bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plasmons in a Superlattice with a Doped Surface Layer
Authors: Sy H. K. , Chua T. C. 
Published: July 2007

AbstractFinite semiconductor multilayers consisting of a doped surface layer in addition to a periodic array of underlying two‐dimensional charge layers are studied. The frequency of the plasmons can be obtained in terms of a determinant equation. The possible existence, and the dispersion relation of the surface plasmon modes, are discussed in the semi‐infinite limit. Numerical results are shown for surface densities greater or smaller than the underlying charge density, for both finite and semi‐infinite systems.
Electron Structure and Residual Resistivity of Aluminium Clusters with 3d‐Impurities
Authors: Kurkina L. I. , Gorbunov V. A. , Farberovich O. V. 
Published: July 2007

AbstractThe self‐consistent electron structure and residual resistivity of Al clusters containing substitutional impurity atoms of Fe, Co, and Ni are calculated within the framework of the model “atom embedded in spherical jellium cluster” and local density approximation. The residual resistivity is obtained to oscillate with increasing cluster size.
Resonant Raman Scattering near the Band Gap in 4H‐PbI2, Crystals)
Authors: Baltog I. , Lefrant S. , Mihut L. , Mondescu R. 
Published: July 2007

AbstractNew data are given of the resonatn Raman scattering (achieved by incident excitation tuning or by sample temperature variation) fo rthe 4H polytype of pure and doped PbI2 single crystals. A new Raman line, considered by us as a two‐TA‐phonon line, is observed at 30 cm−1. Some new features of the Raman spectra in the region of 75 cm−1 are revealed for pure and doped crystals, when excitation approaches resoncance. As for the two‐LO‐phonon line (224 cm−1) the same enhancement at resonance is found for a new line apperaing at 126 cm−1.
Distributed Relaxation Response for Two Classes of Material Temperature Behavior
Authors: Macdonald J. R. 
Published: July 2007

AbstractExpressions for the transient and frequency response of materials showing exponential distributions of transition rates are summarized and related to recent work in the field. Responses arising from temperature‐independent distributions (class I) are contrasted to those that depend in a simple way on temperature (class II). The distinction between dielectric and conducting systems is particularly emphasized, and the different temperature dependences of their frequency power‐law exponents for class‐1) situations are discussed in detail. Besides presenting model frequency‐response curves, it is shown that an exponential distribution of activation energies can lead to conductance frequency response very similar to that recently found by Lee et al. for two glasses and several ionically conducting single crystals.
Optical Properties of Multi‐Layer Structures. IV. Non‐Linear Absorption of light in Multi‐Layer Structures
Authors: Fomin V. M. , Pokatilov E. P. 
Published: July 2007

AbstractThe theory of non‐linear response of an electronic subsystem in planar multi‐layer structures (including quantum wells) to a strong electromagnetic field is developed. On the basis of the exact Hamiltonian of the electron‐phonon interaction for such structures a non‐linear dielectric permittivity tensor is obtained by the statistical operator method in the path integration representation. In the three‐layer structures with a thin middle semiconducting layer and moderate values of the dielectric permittivity of the outer dielectric media the contribution to the absorption due to the interaction of electrons with surface phonons is found to prevail over that of bulk phonons and to ensure a substantially more rapid rise in the absorption coefficient with increasing intensity in comparison with the case of a semiconductor crystal.
Phonon Frequencies, Elastic and Grüneisen Constants of Liquid Chromium
Authors: Rao R. V. Gopala , Venkatesh R. 
Published: July 2007

AbstractThe potential function as formulated by Bretonnet and Deroache is used to evaluate the phonon frequencies, elastic and Grüneisen constants. The latter is also evaluated by a different method as well. The elastic constants are also calculated through Schofield's equations. All the results are found to be in agreement with each other. From the parameters used for the computation of the structure factor we obtain S(0), the structure factor in the long‐wave limit and hence the compressibility from which the velocity of the sound is calculated. Assuming Ziman's theory that the structure factor peaks around 2kF, we find that the longitudinal phonon frequency maximum occurs at kF and from this value and sound velocity the maximum of the phonon frequency could be predicted. From the sum rules of frequency dependent structure factor the maximum value of ωL(k) is predicted. The maximum values so obtained by different methods are in satisfactory agreement with each other.
Quantum Mechnical Hartree‐Fock Study of the Elastic Properties of Li2S and Na2S
Authors: Lichanot A. , Aprà E. , Dovesi R. 
Published: July 2007

