bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bose commutation rule approximation in the theory of spin systems and elementary excitation spectrum
Authors: Derzhko O. V. , Ph. Moina A. 
Published: July 2007

AbstractThe Bose commutation rule approximation for spin operators has been examined using as a testing ground the 1D s = 1/2 generalized XY model. The conditions under which the dependence of the elementary excitation energy on quasi‐momentum is not changed after such an approximationhave been found.
A study of amorphous PdCuSi by internal friction and DSC measurements
Authors: Shui Jiapeng , Chen Xiumei , Wang Can 
Published: July 2007

AbstractThe internal friction of amorphous Pd77.5Cu6.0Si16.5 (a‐PdCuSi) was measured with a conventional torsion pendulum (Ke torsion pendulum) at increasing temperature, and it was found that there are two internal friction peaks (P1 and P2) near the glasstransition temperature Tg and the crystallization temperature Tx of a‐PdCuSi, respectively. From DSC measurements it was found that the origin of the peak P2 is directly related to crystallization, while the peak P1 may be a relaxing internal friction peak. The sensitivity of the inverted torsion pendulum and the Collette pendulum was discussed. We found that the controversy on the measured results of internal friction on a‐PdCuSi is due to the lower sensitivity of thesetwo pendulums.
Electrooptical constants in spherical quantum dots
Authors: Casado E. , Trallero‐giner C. 
Published: July 2007

AbstractThe electrooptical properties of a spherical quantum dot (QD) are theoretically investigated when the QD radius R is smaller than the bulk exciton Bohr radius. The electronic energy levels are obtained as a function of one universal parameter t = 2 [q]m*FR3/h2, where m* and q are the quasiparticle mass and charge, respectively, and F is the applied electric field. The carrier polarization and the interband electron‐hole oscillator strength are investigated as functions of both t and the electron‐hole mass ratio. Using the Kramers‐Kronig relations the change of the complex dielectric constant due to the electric field is derived. A definition of the complex electrooptical function, which describes the main features of the spherical QD optical constants in presence of an electric field, is given. In the strong electric field regime, where perturbation theorycannot be applied to the Schrödinger equation, a quasi‐linear dependence on F is predicted for the electroabsorption variation spectrum. The obtained results are used to explain recent experimental data forthe decay of electron‐hole pairs.
Magnetic properties and band structure of ordered Co2−xNixTiSn compounds
Authors: Jezierski A. 
Published: July 2007

AbstractThe band structure and magnetic properties of the ordered Co2−xNixTiSn Heusler‐type alloys for x = 0, 1, and 2, are studied by using the spin‐polarised TB LMTO method. We found that the Ni2TiSn system is paramagnetic. The self‐consistent band calculations for the systems with vacancy (□) have shown that Co2−x □xTiSn is ferromagnetic but for Ni2−x□xTiSn we did not observe any magnetic moment.
Phonon‐drag effects on thermoelectric power in linear and nonlinear transport conditions
Authors: Wu M. W. , Sun W. , Horing N. J. M. , Cui H. L. 
Published: July 2007

AbstractWe carry out a calculation of the phonon‐drag contribution Sg to the thermoelectric power of bulk semiconductors and quantum well structures for the first time using the balance equation transport theory extended to weakly nonuniform systems. Introducing temperature‐, wavevector‐, and modedependent phonon relaxation times due to phonon‐phonon interactions, the formula obtained can be used not only at low temperatures where the phonon mean free path is determined by boundary scattering, but also at high temperatures. Our analysis of the role of the phonon relaxation times in regard to dependencies on temperature, wavevector, and mode provides results for the linear thermoelectric power Sg which are in agreement with experimental data over a broad range of densities and temperatures. The role of hot‐electron effects in Sg isdiscussed. The importance of the contribution of Sg to the thermoelectric power in the hot‐electron transport condition is emphasized.
Ladder ising spin configurations. I. Heat capacity
Authors: Mejdani R. , Lambros A. 
Published: July 2007

