bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simple Exciton in Intermediate Magnetic Field Application to Cdx−1MnxTe Mixed Crystals
Authors: Twardowski A. , Ginter J. 
Published: July 2007

AbstractThe energy levels, both discrete and resonant of a simple, anisotropic exciton in external magnetic field are calculated. Obtained results are used to describe excitonic spectra of CdMnTe mixed crystals reported earlier, for which giant spin splittings offer on exceptional possibility to observe simple excitons.
Localization in a Random System of N Coupled Chains I. Microscopic Model, General Scheme
Authors: Weller W. , Prigodin V. N. , Firsov Yu. A. 
Published: July 2007

AbstractOn the basis of a microscopic model describing the motion of an electron under the influence of a weak random potential in a system of N weakly coupled chains localization of all eigenstates for finite N is proved. Using Berezinskii's idea of ordering the diagrams along the chain the diagram analysis for this system with N states in each cross section and an effective method for treating this N2‐variable problem are developed. The localization length is shown to be equal to Nl2 (l2 mean free path for backward scattering at one chain). In the limit N → ∞ diffusion is obtained for d = 3.
The Excitation Map of Surface Barrier Resonances I. The Excitation Map for Ni(001) in the (10) Azimuth
Authors: Solbrig H. 
Published: July 2007

AbstractA map of ∣det (I – RphS+−)∣ as a function of the energy E and the surface‐parallel momentum k∥ is called an excitation map (Rph substrate reflection matrix, S+− matrix of inner reflection by the barrier). The information content of such an excitation map is analyzed. An example is given (Ni(001), (10) azimuth) and discussed with emphasize on the ground resonance which yields most of the information on the saturation of the barrier potential.
Infrared Spectra of NiO Microcrystals at High Temperatures
Authors: Mochizuki S. 
Published: July 2007

AbstractThe infrared spectra of NiO microcrystals are measured at various temperatures from 300 to 1273 K in the spectral region from 250 to 700 cm−1 by the thermal‐emission and reflection methods. The results are discussed in the light of the theory of anharmonic crystals. The anharmonic phonon frequency shift of the microscrystals is seen to be larger than that of the infinite single crystal.
Cluster Calculations of Alkaline‐Earth Fluorides by the MSXα Method
Authors: Bielschowsky C. E. , Maffeo B. 
Published: July 2007

AbstractThe MSXα method is employed to calculate the electronic structure of clusters representing CaF2, SrF2, and BaF2 perfect crystals. Interband energy intervals are calculated and compared with experimental data, when two different boundary conditions are employed. It is shown that the commonly used “Watson model” produces results in systematically poorer agreement with experiment.
Secondary Electron Radiation from Different Targets Exposed to Photons with Energy 0.1 to 3 MeV
Authors: Akkerman A. F. , Botvin V. A. , Grudskii M. Ya. , Smirnov V. V. , Chernov G. Ya. , Shilenkova M. V. 
Published: July 2007

AbstractDifferential and integral yields of secondary electrons from different targets bombarded by monoenergetic photon beams are calculated using the Monte Carlo method. The results are compared to experimental data and values calculated by other authors. The discovered 20 to 30% decrease of calculated backward yields according to experimental data for heavy elements is explained by the limited applicability of Sauter's formula for the description of photoelectron angular distribution.
Magnetic States of a Quenched Random Site Heisenberg Magnet with Competitive Exchange Interactions II. Magnetic States with Partial Spin‐Glass Freezing in Simple and Body‐Centered Cubic Latticess
Authors: Medvedev M. V. , Zabrovo A. V. 
Published: July 2007

AbstractThe typical magnetic phase diagrams of a random site Heisenberg magnet with competitive exchange interactions of the nearest neighbours are investigated. It is emphasized that there appear magnetic states which are superpositions of the long‐range magnetic ordering of some spin vector components and the spin‐glass freezing‐in of other components, namely, the asperomagnetic (random noncollinear ferromagnetic) state, the antiasperomagnetic (random noncollinear antiferromagnetic) one, and the noncoplanar canted one.
Influence of Semiconductor Dielectric Function Spatial Dispersion on Charge Electrostatic Energy near the Semiconductor/Vacuum Interface and Field Emission Current
Authors: Gabovich A. M. , Voitenko A. I. 
Published: July 2007

