bluuebunny/crossref_metadata_2025 huggingface dataset:
Radial Energy Transfer Density Distribution around the Fast Ion Tracks in Silicon and Germanium
Authors: Khlupin S. I. , Akkerman A. F.
Published: July 2007

The radial energy transfer density distributions around the tracks of fast protons (p), α‐particles, and C‐ions in Si and Ge targets are obtained by the Monte‐Carlo method using individual collision scheme. A semiempirical formula for D(r) is proposed based on these calculations. Some aspects of its application are discussed.
Suppression of Transparency Effect and Enhancement of Particle Reflection in an Asymmetric Potential Well
Authors: Gevorgyan L. A. , Atsagortsyan K. Z.
Published: July 2007

The one‐dimensional motion of a particle in the field of the Pöschl‐Teller asymmetric potential well is considered. It is shown that at positive energies the transparency effect is suppressed, as compared to the symmetric well case. The reflection coefficient increases with the well asymmetry, while at high energies its exponential decrease versus energy is replaced by a power‐like dependence. The results can be useful to those concerned with particle channeling in complex crystals.
Electron–Phonon Interaction Induced Hybridisation in Mixed‐Valence Systems
Authors: Ghosh N. K. , Ghosh S. C. , Sarkar R. L.
Published: July 2007

The two‐site extended spinless Falicov‐Kimball model with electron phonon (EP) interaction is considered. The usual electron‐phonon interaction term is electron operators. Average occupation number of f‐electrons, the correlation function between f and d‐hands, and the correlation between sites are calculated. It is shown that the discontinuous change in f‐electron occupation number depends on EP interaction. Finite temperature specific heat is calculated. A comparison is also made with previously obtained results.
Magnetic Structure and Phase Transformations in Mn5Si3
Authors: Menshikov A. Z. , Vokhmyanin A. P. , Dorofeev Yu. A.
Published: July 2007

A symmetry analysis of possible magnetic structures in crystals with the space group D is made for the wave vector of star {k12}. This analysis allows deciphering the neutron diffraction data on the character of antiferromagnetic ordering in the AF1 (below T1 = 66 K) and AF2 (below T2 = 99 K) phases. It is shown that the magnetic phase transitions arise mainly from the structural transformations that occur at T1 and T2.
Emission Processes in Thermally Stimulated Exoelectron Emission and Thermoluminescence of KCl:Ag Single Crystals
Authors: Tomita A. , Fukuda Y. , Kutomi Y. , Takeuchi N.
Published: July 2007

The emission processes in the TSEE and TL glow peaks of KCl:Ag single crystals are discussed from the results of simultaneous recording of TSEE and TL glow curves, the spectral measurements of the TL and the optical re‐excitation study. A large fraction of the exoelectron emissions at 400 K may be considered to arise from Auger‐like decays of the excited Ag+ centers induced by the recombination of electrons from Ag0 with Ag2+ via the conduction band. The 275 nm emission band of TL at 400 K may be due to competing radiative decays of the excited Ag+ centers. The electron emissions and the 275 nm component of TL at 250 K may originate from the excited Ag+ centers resulting from the recombination of F′ (or F) centers with Ag+ centers.
Hydrides and Deuterides of Lithium and Sodium. I. Model Potentials and Their Use in Perfect Lattice
Authors: Haque E. , Islam A. K. M. A.
Published: July 2007

An interionic potential model is developed for lighter and heavier alkali hydrides and deuterides. The method uses a combination of theoretical techniques, empirical fit, and a few plausible assumptions. An assessment of the derived potentials is made by calculating the lattice statics and dynamics of the crystals and by comparing both with experiment (where available) and with other calculations. The potentials are found to describe the elastic and dielectric properties reasonably well. The phonon dispersion curves of hydride and deuteride of sodium are compared with the calculations of Dyck and Jex based on force constant model approach and the results are discussed. The need for further experiments on heavier hydrides and deuterides is stressed.
Phase Transition in Rb3H(SeO4)2‐Type Crystals. II. The Molecular Field Approximation
Authors: Salejda W. , Dzhavadov N. A.
Published: July 2007