AbstractWe consider a ladder Ising spin model (with two coupled Ising spin chains), characterized by two couplings (interchain and intrachain couplings), to study in detail, in an analytical way, its thermal behaviour and particularly the variation of the specific heat versus temperature, the ratio of interaction constants, and the magnetic field. It is interesting that when the competition between interchain and intrachain interactions is strong thespecific heat exhibits a double peak and when the competition is not so strong the specific heat has a single peak. Further, without entering into details, we give, in a numerical way, some similar results for more complicated ladder configurations (with more than two linear Ising chains). The spin \documentclass{article}\pagestyle{empty}\begin{document}$\documentclass{article}\pagestyle{empty}\begin{document}$ \- \frac{1}{2} $\end{document}$\end{document} ladders or systems of spin chains may be realized in nature by vanadyl pyrophosphate ((VO)2P2O7) or similar materials. All these intermediate systems are today important to gain further insight into the physics of one‐dimensional spin chains and two‐dimensional high‐Tc spin systems, both of which have shown interesting and unusual magnetic and superconducting properties. It is plausible that experimental and theoretical studies of ladders may lead to other interesting physical phenomena.
Local structure in Zn1−xMnxS: EXAFS study
Authors: Łażewski J. , Zimnal‐Starnawska M. , Kisiel A. , Boschbrini F. , Pascarelli S. , Giriat W. 
Published: July 2007

AbstractThe extended X‐ray absorption fine structure (EXAFS) has been measured on the K edge of sulphur in Zn1−xMnxS solid solutions for various manganese contents (0 ± x ± 0.4). Using the wellknown procedure of data reduction, we observed a weak linear increase of anion‐cation and anionanion distances for Mn concentrations changing from x = 0 to 0.4. On the basis of the simulation, using theoretical phases and amplitudes calculated by McKale, the possibility of peak separation in the Fourier transform both in the first and second shells has been discussed.
A study of a fast ionic conductor AgI‐CsI
Authors: Nalini B. , Selvasekarapandian S. , Janaki K. 
Published: July 2007

AbstractOne molar ratio of the compound AgI‐CsI has been taken for the ionic conductivity study. The activation energy has been obtained from the Arrhenius plot. The theory of Rice and Roth has been applied to calculate the number of potentially mobile ions of the conducting species.
Diffusion model of dechanneling based on the Boltzmann equation: Three regimes of energetic particle motion in crystals
Authors: Kashlev Yu. A. , Sadykov N. M. 
Published: July 2007

AbstractThe generalized local Boltzmann equation is derived for the distribution function of energetic particles interacting with the thermal vibrations of the lattice. On using the Boltzman collision term the particle energy losses A(ϵ⊥) and the diffusion function B(ϵ⊥) are obtained. The functions A(ϵ⊥) and B(ϵ⊥) have singularities (fracture, peak) connected with the difference of the contributions of the particles moving in the regimes of channeling, quasichanneling, and random motion.
Photoconductivity and optical absorption of dimorphite thin films
Authors: Tsiulyanu D. , Golban G. , Kolomeyko E. , Melnic O. 
Published: July 2007

AbstractOptical absorption and photoconductivity of As4S3 thin films have been studied. The absorption coefficient is shown to be influenced by the technology of film preparation, in particular by growth velocity and substrate temperature. An absorption band with maximum at hv ≈ 1.9 eV has been observed at the absorption edge for films prepared at low growth velocities. Simultaneously a maximum appears in the spectral distribution of photoconductivity, the position and width of which also depend on the technology of film preparation. The results are explained with taking into consideration the inhomogeneity of films containing α and β dimorphites revealed by X‐ray diffraction studies.
Electronic states in B δ‐doped Si quantum well
Authors: Gaggero‐Sager L. M. , Pérez‐Alvarez R. 
Published: July 2007

AbstractThis work presents a self‐consistent calculation of the electronic structure of B δ‐doped Si quantum well. By examining the dependence of the energy levels, the Fermi level and the depth of the well with the impurity concentration, it is shown that the model is valid for impurity concentration not higher than 1 × 1014 cm−2 and that the Fermi level is very close to the valence band. Calculations are compared with experimental data obtained for p2D = 2.4 × 1013 cm−2, 3.5 × 1013 cm−2, and 9.5 × 1013 cm−2. The results agree quite well with the experimental results available for this system.
Diluted Ising spin‐1/2 lattice with an arbitrary coordination number
Authors: Cong Bach Thanh , Amraoui Y. El 
Published: July 2007

AbstractA useful representation for the Callen identity in the case of spin‐1/2 is introduced by a simple technique. The phase diagrams and percolation problems of the diluted Ising lattice with arbitrary coordination number z are also discussed.
Structure and optical properties of lithium niobium‐phosphate glasses and glass ceramics
Authors: De Araujo E. B. , De Paiva J. A. C. , De Araujo M. A. B. , Sombra A. S. B. 
Published: July 2007

