bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intramolecular Excitation Dynamics in a Thermalized Chain. II. Formation of Autolocalized States in a Chain with Free Ends
Authors: Kadantsev V. N. , Lupichev L. N. , Savin A. V. 
Published: July 2007

AbstractA numerical study of the Davydov soliton dynamics in a thermalized unclosed molecular chain with asymmetric exciton–phonon interaction is carried out. The effect of thermal vibrations in the scope of the quantum‐mechanical model is taken into account. When initiating the excitation at the free end of the chain, the soliton transport is shown to be able to occur at temperatures close to 300 K only. In this case the soliton formation is dependent on which of the end molecules in the chain is excited first.
Large Polarons in the Discrete SSH Model
Authors: Ruckh R. , Sigmund E. 
Published: July 2007

AbstractStationary polaron solutions are derived for the discrete version of the Su‐Schrieffer‐Heeger (SSH) model in two different ways. First Holstein's large polaron theory is applied. Second, the polaron solution is derived from Heisenberg's equations of motion. It turns out that the results obtained from the continuum version of the SSH Hamiltonian are different from those obtained from Holstein's molecular crystal model (MCM).
Influence of Bond‐Angle and Dihedral‐Angle Disorders on the Top of the Valence Band of Amorphous Germanium
Authors: Ratag V. M. 
Published: July 2007

AbstractThe electronic structure of amorphous germanium (a‐Ge) is considered using a tight‐binding scheme with all first‐neighbor couplings in a continuous random network. The dihedral‐angle and bond‐angle disorders are found to be important at the valence‐band‐edge and responsible for the observed features near the top of the valence band. At the top of the valence band of a‐Ge a tail of localized states ≈︁ 0.4 eV in width is found.
Band‐Gap Narrowing Due to Many‐Body Effects in n‐Type Degenerate GaAs Crystals
Authors: van Cong H. , Charar S. , Brunet S. 
Published: July 2007

AbstractThe band‐gap narrowing due to many‐body effects in n‐type degenerate GaAs crystals is analytically expressed in terms of the total donor concentration Nd, basing principally on the integral expressions of conduction‐and‐valence band edge shifts, established and numerically computed by Abram et al. in the plasmon pole approximation and a self‐energy approach. Here, the additional screened Coulomb hole effect is also considered. Then, the numerical results are compared with the corresponding results deduced from other works. Finally, it is suggested that, at both, very low and high concentrations, the result of band‐gap narrowing is reduced to that given by the traditional Hartree‐Fock exchange effect, and thus proportional to N.
Solitons and Polarons in Polyyne. Discrete Lattice and Broken Electron–Hole Symmetry Effects
Authors: Malek J. , Drechsler S. L. , Heiner E. , Kahnt R. 
Published: July 2007

AbstractA SSH‐like Hamiltonian proposed by Rice et al. for polyyne extended by second neighbour hoppings is investigated. The discrete system of electron eigenvalue equations together with selfconsistency conditions for relative atomic displacements is numerically solved for a rich variety of soliton and polaron states. In particular, it is found that various degeneracies inhererent for the model mentioned above are lifted due to terms which break the charge conjugation symmetry. Discrete lattice effects enhance the symmetry breaking. For polarexcitons and neutral solitons (antisolitons) an internal charge structure is found.
Collective Excitation Effects on the Electrical Resistivity of Singlet Ground State Paramagnets of Metallic Conduction
Authors: Szukiel A. E. , Markowski P. J. , Durczewski K. 
Published: July 2007

AbstractThe possibility of the occurrence of a maximum in the temperature dependence of the electrical resistivity in the paramagnetic phase of singlet ground state crystal field materials is examined theoretically on the basis of an earlier developed formalism for a many‐level system (PrIn3) and a simple two‐level model. It is shown that the existence of a weak exchange interaction in paramagnetic PrIn3 improves the fitting of the theoretical results to experimental data but the occurrence of the maximum in the temperature dependence of the resistivity in ferromagnetic Pr3Tl in an earlier paper by using the same formalism may be questioned. Further investigations are required to explain the effect.
Model Calculations for Spin‐Density‐Wave Instabilities in Itinerant Magnets
Authors: Jelitto R. J. 
Published: July 2007