AbstractThe binding energy and elastic constants of Li2S and Na2S are investigated at an initio all electron Hartree‐Fock level. The comparison between calculated and experimental value leads to satisfactory agreement for Li2S and a substantial difference in the Na2S case. The comparative evolution of the elastic constants in the series of alkaline oxides and sulphides with the size of the cation seems to indicate that the discrepancy is mainly due to an overstimation of the experimental elastic constants of Na2S.
To the Theory of High‐Temperature Superconductivity
Authors: Naimi E. K. 
Published: July 2007

AbstractA new attitude towards the problem of high‐temperature superconductivity is suggested. The main attention is focused on the principal differences between electrodynamics of high‐temperature and low‐temperature superconducting state. While describing the electromagnetic field in high‐temperature superconductors (HTSC) it is necessary to take into account both conducting currents and displacement currents in general case. It is shown that the transition of HTSC into the superconducting state is accompanied by its spontaneous polarization, so that the external electric field is completely compensated inside the superconductor volume. The Messiner magnetic effect in HTSC is a secondary one. It is found that the excitation spectrum of HTSC has a multi‐gap structure. Estimations of all fundamental parameters of HTSC are given. Comparison of theoretical with experimental results shows good agreement. Some aspects of anisotropy and high‐frequency properties of HTSC are discussed.
The Physical Nature of Changes of Lattice Parameters in Small Particles
Authors: Ya Gamarnik M. 
Published: July 2007

AbstractThe nature of size‐related changes of lattice parameters is determined by the difference in bond energies of surface and inner unit cells of a particle, which (the difference) leads to an excess or a deficit of the intracrystalline pressure in a small particle, stipulating a compession or tension of its lattice. It is shown that the size‐related change of the length of each lattice edge is determined by crystal sizes in perpendicular direction and practically does not depend on the crystal size along this edge. This property, called transversality, is explained by an energetic non‐equivalence of different unit cells, which is realized within cell monolayers or columns perpendicular to the edge. It is shown that the sign of the size effect – decrease or increase of the lattice parameter – is determined by the sign of the interaction energy v of a unit cell with crystal unit cells excepting the nearest ones. To the positive sign of this energy there corresponds compression, to the negative sign tension of a small particle. The structural features are analysed for substances with ionic, covalent, and metallic bond types, determining the sign of v and therefore the sign of the size effect.
Physical Properties of Thorium under Pressure
Authors: Mahalingam A. , Vidya K. , Kalpana G. , Palanivel B. , Rajagopalan M. 
Published: July 2007

AbstractA theoretical calculation of the band structure, electrical resistivity, and superconductivity of f.c.c. thorium under pressure is reported. The effect of pressure on the band structure is obtained by means of the linear muffin‐tin orbital (LMTO) method. The superconducting transition temperature (Tc) is calculated using McMillan's as well as Allen‐Dyne's modified formulae. The parameters necessary to calculate Tc are taken from the band structure outputs. The calculated values of Tc initially decrease with the increase in pressure up to 154 × 108 Pa and then begin to increase. The sudden increase in the value of Tc around 181 × 108 Pa is attributed to the change in the Fermi surface topology. The theoretically calculated values of resistivity initially decrease with increase in pressure up to 154 × 108 Pa and then begin to increase in accordance with the experimental results. The change in slope around 181 × 108 Pa may be due to a change in Fermi surface topology. The calculated values of ϱ are in correct trend with the experimental values.
X‐Ray Diffraction and Mössbauer Effect Studies on Smb−x CaxFeO3−y (0 ≦ x ≦ 0.70)
Authors: Li J. , Cai X. , Yang X. , Wang T. M. 
Published: July 2007

