bluuebunny/crossref_metadata_2025_split huggingface dataset:
Field Ionization of Shallow Donors in Germanium
Authors: Žurauskas S. , Dargys A. , Žurauskienė N. 
Published: July 2007

AbstractTransient currents due to field ionization of shallow donors are investigated in thin germanium samples by transient tunneling spectroscopy. In particular, the electron tunneling time from antimony atoms to the conduction band is measured as a function of electric field strength, lattice temperature, and electric field direction. The results are compared with a simple hydrogenic model. Various factors which may influence the TTS spectra, such as impurity impact ionization, doping inhomogeneity, etc., are discussed. It is concluded that pure electron tunneling from the ground 1 s state of antimony atoms takes place at lattice temperatures smaller than 7 K.
Anomalous Hall Effect in a Nonmagnetic Semiconductor
Authors: Obukhov S. A. , Volkova I. K. 
Published: July 2007

AbstractThe anomalous Hall effect is considered in a system of magnetic impurities on the example of the nonmagnetic semiconductor InSb: Mn. From an analysis of the Hall constant as a function of impurity (Mn) concentration, temperature, and magnetic field strength the magnetic susceptibility of the system and the magnetic ordering temperature,T≈ 1 K, are determined. A physical model is proposed giving a qualitative explanation of the anomalous Hall effect in a system of magnetic impurities. It is argue that the exchange interaction at the boundary for the metal–insulator transition in a system of magnetic impurities damps Coulomb fluctuations.
Anisotropy of the Cuprate Superconductors in the Three‐Dimensional Bigausson Model
Authors: Rajilić; Z. , Mirjanić D. 
Published: July 2007

AbstractThe bigausson model of high‐temperature superconductivity is generalized to three dimensions. The stability of the bigaussons is investigated and the possibility of a bigausson condensate is shown. The anisotropy for the following parameters of cuprate superconductors is calculated: coherence length, energy gap, and critical current density. The obtained results are in agreement with the experimental data for Y1Ba2Cu3O7–δ.
Electromagnetic Response of the η‐Pairing Eigenstate in the Hubbard Model
Authors: Su Gang , Ge Mo‐Lin , Zhao Bao‐Heng 
Published: July 2007

AbstractSome electromagnetic properties of the η‐pairing eigenstate of the Hubbard model are investigated. The persistent current density Js in the eigenstate is discussed, and the distribution of magnetic field in the studied periodic lattice is analyzed. It is shown that the behaviour of the electromagnetic response is peculiar.
Analysis of the New Unrestricted Hartree‐Fock Vortex Solution of the Hubbard Hamiltonian in Two‐Dimensional Systems A Small‐Cluster Study
Authors: Louis E. , Galán J. , Guinea F. , Vergés J. A. , Ferrer J. 
Published: July 2007

AbstractThe properties of a recently discovered unrestricted Hartree‐Fock solution of the Hubbard Hamiltonian is analysed on the square lattice that shows a really two‐dimensional spin polarization of a vortex‐like character. This and other several mean‐field solutions are compared with the exact ground‐state energy and wave function of two and four electrons on a four‐site system (square). Results for two correlated electrons in large 3 × 3 and 4 × 4 clusters are also given and discussed. The vortex mean‐field solution provides the best solution in almost all systems that deviate from half‐filling.
Theory of superconductivity for quasiparticles with parastatistics
Authors: Safonov V. L. 
Published: July 2007

AbstractThe superconducting state of pairs of spinless quasiparticles with parastatistics is considered on the basis of a model Hamiltonian in mean‐field approximation. It is shown that the energy gap δ0 and critical temperature Tc increase as exp (−1 sol;p2λ) at a definite weak‐coupling parameter λ with increasing rank p of parastatistics. The characteristic ratio 2δ0/Tc and the typical pair size diminish. Thermodynamic properties of the system near the phase transition and parameters of the Ginzburg‐Landau theory are calculated. The obtained results are discussed in connection with a set of experimental data.
Superconducting gap substructure in bisoliton HTSC theory
Authors: Ermakov V. N. , Kruchinin S. P. , Ponezha E. A. 
Published: July 2007

AbstractThe conditions and peculiarities of the realization of the superconducting gap substructure in a bisoliton superconductivity model are considered at temperatures much lower than the critical one in the case when the temperature dependence of the gap can be neglected.
TL spectra from optical fibres at 80 K after ultraviolet illumination
Authors: Khanlary M. R. , Townsend P. D. 
Published: July 2007