AbstractBy evaluation of a generalized Stoner criterion everywhere on the Brillouin zone the instability of the paramagnetic state (PS) vs. a first ordered state (FOS) of spin‐density‐wave type at T = 0 is investigated for a simple but non‐trivial two‐dimensional model of itinerant magnetism. As main results (i) the pitch q0 of the FOS varies continuously with the band‐filling leading to an incommensurate magnetic structure in the most cases, and (ii) the variation of q0 occurs along some symmetry axes of the Brillouin zone. By (ii) a long‐standing conjecture is proved for the model considered. (i) shows that it is not justified to restrict to fixed magnetic structures when setting up theories of itinerant magnetism. First discussions on the meaning of these findings for the results of a more complete description (including the fully developed ordered state and finite temperatures) are given.
Anderson Localization in Ferromagnetic Semiconductors Due to Spin Disorder I. Narrow Conduction Band
Authors: Kogan E. M. , Auslender M. I. 
Published: July 2007

AbstractTheoretical investigation is made of the temperature induced metal‐insulator transition in doped ferromagnetic semiconductors, described by s‐d exchange model. The transition is a result of the mobility edge movement, the disorder being due to magnetic ions spin density fluctuations. The electrons are described in tight binding approximation. Using ideas and methods of Anderson localization theory simple formulas are obtained, which connect the mobility edge with shortrange order characteristics of the magnetic subsystem‐static spin correlators. The theory developed is applied to the description of the resistivity of CdCr2Se4. The theoretical results are in agreement with experiment in a wide temperature range.
Effect of Monoclinic Symmetry on the EPR Spectra of Gd3+‐Doped Hydrated Single Crystals of Rare‐Earth Trichlorides
Authors: Misra S. K. , Rudowicz C. 
Published: July 2007

AbstractRoom‐temperature X‐band EPR data for Gd3+‐doped isostructural rare‐earth trichloride hexahydrates are analyzed using a rigorous least‐squares‐fitting procedure. Discussion of the three forms of spin Hamiltonian corresponding to the orientations of the two‐fold monoclinic symmetry axis C2 parallel to the magnetic axes X, Y, and Z is provided. It is found that for, C2 ∥︁ Y, a significantly lower value of χ2, representing the goodness of fit, is obtained. A discussion of the determination of degree of monoclinicity, as revealed by the spin Hamiltonian parameters, is provided. Systematics of the spin Hamiltonian parameters b and b, as functions of the host–ion radius, are also studied.
Photoluminescence of GaSe
Authors: Dobynde I. I. , Bobrysheva A. I. , Razdobreev I. M. , Shekun Yu. G. 
Published: July 2007

AbstractThe photoluminescence and absorption in GaSe over the energy range 2.00 to 2.12 eV at 77 K is investigated under different conditions, namely with different excitation quantum energies and low and high pumping power. The observed features of the spectra are explained using the energetic band model proposed by Voitchovsky and Mercier.
Optical Bistability and Multistability in a System of High Density Excitons and Biexcitons in Semiconductors
Authors: Khadzhi P. I. , Shibarshina G. D. , Rotaru A. Kh. , Slavov Yu. D. 
Published: July 2007

AbstractResults are given on the investigation of optical bistability and multistability phenomena both, in the exciton range of the spectrum due to exciton‐photon and exciton‐exciton interactions and in the range of two‐photon generation of the biexcitons (excitonic molecules). For each case the steady‐state equations are obtained.
Phase Transition in 1D KDP‐Type Ferroelectrics
Authors: Sajfert V. D. , Mašković Lj. D. , Djajić‐Jovanović R. P. , Kozmidis‐Luburić U. F. 
Published: July 2007

AbstractThe behaviour of quasi‐one‐dimensional ferroelectrics of the KDP‐family is investigated in the vicinity of the transition temperature. Three forms of the proton–proton potential are examined and it is concluded that long‐range forces are responsible for the second‐order phase transition in these materials.
Radiative and Non‐Radiative Processes of Localized Impurity Centers in Alkali Halides: KBr:Ag−
Authors: Shimanuki S. 
Published: July 2007

AbstractThe C and A emissions in KBr:Ag− are measured in detail between 11.2 and 300 K. At 11.2 K, excitation in the peak position of the C band exhibits the C emission but it hardly produces A emission. Changing the excitation position to the higher energy side of the C band peak, the A emission is produced a little. The intensity (emitted photon number) ratio of the A to C emission, η, shows an excitation photon‐energy dependence and changes over three orders within both sides of the C band. Increasing the temperature, η itself increases as a whole and its excitation photon‐energy dependence weakens and disappears at about 80 K. The values of η in the lower energy edge show an activation process of Arrhenius type over four orders above around 45 K, whose activation energy is 0.076 eV, and below 30 K, another activation process of the same type with an activation energy of 0.0025 eV. A few causes of the exciting energy dependence of η at low temperatures are considered and the mechanism due to the dynamical nonradiative transition is proposed.
Weak Impurity Metallic Behaviour of p‐Hg1−xCdxTe
Authors: Höschl P. , Moravec P. , Grill R. , Čápek V. 
Published: July 2007

