bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polarized Singlet and Triplet Luminescence and Off‐Centre Position of Excited In+ Ions in a CsBr :In Crystal
Authors: Nagirnyi V. , Vaino P. , Zazubovich S. 
Published: July 2007

AbstractSpectral and polarization characteristics as well as the decay kinetics of the CsBr : In luminescence are investigated in the temperature range from 1.75 to 300 K. Four emission bands (at 2.44, 2.75, 3.27 and 3.32 eV) are observed at low temperatures and interpreted correspondingly as AT, Ax, B, and C emission of In+ centres. The symmetry of the Jahn‐Teller minima of the triplet relaxed excited state (RES) responsible for the Ax and the B emission is established to be trigonal and rhombic, respectively. The AT and the C emission is caused by the radiative decay of the tetragonal Jahn‐Teller minima of the triplet (A) and the singlet (C) excited state. Two slow components are found in the decay kinetics of both, the AT and the Ax emission at T ⪅ 3 K. It points to the splitting of the metastable level both, in the tetragonal (T) minima and in the trigonal (X) minima of the triplet RES. It is shown that the effects observed are caused by an off‐centre displacement of the In+ ion in the triplet RES from a crystal lattice site. For excited ns2 ions in CsCl‐type hosts these effects are not observed before. This is the first observation of the off‐centre effects in the trigonal minima of the triplet RES of ns2 ions.
Dislocation Bound States in Compound Semiconductors
Authors: Farvacque J.‐L. , Pödör B. 
Published: July 2007

AbstractIn semiconductors, which have crystal structure without inversion symmetry, charge carriers interact with the long‐range strain field of dislocations through the deformation potential and the piezoelectric couplings. The ground state energy level of the one‐dimensional (1D) band in the potential, due to the long‐range strain field of an edge dislocation, is estimated theoretically, using simple variational and perturbational methods. The ground state energy levels of the 1D band in n‐type direct bandgap III–V and II–VI compound semiconductors are of the order of a few tens to one hundred meV. The contribution of the effect of the piezoelectric potential to the ground state energy level is relatively small, amounting to about 10 to 30% of the total energy. Finally the analogy of the 1D band associated with the dislocations with the 1D quantum well wire (QWW) is also pointed out.
A New Model Variant for Describing Dielectric Response on the Basis of the Impact of Low‐Energy Excitations
Authors: Danziger M. , Bernhardt A. 
Published: July 2007

AbstractThe anomalous behaviour of very different physical characteristics in vitreous solids, particularly their dielectric behaviour, can be described by a system of additional low‐energy excitations. This holds also for the amorphous SiO2 layers in MOS structures. Therefore, an available model of time‐dependent dielectric response is completed. This model represents the basis for further research, especially of the dielectric behaviour of vitreous solids.
Critical Temperatures of Two Phase Transitions in Mixtures of Spherical and Ellipsoidal Molecules
Authors: Mejdani R. 
Published: July 2007

AbstractIn the usual molecular‐field approximation, an equation is derived for the thermodynamic potential for determining the critical temperatures of two phase transitions in a mixture of ellipsoidal and spherical molecules. These molecules are dispersed on b.c.c. lattice and their ratio of concentrations is different from 1: 1. Also the boundary lines are obtained of the orientational and positional transitions in the temperature‐concentration diagram for different values of molecular parameter (of ellipsoidal molecules) and interaction parameters.
Systematics of the Binary Intermetallic Phases
Authors: Walzer U. 
Published: July 2007

AbstractFirst, a survey is given of semiempirical approaches designed for predicting physical and chemical properties of binary alloy systems from the properties of the elements. The same goal is pursued with the help of a pseudopotential theory with optimum transferability derived from relativistic quantum mechanics. The curves of the l‐dependent bare‐ion pseudopotentials are computed, the spin—orbit coupling being taken into account, and a characteristic radius and a characteristic energy are determined for each of these curves. These dual coordinates are used for the preparation of structure maps in order to predict for binary (1:1) alloys and compounds with a fair degree of probability: space group and structure type of the crystals under normal temperature and pressure conditions, lattice constants, melting temperature, etc. A particularly successful approach is to compute from the dual coordinates a kind of size difference and a function of the hybridization, which then in turn are used as new dual coordinates.
Local and Long‐Range Diffusion of Hydrogen in Amorphous and Partially Crystallized Fe90Zr10 Alloys
Authors: Maier C. U. , Kronmüller H. 
Published: July 2007

