bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical Calculation of Positron Annihilation Angular Correlation Anisotropy in GaP
Authors: Panda B. K. , Mahapatra D. P. , Padhi H. C.
Published: July 2007

Angular correlation of positron annihilation radiation along [100] and [111] directions of GaP are calculated using pseudopotential formalism. The positron wave‐function is solved in point core approximation. The calculated 2γ momentum distribution anisotropy agrees reasonably with the experimental data.
Photochemical Reorganization of Deep Impurity Centres in Silicon. Dissociation of Donor–Acceptor Pairs
Authors: Adilov K. A.
Published: July 2007

Reversible processes are observed of photochemical reorganization of deep centres in p‐type silicon doped with zinc, selenium, and chromium under the illumination of light in the impurity absorption region. The dissociation is found of donor–acceptor pairs (Zn+iB−s, (Se+iB−s)°, and (Cr+iB−s)° followed by isolated centres of Zn+i and Se+s.
Localized States Induced by Self‐Interstitial Defects in Ultra‐Thin GaP/InP Strained‐Layer Superlattices
Authors: Wang En‐Ge , Wang Ding‐Sheng
Published: July 2007

By the recursion method a theoretical study is made of the electronic structure of a (001)‐oriented (GaP)1/(InP)1 strained layer superlattice with interstitial defects. A Keating model is used to determine the structural parameters. The density of states of all possible interstitials and their neighbors in the stable monolayer superlattice are calculated. Some new self and impurity diffusion mechanisms, which are not found in a GaAs/AlAs matched superlattice, are proposed for the first time.
The Charge Distribution and the Electric Field Gradient in the High‐Temperature Superconductor TlBa2Can−1CunO2n+3 (n = 1 to 3)
Authors: Jia Y. Q.
Published: July 2007

The net charges at atoms in the high‐temperature superconductor TlBa2Can−1CunO2n+3 (n = 1 to 3) are calculated by means of the tight‐binding approximation based on the EHMO method. The results indicate that the charge distribution in this kind of compounds possesses a specially layered arrangement. An insulating Ba–Ba layer is inserted between the CuO layer and the TlO layer. There may exist a weak coupling between the CuO layer and the TlO layer through the interaction of the same O(2) atom with both the Cu atom and the Tl atom. The existence of the Ca in the compounds can cause the valence fluctuation at the Cu atom. The calculated electric field gradients at atoms implies that the conducting electron or hole may move in the CuO layer, which is closest to the TlO layer, along the a–b plane.
On the Gilinskii Branch of the Spectrum of Excitations of a Domain Wall in Uniaxial Ferromagnetics
Authors: Shimokhin I. A.
Published: July 2007

A high‐frequency branch of the spectrum of excitations of a domain wall in uniaxial ferromagnetics, discovered by Gilinskii, is studied. A dispersion law for all directions of the wave propagation is derived from the Landau‐Lifshitz equation in magnetostatic approximation. Results are obtained in the long wave limit. A comparison of the theoretical and numerical results is presented.
Frequency and Temperature Dependences of Exciton Damping in CdS Crystals
Authors: Ya. Reznichenko V. , Strashnikova M. I. , Cherny V. V.
Published: July 2007

Dispersion curves of the refractive index and absorption spectra measured on thin wedge‐shaped and plane‐parallel CdS crystals are compared with corresponding dependences calculated on the framework of Pekar's theory. Frequency and temperature dependences of exciton polariton relaxation parameter are determined from the best fit.
Raman Spectra of [N(CH3)4]2ZnCl4 Single Crystals. II. Raman Spectra of Low‐Symmetry Phases
Authors: Torgashev V. I. , Yuzyuk Yu. I. , Rabkin L. M. , Durnev Yu. I.
Published: July 2007

Polarized Raman spectra of [N(CH3)4]2ZnCl4 single crystals are studied in five low‐symmetry phases in the frequency range 10 cm−1 < ν < 3500 cm−1. The observed lines are assigned on the basis of a factor‐group analysis and corresponding correlational relationships. The order of the crystal lattice is increased as the temperature is lowered. The phase transition in this compound are of order–disorder type.
Channels of Relaxation of Elastic Stresses in Pentagonal Nanoparticles
Authors: Gryaznov V. G. , Kaprelov A. M. , Romanov A. E. , Polonskii I. A.
Published: July 2007

