bluuebunny/crossref_metadata_2025_split huggingface dataset:
Amorphization of a Disordered Ferrimagnetic Alloy
Authors: Kaneyoshi T. 
Published: July 2007

AbstractThe effects of amorphization on the resultant magnetization in a disordered ferrimagnetic alloy consisting of spin‐1/2 and spin‐3/2 atoms are discussed by the use of mean‐field theory. A number of interesting phenomena, such as the magnetization curves not predicted by the Néel theory, are obtained from the amorphization process.
Angle‐Dependent Scattering at Interfaces in Magnetic Multilayers
Authors: Gu R. Y. , Sheng L. , Xing D. Y. , Liu M. 
Published: July 2007

AbstractAn extended quasiclassical model with angle‐dependent transmission coeficients at interfaces is used to give a more realistic picture of transport processes which take place in Fe/Cr multilayers. Each Fe/Cr interface is considered as a thin region where Fe and Cr are mixed, its effective transmission coefficients are derived. Calculations of resistivities and magnetoresistance (MR) show that the new treatment of interfaces can enhance the contribution of interfaces to the MR and, in order to fit the experimental results for the MR, requires mean free paths which are closer to their real values estimated from resistivity measurements.
Theory of Twofold Coordinated Silicon and Germanium Atoms in Solid Silicon Dioxide
Authors: Sokolov V. O. , Sulimov V. B. 
Published: July 2007

AbstractComputer simulation of twofold coordinated silicon and germanium atoms in solid silicon dioxide is performed in a cluster approach with various boundary conditions with the help of the quantumchemical MO method MNDO. Optical absorption and luminescence in the twofold coordinated atoms are found to disagree with those of oxygen‐deficient centres in solid silicon dioxide. It is concluded that the twofold coordinated atoms are no good models of oxygen‐deficient centres.
Interactive Kinetics in Thermoluminescence (TL) and Its Effect on Glow Curves and Their Growth as a Function of Dose
Authors: Sunta C. M. , Kulkarni R. N. , Yoshimura E. M. , Mol A. W. , Piters T. M. , Okuno E. 
Published: July 2007

AbstractGlow curve calculations are presented for a system of interactive traps in which the deep trap population is an order of magnitude greater than that of the active TL traps. It is shown that the glow peak exhibits a first‐order type of kinetic behaviour even when recombination does not predominate over retrapping. Under most of the dose ranges it is the recapture by the deep traps which is responsible for this kinetic behaviour. The likely reason for the apparent dominance of first‐order kinetics appears to be the interaction between the active TL traps and the deep traps. Another important consequence of interactive kinetics is that the growth of TL intensity with dose becomes supralinear. The interactive nature of the traps thus provides an interpretation not only for the kinetic behaviour of the glow peaks but explains also their supralinearity.
Electron Transport in Vapor‐Deposited Layers of 2‐Methyl‐2‐Pentyl‐1,3‐Bis(Dicyanomethylene)Indane
Authors: Borsenberger P. M. , Magin E. H. , van der Auweraer M. , de Schryver F. C. 
Published: July 2007

AbstractElectron mobjlities are measured in vapor‐deposited amorphous layers of 2‐methyl‐2‐pentyl‐1, 3‐ bis(dicyanomethylene)indane, a highly polar acceptor compound with a dipole moment of 3.9 D. The results are described within the framework of a formalism based on disorder, due to Bässler and coworkers. The parameters of the formalism are σ, the variance of the hopping site energies, μ0 a prefactor mobility, and Σ, the degree of positional disorder. Experimental values of σ, μ0, and Σ are 0.112 eV, 1.6 × 10−3cm2/Vs, and 1.6. The variance of site energies can be described by a model based on dipolar disorder. A comparison of the prefactor mobility with literature values for vapor‐deposited acceptor glasses suggests that the prefactor is dependent on dipole moment, decreasing with increasing moment. The degree of positional disorder is similar to that observed in a wide range of vapor‐deposited molecular glasses and attributed to packing constraints.
Matching of a Bent Step‐Index Single‐Mode Fiber by a Modal Equivalent Slab Waveguide Structure
Authors: Haubenreisser W. , Ecke W. , Schröter S. , Schwotzer G. , Willsch R. 
Published: July 2007