AbstractThe magnetic after‐effect spectra of hydrogen (H) charged amorphous Fe90Zr10 alloys containing different degrees of crystallization (10% and 50%) are measured in the temperature range between 4.2 and 480 K. For the partially crystallized specimens one broadened asymmetric relaxation maximum is observed. With decreasing H content a shift of the maximum temperature from 140 to 196 K takes place due to the increase of the average activation enthalpy from 0.33 up to 0.49 eV. Using a phenomenological diffusion model for H in amorphous alloys, which takes into account a broad distribution of equilibrium sites as well as of saddle point energies the H‐induced relaxation maxima and their annealing behaviour are assigned to local jumps of hydrogen in the amorphous phase. In addition, the long‐range H diffusion above 300 K is measured by thermal degassing at different heating rates. The observed similar H degassing kinetics of the amorphous and partially crystallized samples show that the long‐range diffusion is exclusively determined by H atoms in the amorphous phase. The average activation parameters Qdiff = (0.53 ± 0.1) eV and Do = 7 × 10−7±2 m2/s are evaluated for a H concentration of 1.7 at%.
Electronic and Optical Properties of AuAl2 and PtAl2
Authors: Gupta A. , Gupta R. Sen 
Published: July 2007

AbstractElectronic energy bands of two isostructural intermetallic compounds, AuAl2 and PtAl2, are calculated using the composite wave variational version of the APW method. The crystal potential is constructed by superposition of the atomic potential of Herman and Skillman. A comparative study between the 9d noble metal system (PtAl2) and the 10d noble metal system (AuAl2) is attempted. From the band structure data, density of states, joint density of states, ϵ2(ω) spectra and the Fermi surfaces are worked out. Results are interpreted in the light of band structure data and compared and correlated with available experimental results.
Electronic Structures of (ZnSe)2n/(ZnS)2m Strained Layer Superlattices
Authors: Huang He‐Luan , Zhang Guo‐Ying , Wang En‐Ge 
Published: July 2007

AbstractThe electronic structures of (ZnSe)2n/(ZnS)2m strained‐layer superlattice (SLS) are investigated by the recursion method in the tight‐binding approximation. The total, local, and partial density of states are calculated for three cases (n = m = 1; n = m = 2; n = 2, m = 3). The band gap, the Fermi energy, and the valence of an atom for Zn, Se, and S near interface are found in (ZnSe)2n/(ZnS)2m SLS. The relationship between LDOS and PDOS for every atom is analyzed. Also the influence of different (n, m) on the electronic structures of (ZnSe)2n/(ZnS)2m SLS is discussed. Furthermore, this paper indicates that the characters of ionic and covalent bonding are coexistent in (ZnSe)2n/(ZnS)2m SLS.
Reference System Approach in the Electron Liquid Theory I. General Relations
Authors: Vavrukh M. , Krokhmalskii T. 
Published: July 2007

AbstractA new formalism of the statistical description of the electron liquid is proposed. The renormalized statistical perturbation theory is formulated in terms of n‐particle correlation functions of some simpler model system, called the reference system. The functional representations of the partition function, free energy, ground state energy, and two‐particle correlation function are obtained for quantum systems on the basis of the method of collective variables. The approach under consideration describes, in particular, the strongly coupled electron liquid, it is general enough and can be generalized to the case of superconducting electron systems, systems in external fields, and also Bose systems.
Calculation of the Hyperfine Interaction of the Vacancy in Silicon
Authors: Kuzmiak V. , Zavadil J. , Žďánský K. 
Published: July 2007

AbstractUsing the self‐consistent Greens' function method the neutral vacancy in silicon crystal is calculated. The calculation differs from that reported in original approach in using tight‐binding approach also for the band structure and the Green's function calculation and in using full advantage of analytical properties of Gaussian orbitals without any expansion into plane waves. The calculated pseudopotential wave functions of the bound T2 state of the vacancy are used to determine correct wave functions by orthogonalizing them to the core functions of Si atoms in the neighborhood. These functions are used to determine values of the isotropic parts of the hyperfine interaction between the unpaired electron of the vacancy distorted by Jahn‐Teller effect and 29Si nuclei on its nearest‐neighbor sites. The values agree very well with the results of the published ENDOR measurements.
Acoustic Second Harmonic Generation in Magnetised Piezoelectric Semiconductors. Effect of Nonlinearity in Electron Effective Mass and Collision Frequency
Authors: Dey (Bose) M. , Ghosh S. 
Published: July 2007

