bluuebunny/crossref_metadata_2025_split huggingface dataset:
Optical Nonlinearities in n–i–p–i and Hetero‐n–i–p–i Structures
Authors: Malzer S. , Linder N. , Gulden K. H. , Höfler A. , Kiesel P. , Kneissl M. , Wu X. , Smith J. S. , Döhler G. H. 
Published: July 2007

AbstractOptical nonlinearities in n–i–p–i and hetero‐n–i–p–i structures with selective ohmic contacts, are reported. In this kind of structures strong changes of the absorption and refractive index are achieved either by field effects and/or with phase space filling. The latter one is always present in normal n–i–p–i structures but relatively weak because of the 3D character of the DOS. In QW structures this effect is much more pronounced because of the reduced real and momentum space and the enhanced excitonic oscillator strength. First the dynamics of n–i–p–i structures is discussed and then first experimental results of electrically tuned absorption changes due to band filling are shown. Field effects are also known to give large transmission changes. In particular, results for the transmission modulation in a n–i–p–i structure with a contrast ratio 2 are shown. It is also demonstrated that fast switching can be achieved in n–i–p–i structures. In a device with a 32 μm distance between the n‐ and p‐contacts, a 3 dB frequency of 16 MHz is obtained in excellent agreement with the theoretical prediction. By scaling down the structure to 3 μm frequencies in the GHz range are expected to be feasible.
Hole Transport in Bis (4‐N,N‐Diethylamino‐2‐Methylphenyl)‐4‐Methylphenylmethane Doped Polymers
Authors: Borsenberger P. M. 
Published: July 2007

AbstractHole mobilities have been measured in bis (4‐N,N‐diethylamino‐2‐methylphenyl)‐4‐methylphenylmethane (MPMP) doped polystyrene (PS) and polycarbonate (PC) over a range of MPMP concentrations. The results are described by the disorder formalism. The formalism is based on the assumption that charge transport occurrs by hopping through a manifold of hopping sites subject to energetic and positional disorder. The results show that the width of the density of hoppiny states increases with increasing PC concentration and decreases with increasing PS concentration. The concentration dependencies are attributed to dipolar fields associated with dipole moments of MPMP or the host polymer. The positional disorder increases with increasing polymer concentration in both materials.
The cluster approach to ground state determination and statistical thermodynamics of lattice systems
Authors: Steinberg A. S. , Kats D. Ya. , Men B. A. 
Published: July 2007

AbstractThe generalization of the cluster approach to the ground state problem and the statistical thermodynamics of lattice systems is discussed. The special attention is paid to some analytical possibilities. For an illustration of the cluster approach achievements the set of available superstructures in the b.c.c. lattice is obtained and the problem of critical point determination in the f.c.c. lattice is solved in various approximations.
Broadening of the plasma resonance in metallic microcrystals
Authors: Yatom H. , Ruppin R. 
Published: July 2007

AbstractThe broadening of the plasma resonance absorption peak in metallic microcrystals is calculated for spherical and cylindrical geometries. A high, but finite surface barrier is employed in the quantum mechanical model. The finiteness of the barrier is found to lead to a larger broadening than predicted by previous calculations, in which an infinite surface barrier was assumed.
Effect of an electric field on size‐quantized photoemission from nanometer films of semiconductors
Authors: Das N. R. , Ghosh S. , Chakravarti A. N. 
Published: July 2007

AbstractAn attempt is made to investigate the electric field‐aided photoemission from quantum wells in ultrathin films of degenerate wide‐gap semiconductors, taking n‐type GaAs as an example. It is found that the photoemission varies in a step‐like manner with photon energies close to the electron affinity and exhibits oscillatory character in its dependence on the film thickness, both in presence and absence of an electric field. For photon energies significantly lower than the electron affinity, a quantized nature of the emission is observed in certain ranges of film thicknesses. Besides, the rate of increase of the photoemission with electric field is seen to increase with increasing film thickness over the range of thicknesses of interest in ultrathin films.
Three resonant energy levels in the presence of a asymmetric damping. A quantum non‐perturbative approach
Authors: Giry M. , Henri‐Rousseau O. 
Published: July 2007

AbstractThe irreversible evolution at zero temperature of a linear chain of three resonant excited states, the last of them being damped, is studied at zero temperature, using the resolvent method. The matrix elements of the time‐evolution operator and of the reduced density operator are obtained in closed form. The decays contain always three exponentials. Relaxation is always underdamped. Comparison is made with the corresponding classical kinetic model.
Density of states and localization length in weakly disordered peierls chains
Authors: Mertsching J. 
Published: July 2007