AbstractEmission spectra of thermoluminescence below room temperature are reported from several types of optical fibre after ultraviolet illumination at 80 K. The spectra are modified by previous X‐ray irradiation at room temperature. Since the light energy is insufficient to form new intrinsic defects all the signals are thought to arise from phototransfer from deep stable defect states formed during fibre production. An X‐ray irradiation history at 300 K, before cooling to 70 K, significantly enhances subsequent optically generated glow peaks, in particular that at 120 K which emits at 545 nm. The phototransfer efficiency of the fibres is greater than for “pure” bulk silica. It is therefore proposed that the high phototransfer efficiency found in the optical fibres is related to a combination of the fibre dopants and defect retention during the rapid cooling used in fibre drawing.
Optical reflectivity of Si above the melting point
Authors: Boneberg J. , Yavas O. , Mierswa B. , Leiderer P. 
Published: July 2007

AbstractThe variation of the optical reflectivity of a Si single crystal during irradiation with two successive Nd:YAG laser pulses is investigated with ns resolution. The first pulse melts the surface and therefore the reflection coefficient increases up to the value of the metallic liquid at the melting temperature (1685 K). Upon further heating the surface with the second, time‐delayed pulse, a decrease of the reflection coefficient is observed, resulting from the temperature‐dependent dielectric function of the molten Si. The largest decrease in the reflectivity that could be reached before damaging the surface amounted to 9% for a probe wavelength of 633 nm. The application of a simple Drude model for the optical constants above the melting point is discussed.
Determination of complexes and diffusion mechanisms in a GaP/InP strained‐layer superlattice
Authors: Wang En Ge 
Published: July 2007

AbstractA theoretical study of the defect characteristics in a GaP/InP strained‐layer superlattice is presented. Based on the calculated charge states, some closely bound interstitial‐antisite pairs are found to form at a distance of a bond length in a stable GaP/InP (1 × 1) structure. The defect‐related states localized in the energy gap suggest that the formation mechanism of the EL2 complex in the GaAs system is unsuitable for GaP/InP multilayer structures. A slow self‐diffusion procedure is proposed for both group III and V atoms in this superlattice. Besides the investigation of some mobile species in silicon diffusion, the kick‐out reactions are suggested to be favored at higher doping concentration.
Lattice dynamics of the superconductor YBa2Cu3O7
Authors: Hu Bengang , Katiyar Ram S. 
Published: July 2007

AbstractA lattice dynamical formalism using the rigid ion model is applied to the superconductor YBa2Cu3O7. The model includes the short‐range repulsive interactions of axially symmetric type and long‐range Coulomb interactions among ion pairs. In order to determine the short‐range parameters, the Born‐Mayer approximation and the stability conditions were used. The crystal parameters determined by neutron powder diffration technique and the frequencies from Raman and infrared measurements on single crystal have been utilized to obtain the best fit. The proposed model yields an excellent agreement between the observed and calculated frequencies and gives all phonon modes of YBa2Cu3O7, which can serve as a guide for further experimental and theoretical investigations on YBa2Cu3O7 and other XnBa2Cu3O7 with similar structure. The realistic values of calculated effective charges and bond force constants and the agreement between the observed and calculated frequencies indicate the suitability of the rigid ion model with the proposed approximations to such materials. On the basis of our results, it is found that the atoms Ba and Cu(1) are strongly bonded to out‐of‐plane oxygen atoms. From the eigenvector analysis it appears as if the in‐plane oxygen atoms vibrate alone against the cage lattice with nearly half the frequency for x‐ and y‐directions in comparison to the z‐direction motion. This may have significance in connection with superconducting phenomena below Tc.
Vibrational modes around a moving soliton in trans‐polyacetylene (CH)n
Authors: Ye Zhen 
Published: July 2007

AbstractThe vibrational modes of a soliton in trans‐polyacetylene are studied. Using a quasi‐realistic continuum model which generalizes the Takayama‐Lin‐Liu‐Maki model by including acoustic‐phonon effects, a self‐consistent mean‐field eigenequation for the vibrational modes of the soliton is derived. Then it is shown that these vibrational modes are damped due to the acoustic‐phonon effects, which contributes to the linewidths in the lineshape observation.
Influence of tunneling on trapping kinetics in thin insulating layers
Authors: Schmidt M. , Köster H. 
Published: July 2007