AbstractTheoretically the acoustic second harmonic generation is studied in transversely magnetised piezoelectric semiconductors in the presence of an electrostatic field parallel to the direction of wave propagation. In this paper, the effect of nonlinearity in electron effective mass and collision frequency due to heating of the carriers on the second harmonic power flux is studied. It is shown analytically that this nonlinearity arising from the electric field associated with the fundamental mode increases the power flux of the second harmonic. A numerical estimation are made for n‐InSb at 77 K.
Complex Permittivity for an Ideal Dielectric of Stochastic Structure
Authors: Shermergor T. D. , Dikarev A. V. , Kruglyakova E. G. 
Published: July 2007

AbstractThe effective complex permittivity is calculated of a microheterogeneous dielectric, which is a composite material or a polycrystal. The Bourret approximation is used and the binary correlation function of the permittivity tensor is taken to be exponential. Asymptotic formulas are presented for long, short, and ultrashort electromagnetic waves. The results are presented in the form of plotted frequency dependences of the imaginary and real parts of the effective permittivity and the Cole‐Cole diagrams for real and virtual waves.
High Temperature Dielectric Relaxation in Ferroelectric PbHPO4 in the kHz Range
Authors: Happ H. , Wollenburg P. , Briskot M. , Spiegelberg M. 
Published: July 2007

AbstractThe complex dielectric constant,

, of PbHPO4 is measured in the high temperature range of the paraelectric phase between 420 and 590 K at frequencies below 30 kHz. A dielectric response of relaxation type is observed. The real and imaginary part of

take on values of the order of 104 at 100 Hz. This response can be well described by a superposition of two Debye‐terms with relaxation times in the millisecond region. Arrhenius plots of the real part of the conductivity show that the crystal passes to a new phase at about 420 K by an activated process with an activation energy of 1.0 eV. This process is assumed to be due to the onset of hindered rotation of HPO4 groups.
Self‐Consistent Scheme for Evaluating the Pressure Dependent Zero‐Sound Velocity in Normal Liquid 3He
Authors: Singh R. P. , Mishra L. K. 
Published: July 2007

AbstractUsing the theoretical model developed recently for liquid 3He, the pressure dependent zero‐sound velocities at T = 0 K are calculated by a self‐consistent procedure. Introducing a pseudopotential for the effective interaction between two 3He atoms of parallel and antiparallel spin, reasonable agreement with the experimental data of Wheatley et al. is found. An exact agreement with the experimental value is obtained by introducing a term into the theory to account for the local field corrections to the bare particle‐hole propagator beyond the random phase approximation (RPA) in a parametric way. The present theory seems to indicate the propagation of a new kind of sound wave in liquid 3He.
Equilibrium Position of Misfit Dislocations at the Interface of Thin Film on Substrate
Authors: Junqua N. , Grilhé J. 
Published: July 2007

AbstractIn a thin epitaxial film on a substrate, misfit dislocations at the interface can reduce the elastic energy due to coherency stresses. When the elastic moduli of film and substrate are different, the misfit dislocations are repelled towards the softer material. Their equilibrium positions are derived.
A New Method for Calculating the Electron Spectrum in Solids. Application to High‐Temperature Superconductors
Authors: Baryakhtar V. G. , Belokolos E. D. , Korostil A. M. 
Published: July 2007

AbstractOn basis of the model of the separable finite‐gap potential a new method for calculating electron energy spectra with arbitrary ratio of gap to band widths in solids is proposed. The possibility of its application to the analysis of the isoenergetic surfaces of high‐temperature superconductors is discussed.
Variable‐Range Hopping in Finite Quasi‐Two‐Dimensional Systems
Authors: Van Lien Nguyen 
Published: July 2007

