bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Hole Effective Mass in Pb1—xSnxTe near the Zero Band Gap
Authors: Kushev D. B. , Zheleva N. N. , Yordanov S. P. 
Published: July 2007

AbstractUsing reflection methods in the plasma frequency range, nonparabolic valence bands of solid solutions Pb1—xSnxTe with composition near the inversion point of the bands (x = 0.55, 0.6, 0.65) are investigated. The Hall concentration of the samples are in the interval 6 × 1018 to 2 × 1020 cm−;3. The concentration dependence on wavelength in the reflection minimum and the effective masses correspond well with Kane's model. For the composition x = 0.6 the parameters of this model are evaluated.
Frequency Dependence of Warm Carrier Conductivity in Germanium
Authors: Dienys V. , Kancleris Ž. , Martūnas Z. 
Published: July 2007

AbstractThe frequency dependence of the warm carrier conductivity in n‐ and p‐Ge is measured in the frequency range 0.4 to 150 GHz. The experiments are carried out at 80 and 273 K. A phenomenological theory of the warm carrier conductivity for the semiconductor having two degenerate bands at k = 0 is developed. By applying this theory to the experimental data it is shown that in p‐Ge at 80 K the warm carrier conductivity relaxation process at microwave frequencies is strongly influenced by the hole interband repopulation effect. The values of the energy relaxation time τϵ are evaluated for both materials at both temperatures. It is established that τϵ in p‐Ge is isotropic and the anisotropy of the conductivity relaxation time observed is caused by the warping of the constant‐energy surfaces of heavy holes.
OD Stretching Vibrations in Deuterated Potassium Ferrocyanide Trihydrate
Authors: Savatinova I. , Chisler E. V. , Rohleder J. , Jakubovski B. 
Published: July 2007

AbstractDeuterated and isotopically dilute single crystals of K4Fe(CN)6. 3 D2O are investigated using low temperature Raman spectra. The work involves an attempt to asses the origin of the numerious OD modes using the isotope dilution technique. An estimate of the magnitude of the intra‐ and intermolecular interactions in formation of OD stretchings is made from available experimental data. Three crystallographically nonequivalent water molecules with different extent of vibrational distortion are established in the ferroelectric phase of the crystal.
On the Theory of Plasmon Satellite Structures in the Photoelectron Spectra of Non‐Metallic Solids I. Soluble Model
Authors: Becrstedt F. 
Published: July 2007

AbstractIntrinsic and extrinsic plasmon effects on the photoelectron spectra of non‐metals are studied simultaneously. The spectral behaviour of the photoionization cross‐section is represented by a convolution integral of the spectral functions of the outgoing electron and the excited core hole. Considering the relaxation of the valence electron gas the spectral functions are calculated in the frame of a linear dielectric formalism. It is shown, that the relaxation of the valence electrons in the presence of the electron depends strongly on the kinetic energy. For large kinetic energies (XPS) the electron effects are small and the photoelectron spectrum is nearly represented by the hole spectral function. For small kinetic energies (UPS) neither the hole mechanism nor the electron one dominates and the plasmon satellites are due to both, intrinsic and extrinsic effects.
Charge Order in the Spinless Fermion Model
Authors: Lorenz B. 
Published: July 2007

AbstractThe spinless fermion model which takes into account the transfer and the nearest neighbour Coulomb interaction of fermions is treated in a two site cluster approximation. For the linear chain the results are compared with the exact solution for the ground state and with other approximations. In two‐and three‐dimensional lattices the order–disorder transition is considered in dependence on the transfer energy and the phase diagram is calculated. The validity of the theory for the description of the order–disorder transition in superionic conductors is discussed.
Optical Spectra of EuP5O14 between 77 and 583 K
Authors: Sekita M. , Minami F. , Okamoto E. , Masui H. 
Published: July 2007

AbstractThe polarized absorption and fluorescence spectra of Eu3+ in a single crystal of EuP5O14 are studied from 77 to 583 K. The energy levels and eigenvectors are presented for septet and quintet states of Eu3+ in an intermediate coupling scheme. Values of E1 = 6420.08, E2 = 26.12, E3 = 765.93, and ζ = 1290.13 cm−1 are found to give the best overall agreement between the observed and calculated energy levels. The change in spectral structure is observed in the 7F0 to 5D2 absorption spectra at temperatures between 297 and 583 K. This change is attributed to the structural phase transition of the crystal by observing the temperature dependence of degree of polarization and of the oscillator strength of the lines.
The Effective Density of States in the Conduction and Valence Bands for Arbitrary Band Structures
Authors: Van Vliet K. M. , Marshak A. H. 
Published: July 2007

