bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fluctuation‐induced broadening of exciton reflection spectra in AII BVI solid solutions
Authors: Ablyazov N. N. , Akeshkin A. G. , Melekhin V. G. , Suslina L. G. , Fedobov D. L. 
Published: July 2007

AbstractThe validity of different fluctuation models for an explanation of the concentration dependence of exciton reflection line broadening in AIIBVI solid solutions is discussed on the example of ZnxCd1—xS, ZnxCd1—xTe, and ZnSxSe1—x systems. It is shown that the concentration dependence can be explained with the help of models describing the interaction of excitons with largescale fluctuations of solid solution composition. At small concentrations of one component of solid solution the model of localization of the exciton as a whole by a fluctuation potential can be used. In the range of comparable concentrations of components there can be applied models accounting for the interaction of only the hole, or only the electron with the fluctuation potential, depending on whether there is anion or cation substitution.
The influence of uniaxial strain on the band to band recombination in Pb1‐xSnxTe
Authors: Genzow D. , Mocker M. , Normantas E. 
Published: July 2007

AbstractThe theory of radiative and Auger‐recombination in multivalley semiconductors with nondegenerate valleys is developed. The lifetime of excess carriers is enhanced because of repopulation of the energy valleys. The theory is applied to Pb1‐xSnxTe where uniaxial strain in (lll)‐direction removes the star‐degeneracy of the L‐point valleys. Lifetime enhancements of more than two orders of magnitude at 10 K are possible.
Anomalous asymmetries in X‐ray π‐modes near n‐beam interactions
Authors: Juretschke H. J. 
Published: July 2007

AbstractGeneral conditions are established for the asymmetries in the shoulders of multiple interaction peaks in Renninger scans to be of opposite sense for σ‐ and π‐polarizations. The method is applied to identify all possible anomalous asymmetries in Ge for CuKα radiation. Several specific cases are worked out in detail to contrast scans for the two polarizations, and to compare their contributions to reflections observed for unpolarized incident radiation. Excellent agreement is found between experiment and theory in the neighborhood of the prominent anomalous asymmetry of Ge 222/131. The two polarizations give strikingly different scans, but neither here, nor in the other cases examined, is the anomalous asymmetry of the π‐mode sufficiently strong to change the direction of the asymmetry observed with unpolarized incident radiation.
Phase shift functions in rare‐earth ternary compounds
Authors: Ghatikar M. N. 
Published: July 2007

AbstractThe empirical phase shifts in the extended X‐ray absorption fine structure (EXAFS) are calculated in a series of rare‐earth based ternary compounds. The phase shifts are compared with the experimental phase shifts obtained from the measured EXAFS data in these systems. The dependence of the phase shift function on the atomic number of the back scattering atom is critically examined.
Optical superradiance in pyrene‐doped biphenyl crystals and effect of phonons on its formation
Authors: Naboikin Yu. V. , Andrianov S. N. , Zinoviev P. V. , Malyukin Yu. V. , Rudenko E. N. , Samartsev V. V. , Silaeva N. B. , Sheibut Yu. E. 
Published: July 2007

AbstractFor the first time peculiarities of the formation of Dicke optical superradiance are studied experimentally and theoretically in a pyrene‐doped biphenyl crystal under active phonon effect (the energy level is 1Ag−1B2u; wavelength 373.93 nm; pyrene concentration 0.25 mol%; temperature 1.5 to 4.2 K). The possibilities of this phenomenon to obtain spectroscopic data are demonstrated. The pseudolocalized phonon lifetime τphon and the activation energy ΔE are estimated to ΔE = (7 ± 3) cm−1 and τphon = 2 to 20 ps by the temperature dependence of the superradiance intensity.
Thermodynamic properties and the equation of state of alkali hydride crystals
Authors: Srivastava G. M. S. , Agrawal G. G. , Shanker J. 
Published: July 2007

AbstractRecently developed interionic potentials are used to evaluate some important thermodynamic quantities and the high‐pressure equation of state of alkali hydride crystals. Values of short range overlap repulsive interactions estimated with the help of overlap integrals along with recent values of van der Waals interactions are used in calculations. Values of the Grüneisen parameter and its volume derivative, the Anderson parameters, volume thermal expansion coefficient, and the Debye temperature are calculated and reported. The high‐pressure equation of state for LiH and NaH are investigated using a detailed picture of the interionic potentials.
Nonhomogeneous generalized master equation and nonhomogeneous second‐order integrodifferential equation for the time‐dependent back‐jump effect
Authors: Kutner R. 
Published: July 2007

