bluuebunny/crossref_metadata_2025_split huggingface dataset:
Energy‐Dependent Excitonic Injection of Charge into Anthracene Crystals
Authors: Strzelecka B. , Godlewski J. , Kalinowski J. 
Published: July 2007

AbstractSteady‐state exciton‐injection currents (EIC) as a function of electric field and temperature are measured in anthracene crystals upon energy‐selective excitation within the S0→ S1transition. The current for each given absorption coefficient decreases as the excitation energy (ℏω) passes through the high‐energy wing and is swept downward the low‐energy wing (Urbach tail) of the absorption band, demonstrating that the flux of excitons reaching the injecting contact is energy dependent. The maximum absorption at the S0→ S1transition establishes a demarcation energy ℏω0. Above ℏω0only diffusion of mobile (band) excitons (S) is an injection‐determining process, below ℏω0thermal activation of localized states (St) becomes an unavoidable step in the S‐exciton creation process, diminishing the effective flux of S‐excitons reaching the contact. An analysis of the dependence of the activation energy on the localization energy ℏω0— ℏω of primarily excited Ststates indicates that EIC are the sum of a singlet exciton‐injection contribution and a triplet exciton‐injection contribution, the triplets being produced via iniersystem crossing transitions from S and Ststates. A theoretical description of excitonic processes underlying charge injection is presented and applied to the experimental results. Agreement between theoretical predictions and experiment is good if the frequency factor for the thermally activated St→ S excitation is assumed to be ≈︁ 109s–1.
Strong Non‐Adiabatic Interactions and Phase Transitions in Conductive Jahn‐Teller Crystals
Authors: Kiselev A. A. , Liaptsev A. V. 
Published: July 2007

AbstractA model of a conducting crystal composed of quasi‐molecules with D4hsymmetry and with nearly degenerate A1gand B1gstates is considered. The model Hamiltonian includes intramolecular strong non‐adiabatic interactions, which are non‐diagonal with respect to the electronic quantum numbers and linear (Jahn‐Teller type) and quadratic (Renner‐type) in the vibrational coordinates. The model Hamiltonian is analysed with the help of the mean field method. It is shown that the non‐adiabatic electron‐phonon interaction causes a structural phase transition which splits the degenerate vibrational mode involved in the interaction, the minimum frequency of the lower branch decreasing when the temperature decreases. For the electrons the two‐band BCS equation follows from the calculation, the interaction constant being multiplied by the average number of low‐frequency phonons.
Magneto‐Optical Phenomena in Semiconductor Superlattices
Authors: Shon Nguyen Hong 
Published: July 2007

AbstractThe Faraday and birefringence effects due to infrared radiation in semiconductor superlattices in quantizing magnetic field are investigated. It is shown that for a non‐degenerate electron gas in the one‐mini‐band approximation the frequency behaviour of magneto‐optical coefficients exhibits finite jumps at ω = nωc ± 2Δ ω is the frequency of electromagnetic radiation, ωc the cyclotron frequency, and Δ the half band‐width). The natural birefringence and dichroism in superlattices are also calculated.
On a Simplified Analysis of the Carrier Contribution to Elastic Constants of Ternary and Quaternary Compounds
Authors: Ghatak K. P. , Mondal M. 
Published: July 2007

AbstractAn attempt is made to study the carrier contribution to the elastic constants of degenerate ternary and quaternary compounds on the basis of a newly derived electron dispersion law taking into account the presence of band tails. It is found, taking n‐Hg1−xCdxTe and In1−xGaxAsyP1−y lattices matched to InP as examples, that the said contribution increases with increasing carrier concentration in different manners. The band tail diminishes the numerical values of the carrier contribution to the second and third order elastic constants for both the compounds. An experimental method is suggested of determining the electronic contribution to the elastic constants in degenerate materials having arbitrary carrier dispersion laws. In addition, the corresponding well‐known results for non‐degenerate wide‐gap materials in the absence of band tails are also obtained from the generalized expressions under certain limiting conditions.
FIR Absorption in Monoclinic ZnAs2
Authors: Weszka J. , Mazurak Z. , Pishchikov D. I. 
Published: July 2007

AbstractFIR absorption in powdered ZnAs2 crystals is studied. The features within the frequency area 194 to 270 cm−1 are attributed to As helix modes. Low‐frequency features are attributed to modes involving important contributions of Zn atoms. There are some indications that inter‐As helix correlation splitting exists.
Anharmonic Effects in KDP near the Ferroelectric Phase Transition
Authors: Serra K. C. , Melo F. E. A. , Filho F. Mendes , Moreira J. E. , Lemos V. 
Published: July 2007

