bluuebunny/crossref_metadata_2025_split huggingface dataset:
Time‐Resolved Polarization Spectroscopy and Off‐Centre Position of Excited Ga+ Ions in NaCl:Ga Crystal
Authors: Nagirnyi V. , Stolovich A. , Zazubovich S. , Janson N. 
Published: July 2007

AbstractIn the temperature region from 0.35 to 4.2 K the decay kinetics of the triplet AT and Ax emission of NaCl:Ga crystals as well as the spectral and polarization charcteristics of the single decay components of the emission are investigated. An off‐centre displacement of the Ga+ ion in the tetragonal (T) minima of the relaxed excited state (RES) is found. No manifestations of the off‐centre displacement of the Ga+ ion in the trigonal (X) minima are observed. It is shown that fast tunnelling transitions between various equivalent off‐centre positions of an excited Ga+ ion in the plane normal to the tetragonal Jahn‐Teller distortion axis lead to the tunnel splitting of the metastable as well as of the radiative T minima of the triplet RES of the Ga+ centre. It is evident from the existence of two slow and two fast components in the low‐temperature decay kinetics of the AT emission. In case of NaCl:Ga the energy (δ) of tunnel splitting of the radiative minimum is assumed to be larger than the energy (2E) of the spin–orbit splitting of this minimum which is caused by the lowering of the RES symmetry due to the off‐centre displacements of the Ga+ ion. As a result, off‐centre effects are not observable in the ODMR spectra of Ga+ centres in NaCl:Ga crystals, unlike Ga+ centres in other alkali halides, where the energy δ is probably smaller than 2E.
Electroabsorption in Conjugated Polymers
Authors: Horváth Á. , Bässler H. , Weiser G. 
Published: July 2007

AbstractElectroabsorption measurements are peformed with solution cast films of poly‐(dodecylthiophene) and poly‐(phenylphenylenevinylene). The spectra are described within the framework of second‐order Stark effect acting on an excitonic transitonic including field‐induced transfer of oscillator strength to higher lying states. The spatial extent of the exciton is two to three repeat units of the polymer backbone consistent with the notion that the absorbers are ordered subunits of the conjugated chain.
Hole trap analysis in SiO2/Si structures by electron tunneling
Authors: Schmidt M. , Köster H., 
Published: July 2007

AbstractHole trap parameters in Si/SiO2 structures are investigated by their charge relaxation after a foregoing hole trap population. A concept based on tunneling between extended Si states and localized SiO2 states is developed to explain the logarithmic time dependence, gate voltage dependence, and temperature dependence of hole trap depopulation. A positively charged hole trap level with a trap energy of E = (6.3 ± 0.2) eV above the SiO2 valence band edge is found. The corresponding value of the wave vector is |K(E)| = 6.1 nm−1 according to the two‐band approximation for the K(E) relation in the SiO2 gap. The hole trap concentration is N = 2 to 5 × 1019 cm−3 inside a small (5 nm) near‐interface region. These results are in agreement with EPR experiments and confirm that the E'‐centre (oxygen vacancy) constitutes a dominating paramagnetic defect and a hole trap.
The electronic structure of single crystal YBa2Cu3O7–δ studied by polarized Cu Kβ2,5 X‐ray emission
Authors: Czolbe W. , Dick U. , Dräger G. , Fischer K. 
Published: July 2007

AbstractThe polarized Cu Kβ2,5 valence band spectra of an oriented YBa2Cu3O7–δ sample measured on a Johann‐type X‐ray spectrometer, are presented. The experimental spectra are aligned in a binding energy scale together with calculated partial Cu pη DOS (η = x, y, or z), taken from the literature. Due to a detailed comparison between the spectra and the DOS features the distribution of occupied Cu p‐like states along the valence band of this high‐Tc superconductor, their symmetry and contribution to different CuO bonds can be discussed and explained in principle.
Ruderman‐Kittel‐like interaction of electric dipoles in systems with carriers
Authors: Glinchuk M. D. , Kondakova I. V. 
Published: July 2007

AbstractThe energy of indirect interaction of off‐center ions via conduction electrons is derived. The calculations are carried out for ions described by double‐well potentials with the axis along a cubic axis of the lattice. Tunnel motion of ions is taken into account. It was shown that the obtained electric dipole‐dipole interaction Vdd depends on the values of the ion electric dipole moment, electron wave vector on the Fermi surface, and is an alternating sign function of the distance between the dipoles. The form of this function for the main part of Vdd looks like the well‐known Ruderman‐Kittel interaction of magnetic dipoles. Estimations show that the value of interaction is comparable with the conventional electric dipole‐dipole interaction.
Redistribution of electrons to the impurity level in Hg1–xMnxSe under pressure
Authors: Chudinov S. M. , Mancini G. , Stizza S. 
Published: July 2007

