bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Effect of Giant Striction and Thermal Expansion Anomalies in Systems with Structural Instabilities
Authors: Solontsov A. Z. , Orlov V. K. 
Published: July 2007

AbstractA simple fluctuation theory analogous to the spin‐fluctuation theory of the magneto‐volume effect is presented to discuss the phenomenon of giant striction, associated with displacive phase transitions, and thermal expansion anomalies. It is argued that the giant striction accompanying the phase transition to the incommensurate charge density wave state is responsible for the low temperature anomalous expansion of α‐uranium and α‐plutonium. The spontaneous striction values in these materials are estimated to be 4.57 × 10−3 and 1.82 × 10−2 comparable with those known for systems with giant magnetostriction.
Effect of Lithium Intercalation on Lattice Dynamics of Molybdenum Disulfide
Authors: Sekine T. , Julien C. , Jouanne M. , Weber M. , Samaras I. , Balkanski M. 
Published: July 2007

AbstractIn order to explain new peaks in the Raman spectra of MoS2 after intercalation with Li, the lattice dynamics in LixMoS2 is calculated by applying the central force model. It is found that they can be attributed to new vibrational modes in which the intercalant atoms strongly vibrate against the host lattice. The force constants between Li and S atoms are much smaller than the intralayer force constants and have almost the same order value as the interlayer ones.
Uniaxial Stress Effect on the Charge Transfer in Highly Oriented Films of Iodinated Palladium Phthalocyanine
Authors: Tanaka M. , Tsuyoshi H. , Yudasaka M. , Kurita S. 
Published: July 2007

AbstractThe electronic structure of highly oriented films of iodinated palladium phthalocyanine (PdPcIx), which are obtained by vacuum‐evaporation of PdPc on mica substrates and subsequent iodine‐doping, are studied by the piezoabsorption spectroscopy. Iodines are present as linear chains of I ions in between PdPc stacks, which is confirmed by resonant Raman scattering spectroscopy. The piezoabsorption spectra is measured under a uniaxial stress along the PdPc stacking axis. It is found that the tensile stress induces charge transfer from PdPc molecules to iodines in the lightly doped films and charge back‐transfer in the heavily doped films, and the charge transfer is not induced at the critical doping level.
Electronic Structure of AgCl, AgBr, and AgI
Authors: Gordienko A. B. , Zhuravlev Yu. N. , Poplavnoi A. S. 
Published: July 2007

AbstractSelf‐consistent calculations are made of the band structure and charge density in the AgHal series by the density functional method using norm‐conserving pseudopotentials. The valence band top is found to be realized at the L point in the series of AgCl, Br, and I for the rocksalt structure; there are competing minima at the Γ and X points in the conduction band, the conduction band bottom being at Γ for AgCl, while that for AgBr and AgI is at X. However both, the valence band top and conduction band bottom for the zinc‐blende structure (AgI) are realized at the Γ point.
Solitary Excitations in an Anharmonic Molecular Chain with Second‐Neighbour Interaction
Authors: Primatarowa M. T. 
Published: July 2007

AbstractNonlinear effects caused by the interaction of an exciton with phonons in deformable molecular chains are considered in the second‐neighbour approximation. The cubic anharmonicity of the intermolecular potential leads to a nonlinear Schrödinger equation with nonlinearities of third and fifth power with respect to the function. Two types of solitary bound states are shown to appear situated at the bottom and the top of the exciton energy band, respectively. The parameters of the solitary excitations are calculated.
Study on Momentum Density and Fermi Surface in Paramagnetic Cr and W by Positron Annihilation
Authors: Kubota T. , Kondo H. , Nakashima H. , Murakami Y. , Tanigawa S. 
Published: July 2007

AbstractThe three‐dimensional electron‐positron momentum densities in paramagnetic Cr and W are reconstructed from measurements of two‐dimensional angular correlation of positron annihilation radiations (2D‐ACAR) by the image reconstruction technique based on a direct Fourier transformation. The experimental momentum density for paramagnetic Cr and W shows the contribution of the Fermi surface sheets; the electron surface at Γ, the hole surface at H, the hole surface at N. The Fermi surface topology obtained from the present results agrees with the theory and other experiments.
Theory of High‐Temperature Superconductivity
Authors: Chen Liangheng , Lu Tianquan 
Published: July 2007

