bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Coherent Pairing and Bose‐Einstein Condensation of Excitons in Semiconductors
Authors: Bobrysheva A. I. , Moskalenko S. A. , Shvera Yu. M. 
Published: July 2007

AbstractThe possibility of particle and pair Bose‐Einstein condensation in a system of four species of excitons with different values of spin projections of the electron and of the hole is studied. It is known that the system has the following properties: 1) the interaction of the exciton of either type with all the exciton species is repulsive on the average; 2) the pairs of excitons with antiparallel spins of electrons as well as of holes interact attractively and biexcitons can be formed. In two limiting cases when the exciton–exciton interaction energy W is greater or smaller than the ortho–para‐exciton splitting Δ, it is shown that: 1. the coherent pairing of excitons with momenta k and −k coincides with Bose‐Einstein condensation of biexcitons with zero translational momentum. Such a state persists without collapse due to the internal spin structure of excitons. 2. In the system of para‐ and ortho‐excitons the Bose‐Einstein condensation of para‐excitons and biexcitons formed by two ortho‐excitons with zero total spin can take place simultaneously.
Picosecond Kinetics of Luminescence in Highly Excited Direct‐Gap Semiconductors
Authors: Klochikhin A. A. , Razbirin B. S. , Nelson D. K. , Amand T. , Brousseau M. , Collet J. , Cornet A. , Pugnet M. 
Published: July 2007

AbstractExperimental and theoretical investigations of luminescence spectra kinetics are carried out in CuI, CdS, and CdSe crystals at concentrations below the Mott threshold. The observed radiation is shown to be due to exciton‐phonon‐plasmon interaction caused by the coexistence of excitons and an electron‐hole plasma (EHP) during the time interval shorter than the time, necessary for the EHP to undergo the transition into the gas of excitons. It is found that the inhomogeneous distribution of excitons and EHP is developing in a crystal despite the initially homogeneous excitation. Theoretical lineshape analysis of exciton‐phonon‐plasmon luminescence is shown to be able to provide information of its spatial distribution.
The Dispersion Relations of the Nonlinear Surface Waves Due to the Exciton and Biexciton Formation
Authors: Khadzhi P. I. , Kiseleva E. S. 
Published: July 2007

AbstractNonlinear surface waves (NSW) are considered taking into account both, the exciton‐photon interaction and the exciton‐biexciton conversion. Two different types of NSW solutions for the longitudinal component of the electric field Ex are obtained: monotonous and nonmonotonous ones. Dispersion laws are obtained and disussed for each type of the NSW solutions.
Effect of Magnetic Field on 3A1u → 1A1g Luminescence of Pb2+ in CaF2 and SrF2 and of Au− in NaCl
Authors: Overberg A. , Fischer F. 
Published: July 2007

AbstractThe magnetic field dependence of the zero‐phonon line intensity I0 and of the lifetime of the 3A1u → 1A1g emission is measured between LHeT and LNT. It is found that I0 prop. B2 up to 2.37 T. In NaCl:Au− already at this field strength the emission is completely π‐polarized. The structured phonon sidebands are strongly changed in the B field. Reciprocal lifetime versus B2 follows a straight line with a slope nearly independent of temperature. The results are discussed in analogy to those obtained on Pb2+ an Bi3+ alkaline‐earth chalcogenides.
Final State Core Level Shifts in Supported and Free Metal Particles
Authors: Castellani N. J. , Leroy D. B. 
Published: July 2007

AbstractThe final state contribution to core level electron binding energy shifts is analysed in the case of small free and supported particles. The results of a pseudopotential–electron gas linear response model that was developed in a preceding paper are compared with other jellium models (atom‐in‐jellium vacancy DFT, semi‐classical). As small particles are generally supported as clusters, the support contribution is also calculated, considering a possible charge transfer. Total relaxation contribution is then compared with the experimental results of Kohiki for the Pd/SiO2 system. Good agreement is obtained in the range 10 to 40 at. units.
Size‐Quantum Effect of the Energy of a Charge Carrier in a Semiconductor Crystallite
Authors: Pan J. S. , Pan H. B. 
Published: July 2007