AbstractThe galvanomagnetic effect and the Shubnikov‐de Haas oscillation in n‐type Hg1–xMnxSe are investigated under hydrostatic pressure up to 1.6 GPa. The measurements are made at magnetic fields H ≦ 6.5 T in the range of helium temperatures for Mn concentrations x = 0.032, 0.07, 0.075. A significant decrease of concentration and Fermi energy of the Γ‐electrons under pressure are observed. Pressure induced electron redistribution between different bands in the energy spectrum of Hg1–xMnxSe is discussed.
Transfer matrix approach to the optical reflectance of non‐local periodic superlattices
Authors: Mochán W. L. , del Castillo‐Mussot M. , Vázques‐Nava R. A. 
Published: July 2007

AbstractA generalized transfer matrix is applied to calculate the reflectance of a semi‐infinite periodic superlattice made up of spatially dispersive conducting layers, accounting for the propagation of plasma waves allowed by non‐locality. The field inside the superlattice is written as a superposition of the two outgoing solutions of the bulk dispersion relation, with amplitudes given by the electromagnetic boundary conditions supplemented by additional boundary conditions. The discrepancies of the used formalism with that of Trutschel et al. are discussed.
On effective diffusivity of periodic non‐homogeneous solid media
Authors: Mishin Yu. M. 
Published: July 2007

AbstractDiffusion in a non‐homogeneous medium with periodic spatial variations of diffusivity and driving force is analyzed in detail. After a time t ≪ τ (τ being time to attain local quasi‐stationarity) diffusion proceeds like in a homogeneous medium with an effective diffusivity D̃ij. Correct procedure of D̃ij calculation includes solution of a stationary diffusion problem in a periodic unit cell with special boundary conditions. Methods of exact calculation and estimation of D̃ij are discussed, some simple estimates are presented. Possible applications of the theory are sketched.
Pressure dependence of Zr diffusion in the equiatomic B.C.C. TiZr alloy
Authors: Büscher M. , Herzig C. , Köhler U. , Mehrer H. , Lojkowski W. 
Published: July 2007

AbstractPositive as well as negative activation volumes have been measured in the past for self‐diffusion in “anomalous” b.c.c. metals. To contribute to this problem and to obtain further information on the diffusion mechanism in b.c.c. transition metals the pressure dependence of diffusion of 95Zr is measured in the equiatomic b.c.c. TiZr alloy at 1003 and 1493 K in the pressure range up to 14.4 × 108 Pa. The rather small but positive activation volumes ΔV = 0.31 ± 0.06Ω and ΔV = 0.35 ± 0.10Ω, respectively, are obtained. The results are in conflict with negative ΔV values reported for this alloy by Smirnov et al., however, they agree very well with ΔV of self‐diffusion in β‐Ti. Within the limits of error ΔV is independent of temperature which indicates that only one diffusion mechanism is operating despite of the strongly curved Arrhenius relations of 95Zr and 44Ti diffusion in TiZr alloy. The present results confirm a monovacancy mechanism in group IVA b.c.c. metals.
Evaluation of the correlation length critical exponent of the N‐vector model
Authors: Silva P. R. 
Published: July 2007

AbstractAn extension of a heuristic treatment of the critical behavior of the Ising model (N = 1) developed by Thompson, to the general N‐vector model is made. Two approximations for the correlation length critical exponent v as a function of the lattice spatial dimension d and of the number of components of the order parameter N are obtained. Using the hyperscaling relation, the specific heat critical exponent α is also evaluated. Finally, diagrams are constructed displaying in the plane (d, N) various regions, namely: classical critical indexes, non‐classical critical indexes, and no‐phase transition regions or regions where the critical temperature goes to zero. These diagrams are also used to separate regions with divergent specific heat (α > 0) from the ones where it has a cusp‐like behavior (α < 0).
Spin waves in a semi‐infinite field‐induced metamagnet with three‐ion anisotropic interactions. I. Green function approach
Authors: Rudziński W. , Maciejewski W. 
Published: July 2007

