bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bistability and hysteresis phenomena in an optical parametric oscillator
Authors: Lugovoi V. N. 
Published: July 2007

AbstractThe optical parametric oscillator involving the analogue of the inverse Čerenkov effect is considered for the case when the pumping (with a frequency ωp) consists of two plane waves incident at two different angles onto an optical waveguide (terminated by mirrors). Here, a bistability of the oscillator output emission (with frequencies ωs, ωv satisfying the relation ωs + ωr = ωp) and hysteresis phenomena caused by the bistability are shown to be realized. Also, bistability and hysteresis phenomena are shown to appear in the weaves with the frequency ωp reflected from (transmitted through) the waveguide layer, and in the waves with new frequencies 2ωs, 2ωr which are due to the transformation of the pumping in the waveguide layer.
On the theory of the complex dielectric function of a heavily doped degenerate semiconductor
Authors: Quang Doan Nhat , Esser B. , Keiper R. 
Published: July 2007

AbstractStarting from the Kubo formula the interband part of the complex dielectric function (DF) of a heavily doped degenerate semiconductor is calculated. In the real part of the interband DF a logarithmic singularity is obtained which is smoothed by the random impurity potential into a peak of a finite height. The peak is located at the energy of Burstein‐Moss shift of the imaginary part of the interband DF. The height of the peak is connected with the r.m.s. of the impurity potential fluctuations and particularly an estimate of the impurity concentration might be possible from its measurement.
Ebene Elastostatik anisotroper Medien mit antisymmetrischen Spannungen und ihre Anwendung auf die Theorie des Flußliniengitters
Authors: Eberhardt O. 
Published: July 2007

AbstractWie Kröner gezeigt hat, können die Probleme der ebenen Elastostatik isotroper Medien unter Berücksichtigung antisymmetrischer Spannungen so formuliert werden, daß die Verschiebungen und die Spannungsfunktionen Differentialgleichungen von derselben Form genügen. Es wird gezeigt, daß dies auch im allgemoineren Fall der anisotropen Medien möglich ist. Der Greensche Tensor der Verschiebungen und der Spannungsfunktionen für kubische und rhombische Symmetrie wird angegeben. Als Beispiel für die Verwendung antisymmetrischer Spannungen wird die anisotrope Wechselwirkung des Flußliniengitters mit dem Atomgitter in Supraleitern II. Art betrachtet.
Effect of exchange on the impurity magnetoabsorption in zero‐gap Hg1−kMnkTe mixed crystals
Authors: Bastard G. , Rigaux C. , Couder Y. , Thome H. , Mycielski A. 
Published: July 2007

AbstractNear infrared (ħω>|ϵ0|) and submillimeter magnetotransmission experiments have been performed on zero‐gap Hg1‐kMnkTe alloys (k ≦ 2%). The observation of impurity magnetooptical transitions is crucially dependent on the Mn composition. The experimental results obtained in both the photon energy ranges indicate that the acceptor level is located below the upper valence level bV(−1) for Mn content k ≧ 0.8%.
Raman spectra of lanthanide sesquioxide single crystals with A‐type structure
Authors: Zarembowitch J. , Gouteron J. , Lejus A. M. 
Published: July 2007

AbstractPhonon data are given for La2O3, Pr2O3, and Nd2O3 single crystals. The polarized Raman spectra of Nd2O3 are presented and analysed according to Pauling's structure: D3d3 (P3ml), Z = 1. A factor group analysis leads to the symmetries 2A1g + 2 Eg for the q = O lattice vibrations which give a non zero contribution in the first order Raman scattering. The experimental data are in complete agreement with these previsions. The four Raman active vibrations are shown to be those of Ln2O(II)2 entities within cages of O(I) atoms, O(I) and O(II) lying in D3d and C3v crystal sites, respectively. There are two stretching (A1g + Eg) and two bending (A1g + Eg) modes, the assignments of which are made. A tentative comparison with the oxysulphides Ln2O2S, which have also a P3ml structure, is presented. A linear correlation is found between the Ln‐O(II) stretching mode frequency of the three studied sesquioxides and the c/a ratio of their hexagonal A‐type structure.
A preliminary study of the electronic structure of uranium chalcogenides and pnictides using a relativistic single‐site scattering model
Authors: Mallett C. P. , Weinberger P. 
Published: July 2007

