bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alternative Quasi‐Classical Transport Equations. I. General Formalism for the Inclusion of Wave Functions
Authors: Paasch G. 
Published: July 2007

AbstractThe usual quasi‐classical description of transport processes does not contain directly the influence of wave functions. But the latter becomes important near interfaces. Due to the potential barrier at the semiconductor‐insulator interface the wave functions go to zero there. An expression is derived for transport coefficients which (a) within the local‐density approximation coincides in the bulk material with the standard formula and (b) contains the behaviour of the wave functions near the interface via the averaged local density‐of‐states matrix. The new approximation is discussed for a simple case. Applications and the inclusion of diffuse surface scattering will be treated in further papers.
Transport Phenomena of Ferroelectric Solid Solutions (GeTe)1−x((Ag2Te)1−y(Sb2Te3)y)x with y = 0.60, 0 ≦ x ≦ 1 at 300 K
Authors: Christakudis G. Ch. , Plachkova S. K. , Avilov E. S. , Shelimova L. E. , Abrikosov N. Kh. 
Published: July 2007

AbstractThe variation of the transport coefficients at 300 K, Seebeck coefficient (α), specific resistivity or conductivity (ϱ = I/s̀), Hall coefficient (RH), and thermal conductivity (K) with the composition (x) for solid solution (GeTe)1−x((Ag2Te)1−y(Sb2Te3)y)x) with y = 0.60 is investigated. The Hall coefficient decreases, reaches at x = 0.40 the minimal value and increases then up to x = 1, but the variation of the other transport coefficients are monotonous with composition: α and ε increase but K decreases with composition. The results are interpreted qualitatively on the base of the band edge model of GeTe with splitting of the L‐ and ∑‐valleys of the Brillouin zone (BZ) at the ferroelectric Oh–C3v phase transition and the complicated form of the surfaces of constant energy.
Vibrational Spectrum of TlSxSe1–x Solid Solutions
Authors: Allakhverdiev K. R. , Aleshenko U. A. , Bakhyshov N. A. , Vodopyanov L. K. , Gashimzade F. M. , Sardarly R. M. , Shteinshraiber V. Ya. 
Published: July 2007

AbstractThe results of an experimental investigation of infrared reflection and Raman scattering spectra for TlSxSe1–x crystals are presented. The concentration dependence of infrared phonon frequencies on the composition of solid solutions is described by a modification of the isodisplacement model. The equations of motion in the model are written for a symmetrized displacement of the atoms. The results of the numerical estimations performed in the framework of this model are in good agreement with the experimental data on infrared reflection of TlSxSe1–x solid solutions (where 0 ≦ x ≦ 1). The values of the force constants and effective charges are derived from the best fitting of the estimated curves with those obtained experimentally.
Crystalline Properties of Alkali Halides Using the Generalized Huggins‐Mayer Potentials
Authors: Gupta R. K. , Shiromany A. , Bakhshi P. S. , Shanker J. 
Published: July 2007

AbstractThe crystalline properties of sixteen alkali halides of NaCl type are calculated using the generalized Huggins‐Mayer form of the Born model for an ionic solid. Values of potential parameters calculated from recent thermodynamic data and new van der Waals coefficients are used. The pressure dependence of bulk modulus, Grüneisen parameter, Anderson parameters, thermal expansion coefficient, volume derivatives of the Grüneisen parameter are calculated, and compared with experimental data. The present investigation is superior to other previous studies in respect of taking consistent account of the thermodynamic contribution in determining potential parameters.
On the Electronic Structure of Clusters. Convergence to the Solid State Properties
Authors: Skála L. 
Published: July 2007

AbstractThe relation of the electronic structure of clusters and solids, the consequences of the surface relaxation, and the conclusions following from the analytic cluster model and numerical calculations are investigated. It is shown that the electronic properties of clusters converge with increasing number of atoms at least as quickly as 1/N1/d to zero, N being the total number of atoms and d the number of dimensions of the cluster (d = 1, 2, 3). The binding energy is characterized by 1/N1/d convergence while the bandwidth, the lower band edge, and the bond order converge as the second power of this parameter.
Transition Region Effect in the SiO2–SiOx–Si System on the Si Two‐Dimensional Electron Gas
Authors: Ye Qiu‐Yi , Wang Zhi‐Chekg 
Published: July 2007

