomena quantitatively. It is shown that the nonlinear effects are caused by a competition between the one‐ and two‐particle excitations. The physical nature of the two‐particle excitations is discussed as well their role in a coherent energy transfer process in photosynthetic membrane.
Localized Hole States in a Two‐Dimensional Antiferromagnet
Authors: Rubin P. , Sherman A. 
Published: July 2007

AbstractA connection between band excitations and sublattices in the Hubbard antiferromagnet leads to the appearance of two types of localized states arising due to an impurity on the “own” (for given band excitations) and “alien” sublattices. In the case of the substitutional impurity the conditions of the appearance of these localized states, their energies and symmetries are obtained in dependence on the ratio of the exchange constant to the hopping matrix element. These dependences and the number of the localized levels are different for the two types of states mentioned.
The Effective s‐Matrices in the Theory of Magnetic Breakdown with Spin Flip Magnetoresistance of a Simple Model
Authors: Proshin Yu. N. , Kh. Useinov N. 
Published: July 2007

AbstractThe consistent theory of magnetic breakdown in metals taking into account the existence of spin and spin‐orbit interaction of conduction electrons is developed. The effective s‐matrix and probabilities for small orbits of “diangular” and “triangular” type are calculated. The magnetoresistance of magnetic breakdown linked networks with one‐dimensional topology is calculated for the case of coherent movement of electrons on the small orbit of the network. The double‐peaked structure of magnetoresistance oscillations for a simple hypothetical metal is obtained.
Electromagnetic Fields and Power Losses for Superconducting Slabs
Authors: Refai T. F. , Saif A. G. 
Published: July 2007

AbstractThe distribution is investigated of the London penetrating magnetic field, vortex field, and the stray magnetic field within a semi‐infinite type II superconducting slab subjected to a vibrating wire carrying a direct current. Exact analytical solutions of the fields are obtained and the avarage time power loss on the surface of the superconductor slab is calculated. It is shown that the only field that contributes to the power loss is the London electromagnetic field. The effect of the London penetration depth on the power loss is investigated.
Temperature Dependence of the EPR Spectra of Gd0.5RE0.5 Ba2Cu3O7‐δ Compounds in the Orthorhombic and Tetragonal Phases
Authors: Guskos N. , Triberis G. P. , Lykodimos V. , Windsch W. , Metz H. , Koufoudakis A. , Mitros C. , Gamari‐Seale H. , Niarchos D. 
Published: July 2007

AbstractThe materials Gd0.5RE0.5 Ba2Cu3O7‐δ (Re = Y, Sm, Eu, and La) are investigated in the orthorhombic (HTC) and tetragonal (non‐HTC) phases using EPR method. For both phases EPR signals associated with Gd ions are detected. In the tetragonal phase a strong temperature dependence of the intensities of this line is observed. These characteristics can be ascribed to the skin effect. A small polaron model is proposed to interpret the conduction mechanism of the tetragonal phase (semiconducting) of these samples.
Resonance Dechanneling in Quasiperiodic Superlattices
Authors: Rudko V. N. 
Published: July 2007

AbstractPlanar dechanneling of ions is investigated in strained‐layer quasiperiodic superlattices with two types of layers, A and B, arranged according to the recurrent Fibonacci rule. It is shown that in quasiperiodic superlattices withτlA+lB< λ (wherelAandlBare the respective thicknesses of the layers A and B, λ is the golden section, λ the wavelength of transverse particle oscillations in the channel) the dechanneling is a resonance process. Angular dependences of the dechanneling length are asymmetric and stepwise. The resonance dechanneling in strained‐layer quasiperiodic superlattices may be used for the determination of elastic distortions even in the case when the layer thicknesses are as small aslA,lA< λ. This feature is absent in the case of periodic superlattices.
The IR‐Optical Behaviour of Polycrystalline Dielectric Films An Anisotropic Maxwell Garnett Model
Authors: Lehmann Annemarie 
Published: July 2007