AbstractThe electrostatic charge energy W near the semiconductor/vacuum interface is calculated for a variety of models describing the semiconductor static dielectric function ε(k) dependent on a momentum transferred k. It is shown that the correct account of this dependence leads to the finiteness of the energy W and the image force electrostatic field – σW/σz, when z → O, where z is the distance from the interface. The potential barrier shape for the field emission from semiconductors is found and the dependences of the tunnel current density j on the applied field F, the temperature T and the doping impurity concentration n0 are calculated. It is shown that the spatial dispersion effects of ε(k) essentially affect the magnitude of j, but do not change the dependence j(F) which follows from the Fowler‐Nordheim classical formula.
The F+ Center in Lithium Tantalate
Authors: Ho Fat Duen 
Published: July 2007

AbstractA study of the electronic states associated with an oxygen vacancy in lithium tantalate (LiTaO3) is reported. The F+ center (one oxygen ion vacancy with one trapped electron) is treated by the similar model used in the study of the isomorphous crystal, LiNbO3, by the author. Treating the crystal as an array of point charges the potential of the lattice of 810 ions is computed. The convergence of the lattice sums is demonstrated. The potentials resulting from polarization of the medium are also taken into account. Using a variational method the Schrödinger equation is solved in a self‐consistent manner. The calculations show that one of the absorption bands (450 nm) observed may be ascribed to the presence of the F+ center.
Magnetic After‐Effects in Single‐ and Poly‐Crystalline Magnetite
Authors: Walz F. , Brabers V. A. M. , Chikazumi S. , Kronmüller H. , Rigo M. O. 
Published: July 2007

AbstractThe magnetic relaxation spectra of different types of single crystalline magnetite are investigated in the temperature range 4 K < T < 450 K and compared with corresponding spectra obtained on stoichiometric (Fe3O4) and vacancy‐doped polycrystals (Fe3−ΔO4). Three basic relaxation mechanisms are revealed within the following temperature ranges 4 K < TI < 35 K, 40 K < < TII < 130 K and 200 K < TIII < 450 K, which may be associated to either electronic (TI, TII) or ionic (TIII) hopping processes. In crystals with systematically reduced stoichiometry characteristic modifications in the structure of these spectra are observed from which additional information for a theoretical understanding may be obtained.
Electron‐Energy‐Loss Spectroscopy of Different Al2O3 Modifications II. Lineshape‐Analysis of Energy Derived Dielectric Function
Authors: Tews W. , Zimmermann R. 
Published: July 2007

AbstractThe dielectric function ε(E) = ε1(E) + iε2(E) deduced from electron‐energy‐loss measurements of amorphous and polycrystalline γ‐ and α‐Al2O3 is investigated in the spectral range from 5 to 30 eV. A lineshape analysis applied to the energy derivative of the dielectric function gives parameters of an exciton and an M0‐singularity in the band‐edge region. At higher energies, a set of critical points is identified. The data are interpreted in terms of the electronic structure of Al2O3 with special emphasis on a comparison between amorphous and polycrystalline films.
Study of Relaxation Processes in Antiferromagnets Using Sound Absorption Measurements
Authors: Tarasenko S. V. , Chepurnykh G. K. 
Published: July 2007

AbstractFor antiferromagnets of easy‐plane type outside nuclear magnetoacoustic resonance conditions at different temperatures the interaction of nuclear spins with lattice vibrations via electron spin waves is studied at conditions when between spin and sound waves a strong coupling takes place (the linear coupling parameter is of the order of unity). Simple relations (nuclear spin subsystem considered) are obtained for spin wave and additional sound attenuation due to coupled magnetoelastic waves. They are necessary for studies of relaxation processes in a magnon subsystem using sound absorption.
The E Centre in SiO2 MO Calculation of the 17O, 20Si, and 1H Hyperfine Splittings
Authors: Haberlandt H. 
Published: July 2007

AbstractStarting from the relaxed O− vacancy model the 29Si, 17O, and 1H hyperfine splitting (hfs) parameters are calculated by means of the extended Hückel theory (EHT) within the cluster approach for different models of the E'1 centre in SiO2. The 29Si hyperfine splittings strongly depend on the lattice relaxation. The accordance of calculated and experimental hfs data, recently observed by Griscom, is checked. Two modified O− vacancy models are proposed to explain the E centre: one for the centre exhibiting “weak” hfs and the other for the centre exhibiting no “weak” hfs.
Electron Emission from Gold Island Films
Authors: Blessing R. , Pagnia H. 
Published: July 2007