AbstractA formula is proposed for the effective density of states for materials with an arbitrary band structure. This effective density is chosen such that for nondegenerate statistics the conventional form n = Nee−z where z = (Ec ndash; Ef)/kT remains valid. The result is applied for some simple cases, including the Kane band for InSb. For parabolic bands, Nc → Nc. Results for holes are analogous.
Dielectric Function of Free Carriers with a Nonparabolic Dispersion Relation
Authors: Tsipivka Yu. I. , Neumann H. , Unger K. 
Published: July 2007

AbstractGeneral expressions for the Bloch density matrix, the Dirac density matrix, and the generalized density matrix for free carriers with a spherical but nonparabolic dispersion relation are derived in arbitrary order of perturbation theory. The linear response function of a free carrier gas with Kane's dispersion law is considered in detail. The deviations from the case of parabolic bands are discussed.
Theory of Intensity Dependence of Refractive Index
Authors: Moss T. S. 
Published: July 2007

AbstractThe variation of refractive index with intensity of irradiation is explained on the basis of a three stage process, viz. (i) photogeneration of free carriers, (ii) shift of the absorption edge by a dynamic Burstein‐Moss effect, and (iii) reduction in total absorption and hence of refractive index as a result of the inter‐relation of the optical constants. The theory gives the correct sign, magnitude, and wavelength dependence of the effect.
Decimation and Anderson Localization
Authors: Lambert C. J. , Weaire D. 
Published: July 2007

AbstractA numerical decimation procedure is applied to a Hamiltonian with diagonal disorder for a square lattice in two dimensions. The renormalized interactions are found to scale towards weak coupling (indicative of localized states) for large disorder and towards strong coupling for low disorder, consistent with previous estimates of an Anderson transition at W ≈︁ 6.
Environment Effects on Electronic Density of States in Narrow‐Band Alloys Using the Cluster‐Bethe‐Lattice Method
Authors: Maiti P. B. , Moitra R. K. 
Published: July 2007

AbstractThe cluster‐Bethe‐lattice method is used to study the environment effects on the electronic density of states in narrow‐band alloys. The intra‐atomic Coulomb interaction, U, is treated in the statistical (0, 1) approximation and the coherent potential approximation is used for the alloy disorder. These approximations lead us to consider the alloy system as a quaternary alloy. A general approach for an n‐component alloy in the Bethe lattice is presented using Yonezawa's approach. It is shown that the result obtained gives the result of Yonezawa in the limit z → ∞, z being the coordination number of the alloy system. The quaternary alloy is then treated as a special case of an n‐component alloy. A cluster consisting of (Z + 1) atoms is chosen to study environment effects. A comparison is made between the electronic density of states for the Bethe lattice and that for the cluster‐Bethe lattice. Interesting features in the electronic density of states are observed due to clustering effects.
Hydrostatic Pressure and Kinetic Phenomena in NaNbO3 Single Crystals
Authors: Pisarski M. 
Published: July 2007

AbstractElectrical conductivity σ, electric permeability Σ, and the Seebeck coefficient α in the 20°C < T < < 500 °C temperature range and in the 0 < p < 1 GPa pressure range are investigated. A strong linear dependence of these quantities on pressure for T < 360 °C and a shifting of the P ⇌ R phase transition temperature at a rate of dTa/dp = (120 ± 12) K/GPa are determined. From the linear dependences In σ(l/T) and In μd(l/T) for various p = const, the activation energy is determined. The experimental relationship Ea = E0 — Bp is derived on the basis of the small‐polaron theory. Results related to transport phenomena are interpreted through the small‐polaron non‐adiabatic hopping theory. On the basis of the experimental and theoretical relations σ(T, p) = = σ0(T) (1 + Cp), and In μb(T) the LO phonon energy ħωo, = 0.12 eV is determined, as well as the band half‐width J = 0.14 eV at normal pressure, and also the remaining small‐polaron parameters.
Electronic Structure of Thin Alloy Films
Authors: Wysokiński K. I. , Sobczuk H. , Pilat M. 
Published: July 2007