AbstractThe energy levels of the Si two‐dimensional electron gas (2 DEG) subband is theoretically investigated, considering a graded composition in a transition region of the SiO2–SiOx–Si system. An expression is found of an effective atomic potential of the transition, varying continually along the space coordinate, and variational calculations are performed with trial wave functions to obtain the subband energy of the 2 DEG. The theoretical results coincide satisfactorily with some known FIR experimental results about Si‐2DEG. It is shown that the properties of the Si‐2DEG are quite sensitive to the transition and, further, that if the transition width is above a certain critical value, there is no 2DEG in the SiO2–SiOx–Si system.
Electron Spin Resonance Study of Fe+ Centers in NaCl:Fe++ and Motion of the Associated Vacancies
Authors: Yang B. R. , Bouwen A. , Schoemaker D. 
Published: July 2007

AbstractX‐irradiation at 77 K of a NaCl:Fe++ crystal produces orthorhombic and axial Fe+ ESR spectra of comparable intensities. The corresponding Fe+ (ortho) and Fe+ (tetra) centers are identified with, respectively, a substitutional Fe+ perturbed by a nearest and a next nearest cation vacancy. At 170 K the cation vacancy of Fe+ (ortho) jumps to the next nearest neighbour position enhancing the Fe+ (tetra) intensity. Above 215 K the vacancy moves away completely and the unperturbed Fe+ (cubic) is formed. It is concluded from this study that before X‐irradiation Fe++ perturbed by either nearest or next nearest cation vacancies occur in roughly comparable amounts and that the activation energy for cation vacancy motion in NaCl is 0.72 eV.
A Refinement of the Mollwo‐Ivey Rule for F‐Centres in Alkali Halides
Authors: Maduemezia A. , Vega‐Catalan F. J. 
Published: July 2007

AbstractIt is found that the simple formula , where A = 328, B = 9.3118, and a = 1/x the nearest‐neighbour distance in Bohr radii, is a very good fit for the detailed variation of the F‐centre peak absorption energy, E (in Ryd), with a, for the 16 alkali halides with NaCl structure, excluding CsF. The first term arises from incoherent photon scattering leading to electronic level transitions. The second term is a diffraction term, arising from the coherent scattering of photons from relaxed ionic aggregates around F‐centers separated on the average by distances of the order of optical wavelengths.
Isotopic Impurity Modes and Polariton Dispersion in Li2GeO3 Crystals
Authors: Orel B. , Klanjšek M. , Moiseenko V. , Volnyanskii M. , Le Calvé N. , Pasquier B. , Novak A. 
Published: July 2007

AbstractInfrared reflection and Raman spectra of single crystals of 7Li2GeO3 and 6Li2GeO3 containing 7.42 and 9.10% of 6Li and 7Li, respectively, are measured and the oscillator parameters \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \nu $\end{document}LO, \documentclass{article}\pagestyle{empty}\begin{document}$ \tilde \nu $\end{document}TO, γLO, and γTO determined using the Kurosawa dispersion relation. The experimental attenuated total reflection spectra are in good agreement with the calculated polariton dispersion curves. The resonance type interactions between parent and isotopic impurity deformation modes are interpreted; the behaviour of the corresponding phonons depends on their symmetry species.
Soft Mode Spectroscopy in Potassium Dihydrogen Phosphate
Authors: Brehat F. , Wyncke B. 
Published: July 2007

AbstractThe infrared reflectivity spectra polarized along the c‐axis of potassium dihydrogen phosphate are studied for both, the ferro‐ and paraelectric phase, over a wide temperature range: 10 to 420 K. The reflectivity spectra are fitted to the factorized form of the dielectric function. The temperature dependence of the optical mode parameters: frequencies, damping, and oscillator strengths are reported for both the phases. The analysis shows that besides the soft mode, a relaxational process of the very low‐frequency region plays an important role near the phase‐transition temperature.
Two‐State Mean‐Field Theory of Reentrant Phase Transitions
Authors: Kventsel G. F. , Katriel J. 
Published: July 2007

AbstractA generalized mean‐field theory allowing for the possibility of the microscopic constituents to be in two different internal states with an ordering interaction in each one of them, is formulated. The explicit criterion of reentrance is established and a corresponding Landau theory is presented. A two‐state extension of McMillan's model is discussed, exhibiting a large variety of sequences involving reentrant nematic, smectic, and isotropic phases. Some of these sequences, such as I → N → S → rN → rS → rI, have not yet been observed experimentally.
Magnetic Properties of the Transition Metals in a Superconductor
Authors: Bortel K. 
Published: July 2007