AbstractOn samples of p‐Hg1−xCdxTe (x ≈ 0.2) with critical concentration of Hg‐vacancies at which shallower acceptor level disappears completely, the electric conductivity and Hall coefficient are measured. An impurity band model is reported for a simultaneous analysis of the Hall coefficient and Hall mobility data in the region of 4.2 to 100 K. Concentrations of Hg‐vacancies and of compensating donors are determined. It appears that there is no physical reason to distinguish between heavy hole and impurity band conduction.
A Molecular‐Dynamical Study of the Changes in the Atomic Structure of a Material Induced by a Shock Wave with a Distorted Front
Authors: Korostelev S. Yu. , Psakhe S. G. , Panin V. E. 
Published: July 2007

AbstractAtomic structure changes of a crystal induced by shock waves are studied by molecular dynamic method. α‐Fe crystallites are used for simulation having a rectangular area in the (110) plane and containing about 104atoms. The radial distribution function of atoms is shown to lose its discrete form, typical of a crystal and to become continuous when the shock wave planar front is distorted. Microfragmentation in the corresponding areas of a crystal is shown at the same time to be the result of the shock wave distortion with a planar front.
Quantum Fluctuations and Time Structures of High Density Polaritons
Authors: Moskalenko S. A. , Rotaru A. H. , Shvera Yu. M. , Zaloi V. A. 
Published: July 2007

AbstractThe quantum fluctuations of coherent polaritons in bulk samples are quenched due to the macroscopic occupation number of the single‐particle state. But in the microcrystallites at low levels of excitation antibunching of the quasiparticles can occur. The nonstationary behavior of the coherent polaritons is characterized by the periodic, quasiperiodic, and chaotic self‐pulsations. The phase trajectories are characterized by the limiting cycle, torus or strange attractor.
Nuclear Polaritons in the Mössbauer Absorber
Authors: Haas M. , Hizhnyakov V. , Realo E. , Jōgi J. 
Published: July 2007

AbstractA transient pulse of the Mössbauer radiation in a thick resonant absorber in the case of a significant isomer shift is investigated theoretically and experimentally. It is shown that on transmission the incident pulse decomposes into 1. a fast pulse ‐ an analog of the Sommerfeld‐Brillouin precursive pulse in optics and 2. a slow pulse connected with the motion of a nuclear polariton packet. The group velocity of the polaritons is determined.
Manifestation of Hot Phonons in the Luminescence Spectra of Highly Photoexcited AIIBVI Crystals
Authors: Baltramiejūnas R. , Žukauskas A. 
Published: July 2007

AbstractThe quasi‐stationary and transient spectra of the nonequilibrium electron‐hole plasma (EHP) emission are investigated in CdSe crystals. A broadening of the low‐energy side of the luminescence band due to the heating of longitudinal‐optical (LO) phonons is established. A slow stage of the EHP energy relaxation with a time constant of 150 ps is observed and referred to the accumulation of decay products of nonequilibrium LO phonons in the narrow interval of the k‐space. A model of the two‐stage relaxation of the phonon subsystem in a photoexcited semiconductor is used to calculate the power of energy‐loss in hot EHP and the nonequilibrium LO phonon distribution.
Stable Configuration of an Interstitial Atom with Relaxation Effect in Si and Ge
Authors: Soma T. , Atarashi N. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractThe stable configuration of an interstitial atom in Si and Ge are studied using the perturbational formalism presented earlier and considering the relaxation effect around the interstitial atom. The interstitial atom is most stable at the hexagonal site for Si and Ge. The calculated migration energy of the interstitial atom is smaller than 0.1 eV for Si and about 0.4 eV for Ge.
Investigation of the Thermodynamic Properties of Anharmonic Crystals by the Momentum Method. I. General Results for Face‐Centred Cubic Crystals
Authors: Tang Nguyen , van Hung Vu 
Published: July 2007

