bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Crystalline Cluster Method for Ionic Solids. The F Center in NaCl
Authors: Guimarães P. S. , de Siqueira M. L. 
Published: July 2007

AbstractThe electronic structure of the F center in sodiun chloride is investigated by the multiple scattering Xα method with proper crystalline embedding conditions. Several different clusters are used in order to determine the influence of the choice of the muffin‐tin radii and Xα parameters on the cluster energy spectrum. The calculated value of the first absorption line is compared with the experimental results and other theoretical work. It is found that the results obtained agree very well with experiment, provided clusters with at least 27 atoms are used in the calculation.
Coulomb Gap in n‐ZnSe and Its Critical Behaviour in the Region of the Metal–Dielectric Transition
Authors: Kasiyan V. A. , Nedeoglo D. D. , Simashkevich A. V. , Timchenko I. N. 
Published: July 2007

AbstractIn the temperature interval from 1.65 to 300 K the conductivity of n‐ZnSe crystals on the dielectric side of the metal‐dielectric transition (MD) induced by a change of the compensation from 0.39 to 0.98 or of the concentration of the donor impurity from 2 × 1016 cm−3 to 2 × 1018 cm−3 is studied. It is established that at sufficently low temperatures on the dielectric side of the MD transition Q ∼ exp (ToT)1/2 which is indicative of the presence of a parabolic Coulomb gap at the Fermi level. The main parameters of the Coulomb gap: width, depth, density of states are determined and their concentration dependences also investigated. It is shown that the compensation blurs the MD transition and shifts it to the region of large critical concentrations. The critical behaviour of the Coulomb gap parameters within the scope of the scaling theory and the dynamics of its collapse at the transition are described.
Weak Pair Exchange Interactions between Cobalt Ions in Quasi‐One‐Dimensional Antiferromagnet CsCoCl3
Authors: Voronkova V. K. , Mosina L. V. , Usachev A. E. , Yablokov Yu. V. 
Published: July 2007

AbstractThe EPR spectra of single Co2+ −Co2+ pairs in CsMg1−xCoxCl3 (x = 0.0001 to 0.04) in X‐ and Q‐ bands are investigated. One type of single Co2+ spectra and four types of additional spectra attributed to Co2+ Co2+ pairs coupled by weak spin‐spin interactions are observed. Using computer simulation of EPR spectra the parameters of spin‐spin interaction are determined. The observed EPR spectra and the expected pair Co2+ Co2+ interactions in CsMg1−xCoxCl3 are analysed. The exchange parameters for the nearest neighbour Co2+ −Co2+ pairs in the ab‐plane are estimated. The nature of the exchange anisotropy is discussed.
Embedded‐Atom Method for Surface Lattice Dynamics in Copper
Authors: Luo Ningsheng , Xu Wenlan , Shen Shuechu 
Published: July 2007

AbstractThe embedded‐atom method (EAM) based on results from density functional theory is applied to surface lattice dynamics. From the model within the framework of the EAM, the formula of surface interplanar force constant and surface lattice dynamical matrix are derived. It is found that the EAM can distinguish well the difference between atomic interactions in the bulk and near the surface without any additional parameter by its description of many‐body interaction. It is also found that the changes of surface force fields in the EAM are caused not only by the changes of interatomic distances but also by the changes of electron density background, which is quite different from ordinary empirical potential models. As an example, in the quasiharmonic approximation, the surface interplanar force consants and the surface‐phonon dispersions on unrelaxed Cu(100), (110), and (111) surfaces are calculated and analyzed without any adjustable parameter. The calculated results are in good agreement with experimental data by electron‐energy‐loss‐spectroscopy (EELS) and inelastic helium scattering. Although only the vibrational properties of Cu unrelaxed surfaces are calculated, it can be concluded that the EAM gives two competitive physical reasons affecting surface force fields: interatomic distances and electron density backgrounds.
Excitons in Indium Halide Thin Films
Authors: Brothers A. D. , Feuerborn F. J. , Bauer S. E. 
Published: July 2007

AbstractOptical absorption spectra for thin films of InBr, InCl, and Inl are studied as a function of temperature from 90 to 300 K and as a function of hydrostatic pressures up to 0.35 GPa. Temperature shifts of the exciton peaks in InBr, InCl, and InI are −1.87, −0.5, and −1.1 in units of 10−4 eV/K, respectively. Pressure shifts of these peaks are reported as −2.5, −0.9, and −3.0 in units of 10−10 eV/Pa, respectively. A discussion of the implications of these results on the band structure of these materials is presented.
A Contribution to Reversed Transport
Authors: Gerlach E. 
Published: July 2007

