bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two‐Mode Approximation in the Low‐Temperature Region. Biquadratic Exchange and Single‐Ion Anisotropy
Authors: Kazakov A. A. , Kleshchev S. M. 
Published: July 2007

AbstractFor the case of strong biquadratic‐law exchange and large energy of single‐ion anisotropy taken into account in the Heisenberg model, it is shown that the low‐temperature thermodynamics is not always reduced to the spin‐wave approximation. The hybrid character of the magnon excitation energy along with the excitation branches stipulates a more intensive temperature dependence of magnetization.
Effect of Doping on Parametric Amplification in Piezoelectric Semiconductors
Authors: Aghamkar P. , Sen P. , Sen P. K. 
Published: July 2007

AbstractUsing the straightforward coupled‐mode theory, the parametric amplification is analytically investigated in a doped piezoelectric semiconductor. The origin of the nonlinear interaction is taken to be in the second‐order optical susceptibility χ(2) arising from the nonlinear induced current density. The threshold value of the pump electric field E0th and the corresponding excitation intensity are obtained for crystals for various concentrations. E0th is found to decrease with rise in doping concentration. The investigation also reveals that the phenomena of self‐focusing and self‐defocusing can be enhanced in these crystals. The parametric gain constant is obtained for both, lightly and highly doped semiconductors. Numerical estimations made for n‐InSb crystal, at 77 K duly irradiated by frequency doubled pulsed 10.6 μm CO2 lasers, yield ∣χ(2)∣ comparable with that observed experimentally.
Microscopic Mechanisms of Paramagnetic Probe—Lattice Interaction for the System RbCdF3:Cr3+ near the Structural Phase Transition
Authors: Chernitskii M. V. , Nikiforov A. E. , Krotkii A. I. 
Published: July 2007

AbstractMicroscopic mechanisms of the interaction of the Cr3+ ion spin system with fields due to the lattice distortions in RbCdF3 crystals are studied. These mechanisms determine changes in the EPR spectrum below 124 K after structural phase transition. The order parameter dependence of the spin‐Hamiltonian parameters both, for centres with local charge compensation and for non‐local charge compensated centres is obtained. The significance of crystal distortions caused by the second order uniform deformation is revealed. Such distortions change considerably the constants determining the interaction of the spin system with the order parameter. To obtain reliable information about the phase transition using an EPR method it is necessary to apply microscopic analysis. The obtained results are compared with experimental data.
Fourth‐Order Elastic Constants of Fluorite Structure Solids
Authors: Goyal S. C. , Sharma A. K. 
Published: July 2007

AbstractThe homogeneous deformation method is extended to study the fourth‐order elastic constants for nonprimitive lattice structure solids. The extended theory is used to study the fourth‐order elastic (FOE) constants of CaF2, SrF2, and BaF2 solids. The second‐order pressure derivatives of the second‐order elastic (SOE) constants for these solids are also calculated.
An Application of the Extended CPA Method to Electron Work Function and Surface Charge Calculation for Cu Single Crystals
Authors: Romanowski S. 
Published: July 2007

AbstractElectron work function calculations from Cu(100), Cu(110), and Cu(111) monocrystals as a function of boundary conditions and surface charge of metal are carried out by means of the extended coherent potential approximation (ECPA) method. A special parameter describing the polarization of a metal sample by an external source of voltage is also introduced. The work function dependence on crystallographic faces of monocrystalline sample has been explained on the basis of local Fermi level idea.
Electron Paramagnetic Resonance of the Mn Cluster in Silicon
Authors: Kreissl J. , Gehlhoff W. 
Published: July 2007

AbstractIn high‐resistivity p‐type and n‐type silicon doped with manganese the Mn cluster is identified by EPR. The spectrum shows a characteristic hyperfine structure and an angular dependence of fine structure at 20 K. The analysis of the spectrum yield the assumption of the following cluster model: the cluster consists of four Mn0 atoms on nearest interstitial sites; it has cubic/tetrahedral symmetry; spin multiplets with S = 0, 1, 2, 3, 4, 5, and 6 are produced by a dominant exchange coupling where the multiplet with S = 6 is the ground state observed by the EPR experiments. The photo‐EPR results suggest a donor level (Mn4)0/+ near midgap.
Superconductor—Semiconductor Transition in BaPb1−xBixO3
Authors: Hidaka M. , Fujii H. , Horie Y. , Mase S. 
Published: July 2007