The microscopic model of the phase transitions in superionic Rb3H(SeO4)2‐type crystals is proposed. The phase diagrams are studied within the molecular field approximation. The phase diagram obtained is in agreement with the phase diagram of Rb3H(SeO4)2 crystals. Application of the proposed model to the description of phase transitions observed in Cs3H(SeO4)2 crystals is discussed.
The New Mechanism of Physical Adsorption on Solid Surface. I. Adsorption of Nonpolar Molecules
Authors: Lozovskii V. Z. , Khudik B. I.
Published: July 2007

A phenomenological theory of a new type of physical adsorption is constructed. The mechanism of the adsorption is due to softening of one of the energy levels of an nonmonoatomic molecule. This mode‐softening occurs due to the interaction of the molecule with the adsorbent surface. It is shown, that the nonlinear polarizabilities of a molecule and solid can play an essential role in forming of the adsorption potential.
Non‐Resonant Energy Transfer between Donor and Acceptor Systems in Presence of Relaxation
Authors: Boulil B. , Giry M. , Henri‐Rousseau O.
Published: July 2007

The non‐resonant energy transfer at zero temperature between two interacting two‐level quantum systems in the presence of relaxation is studied by aid of the density matrix formalism in the framework of the Markoff approximation. This gives the time evolution of the four probabilities to find the system in each of the four levels owing to the fact that at the initial time, the energy is in the excited state of the donor. The results obtained lead to the Davydov and Serikov solutions for resonant transfer of energy, and to the special one for the indirect coupling between a single level and a continuous medium.
Fine Structure of the Luminescence of Solid Neon and Its Relation to Exciton Trapping and Desorption Induced by Excitonic Excitation
Authors: Laasch W. , Hagedorn H. , Kloiber T. , Zimmerer G.
Published: July 2007

The luminescence of Ne* centers in solid Ne is investigated. The samples are excited with synchrotron radiation in the excitonic range. By an appropriate selection of the excitation energy and by time correlated measurement of the emission spectra, overlapping luminescence bands are separated and assigned to Ne* centers in different electronic states (1P1, 3P1, 3P2) and different environments in the bulk and at the surface of the solid. Lifetime measurements and excitation spectra of spectrally selected luminescence bands support the assignments, Electronic relaxation from n ≧ 2 free excitons to the n = 1 state is found to be less effective than exciton trapping into Ne* centers. Resonance fluorescence of free Ne* atoms indicates a close connection between exciton trapping and desorption.
Kinetics of Screening in Optically Excited Semiconductors
Authors: Hartmann M. , Stolz H. , Zimmermann R.
Published: July 2007

Kinetic equations for the density correlation and density‐density response function are derived. Solving these equations numerically and comparing its solution with the adiabatic approximation the change in the transmitted spectrum of a single electronic transition is calculated where a red‐shift can be observed.
Single and Many Particle Effects in the Emission Spectra of Laterally Homogeneous 2D Plasmas
Authors: Lach E. , Kulakovskii V. D. , Forchel A. , Reinecke T. L. , Straka J. , Grützmacher D. , Weimann G.
Published: July 2007

By the use of homogeneously excited small mesa structures a highly uniform electron‐hole plasma (EHP) is created in InGaAs/InP and GaAlAs single quantum wells. The spectra obtained from mesa structures differ strongly from data of usually used inhomogeneously excited samples. The spectra clearly show band‐filling up to the of the potential well and strong renormalization effects. The emission spectra are analyzed by a lineshape model including the full coupled non‐parabolic valence bands for the dispersion of the holes and the transition matrix elements in the case of GaAs/GaAlAs and by the use of parabolic subbands for electron‐hole plasmas in InGaAs/InP quantum wells. A strong dependence is observed of the renormalization on the subband index for low plasma temperatures.
Optical Properties of Biexcitons in ZnSe/Zn1−xMnxSe Quantum Wells
Authors: Bobrysheva A. I. , Russu S. S.
Published: July 2007