AbstractA generalization of the energy‐loss transport concept including carrier‐carrier scattering is applied to a periodic arrangement of pairs of conducting films. It is shown that for certain parameters a metal‐p‐semiconductor system should exhibit reversed transport (carrier‐drag) in the semiconductor, i. e. the holes move in the opposite direction relative to the external electric field.
On the Density of States of a Disordered Peierls‐Fröhlich Chain
Authors: Fischbeck H. J. , Hayn R. 
Published: July 2007

AbstractUsing the supersymmetry method an exact analytic formula for the integrated density of states of a disordered half‐filled Peierls‐Fröhlich system is derived. All kinds of disorder which can be handled in the continuum approximation, i. e. forward and backward scattering as well as (alternating) bond disorder, are included. Special cases are discussed.
Temperature Dependence of EPR Linewidth of Impurities in Van‐Vleck Paramagnets
Authors: Aminov L. K. , Kostetskii Yu. Yu. 
Published: July 2007

AbstractThe specific spin‐lattice relaxation mechanisms (“fluctuation” and “Waller” mechanisms) of impurity paramagnetic ions in rare‐earth Van‐Vleck paramagnets are shown to be the effective mechanisms of EPR line broadening too. On the basis of these mechanisms one can interpret qualitatively and, in a great extent, quantitatively all peculiarities of the temperature dependence of Gd3+ impurity ion EPR linewidth in rare‐earth zircons, observed by Mehran, Stevens et al. It is concluded, that in interpretation of their experimental results one can avoid the consideration of the hardly perceptible quasi Jahn‐Teller effect on excited doublets of the host Van Vleck ions.
Energy Transfer Mechanisms in Zn1−xMnxSe (0.005 < x < 0.017) Detected by ODMR
Authors: Zink K. , Krost A. , Nelkowski H. , Sahm J. , Stutenbecker H. 
Published: July 2007

AbstractODMR investigations of Zn1−xMnxSe (0.005 < x < 0.017) are presented. Starting from the observation of the resonance of the Mn2+ ground state in the Mn emission and in the SA emission as well, the necessary energy transfer is investigated using excitation dependent ODMR. The spectra, taken for the first time for this system show that the occurrence of the Mn2+ ground‐state resonance in the Mn emission can be referred to a spin dependent transfer of optical excitation energy. In the SA emission, on the contrary, a cross relaxation between manganese and donor‐acceptor pairs is responsible for the occurrence of the Mn2+ resonance in the ODMR spectra.
Covalent Bonds in Amorphous Semiconductors and Their Influence on the Structure of the Energy Spectrum
Authors: Unger H. ‐J. 
Published: July 2007

AbstractThe structure of the energy spectrum of amorphous semiconductors as determined by the formation of covalent bonds is analyzed. In contrast with other theoretical models all considerations are based on a realistic model of the atomic structure of a‐Si and a‐Ge. The mathematical method used throughout the paper is, within certain subspaces (cells) of the total Hilbert space, the partial diagonalization of the Hamiltonian represented in an “extended Hilbert space”. Existing model Hamiltonians, e. g. the Weaire‐Thorpe model, are generalized in such a way that real disordered solids can be described. The molecular model used in this paper yields the basic feature of the structure of the energy spectrum. For positionally disordered systems an Anderson‐like Hamiltonian is obtained. The formation of extended and localized states in disordered solids is explained by taking into account the residual interactions. Conditions for the localization of electronic states and the existence of mobility edges depending on the local and global atomic structure of amorphous semiconductors are given. A generalization of the cell model in the spirit of the scaling theory of localization leads to a method for the determination of the position of the mobility edges. Structural correlation in amorphous semiconductors manifesting itself in short‐range order and in the existence of voids, which is not taken into account e. g. in the Anderson model, is found to be the origin of the basic structural properties of the energy spectrum of disordered semiconductors. Conclusions from the theory proposed are in accordance with experimental findings and explain them.
Charge Carrier Transfer in Ferrite Spinels Affected by Magnetic Ordering
Authors: Berzhanskii V. N. , Evstafev I. I. , Ivanov V. I. 
Published: July 2007