AbstractThe origin of superconductor—semiconductor transition in BaPb1−xBixO3 is studied from the structural and dielectric properties obtained by measurements of the energy‐dispersive X‐ray diffraction, piezoelectric resonance, electric capacitance, and (D—E) hysteresis loop. The transition is clearly characterized by a rapid vanishing tendency of some characteristic temperatures associated with the above‐mentioned properties in the semiconductor region toward the limiting bismuth composition x ≈ 0.35.
Magnetic Relaxation in the Heisenberg Spin Glass
Authors: Schreiber J. , Schulz D. 
Published: July 2007

AbstractOn the basis of a dynamical theory for Heisenberg spin glasses the isothermal magnetic relaxation R(t) = M(t)/H after switching off a magnetic field H at t = 0 is calculated. The extreme short time relaxation shows an exponential decay with a temperature dependent relaxation time τ(T) and is essentially influenced by many‐body quantum effects in the spin glass state. An estimation of the long time relaxation yields in the qualitative agreement to experimental investigation a non‐exponential behaviour R(t) ∼ t−1/γ, where γ = 2 in an intermediate time region is found for T ≦ Tf. This anomalous relaxation is caused by a broad distribution of relaxation times owing to a distribution of local fields.
Decay Kinetics of UV Luminescence from Undoped PbCl2 Crystals
Authors: Polák K. , Birch D. J. S. , Nikl M. 
Published: July 2007

AbstractThe kinetics of the UV luminescence from PbCl2 crystals are measured from 3.8 to 25 K. Two components in UV luminescence are found. The form of the long time component of the UV luminescence decay curve is thoroughly investigated and compared with theoretical predictions. A model based upon exciton—exciton annihilation leading to free electron—hole pairs is used to describe the decay at temperatures above 15 K.
The Melting Laws
Authors: Kumari M. , Dass N. 
Published: July 2007

AbstractIt is shown that Simon's melting law is not a mere empirical relation but is based on the theoretical concepts of Lindemann. Thus, for the first time, Simon constants are identified correctly in term of the physical properties of the concerned solid. Moreover, it is shown that the other melting laws as given by Kennedy, Reynold et al. and Dass et al. follow well from it. The calculations of the melting temperature, Tm, are done in the case of argon and sodium chloride. Good agreement is found in each case.
Interaction Between Two Surface Excitations in Degenerate Polar Semiconductors
Authors: Srivastava K. S. , Sinha Achla , Srivastava Reena , Tandon Ajay 
Published: July 2007

AbstractA systematic study of the interaction of surface plasmons with surface optical phonons is made for III–V group polar semiconductors to find the factors which can influence the coupling between the two modes of vibrations. It is found that the extent of coupling depends upon the Szigeti effective charge or the ionicity of the compound.
Indirect Nuclear Spin Interaction in Ferromagnets. Highest Approximation
Authors: Bokuchava G. G. , Buishvili L. L. , Tugushi A. I. 
Published: July 2007

AbstractThe problem of obtaining the nuclear spin interaction Hamilton operator via magnon field in ferromagnets is discussed by consecutive canonic transformation method. Using this method the one magnon nuclear spin interaction in any order of perturbation theory is taken into account. The indirect spin interaction Hamilton operator constant obtained is compared with the well known Suhl‐Nakamura interaction constant. It is shown, that in the second order of perturbation theory these results coincide.
On the Probability of Recoilless Absorption f′ and Reemission f″ in Some Fe‐Containing Compounds
Authors: Angelov V. , Bonchev Ts. , Rusanov V. , Mandjukov I. 
Published: July 2007

AbstractThe recoilless absorption probability f′ and the probability f″ of recoilless reemission after absorption are measured for four Fe‐containing compounds. It is established that f″ > f′. This discrepancy has already been observed for 119Sn. The results obtained disagree with the commonly accepted assumption that f′ and f″ are equal. The interpretation of this inequality is made in terms of two relaxation models.
On the Multipole Character of the X‐Ray Transitions in the Pre‐Edge Structure of Fe K Absorption Spectra. An Experimental Study
Authors: Dräger G. , Frahm R. , Materlik G. , Brümmer O. 
Published: July 2007