AbstractThe intrinsic anisotropy associated with any inhomogeneous or polycrystalline film is considered in a framework similar to the Maxwell Garnett theory by fields adjusted for a slab. While an earlier paper demonstrates this theory for small ionic volume fractions the case of high packing density of the ionic material is investigated here. Analytical solutions for vibrational frequency shifts and intensity changes in IR spectra are obtained in the approximation of a small fraction of nonabsorbing ellipsoids incorporated into the ionic film material.
Light‐Hole Non‐Parabolicity in the Single Band Approximation
Authors: La Rocca G. C. , Cardona M. 
Published: July 2007

AbstractIn the envelope function treatment of quantum wells and superlattices, an effective mass Hamiltonian including corrections to the quadratic dispersion relation is commonly employed to describe non‐parabolicity and other complications of the band structure. A careful definition of the boundary conditions used to connect the envelope functions at the interfaces is required to consistently take such higher order effects into account to a given order of approximation. It is possible to develop a single band scheme to describe the light‐hole non‐parabolicity implicitly accounting for the coupling to other bands. With respect to the conduction electron case, the coupling between the split‐off and light‐hole bands brings about qualitative changes in the boundary conditions. Model calculations show how the non‐parabolicity affects the energy levels not only through the modified (i.e. non‐quadratic) dispersion relation, but also through the consistently modified boundary conditions. The present simple theory compares favorably with experimental data and more refined theoretical treatments.
The Effects of Lattice Constant Variations on Electron and Positron Charge Densities in Grey Tin
Authors: Soudini B. , Aourag H. , Khelifa B. 
Published: July 2007

AbstractElectron and positron charge densities are calculated as a function of the lattice constant variations in grey tin. The calculations of the electron–positron momentum densities are carried out by using the independent particule approximation coupled with the Gaussian nonlocal pseudopotential method. The results are correlated to the effects of pressure.
Dispersion of the Exciton Polariton Branches in CuCl and Their k‐Dependent Splitting in a Magnetic Field
Authors: Fröhlich D. , Köhler P. , Nieswand W. , Mohler E. 
Published: July 2007

AbstractThe method of three‐photon difference‐frequency generation is used to measure resonances on the lower polariton branch in CuCl. Due to the small linewidth of the resonances (smallest width 80 μeV) it is possible to determine the splitting of the lower branch in a magnetic field at different k‐values for the first time. Resonances on the upper polariton branches and on the longitudinal exciton branches can also be excited with the use of two‐ and three‐photon sum‐frequency generation and two‐photon absorption. The rather peculiar wavevector‐dependent splitting of the lower polariton branch is explained quantitatively by taking into account the field induced mixing of the Z3‐ and Z1,2‐excitons.
Optical Excitation of DX Centers in GaAlAs Alloys Doped with Si and Te
Authors: Seguy P. , Yu P. Y. 
Published: July 2007

AbstractThe effect of light illumination on the deep level transient spectroscopy (DLTS) and constant temperature capacitance transient spectra of DX centers in GaAlAs alloys doped with Si and Te is studied. The experimental DLTS spectra are compared with theoretical spectra based on a model in which the only effect of light is to photoionize the DX centers. The calculated spectra reproduce satisfactorily the experimental spectra only in the Te doped samples. In Si doped samples the calculated spectra cannot reproduce the light‐induced peak reported recently by Jia et al. Thus the results confirm that this peak may be associated with a light‐induced shallow metastable center related to Si in GaAlAs. The identification of this shallow metastable state based on the present work and other recent experimental and theoretical investigations is discussed.
Quantum Corrections to the Conductivity in Magnetic Field and Negative Magnetoresistance of Zinc Selenide
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N. 
Published: July 2007

AbstractAn analysis of the negative magnetoresistance (NMR) of n‐ZnSe crystals is made for the first time in frames of a new theory of this phenomenon based on quantum corrections for the conductivity in a magnetic field. The study is carried out for a wide concentration range (2.5 × 1016 to 7.4 × 1017 cm−3) at low temperature (1.65 to 4.2 K). In samples with metallic conductivity the NMR is shown to be well described by means of a localization quantum correction only for weak magnetic fields. With increasing strength of the magnetic field the contribution of anomalous positive magnetoresistance also increases, being related to the quantum correction, which arises from the state density decrease due to electron–electron interaction. The NMR is detected in heavily doped compensated (HDC) samples with low‐temperature conductivity of the Mott type, caused by the state density increase near the Fermi level in the magnetic field.
Temperature and Pressure EPR Studies of Superexchange Coupling in Cu(1‐Phenylpyrazole)2Cl2 Crystals
Authors: Goslar J. , Hilczer W. , Hoffmann S. K. , Krupski M. 
Published: July 2007

