bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonlinear Quantum Beats of Excitons in CdSe
Authors: Pantke K.‐H. , Schillak P. , Erland J. , Lyssenko V. G. , Razbirin B. S. , Hvam J. M. 
Published: July 2007

AbstractBy observing quantum beats in the self‐diffracted signal from a nonlinear mixing process in a crystal, and by spectrally resolving this signal, information is obtained about solid state parameters, such as energy splittings and energy shifts. This technique is used to study bound excitons in CdSe with a strong, resonant third‐order susceptibility. Furthermore, in the region of free exciton propagation, effects on the third‐order nonlinear polarization are observed and explained by quantum beats between propagating polaritons.
Quantum Beats and Exciton Coherence in Time‐Resolved Resonant Light Scattering
Authors: Stolz H. 
Published: July 2007

AbstractThe time‐resolved resonant light scattering spectrum following short pulse excitation provides information on the various inelastic (energy relaxation) and elastic (phase relaxation) relaxation processes of an exciton system. Taking properly the implications of the measurement process into account this can be exploited to discriminate between Raman scattering processes, proceeding without loss of coherence, and hot luminescence, occurring after phase relaxation. The coherent nature of the states can be directly revealed by quantum beats in the time‐dependent scattering spectrum if the resonant states are energetically split. Such experiments are presented for bound excitons in CdS and the lowest exciton‐polariton in Cu2O. These measurements allow to deduce refined magneto‐optical parameters due to the high energy resolution of this method. The exciton dephasing times found are surprisingly long (up to 1 ns) and determined by energy relaxation due to phonon scattering. Pure dephasing due to elastic scattering gives only a minor contribution.
Microscopic Theory of Rabi Flopping, Photon Echo, and Resonant Pulse Propagation in Semiconductors
Authors: Koch S. W. , Knorr A. , Binder R. , Lindberg M. 
Published: July 2007

AbstractThe phenomena of Rabi oscillations, resonant pulse propagation, and photon echo in semiconductors are investigated by numerically solving the full semiconductor Bloch equations for the example of bulk CdSe. The calculations are done for resonant femtosecond excitation at the exciton resonance. The many‐body modifications of Rabi flopping and semiconductor photon echo are discussed for a thin medium, whereas the propagation of weak and strong pulses is analyzed for an extended material. Rabi flopping of the density can lead to field reamplification and thus to long propagation distances of sufficiently strong pulses and to pulse break‐up. The area theorem known from self‐induced transparency (SIT) in atomic systems is generalized for the case of phase modulated fields and shown to be modified significantly in semiconductors. Even though no ideal SIT occurs, the Coulomb interacting electron–hole system nevertheless seems to support extremely long propagation distances of so‐called π‐pulses.
Evolution Equations for the Nonequilibrium LO‐Phonon Dynamics in Laser Excited Polar Semiconductors
Authors: Wenschuh U. , Heiner E. , Fulde P. 
Published: July 2007

AbstractStarting from an extensive model Hamiltonian a system of evolution equations is derived by means of a time‐dependent projection operator technique which describes the nonequilibrium dynamics of the LO‐phonon system in a laser excited polar semiconductor. The carrier system is described in a hydrodynamic stage, whereas the phonon system is treated in an athermal stage. Third‐order anharmonic interactions between optical and acoustic phonons as well as between the acoustic phonons are contained in the theory.
Effects of Trapped States on Spectrum of Four‐Wave Mixing
Authors: Hanamura E. 
Published: July 2007

AbstractExcitons are sometimes trapped at impurities in crystals and at defects on interfaces in the confined systems, such as quantum wells and microcrystallites. These trapping effects on the third‐order optical responses are discussed: (i) excitonic and trapped‐state enhancement, (ii) nearly degenerate four‐wave mixing spectrum, and (iii) differential transmission spectrum under nearly resonant pumping of the lowest exciton. It will be shown how these and linear responses give information on the surface states in semiconductor microcrystallites.
A New Approach to the Study of Bose‐Einstein Condensation of Biexcitons
Authors: Hasuo M. , Nagasawa N. , Mysyrowicz A. 
Published: July 2007

