bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Pulsed Nonresonant Optical Stark Effect and the Urbach Tail in Semiconductors
Authors: Haug H. , Banyai L. , Liebler J. , Wicht T. 
Published: July 2007

AbstractThe theory of the intrinsic Urbach tail absorption in semiconductors is discussed. Some recent results of a cumulant expansion up to second order are presented which fit experimental observations excellently. The results can be simulated with a frequency‐dependent broadening which gives rise to memory effects for the optically induced polarization. The importance of these effects for the understanding of the pulsed nonresonant optical Stark effect is discussed.
Induced Absorption and the Dynamical Stark Shift Associated with Biexcitons
Authors: Balslev I. 
Published: July 2007

AbstractThe nonlinear optical phenomena associated with the formation of virtual biexcitons in direct gap semiconductors are studied. Relations are set up for real‐space two‐fermion operators using methods similar to those used when deriving a well known conservation law of k‐space operators for intraband and interband transitions. Restricting the analysis to the χ(3) level, or set of density matrix equations are obtained for the exciton‐biexciton system. Analytical solutions in the limit of small detuning show that the biexcitonic induced absorption and the dynamical Stark effect are closely related, and that the Stark shift as function of the pump frequency has a pole at the frequency of the exciton‐to‐biexciton transition.
The Origin of Third‐Order Optical Nonlinearity in Exciton Systems
Authors: Ishihara T. 
Published: July 2007

AbstractThe third‐order optical nonlinearity is estimated to be −10−4 e. s. u. at the exciton resonance in PbI2 evaporated films from the population oscillation effect. Such a large nonlinearity cannot be explained if the system is regarded as independent oscillators. The origin of the third‐order nonlinearity is examined in the density matrix formalism. The observed large nonlinearity is shown to come from the exciton‐exciton interaction.
Second Harmonic Generation on the Grating of Optical Inhomogeneities in ZnSe and ZnS
Authors: Gribkovskii V. P. , Zyulkov V. A. , Kazachenko A. E. , Shakin V. A. 
Published: July 2007

AbstractNoncollinear second harmonic generation in ZnS and ZnSe crystals with quasi‐regular grating of optical inhomogeneities is discovered and investigated. The observed effects are described by a model in which the vector phase synchronism may be realized in the region of normal crystal dispersion due to the contribution of the wave vector of the grating.
Mott Transition in CdS Revealed by Picosecond Nonlinear Absorption Measurements
Authors: Egorov V. D. , Nguyen Hoang Xuan , Zimmermann R. , Dneprovskii V. S. , Kaschke M. , Khechinashvili D. S. 
Published: July 2007

AbstractOptical spectra above the Mott transition of excitons are calculated from the inhomogeneous integral equation for the polarization function including self‐energy, screening, and band filling. Taking CdS parameters and adjusted values of the electron‐hole temperature and density, good agreement is achieved with the results of transmission measurements made at room temperature on a thin CdS crystal using two‐beam excite‐and‐probe technique with 5 ps time resolution.
Impact Excitation and Auger Decay of Bound Exciton Complexes in a Dense Exciton Gas
Authors: Kharchenko V. A. , Mikhailov G. V. , Nelson D. K. , Razbirin B. S. 
Published: July 2007

AbstractImpact excitation processes due to free exciton collisions with bound exciton complexes D°X are studied in CdS. It is found that the excitation power increasing from 103 to 104 W/cm2 leads to a considerable decrease of the I2 line intensity followed by the disappearence of the I2 line at the upper limit, whereas the I1 line can be distinctly seen in the luminescence spectra in the whole range of the excitation power. A model explaining the quenching of the I2 emission line by the Auger‐decay of an excited state of the D°X complex at high concentrations of free excitons is proposed. Experimental data are in good agreement with predicted dependences.
The Statistical Properties of the Coherently Excited Polariton Wave in a Small Volume Crystal
Authors: Misko V. R. , Moskalenko S. A. , Rotaru A. H. , Shvera Yu. M. 
Published: July 2007

AbstractA selfconsistent steady state solution is given of the Fokker‐Planck equation for polaritons with wave vector ko and the kinetic equations for the scattered ones are found. The statistics of the coherently excited polaritons ko differs in a most general case from the pure coherent state. It depends on the crystallite volume V, the frequency detuning Δω between the polariton bare frequency ω(ko) and the laser one ωL, and the driving field energy flow SL. In the case of small values of the product V · SL polariton bunching takes place when Δω < 0, and antibunching in the opposite case. Polariton squeezed states can arise in both the detuning cases.
A New Hole Centre in Neutron Irradiated LiF Crystals
Authors: Kamikawa T. 
Published: July 2007

