bluuebunny/crossref_metadata_2025_split huggingface dataset:
Renormalization of Electron Mass by 2D Coulomb Interactions in a Laterally‐Microstructured Silicon Inversion Layer
Authors: Parish J. L. 
Published: July 2007

AbstractThe effect is considered of high‐momentum plasmons on electrons in a 2D EG. It is found that the high‐momentum, low‐velocity plasmons can form electron‐plasmon pairs. Renormalizing the mass due to Coulomb interactions of these paired electrons, it is possible to explain very accurately the large mass shift measured in far‐infrared transmission experiments.
Fluctuation Effect on the Excess Conductivity of Layered Superconductors
Authors: Ye Zhen 
Published: July 2007

AbstractBy using thermo field dynamics (TFD) and Ginzburg‐Landau theory, the fluctuation effects on conductivity are studied for layered superconductors above critical temperature. It is argued that the broadness of the resistivity is due to the decoupling of electron tunneling among layers. The results are compared with experiments.
Electromagnetic Properties of a Type‐II Superconducting Cylinder
Authors: Saif A. G. 
Published: July 2007

AbstractThe electromagnetic field distributions and solutions for an infinitely long superconducting cylinder placed parallel to an infinitely long normal conducting wire carrying an alternating current, are obtained. The propagation behavior of the fields within the cylinder is investigated in terms of the propagation constant as a function of the London penetration depth. The power loss on the cylinder surface is calculated.
Intergranular Diffusion in Real Polycrystals
Authors: Kondratev V. V. , Trachtenberg I. Sh. 
Published: July 2007

AbstractAn analysis of grain‐boundary diffusion for a real polycrystal is given. The non‐uniformity of diffusion permeability of the grain interface and the non‐uniform pumping of diffusants from the boundary into the bulk due to dislocations are taken into account. The meaning of the grain‐boundary and volume diffusion coefficients for different annealing regimes is elucidated. The conditions of the true C‐regime for a polycrystal is obtained.
The Influence of the Exchange Interaction on Atomic Ordering in Alloys with F.C.C. Lattice
Authors: Binnatov K. G. , Masharov S. I. , Rybalko A. F. , Safarov D. A. 
Published: July 2007

AbstractThe investigation of ordering in binary substitution alloys with f.c.c. lattice, in which magnetic ordering can exist along with the f.c.c. structure is performed in second approximation of the Kirkwood method. It is shown that the exchange interaction essentially effects the development of atomic ordering. The possible types of phase diagrams are investigated. It is shown that the correlation considered makes a correct description possible of the kind of order‐disorder phase transition in the alloys of L1 superstructure. The correlation contributions to the heat capacity of alloys are calculated.
Crystal Structure and Electronic Properties of (2,6‐DMbTN)3(ClO4)2
Authors: Söderholm S. , Von Schütz J. U. , Noreland J. , Olovsson I. , Hellberg J. 
Published: July 2007

AbstractCrystal structure, conductivity, and magnetic properties of the monoclinic cation radical salt 2,6‐dimethoxy‐3,6‐bis(methylthio)naphthalene‐perchlorate [(2,6‐DMbTN)3(ClO4)2] are presented. The trimerization of the 2,6‐DMbTN stack causes the salt to be semiconducting, σ(300 K) ≈︁ 0.5 S cm−1, with a band gap of 0.5 eV. The susceptibility is quite low 0.02 spins/complex at 300 K, above 200 K the susceptibility originates from the thermal excitation of triplet spin excitons of the Wannier type from an antiferromagnetically coupled ground state with J = 0.11 eV. The electrical and magnetic properties below roughly 200 K are governed by deep defect levels in the band gap. The unusually narrow ESR linewidth for a sulphur containing ion‐radical salt, 0.8 × 10−4T at 300 K, implies that the electron structure is “one‐dimensional” and/or the spin density on the sulphur atoms is low.
Chemical Bond Approach to the Dielectric Constant of Semiconductors
Authors: Esperidião A. S. C. , Brum J. A. , Ramos J. G. 
Published: July 2007

AbstractThe extension of the Nucho, Ramos, and Wolff method for the non‐tetrahedral semiconductors was made by Brum and Ramos. This extended NRW method is applied to the elemental, group III‐V, and group II‐VI semiconductors and better accuracy is claimed. The ionicity for the II‐VI semiconductors (zinc‐blende structure) is also calculated and confirms the ionicity scale established by Phillips. Again, Coulson's definition is reconciled with that of Phillips.
Volume Dependence of Effective Charge Parameter and Photoelastic Behaviour of Alkali Halide Crystals
Authors: Dikshit U. C. , Kumar M. 
Published: July 2007