AbstractThe electron energy distribution from Au island films shows field emission and hot‐electron emission in two different regions of the applied voltage. The two processes can be determined by their relative energetic position compared with UV photoelectrons and their dependence on the voltage applied. There are field emission in the high‐voltage region (Up > 8 V) following the Fowler‐Nordheim equation and electron excitation at low voltages (Up < 8 V).
The Excitation Map of Surface Barrier Resonances. II. Some Qualitative Arguments Concerning the 2D NFE Behaviour of Surface Barrier Resonances
Authors: Solbrig H. 
Published: July 2007

AbstractUsing the example of the {10} emergences for normal incidence on the Ni(001) surface the levels of the Rydberg series are demonstrated to depend on the speculiar reflection by the substrate rather than on the reflection by the corresponding laterally averaged potential of the substrate.
Effets des pièges sur la fusion triplet–triplet dans les cristaux de naphtalètne
Authors: Bonno B. , Laporte J. L. , Rousset Y. 
Published: July 2007

AbstractL'étude de 300 à 77 K des fluorescences retardées de polycristaux de naphtalène purs ou dopés à l'anthracène permet de préciser l'effet de l'introduction dans le cristal de petites quantités de cette impureté. Lorsque la température décroǐt, l'intensité des fluorescences retardées varie de façons très différentes pour le cristal pur et les cristaux mixtes. Ces comportements sont interprétés à partir de la présence d'un piège pour l'exciton triplet (ΔE = 1575 cm−1, τ = 3,6 × 10−2 s) liè à l'introduction de l'anthracène au sein du cristal. La concentration de ce piège varie comme celle de l'impureté.
Anisotropy of the Free Carrier Piezoelectric Scattering by Dislocations in III–V Compounds
Authors: Vignaud D. , Farvacque J. L. , Ferre D. 
Published: July 2007

AbstractCalculations of the piezoelectric potential associated with dislocations of sphalerite structure are made, i) by taking into account the elastic anisotropy of the materials, ii) by neglecting it. The results show a large similarity in the behaviour of the induced resistivity calculated in both cases. These results allow to make use of the isotropic approximation for the elastical medium for any calculation of the electrical properties associated with dislocations.
On the Anomalies in the Temperature Dependence of Conductivity in Hg1−xCdxTe
Authors: Arapov Yu. G. , Davydov A. B. , Tsidilkovskii I. M. , Shelushinina N. G. 
Published: July 2007

AbstractThe temperature (1.8 K ≦ T ≦ 77 K) and magnetic field (0 ≦ H ≦ 22 kOe) dependence of the conductivity σ, longitudinal magnetoconductivity σzz, and of the Hall coefficient R for gapless Hg1−xCdxTe crystals are measured. At temperatures Tmin = 6 to 11 K there occur deep minima of conductivity σ(T). It is shown that the origin of these minima cannot be accounted for by the resonance scattering of electrons by acceptors. The minima in σ(T) arise from the decrease in electron mobility caused by the increase of the number of charged centres with increasing temperature when T < Tmin and by the increase of the concentration of electron‐hole pairs when T > > Tmin. The anomalies in the conductivity (plateau) and the Hall effect (double inversion of sign) observed in the temperature range 20 K < T < 40 K are due to the contribution of three types of carriers, viz. light conduction band electrons, heavy acceptor band electrons, and valence band holes.
Band Structure, High Temperature Electrical Resistiviy, and Exchange‐Induced Magnetic Moment of the Itinerant Electrons in Gd‐La Alloys
Authors: Beznosov A. B. , Nikolskii G. S. , Feher A. 
Published: July 2007

AbstractThe electrical resistivity ϱ of the Gd‐La alloy system containing up to 12 at% of La is measured in the temperature range from 300 to 1000 K. Above the magnetic transition temperature a deviation of the dependence ϱ(T) from the linear behaviour is found for all alloys investigated. The analysis of the dependence ϱ(T) in the temperature range 500 to 1000 K shows a negative contribution to the electrical resistivity due to the temperature dependence of the Fermi distribution. The posibility of using the information obtained in the study of the magnetic properties of rare earth metals in discussed.
Exchange Contributions and Plasmon Spectra of One‐Dimensional Systems
Authors: Brosens F. , Devreese J. T. , Kahn L. M. , Ruvalds J. 
Published: July 2007