AbstractA new method is described that allows to detect the presence of a Bose condensate of biexcitons in a direct band gap material. It probes the accumulation of biexcitons in the coherent k = 0 state by measuring the increase of the optical phase conjugation signal of a crystal simultaneously pumped by an intense incoherent pump source. Experimental verification of the method is achieved in CuCl at low temperature. Results show an increase of the k = 0 biexciton mode occupation number by at least 8.6 × 105 when the randomly injected biexciton density exceeds the critical value for Bose condensation.
Quantum Confined Structures and Coherent Light Emitters in II–VI Heterostructures
Authors: Nurmikko A. V. , Gunshor R. L. 
Published: July 2007

AbstractRecent developments in wide‐gap II–VI quantum wells and p–n‐junction heterostructures with emphasis on two‐dimensonal exciton physics are reported. Current device issues related to blue and green diode lasers and light emitting diodes in the ZnSe‐based configurations are briefly summarized. This is followed by experimental review of evidence which strongly suggests that exciton effects, which dominate interband absorption, are also of importance in both spontaneous and stimulated emission processes.
1D Charge Carrier Dynamics in GaAs Quantum Wires Carrier Capture, Relaxation, and Recombination
Authors: Christen J. , Kapon E. , Grundmann M. , Hwang D. M. , Joschko M. , Bimberg D. 
Published: July 2007

AbstractTime‐ and spatially resolved luminescence of GaAs/AlGaAs quantum wires (QWRs) grown by organometallic chemical vapor deposition on nonplanar substrates is reported. The effective width of these nanoscopic wires is as small as 9.5 nm, giving rise to a separation of 45 meV for the quasi‐one‐dimensional conduction subbands. The QWRs exhibit high luminescence efficiency and the radiative recombination lifetime of the quantum confined carriers is found to be larger than 310 ps. Combined spectral‐time‐resolved experiments directly visualize the carrier capture process and the thermalization of the 1D carriers in the QWR structures.
Ultrafast Ligth Induced Transmission Changes and Laser Emission of Semiconductor Quantum Dots
Authors: Dneprovskii V. S. , Klimov V. I. , Okorokov D. K. , Vandyshev Yu. V. 
Published: July 2007

AbstractTransitions between energy levels of carriers spatially confined within CdSe nanocrystals are observed as bleaching bands in time‐resolved nonlinear transmission spectra. Gain and laser generation at the transition between the lowest levels of size quantization are achieved.
Optical Bistability Induced by Charge Separation in Asymmetric Quantum Wells
Authors: Scandolo S. , Tassone F. 
Published: July 2007

AbstractA novel mechanism for intrinsic optical bistability in quantum wells is proposed. In suitable structures the intrinsic electric field generated by optical excitation leads to the lowering of some interband transition energies. Therefore, increasing‐absorption bistability occurs for proper choice of operation conditions, without considering excitonic or many‐body effects. A numercal study of a InAs–GaSb quantum well is carried out and switch‐on intensities of the order of 102 kW/cm2 for a nanosecond response time are found.
Saturation of Band‐Tail Absorption in Multiple Quantum Wells and Its Link with the Nonlinear Index Saturation
Authors: Raj R. , Sfez B. G. , Pellat D. , Oudar J.‐L. 
Published: July 2007

AbstractA pump and probe measurement of the nonlinear transmission reveals that the origin of the saturating behaviour of the nonlinear index δnNLobserved in the band tail of GaAs/GaAlAs multiple quantum wells is due to the saturation of the photoexcited carrier density.
Direct Summation of Coulomb Potentials over an Ionic Lattice
Authors: Fisenko I. G. , Kholopov E. V. 
Published: July 2007

AbstractThe possibility of performing the direct summation of Coulomb potentials over an ionic lattice is discussed. The regular way of enhancing the convergence is investigated, provided that artificial unit cells of high symmetry are introduced. The simplest ionic structures are considered as examples. The universal algorithm is proposed of calculating the appropriate surface contribution within the framework of the direct summation. As a result, Coulomb potentials for a boundless lattice can be reconstruced.
Unified Study of the Lattice Mechanics of Fluorites Indications of the Superionic Phase Transition
Authors: Makur M. , Ghosh S. 
Published: July 2007