AbstractA quartic spin model with three‐ion anisotropic interactions is employed to study surface and bulk spin waves in a layered structure of a semi‐infinite field‐induced metamagnet with a (001) surface at low temperatures, T ≪ TN. The three‐ion surface anisotropy field is allowed to deviate from the bulk value. The calculations involve a derivation of expressions for the spin‐spin Green functions for the semi‐infinite medium. The Green functions are found to have poles at energies corresponding to bulk and surface spin‐wave modes. The theory includes an evolution of the dispersion relations for both the antiferromagnetic and paramagnetic phases.
Effective Pair Potential and Dynamic Correlations in Ni53B47 Melt
Authors: Gopala Rao R. V. , Debnath D. 
Published: July 2007

AbstractUsing experimental values the structure factor of the Ni53B47 melt measured by Nassif et al., the potential function is derived through the use of Rao‐Joarder's equation. The calculated potential function exhibits a repulsive hump corresponding to the first nearest‐neighbour distance. The potential function is also calculated using Percus‐Yevick (PY) and hyper‐netted chain (HNC) equations. In all the cases the repulsive hump appears. The nearest‐neighbour distances obtained by different methods are compared and found in fair agreement with each other. The potential function is used in the evaluation of phonon frequencies. From these phonon frequencies the elastic constants are computed. They are also calculated from I1 and I2 integrals of Schofield. Using the potential function, the characteristic frequency is also calculated and compared with the average frequency by other methods.
Influence of a Quantizing Magnetic Field on the Effective Electron Mass in HgTe/CdTe Superlattices with Graded Structures
Authors: Ghatak K. P. , Mondal M. 
Published: July 2007

AbstractAn attempt is made to study the influence of magnetic quantization on the effective electron mass at the Femi level in HgTe/CdTe superlattices with graded structures by formulating a new dispersion relation and to compare the same with that of the constituent materials. It is found that the effective mass increases with increasing electron concentration and oscillates with reciprocal quantizing magnetic field in all the cases due to the SdH effect. The effective mass also depends on the magnetic quantum number in addition to the Fermi energy which is the characteristic feature of such superlattices and the presence of the finite interface width enhances the effective mass. The numerical values of the same mass in superlattices are greater than those of the constituent materials. In addition, the corresponding well‐known results of relatively wide band gap materials are also obtained from our generalized formulations under certain limiting conditions.
Magnetic Properties of Layered Heisenberg Antiferromagnets
Authors: Wei G. Z. , Du A. 
Published: July 2007

AbstractThe method of double‐time—temperature spin Green's function is used to study the magnetic properties of layered antiferromagnets with arbitrary spin S within Tyablikov's decoupling approximation. According to the extent of suppression of interlayer coupling on the two‐dimensional spin fluctuations, we divide the low‐temperature region into two new regions, and give the asymptotic expressions of sublattice magnetization and parallel susceptibility for each of these temperature regions. The relation between Néel temperature and interlayer coupling strength is calculated and compared with other works.
Semi‐Classical Approximation to the Soliton Energy in a One‐Dimensional Antiferromagnet
Authors: Pires A. S. T. 
Published: July 2007

AbstractThe quantum‐statistical mechanics, at low temperature, of a one‐dimensional antiferromagnetic Heisenberg model with two anisotropies is studied in the weak‐coupling limit. The temperature dependence of the magnon masses, the soliton energy, and the soliton density are determined. Experimental data for TMMC are analysed.
Composition Dependence of Raman Bands in Amorphous AsxSe100−x
Authors: Mikla V. I. , Baganich A. A. , Sokolov A. P. , Shebanin A. P. 
Published: July 2007

AbstractRaman scattering spectra are studied for Se‐rich amorphous semiconductors AsSe. By comparing peak width, peak position, and Raman intensity in the range of bond modes it is derived that the changes occur not monotonically with increasing As content. The change of the spectra is explained as due to cross linking Se chains.
Stochastic Dynamics Crossover From 1/ƒ3 to Flicker Noise
Authors: Canessa E. , Nguen V. L. 
Published: July 2007