AbstractThe temperature dependences of the conductivity of single crystals of nickel‐zink Ni0.39Zn0.61Fe2.00O4 (Tc = 380 K) and manganese‐zink Mn0.66 Zn0.27 Fe2.07 O4 (Tc = 464 K) ferrites are studied in the temperature range 78 to 550 K. Measurements of thermoelectromotive force show that all the samples investigated have n‐type conductivity. In the region of the phase transition to the magnetically‐ordered state the logarithm of conductivity depends anomalously on the inverse temperature with increasing conductivity.
Anderson Localization in Ferromagnetic Semiconductors Due to Spin Disorder. III. Self‐Consisten Localization Theory and Inelastic Scattering
Authors: Kogan E. M. 
Published: July 2007

AbstractTheoretical investigations are made of the temperature dependence of n‐type EuS electroconductivity. The scattering of electrons by magnetic ion spin‐density fluctuations is found to be strong; selfconsistent localization theory is used to calculate the conductivity and the inelasticity of scattering due to spin dynamics is also taken into account. It is shown that due to inelasticity the states which are localized in the elastic scattering approximation become weekly conducting, and the change of the conductivity of the extended states can be neglected. Hence in the case of quasielastic scattering (though not very rigorously) the notion of the “mobility edge” i. e. the energy which separates large and small conductivity can be introduce. The conductivity in the “dielectric phase” i. e. at temperatures close enough to TC when the “mobility edge” lies above the Fermi level, is estimated. The estimation obtained agrees well with the experimentally observed values.
Scattering and Velocity Dispersion of Electromagnetic Waves in Multiphase Dielectric Materials
Authors: Shermergor T. D. , Fokin A. G. , Dikarev A. V. 
Published: July 2007

AbstractThe parameters are calculated of an electromagnetic wave propagating in a dielectric medium, which is a multiphase mixture of isotropic and anisotropic components. The dispersion equation is studied which is derived allowing for spatial dispersion giving rise to an additional branch in solving the equation and, correspondingly, to two waves, namely, a real wave and a virtual wave. The results are given of calculating numerically the scattering indices and the phase and group velocities of the two waves. In the case the calculations are made in terms of the Bourret approximation, the real wave alone must be treated.
Transient Energy Transfer in ps Two‐Photon Absorption Experiments in CdTe at Room Temperature
Authors: Rückmann I. , Kornack J. , Kolenda J. , Petrauskas M. 
Published: July 2007

AbstractOne‐beam transmission experiments and two‐beam‐coupling experiments with 35 ps‐pulses at 1.06 μm are performed in CdTe and CdTe: Ge to investigate (i) the nonlinear (two‐photon (TPA), free‐carrier and two‐step) absorption processes, (ii) their kinetics, and (iii) the transient energy transfer (TET) from stronger pump beam to the weaker probe beam, caused by coherent coupling which is observed around (with its maximum just before) zero delay. The competition between TPA and TET is demonstrated by oscillating intensity dependences of the probe‐beam transmittivity measured and calculated at small delays, which can be used to realize a continuous transition from optical beam amplification to attenuation at a fixed delay in dependence on the pump intensity only. The influence of the pump‐to‐probe intensity ratio on TET is discussed.
Photon Echoes and the Structure of Wannier Excitons
Authors: Abram I. 
Published: July 2007

AbstractThe coherent polarization of a Wannier exciton system, induced by a short incident resonant light pulse, is calculated within a formalism that takes into account explicitly the internal structure of excitions. By examining the phase‐space filling interactions among excitons, it is shown that the hydrogenic structure of excitions causes significant deviations in their coherent optical response when compared with the response of the traditional two‐level model of optical coherence. This suggests that photon echo experiments, which measure directly the coherent polarization, may provide information on the structure of Wannier excitons.
Nonequilibrium Description of the Intense Resonant Laser Excitation of a Semiconductor
Authors: Jahnke F. , Henneberger K. 
Published: July 2007

AbstractGeneration of a nonequilibrium electron hole plasma by resonant excitation above the fundamental gap but below threshold for LO‐phonon emission is theoretically investigated. At high intensities, where the Rabi frequency dominates the spectral width of the exciting pulse as well as well as the damping due to relaxation, an intensity‐dependent renormalization of bands, i. e. additional laser‐induced branches and gaps, occur. Boltzmann equations governing the generation and distribution of electron‐hole pairs in these renormalized bands and an equation of Bethe‐Salpeter type for the interband polarization governing the band renormalization are numerically solved. Beside others it is found, that virtual electron hole Coulomb interaction tends to stabilize the formation of laser‐induced gaps and enhances spectral hole burning.
Nonlinear Optical Study of Semiconductor Microstructures, CuCl Quantum Dots, and GaAs Quantum Wells
Authors: Masumoto Y. , Ideshita S. , Wamura T. 
Published: July 2007