AbstractA unified study of the different lattice mechanical properties of the three fluorites CaF2, SrF2, and BaF2 is presented, using a semi‐microscopic model and a single set of parameters. The cohesive energy, elastic constants, dielectric constants, and phonon dispersion curves are calculated. The temperature dependence of the phonon frequencies is estimated from a simple quasi‐harmonic approach which indicated softening of a 〈100〉 zone boundary phonon mode which may lead to the diffuse transition to the superionic state.
Theory of Size Quantization of Exciton in Quasi‐Zero‐Dimensional Semiconductor Structures
Authors: Pokutnyi S. I. 
Published: July 2007

AbstractA theory of size quantization of the exciton energy spectrum in a small semiconductor crystal is developed under condition where polarization interaction of electron and hole with the surface of a microcrystal plays an important role. From the comparison of the theory with experiments the effective mass of an exciton in a simple parabolic band microcrystal is determined.
Light‐Induced Ferrielectric Structures in Exciton Systems in Molecular Crystals
Authors: Izvekov S. V. , Sugakov V. I. 
Published: July 2007

AbstractThe possibility of spatial stratification of excitons and polarization in molecular crystals with traps for excitons at stationary pumping is considered. Such a structure can exist only under external irradiation and may be considered as an example of a dissipative structure which can arise in nonequilibrium systems. The numerical calculations are carried out for α‐benzophenon crystals. It is shown that at some critical values of pumping rate and crystal temperature the homogeneous density of excitons becomes unstable and spatial stratification of excitons arises in the crystal. The dipole moment of the elementary cell becomes uncompensated and a periodically changing dipole moment exists. The critical values of pumping rate and crystal temperature and the period of the spatial stratification of exciton density are calculated.
The Dependence of Tc on Pressure, Heat Capacity, and Thermal Expansion Coefficient Near Tc for Quasi‐Two‐Dimensional Superconductors with Paramagnetic Impurities
Authors: Zhernov A. P. , Chulkin E. P. 
Published: July 2007

AbstractThe phonon model of the high‐temperature superconductors is considered, taking into account the quasi‐two‐dimensional spectrum of carriers. The influence of paramagnetic impurities on the dependence of Tc on pressure, as well as on the value of jumps of the electron heat capacity and thermal expansion, is analyzed.
Microphysical Analysis of the Magnetooptical Interband Effects of Amorphous Semiconductor Films
Authors: Kessler F. R. , Schulz R. , Sievers B. 
Published: July 2007

AbstractThe polarization modulation spectroscopy of the (integral) Faraday and Kerr rotation of amorphous germanium and silicon films permits the separation of the magnetooptical contributions from various interband transitions with high sensitivity. The analysis is based primarily on a mathematical matrix calculation. This method yields the differential magnetooptical effects of arbitrary successions of multilayer systems including coherent and incoherent multiple reflections and magnetooptical interface effects. A quantum‐mechanical “density of states model” has been developed for the microphysical interpretation which is based on the optical constants and on the Mott‐CFO‐model of amorphous semiconductors. In this microphysical model the energy‐dependent integral sum‐g‐factor is obtained from the sign‐correct superposition of the magnetooptical contributions of the interband transitions at all critical points of higher energy. The weight of these magnetooptical contributions is significantly different for amorphous germanium and silicon.
A novel approach for constructing symmetry‐adapted basis sets for quantum‐chemical calculations. I. Real symmetry‐adapted orbitals
Authors: Kantorovich L. , Livshits A. 
Published: July 2007

AbstractA novel method for generating symmetry‐adapted basis orbitals (widely applied in quantum chemistry) is proposed. It extensively combines the ideas of both the local‐group and projection‐operator methods. Some important improvements of the previous formalisms are made, namely: (i) the simple procedure for the construction of the transformation matrix (TM) while the matrix making this TM unitary is extracted individually for further usage, (ii) the partial reduction of the initial reducible representation results in the possibility of conserving all matrices real even in the cases when the group in question has complex irreducible representations. The procedure proposed in this paper is applied to the general finite group which could be both the usual point or large unit cell group. Our method is well suited for computer utilization.
Electronic structure of point defects in antiferromagnetic insulating cuprates
Authors: Loktev V. M. , Prosandeev S. A. , Tarasevich Yu. Yu. 
Published: July 2007