AbstractThe temperature dependence of some Raman modes of KDP, below the ferroelectric phase transition, is investigated. Two lattice modes display an exponential dependence with T which is explained by third and fourth order anharmonic effects.
Characterization of GaSb Epitaxial Layers on GaSb and GaAs Substrates by Infrared Reflectivity
Authors: Mezerreg A. , Llinares C. 
Published: July 2007

AbstractInfrared reflectivity measurements on p‐GaSb epitaxial layers on n‐GaSb substrate and n‐GaSb epitaxial layers on semi‐insulating (SI) GaAs are made to determine the mobility and density of free carriers in the bulk and the layer simultaneously by fitting a theoretical model to experimental data. The results obtained are generally in good agreement with those given by Hall measurements.
Electronic Structure of La2O3 and LaF3 Crystals
Authors: Evarestov R. A. , Leko A. V. , Murin I. V. , Petrov A. V. , Veryazov V. A. 
Published: July 2007

AbstractThe band structure and local properties of La2O3 and LaF3 crystals are investigated within the framework of CNDO approximation.
Semiempirical Crystal Field Calculations for fN‐Systems. II. Crystal Field Effects in Hexahalogenide PaX, UX, and UCl Complexes and in UCl4 Crystal
Authors: Mironov V. S. , Rosov S. P. 
Published: July 2007

AbstractOn the basis of a many‐electron semiempirical method developed in the previous paper a program for practical crystal field energy calculations for fN‐systems is written and applied to octahedral PaX, UX, and UCl complexes, and the UCl4 crystal. The results obtained are in very good agreement with the experimental data on crystal field levels in these compounds. The vibronic coupling constants are also calculated for the series of PaX and UX complexes in the frame of this method.
Mechanism of Temperature‐Induced Transitions between Stripe and Undulation Domain Structures
Authors: Zablotskii V. A. , Mamalui Yu. A. , Lamonova K. V. 
Published: July 2007

AbstractThe temperature‐induced instability of thin magnetic film stripe domain structures (SDS) is studied. Dislocations present in the SDS are shown to be nuclei for the formation of an undulation structure, the domain wall bend period being determined by the dislocation strength. The range of thermal stability of the stripe domain structure is calculated.
Structural Studies of Liquid Germanium Using Lebowitz's Solution of Hard‐Sphere Mixtures
Authors: Rao R. V. Gopala , Debnath D. 
Published: July 2007

AbstractExperimental investigations on liquid germanium show a small subsidiary shoulder in the main peak of the structure factor S(k) near the melting point. Through Lebowitz's solution of hard sphere mixtures the structure factors are treated theoretically investigated. Experiments and molecular dynamic studies conclusively point out that the liquid structure arises from the interplay of two characteristic distances and these are figuratively treated as different diameters. The present theoretical results are in good agreement with those obtained by other methods in the whole range of momentum space. The isothermal compressibilities are calculated by using Kirkwood‐Buff's equation.
Phonon‐Limited Electron Mobility in a Polar Semiconductor Quantum Well
Authors: León H. , León F. , Comas F. 
Published: July 2007

AbstractLow‐field drift mobility for transport parallel to the interfaces in a polar semiconductor quantum well is calculated following an iterative procedure. Calculations are carried out in the size‐quantum‐limit approximation for a degenerate electron gas. Screening of the electron–phonon interaction via acoustic deformation potential, piezoelectric of the accoustic branch, and longitudinal optical mode couplings is taken into account by means of a dielectric function deduced in an earlier work. Confinement of LO vibrations is also taken into account by means of an appropriate Hamiltonian successfully employed in previous works. The role of the electron–LO‐phonon interaction is accurately established and the conclusion is drawn that this coupling becomes considerable at intermediate and very important at sufficiently high temperatures for quantum wells of the GaAs/AlGaAs type. Comparison with experiment gives an acceptable agreement between calculated and measured mobility values.
Study on Momentum Density of Electrons and Fermi Surface in Magnesium by Positron Annihilation
Authors: Nakashima H. , Kubota T. , Kondo H. , Tanigawa S. 
Published: July 2007