AbstractThe coherent potential approximation is adopted to the problem of an electron moving in a sub‐stitutionally disordered alloy with thin film geometry (i.e. thin alloy film). The theory is formulated for a one‐band tight‐binding Hamiltonian of the alloy film consisting of N atomic planes. The numerical calculations illustrate the dependence of the local density of states for various layers on the parameters describing the alloy film.
Determination of the Cyclotron Masses of the Conduction Band of Bi1−xSbx near the Semimetal‐Semiconductor Transition
Authors: Fellmuth B. , Krüger H. , Rudolph R. , Herrmann R. 
Published: July 2007

AbstractIn a number of n‐doped Bi1−xSbx samples approaching the semimetal‐semiconduct or transition (0.070 ≦ x ≦ 0.083), the propagation of magnetoplasma waves is investigated in the B ⊥ C2, ∥ k orientation at 4.2 K. The plane‐parallel samples are prepared from a single crystal exhibiting a slight gradient in the antimony concentration. By means of an ellipsoidal model of the conductivity tensor, the low cyclotron mass mc2 and the anisotropy mc3/ mc2 are determined from the experimental dependence of the wave vector on the frequency and the magnetic field. In the samples with x < 0.073, the dispersion and the attenuation of the waves show peculiarities which can be explained by the presence of holes at the point T. The results obtained indicate a continuous dependence of the band characteristics on the antimony concentration in the neighbourhood of the point x0, where the overlapping of the bands at L and T is removed.
Equation d'état et structure de bandes d'énergie de l'argent métallique
Authors: Perrot F. 
Published: July 2007

AbstractLa méthode linéarisée des “orbitales muffin‐tin” (LMTO) est appliquée au calcul auto‐cohérent de la structure électronique de l'Argent métallique. La pression est calculée en fonction de la densité, dans une gamme allant de la densité normale ϱ0 à 5ϱ0. L'accord avec les résultats de mesures statiques, jusqa' à 170 kbar, est bon; il en est de měme avec l'isotherme 0 K déduite de mesures dynamiques, jusqu' à 1,3 Mbar environ. Les modifications de la structure de bandes d'énergie sous pression sont ensuite discutées.
The Metal‐Insulator Transition in Electron‐Hole Systems
Authors: Balslev I. 
Published: July 2007

AbstractTheoretical studies of the metal‐insulator transition in electron‐hole systems in indirect semiconductors are presented. The model is based on various screening theories and on thermodynamical continuity requirements. In case of Debye‐Hückel‐like screening the phase diagrams of Si and Ge contain two separate transitions, the gas‐liquid and the metal‐insulator transition. Stronger and weaker dependence of the band energies on the free pair density favors the metal‐insulator and the gas‐liquid transition, respectively.
X‐Ray Compton Scattering Study of Electronic Distribution in Beryllium
Authors: Loupias G. , Petiau J. , Issolah A. , Schneider M. 
Published: July 2007

AbstractCompton scattering of 10 keV X‐rays by single crystals of beryllium is performed using the synchrotron radiation beam provided by the LURE‐DCI storage ring of Orsay. By means of a three‐axes spectrometer the scattering of the monochromatized beam, the spectral analysis by a focusing curved crystal, and the detection by a position sensitive counter are performed. A resolution of 0.15 momentum at. units is obtained. Seven directional profiles are measured with 106 counts in each of them. Anisotropies of the Compton profiles and of their Fourier transforms are compared to those predicted by the available theories. None of the models gives a good description of the profiles especially in the region of the Fermi momentum. The pseudopotential calculation is in a qualitative agreement with the momentum distribution anisotropy.
Absolute Cross‐Section for Raman Scattering by Phonons in Silicon
Authors: Grimsditch M. , Cardona M. 
Published: July 2007

AbstractThe absolute cross‐sections for Raman scattering in silicon measured at various frequencies in the visible spectrum by two different experimental techniques are reanalysed in the light of recent developments. Agreement between the results obtained by both the methods clears the discrepancies previously observed at high frequencies. Experimental results are compared with theoretical calculations.
Optical Determination of Mean Free Path of Hot Electrons in Metals
Authors: Kroó N. , Szentirmay Zs. , Félszerfalvi J. 
Published: July 2007

AbstractLight emission via surface plasmon excitation can be used as a sensitive detector for hot electrons in metal‐insulator‐metal structures. Ballistic and electron‐electron scattering mean free pathvalues obtained for silver with this method in the 2.19 to 2.44 eV energy range are in good agreement with theoretical predictions.
A Theory of the Motion of an Extra Electron in Quasi‐One‐Dimensional Structures
Authors: Davydov A. S. 
Published: July 2007