AbstractSamples of Sm1−x CaxFeO3−y are prepared in air for x ranging from 0 to 0.70. X‐ray powder diffraction analysis shows that the samples are the single‐phased perovskite‐type compounds with the space group Di162h‐Pbnm. The accurate lattice constants of Sm1−x CaxFeO3−y are calculated from the observed diffraction peaks by the least‐squares refinement. Sm1−x CaxFeO3−y yields two hyperfine splitting patterns which would be assigned to iron(III) on octahedral sites and iron(III) on tetrahedral ones. The percentage of the iron on the tetrahedral sites increases almost linearly with increasing x, indicating that the oxygen vacancies in the lattice increase with the increasing substitution of Ca for Sm. The compounds prepared contain only trivalent iron, suggesting that they would have the chemical formula Sm1−x CaxFeO3−x/2.
Coherent Relaxation and Acceleration of Atoms in Nonequilibrium Crystals
Authors: Sugakov V. I. 
Published: July 2007

AbstractIt is shown that in a nonequilibrium system of atoms, which are situated along a crystal line, in the presence of two minima of potential energy for every atom and in case of atom localization in the higher‐energy minimum a series of successive collisions resulting in acceleration of one of the atoms may occur. The above‐mentioned systems can appear in the vicinity of the coherent boundary of different phases in crystals or in the case of strong shear deformation. The excited crystal state, in which the successive atom relaxation leads to the energy rise of one of the atoms, is called “acceleron”. The role of various processes, which restrict the acceleron energy, is analyzed. The possibility to manifest the phenomenon is discussed.
Low‐Temperature Mobility of a Two‐Dimensional Hole Gas in GaAs–AlGaAs Heterojunctions
Authors: Datta R. , Chaudhuri S. R. , Kundu S. 
Published: July 2007

AbstractA theoretical model for the calculation of the mobility of a two‐dimensional hole gas (2DHG) supported by a heterojunction is presented. Different scattering mechanisms that put a limit to the inherent mobility of the 2DHG system, like the background impurity scattering, remote impurity scattering, deformation potential, and piezoelectric acoustic phonon scattering, and polar optical phonon scattering, have been included. Dynamic screening of the hole gas has been derived. Screening plays a very important role in the scattering of the heavier hole gas than for the lighter electrons. A discrepancy between the experimental and the theoretical effective hole masses existing in earlier theoretical models has been overcome in the present communication.
Filling‐Factor‐Dependent Cyclotron Resonance in GaInAs/AlInAs Modulation‐Doped Single Quantum Wells
Authors: Jianc D. S. , Goiran M. , Leotin J. , Askenazy S. , Zhanc Y. H. , Plooc K. 
Published: July 2007

AbstractThe line shape of cyclotron resonance (CR) absorption is investigated for a two‐dimensional electron gas (2DEG) in modulation‐doped GaInAs/AlInAs narrow SQW structures. CR absorption is measured as functions of far infrared (FIR) frequency, temperature, and carrier concentration. At low temperature and short FIR wavelengths, a well‐defined filling‐factor‐dependent quantum oscillation structure is obtained for samples with high 2DEG concentrations, exhibiting clear maxima and minima and a phase change point at the top of the CR peak. The modulated scattering is attributed to short‐range scatterers originating mainly from alloy scattering. A part of the contribution comes from ionized impurity scattering. The analysis of the temperature dependence of the CR line width and Hall mobility gives additional support to this argument. An electron effective mass as high as 0.063mo in In0.53 Ga0.47As is observed due to the non‐parabolicity effect.
Properties of the Ground State in the Hubbard‐Hirsch Model
Authors: Zhong Qiang , Nie Hui‐Quan , Wei Guo‐Zhu 
Published: July 2007

AbstractUsing Bogolyubov's variational principle and the mean‐field theory the properties of the ground state in the Hubbard‐Hirsch model are discussed for weak coupling condition, and the phase diagrams are plotted. It is pointed out that the ground state of the system can be paramagnetic, ferromagnetic, or antiferromagnetic, depending on the intensity of the Coulomb interaction U and the exchange interaction J; the charge‐ordered phase does not exist.
EPR Studies on Dimers in a Diamagnetically Dilute Copper Calcium Acetate Hexahydrate
Authors: Samanta (Sikdar) R. , Pal A. K. 
Published: July 2007