AbstractThe electron density of states and localization length are calculated for weakly disordered dimerized tight‐binding chains. Pure bond disorder causes a singular density of states for small bond gaps, and a singular localization length for zero bond gap, whereas larger bond gaps are transformed into pseudogaps. A site gap for diatomic chains is preserved under bond disorder. Site disorder destroys any gap and does not create singularities in the density of states or localization length. These results are compared with those obtained from the continuum approximation with Gaussian disorder, which is not strictly justified for short‐ranged disorder potentials. However, the continuum results are valid for weakly disordered chains provided the bond and site disorders in the chain correspond to bond‐gap and combined site and site‐gap disorders in the continuum model, respectively.
Electronic excitations localized in KBr and KI crystals near vacancy defects of different sizes
Authors: Vasilchenko E. , Sarmukhanov E. , Shunkeev K. , Elango A. 
Published: July 2007

AbstractThe luminescence and excitation spectra of electronic excitations localized near a single anion vacancy (eα), a divacancy (ed), and a vacancy quartet (eq) are investigated. The shifts of spectral characteristics of these excitations with respect to those of the excitations in regular lattice sites (er) have regular behavior. It turned out that the charge of vacancy defects is the main perturbing factor for eα, ed, and eq creation and the dimension of vacancy defects is the main perturbing factor for the radiative decay eα, ed, and eq. The peculiarities of eα, ed, and eq relaxation are discussed in terms of strong and weak off‐centers for er in KBr and KI, respectively.
Ab initio calculation of magnetic moments and hyperfine fields in Y2Fe17Z3 (Z = H, C, N)
Authors: Beuerle T. , Fähnle M. 
Published: July 2007

AbstractThe local magnetic moments and hyperfine fields on the crystallographically different Fe and Y sites and on the interstitial atoms Z are calculated for the technologically important hard magnetic compounds Y2Fe17 and Y2Fe17Z3 with Z = H, C, N by means of the local‐spin‐density approximation and the linear‐muffin‐tin‐orbital theory in atomic‐sphere approximation. The competing effects of volume expansion and hybridization between the interstitial atoms and the neighbouring Fe atoms are discussed, and the limitations of the atomic‐sphere approximation are elucidated.
Rows in two‐dimensional quasilattices
Authors: Hoffmann S. , Trebin H.‐R. 
Published: July 2007

AbstractPentagonal Penrose tilings and their octagonal and dodecagonal counterparts represent simple models for two‐dimensional quasicrystals. We investigate the properties of rows, which are the analogues to lattice lines of periodic lattices, by a method based on the projection formalism. It enables us to derive the vertex pattern and the mean vertex density of an arbitrary row as well as the mean vertex density of the corresponding family and its dependence on the row direction. The row separation and their quasiperiodic sequences are also being studied.
Change of exciton energy in ultrafine particles with a charge on its surface
Authors: Lai Zu‐You , Gu Shi‐Wei , Zhou Bingsuo , Xiao Liangzhi , Lee Tiejing 
Published: July 2007

AbstractThe Hamiltonian of the exciton in an ultrafine particle (UFP) with a charge on and a dipole at its surface is given. The exciton energy is calculated as a function of the charge number, the dielectric constant of the medium outside the UFP, and the strength of the dipole. The results for ZnO and CdS UFP indicate that the changes of the exciton energy due to the charge and the dielectric constant outside the UFP are of the same order.
Magnetic properties and structure of (FexAl1–x)2O3 solid solutions
Authors: Viktorov V. V. 
Published: July 2007

AbstractOn basic of the magnetic properties the statistical homogeneity of the Al2O3–Fe2O3 solid solution system is estimated. Summarizing the data obtained the conclusion is made that the distribution of Fe3+ ions in the (FexAl1–x)2O3 lattice for concentrations 0.005 ≦ x ≦ 0.07 does not obey statistical regularities.
Thermodynamics of the one‐dimensional Blume‐Capel model with an arbitrary spin
Authors: Jaščur M. , Kaneyoshi T. 
Published: July 2007

AbstractThe one‐dimensional Blume‐Capel model with an arbitrary spin S is studied by the use of a recently developed effective‐field theory. The internal energy, susceptibility, specific heat, and all the two‐spin correlations are obtained analytically and for spin‐1/2 the exact results are reproduced.
Free carrier contribution to dynamic dielectric function of heavily doped semiconductors. Application to n‐type silicon
Authors: Auslender M. , Hava S. 
Published: July 2007