AbstractA novel procedure of matching the modal properties of a bent step‐index single‐mode fiber (BSSF) by the ones of an equivalent slab waveguide (ESW) structure is presented. On applying this procedure the actual BSSF structure is modelled in the first step by an equivalent straight anisotropic single‐mode fiber (SASF) and in the second step this SASF structure is modally matched by an ESW structure. It is shown that for given BSSF (or SASF) input parameters only the derived ESW parameters can describe the modal features (birefringence, cut‐off thickness and wavelength, single‐mode operation range as well as the numerical aperture) of an actual BSSF structure rigorously and consistently within the framework of a slab model analysis.
Segregation Driving Forces on the (111) and (110) Faces of a CuAg Alloy
Authors: Jouaiti A. , Mosser A. , Raiser D. , Romeo M. 
Published: July 2007

AbstractUsing a tight‐binding Isingmodel (TBIM), the segregation energy on the (111) face of a Cu‐Ag 0.45 at% alloy and on the (110) face of a Cu‐Ag 0.30 at% alloy as a function of surface coverage, is derived from equilibrium segregation experiments. It is shown that a surface size effect term which depends on the square of the surface concentration has to be introduced in the segregation energy of the (111) face in order to take into account the surface strain energy which occurs in the first layer when the silver atoms segregate at the surface. On the contrary, on the (110) face the segregation energy expression reveals that the surface size effect does not depend on the silver surface concentration. Also, the effective surface pair interaction βs can be determined and related to the effective bulk pair interaction βb through the relation βs = 1.37βb, for the (111) face and βs = 1.61βb for the (110) face, which is in good agreement with theoretical predictions.
The Properties of Isolated Magnetic Vortices
Authors: Bocdanov A. , Hubert A. 
Published: July 2007

AbstractIsolated magnetic vortices are stabilized by an antisymmetric exchange interaction, the so‐called Dzyaloshinsky interaction, which can be represented as an energy contribution linear in the first spatial derivatives of the magnetization vector. In contrast, vortex lines are demonstrated to be unstable in the bulk of regular uniaxial ferromagnets. They collapse spontaneously under the influence of anisotropy or an applied magnetic field. In reduced units the differential equation for isolated vortices contains two parameters: the reduced magnetic field h along the crystal axis and the material parameter \documentclass{article}\pagestyle{empty}\begin{document}$ \overline \chi $\end{document} which describes the relative contribution of the Dzyaloshinsky interaction term. Isolated vortices turn out to be always metastable for large fields, independent of \documentclass{article}\pagestyle{empty}\begin{document}$ \overline \chi $\end{document} as long as this parameter is positive. At low or negative fields they become unstable by two different mechanisms depending on the \documentclass{article}\pagestyle{empty}\begin{document}$ \overline \chi $\end{document}‐value, but altogether these micromagnetic structures turn out to be stable in a remarkably wide range of parameters. At the end possible applications are considered.
Interband Transition Strength and Magneto‐Absorption Spectrum in Type‐I Superlattices in In‐Plane Magnetic Fields
Authors: Gondar J. López , da Costa B. A. S. , Dickstein F. 
Published: July 2007

AbstractUsing a simplified parabolic band model approach within the framework of the envelope function approximation, the influence of in‐plane magnetic fields on the electronic and optical properties of type‐I superlattices is studied. The results are in qualitative agreement with experimental facts previously reported, as well as with previous theoretical results obtained using more elaborated and toilsome methods. Furthermore, this approach allows to advance, in a great extent, in the analytical treatment of interband transitions, leading straightforwardly to some general conclusions. The not well understood case of high magnetic field effects (magnetic length comparable with the superlattice period) is studied in detail. There strong variations of the interband transition strengths as function of the cyclotron orbit center position are found, a fact which is directly connected with the broadening and final saturation of the magneto‐absorption spectrum with increasing fields. A consistent explanation of such strong variations is given in terms of magnetic subband mixing.
Theory of Third‐Order Nonlinear Photoconductivity and Third‐Order Photogalvanic Effect in Glass
Authors: Sokolov V. O. , Sulimov V. B. 
Published: July 2007

AbstractThe general theory of a third‐order generalized photoconductivity in glass is developed using a density matrix approach in the generalized master equation approximation. The theory is applied to third‐order photogalvanic effect in glass in connection with photoinduced second‐harmonic generation in silica.
The 130 K Transition in Bi Oxides Heavily Doped by Iron Phthalocyanine Superconductivity versus Magnetism
Authors: Grigoryan L. , Yakushi K. , Chakravarty N. 
Published: July 2007