AbstractThe K absorption edge of pure Fe and the pre‐edge Fe K absorption of FeS2 (pyrite), Fe2O3 (hematite), and FeCO3 (siderite) are investigated with single crystal absorbers of these materials using linearly polarized synchrotron X‐radiation. From the angular dependence of the pre‐edge K absorption the existence of predominantly ligand‐field‐induced dipole transition in Fe2O3 and of quadrupole transitions in FeCO3 is concluded. The multipole character and the mechanism of the pre‐edge K absorption are discussed.
Excitons at High Density in CdS and GaSe, and Optical Bistability
Authors: Dneprovskii V. S. , Furtichev A. I. , Klimov V. I. , Nazvanova E. V. , Okorokov D. K. , Vandishev U. V. 
Published: July 2007

AbstractChanges in the absorption and refractive index caused by laser absorption in CdS and GaSe are investigated and used to produce absorptive resonatorless bistability in CdS and to explain dispersive optical bistability in a GaSe Fabry‐Perot cavity.
A MREI Model for the Zincblende‐Like Phonons in the Mixed Defect Chalcopyrite ZnGa2(SxSe1–x)4
Authors: Lottici P. P. 
Published: July 2007

AbstractResults are given on the compositional dependence of the optical phonon frequencies in the pseudoternary defect chalcopyrite mixed crystals ZnGa2(SxSe1–x)4 over all the composition range. The compositional variation of the TO and LO highest frequency polar zincblende‐like phonons is explained in terms of a MREI (modified random element isodisplacement) model.
Simplest Properties of Guided Wave Polaritons in Three‐Layer Structures
Authors: Burshta I. I. , Venger E. F. , Pasechnik Yu. A. , Snitko O. V. 
Published: July 2007

AbstractThe properties of guided‐wave polaritons of E‐ and H‐types are studied both, theoretically and experimentally. It is shown, that the interaction of an electromagnetic wave with film and substrate lattice oscillations changes the field spatial structure, ranges of existence, and dispersion dependences of surface excitations, i.e. of optical guided wave modes. Expressions describing the frequency dependences of attenuation and absorption factors of guided wave polaritons are received. It is shown that the course of these dependences is determined by peculiarities of the energy distribution between the system layers.
Ground State and Electronic Properties of Silicon Carbide and Boron Nitride
Authors: Van Camp P. E. , Van Doren V. E. , Devreese J. T. 
Published: July 2007

AbstractThe results of ab‐initio calculations of the ground state and electronic properties of the IV‐IV and III–V compounds, SiC and BN, are presented. These properties are derived from the total ground state energy of the crystal calculated in the local density approximation and from the one‐Particle Kohn‐Sham equations. The ab‐initio norm‐conserving non‐local pseudopotential of Bachelet, Hamann, and Schlüter is used. The bulk modulus, its pressure coefficients, and the pressure coefficients of the electron energy differences between the top valence band and lowest conduction bands are also derived. The results are compared with the few existing measurements and with calculations by other investigators.
Stimulated Emission of the I1 – TA (PM) Band in CdS
Authors: Hönig T. , Gutowski J. 
Published: July 2007

AbstractIn CdS, a strong transverse‐acoustic phonon replica of the acceptor–exciton recombination line I1 is observable. This band is called I1 – TA or PM band. Under high excitation desities, the I1 – TA shows a stimulated emission behavior, which leads to laser activity under suitable arrangements. By means of excitation spectroscopy, this behavior is shown to be strongly correlated with the creation of acceptor–exciton complexes (A0,X) in their ground and excited electronic states. Thus, the I1 – TA is not only unambiguously demonstrated to be an efficient recombination channel of acceptor–exciton complexes but also offers an excellent possibility to realize a four‐level bound‐exciton laser in CdS. This emission band is a valuable object to deepen the study of excited states of bound excitons in semiconductors under the use of high excitation densities.
Soliton Generation in Semi‐Infinite Molecular Chains
Authors: Brizhik L. S. , Gaididei Yu. B. , Vakhnenko A. A. , Vakhnenko V. A. 
Published: July 2007

AbstractA mechanism for generating solitons in semi‐infinite molecular chains by exciting the impurity molecules is considered. The generation criteria of solitons are found and their dependence on molecular chain parameters, the input place, and localization degree of initiating excitation. The possibility to govern the generation efficiency and solitons velocity by changing the parameters of exciting singal is pointed out.
Vibrational Structure of Hydrogenated Amorphous Silicon Carbide Alloys
Authors: Ghosh B. K. , Agrawal Bal K. 
Published: July 2007