AbstractThe three dimensional electron–positron momentum density in magnesium is reconstructed from measurements of two dimensional angular correlation of positron annihilation radiations (2D‐ACAR) followed by the image reconstruction technique based on a direct Fourier transformation. From these data, informations are obtained about the Fermi surface topology, the high momentum components (HMC), the enhancement effect, and autocorrelation function.
Application of the Linear Response Theory to the Perfect Diamagnetism in Superconductors
Authors: Tokita M. , Zenmyo K. , Haga E. 
Published: July 2007

AbstractTaking account of the Meissner effect (B = 0 for the superconducting state), the vector potential A is defined not by B = rot A but by H = rot A to calculate the linear magnetic field response of a bulk superconductor. The magnetic interaction in the Bohm‐Pines theory is consistently introduced into the Hamiltonian of the system. On the basis of both the usual linear response theory and the BCS‐Bogolyubov theory, the static magnetic susceptibility χ = −1/4π, i.e. perfect diamagnetism, is obtained for the bulk superconductor at zero temperature.
Electron Irradiation Damage in Pure and Impurity‐Doped RbMgF3 Crystals
Authors: Sardar D. K. 
Published: July 2007

AbstractThe radiation damage processes in pure and impurity‐doped RbMgF3 crystals are studied by identifying and monitoring the radiation induced defects. Interstitials and Vk centers are observed at low temperatures. One of the most important characteristics of RbMgF3 is that the F centers form in this host without their aggregation even at room temperature. Annealing of these samples at higher temperature after room temperature irradiation however forms F‐center aggregates such as F2‐centers and F3‐centers and also impurity‐F center pairs. In the case of impurities such as Er3+ or Mn2+ which substitutionally replace Mg2+ ions in the RbMgF3 lattice, there is no effect on the early stage production of F centers. It is observed that the statistical productions of the F aggregates and Mn2+‐F pairs occur during room temperature irradiation. On the other hand, the larger Eu2+ or Cu2+ ions substitute for Rb+ ions in this host and significant enhancement of the early stage formation of F centers at room temperature is observed. The experimental observations are compared with the proposed model on radiation defect production.
Method of Functional Derivatives in the Theory of Point Defects in Crystals: I. General Theory. Representations of the Self‐Energy
Authors: Kantorovich L. N. 
Published: July 2007

AbstractA novel method is suggested for the calculation of point defect electronic structure in arbitrary crystals using a non‐orthogonal localized atomic orbital basis set. The method is based on the concept of a cluster Green's function and uses a special truncating procedure for the Green's function chain, such that only the defective region of the crystal is considered precisely, while the rest of the crystal as well as its interaction with the defective region are considered in Hartree‐Fock approximation. It is shown, that the correct incorporation of an electronic correlation in the defective region is connected with a relevant choice of a cluster self‐energy operator. Decompositions of this operator into a series either over screened or unscreened interaction are investigated. An approximation analogous to the simplest Hedin's GW‐approximation is considered. Qualitatively this approach is equivalent to that which uses the generalized Anderson Hamiltonian.
Features Peculiar to Transport Phenomena in Cobalt‐Doped HgSe Crystals
Authors: Tsidilkovskii I. M. , Lerinman N. K. , Sabirzyanova L. D. , Paranchich S. Yu. , Paranchich Yu. S. 
Published: July 2007

AbstractOn Hg1−xCoxSe (5 ⪅ 10−5 x ⪅ 1 × 10−2) crystals the Hall coefficient, resistivity, and Shubnikovde Haas oscillations of transverse magnetoresistance are measured. Experimental findings permit the conclusion that in mercury selenide, cobalt atoms form a resonance donor level. However, by contrast with mercury selenide crystals doped with iron and chromium, the cobalt impurity does not lead to the known electron mobility “anomaly” due to the ordering of the system of charged impurities. Shubnikov‐de Haas oscillations exhibit peculiarities arising from a substantial exchange interaction of conduction band electrons with 3d electrons of cobalt ions.
The Conductivity Anisotropy in Uniaxially Stressed p‐InSb
Authors: Germanenko A. V. , Minkov G. M. , Rut O. E. 
Published: July 2007