AbstractAn analysis of the volume dependence of effective charge parameter and electronic strain polarizability parameter is presented for alkali halide crystals. The deformation dipole model due to Hardy is used along with the seven different potential forms for the short‐range overlap repulsive energy and the modified form of the additivity rule for the crystalline state polarizabilities as proposed by Raghurama and Narayan. The effective charge model due to Hanlon and Lawson is adopted to obtain the strain polarizability parameter within the framework of Coker's theory. The results are compared with the available experimental data. It is found that the results are fairly insensitive to the form of the overlap repulsive potential used whereas they depend sensitively upon the choice of polarizability.
Polaron Pairing in Multi‐Layer Structures: II. Interlayer Bipolaron States in Structures with Quantum Wells
Authors: Pokatilov E. P. , Beril S. I. , Fomin V. M. , Ryabukhin G. Yu. , Goryachkovskii E. R. 
Published: July 2007

AbstractA structure containing conductive planes separated by polar dielectric interlayers is shown to possess the possibility to create bipolaron states by charge carriers moving in the different planes. The attraction is due to the inertial polarization induced by similar charges in polar interlayers which separate them from each other (interlayer polaron pairing). The potential energy of electron‐electron interaction and the bipolaron binding energy are calculated as functions of material and geometric parameters of the structure.
On the Electrical Conductivity of PrREBaCuO (RE = Er, Yb, Lu, Tm): Compounds in Orthorhombic Phase
Authors: Triberis G. P. , Guskos N. , Svoboda P. , Vaŝek P. , Z̆emanova D. , Koufoudakis A. , Mitros C. , Gamari‐Seale H. , Niarchos D. 
Published: July 2007

AbstractExperimental results showing the temperature dependence of the conductivity of a variety of PrREBaCuO (RE = Er, Yb, Lu, and Tm) compounds are presented. The semiconducting behavior of the conductivity observed is analysed using In σ ∼ T−2/5 and In σ ∼ T−1/4 laws suggested, using the small‐polaron hopping model by Triberis et al., for the high‐ and low‐temperature regime, respectively. The agreement of the experimental data with these models is very satisfactory, giving a meaningful interpretation of the transport mechanism of these materials.
Electrical Properties of Silver‐Doped As2S3
Authors: Goyal N. , Vohra A. 
Published: July 2007

AbstractTemperature and frequency dependent ac conductivity studies are made for silver‐doped a‐As2S3. The temperature dependence of σac for the As2S3‐Ag system can be well explained by correlated barrier hopping model. Numerical calculations agree well with the experimental results. The energy levels and the concentration of charged defects are also estimated for these materials.
Configurational Energy Change Caused by Slip in Short‐Range Ordered Ni–Mo
Authors: Schwander P. , Schönfeld B. , Kostorz G. 
Published: July 2007

AbstractBased on short‐range order parameters determined from X‐ray diffuse scattering measurements on a Ni–11.2 at% Mo single crystal and effective pair potentials obtained from applying the inverse Monte‐Carlo method, the configurational energy change caused by the successive slip of a variable number of unit dislocations on the same {111} plane is calculated. A fraction of 97% of the diffuse antiphase boundary energy of 25 mJ/M2 has to be provided by the first slip step. The glide of subsequent dislocations on the same glide plane is thus favored which leads to planar slip as observed by transmission electron microscopy. Monte‐Carlo simulations also show that the diffuse antiphase boundary energy depends more sensitively on the concentration of the alloy than on the temperature where thermodynamic equilibrium was established.
Internal Solid State Reactions
Authors: Schmalzried H. 
Published: July 2007

AbstractInternal solid state reactions have first been studied as internal alloy oxidation reactions. The concept of this type of solid state is reactions is generalized and applied to nonmetallic systems. Firstly, interal oxidation reactions with (A,B)O solid solutions are discussed. Then it is shown how one can induce internal reduction reactions with systems such as (A,B)O or (A,B)3O4. A third type of internal solid state reactions is met if A and B diffuse in the solvent crystal C from opposite sides and form a stabel compound AB internally. Finally we discuss AO–BO interdiffusion in in extended solid solutions. It is shown that diffusion potentials can build up which change the local oxygen potential to such an extent that new phases form internally.
Pairing between Fast Diffusing Donors and Shallow Acceptors in p‐CdTe
Authors: Zoth G. , Ridel F. G. , Schröter W. 
Published: July 2007