AbstractMott variable‐range hopping conductions in finite quasi two‐dimensional (2D) systems of size l × d, where d is the length of conducting side, and l/d ≫ 1, are studied. It is shown that, independently of l/d‐values, the temperature dependence of averaging resistances has the 2D characteristic form ℛ ∝ exp (To/T)1/3 but, as a difference, the temperature To decreases with increasing the ratio l/d. Furthermore, a non‐periodic fluctuation in resistances of particular samples is found as a function of the chemical potential. The present results are qualitatively analyzed in the model of parallel conducting paths and compared with experimental data of GaAs field‐effect transistors‐based conducting channels.
Magnetoplasma Reflection of Heavily Doped Silicon
Authors: Dildey F. , Kessler F. R. 
Published: July 2007

AbstractMagnetoplasma reflection spectra of heavily doped silicon in terms of Kerr ellipticity and rotation are presented in the infrared wavelength range from 4 to 25 μm. For carrier concentrations from 3 × 1019 to 1020 cm−3, peak rotation angles of about 0.7° and 2° for p‐type and n‐type samples, respectively, were measured in static magnetic fields with inductions up to 15 T by a double modulation technic. In order separate the atomic parameters (carrier concentration N, effective mass m*, and collision time τ) without any additional measurements, the spectra of plasma reflection, ellipiticity, and rotation are analysed by different theoretical models. It is shown that the simple Drude model does not fit the lineshape of the measured spectra consistently. Near the plasma resonance an additional contribution to the dielectric function was found, which is attributed to the influence of plasmon excitation. The effect is more prononced in p‐type samples and has to be taken into account when determining the effective hole mass. For electrons, m* = (0.29 + 0.015) mE was derived from the spectra, whereas for p‐type samples an increasing hole mass with higher doping levels was determined.
Ising Spin System of S = 1 on a Triangular Lattice with Three‐Site Four‐Spin Interaction
Authors: Iwashita T. , Uryǔ N. 
Published: July 2007

AbstractFor the Ising ferromagnet of S = 1 on the triangular lattice, the effects of the three‐site four‐spin interaction J′(Si · Sj) (Sj · Sk) on the magnetization Sz is studied by the use of the four‐spin model approximation. The ferromagnetic order established by the ferromagnetic bilinear exchange interaction J and by the three‐site four‐spin interaction J′ are destroyed by the three‐site four‐spin interaction at the condition of J′ = −J/16 and by the antiferromagnetic bilinear exchange interaction at the condition of J = −6J′, respectively. Furthermore, the ground state spin structures and the condition for an occurrence of the phase transition are determined from the behavior of the J′‐dependence of the energy for a single spin in various spin structures.
Interaction between 111In Atoms and Impurity Atoms of Ni and Rh Dissolved in Silver
Authors: Sternik M. , Krolas K. 
Published: July 2007

AbstractPerturbed angular correlation measurements are performed with 111In in dilute binary alloys of Ag with Ni and Rh impurities. It is demonstrated that In atoms attract these impurities and the binding energy for In‐Ni and In‐Rh pairs in the silver matrix is determined. Besides the solute atoms of Ni and Rh the precipitates of these two elements are also observed in the alloys. It is possible to estimate the solid solubility limit for Ni and Rh in Ag.
A Cluster Approach for Interface Electronic Structures in a Cu/Fe System
Authors: Zeng Zhi , Zheng Qing‐Qi 
Published: July 2007

AbstractThe self‐consistent spin‐unpolarized electronic structure and adhesive binding energies are obtained for the contacts of Fe(100)Cu(100) and Fe(110)Cu(100), using the cluster approach. The core‐level energies and local density of states give the behaviour of interfacial atoms and interior atoms. The charge transfer is hardly observed in the interface of Fe/Cu. The force coefficient results from the curve of binding energy versus seperation.
Resonant Interband Tunneling in Heterostructures
Authors: de Dios‐Leyva M. , López‐Gondar J. , Bruno A. 
Published: July 2007

AbstractA theoretical study of resonant interband tunneling in quantum well structures in the uniform‐field model (Zener model) is presented. The analysis is carried out in the framework of a simplified two‐band Kane's model. It is shown that the transmission coefficient, T(E), as a function of the electron energy exhibits a well defined resonant structure. Some interesting properties of T(E), as well as of the corresponding peak values and of the resonance energies, as a function of the well width and of the applied electric field are reported.
On the Magnetic Susceptibility of the Electrons in a Quantum Box of a Wide‐Gap Semiconductor
Authors: Das N. R. , Chakravarti A. N. 
Published: July 2007