On the basis of continuous elastic models relaxation channels of elastic stresses inside the pentagonal needle‐like nanoparticles (PNNPs) are considered. Six models are analyzed: 1. creation of a dislocation inside the PNNP; 2. opening of a gap in the PNNP; 3. creation of a disclination bound with the PNNP surface; 4. splitting of the pentagonal axis; 5. growth of monocrystalline region around the PNNP axis; 6. displacement of the pentagonal axis towards the periphery of the PNNP. An energetic balance and the possibility of realization for each of these channels are discussed.
A Correlation Study of Large Potassium Cationic Clusters
Authors: Ray A. K. , Kanal K. M. , Howard I. A.
Published: July 2007

Fourth‐order many body perturbation theory is used to investigate the properties of large potassium cationic K (8 ≦ n ≦ 13) clusters. Detailed electronic structures of these clusters are studied. Stabilities from the points of view of binding and fragmentation energies are discussed and, wherever possible, results are compared with published data in the literature.
Investigation of Cu and Ni Band Structure above the Vacuum Level Using Low Energy Electron Reflection
Authors: Strokov V. N. , Komolov S. A.
Published: July 2007

Incidence angle dependent elastic electron reflection curves in the 0 to 30 eV range are measured on Cu(111) and Ni(111) using target current regime. They are compared with the calculated ones. Computations are made very fast using a simple approximation. The extrema of the reflection energy derivative are shown to correspond unambigiously to definite critical points of bands. These points are mapped when the energies of the experimental extrema are compared with the calculated ones. Varying the incidence angle, in this way bands in the variety of Brillouin zone directions may be investigated.
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

Spectral 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

In 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

The 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

In 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

First, 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

The 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

Electronic 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

The 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

A 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

Using 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

Theoretically 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

The 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

The 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

Using 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

In 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

On 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

Mott 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

Magnetoplasma 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

For 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

Perturbed 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

The 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

A 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

An 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

On 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

Polarized 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

A 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

A 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

The 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

The 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.
Time Dependence Calculation of the Breakdown Rate for Electrical Breakdowns in Vitreous Solids
Authors: Danziger M. , Bernhardt A.
Published: July 2007

The anomalous behaviour of different physical quantities in vitreous solids contrary to the behaviour in crystalline solids, mainly the dielectric behaviour, can be described by the effect of a system of additional low‐energy excitations in these solids. This also applies to the amorphous SiO2‐layers in MOS structures. Therefore, a model of breakdown behaviour is developed basing on the assumption that there are fluctuations of the correlated local electrical fields and low‐energy excitations present in these layers. On this basis, the time dependence of breakdown rate is determined. By these calculations, a good correspondence of the experimentally and theoretically determined characteristics is obtained. In these calculations, it should be paid attention to the fact, that the properties of the vitreous solids and the character of the internal interaction change by breakdowns already occured.
Investigations of the Dynamic Properties of the Liquid Phase of Glassy CaAl Alloys
Authors: Rao R. V. Gopala , Venkatesh R.
Published: July 2007

The Ashcroft pseudopotential is used in the evaluation of the partial potentials in the case of Ca60Al40 glass melts. These potentials are found to give minima at the principal peaks of the partial radial distribution functions. The partial structure factors are evaluated and compared with literature values. From the partial potentials and partial structure factors the corresponding effective potential and total structure factor are evaluated. The effective radial distribution function is calculated from the total structure factor. These effective quantities are used in the evaluation of phonon frequencies through Takeno and Goda's equations. It is found as predicted by Bhatia and Singh that the structure factor maximum is around the first minimum of the longitudinal phonon frequency. From the slopes of the phonon frequencies the elastic constants are evaluated. The elastic constants are also evaluated from Schofield's I1 and I2 integrals. Further from Kirkwood‐Buff's equation using the partial direct correlation functions in the long‐wave limit the compressibility is evaluated and the elastic constant C11 is calculated. There is a good interconsistency in the computed values of the elastic constants.
Real Space Approach to the Linear Phason Strain
Authors: Cheng Y. F. , Pan G. Z. , Li F. H.
Published: July 2007

It is illustrated that the quasilattice distortion originated from a linear phason strain can be treated as the projection strip rotation. A fictitious strip is obtained by rotating the original strip with the phason matrix. The distorted reciprocal quasilattice can be obtained by projecting the undistorted high dimensional reciprocal lattice onto a newly defined physical space parallel to the fictitious strip with a new projection matrix. The transformation from icosahedral quasilattice to body center cubic lattice caused by strip rotation or linear phason strain is demonstrated with the change of tiling.
Ordering of Protons at the Phase Transition in Superionic Crystals of CsHSO4 Type
Authors: Dzhavadov N. A. , Rustamov K. A.
Published: July 2007