AbstractA theory of the motion of an extra electron, strongly interacting with acoustic phonons, along a molecular chain is developed. It is shown that as the binding energy increases a discontinuous autolocalization of an electron can occur when the electron goes into a “superconducting” state.
Effect of High Excitation on Carrier Density in Direct Gap Semiconductors
Authors: Egorov V. D. 
Published: July 2007

AbstractA rate equation for quasiparticles (electron‐hole pairs, excitons) including stimulated optical transitions is solved at simplifying assumptions. The density of quasiparticles at high excitations in direct gap semiconductors with insignificant Auger recombination and without any resonator is shown to be limited by a root function of generation rate with the exponent depending on the dimension of the excited region.
Calculation of the Spin Wave Energy Gap at k = o for a Simple Cubic Ferromagnet with Anisotropic Exchange Interactions
Authors: Belorizky E. , Casalegno R. , Niez J. J. 
Published: July 2007

AbstractSpin waves in a system of pseudo‐spins forming a simple cubic ferromagnetic lattice are analysed by considering the most general bilinear interaction between nearest neighbors allowed by a four‐fold order symmetry of the bond ℋ︁ij = J∥SizSjz+J⟂(SixSjx+SiySjy) for a pair (i,j) oriented along the z axis. For that extended Heisenberg system, the excitation energy a t the center of the Brillouin zone is found to be zero with the usual theory, a result which violates the Goldstone theorem predicting a gap a t this point. This gap is calculated through two different but consistent methods and its variation with the anisotropy of the exchange parameters is determined numerically. It is seen that even for a small gap, strongly anisotropic exchange is possible.
Family of O Centres in SrO Crystals
Authors: Seeman V. , Reifman S. , Lehto T. , Haldre Ü. 
Published: July 2007

AbstractSeveral types of O centres are found and investigated by the electron spin resonance method in X‐irradiated SrO single crystals. All the centres consist of an O molecule stabilized near various defects. The presence of superhyperfine structure in the spectra of two of the centres allows to perform an identification of these centres.
Analysis of the Repulsive Hardness Parameters in Alkali Hydrides, Silver Halides, and Alkaline‐Earth Fluorides
Authors: Shanker J. , Agrawal D. P. 
Published: July 2007

AbstractThe validity of an additivity rule is demonstrated for the repulsive hardness parameters in three crystal families viz. alkali hydrides, silver halides, and alkaline earth fluorides. The additivity rule provides a direct method of determining the repulsive hardness parameters for individual ions and thereby reduces the number of parameters considerably. Using the repulsive hardness parameters for individual ions derived from the overlap integrals an investigation is made on the crystal binding of LiH, NaH, KH, RbH, CsH, AgCl, AgBr, CaF2, SrF2, and BaF2. The interionic force model used here takes into account the long‐range electrostatic interactions, three‐body forces, shortrange repulsive, and van der Waals interactions. The cohesive energy and the pressure derivative of bulk modulus are calculated. The results are found to compare well with experimental data.
Stability of Relaxed States of Excitons in Cesium Halides
Authors: Nakaoka Y. , Iida T. 
Published: July 2007

AbstractStability of relaxed excitons in CsCl‐type cesium halides, which are described by a cluster model already developed in a previous paper, is studied. The particle (electron or hole)–phonon interaction is used, in which the discreteness of crystal is emphasized. By a semi‐empirical method based on the Landau‐Pekar theory, the relaxation energies are calculated for one‐particle states as well as exciton states. The results are consistent with those obtained experimentally.
Electron Density Distribution at Point Defects. Application of the Quadratic Response Theory
Authors: Heinrich A. , Paasch G. 
Published: July 2007

AbstractThe static quadratic response theory of the electron gas including exchange and correlation corrections is applied to point defects. Induced electron densities, potentials, and screening lengths are calculated for a point charge and for a vacancy in the jellium. The results are compared with existing self‐consistent calculations for these systems as a test for the reliability of the quadratic screening. In general a large part of the deficiency of the linear screening is removed already by the quadratic terms. The calculations presented here are a first step towards an ab initio inclusion of the host ion potentials in a non‐linear screening of defects in simple metals.
Relaxations Due to Vacancies in Copper
Authors: Sen S. K. , Dutt M. B. 
Published: July 2007