AbstractResonant differential Friedel summands for uranium monopnictides and monochalcogenides are calculated using a fully relativistic single‐site scattering model. It is found that relativistic effects are important in discussing the electronic structure of these compounds, especially for those with heavy non‐metal atoms. The bonding between the uranium and non‐metal constituents is predicted to have considerable covalent character, which increases with atomic number and is particularly important for the heavier group Vb elements. The calculations indicate that the uranium f‐electrons form a narrow well‐localized band.
Raman spectra and the structure of rutile at high pressures
Authors: Hara Y. , Nicol M. 
Published: July 2007

AbstractRaman spectra of rutile crystals under hydrostatic pressures to 80 kbar and non‐hydrostatic stresses to 155 kbar are reported. Spectral changes near 35 kbar, previously interpreted in terms of a transformation to TiO2 II, are shown to represent an intermediate case between the spectra of a very anharmonic material at low pressures and a relatively harmonic material at pressures greater than 50 kbar.
Local and resonance vibrations in defect polymer solids
Authors: Loghinov A. P. 
Published: July 2007

AbstractThe problem of local and resonance vibrational frequencies in a chain with a large number of degrees of freedom in a unit cell is studied. Repeat unit normal coordinates (RUNC's) are suggested as the most convenient representation for the numerical solution of this problem. The formulas obtained are applied to the calculation of local and resonance vibrational frequencies in a polyethylene chain with a single deuterized unit.
Phase transitions in two‐sublattice biquadratic systems (S = 3/2)
Authors: Błaszczak E. , Westwański B. 
Published: July 2007

AbstractThe (1/z)0‐ and (1/z)1‐approximations are confronted for (1) dipolar susceptibility in the ferri‐antiquadrupolar limit for the Blume‐Emery‐Griffiths interactions, (2) antiquadrupolar susceptibility in the paramagnetic limit for the purely quadrupolar Blume‐Emery‐Griffiths and Heisenberg biquadratic interactions. The critical temperature in the first case is shown to be different than in the corresponding one‐sublattice situation (ferro‐quadrupolar limit). In the second case the critical temperature is compatible with that arising from (one‐sublattice) quadrupolar susceptibility in the paramagnetic limit.
Magnetoreflectance of exciton‐polaritons in cubic II–VI compounds. II. Semiclassical treatment
Authors: Uihlein Ch. , Feierabend S. 
Published: July 2007

AbstractThe magnetoreflectance of a 2 × 4‐fold degenerate S3/2excition is discussed within the semiclassical approach taking account of spatial dispersion and exchange interaction. The reflectance minimum shows a rigid shift behaviour in the Faraday configuration. The energy shift of the reflectance does not depend on the magnitude of the exchange interaction, which is in contrast to the Zeeman splitting of the pure S3/2‐exciton. It is demonstrated that the adequate analysis of magnetoreflectance allows the determination of Δexch + ΔLT and the g‐value g = −5x̃ — gc/2.
Functional integral approach for a doubly degenerate Hubbard model
Authors: Richter A. , Röpke G. , Goedsche F. 
Published: July 2007

AbstractThe method of the functional integral is applied to a doubly degenerate Hubbard model with arbitrarily filled bands. The relation between the number of electrons per atom n, and the chemical potential μ, the local moments, and the static susceptibilities corresponding to the magnetic, orbital, and charge‐ordered states are studied. At zero temperature a phase diagram is obtained in dependence on the electron concentration n, correlation energy U, intra‐atomic exchange energy I, and half bandwidth Δ. The exchange energy is important for the stability of the ferromagnetic state. Additionally to magnetic long‐range ordering an ordering of the orbital states within the ferromagnetic region is possible.
Single‐site theory of Wannier excitons in disordered semiconductors. I. General considerations
Authors: Fischbeck H. J. , Strehlow R. 
Published: July 2007

AbstractStarting from the general theory of interacting disordered systems a Bethe‐Salpeter equation is derived which describes Wannier excitons in disordered semiconductors. It contains both the Coulomb and the disorder vertex. The former is taken in the static vs approximation whereas the latter is derived from a single‐site approximation. Replacing the Coulomb vertex by an approximate product kernel this equation can be solved. An expression for the imaginary part of the dielectric function is obtained which is accessible to numerical evaluations.
Investigation of the reproducibility of electronic properties in n‐type inverted silicon MOSFET surfaces
Authors: Roos M. , Köhler H. 
Published: July 2007