It is shown that in ZnSe/(Zn, Mn)Sequantum wells six biexcitonic states can exist. The group‐theoretical classification of these states is performed. The probabilities of biexciton two‐photon absorption, hyper‐Raman scattering, and radiative recombination are calculated. The polarization properties of two‐photon absorption of two‐and three‐dimensional excitons are discussed.
Dynamics of Carrier‐Screened Photon‐Exciton Interaction
Authors: Mareyen M. , Schütte F. ‐J. , Tiebel R.
Published: July 2007

The exciton‐photon interaction in a semiconductor‐optical device is influenced by the carrier pair density. To take this into account, the coupling constant is corrected to the first order. This simple model shows remarkable dynamical behaviour as, for instance, up to five coexisting fixed points and chaos. Chaotic transients are found which are precursors of permanent chaotic motion.
Nonlinear Optical Properties of Quantum Confined Semiconductor Microcrystallites
Authors: Ricard D. , Roussignol P. , Hache F. , Flytzanis Ch.
Published: July 2007

Results are given of recent studies on the nonlinear optical properties of quantum‐confined semiconductor (CdSSe) particles. The nonlinear mechanism is saturation of the first or 1s‐1s transition which behaves as a two‐level system. The intrinsic broadening of this transition by electron‐phonon coupling is very important and dominant at room temperature. The enhancement of the nonlinearity due to quantum confinement could however be observed, which may lead to important applications. Similarly, for hybrid devices, the static Kerr effect studied through the change in absorption spectrum induced by a defield shows a large nonlinearity which can be fully understood in terms of a Stark effect.
Experimental Investigation of Three‐Level Optical Stark Effect in Semiconductors
Authors: Fröhlich D. , Neumann Ch. , Uebbing B. , Wille R.
Published: July 2007

The three‐level optical Stark effect is due to a dynamical coupling of two excited levels. The coupling is achieved by a high intensity CO2 laser. Results of experiments on multiple quantum wells (MQW) and excitons in Cu2O are presented. In the MQW the coupling between the two lowest conduction band sublevels leads to characteristic changes in the one‐photon spectra of the lowest exciton transitions. In Cu2O the CO2 laser pulse couples 1 S and 2 P excitons. In this case the one‐photon spectrum of the 2 P exciton (dipole allowed) and also of the 1 S spectrum (quadrupole allowed) show drastic changes. Most of the experimental results can be explained quantitatively in terms of a nonlinear susceptibility.
Transverse Relaxation and Polarization Specifics in the Dynamical Stark Effect
Authors: Zimmermann R.
Published: July 2007

The transverse relaxation of excitons in the dynamical Stark effect is treated on a microscopic level within a density‐matrix approach explaining the strongly suppressed damping for the off‐resonant pump pulse. An expression for the differential transmission spectrum is derived including the dependence on pump‐ and test polarization. Calculations for CdS with its three exciton series are given.
Coupled Two‐Level Systems and the Dynamics of Semiconductor Electrons
Authors: Stahl A.
Published: July 2007

A basic model in quantum optics is a system of interacting two‐level atoms. The simplest case where the interaction is only via macroscopic electromagnetic fields leads to the so called Maxwell‐Bloch dynamics. When a tunneling interaction and Coulomb potentials are added the model may by extended to yield the density matrix dynamics for a two‐band semiconductor. A typical property of this dynamics is the coherent coupling between electromagnetic and quantal waves. This is exploited in a solution of the ABC‐problem. The basic nonlinearities of the electron dynamics in the two‐band model are reviewed. Some of them are related to the various manifestations of the dynamical Stark effect.
Nonlinear Optical Properties of CdS at Room Temperature. A Comprehensive Study
Authors: Spiegelberg Ch. , Puls J. , Henneberger F.
Published: July 2007