AbstractEquivalence between the nonhomogeneous generalized master equation and the generalized continuous‐time random walk model, including the time dependent correlations over consecutive jumps of a tagged particle diffusing in a concentrated lattice gas, is established by means of an explicit general relation between the waiting‐time distributions and the memory kernels. It is proved also that for the Bravais nontriangular lattice the self‐correlation function obeys with good approximation the nonhomogeneous second‐order integrodifferential equation. A special example of the waiting‐time distributions, and hence of the memory kernels is also presented; application of the latter in the formalism proposed leads to the higher‐order differential equations, already without the integral kernels.
Small vacancy clusters in H.C.P. metals
Authors: Bisio P. H. , Monti A. M. 
Published: July 2007

AbstractStatic properties of small vacancy clusters are investigated in an h.c.p. lattice by using computer simulation techniques and a short‐range pair interatomic potential representative of magnesium. The defect relaxation volume and the corresponding formation and binding energies and entropies are calculated for 20 clusters of up to seven vacancies. The most closely‐packed clusters are found to have the lowest energies and unlike the f.c.c. structure, only small defect lattice relaxations are observed in every studied case.
Anisotropy in the Shubnikov‐de Haas effect in Hg1−xMnxSe
Authors: Schleijpen H. M. A. , Blom F. A. P. 
Published: July 2007

AbstractAnisotropy in the Shubnikov‐de Haas effect in Hgo.0.975Mn0.025 is studied in fields up to 2 T. The angular dependence of the oscillation period is well described by the modified Pidgeon Brown model (PB), using parameters reported in literature. The anisotropy observed in nodes in the SdH oscillation amplitude cannot be explained by the PB model. A (simple) model shows that the spin splitting of the Landau levels is augmented by an extra splitting due to the lack of inversion symmetry in the zinc blende lattice.
Optical activity of semiconductors with chalcopyrite structure
Authors: Marcinkevičius S. , Babonas G. , Korzun B. V. , Tregub I. G. 
Published: July 2007

AbstractThe spectra of the gyration tensor component g11, are measured at 300 K for CdSiP2, CdSnP2, ZnSiP2, ZnGeP2, and CuInS2, using the polarization modulation technique. The dispersion of g11 is analyzed according to the model of the effective oscillators and the band theory of optical activity. A correlation between the magnitude of the optical activity and the distortion of the characteristic building units of the chalcopyrite structure is found.
Recombination radiation and electroreflection of excitons in ZnxCd1−xSe solid solutions
Authors: Mashchenko V. E. , Ziborov A. I. 
Published: July 2007

AbstractThe simultaneous investigation of electroreflection (ER) and secondary radiation (SR) spectra of ZnxCd1−xSe solid solutions under off‐resonance (resonance) laser excitation at 5 to 300 K reveals the fine structure of the fundamental absorption edge which arises from the direct and indirect creation and annihilation of excitons of series Γ6–Γ8 or Γ7–Γ9 und Γ7–Γ7. The shape of the SR exciton line at low temperatures is determined by the exciton trapping processes at random potential fluctuations of composition. This statistic random potential manifests itself in a blue shift of the SR exciton line with the N2‐laser excitation. The behaviour of the SR exciton line at 77 K is strongly governed by the exciton annihilation processes with the simultaneous emission or absorption of LO phonons. A possible effect of extended and self‐trapped exciton states in SR spectra at high temperature is considered.
An efficient technique for the evaluation of lattice sums in crystal orbital (CO) calculations
Authors: Ramírez R. , Böhm M. C. 
Published: July 2007

AbstractAn approximate approach for the determination of lattice sums is presented in two‐ or three‐dimensional solids within the crystal orbital (CO) formalism as derived in the tight‐binding approximation. The solid is divided into two domain types (I and 11) where the interatomic interaction energies are determined in different degrees of sophistication. The matrix elements of the Fock operator are treated exactly within the (inner) spherical domains of type I. An electrostatic model is employed to calculate the coupling terms to atoms localized in the outer domain 11. In this case only the diagonal elements of the mean‐field Hamiltonian are taken into account. Numerical examples to estimate the convergence properties of this approximation are presented for the graphite layer, diamond, two‐ and three‐dimensional BN in the framework of an improved INDO CO approach.
Indirect forbidden fundamental absorption edge in germanium selenide single crystals
Authors: Elkorashy A. M. 
Published: July 2007