AbstractThe magneto‐quantum oscillations in the channel resistance as a function of the magnetic field or the gate voltage are used to investigate the reproducibility of the electronic properties in n‐type inverted silicon surface channels depending on the history of the same sample. A model is proposed in order to explain the variable data up to ns ≈︁ 1.5 × 1012 cm−2 for (100) surfaces, where the lowest electric subband edges are less distant than supposed before. The additional assumption of elastic intervalley scattering at low electron concentrations and tunnelling of electrons into traps in the SiO2 near the Si/SiO2 interface allows a thorough discussion of all the properties in the “activated” and “metallic” conduction range. The variable data seem to depend on the density and distribution of trapped electrons deep inside the SiO2.
One‐dimensional ising model with an infinite radius of interaction in a transverse magnetic field. Some thermodynamic properties of the rigorously solvable part
Authors: Georgiev G. I. , Sandalski M. P. 
Published: July 2007

AbstractThe rigorously solvable (quadratic in Fermi creation and annihilation opreators) part of the Hamiltonian of the ID Ising model (S = 1/2) with an infinite radius of interaction is studied in a transversal magnetic field H. After diagonalization of the Hamiltonian, an analytical and numerical investigation is made for the spectrum and some basic thermodynamic quantities at two long‐range interaction laws. The spectrum has some peculiarities; the energy gap vanishes only in the centre of the zone at H = H/cr which leads to singularities in some quantities and is reflected in the phase transition in the model considered. Some dependences of the thermodynamic quantities on H and on the coupling constants are obtained from the numerical data.
Energie dispersive dans les semiconducteurs
Authors: Ance C. 
Published: July 2007

AbstractNous avons analysé pour plusieurs semiconducterus l'énergie dispersive Ed, définie dans le modèle de Wemple et Didomenico, en relation avec les énergies covalentes et ioniques Eh et C. Une courbe continue de l'ionicité est donnée en fonction du rapport de deux énergies EA et EB reliées à Eh et C. Le modèle développé par Afromowitz, à partir des moments optiques, est appliquè au composé ternaire Ga1−xAlxSb. A partir de ces résultats, l'énergie du gap moyen Eg est donnée par Eg = D0M/(ϵ1(0) ‐ 1) où M est la contribution des transitions interbandes au moment optique M0.
Electronic structure and optical properties of AlP, AlAs, and AlSb
Authors: Sarkar R. L. , Chatterjee S. 
Published: July 2007

AbstractThe composite wave variational version of the APW method is used in conjunction with the semiempirical tight‐binding interpolation scheme to obtain the electronic band structure and optical absorption characteristics of the compounds AlP, AlAs, and AlSb. The results show that all these materials are indirect band gap semiconductors. The overall feature of the energy bands and the optical characteristics agree fairly well with existing theoretical and experimental results. The implication of the interpolation parameters is also emphasised.
Infrared studies of lattice vibrations in Bi12GeO20 and Bi12SiO20 crystals
Authors: Wojdowski W. , Łukasiewicz T. , Nazarewicz W. , Żmija J. 
Published: July 2007

AbstractThe reflection spectra of Bi12GeO20 and Bi12SiO20 single crystals are studied in the spectral region 50 to 1000 cm−1 at 90 and 300K. Both the single crystals are found to exhibit several reflection bands which are ascribed to the interaction of electromagnetic radiation with normal modes of F‐symmetry in the central region of the Brillouin zone. The frequencies of the longitudinal (LO) and the transverse (TO) component is calculated from the obtained reflection spectra by the Kramers‐Kronig method. The results are compared with Raman data. In order to verify the applicability of the notion of molecular crystal to the compound studied, the frequencies of the normal modes of the groups GeO4 and SiO4 are calculated and the results are compared with the experimental data obtained in this work.
Phenomenological theory of electromagnetic and sound energy attenuation in many‐domain magnetics
Authors: Mitsek A. I. , Sirota D. I. , Kolmakova N. P. 
Published: July 2007

AbstractThe attenuation of the electromagnetic and sound waves interacting with a transitional domain structure in the neighbourhood of orientational phase transitions of the first‐order type is calculated. It is taken into account that the domain wall displacement under wave action is irreversible, i.e. the magnetoelastic or magnetic hysteresis occurs. It is shown that in the general case contributions of reversible and irreversible domain wall displacements into the wave attentuation are not additive.
Electron spin‐echo (ESE) investigations of critical paramagnetic relaxation anomalies in X‐irradiated triglycine sulphate (TGS:X)
Authors: Völkel G. , Brunner W. , Windsch W. , Steudel D. 
Published: July 2007