AbstractA new colour center is observed by ESR in low temperature γ‐irradiated and then heat treated LiF crystals which are heavily neutron irradiated previously. From the analysis of the ESR spectra this center is assigned to an asymmetric interstitial fluorine atom associated with a lattice fluoride ion. This center lies in one of the (110) planes and its molecular axis makes an angle of 23° with the [110] axis. The ESR parameters are determined by fitting the calculated resonance fields to the experimental ones.
Heavy Ion Channeling Implantation Processes in Single Crystals
Authors: Abbas M. , Kerkow H. , Wedell R. 
Published: July 2007

AbstractImplantations of Ne‐, Mg‐ and Ca‐ions into silicon have been performed for different channeling orientations with energies ranging from 30 to 300 keV. The produced radiation damage distributions are investigated by using RBS, the depth distributions of implanted foreign atoms are measured by SIMS. A correlation between dechanneling, damage production, and depth distributions of the channeled ions could be observed. Simple models for dechanneling and energy losses allow an explanation of some experimental results.
Angular Force Models in the Lattice Dynamics of Cubic Systems
Authors: Upadhyaya J. C. , Lehri S. , Sharma D. K. , Upadhyaya S. C. 
Published: July 2007

AbstractAngular force models of de Launay (DL) and Clark‐Gazis‐Wallis (CGW), as applied to study the lattice dynamics of b. c. c. and f. c. c. systems, are analysed and discussed. Removal of the deficiencies from the DL angular force model results in a scheme identical to the central pairwise potential procedure. As far as the calculation of phonon frequcncies in cubic metals is concerned, the CGW model gives dispersion results identical to those obtained by applying the general tensor force (GTF) model. It is observed that the GTF constants are composite quantities, expressible in terms of elementary CGW force constants. The two schemes are applied in the calculation of phonon dispersion curves of some b. c. c. and f. c. c. metals and numerical results are discussed. Finally the stability of the lattice is discussed.
Third‐Order Constants of a Cubic Quasi‐Isotropic Solid
Authors: Wasserbäch W. 
Published: July 2007

AbstractThe isotropic third‐order elastic constants l, m, n, and v1, v2, v3 as defined by Murnaghan and Toupin and Bernstein, respectively are evaluated from the single‐crystal data and are compared with experimental values as available in the literature.
Influence of Level Broadening in Mobility Calculations for Low‐Dimensional Semiconductor Heterostructures
Authors: Leon H. , Comas F. , Suhrke M. 
Published: July 2007

AbstractThe influence of constant level broadening in momentum‐relaxation rate and low‐field mobility calculations is investigated if acoustic‐phonon scattering, via deformation‐potential (DP) and piezoelectric (PZ) coupling, is present in low‐dimensional semiconductor heterostructures such as quantum wires or quantum wells. An approach is developed using the quasi‐particle approximation on the basis of the method of Kadanoff and Baym. Calculations are done in the low carrier concentration case, neglecting screening effects and using non‐degenerate carrier statistics. The role of PZ scattering is established and comparison with earlier results is made.
Determination of the Indirect Exciton Energy Gap of GaP Using Thermomodulation in the Temperature Range 80 to 350 K
Authors: Beckmann A. , Dettmer K. , Kessler F. R. 
Published: July 2007

AbstractThermoabsorption studies were performed of the first indirect band edge of n‐GaP in the temperature range from 80 to 350 K. The energy of the indirect exciton bandgap and its temperature dependence are determined from the thermoabsorption spectra. The temperature dependence is fitted to Varshni's equation as well as to an expression containing the Einstein‐Bose statistical factors for phonon absorption and emission. The energies of the involved phonons are deduced from the energy difference between the transitions with absorption and emission of a particular phonon: E(TA) = (13.2 ± 0.2) meV, E(LA) = (29.6 ± 0.7) meV, and E(TO) = (43.5 ± 0.3) meV.
Internal Conversion Coefficient for Valence Electrons of Metals. Theory and Application to 110Ag
Authors: Schober C. , Antonov V. N. , Ziesche P. 
Published: July 2007

