bluuebunny/crossref_metadata_2025_split huggingface dataset:
Secondary emission of excitons in CuCl polycrystals
Authors: Mashchenko V. E. , Kharsik V. F. , Brezhneva S. V. 
Published: July 2007

AbstractSecondary emission (SE) spectra of CuCl platelets and quenched bulk polycrystals, grown from a solution at 4.5 to 200 K, are studied. The low‐temperature SE spectra are caused by the radiative decay of free and bound excitons of the Γ6—Γ8 series. The SE at T ∼ 77 K is due to the annihilation of free excitons of the Z3(Γ6—Γ8) series. The growth of excitation gives rise to considerable increasing the phonon replica intensity (Z3−2LO), which is dominating in a spectrum within the range of excitation rates from 1027 to 1030 cm−3 s−1, when the emission appears to be stimulated one. The translational mass of excitons and the reduced mass of a hole (3.4m0 and 2.9 to 3.0 m0, respectively) are calculated from the line approximation by a Maxwellian contour. The increase of the exciton—phonon coupling constant when introducing imperfections is found experimentally, and the new data obtained are discussed.
Computed X‐ray emission spectra for rhodium under high pressure
Authors: Petrů J. 
Published: July 2007

Abstract“Ab initio” calculations of the shapes of the X‐ray emission L‐spectra for f.c.c. rhodium are described for ambient pressures up to 65 GPa. The calculations are based on a self‐consistent density‐functional single‐particle electronic structure recently determined by the quadratic‐augmented‐plane‐wave method.
Energy gap, effective mass, and critical phenomena in NaNO2 crystal
Authors: El‐Dib A. M. , Hassan H. F. 
Published: July 2007

AbstractThe effect of thermal expansion on the energy gap of NaNO2 is studied. An attempt is made to estimate the effect of thermal vibrations on the energy gap. The temperature dependence of the effective mass in the conduction and valence bands is also studied. The energy gap shows a non‐linearity near the phase transition region. A sudden change is also observed at about 3 K above Tc. Both the effective masses show some oscillations in a wide range of temperature (from ∼ 140 to ∼220 °C). The results of the energy gap and the effective mass give evidence that a new phase transition exists at about 3 K above Tc. They also give an interpretation for the deviation of the dielectric constant from the Curie‐Weiss law.
Self‐consistent calculation of the electronic structure of n‐inversion layers adjacent to the grain boundary in InSb bicrystals
Authors: Gobsch G. , Paasch G. , Übensee H. 
Published: July 2007

AbstractSelf‐consistent calculations on the quantized electron inversion layer adjacent to the grain boundary in p‐doped InSb bicrystals are performed for the first time. A simple model of the fixed positive charge in the grain boundary is applied. Within a self‐consistent approximation scheme, taking into account the band non‐parabolicity, the band bending and the carrier concentrations in vicinity of the grain boundary are calculated. In addition, the calculation of the complete two‐dimensional subband structure is performed. The results are discussed for a wide range of the total electron inversion density n□ = 1011 to 5 × 1012 cm−2. In case that n□ > 2 × 1011 cm−2 charge self‐consistency is obtained. The theoretical values are compared with experimental ones taken from literature. The quality of the model and of the approximation scheme is demonstrated.
Electronic Structure of a‐SiHx with Arbitrary Hydrogen Concentration
Authors: Wilke S. , Mašek J. , Velický B. 
Published: July 2007

AbstractThe Bethe‐lattice approach is used to describe the electronic structure of a‐SiHx with arbitrary concentration of hydrogen. This is treated as a ternary alloy containing Si atoms, SiH and SiH2 units interconnected randomly, or clustered. The tight‐binding density of states is calculated for representative examples. Beside widening of the band gap, the local effects due to different hydrogen incorporation are obtained and discussed in terms of different degree of localization of H‐Si bonds.
Coherent four‐photon spectroscopy of two‐photon eesonances of trivalent rare‐earth ions
Authors: Yuguryan L. A. , Makhanek A. G. 
Published: July 2007

AbstractUsing wave functions which are transformed in irreducible representations of corresponding point groups of symmetry, an analysis is carried out of the tensor structure of resonance cubic susceptibility. Polarization characteristics are found of a four‐photon parametric process in the conditions of two‐photon resonance between the components of fine structure of trivalent rare‐earth ions in crystals. The number of independent and nonzero tensor components of resonance cubic susceptibility is determined and their number is shown to be much smaller than it follows from the general features of the crystal symmetry. The signs of resonance cubic susceptibility are calculated for concrete two‐photon transitions.
Diffusion of non‐interacting quantum particles in a disordered system the structure of the density matrix and an effective wave number
Authors: Lenk R. 
Published: July 2007