AbstractA new approximation to calculate the free carrier contribution to the infrared dielectric function in n‐type silicon at room temperature that interpolates the quantum and classical absorption regimes is proposed. This approximation generalizes the Drude‐Lorentz approximation by introducing a frequency dependence of the relaxation parameter which is calculated via Mori formalism. Calculations of carrier concentration and wavelength dependences of the relaxation parameter, dielectric constant and optical constants for concentration intervals from 1.3 × 1015 to about 1.3 × 1020 cm−3 and in the wavelengths range from 1 to 30 μm are performed. The deviations from the Drude‐Lorentz approximation are discussed.
Energy Levels in Quantum Wells of Nonparabolic Semiconductors
Authors: Nag B. R. , Mukhopadhyay S. 
Published: July 2007

AbstractEnergy eigenvalues are given for quantum wells of the GaAs/GaAlAs, GaInAs/AlInAs, and InAs/GaAlSb systems, for widths ranging between 0.5 and 20 nm. The energy band nonparabolicity is shown to affect the values significantly particularly for wells with widths of about 2 nm. The InAs/GaAlSb wells are shown to have lowest energy levels with odd parity because of the negative effective mass in the barrier layer for energies below the mid‐gap energy. Experiments are suggested for the detection of these levels.
EPR Linewidth Studies of Gd3 +‐Doped LaxNd1−xF3 Single Crystals
Authors: Paradowski M. L. , Korczak W. , Pierre J. , Subotowicz M. 
Published: July 2007

AbstractThe dependence of the EPR linewidths of Gd3+ ion in LaxNd1−xF3 single crystals on temperature (77 K ≦ T ≦ 510 K) and composition (0 ≦ x ≦ 1) is analyzed to study the interactions between the paramagnetic Gd3+ and Nd3+ ions. The effect of the dilution of the paramagnetic Nd3+ ions with the diamagnetic La3+ ions is also discussed.
Thermodynamic Characteristics of a High‐Tc Two‐Band Superconductor
Authors: Konsin P. , Örd T. 
Published: July 2007

AbstractThermodynamic characteristics are calculated for a two‐band HTSC where superconducting pairing is caused by the dominating interband Coulomb interaction. From the expansion of free energy near Tc in powers of two gap order parameters the expressions for entropy, specific heat with its jump at T = Tc and Hc are derived. A comparison of the calculated values of ΔC/Tc, ΔC/Cn for La2−xSrxCuO4+δ and Y1Ba2Cu3O7, with the experimental ones is made. The theoretical dependence of ΔC on the hole concentration is obtained.
Polarized Neutron Experiments on REBa2Cu3O7—δ with Polarization and Time of Flight Energy Analysis
Authors: Schärpf O. , Chattopadhyay T. , Weber H. W. , Hyun O. B. , Finnemore D. K. 
Published: July 2007

AbstractExperimental data on HoBa2Cu3O7—δ (with δ = 0 and 1), obtained with a diffuse neutron scattering instrument and employing full polarization analysis, are used to evaluate the magnetic scattering cross sections. The validity of the evaluation is confirmed by a comparison with calculations based on published crystal field parameters for this compound. Similar experiments on Tm‐ and Yb‐substituted materials and the corresponding evaluations show, that both ions are in a 3 + state (Tm3+, Yb3+) at low temperature, whereas a change of valence occurs somewhere below 300 K.
Electron—Electron Scattering in a Hot Electron Gas Interacting with Optical Phonons
Authors: Dedulevich S. , Kancleris Ž. 
Published: July 2007

AbstractThe electron—electron scattering influence on the hot electron gas is analyzed. The strongest influence is observed in the slightly heated electron gas (in the case of so‐called warm electrons) at the lattice temperature T ∼ T0/5 (T0 being the characteristic temperature of the optical phonon). The interparticle collisions are shown to increase the electron energy loss via optical phonons and to decrease by the same amount the energy loss conditioned by acoustic phonon scattering.
Contribution to the Theory of the Spin 5/2 Blume‐Capel Model
Authors: Kaneyoshi T. , Jaščur M. 
Published: July 2007