AbstractThe process of trap occupation in Si/SiO2/M structures might be accompanied by a tunneling (detrapping) process near the adjacent contact (x < 5 nm), depending on the distance, the trap energy relative to the Fermi level of the adjacent contact, and the actual trap filling state. The equilibrium between the two opposing processes gives rise to a dynamical trapping behaviour and adjust itself at xg, the boundary position between stationarily occupiable and unoccupiable traps. For a given tunneling rate constant the equilibrium depends on the capture rate constant and therefore on the current density j only. The realistic values of the capture cross‐section σ and of the effective trap concentration Neff can differ by more than one order of magnitude from the value determined by using a simple first‐order kinetic which neglects tunneling phenomena. The developed dynamic trapping model gives a reliable basis for trap analysis in thin oxide layers. For hole traps at E = 6.3 eV we determined σh = 1.5 × 10−14 cm2 and Neff = 1.47 × 1013 cm−2.
The electronic structure and superconductivity of the lanthanum monochalcogenides LaX (X = S, Se, Te)
Authors: Sankaralingam S. , Jaya S. Mathi , Pari G. , Asokamani R. 
Published: July 2007

AbstractThe first band structures and calculated electronic properties of the compounds LaSe and LaTe are reported. The energy band structure of lanthanum monochalcogenides are obtained using the self‐consistent LMTO method within the atomic sphere approximation. The band structure outputs were used to calculate the physical properties such as the electronic specific heat, the Pauli paramagnetic susceptibility, and the superconducting transition temperature. The calculated results are compared with the available experimental values.
The influence of structural defects on the electronic properties of amorphous Ta2O5
Authors: Khanin S. D. , Ivanovskii A. L. 
Published: July 2007

AbstractThe non‐empirical self‐consistent method of discrete variation is employed to calculate the electronic structure of clusters simulating amorphous Ta2O5, which contains anionic vacancies, hydrogen impurities, and substitutional defects (in anionic (N and F) and cationic (Mo and W) sublattices). The influence of these defects on the electronic structure, as well as interatomic bonds, charge distributions, and dielectric properties of amorphous Ta2O5 is discussed.
Bound energy of the Wannier exciton in similar heterogeneous double structures
Authors: Boichuk V. I. , Bilynskii I. V. 
Published: July 2007

AbstractThe problem of the ground state of the Wannier‐Mott exciton in a thin semiconductor film is solved by a variational method. The test wave function has been chosen with two variational parameters. Electron‐hole interaction is considered Coulombic, logarithmic, and general. The binding energy of the exciton in dependence on L−2 is calculated for a WSe2‐type crystal. Qualitative agreement of theory with experiment is obtained in the region of small L.
Interpretation of the semiconducting and metallic phases in the sodium titanium bronze Na1–xTi4O8
Authors: Colaitis D. 
Published: July 2007

AbstractThe electron transfer process is systematically examined in Na1–xTi4O8 as a direct consequence of cation‐anion orbital overlaps. The critical interatomic distance below which the overlap occurs is presumed to be nearly 0.195 nm. On the basis of distortions present in the octahedra of the host lattice, it is shown that molecular‐type orbitals can be imagined in the semiconducting state orthogonally to the infinite chains of octahedra. In the metallic state two infinite ‐TiO‐ chains with transverse correlations are considered as conveying the collective d‐electrons. The occurrence of a Peierls distortion is discussed and excluded. An additional deformation modulation of Ti atoms is proposed, triggered by the fundamental modulation of the interstitial site occupation. The model can describe, in terms of molecular‐type orbitals, the electrical and magnetic behaviour with varying temperature and Na content.
Vapor of pairing particles near the Fermi level of high‐Tc superconductors
Authors: Davydov A. S. 
Published: July 2007

AbstractThe effect of the presence of isolated excited pairs of quasi‐particles at finite temperatures in a cloud over the Fermi level is investigated. It is shown that at inelastic scattering of particles or radiation the decay of pairs from a condensate just as the decay of pairs from a cloud of isolated pairs introduces a contribution to the temperature dependence of the effective gap.
Magnon modes in quasi‐periodic ferromagnets
Authors: Liu Tian‐Shi , Wei Guo‐Zhu 
Published: July 2007