AbstractThe conductivity anisotropy induced by uniaxial stress in p‐InSb with acceptor concentration NA ≈︁ (1014 to 2 × 1016) cm−3 is investigated in the temperature range T = 2 to 70 K under uniaxial stress up to 6 × 108 Pa. In pure materials pressure and temperature dependences of the conductivity anisotropy are explained by ordinary models in the hopping regime and regime of free hole conductivity. In doped semiconductors these dependences cannot be explained without taking into account the peculiarities of the metal‐dielectric transition induced by uniaxial stress in p‐type narrow‐gap semiconductors with degenerate valence band ⌜8.
Spectrum of Interface Coupling‐Affected Spin‐Wave Modes in Ferromagnetic Bilayer Films. The Emergence of Interface Mode
Authors: Puszkarski H. 
Published: July 2007

AbstractA microscopic theory of spin‐wave modes in exchange‐coupled bilayer films is presented. Using the interface inhomogeneity model (an effective interface exchange coupling parameter is introduced) as well as the Heisenberg model in the spin (exchange and Zeeman) Hamiltonian, an energy dispersion relation and spin‐wave mode functions for the exchange‐coupled bilayer ferromagnetic films are derived. The theory is valid for Bravais lattices with arbitrary type of film surface/interface orientation at perpendicular (to the film surface) configuration of the static external field and arbitrary ferro/antiferro‐magnetic value of the interface exchange coupling. The semi‐classical picture of the bilayer spin‐wave modes is elaborated and the influence of the interface coupling parameter on the shape of the modes is discussed. Then, a detailed discussion of the conditions for the occurrence of interface‐localized spin‐wave modes is given. The analysis of the interface mode properties is based on the exact solution of the eigenvalue problem of a bilayer film achieved by the interface rescaling approach. Subsequently, a microscopic theory of the ferromagnetic resonance effect in the exchange‐coupled bilayer films is developed. It is shown that when intrinsic surface anisotropies are absent the pattern of the resonance spectrum is determined solely by the nature of the interface exchange‐coupling integral JAB. When this integral couples ferromagnetically (JAB > 0) the sublayer spins at the interface, the resonance spectrum consists of only one resonance line which is insensitive to the strength of the coupling. On the contrary, when coupling is antiferromagnetic (JAB < 0), the resonance spectrum is multipeak in nature with the first two (high‐field side) lines exhibiting pronounced intensities. When antiferromagnetic coupling is weak, the intensity pattern of these two lines is “regular” (i.e. l1 > l2); however, for stronger antiferromagnetic coupling, an inversion of these intensities occurs leading to an “inverted” intensity pattern (l1 < l2) in accordance with certain experimental results. Moreover it is shown that inversion of the intensities (caused by negative JAB) is due to the fact that the highest‐field line arises by excitation of the mode which is localized on the bilayer interface. It is also shown that this mode represents a bilayer complex vibration formed by the in‐phase combination of the sublayer vibrations, and this result corrects the general belief of experimenters that the mode under consideration is due to out‐of‐phase combination of sublayer vibrations.
Electron Paramagnetic Resonance Studies of Cu2+ Ions Doped in Tl2Zn(SO4)2 · 6 H2O Single Crystals
Authors: Krishna R. M. , Rao J. L. , Bhaskar V. V. , Lakshman S. V. J. 
Published: July 2007

AbstractThe results of EPR and optical absorption studies of Cu2+ ions doped in TZSH single crystals in the temperature range 420 to 120 K at X‐band frequency are reported. The ground state wave function for the Cu2+ ion in TZSH is evaluated. The principal g and A parameters are fitted to orthorhombic symmetry.
Surface Magnetizations of a Semi‐Infinite Ferrimagnetic System with a Compensation Point in the Bulk
Authors: Kaneyoshi T. 
Published: July 2007

AbstractThermal variations of magnetizations at or near a surface are investigated by using a semi‐infinite mixed spin ferrimagnetic system within the framework of the effective‐field theory and the three‐layer approximation. Depending on the value of single‐ion anisotropy in the bulk or at the surface, the system can exhibit the compensation point in the bulk magnetization or magnetization near the surface. The effects of compensation point in the bulk on magnetizations at or near the surface are in particular examined. A number of interesting phenomena are found, such as a fact that the compensation temperature in the vicinity of the surface may be different from that in the bulk.
Surface Magnetic Properties of an Amorphous Semi‐Infinite Ferromagnet with Random Fields
Authors: Sarmento E. F. , Saber M. , Kaneyoshi T. 
Published: July 2007