AbstractThe superconductivity as a sensitive probe of the magnetic properties of transition metals is investigated. A theory of magnetic impurities in a superconductor is presented within the Nagaoka‐Suhl approximation (with the double renormalization of energy parameters). Application of Anderson's theory to superconducting host metals permits to determine the relation of the interactions responsibles for magnetic properties of transition metals.
Mössbauer Studies of the System La1−xSrxCo1−yTiyO3
Authors: Kumar V. , Singru R. M. , Parkash O. , Bahadur D. 
Published: July 2007

AbstractThe system La1−xSrxCo1−yTiyO3 for (a) x = 0 and (b) x = y is investigated through Mössbauer spectroscopy measurements carried out between 77 and 800 K. None of the Mössbauer spectra show hyperfine splitting even at 77 K as Ti4+ substitution restricts the generation of Co+ which is primarily responsible for itinerant electron ferromagnetism in La1−xSrxCoO3. In all the samples, two resonances are observed except in the samples with y = 0.3 and 0.5 in the system (a) where three resonances are observed. Three resonances are assigned to low spin cobalt states (i.e. CoII, CoIII and CoIV), high spin Co3+(t2g4eg2) and high spin Co2+(t2g5eg2) states, the first two being common in all the samples. The variation of the isomer shift and other data with temperature is discussed in the framework of spin‐state and valence‐state equilibria of cobalt ions in these materials. The difference in behaviour between the systems (a) and (b) is explained in terms of generation of different valence and spin states of cobalt with the increase in x and is further compared with the system La1−xSrxCoO3. The susceptibility, electron transport, and other data reported earlier support the results obtained from Mössbauer studies.
The Surface or Interface Polaron in Polar Crystals. II. Strong‐Coupling Limit
Authors: Jin‐Sheng Pan 
Published: July 2007

AbstractThe effective Hamiltonian and effective potential are given for the surface strong coupling polaron in polar crystals. Their binding energy and effective mass are also evaluated. When a piece of a polar crystal contacts with a piece of another non‐polar material, and the high frequency dielectric constant ε∞2 of the non‐polar material is larger than that (i.e. ε∞1) of the polar crystal, or is larger than a certain critical value (ε∞2)min, polarons can exist in the interface. Reversely, when ε∞2 < (ε∞2)min, the polaron is not able to exist near the interface. If the non‐polar material is metallic (i.e. ε∞2 = ∞), there is a deeper potential well near the interface in which the polaron may be trapped.
Influence of Collisions on the Resonances in Bounded Semiconductor Plasmas
Authors: Nikolov N. A. , Malinov P. N. , Kostov K. G. , Mihailova G. V. 
Published: July 2007

AbstractThe influence of the collisions on the resonances in a bounded non‐isothermal semiconductor plasma in a magnetic field is considered on the basis of the two‐component magnetohydrodynamics. The semiconductor plasma is placed between two metal electrodes. The external magnetic field is perpendicular to the exciting ac electric field. The frequencies of the excited resonances of “hole sound”‐type are found. The results can also be used in the absence of a magnetic field. They can also be applied for a bounded gaseous plasma. When the collision frequencies are neglected, and without magnetic field, the formulae derived coincide with the well‐known resonance formulae, published previously.
Short‐ and Long‐Range Ordering in Binary Alloys
Authors: Dąbrowski L. 
Published: July 2007

AbstractStarting from a pair interaction model a generalized theory of ordered binary alloys is derived. Such approach is applicable for arbitrary alloy structures with any given number of long‐ and short‐range parameters and also for all possible numbers of interaction potentials and component concentrations. On the base of pair correlation functions a new definition of short‐range ordering parameters is proposed. Some explicit forms of correlation functions above critical temperature Tc are obtained. The computed results are compared with experimental data for the case of β‐brass. With the accuracy to third‐order perturbation theory, interactions and ordering in 13 coordination shells are considered.
Two‐Phonon Processes in TISe and TlInSe2
Authors: Abdullaev A. G. , Allakhverdiev K. R. , Ibragimov T. D. , Sardarly R. M. 
Published: July 2007

AbstractPolarization measurements of two‐phonon absorption spectra in TISe and TlInSe2, and of the second‐order Raman scattering spectrum in TISe are carried out in the range of overtone and combination frequencies at room temperature. The observed peaks in the absorption and scattering spectra are interpreted by the selection rules for two‐phonon processes obtained for crystals of TISe type (space group D184h). The peaks which cannot be described by the phonon combination from the centre of the Brillouin zone, are successfully interpreted by selection rules involving the phonons from T and N points of the Brillouin zone.
Phonon‐Polaritons in Bilayer Systems s‐Polarized Guided Wave Phonon‐Polaritons
Authors: Wendler L. 
Published: July 2007

