bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculation of Phonon Dispersion Curves for AlP, AlAs, and AlSb
Authors: Kagaya H.‐Matsuo , Soma T. 
Published: July 2007

AbstractThe lattice dynamics of AlP, AlAs, and AlSb is investigated using the recently proposed binding force and the local Heine‐Abarenkov model potential. The theoretical results of the phonon dispersion curves and the dynamical elastic constants are presented although no experimental information is given on the band calculation, neutron scattering data, and ultrasonic velocity of AlP and AlAs.
Optical Absorption Edge Investigation of CdIn2S4 and β‐In2S3 Compounds
Authors: Kambas K. , Anagnostopoulos A. , Ves S. , Ploss B. , Spyridelis J. 
Published: July 2007

AbstractCdIn2S4 and β‐In2S3 crystals are grown by direct melting of stoichiometric mixtures of their components. The absorption coefficients are measured as a function of the wavelength of the incident light between 500 to 750 nm at various temperatures. For both compounds the energy gap Eg is temperature dependent and the absorption edge shifts to lower energy values with increasing temperature. For β‐In2S3 it is found that the absorption edge is mainly due to direct transitions and the temperature dependence of Eg is linear. At room temperature the value Eg = 2.00 eV is measured. In the case of CdIn2S4 there appear indirect transitions for low values of the absorption coefficient while the temperature dependence of the direct energy gap is linear at high temperatures and quadratic at low temperatures. At room temperature the direct gap has the value Eg = 2.21 and the indirect one E = 2.05 eV. A rough estimation of the Debye temperature gives θD = 665 K.
Electron Momentum Distribution in Niobium and the Renormalised Free Atom Model
Authors: Tomak M. , Singh Hanuman , Sharma B. K. , Manninen S. 
Published: July 2007

AbstractThe Compton profile of polycrystalline niobium is measured using 59.54 keV Γ‐rays from a 241Am source. The results are interpreted in terms of a renormalised free atom model. Best agreement between the measured and calculated values is found for the electronic configuration 4d4,45s0.6.
Effect of Relativistic Mass Variation of the Electron on the Parametric Instability of Acoustic Waves in Transversely Magnetised Piezoelectric Semiconducting Plasmas
Authors: Ghosh S. , Dixit S. 
Published: July 2007

AbstractThe effect of relativistic mass variation of the electron and of a large transverse magnetostatic field on the parametric excitation of acoustic waves is investigated in a piezoelectric semiconducting plasma. The analysis is based on the hydrodynamic model of a plasma in the collision dominated regime for kl ≪ 1. In presence of the relativistic mass variation of electrons the conditions of instability gets modified and is obtained at a much higher value of the high frequency oscillatory electric field with larger growth rate compared with that in nonrelativistic limit. Numerical estimations are made for n‐InSb at 77 K when the crystal is irradiated with a 1.06 μm Nd: YAG laser.
Light Extinction by Colloidal Thallium in Ionic Crystals
Authors: Ekmanis Yu. A. , Radchenko I. S. 
Published: July 2007

AbstractThe calculation of optical extinction spectra in TlCl and TlBr crystals for Tl colloidal particles of various shape: spherical, single and ellipsoidal chains is presented. It is shown that for small spherical particles the spatial distribution of linearly polarized light scattering can be estimated. Comparison with experimental data confirms the presence of such Tl particles as well as the existence of interactions between contacting particles.
Some Peculiarities of the Electrooptical Spectra for n‐GaAs(Cr) at Liquid Helium Temperatures (Wannier Levels?)
Authors: Mironov A. G. , Morozova V. A. , Vavilov V. S. 
Published: July 2007

AbstractElectrooptical effects are investigated for n‐GaAs(Cr) at the field strengths E ⪅ 3 × 104 V/cm, photon energies 0.5 < hv < 1.5 eV and temperatures 10 < T < 80 K. The oscillatory structure of appreciable amplitude is found at 10 < T < 40 K in the spectral regions of extrinsic (due to Cr impurity) and intrinsic absorption. The structure observed agrees with the concept of Wannier levels; the oscillations occur at hv > I and at hv > I (I — impurity ionization energy) and the oscillation period linearly depends on E. At T > 40 K the structure is smeared out due to acoustic phonons. A tentative discussion is given concerning the apparent inefficiency of random fields in smoothing the structure corresponding to Wannier levels.
Crystal Field Study of HoNi5, by Neutron Scattering
Authors: Goremychkin E. A. , Mühle E. , Lippold B. , Chistyakov O. D. , Savitskii E. M. 
Published: July 2007