AbstractLithium niobium‐phosphate glasses [(x Nb2O5(0.5−x) P2O5) 0.5 Li2O]: y Fe2O3 were studied using 57Fe Mössbauer and infrared spectroscopy. The use of both techniques gives new information about the structure and crystalline phases in the pure glassy and glass ceramic systems. The iron atoms are present as Fe3+ and Fe2+ ions and in both cases proved to be surrounded by six oxygen atoms (network modifier). The results suggest that the Nb ions occupy sites of average octahedral symmetry. Precipitation of crystalline phases of LiNbO3 and Li3PO4 was detected.
Optical absorption study of colour centres in SrLaAIO4 single crystals
Authors: Ubizskii S. B. , Savytskii D. I. , Matkovskii A. O. , Gloubokov A. , Pajaczkowska A. 
Published: July 2007

AbstractThe peculiarities of absorption spectra of SrLaAIO4 single crystals are investigated as well as the influence of thermal annealing in air and y‐irradiation (60Co source) on them. A more complex structure of absorption bands was revealed, in contrast to previous investigations. The investigation of changes of absorption spectra induced by annealing and irradiation suggests that both reversible and irreversible processes take place in either case and the oxygen defects are most probably responsible for the observed effects.
Far‐infrared spectroscopy of Hg1−xMnxS alloys
Authors: Popovic Z. V. , Tomic N. , Milutinovic A. 
Published: July 2007

AbstractThe far‐infrared reflectivity spectra of Hg1−xMnxS (x = 0.02, 0.05, 0.10, 0.20, 0.25, and 0.33) alloys were measured in the 30 to 500 cm−1 spectral range at different temperatures and analyzed using a numerical fitting procedure based on the plasmon‐phonon interaction model. The three active modes at about 125, 189, and 305 cm−1 are clearly observed. These modes were assigned as twophonon resonant mode, zone center phonon mode, and disorder‐activated mode, respectively. It was shown that phonons in Hg1−xMnxS alloys (for Mn concentrations x ≤ 0.33) exhibit one‐mode behavior.
Acousto‐helicon interaction in narrow‐gap semiconductors
Authors: Ghosh K. K. , Paul S. N. 
Published: July 2007

AbstractA theoretical investigation is made on the propagation of acousto‐helicon waves through plasmas in narrow‐gap semiconducting piezoelectric crystals. Interaction coupling of the acousto‐helicon mode sets up at lower frequencies in the small‐gap semiconductors as compared to that in wide‐gap ones. This is because of the strong dependence of the electron effective mass on the nonparabolicity of the conduction band of the semiconductors. Results are also shown for wide‐gap semiconductors for the sake of comparison.
Effect of random local crystal fields on the magnetic properties of rare‐earth RNi5−xCux compounds
Authors: Kuchin A. G. , Ermolenko A. S. , Khrabrov V. I. , Makarova G. M. 
Published: July 2007

AbstractIt was experimentally revealed that the concentration variations of the spontaneous magnetization, Curie temperature, and initial susceptibility of RNi5−xCux alloys (R = Pr, Nd, Tb, Er, Y) were different for various R. The obtained results are qualitatively explained in terms of effects of random local crystal fields appearing in the substitutional alloys.
Method of calculating the critical temperature of three‐dimensional Ising‐like system using the non‐gaussian distribution
Authors: Kozlovskii M. P. , Pylyuk I. V. , Usatenko Z. E. 
Published: July 2007

AbstractA method for calculating the phase transition temperature Tc based on the theoretical description of the critical behaviour of the model system on the microscopic level is proposed. The main idea of such a calculation is on based a systematic consideration of the influence of the short‐ and longwavelength fluctuations of the spin density on the value of the phase transition temperature. The equation for Tc is obtained as a result of the analysis of recursion relations for the coefficients of Landau‐Ginzburg‐Wilson‐type “effective forms” and consideration of their singular properties in the critical region. As the interaction potential we use an exponentially decreasing function with effective range b. The equation for the critical temperature is obtained and the value of Tc is calculated. The dependence of Tc on the ratio b/c (c is the lattice constant) is investigated. We obtain the value βcJ = 0.211 in the case when the Ising model is approximated by the quartic measure density (ϱ4 model) and for nearest‐neighbours interaction with the interaction constant J.
On the random transverse field mixed spin Ising model of spin‐1/2 and spin‐1
Authors: Weng X. M. , Li Z. Y. 
Published: July 2007