The phase transition (PT) D → C in CsH(D)SO4‐type crystals by one wave vector of the star {k13} (X‐point of the Brillouin zone (BZ)) and of the wave vector {k14 = 0} (Γ‐point of BZ) is considered. A symmetry analysis of proton ordering at the PT is performed with account of proton–phonon interaction. The method of concentration waves is applied. The expression for the average occupation number of proton positions is obtained. The experimentally observable ordering of protons and the dynamics of SO4 tetrahedra at the PT is described. The entropy jump at the PT is calculated. The obtained theoretical results are in good agreement with experiment.
Perturbation Method of Computation of Entropies of Vaporization of Fused Salts
Authors: Rao R. V. Gopala , Venkatesh R.
Published: July 2007

Based on the assumption that thermodynamic and structural quantities of salts can be divided into contributions from neutral hard spheres and from Coulomb interactions an expression for the entropy of vaporization of fused salts is formulated. The theoretical results of the entropy of vaporization at the melting point are found to be in good agreement with experiment except in the case of lithium salts.
Acousto‐Helicon Interaction in Semiconducting Superlattices
Authors: Misra K. D. , Pandey M. K.
Published: July 2007

Acousto‐helicon interaction in semiconductor superlattices is examined in the presence of an applied magnetostatic field. Assuming that the collective mode propagates along the growth axis of the superlattice, using the self‐consistent‐field and hydrodynamic equations, the dispersion relation of the acousto‐helicon mode for the finite as well as infinite periodic systems having piezoelectric and deformation potential coupling is obtained. The effect of changes in alternating layer thickness on the branch‐folding effect of the acousto‐helicon mode is examined. The modifications in frequency due to phonon–helicon interaction in the strong coupling limit are also obtained.
Optical and Structural Properties of Amorphous Silicon Obtained by Low Pressure Chemical Vapour Deposition
Authors: Amato G. , Fizzotti F. , Manfredotti C. , Menna P. , Nobile G. , Spagnolo R.
Published: July 2007

Optoelectronic and structural properties of thin, hydrogenated amorphous silicon samples grown by thermal decomposition of disilane in different positions along a low pressure chemical vapour deposition reactor are investigated by means of infrared spectroscopy, Raman scattering, and photothermal deflection spectroscopy. Correlations between the character and the hydrogen content versus density of states and between the hydrogen bonding configuration versus transverse optical/acoustic phonon modes are found. The purely thermal excitation of gas molecules gives rise to an amorphous material with a rather low density of states. Samples grown at different positions inside the reactor show different hydrogen concentration and bonding configuration, bond angle deviation, Urbach tail slope, and density of states. The most important parameters governing the LPCVD of a‐Si: H are discussed.
Redistribution of Resonance Bonds and Dynamics of Two‐Center Self‐Trapping in Rare‐Gas Crystals
Authors: Fugol I. Ya. , Ratner A. M. , Tarasova E. I.
Published: July 2007

It is shown that in the process of the exciton two‐center self‐trapping the resonance bonds generating a free exciton state are redistributed so that the total resonance contribution to the energy increases. 50% of the electronic excitation is concentrated inside a two‐center quasimolecule close to the self‐trapping threshold. The rest is distributed in neighbouring atoms, resulting in a generation of weaker extrinsic bonds along with the intermolecular resonance one. The attendant deformation of the molecular term produces a decrease in the self‐trapping barrier and an appreciable increase in its transparency.
Compton Profile Anisotropy Studies in Hexagonal Semiconductors
Authors: Panda B. K.
Published: July 2007

The Compton profile anisotropies are calculated by empirical pseudopotential method for different semiconductors with wurtzite structure. The anisotropies are reduced with increasing ionicity in consistency with the observations in cubic semiconductors. The comparison of the autocorrelation functions of the cubic and hexagonal forms show that the differences in the valence wave functions are quite large for II–VI semiconductors.
The Warm‐Electron Distribution Function in the Energy Noncollision Plasma in Submicron Semiconductor Layers
Authors: Gurevich Yu. G. , Logvinov G. N.
Published: July 2007