AbstractIn a bilayer system consisting of two dielectric media with local, frequency dependent dielectric functions in addition to p‐polarized phonon‐polaritons, s‐polarized phonon‐polaritons can exist. These phonon‐polaritons are associated with electromagnetic fields having standing wave character in one or in both layers in the direction normal to the surfaces. Therefore, they are guided wave phonon‐polaritons. The regions in the ω − k∥ plane where these phonon‐polaritons can exist are discussed and their principle physical properties derived. The dispersion curves and the electric fields of the s‐polarized guided wave phonon‐polaritons are calculated and presented in graphical form. The results of the developed theory of p‐ and s‐polarized polaritons in bilayer systems are discussed.
Ferromagnetism and Elementary Excitations in the Hubbard Model
Authors: Nikolaev M. Yu. , Ryzhanova N. V. , Vedyaev A. V. , Zubritskii S. M. 
Published: July 2007

AbstractTwo pecularities of diagram technique for Hubbard operators are established. Fermi‐type excitations for the Hubbard model with strong Coulomb repulsion are investigated with the help of this technique. The cause of ferromagnetism in the Hubbard model is discovered. Bose‐type elementary excitations are investigated and the region of existence of ferromagnetic ground state is obtained.
Stimulated Emission Spectra and Valence Band Structure in the Cd3(AsxP1−x)2 System
Authors: Arushanov E. K. , Kulyuk L. L. , Lukyanova L. N. , Nateprov A. N. , Radautsan S. I. , Shtanov A. A. 
Published: July 2007

AbstractRecombination radiation in Cd3(AsxP1−x)2 solid solutions near cadmium phosphide (x ⪅ 0.1) is studied. A complex structure of the stimulated emission spectra in Cd3(AsxP1−x)2 single crystals is detected. It is shown that for Cd3P2 the width of emission spectrum and its position relative to the transmission edge may be adequately described in terms of a direct interband‐transition model. The same model is used to calculate the luminescence Icv1(ω) and the optical transmission Tcv1(ω) in the presence of a small (i.e. up to 5% of the Brillouin zone size) K1 shift between the extrema of the heavy hole valence band V1 and conduction band C. It is shown that at k1 ≠ 0 the dependence Icv1(ω) may have two maxima. The structure of stimulated emission spectra and the reference data on luminescence in Cd3(AsxP1−x)2 single crystals are interpreted taking into account the calculations carried out in this work.
Transient Light‐Induced Gratings Due to Excitons in CdSe
Authors: Rückmann I. , Jarašiūnas K. , Gaubas E. 
Published: July 2007

AbstractTransient light‐induced gratings due to free carriers and excitons are created in CdSe in a medium density range of 1015 to 1017 cm−3 by two coherent intense (ns) IR‐pump beams. Detailed investigations of probe‐beam diffraction due to thin excitonic gratings in the spectral region just below the An = 1 ‐exciton line at 85 K and its dependence on sample temperature and on the excitation level are presented. First‐order diffraction efficiences up to 5% and a nonlinear dependence of diffraction on the excitation level can be observed. For the first time numerical calculations of probe‐beam diffraction due to excitonic phase and amplitude gratings are presented. The comparison with the experiment shows, that the damping of a dense exciton gas increases proportional to the excitation intensity in the case of two‐photon interband excitation, and that the light‐induced absorptive changes Δ due to dense excitons dominate over the dispersive changes Δn in the spectral region under consideration.
Systems of Zero‐Phonon Lines Due to Mn2+ Pairs in ZnS
Authors: Benecke C. , Busse W. , Gumlich H.‐E. , Pohl U. W. 
Published: July 2007

AbstractBy time resolved and site selecting spectroscopy at ZnS doped by 0.5 wt% Mn two systems of zero‐phonon lines are detected, which appear at this concentration in addition to the zero‐phonon lines due to isolated Mn2+ ions. These zero‐phonon lines are ascribed to two independent systems of Mn2+ pairs.
Distorted Flux Lines in Bounded Type II Superconductors
Authors: Shehata L. N. , Saif A. G. 
Published: July 2007