AbstractThe absorption coefficient of GeSe is determined from the measured values of transmissivity and reflectivity. The measurements are carried out with plane polarized light with the plane of polarization parallel to the a‐ and c‐axes which lie in the cleavage plane in the temperature range from room temperature to near liquid nitrogen temperature. Near the fundamental absorption edge the results are fitted to an equation corresponding to an indirect forbidden transition with a single type of phonon engaged in the interband absorption process. The optical energy gap at room temperature is found to be (1.075 ± 0.017) and (1.080 ± 0.016) eV for the a‐ and c‐axes, respectively. The dependence of the energy gap on temperature is linear in the temperature range from 96 to 250 K with a negative temperature coefficient dEg/dT equal to −0.43 and −0.49 meV/K for the a‐ and c‐axis, respectively.
Optical absorption lineshape of R′ centres in alkali halides
Authors: Sati R. , Thakur O. P. , Medeiros e Silva J. 
Published: July 2007

AbstractUsing the method of moments an analytical expression for the R′ optical absorption lineshape is obtained, in quantum approach. No use of the Born‐Oppenheimer approximation is made. The electron‐lattice interaction is taken to be linear. The effects of both, E and A1 modes are considered. It is found that the lineshape calculated using moments up to eighth order is convergent and that the presence of the A1 mode accelerates the convergence. The calculated lineshape is more exact than those reported in the earlier works. It is studied under different conditions of temperatures and coupling strengths. The obtained R′ lineshape in KCl and LiF exhibits all the experimentally observed features.
Effects of a thin transition layer on the dispersion relation of surface polaritons on a randomly rough surface
Authors: Pechstedt R. , Leine L. 
Published: July 2007

AbstractThe dispersion relation of an unretarded surface polariton propagating on a rough surface covered with a thin transition layer is derived. The interfaces are assumed to be completely correlated Numerical calculations of the dispersion relation are performed for an Al substrake with an Al2O3 layer. It is found that the magnitude of the frequency shift in comparison with an analogous smooth system depends on the layer thickness and the correlation length of the roughness. The position of the maximum shift depends on the correlation length only.
Two‐ and Three‐Body Interactions and Phonons in Some F.C.C. Metals
Authors: Singh G. , Rathore R. P. S. 
Published: July 2007

AbstractTwo‐ and three‐body interactions in f.c.c. metals are derived from the general Morse potential. These interactions are employed to develope the dynamical matrix, which involves only three force constants. The dispersion curves for the f.c.c. metals like calcium, strontium, ytterbium, and lanthanum are derived from the elements of the matrix so developed. The predictions show good agreement with the recently measured phonon dispersion in the said metals.
An Analytical Theory of FMR in Bulk Metals (Parallel Configuration). IV. Exchange Dominated Surface Modes
Authors: Fraitová D. 
Published: July 2007

AbstractThe analytical FMR surface impedance formula, calculated in Part III of this paper, is applied to the case of arbitrary large uniaxial surface anisotropy energy Es, the symmetry axis of which points normal to the sample surface. It is shown that the theory for certain values of Es > 0 leads to the excitation of exchange dominated surface spin‐wave modes; the discussion concerns the accuracy of the results and the applicability of the theory to the experiments.
Ideal Magnetization in Sintered Iron Materials
Authors: Posselt M. , Diener G. , Seidel M. 
Published: July 2007

AbstractA previously developed self‐consistent approach to the ideal magnetization in heterogeneous ferromagnetics is specified to the case of statistical isotropy, spherical grains, and a Gaussian distribution of the stochastic field. The results are applied to calculate the law of approach to saturation of sintered steel. For this purpose sintered steel can be considered as a mixture of a ferromagnetic and a non‐ferromagnetic component. The magnetization behaviour of the ferromagnetic component is obtained from experimental data of such steels which do not contain any non‐ferromagnetic constituents. The volume fraction of the non‐ferromagnetic component is usually small, i.e. in the order of 1 to 10%. Expanding the fundamental equations of the self‐consistent method with respect to this volume fraction a simple explicit expression is obtained for the effective magnetization. The comparison of the calculated curves with the experimental data shows a satisfactory agreement.
Intermediate Valence Model of the Hyperfine Field and Relaxation Rate of Cerium in Gadolinium Metal
Authors: Foglio M. E. , Schlottmanst P. 
Published: July 2007