AbstractFinite time processes within the limits of the Newton equation and zero inertia motion (i.e., road to chaos) are studied by numerically solving the ordinary, stochastic Langevin equation in 1D for a free particle with inertia moving in a medium with viscosity γ. In these simulations, the scaling behaviour of particle trajectories x(t) and velocities v(t) with time are derived and the inclusion of non‐zero particle masses is shown to define the asymptotic time limit τc at which — independently of γ — the system evolves into the well‐known statistically stationary state characterized by x2(t)> æ t and flicker noise. The time τc is further analysed from the correlation length given by the two‐point autocorrelation function of the particle velocity at each value of γ. It is found that the noise power spectrum of v(t) is characterized by flicker noise for frequencies ƒ ≦ ƒc ≈ 1/τc, whereas for ƒ > ƒc, the noise power spectra behaves as 1/ƒv, where v varies between the limits of Newton's equation (i.e., v = 3) and road to chaos (i. e., v = 1). Furthermore, at times τ < τc and 0 < γ < ∞, an ad‐hoc exponent for the scaling of the variance of particle velocities with time is shown to characterize a subset of multifractal dimensions df(γ) while the single particle trajectories are shown to display a rather different subset of exponents on increasing γ. Generic features of this transition are nicely given by Poincaré maps in the velocity space.
Electrical Conductivity of Hot Electrons in Narrow‐Gap Semiconductors in the Extreme Quantum Limit at Low Temperatures
Authors: Bhaumik S. , Sarkar C. K. 
Published: July 2007

AbstractThe conductivity of hot electrons in narrow‐gap alloy semiconductors at low temperatures is calculated in the extreme quantum limit assuming a displaced Maxwellian distribution. The model includes the non‐equipartition of phonons and the Landau‐level broadening due to electron impurity interactions. It is assumed that the energy relaxation of electrons is governed by the inelastic acoustic phonon scattering via deformation potential and the mobility is limited by the acoustic phonon, ionized impurity, and alloy disorder scattering. The effect of the modified free carrier screening due to magnetic quantization is considered. The magnetic and electric field dependences of the conductivity have also been investigated.
Origin of Superelectrons
Authors: Fukuhara M. 
Published: July 2007

AbstractThe origin of superelectrons lies in the atomic nature. Superelectrons are derived from four special electron pair sets of 1s2, 2p6, 3d10, and 4f14, which can be represented as 1So of s‐type spin‐singlet pairing in the Russel‐Saunders term symbol. Tc increases with the increase of the compressive pressure against these spherical electron clouds by the pinch effect due to excess oxygen in cuprate oxide superconductors and the outermost electrons in the superconducting elements, suggesting the increase of the attractive interaction between electrons.
Subband Effects on High‐Field Electron Transport in Quasi‐One‐Dimensional Systems
Authors: Wang X. F. , Lei X. L. 
Published: July 2007

AbstractA detailed calculation of electron transport in AlxGa1‐xAs/GaAs quantum wires by the use of a balance‐equation approach, considering all possible acoustic and optical phonon scattering and taking fifteen subbands into account, is reported. Crossover from one dimension (1D) to three dimensions (3D) in both low‐ and high‐field regimes is studied by investigating mobility and electron temperature as functions of the radius of quantum wire. At low temperatures, the linear mobility of a quasi‐1D electron system may be ten times higher or ten times lower than that of a 3D system depending on the relative position of the Fermi energy to subbands. At very high electric field, the difference in the transport behavior of quantum wires with differing radii and that of a 3D system disappears as a result of high electron temperature and drift velocity.
Optical Nonlinearities and Carrier Transport in GaAs: EL2 at High Excitation Levels
Authors: Jarasiunas K. , Delaye Ph. , Roosen G. 
Published: July 2007

AbstractLaser induced picosecond transient gratings are used to study carrier transport via free carrier and photorefractive nonlinearities in semi‐insulating undoped GaAs bulk crystals. Carrier lifetime (τR = 1.5 ns), hole and ambipolar mobilities (μh = 410 cm2 V−1 s−1, μa = 760 cm2 V−1 s−1) are measured directly and an electron mobility equal to 5200 cm2 V−1 s−1 is calculated. The optical properties of highly excited GaAs reveal deep donor EL2 transformation and intracenter absorption under picosecond excitation. Rotation of the diffracted beam polarization is observed for the first time in orientation of the grating vector along the crystallographic axis [001]. This signal is attributed to a strain field at dislocations in LEC‐grown GaAs wafers.
Monte Carlo Study of the Order of the Phase Transition in Ising Systems with Multispin Interactions
Authors: Zhang Guo‐Ming , Yang Chuan‐Zhang 
Published: July 2007

AbstractBy analyzing the finite‐size behavior of the maxima of the specific heat near the phase transition temperature, the order of phase transition of two‐dimensional Ising systems with multispin interactions in the horizontal direction and two‐body interactions in the vertical direction are determined. The results strongly support the Turban conjectures.
Compton Profile Studies of CrxNi1−x Alloys
Authors: Pal D. , Padhi H. C. 
Published: July 2007