AbstractSingle crystal EPR data for Cu(1‐phenylpyrazole)2Cl2 in the temperature range 77 to 300 K and at hydrostatic pressures up to 500 MPa are presented. From the merging effect on the EPR lines the temperature and pressure dependence of the weak exchange coupling is determined. The exchange integral is |J| = 0.0040(2) cm−1 and it strongly increases on cooling and under pressure. Because of the large value of d |J|/dT a transition form the intermediate exchange rate (resolved lines in EPR spectrum) to the strong exchange rate (merged lines) is observed. Methods for deriving the exchange integral from the linewidth in the strong exchange range are discussed.
The Role of 4f–4f Transitions in Magnetooptics of Paramagnetic Rare–Earth Glasses
Authors: Klochkov A. A. , Valiev U. V. , Moskvin A. S. 
Published: July 2007

AbstractTheoretical and experimental investigations are made of magnetooptical activity (MOA) of (parity) forbidden intraconfigurational 4f–4f transitions in Er(PO3)3 rare‐earth paramagnetic phosphate glasses. The interpretation of magnetooptical spectra in frames of a theoretical scheme similar to Judd‐Offelt's theory is carried out for the observed 4f–4f transitions. It is shown that the theory may be used successfully for the quantitative description of magnetic circular dichroism (MCD) spectra (and Faraday effect spectra) in rare‐earth paramagnetic glasses.
Evaluation of Structure and Transport Properties of NiB Glass Melts
Authors: Rao R. V. Gopala , Debnath D. 
Published: July 2007

AbstractLebowitz's solution of C(r) for binary mixtures with a square‐well attractive tail is applied to compute three partial structure factors S11(k), S22(k), and S12(k) of NiB glass melts. The total structure factors obtained from these partial structure factors are found to be in excellent agreement with experimental results. The isothermal compressibilities of these melts are calculated from the partial structure factors in the long‐wave limit through the Kirkwood‐Buff equation. An estimate of the Bhatia‐Thornton structure factors is made. The linear trajectory principle due to Helfand is utilised to calculated the diffusion coefficients of the NiB glass melts. It may be pointed out that this is perhaps the first application of Lebowitz's equations to glassy materials.
Trend to Localization of f‐States in Actinide Metals
Authors: Nikolaev A. V. , Ionova G. V. 
Published: July 2007

AbstractBand‐structure calculations of actinide metals from thorium to americium in f.c.c. and b.c.c. lattices are carried out by the relativistic LAPW method with warped potential and nonfrozen core treatment to obtain their density of states at the Fermi energy. Although band‐structure calculations lead to the necessity of taking the f‐state trend to localization into account, they do not get this localization by intrinsic way. Therefore, the f‐state localization is a many electron process, which could not be obtained within density functional theory.
A Study of the Transverse Ising Model
Authors: Zhong Jia‐Lin , Yang Chuan‐Zhang , Jiang Xue‐Fan 
Published: July 2007

AbstractA new method which combines the discretized path‐integral with variational approximation is proposed and used to derive the free energy of the transverse Ising model in a quantum spin system. The transition temperature dependence of both, the transverse field and the coordination number is obtained analytically. The numerical results are compared with those of other methods.
Calorimetric and Raman Study of the Phase Transition in [N(CH3)4]2ZnBr4
Authors: Igartua J. M. , Ruiz‐Larrea I. , Couzi M. , López‐Echarri A. , Breczewski T. 
Published: July 2007

AbstractRaman scattering and calorimetric measurements are used to study the ferro‐paraelastic phase transition undergone by [N(CH3)4]2ZnBr4 at 287.19 K. The knowledge of its vibrational spectrum, together with the available elastic and thermal expansion data, allow to obtain the specific heat of the phase transition and the associated values for the thermodynamic functions. The transition entropy (ΔS = 1.95 R ± 0.1) confirms the order‐disorder character assigned to this phase transition. Finally, the temperature dependence of the thermodynamic functions is discussed within the frame of the Landau theory.