AbstractThe ab‐initio electron theory of the internal conversion coefficient (ICC) is developed for the case of pure crystalline metals, the radioactive nuclei of which emit γ‐quanta with relatively small energy (≦ keV) exciting thus preponderantly valence electrons. In this case the photon wavelength is large in comparison with the radius of the nucleus and the ICC ( = energy spectrum of the emitted conversion electrons) becomes independent of the properties of the nucleus. For any electric or magnetic transition and using spherically symmetric muffin‐tin potentials the ICC is expressed by the characteristic quantitites of the electron making a transition from an occupied valence state to an unoccupied free electron state. The calculations for 110Ag show the ICC to reflect directly the density of states of the valence electrons.
Correlated Pair‐Transfer Mechanism for High Temperature Superconductivity. The Case of YBa2Cu3O6+x
Authors: Sinha K. P. , Singh M. 
Published: July 2007

AbstractA theoretical study of high temperature superconductivity in the system YBa2Cu3O6+x is made using the correlated pair transfer mechanism suggested recently. The mechanism involves the role of electron pairs in the spin singlet state of species \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm X}^{\uparrow \downarrow } (= {\rm Cu}^{{\rm 1 + }},{\rm O}_{\rm 2}^{{\rm 2 - }} {\rm, or O}^{{\rm 2 - }} {\rm)} $\end{document} and their virtual excited state X0(Cu3+, O, or O0) in the pairing interaction of quasiholes. The two states of these species can be likened to a two‐level Bose system. The strength of the interaction depends on the hole and species concentration. The expression for the transition temperature is a combination of phononic and the electronic mechanism and the calculated trend as a function of hole concentration (in effect excess O−) is in agreement with the observed trend. The mechanism is applicable to other oxide systems where such variable species can exist (e. g. Bi3+, Bi5+ or Tl1+, Tl3+, etc.). The theory has electron and hole symmetry, therefore it can also be applied to n‐type high temperature superconductors.
Amplification of Acoustohelicon Waves in Piezoelectric Semiconductors. Effect of Nonlinearity in Electron Effective Mass and Collision Frequency
Authors: Dey (Bose) M. , Ghosh S. 
Published: July 2007

AbstractIt is shown that the attenuation of an acoustohelicon wave crosses over to its amplification at an electron drift velocity (Vd) exceeding the acoustic wave velocity (Vs). Firstly a phenomenological theory is developed to study the variation of the carrier temperature with wave amplitude and cyclotron frequency, and the corresponding relative change in electron effective mass and collision frequency, when the acoustohelicon wave passes through a piezoelectric semiconductor. It is inferred from the analysis that this change, due to carrier heating in high mobility semiconductors, is appreciable at high power flux of the acoustohelicon mode. Then, analytically, it is shown that this nonlinearity in carrier mass and collision frequency, arising due to the electric vector of the field associated with the wave, can also contribute to the acoustohelicon amplification behaviour. Numerical computations are made for n‐InSb at 78 K. It is found that the magnetic field does not have any remarkable effect on the crossover value of the velocity ratio (= Vd/Vs), but at very high magnetic fields (ωc ≧ 1013 S−1) the acoustohelicon mode propagate without attenuation.
Evaluation of Moments from the NMR Solid Echoes in Dipolar Solids
Authors: Kahol P. K. 
Published: July 2007

AbstractTwo‐pulse‐solid echo, formed by the pulse sequence Py(90°)‐τ‐P x(90°)‐t′, can be used as an alternative to the free‐induction‐decay to evaluate the lower order moments of the magnetic resonance lineshape in “molecular” solids, provided τ is small. The applicability of this method in determining the lower moments depends not only on the value of τ and hence the so‐called “error terms” but also on the distributional arrangement of the spins. These aspects of the solid echo method are quantified in this paper from the analytical treatment of a rectangular array of two equivalent pairs of spins‐1/2. Predictions of the rather simple model, when compared with the appropriate experimental data, are found to be in excellent agreement.
Magnetooptical Activity of Allowed Electron Transitions in Atoms in Free State and in Crystals
Authors: Malakhovskii A. V. 
Published: July 2007