AbstractThe observation and detailed investigation of the highly reproducible transition with onset at 130 K are reported in samples of Bi oxides (both 2212 and 2223 systems) doped with iron phthalocyanine, involving effects of temperature, magnetic field, and chemical composition on dc magnetization and microwave absorption spectra of the samples. The experimental magnetic data are suggestive of a superconducting nature of the transition; however, no reliable electrical resistivity drop is observed at 130 K to confirm the occurrence of superconductivity.
Interband Optical Absorption and Plasma Effects in Half‐Metallic XMnY Ferromagnets
Authors: Kirillova M. M. , Makhnev A. A. , Shreder E. I. , Dyakina V. P. , Gorina N. B. 
Published: July 2007

AbstractThe frequency dependence of the real and imaginary parts of the complex dielectric constant ϵ(ω) in compounds XMnY (X = Ni, Pd, Pt, Cu; Y = Sb, Sn) having Clb structure are investigated in the spectral range ħω = 0.05 to 8 eV. The values of conduction electron plasma and relaxation frequencies ωp and γ, respectively, are determined. The evolution of interband conduction and electron energy‐loss function ‐Im (ε−1) for varying compositions is studied. In all the compounds, apart from the main absorption band located in the spectral range 1 to 7 eV, a low‐energy (ħω = 0.3 to 0.7 eV) interband absorption is revealed. An estimation is made of the energy gap at point Γ of the Brillouin zone in the minority‐spin subbands (↓) for NiMnSb using optical data.
Substrate Misorientation, Multi‐Quantum‐Barrier, and Thermal Annealing Effects in MgZnSSe and ZnCdSe Compounds and Blue‐Green II‐VI Light Emitting Devices
Authors: Kishino K. , Ichimura Y. , Yoshida A. , Kuramoto M. , Satake M. 
Published: July 2007

AbstractMulti‐quantum‐barrier (MQB), substrate misorientation, and thermal annealing effects are investigated in MgZnSSe and ZnCdSe compounds and blue‐green II‐VI light emitting devices. The heterobarrier enhancement of MgZnSSe/ZnSe MQBs is analyzed to be 100 meV, using the experimental band offset of ΔEc ≈ 0.65ΔEg. By use of MQB effect, low threshold current density operation below 1 kA/cm2 can be expected in 480 nm blue emission ZnCdSe/MgZnSSe lasers. For N‐doped MgZnSSe grown on intentionally misoriented GaAs substrates, the decreased net acceptor concentration with misorientation angle is discussed, concluding that the enhanced sulfur incorporation by substrate misorientation plays some role in degradation. It is clarified that ZnSe and ZnSSe are not degraded up to 400°C annealing, while MgZnSSe is even at 350 to 400°C annealing. The light output of ZnCdSe/ZnSe MQW LEDs is enhanced by thermal annealing (325°C, 7 min), by a factor of three.
Effect of Tilted Substrates on p‐Type Doping in ZnSe and ZnCdSe/ZnSe Quantum Wells
Authors: Matsuoka T. , Ohno T. , Ohki A. , Kawaguchi Y. 
Published: July 2007

AbstractTilted GaAs substrates are used to increase the acceptor concentration in p‐type ZnSe by nitrogen doping and to improve the properties of ZnCdSe/ZnSe quantum wells. An acceptor concentration twice as large as that on a (100) substrate is obtained reproducibly, except for (111) substrates, on which ZnSe films show high resistivity. The PL characteristics of ZnCdSe/ZnSe single quantum wells (SQWs) on an (n11) substrate are also examined. The PL spectrum shows a blue shift and the PL intensity is higher with an (n11) substrate than with a (100) substrate. A ZnCdSe/ZnSe MQW separate confinement structure (SCH) laser diode (LD) is fabricated on a (711)A substrate. The built‐in voltage of the LD is by 5 V lower than for an LD on a (100) substrate.
Computation of Elastic and Dynamic Properties of the Liquid Phase of Noble Metals Illustrating Typically for Molten Ag and Cu
Authors: Rao R. V. Gopala , Venkatesh R. 
Published: July 2007