AbstractThe relaxation behaviour of a stable free radical in X‐irradiated triglycine sulphate is investigated by means of the electron spin‐echo method in the vicinity of the ferroelectric phase transition. A critical behaviour of the transverse relaxation as well as of the longitudinal relaxation is detected. The critical shortening of the phase memory time TM can be explained by the order parameter fluctuations at the phase transition of TGS. To the contrary the spin–lattice relaxation time T1 critically increases at the phase transition. This unusual behaviour cannot be understood on the basis of a direct interaction with the order parameter fluctuations via direct relaxation processes but points at a coupling of the acoustic lattice modes to the ferroelectric relaxational mode.
Comparison between spontaneous radiation in channelling, coherent bremsstrahlung, and synchrotron radiation
Authors: Greschner O. , Wedell R. 
Published: July 2007

AbstractA detailed comparison is made of the spontaneous radiation in channelling which has been considered recently by Kumakhov, with the coherent bremsstrahlung and the synchrotron radiation. The coherent bremsstrahlung is shown to be suppressed under channelling conditions. It is found that the mechanism of appearance of the Kumakhov radiation differs greatly from that for the coherent bremsstrahlung. The Kumakhov radiation is shown to be more intensive than the synchrotron radiation, especially in the region of high‐energy quanta. It is proposed to set a thin single crystal in the peripheral part of a storage ring in order to obtain intensive fluxes of polarized hard γ‐quanta.
Cluster bethe lattice treatment for phonons in pseudobinary alloy systems
Authors: Kleinert P. 
Published: July 2007

AbstractThe cluster Bethe lattice method is extended to study vibrational properties of pseudobinary alloy systems AB1−cCc. As an example, the phonon density of states and the infrared response function of the alloy system In1−cGacP is calculated. The calculations are in agreement with experimental results. In the approach presented here longitudinal modes do not appear and hence there is not any longitudinal–transversal splitting observed in the first order Raman spectrum.
Disorder‐induced Raman scattering in non‐crystalline films of alkaline‐earth halides
Authors: Harbach F. 
Published: July 2007

AbstractAbove 50 cm−1 the Raman spectrum of quench‐condensed thin films of SrCl2, BaCl2, and BaFCl can be interpreted as a weighted one‐phonon density of states according to the theory of Shuker and Gammon. The weighting emphasizes those normal modes that are related to the Ramanactive F2g mode of the chlorine ions in a fluorite lattice: The maximum of the weighted density of states of non‐crystalline SrCl2 is situated at 180 cm−1, of BaCl2, and BaFCl at 160 cm−1. Above 50 cm−1 the depolarization ratio is approximately frequency independent and fluctuates around 0.5.
Deviations from matthiessen's rule in the low‐temperature resistivity of iron
Authors: Möbius A. , Goedsche F. , Elefant D. , Berthel K.‐H. , Vojta G. 
Published: July 2007

AbstractThe electrical resistivity of iron is measured between 2 and 30 K. The results can be extremely well explained by fitting the data to a simple two‐current model including electron–magnon, electron–phonon, and electron–impurity scattering. Below 10 K large deviations from Matthiessen's rule are observed arising from the two‐current character of the conduction.
Band structure and X‐ray investigation of transition metal aluminides
Authors: Müller Ch. , Wonn H. , Blau W. , Ziesche P. , Krivitskii V. P. 
Published: July 2007

AbstractBand structure and density of states of the transition metal aluminides VAl, CrAl, FeAl, CoAl, and NiAl are calculated using a modified KKR method and compared with various kinds of experimental soft X‐ray spectra. The trends of experimental observed physical properties through the 3d transition metal series are well reflected by the band structure data and turn out to be essentially due to the degree of filling up of the transition metal d‐band by Al p‐electrons. In particular the results are capable of explaining the instability of a homogeneous B2 phase in the case of CrAl.
Photostimulated low‐temperature recombination luminescence in γ‐irradiated KCl:Eu2+ crystals
Authors: Opyrchal H. , Nierzewski K. D. 
Published: July 2007