AbstractThe crystal field parameters in HoNi5 are determined from measurements of inelastic neutron scattering. With the parameter set found good agreement between computed and experimental results of susceptibility and magnetization in single crystals and of the low‐temperature part of the specific heat is obtained.
Transport in Simple Metals in the Framework of a Unified Pseudopotential Study
Authors: Sen D. , Sen S. K. 
Published: July 2007

AbstractThe electrical and thermal transport properties of some simple metals are calculated using a unified local pseudopotential whose parameters have earlier been determined from various lattice mechanical properties. The transport properties include electrical and thermal resistivities both, in solid and liquid phases at different temperatures, resistivities due to vacancies, and thermoelectric power. The overall agreement with the experiment is good for Na, K, Al but for Li and to some extent Rb, the discrepancies in theory and experiments indicate the necessity of a comprehensive non‐local theory and some refinements of transport equations.
Conductivity of Amorphous AxB1−x Semiconductors with Potential Fluctuations of the Mobility Edges
Authors: Agafonov A. I. , Plotnikov A. F. , Seleznev V. N. 
Published: July 2007

AbstractThe deep localized states in the bandgap of amorphous AxB1−x semiconductors are connected with quantum levels of the carrier energy in the fluctuation potential wells of the mobility edges formed by matter A clusters. A theory for the amorphous AxB1−x semiconductor conductivity is presented. The theory takes into account the energy distribution of the localized states in the band gap and the lowering in the electric field of the barrier for thermal ionization of the carriers from the localized states into the mobility band of the amorphous semiconductor. The obtained theoretical results explain the experimental data on the temperature and field dependences of the conduction of some amorphous semiconductors.
A Continuum Model for the Impurity State of Ferromagnets
Authors: Li Zhen‐Ya , Lin Jui‐Teng 
Published: July 2007

AbstractThe spin‐wave spectra of simple cubic ferromagnets with single and few impurities are investigated via a continuum model. Using the Green's function technique, it is shown that only the s‐like localized impurity state exists, in consistency with the experimental results.
Absorption interbande induite dans le silicium sous forte excitation picoseconde à 1,06 μm
Authors: Pugnet M. , Amand T. , Cornet A. , Brousseau M. 
Published: July 2007

AbstractNous présentons ici les résultats et la modélisation de nos expériences de transmission d'une impulsion laser YAG (Λ = 1,064 μm; durée 30 ps) à travers une plaquette de silicium cristallin, à T = 295 K et à fort niveau d'excitation (Ei ⪆ 0,05 J/cm2). Notre modèle est fondé sur les équations de continuité de la densité du plasma n(x, t) et de la puissance instantanée P(x, t). Nous montrons que la saturation de l'énergie transmise Et(Ei), observée expérimentalement, s'explique par une croissance dynamique du coefficient d'absorption interbande α(x, t); nous interprétons cette croissance comme la conséquence de la renormalisation de la bande interdite par un plasma électron‐trou non dégénéré sans échauffement du réseau. Nous prenons une expression phénoménologique: α(n(x, t)) = α0 + α1(n(x, t))r où r et α1 sont des paramètres ajustables tandis que α0 est le coefficient d'absorption interbande à faible excitation (α0 ≈ 9 cm−1); le meilleur ajustement est obtenu pour r ≈ 1; α1 ≈ 6 × 10−18 cm2; coefficient d'absorption par les porteurs libres: à = 4 × 10−18 cm2. Avec ces valeurs, le calcul montre qu'au‐dessus de 0,1 J/cm2, la distribution spatiale des porteurs est modifiée dans le sens d'une localisation vers la surface excitée d'autant plus grande que l'énergie incidente Ei croǐt; nous calculons l'énergie transférée au réseau par la relaxation du plasma et nous montrons qu'on ne peut pas expliquer la diminution dynamique de la bande interdite déduite de la modélisation de nos expériences par un échauffement du réseau. Une variation en n1/2 de la renormalisation de la bande interdite décrit mieux nos résultats que la variation en n1/3 prévue par la théorie.
Luminescence Properties of Rare‐Earth‐Activated Gadolinium Fluoride (GdF3) and Oxyfluorides (GdOF)
Authors: Lammers M. J. J. , Blasse G. 
Published: July 2007