A systematic study is given of the linear and nonlinear optical response at the fundamental absorption edge of CdS at room temperature. It is shown, that at low optical power the strong nonlinearity is due to the screening of excitons in the free carrier system. From single‐beam transmission experiments and degenerate four‐wave‐mixing the change of absorption and refraction, respectively, is deduced induced by one electron‐hole pair. Even 50 meV below the exciton resonances application of the strong dispersive nonlinearity at mW‐power is demonstrated.
Progress on Bose‐Einstein Condensation of Excitons
Authors: Mysyrowicz A. , Snoke D. W. , Wolfe J. P.
Published: July 2007

New results are presented which show evidence for Bose‐Einstein condensation of paraexcitons in Cu2O following creation of a high density of free carriers. Evidence relies on time and space‐resolved analysis of exciton luminescence. Extracted densities of paraexcitons exceed the critical value for Bose‐Einstein condensation by one order of magnitude. Luminescence spectra show anomalies which are discussed in the framework of the non‐ideal Bose gas. Anomalous transport properties are observed at high densities suggesting a superfluid flow of excitons.
High‐Density Spectroscopy of ZnSe/GaAs Epilayers in the Near‐Band‐Edge Region
Authors: Presser N. , Kudlek G. , Gutowski J. , Durbin S. M. , Menke D. R. , Kobayashi M. , Gunshor R. L.
Published: July 2007

ZnSe epilayers grown by MBE on (100) GaAs substrates are optically investigated in comparison with bulk ZnSe crystals using photoluminescence and excitation spectroscopy under high excitation densities. High‐density luminescence bands appear in both materials for relatively low excitation densities (about 30 kW/cm2), but their energetic positions do not correspond. The intensity‐dependent shape, and the behaviour of the dominant band in bulk ZnSe in excitation spectroscopy are similar to that of the M band in other II VI semiconductors. The main bands growing up in the ZnSe/GaAs films are much more corresponding to typical P‐band emission of exciton‐exciton collision. Further, the transmission of ZnSe epilayers released from the GaAs substrate is studied in dependence on the laser intensity.
Theoretical Investigation of Ferroelastic Phase Transition of Pure and Mixed Alkali Cyanide Systems by the Elastic Dipole Model. III. The Dipole‐Diluted and Mixed Alkali Cyanide Systems
Authors: Yang Zhengju , Ortiz‐Lopez J. , Luty F.
Published: July 2007

The elastic dipole model and results presented in two previous papers are applied to study the phase transitions of mixed and diluted alkali cyanide systems. The effect of impurities in the crystal on the phase transition temperature is analyzed at first. It is supposed that part of the CN− ions may be preferentially aligned in some directions and can not rotate freely due to the elastic interaction between CN− ions and impurites. When the concentration of CN− ions, taking part in the ordering process, is less than that corresponding to the suddenly changed amount of order parameter at the phase transition point, the maximum ordering energy in the lattice will not be large enough to permit the ordering process to take place, and the crystal will remain in a disordered state at all temperatures. With this model the experimental results obtained in these systems can be explained reasonably well. The effects of hydrostatic pressure on the phase transition temperature are attempted to be analysed too.
Optical Properties of Multi‐Layer Structures. III. Raman Scattering in Multi‐Layer Structures and Superlattices
Authors: Fomin V. M. , Pokatilov E. P.
Published: July 2007

The theory of Raman scattering is extended over multi‐layer structures with any number of semiconductor and dielectric layers; the explanation is based on the modulation transfer matrices. The location and configuration of Raman peaks are calculated as functions of the polarization of incident and scattered radiation caused by different types of oscillatory excitations in superlattices by spatially extended interface phonons, spatially decreasing phonons and “confined” bulk phonons.
Optical Properties of the Mixed‐Valent TmSe
Authors: Kikoin K. A. , Nizhnikova G. P. , Farberovich O. V.
Published: July 2007