AbstractThe dynamical exchange decoupling method for including exchange in the dielectric function of the electron gas is applied to one‐dimensional systems with a tight‐binding energy band. Depending on the bandwidth and the position of the Fermi energy in the band, dynamical exchange effects are shown to have appreciable effects on the plasmon dispersion. For propagation of the plasmon along the strand axis, and in the long‐wavelength limit, exchange effects drastically lower the slope of the plasmon dispersion. For non‐parallel incidence, the exchange effects are less pronounced, and extended over a smaller wave vector region.
Optical Absorption in PbSe1‐‐xTex Due to Transitions between Band States and Localized Energy Levels
Authors: Finkenrath H. , Franz G. , Uhle N. 
Published: July 2007

AbstractThe optical absorption of thin PbSe1‐xTex films prepared by hot‐wall epitaxy in the frequency range 80 to 660 cm−1. The maximum of a broad absorption band changes its spectral position in a characteristic manner when the composition parameter x is varied. Some possible absorption mechanisms are discussed. The experimental results are mostly understandable by the assumption of electronic transitions between valence band states and localized energy levels within the valence band.
Is the Electronic Structure of Liquid Metals Free‐Electron‐Like or Bloch‐Electron‐Like?
Authors: Halder N. C. , Phillips K. C. 
Published: July 2007

AbstractThe electronic density of states (EDS) are calculated for liquid Na, Hg, Ga, Pb, Sn, and Bi. Calculations are performed using two formalisms: (i) second‐order perturbationtheory and (ii) the Green function theory. The EDS plots resulting from these two sets of calculations reveal that the perturbation calculations give consistently more structure than the Green function calculations. However, the general features of the two sets of calculations are the same and agree within their respective theoretical limitations and basic approximations. It is concluded that the electronic structure of liquid metals is neither free‐electron‐like nor Bloch‐electron‐like.
Microwave Measurements of the Thermal Expansion of Organic Metals
Authors: Miane J. L. , Carmona F. , Delhaes P. 
Published: July 2007

AbstractThe thermal expansion of organic metals is measured by the Buravov‐Shchegolev method (microwave cavity at 9.5 GHz). A relation is found between the frequency shift of the cavity and the length of the sample, independent of the skin depth in the sample. The linear thermal expansion coefficients αb are measured along the organic chains in charge transfer complexes (TTF–TCNQ, HMTTF–TCNQ) and ion radical salts (TMTTF2–I, TMTSeF2–ClO4, TTT2–I3 and TSeT2–I). Organic metals with TTF and its selenium analog TSeF show large coefficients for bi‐chain compounds (like TTF–TCNQ) as well as for monochain compounds (like TMTSeF2–ClO4). These metals are found to exhibit strong anharmonic effects leading to a T2 law for the electrical resistivity (Weger's model). On the contrary metals with TTT or TSeT have weak coefficients αb and their electric properties are more similar to those of inorganic metals (their resistivity follows a Bloch‐Grüneisen law with ϱ ∝ T).
Propagation of Strong Electromagnetic Waves in Kane Semiconductors under Conditions of Electron and Phonon Heating
Authors: Gasymov T. M. , Katanov A. A. , Kocharli F. K. 
Published: July 2007

AbstractThe propagation of a strong electromagnetic wave (EMW) is studied in nondegenerate semiconductors with a Kane spectrum taking into account the heating of electrons and acoustic phonons‐In the limiting cases of a parabolic and strongly nonparabolic spectra it is shown that if the cyclotron frequecy ω is high enough compared to that of the incident wave ω the refraction index of the medium n is independent of the amplitude of the incident wave E0. At ω ≫ ωn depends on E0 if the spectrum is nonparabolic. In the case of a strongly nonparabolic spectrum n increases with the electron temperature θe. The field and temperature penetration lengths LE and Lθe are calculated. In the strongly nonparabolic case where a “thermal reservoir” is present and the electron scattering is due to the piezoacoustic phonons these lengths as well as the dissipative part of the conductivity σRe are found to be independent of E0. In the strong damping region the semiconductor impedance ζ grows with E0. In all the cases considered the field and temperature damping functions are obtained. In absence of a “thermal reservoir” and in a strong magnetic field the thermoelectric and Nernst‐Ettingshausen fields reverse their signs when passing from the parabolic to the strongly nonparabolic spectrum.
Electron Paramagnetic Resonance Studies of Cu2+ Impurities in Ferroelectric LiH3(SeO3)2
Authors: Hefni M. A. , Grecu N. M. , Grecu V. V. , Popescu F. F. 
Published: July 2007