AbstractA new mechanism for the high‐Tc superconductivity is suggested. The antiferromagnetic order of the Cu spins between two neighbour O holes, i.e. the localized antiferromagnetic correlation may be the origin giving rise to the hole pair. The maximum of Tc is calculated for the YBaCuO superconductor using the similar method of calculating the antiferromagnet Neel temperature. The conclusion is made that the maximum of Tc for the YBaCuO superconductor is between 107.9 and 155.2 K, and the energy gap 2Δ(0) = 3.54kBTc.
Effect of Antisymmetric Strain‐Order Parameter Coupling on Elastic Constants in Unconventional Superconductors
Authors: Thalmeier P. 
Published: July 2007

AbstractThe coupling of strains to the superconducting order parameter leads to step anomalies in the elastic constants at the transition temperature. In a unconventional cubic superconductor a very specific step asymmetry of transverse (ex, kz)‐ and (ex, kz) c44‐modes may exist in an external field. It is due to a coupling of pseudoangular momentum of the condensate to rotational, antisymmetric strains which is genuine for a superconducting order parameter belonging to a representation with broken T‐invariance. This effect is calculated on the basis of a Ginzburg‐Landau approach and an estimate of its size is given.
Magnetoconductivity of Disordered Two‐Dimensional Electron Systems
Authors: Kleinert P. 
Published: July 2007

AbstractThe magnetoconductivity of a disordered two‐dimensional electron gas is calculated for low‐intermediate magnetic field strengths. Vertex corrections from the Cooper scattering channel are treated and the influence of the self‐energy is investigated. Special attention is paid to cases where both, Shubnikov‐de Haas oscillations and a negative magnetoresistance appear.
Symmetry and Eigenstates of the 3D Hubbard Model in an Electromagnetic Field
Authors: Su Gang , Ge Mo‐Lin 
Published: July 2007

AbstractThe symmetry and the eigenstates of the 3D Hubbard model in the presence of an external electromagnetic field on a periodic simple cubic lattice are investigated within the pseudospin and spin framework. It is shown that the magnetic flux through the periodic lattice is quantized in units of hc/2e, and in this situation the Hubbard system possesses SO4 symmetry which is proved to be spontaneous breaking in the eigenstates obtained explicitly of the model. The information of ODLRO in those eigenstates is also discussed. The absolute ground state of the Hubbard model is yet obtained, and found that the state may not show superconducting transition.
On the Multispike Structure of a Transmitted Pulse in Monocrystalline Films with Absorption Bistability
Authors: Perelman L. T. , Vitkin E. I. 
Published: July 2007

AbstractThe dynamics of motion of boundaries between strongly and weakly absorbing regions in monocrystalline films with increasing absorption bistability is considered. It is shown that the multispike structure of a transmitted pulse is attributed to the simultaneous influence of the film boundary effects and bleaching of the sample at large exciton concentrations.
Stochastic Resonance under Propagation of Electromagnetic Waves in a Three‐Dimensional Random Medium
Authors: Shermergor T. D. , Dikarev A. V. 
Published: July 2007

AbstractThe Bourret approximation for a many‐component medium, which is homogeneous and isotropic statistically under an exponential coordinate dependence of the permittivity correlation function, is used to calculate the mean Green tensor of the electromagnetic wave equation. The frequency dependence of the wave component amplitudes of the mean Green tensor is calculated numerically. The results of the calculations suggest that a stochastic resonance effect occurs in the frequency band determined by the structure of the medium.
Optical Properties of Zn2CuGaSe4 and Zn2CuGaSe4:Co2+ Single Crystals
Authors: Choe Sung‐Hyu , Yu Ki‐Su , Kim Chang‐Dae , Kim Wha‐Tek 
Published: July 2007

AbstractZn2CuGaSe4 and Zn2CuGaSe4 :Co2+ single crystals are grown by the slow cooling method. The optical energy gaps of these single crystals are found to be 1.510 and 1.490 cV at 298 K, respectively. In the Zn2CuGaSe4 :Co2+ single crystals, the impurity optical absorption peaks are attributed to the electronic transitions between the electron energy levels of Co2+ ions sited at the Td symmetry of the Zn2CuGaSe4 host lattice. The crystal field, Racah, and spin—orbit coupling parameters are given as Dq = 425.5, B = 404, and λ = −348 cm−1, respectively.
Piezoreflectance Spectra of the 1s Exciton in CuI
Authors: Certier M. , Erguig H. , Soltani M. , Sauder T. 
Published: July 2007