AbstractX‐band EPR investigations of mixed crystals of the composition Cu1−xCdxCa(Ac)4 · 6 H2O (Ac = ace‐ tate) with x = 0.858, 0.552,0.328, and 0.148 are carried out at room and liquid nitrogen temperatures. Besides monomer spectra, dimer spectra due to transitions within the spin triplet, singlet‐triplet transitions, and half‐field lines (due to ΔM = 2 transitions within the dimer triplet) are observed. Zero‐field splitting is shown to have purely dipolar origin. Singlet‐triplet spectra enable precision determination of the value of the exchange integral J as well as its sign. J has a much greater value than that derived in case of the concentrated copper salt, and unlike the case of the latter it is isotropic, showing thereby that magnetic dilution plays an important role in determining the magnitude of J.
Growth Kinetics of CdS Nanocrystallites in Glass through Quantum‐Size Effects
Authors: Sukumar V. , Doremus R. H. 
Published: July 2007

AbstractGlasses containing very small particles of CdS are prepared and their properties studied. Changes in the optical absorption spectra of CdS glass result from quantum confinement effects. With very small particle size, large confinement energies of up to 4 eV are obtained, which have not been before. The blue‐shifts in the optical absorption spectra show that the growth rate of the particles at short times are diffusion controlled, and the activation energy for growth is calculated. The band gaps of the CdS nanocrystallites in glass are determined from photoluminescence measurements, which show a high‐energy peak, corresponding to the band gap, that had not been previously observed.
Structural and Electronic Properties of Carbon‐Doped β‐Rhombohedral Boron
Authors: Werheit H. , Kuhlmann U. , Laux M. , Lundström T. 
Published: July 2007

Abstractβ‐rhombohedral boron doped with carbon up to about 1 at% is investigated by X‐ray diffraction, by optical transmission spectroscopy in the spectral range of the absorption edge and its low energy tail, by I R reflection spectroscopy in the lattice vibration range, and by Raman scattering. The carbon atoms substitute for boron sites in the icosahedra shrinking as a consequence of the increased intraicosahedral bonding force. Hence the lattice constants decrease with increasing carbon content. Within the accuracy of measurement the interband transition energies are not influenced by the carbon content, and the p‐type conductivity remains qualitatively unchanged. Additionally to the series of six ionization energies of B12 electron trapping levels, which are equidistantly arranged below the conduction band in pure boron, a second series of B11C trapping levels develops. The traps are esscntially generated by the interaction between one electron each and up to six pairs (probably triples) of defined phonons. These phonons are quenched as a consequence of the occupation of these traps. In correlation with the new optical results ESR investigations of other authors can now be interpreted. Important details of the electronic structure and its modification by carbon doping are determined. The relevance for other boron‐rich solids with icosahedral structure is discussed.
The Bond‐Diluted Spin‐1 Transverse Ising Model with Random Longitudinal Field
Authors: Benyoussef A. , Ez‐zahraouy H. 
Published: July 2007

AbstractThe bond‐dilution effects on the phase diagram of a spin‐1 king ferromagnet in a transverse field with random longitudinal field is investigated within an expansion technique for cluster identities of spin‐ localized spin systems. Longitudinal and transverse magnetizations are studied for several values of thc bond concentration. The critical temperature dependence on the bond concentration, the longitudinal field, and the transverse field are presented. General formulae applicable to structurcs with arbitrary coordination number N are given.
Investigation of the ADC Method for Direct ODF Approximation by Means of Standard Functions
Authors: Raabe D. , Lücke K. 
Published: July 2007

AbstractThree‐dimensional orientation distributions of grains in polycrystalline aggregates are referred to as crystallographic textures. They can be calculated from centrosymmetric two‐dimensional pole figures by means of series expansion methods or by direct methods. Both techniques lead to inaccuracies, caused by the absence of the odd coefficients and by truncation errors in the first case and by the underdetermination of the set of linear equations combining discrete cells in the pole figures and in the three‐dimensional orientation space in the second case. The direct method of “arbitrary defined cells” (ADC) is investigated by means of the component fit method and by use of standard functions, respectively. The maximum value of the orientation density achieved by the ADC method represents a good approximation. However, weak negative and positive ghost adulterations are identified.
Lattice Dynamics of Cyanogen
Authors: Zeng W. Y. , Anderson A. 
Published: July 2007