AbstractDefect reactions of mobile intersitial donors Di with immobile substitutional acceptors Acd in the spacecharge region of Schottky contacts on p‐type CdTe are observed at about room temperature. The results are discussed in terms of formation and dissociation of defect complexes (AcdDi). For copper diffused samples the dissociation kinetics of a complex, presumably (CuCdCui), is determined. The dissociation enthalpy of 0.74 eV leads to the rather low value of 0.2 to 0.3 eV for the migration enthalpy of Cui. Furthermore it is shown that thermally stimulated capacitance (TSCap) yields a step with a shape characteristic of defect complex dissociation and drift of the intersitial donor.
A Combined Cluster‐Dynamic and Deterministic Description of Decomposition Kinetics in Binary Alloys with a Tendency for Clustering
Authors: Kampmann R. , Ebel Th. , Haese M. , Wagner R. 
Published: July 2007

AbstractA novel numerical model is devised to describe the decomposition kinetics in metastable binary alloys with a positive pair exchange parameter. The stochastic process of nucleation and growth of precipitates is simulated on grounds of a novel cluster‐dynamical model, which for a description of the later stages is linked to a deterministic model. The discussion of the precipitation kinetics in a Cu‐Co type alloy yields the interpretation of kinetic experiments in terms of classical theories to be inadequate.
Configuration Dynamics in a Simulated Finite‐Temperature Transition Metal Glass
Authors: Teichler H. 
Published: July 2007

AbstractThe dynamics of configurations and of ‘nearest‐neighbour’ relations are investigated for an amorphous metallic alloy by molecular dynamics computer simulations covering the whole range of temperatures up into the liquid state. The configuration dynamics are expressed in terms of nearest‐neighbour auto‐correlation functions, where at finite temperatures ‘nearest neighbours’ are defined with regard to the force‐free configuration closest to the actual atomic arrangement. Results are presented for an atomistic model adapted to the recent hybridized nearly‐free‐electron‐tight‐binding‐bond description of Ni0.5Zr0.5. The results agree well the predictions of the extended mode‐coupling theory for the time dependence of density fluctuations and related properties around the glass‐liquid transition in ‘real’ systems.
Optical Excitation and Bose Condensation of Excitons in Low‐Dimensional Systems
Authors: Glutsch S. , Bechstedt F. , Zimmermann R. 
Published: July 2007

AbstractThe linear optical response of excitons is studied in low‐dimensional semiconductor systems – bulk, quantum well, quantum wire – pumped near the energy of the lowest exciton transition under inclusion of many‐body interactions. Attention is focused especially to three aspects: (i) influence of dimensionality on the Coulomb interaction, (ii) different behaviour of the optical response for pump frequencies lower than or close to the nominal exciton resonance, and (iii) time dependence until reaching stationarity. For this purpose the two‐band Bloch equations and the generalized gap equations are simultaneously solved. Far from the absorption edge results for the excitonic dynamical Stark effect are confirmed, at least in the collision‐free limit. For pump frequencies near or above the nominal exciton resonance an additional stationary solution of the gap equation is observed that is not vanishing for zero pump field and, therefore, characterizes a Bose‐like condensation in the electron–hole system. In the fully time‐dependent regime it is studied how this so‐called “excitonic insulator” can be reached during the time evolution. The resulting optical spectra as well as the existence and observability of the condensed phase are discussed.
Lattice Dynamics of Methanol
Authors: Weng S. X. , Anderson A. 
Published: July 2007

AbstractA simple ten parameter force constant model is described and applied to the vibrations of molecular methanol. The model is extended to crystalline methanol in its ordered α‐phase, with the use of twelve parameters describing the van der Waals intermolecular interactions, three representing those for the hydrogen bond and twelve for the intramolecular forces. Comparision with experimental frequencies from Raman and infrared studies of CH3OH, CH3OD and CD3OD shows acceptable agreement. The effects of hydrogen bonding on the intramolecular forces are briefly discussed.
Brillouin Instability in Longitudinally Magnetized Crystals with High Dielectric Constant
Authors: Gadkari P. , Ghosh S. 
Published: July 2007

AbstractAn analytical investigation is made of the stimulated Brillouin Scattering of a plane polarized intense electromagnetic wave propagating parallel to the applied magnetic field in a n‐type semiconducting plasma with high dielectric constant. The general dispersion relation is obtained and solved for both, the cases of scattered electromagnetic waves (i.e. in the case of left hand and right hand circularly polarized waves) to study the threshold condition and the growth rate of the unstable Brillouin mode at a pump amplitude well above the threshold. It is found that the threshold pump amplitude is independent of applied magnetic field and is the same for both types of polarization. The growth rate of the unstable Brillouin mode has linear dependence on the magnetic field. Numerical estimations are made for n‐BaTiO3irradiated with a pulsed 10.6 μm CO2 laser to obtain the necessary electric field.
Study of Precipitated Phases in Mn2+ Singly Doped KBr Crystals by Optical Spectroscopy and EPR
Authors: de Lucas M. C. Marco , Rodríguez F. , Moreno M. 
Published: July 2007