AbstractThe size‐quantum effect of the energy of a charged carrier in a spherical semiconductor crystallite embedded in another spherical dielectric layer is discussed and the interaction of the charged carrier with surface optical (SO) and longitudinal optical (LO) vibrations is taken into account. In the first‐order approximation of the energy the charged carrier does not interact with SO vibrations, and it interacts only with LO vibration of the dielectric in which the charged carrier is located. The interaction energy between the charged carrier and LO vibrations will increase with decreasing the size of crystallite.
Theory of Electron Emission from Solids by Proton and Electron Bombardment
Authors: Rösler M. , Brauer W. 
Published: July 2007

AbstractUsing the microscopic theory of kinetic ion‐induced electron emission (IIEE) and secondary electron emission (SEE) developed earlier an improved description of transport processes of excited electrons is given. Electron–electron scattering rates are calculated including the dynamic screening of the Coulomb interaction. The resulting enhancement of these scattering rates compared with the Thomas‐Fermi approximation leads to new statements concerning the magnitude of contributions from different excitation mechanisms. The theory is applied to polycrystalline aluminum. For the proton‐induced electron emission the primary energies are limited to 20 to 800 keV and for the SEE to 1 to 2 keV. Compared to the other excitation mechanisms the excitation of single conduction electrons for IIEE (H+ → Al) and the excitation from inner shells for SEE produces the largest contribution to the yield, respectively. A better agreement between theory and experiment is achieved for both emission phenomena.
Dye‐Laser 4f–4f‐Line Probing of Crystal‐Field Fluctuations in ZnS:Sm3+ Polycrystalline Films
Authors: Löbe K. , Boyn R. 
Published: July 2007

AbstractUsing the dye‐laser site‐selective excitation technique, a study is made of 4G5/2 → 6H9/2, 6H7/2 inter‐Stark level transitions for a special type of Sm3+ centers in ZnS polycrystalline films. It is found that the emission lines become narrowed compared with the case of “nonselective” excitation, with the peak positions and intensities depending on the location of the dye‐laser energy within the 4f–4f excitation line profiles. The results can be quantitatively described by a simple model which involves small centre‐to‐centre fluctuations of crystal‐field parameters. A comparison with the (much sharper) lines measured for the same type of Sm centers in ZnS bulk crystals shows that these fluctuations have a Gaussian distribution with maximum corresponding to the bulk crystal situation. An explanation can be given on the basis of random strain originating from high dislocation densities. A discussion is made of whether the linewidths are affected by interactions between the Sm centres and by electric fields due to dislocation charge.
A Simple Scheme for Studies of Surface Phonons of Covalent Semiconductors. I. Calculation of Force Constants
Authors: Lin Zijing , Wang Kelin 
Published: July 2007

AbstractA framework is given for calculating and interpreting vibrational surface properties of covalent semiconductors. The bond orbital approximation (BOA) in a tight‐binding theory for electronic structural energies is developed and applied to deriving atomic force constants that are essential for calculating dynamical matrix and phonon dispersion relations in these systems. The method used connects force constants with electronic structure directly and is able to predict phonon spectra as well as the change of force constant at the surface. Some analytical expressions for force constant calculation are obtained for the first time with this semiempirical models. It is shown that the scheme is fairly simple, yet accurate enough within the frame of tight‐binding theory.
Electronic Structure of SmH2
Authors: Gupta R. Sen , Chatterjee S. 
Published: July 2007

AbstractThe electronic energy bands of SmH2 are calculated using composite wave variational method. The presence of two low‐lying bands below the d‐bands supports the general characteristic of dihydride. Between the two bands, the antibonding band Γ overlaps the metal d states which indicates a depopulation of metal d bands. The electrical and magnetic behaviour of SmH2 is analyzed in the light of this depopulation. A discussion about the formation and stability of SmH2 is made in terms of the relative positions of various energy bands. From the band structure data, density of states, optical properties, and Fermi surfaces are calculated and interpreted.
EPR of a New O Centre in KCl
Authors: Callens R. , Callens F. , Matthys P. , Boesman E. 
Published: July 2007

AbstractEPR results are given of a new O2− paramagnetic defect, formed following room temperature X‐ray irradiation in KCl, heavily doped in the melt with KNO2. The EPR spectra indicate that the O2− molecular ion has two equivalent equilibrium positions between which it jumps. Above 10 K the EPR spectrum of this molecular ion is orthorhombic, with principal axes [110], [001], and [110]. Below this transition temperature the principal axes are tilted by 1° with respect to the [110] and [110] directions in the (110) plane. A possible model for the perturbing impurity responsible for this tilt is proposed.
Carrier Heating in GaAs by Nonradiative Recombination
Authors: Rühle W. W. , Leo K. 
Published: July 2007