The warm‐electron distribution function is obtained from the kinetic equation in semiconductor submicron layers under the assumption that the surface energy relaxation is considerably higher than the bulk energy relaxation rate and the frequency of the electron–electron interactions as well. A divergence in the point ϵ = 0 is shown (where ϵ is the electron energy) if the surface scatterers are acoustic phonons. The reason of this anomaly is that small energy electrons have infinitly high partial electric conductivity while their energy relaxation rate turns to zero. In order to obtain the correct results it is necessary to take into account the e–e interaction between small and high energy electrons. This interaction leads to energy pumping from one carrier group to another and then to the external thermostats.
Thermal Conductivity and Electrical Resistivity of Intermetallic RECu2 Compounds (RE  Lu, Ho, Er, Dy)
Authors: Bartkowski K. , Gratz E. , Rafałsowicz J. , Tyc T.
Published: July 2007

The temperature dependence of the thermal conductivity, λ (T), and the electrical resistivity, ϱ (T), is measured for the heavy rare‐earth RECu2 (RE  Lu, Er, Ho, Dy) compounds in the temperature region from 2 up to about 30 K. Anomalies observed in both λ (T) and ϱ (T) curves correspond to magnetic transitions as are known from susceptibility measurements. Assuming the validity of the Wiedemann‐Franz law the electronic (λe) and the lattice (λg) contributions of the total thermal conductivity are separated. The anomalies caused by spin‐dependent scattering processes, due to the change in the arrangement of magnetic moments, are much more pronounced in λe, but they are also visible in the temperature dependence of the Lorenz number L (T).
Interaction of the Superconducting Domains Induced by External Electric Field with Electromagnetic Waves
Authors: Shapiro B. Ya.
Published: July 2007

The behavior of a superconductor in time‐independent electric field perpendicular to the surface and in the external electromagnetic wave is theoretically investigated. A new type of the resonance interaction between superconducting domains localized along the magnetic field (if the superconducting phase transition takes place in the external magnetic field perpendicular to the surface) and electromagnetic waves is predicted. The surface impedance of the superconductor with domains is calculated. It is shown that the real part of the impedance has a saturation if the skin length equals the domain size.
The Role of Polar Additives on Charge Transport in Molecularly Doped Polymers
Authors: Borsenberger P. M. , Bässler H.
Published: July 2007

The role of polar additives, o, m, and p‐dinitrobenzene, on hole transport in 1,1‐bis(di‐4‐tolylamino‐phenyl)cyclohexane doped polycarbonate is investigated. The results are described by a model based on hopping through a manifold of states with superimposed energetic and positional disorder that remains static on the time scale of a hopping event. The results lead to the conclusion that the main effect of the polar additives is the enhancement of disorder, both energetic and positional, the dipolar reorientation being relatively unimportant.
Calculation of the Spin System Correlation Functions in the Frames of the Functional Integration Method. II. The Heisenberg Model
Authors: Vakarchuk I. A. , Matskevych P. A.
Published: July 2007

New equations for the correlation functions obtained in the frames of the functional integration method are applied to investigate the magnetic ordering in the Heisenberg isotropic quantum model. The Curie temperature of this model is calculated from the pole of the longitudinal Green function. Good agreement with known data is obtained in the crystalline case. It is shown that the magnetic order can be destroyed by the amorphization of the crystal.
Wave Vector Dependent Two‐Photon Interband Transitions between Landau Levels
Authors: de Salvo E. , Girlanda R.
Published: July 2007

A perturbative calculation, out of the electric dipole approximation (EDA), of the absorption threshold of the two‐photon interband transitions between the Landau levels of direct gap semiconductors without inversion symmetry is presented. This approach allows to explain with good approximation the absorption peaks with selection rule Δμ = 0, also in a simple two‐band model. As an application, the case of cuprous chloride in a 5T external static magnetic field is considered.
Relaxation and Recombination of Photoexcited Carriers in a‐Si: H Calculated by Monte‐Carlo Simulations
Authors: Gutschker O. , Bindemann R.
Published: July 2007

The relaxation and recombination of photoexcited carriers in a‐Si: H is simulated by means of Monte‐Carlo calculations taking into account radiative and nonradiative recombination processes. The results are in good agreement with experimental data. The measured maximum in the luminescence quantum efficiency at a temperature of T ≈ 50 K can be quantitatively explained by nonradiative Auger recombination. The minimum in the negative decay exponent at T ≈ 30 K obtained in long‐time luminescence decay experiments is explained by a shift of the peak position of the lifetime spectrum of the nonradiatively recombining carriers to longer times.
Polarization Dependences of Two‐Photon Absorption in Narrow‐Gap InSb and HgCdTe Type Semiconductors
Authors: Ismailov T. G. , Bagirov M. A.
Published: July 2007