AbstractA simple force constant model is described and applied to the vibrations of crystalline cyanogen, C2N2, at low temperatures. The model uses eleven adjustable parameters (six intermolecular and five intramolecular) to calculate the frequencies of seventeen lattice modes and twenty‐eight components of internal modes, and reasonable agreement with spectroscopic data is obtained. Although cyanogen shows many of the characteristics of a typical molecular crystal, there is some evidence that its large quadrupole moment results in longer‐range forces being more significant than usual, particularly in contributing to the splittings of some internal modes.
About an Increase of Exciton Binding Energy in Layered InSe
Authors: Gnatenko Yu. P. , Zhirko Yu. I. 
Published: July 2007

AbstractAt T > 25 K an increase of the direct free exciton binding energy ΔE in the exciton absorption spectra of InSe is found. The calculations show that this phenomena may be attributed to an increase of the exciton reduced mass μ due to exciton‐interlayer optical phonon interaction. The dynamical processes of exciton‐phonon intcraction with temperature in laycred InSc are discussed.
Response Approach to Current and Noise Power Spectrum of Cooper Pair Tunneling in Ultrasmall Junctions
Authors: Krech W. , Hädicke A. 
Published: July 2007

AbstractUsing the response theory approach, the mean current due to tunneling of Cooper pairs in microwave driven superconducting junctions coupled to an electromagnetic environment is derived. The noise power spectrum is calculated showing shot noise behaviour due to the stochastic character of Cooper pair tunneling if the Josephson coupling energy is much smaller than the charging energy.
Spectroscopic Studies on the Spin Structures in the Magnetic Phases of Erbium Oxisulphate
Authors: Oreans P. 
Published: July 2007

AbstractEr2O2SO4, orders below 1.5 K as an Ising‐like antiferromagnet with its moments parallel to the crystallographic c‐axis. In external fields along c, three ferrimagnetic phases with different magnetizations are crossed before the saturated paramagnetic phase is entered. The lines of the optical absorption spectrum are split owing to different moment configurations in the surroundings of the light‐absorbing Er3+ ion. These line splittings and their Zeeman effect in an external field are studied in order to uncover the spin structures in the different magnetic phases. The analysis is substantiated by calculations in mean‐field theory.
On the Influence of Elastic Strains on Crystallization Processes in Solids. I. Spherical Clusters in Solids of Finite Size
Authors: Möller J. , Schmelzer J. , Gutzow I. , Pascova R. 
Published: July 2007

AbstractThe influence of the finite size of a solid sample on evolving elastic fields and, in particular, on the energy of elastic deformations due to the formation of a new phase inside a solid is analyzed. It is shown that, depending on the ratio between the size of the matrix RM and that of the cluster RC, elastic strains may either stimulate or inhibit the growth of the newly evolving phase. Elastic strains may result in a stable two‐phase equilibrium state. The discussed specific finite‐size effects become important for clusters in samples which are not larger than about 5RC. The outlined model is the basis for the discussion of energies of the elastic strain field caused by the process of formation of a cluster of a new phase near or at the surface of a solid, the detailed analysis of which will be presented in Part II.
On the Influence of Elastic Strains on Crystallization Processes in Solids. II. Formation of Clusters near and at Interfaces
Authors: Möller J. , Schmelzer J. 
Published: July 2007

AbstractDeformations due to the formation of a spherically shaped cluster near a planar free surface are analysed. The dependence of the mechanical energy contained in these deformations on the cluster distance from the surface is computed analytically. The energy is found to be lower for clusters near the surface. Results are obtained for the energy of clusters formed immediately at the surface. It turns out that the lowest value of the elastic energy for clusters of given volume is found for hemispherical clusters. As intermediate steps in the derivation, the independence of the elastic energy of the cluster shape for clusters in an infinite matrix and the general absence of elastic interactions are reconfirmed, provided matrix and cluster are characterized by the same elastic constants. These results explain in this way a number of observations, for example, surface nucleation and surface crystallization.