AbstractThe electron paramagnetic resonance spectra of Cu2+ doped in LiH3(SeO3)2 single crystals are studied. The ions reside in different chemically distinct sites. For two of them, the strongest in the EPR spectra, the g and A matrices and the Q tensor are determined. Within the limit of experimental errors, the EPR spectra of one site exhibits an orthorhombic symmetry with a pronounced axial character, while the other site exhibits a monoclinic symmetry. In the last case low symmetry effects such as asymmetries of g and A matrices are evidenced.
Unsymmetrized Self‐Consistent Field Approximation for Imperfect Strongly Anharmonic Crystals
Authors: Zubov V. I. 
Published: July 2007

AbstractThe nonlinear integral equations of the unsymmetrized self‐consistent field method for imperfect strongly anharmonic crystals are treated. These equations are reduced to a set of transcendental ones. More emphasis is placed on the cubic strongly anharmonic crystals with taking into account the surfaces and monovacancies.
Crystal Structure and Raman Spectra of InSe
Authors: Ikari T. , Shigetomi S. , Hashimoto K. 
Published: July 2007

AbstractA polytype of InSe single crystals is determined to be of γ‐type by means of X‐ray Laue and diffractometer measurements. Polarized Raman scattering studies are carried out at room temperature and the spectra are analysed by using the normal modes of γ‐InSe. Two Raman lines of the A1 mode (118, 228 cm−1) and two of the E mode (43, 180 cm−1) are observed. An additional Raman line at 214 cm−1 is attributed to an LO phonon with E symmetry.
Thermodynamics of Aluminium‐ and Magnesium‐Base Interstitial Solutions I. Analysis of Interaction Parameters
Authors: Bogdanov V. I. , Mikhailov A. V. , Fuks D. L. 
Published: July 2007

AbstractThe pseudopotential method is used to calculate first‐ and second‐order interaction parameters in f.c.c. and h.c.p. interstitial solutions of aluminium and magnesium alloys. Values calculated of interaction parameters are used for an estimation of the series convergence for the logarithm of the boron and carbon activity coefficient. The results show that the series convergence depends, to a great extent, on the selection of the alloying element and its concentration.
On the Theory of Isostructural Phase Transitions in Crystals
Authors: Schneider V. E. , Tornau E. E. 
Published: July 2007

AbstractThe thermodynamics of two types of isostructural phase transitions (IPT) is investigated in the framework of the Mitsui model using the molecular field approximation. The first type of IPT is obtained including four‐particle interaction members into the Hamiltonian. The consideration dealing with the temperature dependence of the asymmetry parameter explains IPT of the second type. It is shown that the maximum of dielectric constant may appear either in the point of IPT or above it. The investigation carried out gives a qualitative explanation of the experimental facts in numerous crystals undergoing IPT.
Isomerization and Disorder of Polyacetylene Induced by Doping
Authors: Schügerl B. , Kuzmany H. 
Published: July 2007

AbstractRaman scattering experiments are reported for cis‐(CH)x and cis‐(CD)x doped with AsF5 in a concentration range between 3 and 13%. The typical cis‐lines in the spectrum decreased with increasing doping concentration until they disappear completely at around 8%. Simultaneously the non‐resonant trans‐line at 1291 cm−1 is observed to increase and a special high‐frequency mode develops around 1590 cm−1. From the experimental results it is shown that the generation of disorder and isomerization by doping is a general phenomenon. A strong increase of the scattering cross‐section observed for red laser light for the heavily doped material is correlated to a band gap closure.
Dynamical Properties of Excitons in Layer Crystals of PbI2
Authors: Brodin M. S. , Blonskii I. V. , Nitsovich B. M. , Krochuk A. S. , Franiv A. V. 
Published: July 2007

AbstractExperimental studies of the temperature shift and halfwidth of the exciton absorption band in pure and intercalated PbI2 single crystals are performed. The exciton–phonon interaction feature are revealed, namely the highly effective scattering of excitons on the bending vibrations of the layer.
Elastic Field and Self‐Force of Dislocations Emerging at the Free Surfaces of an Anisotropic Halfspace
Authors: Lothe J. , Indenbom V. L. , Chamrov V. A. 
Published: July 2007

AbstractThe problem of dislocations emerging at free surfaces is considered. This complicated threedimensional elastic problem can be reduced to a superposition of two‐dimensional fields of infinite straight dislocations which are well defined. A plane fan‐shaped distribution of infinite straight dislocations is introduced which replaces the condition of a free surface. This allows one to construct the whole elastic field of inclined dislocations in the anisotropic halfspace. As an example of the suggested method the formula for the self‐force acting on dislocations emerging at a free surface is obtained. The connection of self‐moments acting on dislocations with the orientational dependence of the dislocation energy is discussed.