AbstractThe luminescence properties of RE3+‐activated GdF3 and GdOF are studied for both uv and X‐ray excitation. GdOF exists in two modifications, an orthorhombic and a tetragonal one and both are used as a matrix. GdF3 is activated with Pr3+, Sm3+, Tb3+, Dy3+, Er3+, and Tm3+ and with a transition metal ion, viz. Mn2+. Both modifications of GdOF are activated with Tb3+, Er3+, and Tm3+. Especially the Tb3+‐activated samples are very efficient green phosphors under both uv and X‐ray excitation.
A Hole Center Causing Rose Coloration in AlPO4 and GaPO4
Authors: Requardt A. , Lehmann G. 
Published: July 2007

AbstractIn synthetic AlPO4 crystals and Sn‐doped GaPO4 hole centers localized on an oxygen showing an almost isotropic hyperfine splitting from a 31P nucleus are observed after X‐ray irradiation and analyzed by EPR. They are evidently caused by substitution of Al and Ga, respectively, by a divalent cation, most likely Mg2+. From the variation of the EPR linewidths with temperature an activation energy of 19 kJ/mole for thermal hopping of the hole is found in AlPO4. These centers cause a rose coloration and the first absorption band in AlPO4 has an oscillator strength near 0.3, in the same range as for the smoky quartz centers. It is interpreted as arising from optical transfer of the hole within the PO4 unit. Thermoluminescence emission is observed with destruction of the centers in AlPO4. From glow curves an activation energy of 136 kJ/mole is obtained which in this case represents the distance of the hole from the valence band. The properties of the center in AlPO4 are compared to those of a similar center in certain natural rose‐colored quartz crystals.
Radiative Optical Modes of Vibration in CeO2 Thin Films
Authors: Mochizuki S. 
Published: July 2007

AbstractThe radiative optical modes of vibration in a CeO2 thin film on a metal substrate are observed at various temperatures from room temperature to 1273 K by the reflection and thermal‐emission methods. A comparison of the experimental spectra and the theoretical ones shows good agreement. The upper branch of the polariton dispersion curve of CeO2 at room temperature is determined by analyzing the incident‐angle dependence of the virtual mode spectra centered near the longitudinal‐optical phonon frequency of CeO2 bulk crystal. The temperature dependence of the longitudinal‐optical phonon frequency of CeO2 is determined by the measurements of the virtual‐mode frequency shift with temperature under small incident (emission) angle condition and is discussed in terms of the thermal expansion and other anharmonic effects.
Thermoelastic Behaviour and Higher‐Order Elastic Constants of Ionic Crystals
Authors: Bhende W. N. , Bakhshi P. S. , Shanker J. 
Published: July 2007

AbstractThe relationships are given between thermoelastic properties and higher‐order (third and fourth order) elastic constants for twenty alkali halides with NaCl and CsCl structures, and for four alkaline earth oxides viz. MgO, CaO, SrO, and BaO crystals. Expressions for thermoelastic quantities such as the Grüneisen parameter and its volume derivative, Anderson parameters, and thermal expansion coefficient, are obtained in terms of higher‐order elastic constants. These expressions provide a new method for estimating thermoelastic quantities from higher‐order elastic constants. Calculations are performed using an interionic potential model which takes account of three body interactions, van der Waals interactions, and overlap repulsive interactions upto second neighbours. The results are discussed and compared with experimental data.
The Effect of Collective Electron‐Hole Plasma Modes on Charge Carrier Mobility in Polar Semiconductors
Authors: Kasiyan A. I. , Russu P. I. 
Published: July 2007

AbstractThe dispersion relations for renormalized plasmon‐phonon modes for PbTe and GaAs are calculated. Electron μe and hole μh mobilities are computed for scattering by these modes. It is found that with the increase of the charge carrier concentration, n, mobilities decrease due to the effect of dynamic antiscreening. In the concentration range where the free‐carrier plasma frequency is comparable to the uncoupled LO‐phonon frequency the mobilities reach minimum values. With further increase of n the antiscreening effect decreases and the mobilities begin to grow tending in the limit of high n to values corresponding to the quasistatic screening.
Excitons in Periodic Structures with Homopolar Semiconductors and Anisotropic Dielectrics
Authors: Fomin V. M. , Pokatilov E. P. 
Published: July 2007