AbstractMagnetic circular birefringence (MCB) is rigorously decomposed into diamagnetic (A) and paramagnetic (B and C) terms without substantial restrictions on the values of the fields and interactions. Peculiarities of the magnetooptical properties of the 3d‐and 4f‐atoms both, in free state and in crystals are analyzed on the basis of most general properties of the atom wave functions, spin‐orbit interaction and interactions of the atom with the magnetic and crystal fields, and the values of MCB terms are evaluated. The crystal field is shown to be in all cases a condition necessary for the B‐terms (mixing term) to exist. The mechanisms of the B‐term occurrance are considered and its values at different mechanisms are evaluated. MCB due to magnetic ordering is considered.
Collective Excitations in a Liquid Alloy
Authors: Bhandari D. , Pratap A. , Saxena N. S. , Saksena M. P. 
Published: July 2007

AbstractA theory of phonons in amorphous solids developed by Takeno and Goda using a self‐consistent method is extended for the numerical calculations of the longitudinal and transverse modes in equiatomic NaK alloy. The computed results are compared with recently reported molecular dynamics results. The longitudinal phonon mode agrees fairly well with the MD results.
On the Relation of Ideal Strength to Other Physical Properties
Authors: Pokluda J. , Šandera P. 
Published: July 2007

AbstractSimple relations of the ideal cohesive strength of crystals with b.c.c., f.c.c., and diamond structures to other physical properties are derived. The interatomic potential is approximated by the generalized Morse and Lennard‐Jones functions. Generally, the calculated values and the data previously published by other authors are consistent within a factor of two.
Electronic Structure of TiB2 and ZrB2
Authors: Anishchik V. M. , Dorozhkin N. N. 
Published: July 2007

AbstractCalculations of the electronic structure of titanium and zirconium diborides are performed using a self‐consistent version of LMTO method. The total as well as partial densities of states are calculated and some detail of the valence band structure are also analyzed, charge transfer and chemical bond in diborides are studied.
Three‐Photon Interband Process in Solids
Authors: Hassan A. R. 
Published: July 2007

AbstractA perturbative approach is used to calculate the three‐photon absorption coefficients through the most energetically favourable band models. Both parabolic and non‐parabolic band approximations are considered. Numerical estimates for three different alkali iodides are compared with a recent experimental result and with a recent theoretical non‐perturbative approach. The results show that the transition mechanisms through the perturbative non‐parabolic four‐band model, in which all the transition matrix elements are allowed, give reasonable agreement with the experiment. The other perturbative models, parabolic as well as non‐parabolic and the non‐perturbative approach, greatly underestimate the experimental results.
The Dependence of the Density of States Tail on the Random Potential Statistics
Authors: Klochikhin A. A. , Kühn O. , Ogloblin S. G. 
Published: July 2007

AbstractThe problem of the long‐range correlated random potential in a dielectric disordered system is studied by means of numerical solution of the saddle point equation. The obtained frequency dependence of the density of states displays the Halperin‐Lax behaviour at a correlation length small compared with the De'Broglie wavelength, it shows the Gaussian decreasing in the opposit limit and a relatively narrow region of a cross‐over Urbach‐like regime. The reasons are given in behalf of a predominant role of the fluctuations with the smallest correlation length possible for the system.
On the Electronic Structure of Small NiP Clusters
Authors: Stepanyuk V. S. , Szász A. , Katsnelson A. A. , Grigorenko B. L. , Farberovich O. V. 
Published: July 2007

AbstractA self‐consistent electronic‐structure calculation for small NiP clusters is performed. There is no charge transfer from P to Ni. It is shown that the cluster effects are important in the mesoscopic ranges.
Dynamics of the Pseudo‐E ⊗ ε Jahn‐Teller Hamiltonian. A Quantum Optical Approach
Authors: Lais P. , Kraus M. 
Published: July 2007

AbstractNew dynamical aspects are investigated of the pseudo‐E ⊗ ε‐Jahn‐Teller Hamiltonian (PJTH). A close relation is found between the PJTH and the Jaynes‐Cummings model in quantum optics. After using a continued fraction method for the diagonalization of the Hamiltonian the exact eigenfunctions are used to investigate some aspects of the dynamics. A rotating wave approximation is introduced which makes the problem exactly solvable. The results of the two approaches are compared.
Calculation of the Normal‐State Resistivity for High‐Tc Superconductors
Authors: Schiller W. , Weschke K. 
Published: July 2007