AbstractThe energies and wave functions of impurity (defect) states which appear in the energy gap of La2CuO4 due to doping are calculated by the unrestricted Hartree‐Fock method. It is shown that the state vectors have such a structure that localized carriers (holes) can occupy not only oxygen ions but also copper ones.
Polarization of dislocation absorption and luminescence in direct gap semiconductors with edge dislocations
Authors: Razumova M. A. , Khotyaintsev V. N. 
Published: July 2007

AbstractThe bound electron states at an edge dislocation in direct gap semiconductors are investigated in the deformation potential model taking into account the triple degeneracy of the valence band maximum. The experimentally observed polarization of dislocation absorption (DA) and dislocation luminescence along the Burgers vector is explained theoretically. The interaction between the anisotropic dislocation field and the anisotropic valence subbands gives rise to three series of hole dislocation levels of different depths, the DA polarization being determined by the polarization of the optical transitions from the deepest holes series to the isotropic states of the conduction band.
Electron paramagnetic resonance and optical absorption spectra of Gd3+ ions in alkali cadmium borosulphate glasses
Authors: Rao A. S. , Rao J. L. , Kumar V. V. R. K. , Jayasankar C. K. , Lakshman S. V. J. 
Published: July 2007

AbstractElectron paramagnetic resonance (EPR) at 9.205 GHz is examined for a series of Gd3+‐doped alkali cadmium borosulphate (R2SO4 · CdSO4 · B2O3; R = Li, Na, K or Cs) glasses. The spectra are similar to the U‐spectra familiar in many oxide, fluoride, and sulphate glasses, indicating very low and disordered site symmetries with a broad distribution of crystal fields. Remarkable changes are observed in the spectrum with changes in temperature, glass composition, and concentration of Gd3+ ions. Optical absorption spectra of Gd3+‐doped cadmium borosulphate glass are also studied at 300 K.
Two‐stage relaxation of the electron‐phonon system in polar semiconductors
Authors: Král K. , Hejda B. 
Published: July 2007

AbstractThe effect of acoustic phonon bottleneck is studied theoretically in the hot electron‐phonon system in the approximation of dispersionless longitudinal optical phonons in polar semiconductors. Kinetic equations for electrons, LO‐phonons, and second generation acoustic phonons are solved numerically for CdSe. The fusion lifetime of acoustic phonons is estimated for the processes of anharmonic acoustic‐optical phonon coupling. The fusion processes are found to be critical for the occurrence of the acoustic phonon bottleneck.
Long‐range order of an exactly solvable model of a quantum antiferrormagnet
Authors: Chamati H. , Tonchev N. S. 
Published: July 2007

AbstractThe thermodynamics of a simple electron‐spin model for the paramagnetic‐antiferromagnetic phase transition is discussed. The spontaneous magnetization m and the root‐mean‐square order parameter mo for arbitrary temperature and band filling are obtained. For the ratio r(T, μ) = m/mo, where μ is the chemical potential, the value r(T, μ) = √3 is found.
Tunneling‐Assisted Photon Emission in MIS(p+) Junctions
Authors: Volkov R. A. , Chuiko A. F. , Dmitriev M. V. 
Published: July 2007

AbstractAnalytical expressions for the tunneling current and the intensity of light emission associated with the inelastic tunneling of electrons in sandwich structures are obtained for semi‐classical and quantummechanical descriptions of the electron gas in the electrodes. A metal—insulator—p+‐semiconductor (MIS(p+)) junction with a crystallographically oriented metal cathode is considered. To increase the spectral density of the tunneling‐assisted photon emission from the MIS(p+) junction, it is proposed to employ a cathode made of such transition metals as Ni, Co, Mn, Ti, Fe, as well as of Pt, β‐NiAl which exhibit peaks of the density of occupied states near the Fermi levels.
The Kinetics of Excitons in Krypton Cryocrystals with Impurity Traps
Authors: Belov A. G. , Ya. Fugol I. , Yurtaeva E. M. 
Published: July 2007

AbstractThe kinetics of energy transport by free (FE) and self‐trapped (STE) excitons is studied for krypton cryocrystals with impurity traps. The experimental data on the dependence of the intrinsic or sensitized luminescence spectrum on impurity concentration in Kr‐O2, Kr‐Ar‐O2, and Kr‐Xe solid solutions are considered. A model description of excitation motion and trapping in the presence of FE and STE is presented. The effect of different impurity centers on the balance relation between FE and STE in the matrix is determined. For small impurity concentrations the energy transport is shown to be realized by FE and forc> 10−1at% by STE.
Luminescence of CsCl: Tl Single Crystals
Authors: Nagirnyi V. , Zazubovich S. , Jaanson N. 
Published: July 2007