AbstractWithin the muffin‐tin concept arguments are given to determine the local structure of the incident field density matrix including higher angular momentum channels. The anisotropy of the incident field in a current‐carrying state is formulated. The result is employed to calculate the mean current density within a scatterer and to define an effective wave number, especially for an over dense model. In this way the double role of the scatterers as obstacles and conducting entities is taken into account.
Generalised morse potential for B.C.C. complex metals
Authors: Singh G. , Rathore R. P. S. 
Published: July 2007

AbstractA generalised Morse potential with exponential repulsive and attractive components is analysed to derive numerically (i) the second and third order elastic constants, (ii) the pressure derivatives of the second order elastic constants, and (iii) the neighbour‐wise contributions towards (a) the cohesive energy, (b) the interatomic forces, and (c) the second order elastic constants, in body centered metals like zirconium (Zr), tantalum (Ta), and thallium (Tl). The potential is assumed to extend out to the eight neighbour in these metals and thus involve couplings among 112 atoms.
Hellmann‐Feynman forces on and between jellia
Authors: Lehmann D. , Ziesche P. 
Published: July 2007

AbstractForce and torque on a finite jellium in an external field or near another jellium — defined via changes of the total energy – are according to the Pauli‐Hellmann‐Feynman theorem expressed by the mean electrostatic potential. Force and torque sum rules following from the Ehrenfest theorem and electrostatics are included into the discussion. For cavities similar relations are valid. An example for the interaction of two jellia is the cleavage of a jellium. Special cases are considered. The cleavage force is simply related to the pressure.
Application of molecular models to electronic structure calculations of defects in oxide crystals
Authors: Geisser Christa , Shluger A. 
Published: July 2007

AbstractAb initio and INDO methods are applied to investigate the interaction between several SiO2 molecules and for electronic structure calculations of idealized β‐cristobalite within the framework of the cluster model. Stoichiometric fragments are chosen for simulating perfect and imperfect crystal structures of SiO2 by means of combinations of interacting structural units OSiO. The boundary conditions for such clusters are imposed in the form of the electrostatic fields in the rest of the crystal. The results of the electronic structure calculations are only slightly dependent on size and shape of the chosen clusters and agree quite well with experimental data.
Induced magnetic form factors for 3d transition metals and 3d–3d alloys
Authors: Röll H. , Pabst J. 
Published: July 2007

AbstractIt is proved that band structure calculations are required for the theoretical discussion of neutron scattering on magnetic moments induced in crystalline solids. Band structure calculations are done using a linearized APW version. Potentials for transition‐metal alloys in CsCl structure are determined from atomic HFS densities of 3dn/482 configuration with the exchange potential according to Slater. Band structure calculations are done for ScCo, TiFe, VMn, FeCo, and MnNi.
Exciton absorption spectrum (II)
Authors: Sherman A. V. 
Published: July 2007

AbstractIn a previous paper the method of the exact calculation of the Green's function and the absorption spectrum of an exciton interacting with phonons a t zero temperature has been developed. For the basis served an expansion of the Green's function into a continued fraction. The calculation of a large number of the continued fraction elements confronts one with some computational difficulties. Here an approximate method of calculating these elements is suggested, which is applicable for arbitrary parameters of the Hamiltonian and allows one to verify the obtained results in the framework of a unified approach. By making use of this method the absorption spectra of a Frenkel exciton interacting with nonpolar optical phonons are calculated for different parameter sets. The spectra reveal the features of both, the limiting cases of nearly free, vibronic, and self‐trapped excitons and the intermediate situations. Direct and indirect band edge cases are considered.
Thermally stimulated depolarization measurements in AsO‐doped potassium halides at different heating rates
Authors: Prakash J. 
Published: July 2007

AbstractThermally stimulated depolarization measurements are carried out in AsO‐doped KCl, KBr, and KI lattices at different linear heating rates. It is observed that with the increase in the heating rate, the position of the maximum depolarization current shifts towards higher temperature side alongwith an increase in its peak value. These changes are utilized to evaluate the dielectric relaxtktion parameters. Evaluated parameters are found to be in good agreement with the reported values.
Carrier density in layer structures of microelectronics. A modified local density approximation for semiconductor layers
Authors: Kelber J. , Schnittler Ch. 
Published: July 2007