AbstractTheoretical investigations of the various vibrational modes induced by hydrogen atoms in amorphous silicon carbide are made using a cluster Bethe lattice method (CBLM). The calculated results are in good agreement with available infrared data. Some theoretically calculated peaks need experimental verification.
Thermal Conductivity of Amorphous Si at Low Temperatures
Authors: Pompe G. , Hegenbarth E. 
Published: July 2007

AbstractMeasurements of thermal conductivity of amorphous Si films from 2 to 50 K are presented. The qualitative and quantitative behaviour is similar to thermal conductivity of other amorphous dielectrics. The temperature range of the plateau of λ(T) correlates with the maximum Tm = 30 K of the function c/T3(T). An analysis of the effective free path of phonons in dependence on the reduced temperature T/θD results in a remarkable coincidence for amorphous As, Se, Si, Ge, and SiO2, GeO2 in the plateau range. This fact leads to a restriction of hypotheses for explanation of the plateau of thermal conductivity at amorphous materials.
The Pressure Effect on the Phase Diagrams of the GeSn and SiSn Systems
Authors: Soma T. , Kamada K. , Kagaya H.‐Matsuo 
Published: July 2007

AbstractThe pressure effect on the phase diagrams of the GeSn and SiSn systems is studied using the previous electronic theory based on pseudopotentials and considering the α–β phase transition under pressure. The calculated results predict the appearance of the α‐phase solid solution for the GeSn system under pressure. The obtained curves near the melting point under pressure are shown for the GeSn and SiSn systems.
Cylindrical Quantum Well with Position‐Dependent Mass
Authors: Pérez‐Alvarez R. , Parra‐Santiago J. L. , Pajón‐Suarez P. 
Published: July 2007

AbstractUsing the envelope function approximation and a one band model, the cylindrical quantum well with position‐dependent mass problem is studied. The boundary conditions to be fulfilled by the radial wave functions are deduced. The transcendental equation for the energy levels, the normalised wave functions, and the confinement are obtained in the flat band approximation considering a sectionally constant mass profile. Also numerical results for the GaAsAl0.32Ga0.68As cylindrical quantum well are reported.
Surface Modes of a Type II Semiconductor Superlattice
Authors: Yonashiro K. , Tomoyose T. , Yamshiro M. , Kobayashi M. 
Published: July 2007

AbstractThe surface excitations are investigated in the three‐medium system of an ionic crystal, vacuum, and a type II semiconductor superlattice by making use of Maxwell's equations. The dispersion relations for the plasmon–optical phonon coupled modes are obtained on the interface between these two materials. The surface modes are discussed in detail in both, the high‐ and low‐frequency regions for the weak coupling limit.
Frequency‐Dependent Solution of the Time‐Dependent Hartree‐Fock Equation in the Electron Gas
Authors: Brosens F. , Devreese J. T. 
Published: July 2007

AbstractA numerical procedure is presented to solve the time‐dependent Hartree‐Fock equation for the homogeneous electron gas. This equation accounts for the dynamical exchange effects in the dielectric function. The analytical and numerical techniques are described, and a comparison is made with the results of a variational approach, developed earlier. In general, the variational localfield correction turns out to be in good agreement with the (exact) numerical results. But the logarithmic singularities in the variational calculation are shown to be an artefact of the variational procedure, and not an inherent property of the dynamical exchange effects.
Conductivity and Dielectric Constant of Interacting Anderson Localized Systems at T = 0
Authors: Chicón R. 
Published: July 2007

AbstractThe electrical conductivity as a function of frequency at zero temperature is calculated for a system of interacting electrons with strongly localized wave functions due to disorder. The calculations are concentrated on the contribution from resonant phononless absorption by singly occupied pairs at low frequencies, where the Coulomb gap in the density of states is important. The static dielectric constant is also obtained using the Kramers‐Kronig relations.
Effect of Broadening of Tail States on the Einstein Relation in Heavily Doped Compensated Semiconductors
Authors: Ghosh S. , Chakravarti A. N. 
Published: July 2007