AbstractSpectral, polarization, and kinetic characteristics of CsCl:Tl luminescence are studied between 4.2 and 350 K. The Ax band at 3.88 eV and the AT band at 3.65 eV are observed in the triplet emission spectrum of Tl+ centres. It is shown that in the triplet relaxed excited state (RES) the trigonal (X) minima are of higher energy than the tetragonal (T) ones. The symmetry of both the emitting and the metastable states in each (X or T) minimum is the same, and in many respects their structure is similar to that of other ns2 ions in alkali halides. However, some peculiarities are observed in the luminescence characteristics of CsCl:Tl crystals (e.g. very small quantum efficiency of triplet emission at excitation in high‐energy absorption bands; population of the lower (T) minima mainly in the process of vibronic relaxation in the triplet excited state; too large polarization degree of the slow decay component of the Ax emission, exceeding 1.5 times its theoretical limit; large difference in the spin‐orbit splitting energies δ of the triplet RES in the × and the T minima as well as in radiative decay probabilities y1 of their metastable states; the absence of an off‐centre displacement of the excited Tl+ ion from the crystal lattice site, etc.). Possible reasons for these features are discussed.
Expansion of Free Energy in Terms of Correlation Functions Within the Landau‐Ginzburg Model I. Fundamental Relations
Authors: Madzhulis I. , Kaupužs J. 
Published: July 2007

AbstractThe free energy can be expanded in terms of correlation functions on the basis of the Landau‐Ginzburg phase transition model for ferroelectrics. An equation for the two‐point correlation function is obtained from the extremum condition of the free energy function. A new criterion is proposed to choose skeleton diagrams for the free energy with an account of fluctuations. Results obtained for any functional integral in statistical physics can be generalized.
Some Typical Features of Relativistic Tunnelling through a Double Barrier System with δ‐Function Potentials
Authors: Roy C. L. 
Published: July 2007

AbstractA comparative study of relativistic and non‐relativistic tunnelling of electrons through double‐barrier systems is reported considering potentials of rectangular barrier and δ‐function barrier types. Among other things, it is found that, for δ‐function barriers, the relativistic treatment predicts resonant tunnelling at all energies for certain quantised values of the strength of the δ‐function barriers, while the corresponding non‐relativistic treatment is not involved with a situation of this sort.
Electronic Structure of α‐Quartz. A XANES Study of Empty States
Authors: Bart F. , Jollet F. , Duraud J. P. , Douillard L. 
Published: July 2007

AbstractX‐ray absorption spectra of α‐quartz in the XANES region are presented both at oxygen and silicon K edges. The consequences of the electric dichroism of the samples on XANES structures are investigated. Polarization effects are detected when the electric field of the incident beam is parallel or perpendicular to the crystallographic c‐axis. The structures after the absorption edges are discussed both in the frame of the Natoli's rule and from a density of states point of view.
Elastic Constants for the H. C. P. Lattice
Authors: Pasianot R. , Savino E. J. 
Published: July 2007

AbstractThe analytic expressions for the five elastic constants of an h. c. p. lattice are deduced. These expressions are appropriate for fitting empirical many‐body interatomic potentials of the embedded atom type. The uniform deformation method is used together with the lattice symmetry properties. These greatly simplify algebraic manipulations and provide for an easy inclusion of the contribution of inner strains.
Polaron Theory of the Image Potential Considering the Spatial Dispersion
Authors: Beril S. I. , Pokatilov E. P. , Goryachkovskii E. R. , Semenovskaya N. N. 
Published: July 2007

AbstractThe quantum‐mechanical theory of the image potential, which was developed recently on the basis of the polaronic approach is completed now with the consideration of the spatial dispersion of dielectric permittivity describing the microscopic inhomogeneity of a crystal lattice. The presence of nonmonotonicity in the coordinate dependence of the image potential energy obtained in the previous theory occurred to take place in our theory as well, but now it is less pronounced.