AbstractThe aggregation states of Mn2+ in KBr Mn2+ doped crystals are investigated using optical techniques. Excitation and luminescence spectra as well as lifetimes are obtained as a function of temperature of different crystals. It is demonstrated that at least three different Mn2+ precipitates are formed inside the KBr. Two of them contain MnBr64‐ units with slightly distorted octahedral symmetries, while the third one involves two non‐equivalent tetrahedral MnBr42‐ units. These centers exhibit a broad green luminescence band.
Time‐Resolved Four‐Wave Mixing in GaAs/AlAs Quantum Well Structures
Authors: Göbel E. O. , Koch M. , Feldmann J. , von Plessen G. , Meier T. , Schulze A. , Thomas P. , Schmitt‐Rink S. , Köhler K. , Ploog K. 
Published: July 2007

AbstractFemtosecond nonlinear laser spectroscopy is applied to study the dynamics of coherent optical excitations in semiconductors. In particular, excitonic excitations in quantum wells and superlattice structures are considered. Two examples demonstrate that four‐wave mixing experiments with time‐resolved detection of the nonlinear signal are able to distinguish between quantum beats and polarization interference.
Coherent and Incoherent Exciton Dynamics in Al1−yGayAs/GaAs Multiple Quantum Wells
Authors: Oberhauser D. , Pantke K. H. , Langbein W. , Lyssenko V. G. , Kalt H. , Hvam J. M. , Weimann G. , Klingshirn C. 
Published: July 2007

AbstractPicosecond lasers allow to detect the dynamics of excitons directly in the time domain. Here examples of such experiments are presented for high quality AlGaAs MQW samples at low temperatures and in the low and medium density regime. The phase relaxation time T2 is measured in FWM experiments and quantum beats are observed between the hh and lh exciton and between exciton and biexciton states. A value of the biexciton binding energy of 1.75 meV is deduced in agreement with our luminescence data. The T2 times are compared with scattering times τ obtained from diffusion measurements using ps and ns laser‐induced gratings. Interface‐roughness scattering occurs only for thermalized excitons. The influence of increasing exciton‐exciton scattering with density is demonstrated for (magneto‐) excitons and Landau levels. Finally the luminescence dynamics of excitons is investigated for resonant and nonresonant excitation. The influence of cooling (intraband relaxation) is discussed and a simple model is presented to explain the generally observed increase of the lifetime T1 with lattice temperature.
Real Time Approach to Relaxation and Dephasing Processes in Semiconductors
Authors: Hartmann M. , Schäfer W. 
Published: July 2007

AbstractStarting from the kinetic equations for the nonequilibrium Green's functions, a practical method is proposed which allows to solve the set of equations for the two‐time propagators numerically. In contrast to the usual semiconductor Bloch equations with phenomenological damping relaxation and dephasing processes are treated microscopically for the case of coupling to a bath of LO‐phonons. Beside a standard approximation for the treatment of LO‐phonon scattering, no further approximations are performed. For the low‐density limit we compare exact results with approximate treatments, as the Marcovian and non‐Marcovian approximations resulting from a density matrix approach. First results concerning nonlinear optical properties are presented.
Monte‐Carlo Simulations of the Coulomb Boltzmann Kinetics in a Quasi‐Two‐Dimensional Electron–Hole Plasma for Various Screening Models
Authors: El Sayed K. , Haug H. 
Published: July 2007

AbstractFor carrier‐carrier scattering the relaxation kinetics of a quasi‐two‐dimensional degenerate electron‐hole plasma is studied in the framework of the Boltzmann equation using both a static and a dynamic RPA screening. The time development of an initial nonequilibrium distribution is calculated by ensemble Monte‐Carlo simulation. A comparison of the results for both screening models for the energy relaxation and the total scattering rate yields conditions for the validity of static screening.
Thermalization of Photoexcited Carriers in Bulk and Quantum Wire Semiconductors
Authors: Lugli P. , Rota L. , Rossi F. 
Published: July 2007