AbstractRecently the local density approximation (LDA) was modified for taking into account the influence of one interface barrier in the potential. In this paper a more general modification of the LDA is presented including the influence of two potential steps at plane parallel interfaces. It is shown to be a relatively simple and nevertheless accurate method for calculating the carrier density and other electronic properties of semiconductor layers and heterostructures. The validity of the modified LDA is tested for a simple model potential which can be treated exactly by solving Schrödinger's equation. Very good results are obtained for the electron density down to a layer thickness of about 10 nm. First self‐consistent calculations are presented for an n‐AlGaAs‐GaAs superlattice.
Optical absorption in binary semiconductors containing substitutional impurities
Authors: Chetouane K. , Hugel J. , Parlebas J. C. 
Published: July 2007

AbstractThe optical absorption spectrum of binary semiconductors with substitutional impurities is studied in terms of a one‐electron theory. A previous tight‐binding calculation of the imaginary part ε2(ω) of the dielectric constant in a two‐independent‐band insulator is extended to a general hybridized multiband binary semiconductor as well as to interatomic optical excitations. As in the previous simplified model it is shown that it is still possible to explore the critical points of the host band structure through wave‐vector non‐conserving transitions due to the presence of the impurity. In order to visualize that, a numerical calculation is performed in the case of a binary linear chain of atoms containing one substitutional impurity.
Metallic systems containing CEF split impurities
Authors: Ahluwalia P. K. , Sharma K. C. 
Published: July 2007

AbstractThe thermoelectric power Q of dilute magnetic alloys in the presence of both, crystal electric field (CEF) and the external magnetic field H, is investigated for the case of metals containing magnetic impurities with crystal field split energy levels. It is found that the so called ‘anomalous’ thermoelectric power gets modified by H such that the maximum of Q gets shifted towards the lower side, i.e. Tm < 0.3δ, increasing its height for a positive aspherical Coulomb potential. Various limiting cases also suggest the change in the behaviour of Q with temperature and H.
The influence of anharmonicity on the electrical resistivity in TTF‐TCNQ
Authors: Schiller W. , Chilla E. , Aksenov V. 
Published: July 2007

AbstractUsing the method of force‐correlation functions the electrical resistivity is calculated for a system consisting of linear chains with quadratic electron‐phonon interaction above the Peierls‐transition temperature. Calculating the resistivity the theory of anharmonic crystals is applied to evaluate the phonon‐correlation functions. The temperature dependence of the electrical resistivity at constant pressure and at constant volume is calculated. The results are compared with experimenta data for TTF‐TCNQ.
Fluorinated Hydrogenated Amorphous Silicon Alloys. Vibrational Excitations of Chains
Authors: Ghosh B. K. , Agrawal Bal K. 
Published: July 2007

AbstractThe vibrational excitations of the various fluorine hydrogen complexes, and the polysilane‐like conformations in amorphous silicon are studied after employing a valence force field mode1 (VFFM) in a cluster Bethe lattice formulation. The calculated high frequencies are seen to be in excellent agreement with the infrared and Raman data. Some calculated peaks appearing at 214 and near 600 cm−1 have not been detected so far. More experimental measurements on a‐Si : F : H alloys need to be performed especially in the low‐frequency region ≈600 cm−1 to detect the predicted structure.
Electron‐Spin‐Resonance Study of Pb+(l) Centers of the Laser‐Active Structure in KCl and RbCl2)
Authors: Heyndebickx I. , Goovaerts E. , Nistor S. V. , Schoemaker D. 
Published: July 2007