AbstractThe potential function as formulated by Bretonnet and Deroache is applied to liquid Cu and Ag to derive longitudinal and transverse phonon frequencies, the power spectrum, and the velocity autocorrelation function. From these phonon frequencies the elastic constants are evaluated. They are also calculated with the help of Schofield's equations which are computed through the first and second derivatives of the potential energy. The values are found to be in satisfactory agreement with each other. The ratio of the areas in negative regions of the velocity correlation function for these f.c.c. packed liquids are found to be equal to the ratio of their atomic weights. The characteristic frequencies calculated by several methods are in satisfactory agreement with each other. The nearest‐neighbour distance obtained by different methods is also given. It is observed that the ωL (k) maximum occurs around kF, the Fermi wave vector. From the velocity of sound calculated from the experimental compressibility and kF the ωL (k) maximum is computed and is found to be in reasonable agreement with other values.
The Electronic Energy Bands of RbNO3 at the Γ‐Point at 461 K
Authors: El‐Dib A. M. , Hassan H. F. , Mohammed M. A. , Gabber A. A. 
Published: July 2007

AbstractA semiempirical self‐consistent charge LCAO method is used to calculate the electronic energy bands of the cubic phase of RbNO3 at 461 K at the Γ‐point. The energy levels of the hypothetical „RbNO3”︁ molecule and the NO3− ion are also calculated. The population densities, overlap charges, and effective charges on atoms are studied. The effect of the first‐ and second‐nearest neighbours is considered in these calculations.
The Thermopower of a Structurally Disordered Hubbard Model
Authors: Liu K. L. 
Published: July 2007

AbstractThe thermopower S of a structurally disordered Hubbard model with a quasi‐exponential transfer integral is studied. Two cases are considered: (i) the infinite‐U case near half‐filling and (ii) the finite‐U case with various electronic concentrations. Approximations for the required correlation functions are constructed based on their short‐time expansions which are carried out to higher orders in the electronic hopping. For both cases, S is found to be in accord with the generalized Heikes formula at high temperatures. In the temperature range where the thermal energy is comparable to the characteristic hopping energy, the thermopower of case (ii) varies rapidly with decreasing temperature.
Correlations in the coherent transient electron‐hole system
Authors: Keldysh L. V. 
Published: July 2007

AbstractIn the frequency domain close to the intrinsic absorption threshold the dynamic polarization, accompanying propagation of a strong electromagnetic pulse, is a dense cloud of electron‐hole pairs, free or bound to excitons or both. In order to investigate the structure and properties of this system in a wide range of pumping field strengths and frequencies, including both the exciton resonance and continuum edge, two simplified models are introduced and discussed, both substituting an effective short‐range interaction instead of the usual Coulomb potential. To go beyond the mean‐field approximation (MFA) the correlation effects are accounted for phenomenologically in this interaction. Results for both ‐ (quasi‐) stationary regime and transient response ‐ are presented. Possible inelastic relaxation mechanisms and kinetics are discussed. For not too fast (in the “excitonic” time scale) varying pumping field strengths the Boltzmann equation for renormalized Galitskii‐Elesin quasi‐particles is derived.
Persistent spectral hole‐burning phenomenon of semiconductor quantum dots
Authors: Masumoto Y. , Okamoto S. , Yamamoto T. , Kawazoe T. 
Published: July 2007

AbstractThe persistent spectral hole‐burning (PSHB) phenomenon is observed generally in nanocrystalline semiconductors, CdSe, CuBI, and CuBr, embedded in glass and crystal. In the inhomogeneously broadened exciton absorption spectra of these quantum dots, the spectral hole and its associated structure are produced by the narrow‐band laser excitation and are conserved for more than several hours at 2K. The hole depth grows in proportion to the logarithm of the burning fluence. Thermal‐annealing and light‐induced hole‐filling phenomena are observed. The hole burning takes place by tunneling through potential barriers with broadly distributed barrier heights and thicknesses. Photoionization of dots and carrier tunneling into traps in the host are the most probable origins of the PSHB phenomenon. A possible application of the PSHB phenomenon is discussed.
Collective optical response of molecular aggregates
Authors: Fidder H. , Wiersma D. A. 
Published: July 2007

AbstractRelative fluorescence quantum yield, fluorescence lifetime, optical dephasing, and absorption line shift data are presented for both excitonic transitions of the pseudoisocyanine (PIC) J‐aggregate. The data indicate activation of the optical dephasing by exciton‐acoustic phonon scattering at low temperatures. Above approximately 80 K the optical dephasing, line shift as well as the fluorescence lifetime lengthening call for activation by high frequency phonons. Moreover, resonance Raman data indicate the delocalization of low frequency vibrational modes in the aggregate.
Optically induced excitation density flops in semiconductors
Authors: Cundiff S. T. , Knorr A. , Feldmann J. , Koch S. W. , Gobel E. O. , Nickel H. 
Published: July 2007