AbstractHeating and cooling of a photoexcited electron–hole plasma is investigated by time‐resolved luminescence at low lattice temperatures (< 10 K) in Czochralski grown GaAs. Heating processes are experimentally detected by generating (with photon energies close to the band gap) a cool plasma and studying its heating process to temperatures higher than the lattice temperature. The influence of these heating processes on the cooling rate of a hot electron–hole plasma is demonstrated.
Analysis of the Intensity and Polarization Dependence of Two‐Photon Absorption in the Channel E3/2(4f)−E3/2(5d) for Ce3+ in CaF2
Authors: Makhanek A. G. , Korolkov V. S. , Yuguryan L. A. 
Published: July 2007

AbstractA calculation is made of the parity‐forbidden two‐photon absorption cross section of the transition between the lowest Stark sublevels for a tetragonal site Ce3+ (symmetry C4v) in a cubic fluorite crystal as well as of polarization characteristics of a CaF2:Ce3+ monocrystal with different orientations (k ∥ [100], k ∥ [110], k ∥ [111], k is the wave vector of the incident laser beam). The calculated cross‐sectional value (σ0 = 3.7 × 10−54 cm−4 s) and the polarization dependences agree with experiment.
Magnetic Behavior and Crystal Field of Pr3+ in Praseodymium Selenate Octahydrate
Authors: Nandi J. , Neogy D. 
Published: July 2007

AbstractMeasurements are made on the principal magnetic susceptibilities and anisotropies of praseodymium selenate octahydrate single crystals in the temperature range 90 to 300 K. Although the effective magnetic moment is close to the free ion value, the anisotropy is quite high at room temperature. A least squares fit of the Curie‐Weiss law to the observed average susceptibility yields −36.5 K as the paramagnetic Curie temperature. An analysis of the results with a crystal field (CF) of D4 symmetry, explains the observed results quite well. The CF and the spin‐orbit interaction matrix is block diagonalized in the complete 33 dimensional basis of the 3H term in order to obtain the Stark energies and their eigenstates. Intermediate coupling effects are also considered. The ground state being a singlet, the g‐factors are absent. Some predictions on the electronic heat capacity and the electronic quadrupole splitting are made in the light of the proposed CF.
A Theory of Higher‐Order Correlations. I. Ising Model with Spin \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{2} $\end{document}
Authors: Šamaj L. 
Published: July 2007

AbstractAn analytic method for finding highly accurate values of the transition temperature for the spin \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{1}{2} $\end{document} Ising model is presented. The method is based on the previously introduced formalism, where certain well defined higher‐order correlations are treated by means of physical considerations. In this way, an inadequate description of the higher‐order correlations within the correlation reduction theory is removed. The results for the critical temperature for all cubic lattices are consistent with series expansions to within ≈ 20%.
On the Pinning of Spin‐Density Waves by Impurities
Authors: Seidel Ch. 
Published: July 2007

AbstractIn a nonperturbative way, using the Bosonization technique the behaviour of longitudinal and transverse SDW's in a random field of impurities is studied. It is shown that magnetic as well as nonmagnetic species can pin SDW's. However, the pinning strength of nonmagnetic impurities is found to be essentially reduced compared to the CDW pinning. In contrast to this, locally strong pinning is expected to appear at kinks in the spin‐density phase. Thus, continuously changing the kink density by a magnetic field applied parallel to the easiest axis a significant enhancement of the pinning should be obtained when the period of kink lattice is commensurate with 2kF, i.e., with the period of the superstructure.
Correlation between the Structures of GeS Glasses and that of Impurity Mn2+ Complexes
Authors: Zhilinskaya E. A. , Lazukin V. N. , Bychkov E. A. , Rosenkov S. B. 
Published: July 2007

AbstractEPR method is used to study the Mn impurity in glass system (GeS)x(GeS2)100−x for 0 ≦ x ≦ 80. Three types of Mn2+ centers homogeneously incorporated in the glass network are found. They have different coordination numbers and different magnitude and symmetry of crystal field. The dependence of the parameters of Mn2+ EPR spectra on glass composition is obtained for every Mn2+ center. The results are compared with known glass structure data.
Lattice Dynamics of B.C.C. Transition Metals
Authors: Mishra S. K. , Singh T. N. 
Published: July 2007