AbstractThe piezoreflectance spectra of CuI single crystals are studied in the 1s exciton line (Z12) with linearly polarized light at 95 K. The wave vector of the incident light is set perpendicular to the cleavage plane (110) and the alternating stresses are parallel to the crystallographic axes [001] and [110]. From the lineshape and sign of the structure it is concluded that the allowed transverse exciton Γ5 is split in two components. Small reflectivity peaks located on the low energy side of the Γ5 exciton are ascribed to the forbidden Γ3 + Γ4 exciton. The shear strain deformation potentials of the excitonic band are calculated from piezoreflectance measurements and assuming the cubic deformation potential c — a = −1 eV are estimated to: b = (−0.5 ± 0.1) eV and d = (−1.7 ± 0.3) eV.
Phase Transition of SBN: Ce Studied by Anisotropic Holographic Scattering
Authors: Rupp R. A. , Seglins J. , van Olfen U. 
Published: July 2007

AbstractLight scattering phenomena in (Sr0.61Ba0.39) Nb2O6:Ce are investigated from room temperature to the phase transition temperature. Temperature dependence and sign of the birefringence are determined from anisotropic holographic scattering at a wavelength of 514.5 nm. The majority charge carriers are electrons.
Magnetic Susceptibility of Heavy Fermions and Mixed‐Valence Systems
Authors: Panwar S. , Singh I. 
Published: July 2007

AbstractThe electronic and magnetic properties of heavy fermions and mixed valence systems have been, in the recent past, described by the periodic Anderson model (PAM). In this paper the magnetic behaviour of the Anderson lattice is studied using the variational method, proposed recently. With this variational method, the variation is studied of average valence and spin susceptibility with temperature for different values of hybridization, different effective values of the f‐level, and for finite as well as infinite interaction U. When the f‐level lies deep below the Fermi level, the susceptibility diverges in most of the temperature region for infinite U, while for weak interaction the divergence is reduced to a small temperature region. When the f‐level lies near the Fermi level, the susceptibility is finite at T= 0 K, increases linearly at low temperature and shows Curie‐Weiss behaviour at higher temperatures.
The Magneto‐Optical Kerr Effect of Fe/Ag Bilayers
Authors: Zhou S. M. , Lu M. , Zhai H. R. 
Published: July 2007

AbstractThe magneto‐optical polar Kerr rotation spectra of Fe/Ag bilayers made by vacuum evaporation are measured. In the spectra an enhancement rotation peak occurs near 560 nm. For comparison, the calculated magneto‐optical Kerr rotation spectra are given. It is found that the necessary conditions for the Kerr rotation enhancement are low values of the optical constants n and k of the reflector, especially the value of n must be less than 1.0. The calculated off‐diagonal element of the effective dielectric constant tensor ϵxye is also given.
Dependence of Phase Shift on Chemical Environment in Extended X‐Ray Absorption Fine Structure
Authors: Murari A. , Chetal A. R. 
Published: July 2007

AbstractThe coefficient of the term linearly dependent on K, αj in the phase shift is calculated from the theoretical phase functions of Teo and Lee and from experimental extended X‐ray absorption fine structure (EXAFS) data for 3 d transition metal systems of manganese, cobalt, and copper. Attempts are made to explain the behaviour of the phase shift of a given atom pair in different chemical surroundings. The dependence of αj on chemical shift and partial charge is also studied.
IR‐Active Lattice Absorption of the α‐ and β‐Phases of Oxygen in the 45 to 150 cm−1 Region
Authors: Fugol I. Ya. , Pritula I. M. , Khashchina L. V. 
Published: July 2007

AbstractNew experimental date on the far IR absorption spectra of solid oxygen in its α‐, β‐, and γ‐phases are presented. The conditions of generating IR‐active optical modes in oxygen crystals is discussed. It is shown that the optical activity of the observed modes is due to the magneto‐elastic interaction with the short‐range magnetic order.
Recombination Processes in Short‐Period GaAsAlAs Superlattices of Type II
Authors: Maaref M. , Charfi F. F. , Scalbert D. , la Guillaume C. Benoità , Planel R. 
Published: July 2007