AbstractThe critical behavior of mixed spin Ising model is investigated when the transverse fields are randomly distributed. The calculation shows that when the transverse fields are both bimodally distributed, the transition temperature decreases with increasing transverse field and eventually vanishes at a finite field. When one of the transverse fields is bimodally and the other trimodally distributed, the temperature decreases but does not vanish. When both transverse fields are trimodally distributed, the transverse field dependence of temperature breaks off and a tricritical point appears due to the interaction between quantum fluctuations and disorder.
Scintillation quenching in cerium‐doped ytterbium‐based crystals
Authors: Korzhik M. V. , Drobyshev G. Yu. , Kondratiev D. M. , Borisevich A. E. , Pavlenko V. B. , Timochenko T. N. 
Published: July 2007

AbstractLuminescence and scintillation in cerium‐activated oxide crystals with complex structure are quenched by co‐doping with ytterbium. It was determined that Ce3+ luminescence is quenched by tunneling ionization and scintillations are suppressed in addition by the destruction of relaxing excited host matrix states by Yb3+ ions and nonradiative transitions Ce3+ → (Yb3+)−.
Mean field behaviour of Sr1−xCaxTiO3
Authors: Chaves M. R. , Almeida A. , Maglione M. , Ribeiro J. L. 
Published: July 2007

AbstractA systematic analysis of the dielectric constant as a function of temperature in SrTiO3: Ca crystals with Ca content of 0.0020, 0.0032, 0.0055, 0.0058, and 0.0110 shows that the Barrett parameters are clearly modified by the Ca content. We have found for each Ca concentration the temperature below which the contribution of the Ca induced clusters becomes sizeable. The values obtained for the fitted parameters in the Barrett formula allow us to trace a boundary between the low‐temperature quantum paraelectric and ferroelectric regimes.
Stable states in ferroelectric liquid crystals
Authors: Pitanga P. , Mundim K. C. , Filho A. Ribeiro 
Published: July 2007

AbstractWe study the stability of the molecular structure of DOBAMBC1‐n‐DecylOxyBenzylidene‐p‐Amino‐2‐MethylButyCinnamate.
, a prototype of ferroelectric liquid crystals, using the linear stability analysis for Hamiltonian systems. We show the existence of thermodynamically stable states in a narrow temperature region ΔT = 1 °C, between the A‐phase and the ordinary smectic C*‐phase.
Pressure Dependence of the Electron Effective Mass in GaAs up to the 1s(Γ)‐1s(X) Crossover
Authors: Jiang Z. X. , Chen R. J. , Tischler J. G. , Weinstein B. A. , McCombe B. D. 
Published: July 2007

AbstractThe effect of hydrostatic pressure (P) on the k = 0 conduction band mass m(P) in lightly Si‐doped GaAs is studied by far‐infrared magnetospectroscopy. The electron cyclotron resonance (CR) at (T = 17 K), and the 1s‐2p+ absorption of Si donors (at T = 4.2 K), are measured up to 40 kbar under fields of 6 to 9 T by Fourier transform and laser magnetotransmission techniques. DX‐center trapping is avoided by visible illumination. A double‐bellows diamond‐anvil cell and 36 mm bore magnet enable in situ P‐B‐T tuning. The slopes dE/dB for the CR and 1s‐2p+ peaks decrease with pressure in accordance with effective mass theory, with no sign of strong deepening for the Si 1s(Γ) state. We find m(P)/m(0) = 1 + (6.1 ± 0.3) × 10−3P – (1.3 ± 0.5) × 10−5P2 (P in kbar) from the CR data, after correcting for nonparabolicity via an effective two‐band k.p model. This agrees well with prior results limited to 17 kbar, and extends the measurement of m(P) in GaAs to the Γ‐X crossover.
Determination of the Linear Pressure Coefficients of Semiconductor Bandgaps
Authors: Prins A. D. , Sly J. L. , Dunstan D. J. 
Published: July 2007

AbstractMeasurement of the pressure dependence of the direct bandgap of a tetrahedral semiconductor shows a pronounced sublinearity. This is explained by the stiffening of the lattice under pressure, so that if the pressure is converted into change of lattice constants using a suitable equation of state, the relation between bandgap and lattice constant is found to be linear within experimental (and theoretical) error. However, fitting to the pressure data, many authors use a parabolic equation, Eg(P) = Eg(0) + aP – bP2. We show that this gives a systematic error in the determination of the linear term a which increases with the pressure range of the experiment. GaAs provides a typical example of the systematic error. We find that the true linear pressure coefficient of GaAs is near 11.5 meV/kbar in agreement with the recent low‐pressure measurement of Perlin et al. rather than the long‐accepted value of 10.7 meV/kbar.
Optical Absorption and Raman Scattering Measurements in CuAlSe2 at High Pressure
Authors: Roa L. , Chervin J. C. , Chevy A. , Davila M. , Grima P. , Gonzáez J. 
Published: July 2007