AbstractThe optically induced excitation density in a semiconductor multiple quantum well is experimentally observed to go through a maximum at sufficiently high excitation intensity. This is achieved by using the interaction of two copropagating ultrafast optical pulses to extract the temporal dependence of the optically induced polarization, which is proportional to the temporal derivative of the excitation density. Solutions to the Maxwell semiconductor Bloch equations show that the observations are a manifestation of Rabi flopping in semiconductors. The results confirm the presence of many‐body modifications to the Rabi flopping for the excitation conditions used in the experiment.
Coherent exciton–photon interaction and pulse propagation effects of bound exciton states in CdS
Authors: Jütte M. , Stolz H. , von der Osten W. 
Published: July 2007

AbstractMeasuring the transform‐limited time‐resolved spectrum of a coherent laser pulse allows one to determine the amplitude and phase of the pulse electric field. From the reshaping of pulses transmitted through a thin semiconductor platelet in resonance with an exciton transition in case of the donor bound exciton in CdS the effects of coherent exciton–photon interaction for different laser intensities can be studied. While at low intensities the expected polariton beating connected with the formation of a 0π‐pulse is observed, at sufficiently high intensities changes in the pulse shape occur that are ascribed to self‐induced transparency of the bound exciton states.
Ultrafast relaxation of photoexcited electrons in undoped GaAs measured by absorption saturation of spin‐orbit‐split transitions
Authors: Alexandrou A. , Berger V. , Hulin D. , Thierry‐Mieg V. 
Published: July 2007

AbstractAn ultrafast redistribution time of less than 40 fs for nonequilibrium photoexcited electron densities as low as 9 × 1016 cm−3 is reported. The electron populations thermalize within 100 to 200 fs after the end of the pump pulse and the cooling of the thermalized electrons to the lattice is observed. These results are obtained from femtosecond pumppprobe measurements yielding differential absorption signals directly proportional to the electron distribution function and independent of the hole distribution. This is achieved by using transitions from the unoccupied split‐off valence band to test the electron populations in the conduction band.
Coherent transport in superlattices and tunneling structures
Authors: Jauho Antti‐Pekka 
Published: July 2007

AbstractSome recent theoretical studies of carrier transport in semiconductor heterostructures are reviewed, where the coherence of the charge carriers leads to significant effects in the time domain. In particular we examine (i) a resonant tunneling system where the current, as a response to a time‐dependent drive voltage, displays oscillations, and (ii) the time‐dependent motion of carriers in a superlattice under external bias, which displays a significant structure in addition to conventional Bloch oscillations.
Four‐wave‐mixing theory beyond the semiconductor Bloch equations
Authors: Axt V. M. , Stahl A. , Mayer E. J. , Bolivar P. Haring , Nüsse S. , Ploog K. , Köhler K. 
Published: July 2007

AbstractFour‐wave‐mixing (FWM) experiments using a dynamical density matrix model of the semiconductor band edge are discussed. Higher‐order correlation functions are retained which are neglected in the commonly used RPA treatment leading to the semiconductor Bloch equations. In order to terminate the hierarchy of the equations of motion for the higher‐order density matrices systematically a truncation scheme controlled by orders in the driving field is applied. For any prescribed order n in the exciting field a closed set of equations is obtained from which the dielectric response up to order n can be calculated exactly. In addition it turns out that in a coherently driven system part of the remaining density matrices become redundant and can be eliminated. Four‐wave‐mixing experiments are dominated by third‐order contributions. Applying the above‐described results one ends up with only two functions in this case. These are the excitonic and the biexcitonic transition densities. As an application of our method the example of a GaAs single quantum well is studied. Two pulses with finite lengths are assumed such that both heavy‐and light‐hole excitons are excited. The influence of the biexciton contribution on the polarization properties of the FWM signal is analyzed and compared with experimental results.
Influence of propagation effects on the coherent optical response of semiconductors
Authors: Knorr A. , Stroucken T. , Schulze A. , Girndt A. , Koch S. W. 
Published: July 2007

AbstractFemtosecond pulse propagation phenomena in semiconductors and semiconductor heterostructures are theoretically investigated. It is shown that the linear pulse propagation through a spatially inhomogeneous structure (multiple quantum wells) is substantially modified in comparison to the homogeneous case. For spatially homogeneous structures (bulk material), the nonlinear interplay between propagation and many‐body effects is investigated in four‐wave‐mixing geometry. For an inverted semiconductor collinear pump‐probe propagation is analyzed to study the ultrafast gain dynamics in amplifiers.