AbstractAn extensive study of time‐resolved photoluminescence is made in the temperature range 1.8 to 50 K on nine samples of type‐II GaAsAlAs (001) superlattices. In previous publications, the region is identified where the states derived from Xz valleys are lower than those derived from Xxy valleys, in agreement with a simple model involving the competition between X‐type valley anisotropy and X valleys splitting caused by the small lattice mismatch between AlAs and GaAs. An analysis is given of the luminescence processes and of their evolution with temperature, as a function of AlAs and GaAs layer thicknesses. Excitons localized by interface roughness are found to decay through radiative processes at low temperature. A model of thermal excitation from the tail of localized exciton states is introduced, which helps to identify the pertinent parameters of temperature behaviour in these samples.
Chemical Bonding and Lattice Relaxation in Substoichiometric Titanium Carbide and Nitride
Authors: Čapková P. , Skála L. 
Published: July 2007

AbstractThe rearrangement of interatomic interactions and redistribution ofelectron densities in titanium carbide and nitride resulting from the existence of the nonmetal vacancy are studied by the CNDO/2 method. The local lattice relaxation is taken into account and the differences and common features in the behaviour of the nonmetal vacancy in titanium carbide and nitride are discussed.
The Asymptotic Time Dependence of the Mean‐Square Displacement of Particles in a Multicomponent Two‐Sublattices One‐Dimensional Alloy
Authors: El‐Meshad N. 
Published: July 2007

AbstractThe mean‐square displacement, 〈r2(t)〉, of a labeled particle hopping on a linear two‐sublattice system through a multicomponent dynamic background with vacancy concentration v is calculated in the limit of very long times. Our result is 〈r2(t)〉 = (2va2/c1/2) (J∼t/π), where c is the background particle concentration and J∼ the collective hopping rate given by \documentclass{article}\pagestyle{empty}\begin{document}$ J^ \sim = \left[{\sum\limits_\lambda {x^\lambda \left({1/J^\lambda + 1/J_\lambda ^T } \right)} } \right]^{ - 1}. $\end{document} Here xλ represents the concentration of the A‐species of atoms whose hopping rate on each sublattice is Jλ and across the two sublattices is J.
The Function of an Impurity Contained in the Support of Catalysts
Authors: Xu G. D. , Wei S. Y. , Zhang T. 
Published: July 2007

AbstractThe function of a substitutional impurity in the support of catalysts is investigated by using the Green's function method and complex‐energy‐plane integration technique. The tight‐binding approximation is employed to model the H‐Ni/ZnO(contaminated) system, which is considered as an example. The Anderson‐Newns theory is used to compute the chemisorption energy and adatom charge transfer. It is found that (1) the impurities with the different effective levels, Δε, have different effects on the chemisorption process, (2) the effect of the impurity to be closest to the surface of the support is most significant, (3) the influences of an impurity in the support on the chemisorption are of secondary importance compared with those of an impurity in the active component of catalysts.
Electronic Structure of Vacancies in Transition Metals
Authors: Stepanyuk V. S. , Kozlov A. V. , Katsnelson A. A. , Szasz A. , Farberovich O. V. 
Published: July 2007

AbstractThe electronic structure of vacancies in Fe, Ni, and Cu transition metals and in Al is calculated by linear augmented plane waves (LAPW) in muffin‐tin Green function approach. The electronic structure of vacancies shows a strong hybridization with metallic d‐states, and a considerable effect is observed on the s‐ and p‐electrons in the density of states. The charge transfer differs from the similar case of the simple metals.
The Critical Conditions for Jerky Flow. Discussion and Application to CuMn Solid Solutions
Authors: Kubin L. P. , Estrin Y. 
Published: July 2007

AbstractThe transitions between smooth and jerky flow have recently attracted a significant interest. Considerations of critical strains and stresses for the onset or disappearance of jerky flow are presented in this paper aiming at explaining some recent observations by Kalk and Schwink on CuMn solid solutions. Three particular intervals of temperature, labelled α, β, and γ, are examined, which correspond to different patterns of behaviour of the critical strains. It is shown that the experimental observations at the lowest temperatures (interval α) are understood reasonably well. An explanation is proposed for the occurrence of an island of stability in the interval β which exploits the thermally activated nature of recovery processes. The particular type of behaviour observed at higher temperatures (interval γ) does not seem to be completely interpretable in terms of the current models.
Theory of Worksoftening in High‐Performance Alloys
Authors: Kuhlmann‐Wilsdorf Doris , Wilsdorf H. G. F. 
Published: July 2007