AbstractThe temperature dependence of the hyperfine field of Ce in Gd, measured by Thiel et al. is interpreted within a model that considers a mixed valent Ce ion in the molecular field of the Gd matrix and the hexagonal crystal field. A simple Brillouin‐Wigner perturbation is employed to obtain the magnetization of the Ce ions and a mode‐mode coupling approach for the relaxation rate.
Nonlinear Effects in the Piezoresistivity of p‐Type Silicon
Authors: Lenkkeri J. T. 
Published: July 2007

AbstractPiezoresistivity measurements are carried out on heavily doped ion‐implanted p‐type resistors on the surfaces of cantilever beams cut from a (100) silicon wafer. Tensile and compressive stresses, up to 85 MPa along the [110] direction, are applied by bending the beams with a micrometer. Nonlinear effects are clearly seen in the measurements where the resistor contains sections both parallel and perpendicular to the stress. The results are analyzed in terms of the first‐ and second‐order piezoresistance coefficients. Values of the piezoresistance coefficients are calculated using analytical expressions for the strain dependent energy‐wave vector relations of the valence bands and the known deformation potentials. The results of the calculations are compared with the experimental data including some earlier measurements reported in literature. The calculated values of the first‐order coefficients are found to agree fairly well with the experimental data. The calculated second‐order coefficients are able to describe the observed anisotropy in the nonlinear piezoresistivity of the second order in stress.
A BCS Theory ot Superconductivity in Heavy Fermion Systems
Authors: Bose I. , Jana A. R. , Chatterjee S. 
Published: July 2007

AbstractA superconducting Hamiltonian is considered in which both intraband and interband pairing interactions are included. This Hamiltonian is recast in a form suitable for the study of heavy fermion superconductivity (HFS). The superconducting transition temperature Tc is calculated and some characteristic features of HFS explained. Effects of interband pairing interaction are discussed.
Application of Band Representations of Space Groups in the Theory of Phase Transitions and Point Defects in Crystals
Authors: Evarestov R. A. , Smirnov V. P. 
Published: July 2007

AbstractIt is shown that simple band representations tables can be used to solve the following two problems: 1) to find the irreducible components of the space group representations induced by the irreducible representations of their site symmetry subgroups; 2) to find the irreducible components of the site symmetry group representations subduced by irreducible representations of a space group. The solution of both the problems requires also the induced representation table for the crystallographic point grousp which is given here. The space group D is considered as an example. The simple band representations table for this group is also given. The application of the band representations of space groups in the theory of second‐order phase transitions and in the theory of point defects in crystals is discussed.
Multipole Interaction Effects on Cohesive and Anharmonic Properties of Alkali Cyanide Crystals
Authors: Singh R. K. , Kumar N. , Varshney G. B. 
Published: July 2007

AbstractThe cohesive and anharmonic properties of alkali cyanide crystals are investigated using a three‐body potential consisting of long‐range Coulomb and three‐body interactions, and the short‐range van der Waals attraction and overlap repulsion operative up to the second neighbour ions. The results on cohesive energy, compressibility, molecular force constant, and infrared absorption frequencies are in better agreement with their experimental data than those obtained earlier from a logarithmic potential. An overall systematic trend, followed by the values of third‐and fourth‐order elastic constants and the pressure and temperature derivatives of the second‐order elastic constants, is discussed.
Directional Compton Profiles of CaF2
Authors: Das G. , Padhi H. C. , Aikala O. 
Published: July 2007

Abstract59.54 keV γ‐ray Compton profiles of CaF2 along the [100] and [110] directions are reported. Both, the absolute profiles and their anisotropy are derived from the LCAO model and compared with experiments. One‐dimensional Fourier transforms are determined from both, experimental and theoretical profiles and compared with each other. Theoretical results are found to be in qualitative agreement with the experiments. It is also shown that momentum distributions are more sensitive to anisotropy in electron distributions than X‐ray structure factors.
Theory of Free‐Carrier Infrared Absorption in GaAs
Authors: Klelnert P. , Giehler M. 
Published: July 2007