AbstractThe charge carrier interaction potential is determined and the exciton energy spectrum in periodic multi‐layer structures with anisotropic permeability constant is calculated. In contrast to three‐layer systems with semi‐bounded outer layers in periodic structures dielectric layers are found to affects the exciton spectrum not only by the mean geometric value of the dielectric permeability tensor component \documentclass{article}\pagestyle{empty}\begin{document}$ \bar \varepsilon _a = \sqrt {\varepsilon _a^\parallel \varepsilon _a^ \bot } $\end{document} but also by the anisotropy parameter εa = ε/ε. The absolute value of the exciton ground‐state energy in semiconductors with a dielectric constant εb > εa and low layer thickness la and lb in the two‐dimensional Coulomb interaction region is found to decrease as the thicknesses ratio λ = la/lb decreases. The effect of semiconductor layers thickness at different values of the anisotropy parameter εa as well as of thickness ratio λin the logarithmic law of interaction on the exciton ground‐state energy is studied.
The Energy Transport from One Molecular Chain to the Other which are in Mutual Contact by a Small Number of Crystal Sites
Authors: Gashi F. , Gashi R. , Shemsedini Z. , Žakula R. B. 
Published: July 2007

AbstractBy methods of non‐equilibrium statistical physics the kinetical coefficient is evaluated of energy transport from one molecular chain to the other which has the same contacting point. Especially the contributions of soliton waves in this energetic transport are studied. It is estimated that only the solitons found at the contact point give contributions compararable with those which in kinetical coefficient give collective exciting‐excitons.
On the Landau Phase Transition Theory for the Magnetic Itinerant Electron System Weakly Interacting with Localized Spins
Authors: Cong Bach Thanh 
Published: July 2007

AbstractThe Landau expansion form of the thermo‐dynamic potential of the magnetic itinerant electron system weakly interacting with localized spins is obtained from its functional representation. The dependence of the Landau parameters A, B (which appear in the expansion of the thermodynamic potential in powers of the magnetization) on temperature and microscopic parameters is presented. The phase transition type in some substituted ACo2 compounds (A is a heavy rare earth metal) is also discussed in the framework of the developed theory.
A Variational Method in Wannier Representation for an Electron Weakly Bound to an Isoelectronic Impurity
Authors: Geistlinger H. , Weller W. 
Published: July 2007

AbstractThe problem of a single electron bound to an isoelectronic impurity (solved in k‐space by Koster and Slater) is reconsidered in lattice space. An analytically tractable variational method for the ground state is developed and compared with the numerically evaluated solution in k‐space. For GaP:N taking into account the real band structure of the lowest conduction band the variational method yields a sufficient agreement with the k‐space eigenwert equation. The variational approach developed in the lattice space allows a straightforward generalization to the binding of an exciton (considered in I) which takes into account the electron‐hole correlation, crucially in the region of weak binding (e.g. GaP:N).
Effect of Irradiation with Intense Laser Light on Trans‐Polyacetylene
Authors: Iwahana K. , Knoll P. , Kuzmany H. 
Published: July 2007

AbstractAn effect of irradiation with intense laser light on trans‐polyacetylene is investigated. It is found that laser radiation gives rise to an enhancement of the background intensity in Raman scattering, which finally develops into a strong luminescence band. This new luminescence band consists of several bands with a peak‐energy spacing of 1200 to 1400 cm−1 and exhibits an unusual dependence on the excitation energy in that each band of luminescence shifts with the laser frequency like a fist‐order Raman spectrum. It is suggested from comparison with the other experimental results that the luminescence observed in the trans‐polyacetylene sample degraded by laser irradiation originates from the excited state with a decay time of 1200 ps.
Study of the Hall Coefficient in p‐Type Germanium Taking into Account Anisotropic Charge Carrier Scattering
Authors: Gutsul I. V. , Kirnas I. G. , Litovchenko P. G. , Marusyak V. I. , Nitsovich V. M. , Ostapov S. E. , Petrosyan E. E. 
Published: July 2007

AbstractA quasi‐momentum distribution function of light and heavy holes in p‐type Ge is found by expanding the field and the collision terms of the kinetic equation in terms of the anisotropy parameter, indicating the degree of non‐sphericity of constant energy surfaces, in the zeroth, first, and second order approximation. The above method for solving the kinetic equation enables one to calculate the magnetic field dependence of the Hall coefficient taking into account the complex structure of the valence band of p‐Ge and the nature of carrier scattering. The calculated RH/R0 = f(B) dependence is compared with the experimental values obtained on samples with p = 1.7 × 1014 cm−3 having an orientation E ∥ 〈100〉, B ∥ 〈001〉 for T = 77 and 300 K.
Thermoelectric Power of Liquid Germanium and Tin
Authors: Bath A. , Hugel J. , Kleim R. 
Published: July 2007