AbstractAn attempt is made to investigate the diamagnetic and paramagnetic susceptibilities of electrons in a quantum box of an n‐type wide‐gap semiconductor by considering perturbational effects of an external magnetic field. The results are computed for quantum cubes, taking n‐GaAs as an example. The susceptibilities are found to be oscillatory in nature because of the quantum size effect, while the ratio of the susceptibilities is observed to deviate significantly from the value well‐known for bulk semiconductors.
Conduction Band Edge Charge Densities in HgxCd1−xTe
Authors: Aourag H. , Khelifa B. , Rezki M. , Tadjer A. 
Published: July 2007

AbstractOn the basis of the charge densities at the conduction band edge Xc the effect of interstitial impurities on the modification of the band structure of the system HgxCd1−xTe is explained. The inversion of the symmetry state at Xc in relation to x bears information on the semimetal‐semiconductor transition.
Polarized VBXES and XANES of GaSxSe1−x (x = 0, 0.6, 1)
Authors: Dräger G. , Schulz E. , Czolbe W. 
Published: July 2007

AbstractPolarized K‐emission and absorption spectra of the layered compounds GaSxSe1−x (x = 0, 0.6, 1) are measured in the range of about 10 eV below and above the gap. The polarization dependence of the spectra enables the investigation of the local p‐like DOS additionally resolved with respect to the m‐quantum number symmetry. By alignment of the energy scales using XPS core‐orbital energies the experimental spectra can be compared with calculated local partial (l, m‐resolved) DOS after Robertson. The spectra are discussed with regard to the calculated DOS and to the structure of the compounds. The polarization dependence of the gap between the Ga K‐emission and absorption spectra shows the anisotropic character of chemical binding.
Semiempirical Crystal Field Calculations for fN‐Systems. I. Many‐Electron Formalism of Crystal Field Effect in fN‐Configurations
Authors: Mironov V. S. , Rosov S. P. 
Published: July 2007

AbstractA new many‐electron crystal field formalism for the fN‐configuration in lanthanide and actinide ions is presented. An effective crystal field Hamiltonian is obtained by projecting the original electronic Hamiltonian of an f‐cluster (fN‐ion + ligand environment) on the subspace of [J, M] > functions of the fN‐configuration of the central ion. On the basis of this formalism a semiempirical many‐electron method is developed that allows for a practical ab initio calculation of crystal field energies in fN‐systems. The important role of many‐electron crystal field effects in fN‐systems with significant covalent contributions is discussed.
Tunneling in the Representation of Scattering States
Authors: Valeev V. G. 
Published: July 2007

AbstractA new gauge‐invariant many‐electron approach is given to the problem of tunneling in condensed systems, based on a Hamiltonian in the representation of scattering states for tunnel junctions with arbitrary strength of coupling. The kinetic equation for the electron density matrix is derived; collision integrals for the cases of electron‐electron, electron‐phonon, and electron‐impurity interactions are found. The noise properties of tunnel contacts of normal metals are analysed.
Influence of Electron‐Phonon Coupling on the Mössbauer Quadrupole Interaction in FeSiF6 · 6 H2O
Authors: Sinha T. P. 
Published: July 2007

AbstractThe Mössbauer quadrupole splitting of 57Fe2+ (3d6, 5D) in FeSiF6 · 6 H2O decreases with temperature increasing from 77 to 300 K. This cannot be explained on the basis of a static crystal field interaction only, which is usually used to obtain the electronic eigenstates and resulting quadrupole splitting. In this paper the effect of electron‐phonon coupling arising from the orbit‐lattice interaction is included to obtain the perturbed electron‐phonon states, and then quadrupole splitting is calculated from these states. The temperature dependence of quadrupole splitting thus calculated agrees reasonably well with the experimental results.
Effect of Interlayer Coupling on Néel Temperature in Antiferromagnets
Authors: Singh R. P. , Singh M. 
Published: July 2007

AbstractThe Néel temperature is calculated for a 3D Heisenberg model taking into consideration the anisotropy in exchange coupling constant. By virtue of the two‐sublattice approach to antiferromagnets the equation of motion is solved for the Green's function and an expression for Néel temperature is obtained. The higher‐order Green's functions are decoupled by random phase approximation. These expressions are applied to evaluate the Néel temperature of YBa2Cu3O6+x and La2CuO4. The effect of interlayer coupling is examined. The theoretical results are compared with experimental values of Néel temperature.