The optical density of states (ODOS) of the mixed‐valent semiconductor TmSe is considered as the superposition of the interband ODOS for the selfconsistent band spectrum of TmSe calculated by the linear augmented plane wave method in the scalar relativistic approximation, and the interconfigurational DOS arising due to the excitation of the Tm f‐shell. This approach is based on the general description of the mixed‐valence semiconductor as an excitonic dielectric. The results of the calculations are compared with the experimental reflectivity spectrum of TmSe.
Plasma‐Electric Effect in Anisotropic Semiconductors in Heating Electric Field
Authors: Gorlei P. N. , Zagorodnyaya T. A. , Shenderovskii V. A.
Published: July 2007

The effect of appearance of a constant current (at a closed circuit) in anisotropic semiconductors at propagation of longitudinal oscillations with an external carrier‐heating electric field applied to the sample is investigated. The departure of the energy dispersion law from the isotropic parabolic one (as, e. g., in tellurium) is ascertained to result in an additional term in the expression for the current, which is absent for an equilibrium plasma; its contribution can be determined under certain conditions. Consideration of the energy dependence of the relaxation time as well brings about additions to the constant current, which may also be in an equilibrium plasma. Dependences of the current on the oscillation frequency and wave vector as well as on orientation of the external electric field relative to crystallographic axes are derived.
Optical Constants of Tin Sulphide Single Crystals Measured by the Interference Method
Authors: Elkorashy A. M.
Published: July 2007

The refractive index, n, of SnS single crystals is measured from reflectance after being normalized to account for the pronounced rise below the energy gap n is also measured by the interference method in the transparency region. An effective thickness smaller than the true one is introduced to account for the photon scattering by the layer structure of the material in this region. The effective thickness hypothesis gives a satisfactory explanation of the pronounced rise in reflectance for E < Eg. The extinetion coefficient, k, is calculated from the measured absorption coefficient. Measurements are performed at room temperature using plane polarized light with the plane of polarization parallel to the a‐ and b‐crystallographic axes which lie in the plane of cleavage. The real and imaginary parts of the complex dielectric constant (εr, εi) are calculated from the values of n and k. It is shown that SnS single crystals exhibit birefringence. Assuming that the SnS binding is partly ionic and partly covalent, the results of the optical constants are satisfactorly fitted to the model of a single effective oscillator.
Confined‐LO‐Phonon‐Limited Mobility in a Semiconductor Quantum Well
Authors: Leon H. , Comas F.
Published: July 2007

Low‐field drift mobility for transport parallel to the interfaces in a semiconductor quantum well is calculated by means of an iterative procedure. Electron–confined‐LO‐phonon‐interaction Hamiltonian is taken from a previous work. Calculations are accomplished in the size‐quantum‐limit approximation (when just the first subband is considered) for a degenerate electron gas. Screening effect is neglected. Comparison with earlier works on the subject is made, and the conclusion is drawn that the effect of LO‐phonon confinement comes out in a increasing of mobility values when only this scattering mechanism is taken into account.
Electronic Structure of (001) Semiconducting MTe Surfaces (M = Zn, Cd, Hg)
Authors: Rodríguez F. , Camacho A. , Quiroga L. , Baquero R.
Published: July 2007