AbstractSeveral Pb+ defects possessing the so‐called laser‐active Pb+(l)‐type structure are examined by ESR in X‐irradiated KCl:PbCl2 and RbCl:PbCl2 crystals. The essential core of these centers consists of a substitutional Pb+ ion associated with a nearest neighbor anion vacancy along a 〈100〉 direction. Small perturbations in the vicinity of this core in the form of a charge compensating cation vacancy or a neighboring Pb2+‐cation vacancy complex generate a large number of Pb+(l)‐type defects, which are similar in KCl and RbCl. Different for both hosts, however, is the influence of oxygen on the production of some centers. In the RbCl crystals the presence of the oxygen ions modifies the structure of one of the defects and induces the production of two supplementary centers, while no effect of the O2− ions is observed on the Pb+(1)‐type defects in KCl crystals.
Formation and Migration Energies of an Interstitial Atom in Si and Ge
Authors: Soma T. , Matsuoka T. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractThe formation and migration energies of an interstitial atom in Si and Ge are investigated using the perturbational formalism and the local Heine‐Abarenkov model potential presented earlier. The interstitial atom is most stable at the tetrahedral site for Si and at the hexagonal site for Ge. The calculated migration energy of the interstitial atom is about 0.4 eV for Si and Ge.
Magnetic Order of Singlet‐Singlet Ions Coupled to Conduction Electrons. Band Structure Effects
Authors: Palermo L. , da Silva X. A. 
Published: July 2007

AbstractThe onset of magnetic order of a system consisting of conduction electrons interacting with localized f‐electrons having only two singlet levels is analysed. The effects of band structure, crystal field and exchange parameters are deduced from a parametric study of the model. It is suggested that the combined role of these effects particularly the shape of energy density of states and number of electrons per band, may be of importance in explaining drastic differences in the magnetic properties of light rare‐earth intermetallics.
Variable Valence of Ce and Pr in Liquid Alloys with Fe, Co, and Ni
Authors: Geld P. V. , Singer V. V. , Radovskii I. Z. , Konovalov S. V. 
Published: July 2007

AbstractThe paramagnetic susceptibility and the electrical resistivity of liquid alloys Ce, Pr‐Fe, Co, Ni are measured and compared with calculations based on Edwards expressions and on the Ziman theory in t‐matrix approximation. In rare‐earth‐rich alloys the valence of Ce and Pr is found to increase monotonously with increasing concentration of the 3d metal. Above a critical concentration the valence remains constant. In this concentration range the 4f electrons of Ce are completely delocalized while Pr is in an intermediate valence state.
Induced Magnetic Form Factors for 3d Transition Metals and 3d‐3d Alloys. II. Induced Spin Form Factors
Authors: Pabst J. , Röll H. 
Published: July 2007

AbstractInduced spin scattering of neutrons on transition metals and transition‐metal alloys is discussed. For a quantitative description of structured stoichiometric alloys, a conception based on atom form factors and spin susceptibilities is proposed. It is shown that spin susceptibilities and form factors of some alloys differ considerably from those of separate constituent atoms. As far as alloys of the chromium group (isoelectronic to chromium) are concerned, this is due to marked destruction of d‐states at the Fermi level. This leads to a reduction of susceptibilties, a rise of sp portions that oscillate more strongly in the form factors and a reduction of enhancement factors. Spin scattering is diminished by one order of magnitude in the alloys. Spin form factors are indicated by their Fourier transforms for all transition metals and alloys calculated.
The Influence of Quantization on the Space‐Charge Layer Capacitance of Si in Strong Accumulation
Authors: Frantsuzov A. A. , Okhonin S. A. , Pogosov A. G. 
Published: July 2007

AbstractA numerical calculation is made of the space‐charge layer characteristics in terms of quantization of carriers. The results are used in processing the experimental capacitance‐voltage characteristics, measured on the MOS‐structures with different oxide thickness. It is shown, that quantization noticeably decreases the space‐charge layer capacitance in strong accumulation.
Zur Theorie des durch das äußere Magnetfeld induzierten Jahn‐Teller‐Effektes in orthorhombischen J = 1‐Paramagneten
Authors: Ulner J. 
Published: July 2007

AbstractEs wird der durch das äußere Magnetfeld induzierte Jahn‐Teller‐Effekt in einem System von paramagnetischen Ionen mit orthorhombischer Symmetrie und dem Gesamtdrehimpuls J = 1 untersucht. Es wird vorausgesetzt, daß die magnetoelastischen Eigenschaften des Systems durch die Wechselwirkung der lokalisierten 4f‐Elektronen mit dem elektrostatischen Kristallfeld bestimmt werden. Mit Hilfe einer Greenfunktionsmethode, die die Eigenschaften des Drehimpulses exakt berücksichtigt, werden die magnetoelastischen Anregungen für bestimmte Richtungen des äußeren Magnetfeldes ermittelt. Es wird die Temperatur‐ und Feldabhängigkeit der Schallgeschwindigkeiten, die mit den elastischen Konstanten c44, c55 und c66 korrespondieren, bestimmt und die sich ergebenden Phasenumwandlungen diskutiert. Darüber hinaus wird die Wechselwirkung der einzelnen elastischen Wellen mit dem magnetischen Untersystem berechnet.
Spin Relaxation in the Presence of Coherent Averaging Pulse Sequences
Authors: Ursu I. , Balibanu F. , Demco D. E. , Bogdan M. 
Published: July 2007