AbstractA theoretical study of the internal thermalization of high‐energy carriers created by laser excitation in bulk and quantum wire semiconductors is presented. For the bulk case the results of our Monte Carlo simulation are compared to luminescence up‐conversion experiments used to monitor the spectral and temporal evolution of the photoexcited carrier distributions with a time resolution of about 100 fs. The agreement between theory and experiment is very good and shows that the Coulomb interaction among carriers is responsible for the initial ultrafast thermalization. On the contrary, a much slower thermalization is found theoretically in quantum wires, which can be mainly attributed to the reduced efficiency of intersubband processes and to the reduced effect of electron‐electron intrasubband scattering. Available experiments seem to confirm such findings.
Sum Rules for Nonlinear Optical Susceptibilities
Authors: Bassani F. , Scandolo S. 
Published: July 2007

AbstractNew sum rules are obtained for the dispersive and dissipative parts of the nonlinear susceptibilities, applicable to pump and probe experimental situations. A three‐level model shows how they clarify the nonlinear lineshapes. A detailed calculation on atomic hydrogen shows how the sum rules allow a global estimate of the magnitude of nonlinear effects.
Absorption Edge Singularities for Non‐Equilibrium Carrier Distributions
Authors: Foing J.‐P. , Joffre M. , Jackson M. K. , Oudar J.‐L. , Hulin D. 
Published: July 2007

AbstractNon‐equilibrium carrier distributions are studied in GaAs by monitoring the induced bleaching in femtosecond pump–probe experiments. Unchirped pump pulses are required in order to avoid asymmetrical coherence oscillations. The observation of an induced absorption on the high‐energy side of the hole burning is explained in terms of absorption edge singularities, emphasizing the importance of many‐body effects in highly excited semiconductors.
Electron–Hole Plasma Decay Time in GaAs/(Ga, Al)As Quantum Wells
Authors: Bongiovanni G. , Staehli J. L. 
Published: July 2007

AbstractA steady state photoluminescence experiment is reported investigating the lifetime of an electron–hole plasma confined in a quantum well. The results are compared with theoretical evaluations of the pure radiative decay rate and good agreement is found. The effects caused by the filling of electron and hole subbands are also discussed.
Tunneling of Charged Particles through a Crystal with Narrow Conduction Band in the Presence of an Electric Field
Authors: Sugakov V. I. , Yatskevich S. A. 
Published: July 2007

AbstractThe energy spectrum and tunneling probability are obtained for charged particle tunneling through a crystal with narrow conduction band in an electric field. It is also shown that the current–voltage characteristic of such a system has a region with negative differential resistance which does not arise in the usual way (due to a resonant level) but due to the small width of the conduction band. Also the role of surface interaction is investigated.
Electronic Structure and Optical Characteristics of Alkaline‐Earth Oxides
Authors: Stepanyuk V. S. , Szasz A. , Grigorenko A. A. , Katsnelson A. A. , Farberovich O. V. , Mikhalin V. V. , Hendry A. 
Published: July 2007

AbstractThe electronic structure of MgO, CaO, SrO, and BaO oxides is calculated by the linear augmented plane wave method. From the electronic structure of the compounds their optical parameters are derived. A satisfying correspondence with the experiments is observed.
Ti Deep‐Level Delta‐Doping in GaAs Schottky Diodes: Capacitance–Voltage Analysis
Authors: Piprek J. , Krispin P. , Kostial H. , Lange C. H. , Böer K. W. 
Published: July 2007

AbstractDeep‐level Ti centers delta‐doped within Al/n‐GaAs Schottky diodes are investigated by CV‐analysis. CV‐profiles are modeled as a function of deep‐level energy and local center distribution using 1D device simulation. The deep‐level analysis is applied to MBE‐grown GaAs samples with almost delta‐like Ti doping (half‐width 12 nm) yielding a double peak structure of the GV‐profile. Besides the well‐known Ti acceptor level in GaAs a yet unknown deeper level at aboutEc–Er= 0.5 eV is observed.
Impurity‐Induced Core–Valence Luminescence in Halide Compounds
Authors: Voloshinovskii A. S. , Mikhailik V. B. , Syrotyuk S. V. , Rodnyi P. A. 
Published: July 2007

AbstractInvestigation of the impurity‐induced core–valence luminescence (IICVL) in doped RbCl:Cs, SrCl2:Cs, and RbCaCl3:Cs crystals is made under pulsed X‐ray excitation (δt ≈ 1 ns). It is shown that the spectral structure and emission intensity of IICVL is determined by the spatial structure of the nearest anion environment of the cesium ion. The model of an isolated emission centre (cluster [CsCln]) for the interpretation of the IICVL peculiarities is proposed.