AbstractSurface magnetic properties of an amorphous semi‐infinite spin 1/2 Ising ferromagnet with random fields at surface and bulk are investigated by the use of the effective‐field theory with correlations. A number of characteristic behaviours is found for the surface magnetic properties. In particular, the effects of competition between the random field and the structural fluctuation parameter δ(the reentrant phenomenon in the bulk) on magnetizations at and near the surface are clarified. The surface crystallization of an amorphous ferromagnet may be important in the sense that a surface transition temperature higher than that ofthe bulk can be obtained from the process of an appropriate amorphous semi‐infinite ferromagnet with a random field in the bulk.
On the Bergman Spectral Function of a Two‐Component Hetero‐System with Interchange Symmetry
Authors: Gerlach E. 
Published: July 2007

AbstractIt is shown that for materials with interchange symmetry the Bergman spectral function g(u) obeys the symmetry relation u g(u) = (1 ‐ u). g (l ‐ u), from which a number of interesting conditions for g(u) can be derived.
Short‐Lived Frenkel Defects in α‐Al2O3
Authors: Aluker E. D. , Gavrilov V. V. , Chernov S. A. 
Published: July 2007

AbstractThe fast luminescence, the transient absorption spectra, and the recombination kinetics are observed and investigated in α‐Al2O3. Absorption spectra reveal short‐lived bands at 2.75 and 2.15 eV. Their decay times remain the same (30 to 200 ns) in the temperature interval 80 to 293 K. They are found to be almost the same as the lifetime of the fast components of the luminescence band at 3.8 eV. They are expected to be due to interstitial aluminium ions. Experimental results argue for subthreshold creation of short‐lived Frenkel defect pairs in the cation sublattice of α‐Al2O3.
Nucleation and Growth of Adsorbed Layer Self‐Consistent Approach Based on Kolmogoroff‐Avrami Model
Authors: Dubrovskii V. G. 
Published: July 2007

AbstractThe kinetic model for the growth of adsorbed monolayer is developed in order to describe the growth process beginning from the initial stage of nucleation up to the formation of a continuous film. The nucleation of clusters on the uncovered substrate region is studied within the frame of kinetic theory of condensation. Direct coalescence of clusters is described by means of Kolmogoroff‐Avrami model for two‐dimensional crystallization. The basic self‐consistent equation for the dynamics of adatom supersaturation is derived. Numerical solutions for supersaturation, mean substrate coverage, boundary perimeter, and total number of clusters are obtained. Depending on the numerical value of the governing parameter, three known experimental growth modes are determined. In the regime of incomplete condensation the analytical solutions for the basic kinetic and morphological characteristics of the growing layer are obtained, which are in agreement with numerical results.
Kubo Formalism for Resonant Tunneling in Double Barrier Heterostructures
Authors: Montenegro N. Porras , Latgé A. , Anda E. V. 
Published: July 2007

AbstractThe electronic and transport properties of double barrier structures are studied using the Kubo formula for the electrical conductivity and a tight‐binding respresentation for the Hamiltonian. The theory is able to reproduce the experimental I‐U characteristic curves. A self‐consistent Hartree treatment permits to study the charge distribution and its influence on the position of the resonant energy levels and on the tunneling properties as a function of the doping of the sample.
Resonant Photoemission from Gd on Cu(100)
Authors: Scarfe J. A. , Law A. R. , Hughes H. P. , Bland J. A. C. , Roe G. M. , Walker A. P. 
Published: July 2007

AbstractSynchrotron‐radiation‐excited photoemission is studied from a monolayer film of Gd on Cu(100). Resonant enhancement of the 5s, 5p, and 4f core‐level intensities is observed for photon energies in the region of the Gd 4d → 4f threshold. The intensity ratios of the components of the Gd 5p and 5s multiplet structures are found to be modified at the resonance as a consequence of the different parentage of the photoexcited final states involved; satellite structures are also observed corresponding to final states that are unobtainable off‐resonance.
Method of Functional Derivatives in the Theory of Point Defects in Crystals: II. General Theory. Total Energy, Electronic Density, and Density of States
Authors: Kantorovich L. N. 
Published: July 2007

AbstractA novel method for the calculation of point defect electronic structure in arbitrary crystals in a non‐orthogonal localized atomic orbital basis set, based on the concept of a cluster Green's function and a cluster self‐energy matrix, has been suggested in the preceding paper. In the present paper the general formulas for the total electronic energy, density of states, and electronic density matrix for a defect‐containing crystal are obtained within an approximation analogous to the famous Hedin's GW‐approximation. Besides relevant properties of the cluster Green's function are carefully derived and discussed.