AbstractNonlinear optical properties of zcro‐dimensional and two‐dimensional semiconductor microstructures, CuCl quantum dots and GaAs quantum wells, are studied with special attention to the bleaching and the blue shift of excitons. In CuCl quantum dots, prominent absorption bleaching of excitons is observed together with a blue shift. The optical nonlinearity is found to increase with an increase of the size of the microcrystals. The blue shift of Z3 exciton absorption increases linearly and becomes saturated with the increase of the excitation density, suggesting the possibility of quantized blue shift. In GaAsAlAs quantum wells, two‐step rise in absorption saturation of the lowest exciton is observed in a few picosecond time domain at 4.2 K under the high‐density band‐to‐band excitation. The former rise takes place simultaneously with the dynamical red shift of the electron‐hole plasma luminescence. The latter rise is accompanied with the blue shift of the exciton. The origin of two‐step rise and blue shift is discussed.
Nonlinear Optical Properties of GaAs/(AlGa)As Multiple Quantum Well Structures under Quasistationary High Excitation Conditions
Authors: Schlaad K. ‐H. , Weber Ch. , Chemla D. S. , Cunningham J. , Miller D. A. B. , Hoof C. V. , Borghs G. , Weimann G. , Schlapp W. , Nickel H. , Klingshirn C. 
Published: July 2007

AbstractThe optical properties are investigated of undoped and n‐modulation doped multiple quantum well structures (MQWS) under quasistationary high excitation conditions. The characteristic nonlinear optical behaviour is due to an electron‐hole plasma. Its density, temperature, and the renormalized bandgap are determined via photoluminescence and pump and probe beam measurements. A model is developed for the line shape analysis of the plasma luminescence taking into account the broadening of the single particle density of states with results deviating from those in literature, but very good agreement is achieved with the experimental findings from pump and probe beam spectroscopy. The study of the renormalization of the higher, unpopulated subbands reveals that the pure intersubband screening is weak with respect to the shift of the fundamental bandgap. The exciton resonances of the higher subbands are found to be stable against high plasma densities in the fundamental subbands and are mainly bleached by direct population. The idea of a rigid shift of the whole subband structure must be clearly rejected.
A Detailed Study Concerning the Main Aspects Influencing Thermally Induced Optical Bistability of CdS
Authors: Hollandt J. , Gutowski J. , Broser I. 
Published: July 2007

AbstractThermally induced dispersive and absorptive optical bistability of CdS is investigated in a temperature range of 20 K to RT. The influence of the geometry of the crystals, e. g., thickness, surface area size, and resonator structure, on the hysteresis feature and switching behavior is investigated. The quality of the thermal contact between the sample and the heat sink strongly influences switch‐back times. Further, starting temperature, light spot diameter, and pulse intensity are varied in order to find a set of optimization criteria for this kind of optical bistability. Experimental results are in good agreement with model calculations.
Bistability in Composites of Linear and Nonlinear Media
Authors: Jungk G. 
Published: July 2007

AbstractAfter the introduction of a simple qualitative model for optical nonlinearity in homogeneous solids, necessary conditions for bistability are derived and the switching properties calculated. The optically nonlinear particles are assumed to be embedded into host‐media. Different effective medium theories (describing different geometrical arrangements) are used to compute reflectivity and transmissivity as function of impinging light intensity. Numerical examples demonstrate possible application for fundamental research but also for device design.
Kinks in Resonatorless Optical Bistability. Stability Limits and Formation Dynamics
Authors: Kuznetsov A. V. 
Published: July 2007

AbstractThe stability of the s. c. kinks which separate the two regions with quasi‐homogeneous density distributions in resonatorless optical bistability, is explicitly investigated within an exactly solvable model. Kinks are found to be stable only when they are not too close to the sample boundaries. The geometric condition of stability linking the characteristic lengths of the problem is formulated, which allows one to predict if the stable kinks are possible at all in a particular experimental situation. The possible instability is caused by the translational mode of the kink motion, and the explicit expression for the translational relaxation time enables one to distinguish between different temporal regimes.
Absorptive Optical Bistability. The Case of Fabry‐Perot
Authors: Šrobár F. 
Published: July 2007