AbstractA theoretical model for the lattice dynamics of b.c.c. metals is develoed. Contribution to ion‐ion interaction is evaluated applying the valence force field. The contribution to the potential energy from ion‐electron interaction is considered by a screened Coulomb potential. Computed phonon dispersion curves and Debye characteristic temperatures for α‐iron and tungsten on the basis of the model compare well with the experimental results. The Cauchy discrepancy is expressed in terms of an angle‐dependent potential energy in the present model.
Electrical Resistivity Due to Electron–Phonon Scattering in Thin Gadolinum Films
Authors: Urbaniak‐Kucharczyk A. 
Published: July 2007

AbstractThe contribution to the electrical resistivity due to the electron–phonon scattering for the special case of h.c.p. structure is derived. The numerical results obtained for the case of polycrystalline gadolinum films show the resistivity dependence on the film thickness and the surface properties.
Low‐Temperature Electron Transport in Quasi‐Two‐Dimensional Systems
Authors: Pratsch Chr. , Suhrke M. 
Published: July 2007

AbstractA theoretical approach including multi‐subband coupling is applied to electron transport in quasitwo‐dimensional systems. This results in a modified contribution of the several scattering mechanisms to the total scattering rate. Taking into account the dominant scattering mechanisms the low‐temperature mobility is calculated in the electric quantum limit and is compared with experimental data for heterojunctions and single quantum wells (particularly consisting of Ga1−x. AlxAs/GaAs).
Behaviour and Hysteresis Losses of Irreversible Type‐II Superconducting Cylindrical Shells
Authors: Saif A. G. 
Published: July 2007

AbstractThe internal magnetic field distribution in a type‐II superconducting cylindrical shell is determined. The superheating – and the supercooling – fields are developed. The effect is shown of a transport current on the creation and annihilating of the potential barrier for high χ‐cylindrical shell. The ac losses are studied in the frame of the general critical state theory. For a high‐Tc superconducting sample, smaller superheating – and supercooling – fields than that for conventional superconductors are obtained.
Macroscopic Dynamic Theory of Polar Interface Modes of Superlattices
Authors: Enderlein R. 
Published: July 2007

AbstractThe dynamic theory of polar interface (IF) modes of superlattices is developed. The former electromagnetic theory of these modes is reformulated in terms of sheet polarization charges and currents. The spatial variations of the various electromagnetic field vectors of IF‐modes as electric polarizations, dielectric displacements, and electric field strengths are calculated. Within the dynamic theory polar IF‐modes are characterized by relative mechanical displacement fields having no bulk sources and vortices but sheet sources and vortices on interfaces. A set of Newtons equations is derived for the relative mechanical displacement fields. This set is solved, and the equivalence of the dynamic and electromagnetic approaches with respect to eigenfrequencies is demonstrated. The displacement field eigenvectors are calculated and proven to be orthogonal and complete. They are discussed with the regard of their polarizations and spatial variations. With the exclusion of vanishing wave vector component q parallel to SL‐layers they are neither longitudinal nor transverse but elliptically polarized with polarization ellipses depending on z. For q = 0 the relative mechanical displacement fields of IF‐modes are confined to one of the two SL‐materials, just like for confined bulk modes. The displacement fields are quantized, and the electron–IF‐phonon interaction Hamiltonians are given both for deformation potential and Fröhlich coupling.
Determination of Polariton–Phonon Interaction Parameters in Anthracene Crystals
Authors: Maksimov A. A. , Tartakovskii I. I. , Krivenko T. A. 
Published: July 2007

AbstractThe resonant Raman scattering of light and luminescence excitation spectra of anthracene crystals (T = 1.5 to 40 K) under resonant excitation by a tunable dye laser near the bottom of the lowest exciton band (ωT = 25096 cm−1) are studied. The mean free paths of polaritons for Stokes and anti‐Stokes scattering by optical and acoustic phonons of different branches and values of polariton phonon interaction matrix elements are obtained. The calculated mean free paths for anti‐Stokes scattering by acoustic phonons at T ⪆ 5 K are in a good agreement with the experimental data.
Investigation of the Valence Band Structure of Thermoelectric (Bi1−xSbx)2Te3Single Crystals
Authors: Stordeur M. , Stölzer M. , Sobotta H. , Riede V. 
Published: July 2007