AbstractUsing the method of force‐correlation functions the electrical resistivity is calculated for the anharmonic model of high‐ Tc superconductors with structurally unstable lattices. This model contains the interaction between electrons and strong anharmonic ion vibrations. The influence of this interaction on the temperature dependence of the electrical resistivity in the normal conducting phase is discussed in the case of weak scattering. The results are compared with experimental and theoretical investigations on YBaCuO compounds.
Energy Spectrum and Elementary Excitation Damping in the Structurally Disordered Ising Model in a Transverse Field
Authors: Vakarchuk I. A. , Tkachuk V. M. 
Published: July 2007

AbstractThe elementary spin excitations in the structurally disordered anisotropic Heisenberg model are investigated by the two‐time temperature Green function method. The Ising model in a transverse field is considered as a special case of an anisotropic model. An equation is obtained for the excitation spectrum and damping, caused by scattering of the excitations on the structure fluctuations. The asymptotics of damping in the long‐wave limit and the critical temperature at which the excitation spectrum gap turns to zero are investigated.
The Optical Properties of Impurity Center Short‐Range Potentials in a Magnetic Field
Authors: Sinyavskii E. P. , Safronov E. Yu. 
Published: July 2007

AbstractThe impurity absorption of light and the luminescence on bound states in solid matter under magnetic fields are studied using the model of zero‐radius potential. The absorption constant K(Ω), at various configurations of the magnetic field intensity,H, and electric field intensity, E, is calculated. The results obtained for K(Ω) and the dependences of the electron binding energies on the short‐range potential on H are compared with experimental data in multivalley semiconductors. The peculiarities of the frequency dependence of the spectral intensity of radiation ϕ(Ω) are discussed. It is noted that ϕ(Ω), as a function of frequency Ω, at great H has an oscillatory character.
Boundary Conditions in Case of Electromagnetic Wave Absorption
Authors: Kudykina T. A. 
Published: July 2007

AbstractBoundary conditions for electromagnetic waves in absorbing media are obtained. The fact is taken into account, that in absorbing media the electric induction has two components: one in phase with the electric field of the incident wave and the other – out of phase by π/2. The Maxwell boundary conditions for each component gives equations enough to determine the amplitudes of all excited waves in the range of exciton resonance and of all waves, charge, and current densities in the band‐to‐band excitation range. For TM‐waves the analogue of Snellius' law is obtained in the case of absorbing media. TE‐waves Snellius' refraction law is valid in case of absorbing media too. In both the cases the reflectivity depends upon absorption and in the limit of great absorption (χ → n, where n, χ are the indexes of refraction and absorption, respectively) tends to unity.
Short‐Range Order in Superstructures
Authors: Rempel A. A. , Gusev A. I. 
Published: July 2007

AbstractRegions of allowed values of short‐range order parameters are calculated for ordered A2t–1B alloys and non‐stoichiometric interstitial Me2tX2t–1 (t = 1, 2, 3, and 4) compounds. A relationship is established between the short‐and long‐range order parameters as a function of solid‐solution composition and superstructure type. Suggestions are made about possible formation mechanisms of various superstructures.
An Evaluation of Structural and Transport Properties of Molten Potassium–Rubidium Alloy
Authors: Rao R. V. Gopala , Bandyopadhyay U. 
Published: July 2007

AbstractIn comprehensive investigations the perturbation treatment of the Lebowitz equation with a square well attractive tail is utilised to calculate the partial and total structure factors at different atomic fractions of potassium in the potassium–rubidium melt. Further the Bhatia‐Thornton correlation functions are evaluated. Using the direct correlation function in the long‐wave limit, the isothermal compressibilities are calculated through the Kirkwood‐Buff equation. The partial structure factors are then utilised to calculate the self‐diffusion coefficients using the linear trajectory approximation due to Helfand.
Incorporation and Aggregation Properties of Bismuth Ions in KCl Crystals
Authors: Nistor S. V. , Stoicescu Gh. , Mateescu C. D. 
Published: July 2007

AbstractThe optical absorption spectra of bismuth doped KCl crystals, grown by the Bridgman method in reactive atmosphere, reveal the presence of both Bi3‐ and (BiO)+ centers in variable ratios. The ratio changes along the crystal axis and depends on the chemical form of the dopant and its initial concentration. The shape, intensity, and peak positions of the optical spectra are sensitive to the thermal history of the crystal, reflecting the aggregation/dissolution of the centers. An apparent third‐order reaction is observed to govern the early stages of the Bi3+ aggregation, with an activation enthalpy of 0.60 eV, in good agreement with earlier results of diffusion and ionic conductivity measurements.