AbstractConsidering ferromagnetic exchange energies J1 and J2 between layers, which are arranged in quasi‐periodic Fibonacci sequence, and the exchange energy J0 in a layer, a rescaling approach to magnons in quasi‐periodic superlattice ferromagnets is presented. An exact decimation transformation is derived for magnon modes of α‐ and β‐layers in ferromagnets. Iteration of the transformation provides numerial results for the local density of states (LDOS) and the magnetization, when J1 + J2 = 2J0 fixed, λ = J2/J1 ( > 1). The band width of LDOS of layer α is 16SJ0(2 + λ)/(1 + λ), but the band width of LDOS of layer β is 24SJ0, the magnetizations of layers α and β decrease as λ is increasing for a given temperature, the magnetization of layer β is always bigger than that of layer α.
Cathodoluminescence of copper‐doped GaAs and its relation to EL2 centres
Authors: Kimpel B. M. , Schulz H.‐J. 
Published: July 2007

AbstractSeveral series of GaAs:Cu crystals are studied with respect to cathodoluminescence properties at cryotemperatures, together with undoped or Si‐doped blank specimens for comparison. A one‐electron model is proposed which comprises the various emission processes related to copper centres in this host material. The presence of EL2 defects in the samples is proved and their energy levels are included in the model. The tendency of Cu and EL2 centres to form complexes is considered. Especially the level hitherto named CuB is now related to an EL2 defect plus a neighbouring copper ion. The 1.0 eV emission of GaAs:Cu thus becomes comprehensible as electron capture at an arsenic antisite defect associated with substitutional copper.
The Exact Fokker‐Planck Type Equation for Planar Channeling of Relativistic Positrons
Authors: Doumanis N. A. , Trikalinos Ch. G. 
Published: July 2007

AbstractThe motion of relativistic positrons under the planar channeling regime is investigated. The corresponding Fokker‐Planck type equation is established considering the longitudinal momentum as constant and then taking into account the exact expressions for the transverse and longitudinal energy. Thus we conclude on the exact form of the Fokker‐Planck type equation. An approximate solution is given without taking into account multiple scattering. This solution, although approximate shows that we have the phenomenon of particles that spread out of the channel instead of damping. The exact solution of the equation requires computer calculation. Our result may be used for the explanation of stronger dechanneling of relativistic particles in planar channeling where the intensity of channeling radiation is less than the expected one.
Absorption Spectra and Low‐Temperature Thermal Conductivity of Irradiated MgO Crystals with Impurity OH− Ions
Authors: Abramishvili M. G. , Akhvlediani Z. G. , Kalabegishvili T. L. , Kvachadze V. G. 
Published: July 2007

AbstractThe influence of γ‐irradiation on low‐temperature thermal conductivity χ (T) and the spectra of optical and paramagnetic absorption of MgO crystals with OH− impurity ions is investigated. It is shown that irradiation leads to strong accumulation of hydrogen‐containing centres and ions of Cr2+ and Fe2+ causing significant changes of χ (T) in crystals. The annealing experiments reveal that in the radiative change of χ (T) the contribution of hydrogen‐containing hole centres is significant.
Improved Raman Effect Studies on Boron Carbide (B4.3C)
Authors: Kuhlmann U. , Werheit H. 
Published: July 2007

AbstractWith a FT Raman spectrometer highly resolved and reliable Raman spectra of B4.3C were obtained largely refuting previous results of other authors. The symmetry selection rules of IR and Raman active phonons are proved to hold. The most prominent Raman doublet at 270/320 and that at 869/928 cm−1are due to pentagonal pyramids of the icosahedra symmetrically vibrating relative to the end atoms of the three‐atomic chain. The broad band at 1065 cm−1is attributed to corresponding vibrations of pairs of pentagonal pyramids in adjacent icosahedra. The remaining Raman‐active phonons, mainly attributed to intraicosahedral vibrations, are comparably weak. At higher photon energies the luminescence radiation due to electron transitions is essential.
Exchange Interaction in the Diluted Semimagnetic Semiconductors Hg1−xMnxSe Under Pressure
Authors: Chudinov S. M. , Yu. Rodichev D. , Mancini G. , Stizza S. 
Published: July 2007