AbstractThe relaxations due to vacancies in copper have been calculated using lattice statics method. Using the measured phonon dispersion relation of copper by Sinha and the elastic constants as constraints, the dynamical matrix is derived including interactions up to five neighbours. Unlike most of the previous calculations all the neighbours are found to relax towards the vacancy. Distortions are found to be large in close‐packed directions as compared to the directions along the cube axes in the crystal.
Thermoluminescence of NaF X‐Irradiated at 80 K
Authors: Ortega A. , Aguilar M. , Meseguer F. , Jaque F. 
Published: July 2007

AbstractA study of the thermoluminescence and the X‐ray induced luminescence in NaF X‐irradiated at 80 K is realized. Activation energy and pre‐exponential factor of the three prominent glow peaks are carefully calculated. These parameters for peak V have a clear dose dependence. The emission spectrum of the various glow peaks is the same as that during X‐irradiation. Finally the thermoluminescence origin is discussed in function of the thermal stability of different defects created by irradiation like hole‐type centres.
Properties of the n‐th Response of a Fermi Gas
Authors: Pickenhain R. , Unger K. 
Published: July 2007

AbstractThe diagonal elements of the Dirac density matrix of a free electron gas perturbed by a potential are considered in the momentum space representation in an expansion of the potential. Conditions for the n‐th order filter functions which are contained in corresponding terms of the Dirac density matrix expansion are derived from general considerations on the symmetry of the problem.
DC Conductivity of a Random Barrier Network
Authors: Sinkkonen J. 
Published: July 2007

AbstractThe current–voltage characteristics of a single potential barrier is highly nonlinear. The conductivity of a random barrier network is analyzed by extending the effective medium theory to the nonlinear case. Below the percolation threshold the conductivity shows nonlinear behaviour similar to the regular barrier network. Above the percolation threshold the conductivity is constant up to voltages comparable to the barrier height. In the ohmic region the activation energy of conductivity decreases when the fraction of barriers decreases. In the case of distributed barriers the activation energy decreases with decreasing temperature.
Optical Phonons and Crystalline Symmetry of InSe
Authors: Carlone C. , Jandl S. , Shanks H. R. 
Published: July 2007

AbstractA survey of the Raman and infra red data for the layered structure InSe shows that there is no agreement upon its crystallographic structure. The polytypes, β, ε, and γ are equally invoked by the various groups. Some experiments on samples from different laboratories are repeated. Infrared transmission at different temperatures and Raman spectra away from resonance are obtained. It is concluded on the basis of the optical data that InSe crystallizes only in the β‐polytype. All previous optical measurements can be explained with the β‐polytype if one takes into account the resonance Raman effect. It is inferred from the Raman and infra red data that the interlayer interaction cannot be exclusively of the van der Waals type and that long range Coulomb forces contribute to the lattice dynamics of InSe.
The Anderson Parameter and Temperature Dependence of Bulk Modulus for Alkali Halide Crystals
Authors: Shanker J. , Singh K. 
Published: July 2007

AbstractThe relation is studied between the Anderson parameter δ and the temperature dependence of the bulk modulus for 16 alkali halides with NaCl structure. Two Anderson parameters δS and δT are considered, corresponding to the adiabatic and isothermal bulk moduli, BS and BT, respectively. It is found that the assumption δS ≈ δT taken by several previous workers is not correct. The difference between δS and δT arises largely due to difference between the temperature derivatives of BS and BT at fixed volume. An analysis of the volume dependence of the bulk modulus is performed in terms of interionic potentials. Values of δS and δT are calculated using seven different potential forms for the short‐range repulsive energy.
X‐Ray Absorption Spectroscopic Study of Rare Earth–manganese Intermetallic Compounds
Authors: Hatwar T. K. , Ghatikar M. N. , Padalia B. D. , Malik S. K. , Vijayaraghavan R. 
Published: July 2007

AbstractChemical shifts of the K‐absorption edge of Mn and the L3‐absorption edges of rare earths (R = Gd, Tb, Dy, Ho, Er, Tm, and Lu) in RMn2 intermetallic compounds are measured and the effective charges on the Mn and R ions are estimated. Extended X‐ray absorption edge fine structures (EXAFS) associated with the absorption edges are investigated and R‐Mn and Mn‐Mn bond lengths in R–Mn2 compounds are determined. The results are interpreted in the light of the available data on these intermetallic compounds.