AbstractThe exact formulation of the spin‐5/2 Blume‐Capel (BC) model is given on the basis of both the exact Ising spin identities and the differential operator technique. The general expressions for evaluating the phase diagram and paramagnetic susceptibility of the spin‐5/2 BC model are obtained within the statistical accuracy equivalent to the Zernike approximation of the spin‐1/2 Ising model. Some numerical results for the phase diagram and paramagnetic susceptibility of the spin‐5/2 BC model on the honeycomb lattice are given.
The Role of Impurity Scattering in the Quantum Waveguide
Authors: Mao J. M. , Huang Y. , Zhou J. M. 
Published: July 2007

AbstractThe effect of elastic scattering due to impurities in the quantum waveguide is investigated with an exact calculation. It is treated as a one‐dimensional scattering problem and any width effect is neglected. The method is applied to the quantum modulated transistor and the Aharonov‐Bohm ring. The overall transmission of the structure is found to be distorted owing to the scattering, the extent of the distortion being not only dependent on the impurity potential strength, but also on the impurity positions. The cutoff frequency of the transistor affected by the scattering is also discussed.
Binding Energy of the Excitonic Ions X− and X in a Weak Electric Field
Authors: Katih M. , Diouri J. , Feddi E. 
Published: July 2007

AbstractThe effect of a uniform and weak electric field on the ground state of the excitonic ions X− and X is calculated using a variational method. The calculation is given for Γ direct gap materials in the framework of an isotropic effective mass approximation with no account of spin and band degeneracy effects. The binding energy of X− and X complexes, as a function of the mass ratio parameter m*e/m*h and the field strength F, is presented.
Electronic Structure of Ordered and Disordered HfRh Alloys
Authors: Jezierski A. , Podgorniak J. 
Published: July 2007

AbstractThe electronic structure of HfRh ordered and disordered alloys is studied by the LMTO and TBLMTO‐CPA methods. The superconducting phase transition temperature is estimated from the band structure calculations. The influence of the short‐range ordering on the electronic structure of HfRh alloys is examined.
Free Magnetic Polarons in Three, Quasi‐Two, and Quasi‐One Dimensions
Authors: Benoit À La Guillaume C. 
Published: July 2007

AbstractThe stability of free magnetic polarons (FMP) is studied as a function of dimensionality in the mean‐field approximation. The non‐linear Schrödinger equation is solved numerically in a self‐consistent manner. Realistic properties of the magnetic medium (here diluted magnetic semiconductors) are included. Hole FMP stability in quantum wells or quantum wires with finite barrier is treated, the magnetic medium being either in the barrier or in the well (or wire). Qualitative extension to exciton FMP is given: the stability of exciton FMP in CdMnTe/CdTe/CdMnTe quantum wells seems unlikely.
Vibrational Mechanics and Binding Energies of Some Rare Earth H. C. P. Metals
Authors: Saxena K. C. , Rathore R. P. S. 
Published: July 2007

AbstractA theoretical study comprising the ion–ion and electron‐ion interactions to predict the phonon dispersion and binding energies in h. c. p. metals like holmium (Ho) and terbium (Tb) is developed. The former interactions are taken care of by the modified generalized exponential potential bearing only two parameters and capable of expressing interactions among any number of ions. The Krebs scheme, combined with the adequate dielectric screening, is employed to describe the latter interactions. The reliable and precise model so developed predicts the binding energies and phonon dispersion in the said metals in a direct and simple manner.
Hopping Mechanism of Hole Transport in SiO2 at Cryogenic Temperatures
Authors: Bolotov V. V. , Vishnyakov A. V. 
Published: July 2007

AbstractOn the basis of the small polaron conductivity conception the hole transport between localized states at cryogenic temperatures in SiO2 is analyzed. The phonon‐hole coupling constant is determined. It is shown that the hopping probability increases exponentially with increasing energy difference ΔE between the initial and final states up to ΔE = 2.5 eV and then rapidly drops. It is shown that both field and time dependencies of the hole transport can be explained by the proposed model.
New Spin‐Reorientation Transition in Irradiated Single Crystal Hematite
Authors: Donbaev K. M. , Zhetbaev A. K. , Mukusheva M. K. 
Published: July 2007

AbstractIt is experimentally observed that irradiation of single crystal hematite Fe2O3 leads to a decrease of the Morin spin‐reorientation transition temperature and to the apperance of a reverse transition, i. e. to recovery of a weakly ferromagnetic phase at very low temperatures. Parameters of the new transition depend on the type and energy of particles. The possible reasons for the new transition and the formation mechanism of the disordered zones produced by atom‐atom collision cascades are discussed. The splitting of the Mössbauer spectra in the temperature interval of the new transition undoubtedly shows that it is a first‐order transition.
The Observation of a New D‐Absorption Band in KBr–In Crystals
Authors: Plavina I. , Popov A. I. 
Published: July 2007