AbstractAn attempt is made to study the dependence of the Einstein relation on carrier concentration in heavily doped compensated semiconductors with broadened tail states, both in the presence and absence of a quantizing magnetic field, taking n‐InSb as an example. It is found that, corresponding to a given free electron concentration, the broadening of the tail states modifies the Einstein relation by enhancing the diffusivity–mobility ratio in the absence of magnetic quantization while the reverse is observed in the presence of a quantizing magnetic field. Besides, the rate of decrease of the ratio with increasing magnetic field in the quantum limit is found to be independent of such broadening effects.
Intrinsic Pinning in Superconductors with Extremely Small Coherence Lengths
Authors: Schimmele L. , Kronmüller H. , Teichler H. 
Published: July 2007

AbstractBy means of a Ginsburg‐Landau‐type theory which takes into account the discrete lattice structure the variation of the energy (“Peierls potential”) of an isolated flux line is calculated when shifted relatively to the crystal lattice. In particular, a primitive cubic lattice is considered with a straight flux line, aligned parallel to a cube axis. The resulting Peierls potential may lead to intrinsic pinning if the coherence length is smaller than about two nearest neighbour distances. The coherence lengths at low temperatures determined for the recently discovered high Tc superconductors of the YBa2Cu3O7 class come very close to this value so that intrinsic pinning might possibly be relevant for these superconductors.
Application of the Embedded Atom Method to Phonon Dispersions and Local Surface Vibrations in Copper
Authors: Luo Ningsheng , Xu Wenlan , Shen Shuechu 
Published: July 2007

AbstractA formula of force constants between planes in lattice dynamics is derived from a new model within the framework of the Embedded Atom Method (EAM), which is based on results from density‐functional theory. Semiempirical functions for the description of the interaction properties in the ground state of Cu are determined by means of the EAM. Finally, force constants between planes of Cu, which lead to agreement between the obtained phonon dispersions and local surface vibrations and experimental results, may be calculated.
Plasma Waves in Degenerate Electron Systems with Random Impurities
Authors: Van Trong Nguyen 
Published: July 2007

AbstractPropagation of plasma waves in degenerate electron systems is considered. A modified dispersion equation for plasma waves is derived by taking into account the influence of random impurities without using perturbation theory. The damping of plasma waves is calculated for the T = 0 limit. It is shown that the damping is non‐zero in long wavelength limit due to the random impurities.
Thermoelectric Properties of p‐Hg1−xCdxTe
Authors: Höschl P. , Moravec P. , Belas E. , Franc J. , Grill R. 
Published: July 2007

AbstractLow temperature (77 to 300 K) thermoelectric measurements of undoped and well characterized p‐Hg1−xCdxTe (x ≈︁ 0.2) samples are reported. Analysis of the thermoelectric power is suggested on the basis of a three acceptor level model with one divalent acceptor (Hg‐vacancy) and one monovalent acceptor (foreign atom). From the temperature at which reversal of sign of the thermoelectric power takes place the concentration of holes at 77 K may be simply determined. The method is also suitable for the investigation of homogeneity of wafers of Hg1−xCdxTe with x ≈︁ 0.2.
Exact Solutions of Few First Passage Problems in Linear Correlated Walks. Applications to the Electron Trapping in a Semiconductor
Authors: Godoy S. , Fujita S. 
Published: July 2007

AbstractThe average number of steps, 〈N〉, in which a walker gets trapped at the origin when he starts at one of L − 1 non‐trap sites on a looping linear lattice of L points, is calculated for an arbitrary correlation. It is given by 〈N〉 = (L/6(1 + δ)) [(1 − δ) L + 1 + 5δ], where δ = α − β is the degree of correlation with α and β respresenting step probabilities for forward and direction‐changing motion, respectively. This result and others are obtained by solving basic difference equations for linear correlated walks with the aid of Fourier‐Laplace transformation techniques. Potential applications of the theory to trappings of electrons in a semiconductor and others are discussed.
EPR of V4+ in Apophyllite
Authors: Vassilikou‐Dova A. B. , Lehmann G. 
Published: July 2007

AbstractIn a natural apophyllite two crystallographically inequivalent centers of V4+ with triclinic point symmetries are observed. The more intense one is assigned to the Ca sites. Superhyperfine splitting due to one F nucleus is evident for many orientations, but a large portion of V4+ is evidently coordinated to an OH group replacing F. The less intense center is assigned to K sites in agreement with results of an earlier publication for a specimen from a different locality. Due to large linewidths its spectra were incompletely resolved. Both centers must arise from replacement of one water molecule by the oxygen of a VO2+ ion.