AbstractBy the moment method established previously on the basis of the statistical mechanics, the thermodynamic properties of a strongly anharmonic crystal with the f.c.c. structure are considered. The analytic expressions for the thermodynamic quantities as the thermal expansion coefficient, the specific heats Cv and Cp, the isothermal and adiabatic compressibilities, etc. are obtained.
Effect of Magneto‐Size Quantization on Electric‐Field‐Aided Photoemission from Quantum Wells in Ultrathin Films of Wide‐Gap Semiconductors
Authors: Maity A. B. , Majumdar C. , Chakravarti A. N. 
Published: July 2007

AbstractAn attempt is made to investigate the quantized photoemission from the magneto‐size‐quantized levels of quantum wells in ultrathin films of wide‐gap semiconductors in the presence of an electric field, taking n‐type GaAs as an example. It is found that the photocurrent changes with photon energy in a step‐like manner in which the number of steps increases for relatively large film thicknesses with consequent decrease of the step heights at given values of the electric and magnetic fields. Besides, it is seen that the photoemission becomes quantized for photon energies significantly lower than the electron affinity whereas it becomes oscillatory as the electron affinity is approached. The effects of continuous variation of either the electric or the magnetic field on the photocurrent corresponding to different film thicknesses are also discussed.
Up‐Conversion from Er3+–Er3+ Pairs in CdF2 Crystals
Authors: Jouart J. P. , Mary G. 
Published: July 2007

AbstractThe effect of preferential clustering on the properties of infrared to visible conversion of Er3+ (between 1 to 4 mol%) is investigated in CdF2 at 77 K. Without preferential clustering, the green emission is predominant. If there is preferential clustering, the red emission is predominant. This emission mainly results from the non‐resonant cross relaxation process in an Er3+–Er3+ pair doubly excited in the state (4I11/2, 4I13/2). The efficiency of this up‐conversion process is two orders of magnitude higher than that of the single Er3+ sites. It is suggested to use the up‐conversion as a technique to inquire about the degree of association of the Er3+ ions in the host lattices.
Excitons Bound to Te Impurities in CdS, ZnS, and Their Mixed Compounds with Wurtzite Structure
Authors: Tchakpele K. P. , Albert J. P. 
Published: July 2007

AbstractA calculation is made of the binding energy of holes to isolated, pairs and clusters of three Te impurities in ZnS, CdS, and their mixed compound ZnxCd1−xS. The calculation takes into account the multiband nature of the bound state as well as the relaxation induced by the incorporation of the impurity, the growing importance of which is shown when going from CdS to ZnS. The only imput parameters are the electronegativity difference between the exchanged atoms modeled by the energy difference of the free corresponding atomic s and p levels and the relaxation of the nearest neighbour distance as previously determined by Martins and Zunger. A very good agreement is obtained between the calculated values and the experimental data.
Magnetism in Thin Chromium Films
Authors: Schröder K. , Hejase H. 
Published: July 2007

AbstractTorque magnetometer measurements show that the magnetic moment of mica sheets with Cr films 0.3 to 28 nm thick is smaller than the magnetic moment of the mica sheet at room temperature. This may mean that the average susceptibilities of the Cr films are negative, and of the order of −10−3 to −10−4, or that small magnetic moments form perpendicular to the plane of the Cr film. Both explanations cannot be reconciled with accepted models of the magnetic structure of chromium.
Nonlinear Refraction Due to Dynamical Burstein‐Moss Effect in Lead Chalcogenides
Authors: Paskov P. P. , Pavlov L. I. , Atanasov P. A. 
Published: July 2007

AbstractA theoretical analysis of the nonlinear refraction due to the dynamical Burstein‐Moss effect in IV–VI semiconductors, is developed. A nonlinear refractive cross‐section in lead chalcogenides at T = 100 K and various compositions is quantitatively evaluated. It is shown that the electronic optical nonlinearity in these ternary compounds is substantial for nonequilibrium carrier concentrations of the order of 1015 to 1016 cm−3. It is possible to use the obtained theoretical results in modeling nonlinear opto‐electronic elements.
Raman Determination of the Faust‐Henry Coefficient of GaAs in the 1.9 to 2.7 eV Range at Ordinary and Low Temperatures
Authors: Zekeng S. , Prevot B. , Schwab C. 
Published: July 2007

AbstractThe Faust‐Henry coefficient of GaAs is determined at ordinary and low (20 K) temperatures by using Raman scattering by the TO and LO first order mode vibrations excited by photons with energies located between 1.9 and 2.7 eV. After careful normalization of the experimental results with respect to optical as well as instrumental conditions, the Faust‐Henry coefficient is found to be nearly constant over the energy range investigated with a mean value of C = −0.48 ± 0.04 at 300 K and a slightly lower value (C = −0.53 ± 0.04) at low temperature. The pure electrooptic contribution to the Raman efficiency of GaAs is also deduced.
Thermoluminescence and Other Optical Studies on γ‐Irradiated RbCl: Gd2+
Authors: Sastry S. B. S. , Muralidharan G. 
Published: July 2007