AbstractExcitation spectra of the activator luminescence directly excited by UV light and creation spectra of the photostimulated luminescence are investigated for KBr‐In crystals with different In+ concentrations. It is shown that the electronic states responsible for these two kinds of luminescence differ. Careful analysis of the excitation spectra allow us to find a new D‐absorption band having Gaussian shape with the following parameters: peak position at E0 = 6.375 eV and halfwidth ΔE = 0.14 eV. The oscillator strength f = 0.12 of the D‐band is also determined.
Quantum Beat Signals and Mössbauer Spectra with Recoil‐Free γ‐Rays Scattered by an Oscillating Quartz Crystal
Authors: Kuhn D. , Jex H. 
Published: July 2007

AbstractThe elastic and inclastic scattering from piezoelectrically excited X‐cut quartz crystals is investigated with γ‐diffractometry from the (1120) Bragg planes using a 57Co Mössbauer source and a resonance absorber. The investigation is performed in the energy coordinate by means of Doppler motion of the source and in the time domain by means of the quantum beat technique. Examples of γ‐Brillouin spectra from the energy analysis and quantum beat signals of the quartz vibrations with frequencies even below the radiation width are presented.
Some Correlation between Exciton–Phonon Coupling Function and Phonon Damping
Authors: Grigorchuk N. I. 
Published: July 2007

AbstractFor isotropic systems the direct correlation between the exciton or polariton damping function Γ (v) and the coupling function ϕ (q) in a general form is obtained for the cases of their interaction both with longitudinal optical (LO) and longitudinal acoustic (LA) phonons. On the basis of such calculations it is shown how from the known Γ(v) dependence one can judge on the explicit ϕ(q) form.
Spin Waves in Superlattices with Exchange Coupling between Nearest and Next‐Nearest Neighbours
Authors: Barnaś J. , Hillebrands B. 
Published: July 2007

AbstractThe spin‐wave spectrum of infinite ferromagnetic superlattices composed of two b. c. c. materials with exchange coupling between nearest and next‐nearest neighbours is analysed theoretically in the exchange‐dominated region. The appropriate dispersion equations are derived by the transfer matrix method. Some numerical examples are presented for superlattices with (100) interfaces.
The Influence of Local Anharmonism on the Low‐Temperature Heat Conductivity in Disordered Systems
Authors: Salamatov E. I. 
Published: July 2007

AbstractA model of a disordered system containing anharmonic quasi‐local modes is considered. The influence of such local anharmonism on the low‐temperature heat coefficient is analyzed. It is shown that taking into account the local anharmonism results in qualitatively differentT‐dependences of the heat conductivity coefficient for different anharmonic parameters. The results obtained can be used in interpreting some experimental data.
Temperature Dependence of the Vibrational Properties of PbI2
Authors: Julien C. , Mavi H. S. , Chévy A. 
Published: July 2007

AbstractInfrared reflectivity measurements are made from 20 to 600 cm−1 at temperatures ranging from 5 to 575 K for the layered semiconductor PbI2. The reflection spectra are analysed by means of a damped Lorentzian‐oscillator model and the calculated optical properties are presented. The infrared reflectivity of PbI2 shows a broad reststrahlen band, pointing to the significantly ionic character of this compound. Optical properties are compared with those of other layered semiconductors. The optical constants, long‐wavelength optical‐phonon frequencies (both TO and LO), and their half‐widths are obtained as functions of temperature. The temperature dependence is discussed using an anharmonic coupling model with a two‐phonon decay. The general behaviour of anharmonic effects in PbI2 agrees qualitatively with the theory of Maradudin and Fein.
Thermal Expansion Coefficient and Bond Strength in Hg1−xCdxTe and Hg1−xZnxTe
Authors: Bagot D. , Granger R. , Rolland S. 
Published: July 2007

AbstractThe thermal expansion coefficient variations in Hg1−xCdxTe (MCT) and Hg1−xZnxTe (MZT) are analyzed between 4 and 280 K. The phonon density of states (DOS) is modelled with seven Einstein peaks whose weight is adjusted to fit the specific heat variations. The mean Grüneisen coefficient associated with each peak is then deduced from a fit of the experimental linear thermal expansion coefficients. The variation with x of these Grüneisen coefficients allows to compare the bond strengths in MCT and MZT. A better stability of MZT as compared to MCT is deduced.