By using the tight‐binding scheme with ten orbitals per atom (SP3S* and two spin orientations) the electronic projected bulk band structure, surface band structure (both anion‐and cation‐terminated surfaces), and the wave‐vector‐resolved density of states for these II‐VI semiconductors are calculated. A quickly convergent iterative technique is employed for calculating the Green function of the actual semi‐infinite crystal. This calculational method allows to precise very accurately, the energy of localized surface states. All the materials considered in this work present surface states with energies lying in the fundamental gap as well as surface states in the lenses opened in the projected bulk valence‐band continum. The atomic weight of each surface state is determined. The states in the fundamental gap turn out to be ‘bridge‐bond’‐type states for anion‐terminated surfaces and ‘dangling‐bond’‐type states for cation‐terminated surfaces.
The New Mechanism of Physical Adsorption on Solid Surface. II. Adsorption of Polar Molecules
Authors: Lozovskii V. Z. , Khudik B. I.
Published: July 2007

The polar molecule adsorption is considered in the framework of an approach developed in a previous work (Part I) for the case of nonpolar molecule adsorption. An expression for the adsorption potential is obtained. Nonpolar molecule adsorption is considered for the case of surface‐induced molecule dipole moment bound at a certain distance from the surface.
Chemical Shifts of Auger Electron and Photoelectron Binding Energies of Phosphorus in Solid Compounds
Authors: Franke R. , Chassé T. , Al‐Araj B. , Streubel P. , Meisel A.
Published: July 2007

A set of experimental 1s, 2s, and 2p photoelectron binding energy and KL2,3L2,3; 1D2 Auger energy shifts of phosphorus in 11 solid compounds referenced to elemental red phosphorus is presented. Correlations between the shifts are discussed. The Auger parameters, ξ, are used to estimate the changes in the extraatomic static relaxation energy ΔR. Line shifts and ΔR values are compared with differences in Pauling's electronegativity between phosphorus and the neighbouring atoms and averaged atomic electronic polarizabilities of the neighbours. Absolute R values are calculated and compared with data of gaseous P compounds which provides a systematic difference.
Band Structure of Sodium and Lithium Azides
Authors: Zhuravlev Yu. N. , Poplavnoi A. S.
Published: July 2007

LiN3, α‐, β‐NaN3 band structure is determined by means of pseudopotential technique on the basis of localized Slater orbitals decomposed along plane waves. The nature of the complex bands and the effect of phase transition on the electron energy spectrum in NaN3 are discussed. Density of states data calculated by means of energy band interpolation by Fourier symmetrized series are compared with those on photoelectron spectra of azide salts. The peculiarities of both optical and photoemission NaN3 spectra are interpreted in terms of band–band electron transitions.
Parametric Interaction of Two‐Dimensional Electron Systems in a Strong Electromagnetic Field
Authors: Epshtein E. M. , Shmelev G. M.
Published: July 2007

Parametric interaction is considered of plasma oscillations in two‐dimensional electron gases (2DEG) placed in two parallel planes in the presence of an intense electromagnetic field (EMF). The spectrum of coupled plasmons is calculated for the case when the EMF frequency is high compared with the frequencies of 2D plasmons in isolated 2DEG's. The frequency of the coupled plasmons is found to be an oscillating function of the EMF amplitude. The case of parametric resonance is considered, and the parametric excitation gain is calculated.
Positron Distribution in Semiconductors
Authors: Aourag H. , Khelifa B. , Belaidi A. , Belarbi Z.
Published: July 2007

The positron distribution of charge along the (111) direction is calculated for elemental and compound semiconductors. The results show that the positron has a strong affinity for one sort of atom in binary semiconductors. This relative positron affinity may lead to the positron preferentially annihilating with the electrons of that sort of atom in compound semiconductors. The trends in going from Ge to CdTe through GaAs show an increase in positron affinity for the anion over the cation.
Surface Magnetic Properties of a Transverse Ising Model with a Diluted Surface
Authors: Sarmento E. F. , Kaneyoshi T.
Published: July 2007