AbstractThe ternary compound CuAlSe2 is a direct energy gap semiconductor (Eg = 2.6 eV at 300 K) crystallizing in the tetragonal chalcopyrite structure. In this work the optical absorption edge and the Raman active modes of CuAlSe2 were measured as a function of pressure up to 30 GPa. The measurements were performed in a membrane diamond‐anvil cell at ambient temperature using neon gas as pressure transmitting medium. The direct energy gap (Γ → Γ) increases linearly with pressure at the rate of 4.7 × 10−2 eV GPa−1. At 6.7 GPa the character of the fundamental gap changes to pseudodirect (Γ → Γ). This gap decreases with pressure at a rate of −2.9 × 10−2 eV GPa−1. The effect of pressure on the phonon frequencies is discussed in terms of the Grüneisen parameters. A first‐order structural phase transition was observed at 12 GPa in the upstroke and at 2 GPa in the downstroke.
Transverse Acoustic Phonons of Germanium up to 9.7 GPa by Neutron Inelastic Scattering
Authors: Klotz S. , Besson J. M. , Braden M. , Karch K. , Bechstedt F. , Strauch D. , Pavone P. 
Published: July 2007

AbstractRecent progress in high pressure neutron techniques now permits the measurement of the phonon dispersion curves of germanium at pressures up to 10 GPa. Inelastic neutron scattering measurements on 25 mm3 single crystals have been performed for the first time up to 9.7 GPa, that is close to its pressure‐induced phase transition. Frequency variations of the phonon modes were measured along the [100], [110], and [111] directions and are shown to have a nonlinear volume dependence for all wavevectors. These results are compared with published data on the behaviour of TA modes in tetrahedral semiconductors and with recent calculations using the density functional formalism. The agreement between experiment and theory is remarkable and underlines the potential of ab initio calculations for accurately describing the lattice dynamics of semiconductors at variable density.
Shubnikov‐de Haas Effect in (Cd1−x−yZnxMny)3As2 under Pressure
Authors: Laiho R. , Lisunov K. G. , Shubnikov M. L. , Stamov V. N. , Zakhvalinskii V. S. 
Published: July 2007

AbstractWe have investigated the Shubnikov‐de Haas effect in single crystals of the group II‐V diluted magnetic semiconductors (Cd1−x−yZnxMny)AS2(x + y = 0.3, y = 0.06 and 0.08) at temperatures T = 4.2 to 16 K and magnetic fields B = 0 to 6.5 T under hydrostatic pressure p up to 14 kbar. Values of the cyclotron mass mc, the effective g‐factor g*, and the Dingle temperature TD have been determined. In both specimens a linear field dependence mc(B) = m + αB is observed, where m is independent of B but increases with pressure and where a does not depend on p and B. Additionally, pressure dependencies of g*, TD and the Hall mobility μR are observed. The dependence of m and g*, on p is interpreted within the three‐band Kane model. The decrease of μR and TD with increasing pressure is consistent with an increase of m.
Far Infrared Spectroscopy of Semiconductors at Large Hydrostatic Pressures
Authors: Haller E. E. , Hsu L. , Wolk J. A. 
Published: July 2007

AbstractThe combination of high resolution far infrared spectroscopy and large hydrostatic pressures produced by diamond anvil cells (DAC) offers a unique approach to the study of dopants, defects, and bandstructure related properties of semiconductors. The problem of small optical throughputs typical of DACs has been solved. Using this unique tool, we have obtained several new results, including the discovery of a local vibrational mode of the DX center in GaAs:Si and the demonstration that the DX center is a negative‐U defect. We have also discovered the first evidence of DX centers in InP and studied the ground to bound excited state transitions of shallow impurities in GaAs at pressures at which GaAs is an indirect bandgap semiconductor with its conduction band minimum near the X symmetry point.
Identification of the L‐Band in InxGa1−xP/In)0.5Al0.5P Multiple Quantum Wells from High Pressure Measurement
Authors: Patel D. , Interholzinger K. , Thiagarajan P. , Robinson G. Y. , Menoni C. S. 
Published: July 2007

AbstractHigh pressure photoluminescence measurements used to study the band structure of the InxGa1−xP/In0.5Al0.5P (x ⩽ 0.48) multiple quantum wells revealed that in narrow‐lattice‐matched and highly tensile strain structures the L1c band is the lowest conduction band state. The L1c minimum was identified as it shifted with pressure at a rate of (60 ± 5) meV/GPa, considerably smaller than that of the direct gap Γ1c states.