AbstractA strong, few seconds lasting post‐luminescence due to Eu2+ emission is excited at 15 K by light flashes in KCl:Eu2+ crystals coloured by γ‐rays at RT. Within the range of 15 to 70 K the intensity of post‐luminescence varies in inverse proportion to the time and does not depend on temperature. Thermoluminescence glow curves photostimulated at 15 K point to the existence of several glow peaks most of which are due to the thermal activation of trapped‐hole centres of H‐ and Vk‐type. The plausible mechanisms responsible both for post‐luminescence and thermoluminescence as well as the role of Eu2+ ions are discussed.
Scattering of phonons by density fluctuations and thermal conductivity of amorphous solids
Authors: Joshi Y. P. 
Published: July 2007

AbstractPhonon relaxation time due to the scattering by spatial density fluctuations is studied in amorphous solids. The relaxation time τf is found to vary with frequency ω as ω−4 in the case of phonons with frequencies small compared with ω0, which is a parameter characteristic of the density fluctuations. When ω is large in comparison with ω0, τf is found to vary as ω−2, and thus it undergoes a transition from a strong to a comparatively weak frequency dependence as ω increases and crosses ω0. It is discussed that the thermal conductivity of a typical amorphous solid can be explained in terms of the scattering by low lying tunnelling states and scattering by fluctuations in density and elasticity. The plateau in conductivity is interpreted as defining a temperature region where the former scattering mechanism with its comparatively weaker frequency dependence starts losing dominance over the latter. Finally the conductivity of vitreous silica is analysed, obtaining a good agreement between theoretical and experimental results.
Energy spectrum, magnetization, and critical field of the uniaxial two‐sublattice ferrimagnet by the Green function method
Authors: Kazakov A. A. , Litvinenko N. A. 
Published: July 2007

AbstractThe energy spectrum and the magnetization of an uniaxial two‐sublattice ferrimagnet in all intervals of fields and temperatures are calculated by the method of two times Green temperature functions both, in easy and hard directions. It is shown that the long‐wave spectrum of elementary excitations can “oscillate” depending on the value of the external magnetic field. It leads to the fact that in the region of critical fields and low temperatures the magnetization of system follows the simple power law T2 in the plane and T3/2 along the axis independently from the type of ferrimagnet anisotropy.
Excitation of magnetoacoustic surface waves by Bloch walls
Authors: Mitin A. V. , Tarasov V. A. 
Published: July 2007

AbstractThe possibility of excitation of magnetoacoustic surface waves by an rf field on Bloch domain walls is considered. The investigation indicates that dispersive and nondispersive surface waves may be generated. The resonance frequency of magnetic moment vibrations in a Bloch wall near specimen surface is received. When the rf field lies in the easy axis of magnetization the magnetoacoustic surface waves are excited actually in one side. The consideration is restricted to the case of dilute YIG for simplicity.
Electron–hole liquid in GaP the influence of the isoelectronic impurity nitrogen
Authors: Schwabe R. , Thuselt F. , Weinert H. , Bindemann R. 
Published: July 2007

AbstractThe radiative recombination of isoelectronic (nitrogen)‐doped GaP is investigated at high optical excitations and low temperatures (T = 2 K). Extensive experimental results on the luminescence in dependence on the excitation intensity, the nitrogen concentration (NN) and its decay behaviour are presented. At low nitrogen concentrations (NN ≦ 1017 cm−3) and highest excitation levels the radiative recombination from an electron–hole liquid (EHL) accompanied by momentum conserving phonons analogous to undoped GaP can be confirmed. At higher nitrogen concentrations in the range of NN = 3 8 × 1017 cm−3 a radiative no‐phonon transition appears from an EHL induced by the isoelectronic impurity nitrogen. The influence of the latter on the energy of the EHL is studied. The rising nitrogen density yields an increase in the EHL work function. At medium and high nitrogen concentrations (NN ≦ 1018 cm−3) a further up to now unknown luminescence band becomes visible arising from the radiative recombination of a “plasma‐like” phase which is strongl influenced by the isoelectronic impurity nitrogen and coexists with the EHL. Its density (np1) depends on the nitrogen concentration. The use of a simplified model basing on the polarization energy of the carriers caused by the short‐range isoelectronic potential enables the understanding of the experimental findings.
Experimental evidence for piezoelectrical free‐carrier scattering by screw dislocations in tellurium
Authors: Estienne J. P. , Farvacque J. L. 
Published: July 2007

AbstractHall effect and conductivity measurements are performed, in the case of tellurium, on samples containing a high density of a screw dislocations and on reference samples. Comparison of these measurements shows that a screw dislocations are responsible for a strong free carrier mobility decrease. A discussion of the results, based on theoretical calculations of the free carrier mobility permits to conclude to a piezoelectric scattering mechanism.