AbstractGalvanomagnetic properties and Shubnikov‐de Haas oscillations in n‐type Hg1−xMnxSe diluted solutions for Mn concentrations 0.001 ≦ x ≦ 0.23 in magnetic fields up to 7 T at temperatures T = (0.2 to 20) K under hydrostatic pressure up to 1.6 GPa are investigated. New methods based on oscillation measurements are proposed to determine magnetic characteristics (value and sign of exchange interaction energy for magnetic ion clusters and average cluster size) of semimagnetic semiconductor diluted solid solutions. These methods permit to determine the magnetic subsystem characteristics in the range of low temperatures between the spin‐glass transition and the temperature corresponding to the binding energy of magnetic atoms in the cluster. In this temperature range, familiar methods (based on measurements of sample magnetic moments) are not effective. The methods proposed are used to determine the dependence of interaction energy on Mn concentration and pressure. It is found that Mn concentration or pressure increase causes a change in the character of cluster interaction from antiferromagnetic to ferromagnetic. The possible exchange interaction mechanisms and their contributions to the interaction energy are discussed.
Spin Waves in a Semi‐Infinite Field‐Induced Metamagnet with Three‐Ion Anisotropic Interactions II. Application to FeBr2 and FeCl2
Authors: Rudziński W. , Maciejewski W. 
Published: July 2007

AbstractTheoretical results for surface and bulk spin‐wave dispersion relations derived in the first paper of this series are applied to field‐induced metamagnets FeBr2 and FeCl2 with a (001) surface. The effect of the three‐ion anisotropy on the surface excitations is examined numerically for both the antiferromagnetic and paramagnetic phases. The obtained results contain modifications of the frequency separation between the surface and bulk modes. Moreover, by allowing the surface three‐ion anisotropy field to differ from the bulk value it is found that in the paramagnetic phase besides optical‐type solutions evaluated in recent analysis of FeBr2 and FeCl2 (001) surface, acoustic‐type surface branches may also occur. A comparison of the results obtained for FeBr2 and FeCl2 confirms the essential influence of the crystal structure on the behaviour of surface spin waves.
On the Interatomic Correlations in Anharmonic Crystals
Authors: Zubov V. I. , Pascual M. F. , Teixeira Rabelo J. N. 
Published: July 2007

AbstractA correlative method of unsymmetrized self‐consistent field is utilized to study the interatomic correlations in anharmonic crystals. Using the statistical perturbation theory up to second order the expression for binary correlations is derived. Corresponding diagrams are constructed and classified. As a simple application, the correlation moments are calculated for the one‐dimensional model.
Calculation of the Lifetime of Slow Positrons at Metal Surfaces
Authors: Shrivastava S. B. , Gupta V. K. 
Published: July 2007

AbstractThe diffusion equation for positrons at metal surfaces is solved to give the rate of positrons reaching the surface. Rate equations are written to describe the various processes at the surface including the trapping of positrons in near‐surface defects. These are solved to yield the lifetime of positrons at surfaces as a function of temperature and for different incident energies. The calculated results show that the positron lifetime increases with the increase in temperature and decreases with the incident energy. The above results are compared with available experimental values.
Spatial Anisotropy of Electron—Phonon Interaction Hopfield‐McMillan Approach Calculation Method and Results for 5d‐Metals
Authors: Zhalko‐Titarenko A. V. , Evlashina M. L. , Antonov V. N. , Nemoshkalenko V. V. 
Published: July 2007

AbstractA method for the theoretical investigation of anisotropy of electron—phonon interaction is developed within the Hopfield‐McMillan approximation. Calculations for Ta, W, Ir, and Pt are carried out. The contributions of separate sheets of the Fermi surface to electron—phonon interactions are found, the origin of the anisotropy of both electron—phonon coupling constant and transport electron—phonon coupling constant is established for these metals.
Phonon Dispersion in Multicomponent Superlattices
Authors: Rath S. , Sanyal S. P. 
Published: July 2007

AbstractThe phonon spectra of a three‐component semiconductor superlattice (SSL) with GaAs, GaSb, AlAs as components along the growth direction are studied by using a one‐dimensional transfer matrix method where one of the components, GaSb, is lattice mismatched with the other two, for various thicknesses. The eigen‐displacements are plotted for various frequencies and thicknesses keeping the thickness of the GaSb layer constant. Also, the frequencies of the confined LO modes of AlAs and GaSb are plotted as functions of the effective wave vector for various thicknesses of the constituting components forming the SSL and compared with the bulk dispersion curves. It is observed that the phonon dispersion in a multicomponent SSL is similar to that of a two‐component SSL, but the large magnitude of lattice parameters of GaSb and its small thickness qualitatively change the superlattice dispersion relation, a feature not reported so far.