AbstractMeasurements of the absolute thermopower S of liquid germanium and tin are reported. It is found that S = −0.5 μV/K for Ge at the melting temperature and S = −1.5 μV/K for Sn at 900 °C. Calculations of the resistivity and the thermoelectric power performed in the framework of Ziman's nearly‐free electron theory, using the pseudopotential approach and the t‐matrix formulation, lead to reasonable agreement with experiment.
Ferroelectric Liquid Crystals in External Fields
Authors: Talim S. L. , Pires A. S. T. 
Published: July 2007

AbstractThe phase transitions of ferroelectric liquid crystals in external fields (electric and magnetic) is studied, using the Landau free energy expansion for the order parameter. The commensurate‐incommensurate phase transition, in the presence of a magnetic field using solitons is analysed in detail. The normal‐incommensurate phase transition in the presence of electric and magnetic fields is also studied. The fluctuation spectrum of the soliton lattice is calculated, and a new branch of oscillation is found.
Atomic Scattering Factors of Solid Elements
Authors: Chakraborty S. , Manna A. , Ghosh A. K. 
Published: July 2007

AbstractThe atomic scattering factor fh for elastic scattering of electromagnetic radiation depends strongly on electronic charge distribution n(r) in the atom. Deviations of recently measured fh's from those calculated from free‐atom electron states confirm the notion that n(r) gets appreciably modified in a solid. Recently it has been shown that the superposition of free‐atom charge densities through Löwdin's α‐expansion can help to find n (r) in a solid, which, in turn, yields a reasonable metallic cohesive energy and binary alloy formation energy. Here it is shown that the same procedure produces fh values that compare well with experiments as well as with more sophisticated band calculations.
A Localized Orbital Description of Si Using Non‐Local Potentials
Authors: Sieh K. S. , Smith P. V. 
Published: July 2007

AbstractIn previous work it has been shown that the band structures and electronic charge density distributions of the homopolar covalent solids can be well described within a tight‐binding formalism employing just a small set of well localized atomic orbital basis functions. In this orginal work the crystal Hamiltonian was defined in terms of purely local pseudopotentials. Recent work on these tetrahedrally bonded systems has shown, however, that a better representation of their overall electronic structure results from the use of non‐local, energy‐dependent pseudopotentials. The aim of the present paper is thus to extend this localized atomic orbital method (LAOM) to enable the description of the crystal Hamiltonian in terms of non‐local, energy‐dependent pseudopotentials. This modified approach is then applied to the case of Si using the non‐local, energy‐dependent pseudopotential of Chelikowsky and Cohen, and it is shown that excellent representations of both the band structure and valence band charge densities are again obtained from a set of just ten atomic orbital basis functions. The fact that these basis functions are also extremely well localised about their respective lattice sites makes them ideal for subsequent defect calculations on these homopolar covalent solids.
On the Shape Dependence of the Kubo Effect and Polyhedral Shapes
Authors: Nara S. 
Published: July 2007

AbstractThe free electron energy levels of ultra fine metal particle are investigated on the basis of two‐dimensional jellium model with including size and shape dependences. Three shapes (a circle, square, and equilateral triangle), for which the energy levels are exactly solvable, are chosen and several electronic quantities are evaluated with the use of obtained eigenvalues, the number of which are ≈ 11000. The results show that when the size becomes smaller than ≈ 100 Å in diameter, some electronic quantities deviate considerably from the asymptotic form which is expected from the thermodynamic limit.
Electric Field Gradient in Dilute B.C.C. Alloys. Application to Vanadium Alloys
Authors: Pal B. , Singh J. , Raj S. D. , Prakash S. 
Published: July 2007

AbstractThe formalism for the size effect electric field gradient (EFG) in dilute alloys with b.c.c. crystal structure is developed. The components of the stress field tensor F̃ are evaluated assuming dressed point ions interacting through the screened Coulomb potential. The size effect EFG is found cylindrically symmetric at the first and second nearest neighbour sites. The valence effect EFG is calculated using the transition metal model potential theory. It is assumed that due to quasilocalized d‐electrons, the shielding and antishielding mutually cancel in host region, however antishielding is accounted for in the outer region. The square well potential for the impurity in conjunction with Friedel's sum rule is used to evaluate the scattering phase shifts. The EFGs for dilute alloys of vanadium (V) with transition metal impurities Ti, Cr, Mn, Fe, Nb, and Ta are calculated. It is found that at both, the first and second nearest neighbour sites, the valence effect EFG is significantly larger than the size effect EFG. The calculated results for VTi, VNb, and VTa are in reasonable agreement with the experimental values.