AbstractIn conventional alloys ductility decreases with rising flow stress to negligible values at some maximum yield stress (τm), whereas high‐performance alloys, e.g. formed throgh mechanical alloying or nano‐powders, can have much higher yield stresses with ductility, but tend to worksoften. A simple theory is presented, based on the LEDS concept, to account for both of these behaviors: The flow stress is τ = τ0 + const √ϱ with ϱ the dislocation density, and the workhardening coefficient is θ ≈ dτ0/dγ + Cβ with β the rate of glide dislocation trapping. β depends on the specific LEDS formed but always decreases with stress and can become negative for τ > τm at artificially high ϱ. Worksoftening results when unconventional manufacturing methodes have produced LEDS with metastable ϱ and/or τ0 values that are higher than conform to the LEDS generated through the conventional straining conditions in testing or use.
Anomalous Galvanomagnetic Properties of Quasi‐Two‐Dimensional η‐Mo4O11 Crystal under High Magnetic Fields
Authors: Inoue M. , Machel G. , Laue I. , von Ortenberg M. , Sasaki M. 
Published: July 2007

AbstractTransverse magnetoresistance and Hall effect of the quasi‐two‐dimensional crystal of η‐Mo4O11, that undergoes twice in the charge density wave (CDW) transitions at Tc1 = 105 and Tc2 = 35 K, are measured in liquid He temperature ranges using a pulse magnet up to 33 T and a Bitter‐type magnet up to 17 T. In the CDW state below Tc2 there appear hysteresis phenomena in the magnetic field dependences of both quantities when a field sweep range exceeds a threshold value of about 10 T, and the Hall voltage has a unique magnetic field dependence. Computer simulations for these unique transport quantities are made using a possible band scheme consisting of multiple conduction carriers (electrons and holes).
Interband Quantum Kinetics with LO‐Phonon Scattering in a Laser‐Pulse‐Excited Semiconductor II. Numerical Studies
Authors: Bá;nyai L. , Thoai D. B. Tran , Remling C. , Haug H. 
Published: July 2007

AbstractA detailed numerical study of the coupled quantum kinetic equations with memory for electron–hole populations and interband polarization induced by an 100 fs short light pulse is performed. The considered model describes the interaction with a LO‐phonon bath. The equations are shown to have stable physical solutions, if collision broadening is self‐consistently taken into account. The completed collision approximation is found to be a good approximation of the fully retarded equations. Ignoring the collision broadening of the particle energy levels in the memory kernel, however, leads to instabilities of the solutions.
Size‐Dependent Thermodynamic Properties of Quasi‐One‐Dimensional Electron‐Hole Plasmas
Authors: Schweizer H. , Lehr G. , Prins F. E. , Lach E. , Fröhlich E. M. , Pilkuhn M. H. , Straka J. , Forchel A. 
Published: July 2007

AbstractThe thermodynamic properties of quasi‐one‐dimensional electron–hole plasmas (1D‐EHP) are studied in a wide range of wire widths. The wires are realized by implantation induced intermixing of GaAs/AlGaAs quantum wells. The 1D‐EHP is analyzed with respect to size‐dependent k‐space filling and band‐gap renormalization. The experimental results indicate strong filling effects depending on the lateral dimensions of the wires.
Many‐Body Effects and Multi‐Mode Behaviour in Semiconductor Lasers
Authors: Henneberger K. , Jahnke F. , Herzel F. 
Published: July 2007

AbstractWithin a quantum theory of semiconductor lasers based on a kinetic description of the interacting carrier–photon system the influence of many‐body and nonequilibrium effects is investigated. For the transient as well as steady state behaviour the lineshape of stimulated emission is discussed that reveals mode selection, mode pulling, and line narrowing, in connection with gain saturation and hole burning in the carrier kinetics.
Optical Properties and Switching Behaviour of Excited III–V Semiconductors near the Direct–Indirect Cross‐Over
Authors: Gürtler S. , Schwabe R. , Staehli J. L. , Unger K. 
Published: July 2007

AbstractIn highly excited semiconductor systems near the transition from direct to indirect band structure (cross‐over) the energetic distance between different conduction band minima is a nonmonotonous function of the excitation intensity. A theoretical explanation of this experimental result is given. Our investigations are based on the evaluation of photoluminescence spectra using a careful lineshape analysis. The nonmonotony is a consequence of the unequal shrinkage of the direct and indirect gaps as a function of the population of energetically comparable conduction band valleys in a material near cross‐over. In the situation discussed an optical switching mechanism is expected, which is explained with special respect to its switching time. Important problems of electron–electron interaction are discussed.