AbstractThermoluminescence (TL) of RbCl:Gd2+ is discussed. Z1 centres are formed even in the irradiation process. Hydroxyl ion related centres are observed in the optical absorption. The TL process is identified to be due to the thermal release of F‐electrons and their subsequent recombination with the hole centres.
Coherent Nonlinear Optical Processes in Semiconductors. Physics and Applications
Authors: Schmitt‐Rink S. 
Published: July 2007

AbstractThe influence of monochromatic nonresonant laser fields is discussed on the elementary excitation spectrum of semiconductors. It is shown that the different renormalizations in inorganic and onedimensional organic materials can be understood in the framework of one and the same theory. Applications, such as generation of ultrashort voltage pulses in biased quantum wells, are discussed.
Theory of the Optical Stark Effect in Semiconductors
Authors: Schäfer W. , Schuldt K.‐H. , Binder R. 
Published: July 2007

AbstractThe light‐induced changes of the properties of a semiconductor caused by an ultra‐short strong laser pulse with a central frequency well below the fundamental absorption edge are investigated. Renormalization and time evolution of one‐ and two‐particle properties are discussed using a nonequilibrium Green's function formalism. Numerical results for the absorption spectra are presented.
Digital Circuits for All‐Optical Computing Based on Thin‐Film Semiconductor Interferometers
Authors: Sinitsyn G. V. 
Published: July 2007

AbstractResults are reported of realizing optically programmable components of digital processors, a full adder, a space switch‐demultiplexer based on optically bistable vacuum‐deposited semiconductor interferometers (interference filters). Examples are given of arranging coupling between elements and synthesis of loop circuits, RS flip–flop, relaxation generators (clocks). The possibility is shown of performing logical operations with the aid of interference filters in nano‐ and picosecond times. Besides thermal nonlinearity, nonlinearities of electronic nature are considered which are due to size effects in semiconductor microcrystalline films.
The Theory of Nonlinear Slab Multistable Transmission
Authors: Khadzhi P. I. , Shibarshina G. D. , Rotaru A. Kh. , Slavov Yu. D. 
Published: July 2007

AbstractA phenomenological theory of the nonlinear multistable light transmission by a semiconductor slab is presented taking into account the variation of the amplitude reflection coefficients of the interfaces versus the level of the excitation. It is shown, that the reflection coefficients of the front and back end faces of the slab are different. In the dispersive limit a generalized Airy formula for the multistable transmission is found.
Strong Dispersive Nonlinearity in the Excitonic Region of Wide‐Gap II–VI Compounds at Room Temperature
Authors: Spiegelber Ch. , Kretzschmar M. , Puls J. , Henneberger F. 
Published: July 2007

AbstractThe intensity‐dependent change of the refraction index of CdS at room temperature is deduced from degenerate four wave mixing experiments. For an application of the very strong dispersive nonlinearity optical switching, and bistability are demonstrated using the 514 nm output of an Ar+‐laser.
Beam Amplification by Transient Energy Transfer in GaAs and Si
Authors: Dubard J. , Smirl A. L. , Cui A. G. , Valley G. C. , Boggess T. F. 
Published: July 2007

AbstractTwo beam coupling experiments with 29‐ps (FWHM) pulses at a wavelength of 1.06 μm have been performed in GaAs and Si. By optimization of pump‐probe energy ratio, time delay and fluence we obtained optical gain up to 25 in GaAs at a fluence of 35 mJ/cm2 compared to roughly 140 mJ/cm2 required to obtain similar gain in Si.
The Effect of Pressure on the Thermodynamic Properties of Crystals near the Lattice Instability Point
Authors: Malinowska‐Adamska C. 
Published: July 2007

AbstractUsing the self‐consistent phonon theory based on the thermodynamic double‐time Green's function method the thermodynamical properties of the cubic crystals in the vicinity of the instability point are investigated. The results of calculations of the pressure dependence of the relative displacement of atoms, internal and free energy, free Gibbs energy obtained with the help of the generalized form of the Lennard‐Jones (n, m) renormalized potential are given and compared with experimental and other theoretical data for a number of cubic metals.