Surface magnetic properties of semi‐infinite spin‐1/2 Ising ferromagnet with a diluted surface in an applied transverse field are investigated by the use of an effective‐field theory with correlations. A number of characteristic behaviors arise in the temperature and transverse field dependences of the surface magnetization. A similarity exists between the temperature plots and the transverse field plots for the surface magnetization, which proposes that the research of surface magnetization in an applied transverse field fixing temperature at a very low one may open a new method for clarifying a variety of problems in surface magnetism experimentally.
Interface States in Subband Structure of Semiconductor Quantum Wells
Authors: Gerchikov L. G. , Subashiev A. V.
Published: July 2007

An analytical investigation is made of semiconductor quantum‐well subband structures using the three‐band Kane model. The analysis is based on the assumption, that electron and light hole masses are much smaller than heavy hole mass in the heterostructure. It is demonstrated, that some anomalies in the subband spectrum are due to the interaction with interface states, others are generated by the repulsion between the subbands near the points of their quasiintersections. For the heterostructure, composed of the gapless layer in a finite‐gap bulk material, the interface state is found to cause a nonmonotonous dependence of the gap on the layer thickness.
Quantum‐Chemical Calculations of Hydrogen Adsorption on the Polar Surface of Titanium Carbide
Authors: Sabiryanov R. F. , Novikov D. L. , Ivanovskii A. L. , Gubanov V. A.
Published: July 2007

Using the discrete variation method (DVM) the modelling of electronic and energy states of the (111) face of TiC, containing adsorbed hydrogen, is carried out. The peculiarities of the electron distributions, the parameters of the interatomic interactions, and the equilibrium distances of H adsorbed on the (111) face of TiC are calculated. The theoretical electron C K VV and TiL23M23V Auger‐spectra are presented for the ideal and containing adsorbed hydrogen polar (111) face of TiC.
On the Bond Orientational Order in Icosahedral Phases
Authors: Radulescu O. , Manaila R.
Published: July 2007

Icosahedral phases in Al—transition metal alloys are characterized by long range bond orientational order (BOO). The composition of the TM sublattice can influence the degree of BOO, presumably by altering the rigidity of the bonds. This fact can be evidenced by measuring the widths of the X‐ray diffraction peaks, which are shown to be very sensitive to this particular kind of disorder. Quantitative comparison of experimental data with Hendricks‐Teller‐type calculations provides estimates for the degree of orientational disorder in AlCrxFe1−x samples.
A Study of the Structure and Thermodynamics of Liquid Metals Based on Some Reference Systems
Authors: Akinlade O.
Published: July 2007

The bulk modulus of liquid alkali metals is calculated using the one‐component plasma model and a perturbative correction to the structure factor. The use of a highly accurate non‐local pseudopotential yields a considerable improvement on previous results. A study of the charged hard‐sphere reference system as applied to metals with strong electron—ion pseudopotentials (Li, Mg, Cd, In, Tl, and Pb) indicates that it is a preferred system since it yields lower free energies. Results for the other thermodynamic quantities investigated are also reasonable.
The Analysis of Rydberg Potential and van der Waals Interactions in Alkali Halides
Authors: Gupta V. P. , Sipani S. K.
Published: July 2007

The short range Rydberg potential which assumes an attractive term along with the frequently used repulsive term for short range interaction is employed to calculate the transverse optic mode Grüneisen parameter (γTO), longitudinal optic mode Grüneisen parameter (γLO), Grüneisen parameter (γ), mode Grüneisen parameter (q), first and second order pressure derivatives of isothermal bulk modulus \documentclass{article}\pagestyle{empty}\begin{document}$\left({\frac{{{\rm dB}_T }}{{{\rm d}T}}{\rm and}\,\frac{{{\rm d}^{\rm 2} B_T }}{{{\rm d}P^2 }}} \right)$\end{document}, and volume expansion coefficient (β) for NaCl‐ and CsCl‐structure alkali halides taking into account the three different sets of van der Waals coefficients and three different theories namely, the Slater theory, Dugdale and McDonald (DM) theory, and free volume (FV) theory. It is observed that the results obtained from DM theory using the values of van der Waals coefficients from Shanker and Rajoria are in good agreement with experiment. The potential has further been extended to take into account the second neighbour and three body contributions. The inclusion of second neighbour and three body interactions improves the results satisfactorily.
Phonon—Phonon Interaction in a One‐Dimensional Anharmonic Lattice
Authors: Chatterjee R.
Published: July 2007