Two‐photon absorption of light in narrow‐gap semiconductors of InSb and HgCdTe type is considered in the framework of the two‐band Kane model. The analytical expressions for the TPA coefficient in dependence on the energies of pumped radiation and band gap of semiconductor is obtained. All the possible nonequivalent geometries of experiment are considered. In the calculations the excitonic effects are neglected. The polarization dependences are discussed and the comparison with experiment is carried out.
Dynamical Correlations and Phonon Dispersion in a Liquid Binary Alloy
Authors: Bhandari D. , Pratap A. , Saxena N. S. , Saksena M. P.
Published: July 2007

Theory of Brownian motion of particles in static harmonic well approximation is applied to study the vibrational dynamics of liquid NaxCs1−x (x = 0.5; 0.85) alloys. Dynamical variables like velocity autocorrelation function, power spectrum, and the mean square displacement are computed. The effective interatomic potential of the alloy used is obtained through the pair‐potentials of individual components. The co‐operative motion of atoms is described in terms of spectral functions of longitudinal current–current correlation functions which are obtained through the mean square displacement. These spectral functions of longitudinal current–current correlations are then used to get phonon dispersion in the alloy. The results are compared with the recently reported quasi‐dispersion results of neutron inelastic scattering (NIS) experiments. Good qualitative agreement is observed.
Thermal and Transport Properties of Liquid Alkali Metals Using a Soft‐Sphere Reference System
Authors: Khanna K. N. , Quayoum A.
Published: July 2007

The density dependent structural properties of liquid alkali metals derived in earlier work are used to calculate thermal and transport properties. The results show improvement over those obtained with the hard‐sphere system. The effect of softness in the pair potential is discussed.
Exact Phonon Green's Functions of One‐Dimensional Quasiperiodic Lattices
Authors: Zhong J. X. , Yan J. R. , You J. Q.
Published: July 2007

A real‐space renormalization‐group (RSRG) scheme is presented for calculating the local phonon Green's functions of one‐dimensional Fibonacci lattices. In this scheme, the phonon diagonal, off‐diagonal, and combined models can be treated in a unified way.
Phonons in F.C.C. Iron
Authors: Singh D. , Rathore R. P. S.
Published: July 2007

A model is reported which accounts for the attractive and repulsive ionic forces in terms of a more realistic and less parametric generalized exponential potential, which incorporates the exchange and correlation effects due to electrons in a simple and effective manner. The electronic contribution is computed by using the Ashcroft model potential combined with the modified dielectric screening due to Shaw. The phonon dispersion in f.c.c. iron shows good agreement with experimental findings.
Mixed Crystal Electronic Structure of MS3−xSex
Authors: Lazo E.
Published: July 2007

The electronic structure of a quasi‐one‐dimensional disordered system represented by mixed‐crystal compounds MS3−xSex, with M  Zr, Hf is investigated. These compounds are made up of weakly coupled pairs of chains, coupled through van der Waals forces. A single chain is considered assumed to be completely independent of the neighboring chains. The problem is formulated in terms of the Green function formalism, using a tight‐binding Hamiltonian with interaction to nearest neighbors with diagonal and off‐diagonal disorder. The infinite set of equations is renormalized by means of the matrix inversion method, and then the average Green functions are evaluated using the transfer function method which is based on a work by Schmidt. Numerical results of the global density of states are provided for the strictly one‐dimensional model of a mixed crystal, and for the quasi‐one‐dimensional model as function of the concentration x.
On the Quantized States in a Cylindrical Quantum Box of a Narrow‐Gap Semiconductor in Crossed Electric and Magnetic Fields
Authors: Das N. R. , Chakravarti A. N.
Published: July 2007

The energy eigenvalues of the electrons in a quantum box of a simple Kane‐type narrow‐gap semiconductor having cylindrical symmetry are investigated through a perturbation technique in the presence of crossed electric and magnetic fields. The effects of changing the dimensions of the box as also of changing the fields on the lowest quantized state are discussed using the relations obtained, taking n‐InSb as a typical example of such a semiconductor.
Studies of the Autocorrelation Functions in Aluminium
Authors: Panda B. K.
Published: July 2007

The long‐slit angular correlation of positron annihilation radiations are measured in the polycrystalline Al sample. The theoretical autocorrelation function (AF) calculated with the band electron and positron wave functions agrees very well with the experimental AF. The AF derived with the positron–electron product wave function is not suitable to explain the oscillations in the experimental AF.