AbstractThe interaction of straight or curved flux lines with the boundaries of a type II superconducting slab, ellipsoid, and sphere is considered. The surface barrier opposing the entry of the vortices into the sample shows to be of different values depending on the place of entry into the sample with iespect to the boundary. The force on different elements of the flux lines is completely determined in terms of the total current density at the position under consideration.
Coordinate Transformations Induced by the Elements of the Permutation‐Inversion Symmetry Group of a Nonrigid Molecular Crystal
Authors: Korolev A. A. , Smirnov V. P. 
Published: July 2007

AbstractSpecial methods of nuclei labelling and of permutation‐inversion symmetry element description in nonrigid molecular crystals are suggested. These methods allow to obtain in a general form the transformation properties of coordinates (vibrational, rotational, and electronic) with respect to the permutation‐inversion elements of the crystal symmetry group. The general approach is illustrated on the example of a nonrigid sodium nitrate crystal.
Metastability and Depinning Threshold in the Random Field Ising Model
Authors: Nattermann T. 
Published: July 2007

AbstractA unified description of the depinning threshold Ec for domain walls in the random field Ising model is given. The coherence length Rc ∼ E of the metastable state is proportional to h−vh, where h is the random field amplitude. For broad walls, the results interpolate between recent findings of Bruinsma and Aeppli (vH = 4/(5 – d)) valid at temperatures T ≪ Th(t) and those of Villain (vH = 2) for Th(t) < T ≪ Tco. Tco is the transition temperature of the pure system and Th(t) ∼ h2(3 – d)/(5 – d)/In t, t denotes the time. For narrow walls vH = 2/(3 – d) is found for T < Th(t), vH = 2 for T > Th(t), Th(t) ∼ h2(2 – d)/(3 – d)/In t and d ≦ 3. For d → 3 an exponential dependence is expected of Rc on h−2. Vacancies are found to be decisive for wall pinning in diluted antiferromagnets in small external fields.
Inverse Spectral Theory and Incommensurate Peierls Phases
Authors: Mertsching J. 
Published: July 2007

AbstractA simple version of the inverse spectral theory for finite‐gap potentials of the Hermitean Zhakarov‐Shabat operator is presented, and the kink and polaron structures in quasi‐one‐dimensional systems with a nearly half‐filled band are discussed in terms of this theory. The gap equation for one kink band in systems with a nearly 1/3‐filled band is solved for special parameters, but no general finite‐gap solution is found in this case.
Electron–LO‐Phonon Interaction near Interfaces. Application to Scattering of Inversion Layer Electrons on SiO2Si Interfaces
Authors: Bechstedt F. , Enderlein R. 
Published: July 2007

AbstractA theory for the electron‐LO‐phonon interaction near semiconductor interfaces is developed. Starting point is the electron self‐energy in the linearly shielded potential approximation which allows to include the interface influence simply by calculating the corresponding screened Coulomb potential. Carrier scattering, screening, and interaction of electrons with longitudinal elementary excitations are treated from a unified point of view. The theory is applied to the scattering of inversion layer electrons in a MOSFET from polar SiO2Si interface phonons. These longitudinal phonons of Fuchs‐Kliewer type are not present in bulk Si. Their polar character is solely due to the polar nature of SiO2. The scattering rate and the zero‐field mobility limited by electron‐interface‐LO‐phonon interaction are calculated and compared with experimental data. It is shown that for high electron concentrations in the inversion channel the new scattering process is a serious rival of other mechanisms.
Optical Properties of the Impurity Intervalley Multiplet in Ge‐Type Semiconductors in Uniform Constant Electric Field
Authors: Savvnikh S. K. 
Published: July 2007

AbstractThe electric dipole transitions between states of the intervalley donor multiplet in Ge‐type semiconductors placed in an external constant electric field are considered. The assumption that a short range component of the impurity potential plays a dominant role is used in the calculations. For transitions of different types expressions for the oscillator strengths, describing their field and angle dependences, are derived.
AC Conductivity of Highly Inhomogeneous Semiconductors
Authors: Chaikovskii I. A. , Shmelev G. M. , German A. I. 
Published: July 2007

AbstractThe ac absorption constant of an inhomogeneous semiconductor is calculated without any assumptions of electron density fluctuations to be small. A generalized Herring's method is used for calculating the effective conductivity. The method leads to a closed formula in the case of a heterogeneous two‐phase system. The presence of a maximum in the frequency dependence of absorption is explained and its connection with the system parameters is determined.