AbstractCompton profile studies of CrxNi1−x alloys are made for concentrations x = 1.0,0.58, and 0.20. Present measurements indicate peaking of the Compton profile around x = 0.5, which is very similar to that of TixNi1−x alloys. The model of electron rearrangement between 3d and 4s states of individual metals with a transfer of about 0.25 electrons seems to explain the observed peaking of the profile at x = 0.58.
Energy Transfer Between AT and AX Minima in KBr: TI, Quantitative Four‐Level‐Model
Authors: Hlinka J. , Mihoková E. , Nikl M. , Polák K. , Rosa J. 
Published: July 2007

AbstractThe decay kinetics of the A‐luminescence in KBr : TI is investigated in the wide temperature region from 4 to 500 K. In the decay of AT emission up to four components with different decay times can be resolved and in AX emission rise time components are found. For the first time the energy transfer between AT and AX emission bands is observed separately between metastable levels (T = 30 to 40 K) and between radiative ones (T = 60 to 120 K). The set of experimental data obtained is sufficient to determine the rate constants for radiative and nonradiative transitions introduced in the semiempirical four‐level model proposed.
Measurement of Planar Channeling Radiation from 19.2 MeV Electrons in Silicon Using a Microtron
Authors: Poturaev S. V. , Kumakhov M. A. , Ognev L. I. , Iskandarian V. M. , Khatkov T. A. , Stirin A. I. 
Published: July 2007

AbstractAn experimental set‐up for studying radiation of channeled relativistie electrons in single crystals is designed. The source of electrons is a 19.2 MeV microtron. With the help of a mirror‐symmetric achromatic magnetic system a beam of electrons wih an angular divergence less than 0.3 mrad is transported to a single crystal target. The measured radiation spectra at planar channeling of 19.2 MeV electrons in silicon single crystals 3, 7, and 18 μm thick are presented and compared with the calculated spectra. Theoretical calculations are based on a newly developed method using a complex potential for describing the line broadening.
Expansion of Free Energy in Terms of Correlation Functions within the Landau‐Ginzburg Model. II. Calculation in Two‐Dimensional and Three‐Dimensional Cases
Authors: Madzhulis I. , Kaupužs J. 
Published: July 2007

AbstractThe asymptotics of correlation functions and critical exponents are investigated within the Landau‐Ginz‐burg phase transition model for ferroclectrics. The new method proposed is based on a subsequent account for fluctuations. Both analytical and numerical calculations are performed showing that the method gives nontrivial critical exponents. Moreover, precise values are obtained in the two‐dimensional case below the phase transition point. The first‐order phase transition is observed in the three‐dimensional case.
Study of Phonon Eigenfrequencies in Metallic Glasses
Authors: Gupta N. , Jain K. C. , Saxena N. S. 
Published: July 2007

AbstractThe density fluctuations in terms of phonon eigenfrequencies are studied in Ni50Zr50 and Cu66Ti34 metallic glasses using two different theoretical approaches. The calculated results of phonon eigenfrequencies show all the main characteristic features of the dispersion curves. The effective interatomic interactions are studied in terms of a pair potential using the extended theory of the Wills‐Harrison potential which includes the effect of d‐band electrons. Finally, from the low wave‐vector transfer region of the dispersion curves, some thermodynamical properties are also calculated which are in agreement with each other.
Computation of Elastic Moduli and Dispersion in (s–d) Interactive Atomic Liquids. The Example of Liquid Pt and Pd Metals
Authors: Venkatesh R. 
Published: July 2007

AbstractA form of Wills‐Harrison's potential is used to derive the longitudinal and transverse phonon frequencies of Pt and Pd through the use of Takeno and Goda's equations. The low k‐values of phonon frequencies are found to be linear with k and from the slopes of these linear plots the elastic constants are calculated for both metals. The potential functions are also used to calculate the elastic constants of these liquid metals through the use of Schofield's equations. Structure factors in excellent agreement with experiment are generated treating the liquids as square‐well fluids. The paramenters are used to calculate S(0), the structure factor in the long‐wave limit. From the computed S(O) the compressibility and hence C11 are calculated. Because of the well‐known caging effect that occurs due to back scattering, effective masses are used in the calcultion of phonon frequencies. It is gratifying to note that the elastic constants calculated by different methods are in satisfactory agreement with each other.