AbstractFree‐carrier infrared absorption spectra in GaAs are calculated for carrier scattering on ionized impurities and phonons due to Coulomb, Fröhlich, and deformation potential interaction. Starting from the Kubo formula and applying the diagram technique the interactions of electrons with electrons, phonons, and ionized impurities are taken into account in the random phase approximation (RPA). The obtained absorption spectra exhibit coupled plasmon‐phonon peaks which collapse for vanishing electron‐LO phonon interaction. By taking into account only plasmon and screening effects of the electron gas the calculated absorption spectra show plasmon bands in the case of carrier‐ionized impurity scattering and both, a LO phonon emission edge and weak plasmon‐LO phonon combination peaks in the case of carrier‐LO phonon scattering. The scattering of electrons by acoustic phonons is not influenced by plasmons. The dependences of various carrier scattering mechanisms on frequency, temperature, and material parameters are determined for n‐GaAs.
Ising Ferromagnet with Biquadratic Exchange Interaction and Uniaxial Anisotropy
Authors: Iwashita T. , Uryǔ N. 
Published: July 2007

AbstractFor Ising ferromagnets with S = 1, S = 3/2, and S = 2, the magnetization 〈Sz〉 and the Curie temperature TC are calculatded with the use of pair mode lapproximation. Assuming the bilinear and biquadratic exchange interactions (J and J′) between nearest‐neighbouring pair of spins and the uniaxial single‐ionic anisotropy D for each spin, the behaviours of 〈Sz〉 and TC as a function of these exchange parameters and the uniaxial anisotropy parameter are investigated for the Ising spin systems with various values of the spin.
Ionized‐Impurity‐Mediated Free‐Carrier Absorption in n‐GaAs Slabs
Authors: Kleinert P. 
Published: July 2007

AbstractThe theory of impurity‐mediated free‐carrier absorption in n‐GaAs bulk material is extended to quasi‐two‐dimensional structures. The surfaces are treated within the classical infinite‐barrier model and the electron—electron interaction within the random‐phase approximation. Screening due to phonons is also considered. Using temperature‐dependent Green's functions and starting from the Kubo formula a general expression is derived for the free‐carrier absorption coefficient including both bulk and surface contributions. In thick n‐GaAs slabs coupled phonon—plasmon bulk excitations give rise to distinct peaks in the absorption spectrum. These structures are increasingly washed out with decreasing thickness. For comparison impurity‐mediated free‐carrier absorption spectra of non‐interacting electrons have also been calculated. At and below the bulk plasmon frequency the absorption is reduced due to screening. The absorption increases on the other hand with decreasing sample thickness.
Photoluminescence Study of the Gallium Defect Spectrum at ≈ 1.049 ev (Ga2) in Irradiated Silicon
Authors: Schall U. , Thonke K. , Sauer R. 
Published: July 2007

AbstractThe Ga2 spectrum with its no‐phonon transitions at 1.0472 eV (triplet) and 1.0501 eV (singlet) is studied as a function of temperature and in magnetic and uniaxial stress fields. Like in the case of Ga3, this singlet—triplet pair exciton emission is accompanied by thermalizing higher energy singlet lines s (+2.9 meV), s* (+3.8 meV), and s** (+4.7 meV). Localized vibrational mode replicas of the triplet/singlet are observed with ħω = 11.0 meV and ħω = 18.8 meV, along with lattice modes and combination lines. Zeeman measurements indicate that the center belongs to the rhombic I (C2v) point group symmetry, and the triplet transition splits as gx = 2.7, gy = 2.1, and gz = 1.6. The effective g‐value of the exciton, geff = 2.13, is consistent with thermal data suggesting the hole to be the tightly bound particle (≈100 meV) whereas the electron is bound by only ≈23 meV. Uniaxial stress measurements can be explained in terms of valley—orbit interactions by the weakly bound “pseudo‐donor” electron. Finally, the gallium related centers Ga 1, Ga2, and Ga3 are compared.
Photon Recycling in Double Heterostructures. I. The Case of Perfect Optical Confinement
Authors: Enders P. 
Published: July 2007

AbstractThe influence of photon recycling onto the minority carrier distribution in double heterostructures is investigated. For perfect optical confinement of the luminescence radiation, the corresponding integro‐differential equation (without drift term) is solved exactly. The enlargement of the radiative lifetime, as measured in photoluminescence experiments, is calculated for various forms of the absorption coefficients, appropriate for band‐to‐band processes in direct‐gap semiconductors.