AbstractStationary Maxwell‐Bloch equations describing saturable‐absorber‐filled Fabry‐Perot resonators are studied by the causal diagram method to bring into prominence the role of interrelations among the factors involved. The representative diagram contains three feedback loops. It is shown that cooperation of all these loops is required to produce conditions necessary for optical bistability. Similar behaviour is encountered in the case of two‐sections semiconductor injection laser. General implications are suggested.
Nonlinear Optical Absorption in I‐VII and II‐VI Microcrystallites under Quantum Confinement of Elementary Excitations
Authors: Zimin L. G. , Gaponenko S. V. , Lebed V. Yu. , Malinovskii I. E. , Germanenko I. N. , Podorova E. E. , Tsekhomskii V. A. 
Published: July 2007

AbstractThe nonlinear absorption of quantum‐confined CuCl and CdSxSe1−x crystallites imbedded in a glass matrix is investigated by means of laser spectroscopy. For CuCl in which the quantum confinement of excitons takes place a considerable light‐induced blue shift of excitonic bands is observed which is attributed to the interaction of exciton‐like excitations under quantum confinement. A decrease of the saturation intensity with decreasing size of the crystallites is detected for CuCl‐doped glasses. In CdSxSe1−x‐doped glasses where quantum confinement of free carriers predominates no distinct correlation between the crystal size and the saturation intensity is observed.
Optical Nonlinearity and Dynamics of an Exciton‐Biexciton System in CuCl in the Weak Excitation Regime
Authors: Kuwata‐Gonokami M. , Shimano R. , Iwamatsu J. , Akiyama H. , Kuga T. , Matsuoka M. 
Published: July 2007

AbstractThe relaxation mechanisms of biexcitons under weak excitation limit are studied in the temperature region 1.6 to 50 K. From the temporal responses of biexciton emissions, the biexciton radiative relaxation time is found to be 50 ps. Single acoustic phonon scattering determines the intraband relaxation at finite temperature. Single acoustic phonon emission process causes the broadening of the biexciton with large wave vector. The experimental data of the wave vector dependence of biexciton line width are analyzed by two‐photon polarization spectroscopy and the biexciton deformation potential of 1.5 eV is obtained.
The Exciton‐Biexciton Spectrum Renormalization in the Presence of a Polariton Pumping Wave. The New Mechanism, Exciton Level Shift, and ABC Problem
Authors: Ivanov A. L. , Panashchenko V. V. 
Published: July 2007

AbstractA new mechanism of the exciton‐biexciton spectrum renormalization determined by direct virtual coupling of excitons to the biexciton owing to exciton‐exciton Coulomb interaction is proposed. Exciton and biexciton shifts depending on pumping intensity are obtained. The macroscopic equations are derived and the ABC‐problem considered. The reflection spectra modification for CdS semiconductor was calculated.
Nonlinear Luminescence of Heavily Doped CdS: In Crystals
Authors: Neukirch U. , Broser I. , Rass R. 
Published: July 2007

AbstractLuminescence data of heavily doped CdS:In crystals at various exciation densities are presented. The spectra are compared to theoretical calculations, which are based upon the assumption of indirect band‐to‐band transitions. At low excitation density some highly self‐compensated samples exhibit an enhanced luminescence at energies around 2.45 cV. This is due to conduction band acceptor transitions, which are easily saturable. Samples of intermediate In concentration show a narrow‐band highexcitation line, which is attributed to an EHP recombination. The temperature‐dependent behavior of this line indicates the occurrence of optical gain in these samples.
Photoluminescence Studies of Anomalous Diamagnetic Properties of the 2D e‐h System on the GaAs Surface
Authors: Averkiev N. S. , Asnin V. M. , Rogachev A. A. , Silov A. Yu. , Stepanov V. I. 
Published: July 2007

AbstractThe diamagnetic properties of the 2D e‐h system on the GaAs surface are studied detailly by the photoluminescence method at T = 1.9 K. An anomalous value of the ground state energy diamagnetic shift δ∥︁, of the 2D e‐h system in magnetic parallel field is found. As well an unusual effect is observed in magnetic parallel field concerned with the self‐consistent origin of the system: a jump of δ∥︁ versus the excitation level G. It is shown that the effects are concerned with the transformation of the energy structure of the system under high magnetic field and pumping level.