AbstractUsing combined optical‐spectroscopic and transport investigations it is succeeded for the first time to determine all relevant valence band data for the whole series of mixed crystals (Bi1−xSbx)2Te3(0 ≦x≦ 1). The reflectivity of polarized infrared light including its anisotropy is measured in the wave number range of 300 to 4000 cm−‐1. In addition to the spectra the Hall coefficients ϱ123and ϱ312, the electrical conductivity σ ⟂c, and the Seebeck coefficientS⟂care also given. In term of a six‐valley band model and scattering by acoustical phonons all experimental data are consistently described. The main axis massesm, the ellipsoid tilt angle ϑ, the effective density‐of‐states massmd, and the susceptibility massesm,∥care calculated in dependence on composition, also the Fermi levelEF, the carrier densityp, the mobility μ ⟂c, the high frequency dielectric constant ϵ∞⟂,∥c, and the relaxation time τopt. For the first time the structure factors in the Hall coefficients are given. In the plotm(x) the distinct maxima ofmandmdnearx= 0.8 are evident and important for the application of these substances.
Measurements of Ultrafast Optical Nonlinearities in Semiconductors
Authors: Fluegel B. D. , Sokoloff J. P. , Jarka F. , Koch S. W. , Lindberg M. , Peyghambarian N. , Joffre M. , Hulin D. , Migus A. , Antonetti A. , Ell C. , Banyai L. , Haug H. 
Published: July 2007

AbstractThe response of a bulk semiconductor platelet under the influence of nonresonant pulse excitation below the band gap is measured using femtosecond laser techniques. These optical Stark effect measurements are analyzed using the effective Bloch equations for semiconductors. These equations are solved (i) dynamically in the large detuning, low intensity limit and (ii) for arbitrary intensities in the adiabatic limit.
Resonant and Off‐Resonant Light–Matter Interaction in Semiconductors Kinetics and Transients
Authors: Zimmermann R. , Hartmann M. 
Published: July 2007

AbstractKinetic problems for off‐resonance excitation (dynamical Stark effect) and resonant excitation (laser‐induced gaps) are studied. Within the Hartree‐Fock theory, Stark shift and bleaching of the exciton line are evaluated. The influence of photon statistics on light‐induced gaps is investigated. Open questions concerning the transient response are clarified.
Evaluation of the Hartree‐Fock Theory of the Excitonic Optical Stark Effect
Authors: Ell C. , Müller J. F. , Sayed K. El , Banyai L. , Haug H. 
Published: July 2007

AbstractSemiconductor band‐edge absorption spectra of a probe beam under the action of a nonresonant pump beam are evaluated and analyzed, both for two and three dimensional systems. Many‐body effects such as phase space filling and carrier–carrier Coulomb interactions are included within the Hartree‐Fock approximation. In contrast to the atomic optical Stark effect one obtains an exciton blue shift with a nearly constant (2d) or sligthly increasing (3d) exciton oscillator strength. In addition, effects due to the time dependence of the fields are studied, taking pump pulse width, polarization relaxation time and the time delay between pump‐ and probe pulse into account. Deviations from the time independent Hartree‐Fock calculations occur both, with respect to the shift itself and with respect to the shape of the outcoming signal. The results do not reflect all features of earlier experiments, but they are in agreement with recent experimental observations.
Spectral Investigation of the Switching Dynamics in CdS Absorptive Bistable Devices
Authors: Daunois A. , Bigot J.‐Y. , Oberle J. , Eddeqaqi N. Cherkaoui , Wegener M. , Witt A. , Klingshirn C. 
Published: July 2007

AbstractThe transmission spectra of CdS platelets are studied at room temperature with a time‐resolved pump‐probe technique. These measurements are also performed during the switching between the two transmission levels of the bistable crystal induced by the pump pulse. In this case, the third beam from a cw argon laser holds the sample around the switching threshold. These spectral and temporally resolved experiments allow the analysis of the switching dynamics of such absorptive bistable devices.
Optical Bistability and Formation of Localized and Moving High Absorption Domains in ZnSe and ZnCdS
Authors: Esipov S. E. , Stadnik V. A. 
Published: July 2007

AbstractResults are given of the experimental study of increasing absorption optical bistability that arises from the formation of high absorption domains in bulk ZnSe and ZnCdS. A periodic domain motion causes output signal pulsations. The average domain velocity proved to be about 102 cm/s. A model that describes the behaviour of the absorption domain in semiconductors is discussed. Results of the experimental study of the domain behaviour are explained by the heat conduction regime of the model.