AbstractTheoretical calculations of the effective transversal relaxation time for homo‐ and heteronuclea dipole‐dipole interaction in the presence of the MW, WHH, and MREV sequences are performed in the theoretical frame of Gründer, Schmiedel, and Freude. The relaxation times are calculated as functions of the correlation time of the dipole‐dipole interactions, the time period, and the pulse length. The possibility of selective cancellation of the dipolar relaxation mechanisms by using multiple pulse sequences is discussed.
Exchange Coupling Model in Neutron‐Irradiated Graphite
Authors: Kazumata Y. , Nakano Y. , Yugo S. , Kimura T. 
Published: July 2007

AbstractThe temperature dependence of the ESR spectrum, in pyrolytic graphite irradiated by neutrons is measured from 4 to 300 K. The experimental result is qualitatively explained by the exchange coupling model proposed by Mrozowski. The validity of the model definitely confirms the presence of localized spins in neutron‐irradiated graphite.
Method of Generalized Bethe Lattices in Chemisorption Theory
Authors: Karpushin A. A. , Sorokin A. N. , Semenova I. Yu. , Tomášek M. 
Published: July 2007

AbstractThe method of cluster Bethe lattices is generalized and this way of treating surface electronic structure of clean surfaces and surfaces covered by the chemisorbate is further improved. The idea consists in better respecting the coordination of bonds in the crystal. Silicon (111) surface and disordered hydrogen chemisorption on it are used as examples to illustrate the proposed method.
Coexistence of Superconductivity and Sinusoidal (Helical) Magnetic Order
Authors: Schmeltzer D. 
Published: July 2007

AbstractThe free energy of a superconductor in the presence of a sinusoidal (helical) magnetic order is considered. The method of projection is used to diagonalyze the electronic Hamiltonian. The wavelength 2π/Q of the sinusoidal (helical) phase of amplitude M is computed self‐consistently. A reduction of the cooper pair, M2/Q, is found which stabilizes the sinusoidal phase.
Metal‐Insulator Transition in Titanium Disulphide Crystals
Authors: Das B. , Bartwal K. S. , Srivastava O. N. 
Published: July 2007

AbstractA temperature induced metal (M) → insulator (I) transition is investigated which is possibly first of its kind in the titanium rich titanium disulphide crystals confirming to the composition Ti1.17S2. This transition is established by monitoring the temperature dependence of the electrical conductivity and the thermoelectric power. The structural characteristics at room temperature and at high temperatures (≈ 573 K) also are explored through electron diffraction. The M → I transition is believed tooccur due to the increase of disorder which occurs at high temperature where the short range order state of excess Ti atoms in the van der Waals gapgives rise to a highly disordered amorphous like state. This may lead toshifting of the mobility edge from below the Fermi energy to above the Fermienergy, thus leading to the observed M → I transition.
The Effect of Phonon‐Phonon Scattering in the Substrate on Temperature Dynamics of a Phonon Film Injector
Authors: Kazakovtsev D. V. , Levinson Y. B. 
Published: July 2007

AbstractIt is shown how the mode of cooling of the metal film injector of phonons can be determined from the heating pulse energy and duration. It can be of a ballistic, diffusion, or heat conduction character. The film temperature and its cooling time are estimated.
Polarizabilities, Energies, and Pressure Derivatives of Bulk Moduli of Some Rutile‐Type Oxide Crystals
Authors: Islam A. K. M. A. , Islam K. , Islam M. N. , Mortuza G. 
Published: July 2007

AbstractAn analysis of the dipole polarizabilities, cohesive energies, and pressure derivatives of bulk moduli of some rutile‐type oxide crystals is presented. Two interionic potentials, within the framework of the ionic model, are considered and the results obtained are compared with available experimental data and other recent theoretical calculations. A discussion of the controversy over the bonding character of these compounds is included. The suitability of a new interionic potential due to Islam as applied to these systems is also shown.