A higher order partial nonlinear differential equation is obtained when phonon—phonon interaction in a one‐dimensional anharmonic lattice is treated quantum mechanically. Few assumptions are made to derive this equation of motion, such as long‐wavelength approximation, omission of normally ordered terms, continuum limit, and no umklapp scattering. The validity of these assumptions is discussed. The limitation to up to sixth higher order phonon—phonon interaction terms agrees with the earlier conclusion, reached from the stability consideration of the solitonic solution of this equation of motion.
Dynamical Correlations in Liquid Metals K and Cs
Authors: Jain K. C. , Gupta Neelam , Saxena N. S.
Published: July 2007

The theory of single particle motion in static harmonic well approximation is employed to study the dynamical correlations in potassium and cesium at their respective melting temperatures. Computation of dynamical variables like velocity autocorrelation function, power spectrum, and mean square displacement in both, potassium and cesium are made using the effective pair potential as obtained from the Ashcroft empty core model pseudopotential. The cooperative modes of motion of atoms is described in terms of the spectral functions of longitudinal current—current correlation which are obtained through the mean square displacement. Frequency corresponding to the peak positions in longitudinal current—current correlation functions are then plotted against the wave vector transfer. The above results of dynamical variables are compared with MD results of Miranda and the results of phonon dispersion with the results of Jacucci and McDonald. Good agreement is observed in the case of potassium.
Magnetoresistivity of a Crystal Field Split Kondo System
Authors: Prabhu R. B. , Barbosa A. F.
Published: July 2007

An expression for the magnetoresistivity of a crystal field split Kondo system is obtained. Numerical calculations are performed for the system Ce0.76La0.14Th0.1 for which all the parameters are available from the experimental data. Results are presented on the partial occupation numbers of the Zeeman split CEF levels as well as on the magnetoresistivity both as functions of temperature and magnetic field. It is found that the Kondo state persists for a field as high as 15 T. The system shows negative magnetoresistance. The magnetoresistivity decreases with increasing magnetic field. The results are in agreement with the experimental data on cerium based Kondo systems.
Discussion of the Ferromagnetic Simple Cubic Ising Lattice with Fluctuating Exchange Integral (s = 1/2)
Authors: Mielnicki J. , Balcerzak T. , Wiatrowski G.
Published: July 2007

Some magnetic properties of simple‐cubic disordered ferromagnets with fluctuating exchange integral are investigated with the use of the 1‐st, 2‐nd, and 3‐rd Matsudaira approximations. The results of various approximations are similar only for small fluctuations. For large fluctuations significant differences appear. This indicates that for a proper description of disordered material besides the simple decoupling of correlation functions, also another commonly used approximations should be significantly improved.
Magnetic and Mössbauer Studies of the System LaCo1−xZrxO3 (x = 0.1, 0.3, 0.5)
Authors: Johri U. C. , Singru R. M. , Bahadur D.
Published: July 2007

Mössbauer studies on well‐characterized LaCo1−xZrxO3 (x = 0.1, 0.3, 0.5) are carried out in the 80 to 700 K temperature range and they show that cobalt ions exist predominantly in the low spin CoIII(te) and CoII(te) states at 80 K which transform partially to high‐spin Co3+ (te) ions upto ≈ 500 K. In the 80 to 700 K region the system LaCo0.9Zr0.1O3 behaves almost similar to LaCoO3. However, above 500 K, in the system LaCo1−xZrxO3 (x = 0.3, 0.5) Co3+ ions capture an electron from CoII and transform into Co2+ (te) and CoIII ions pairs. The magnetic susceptibility data recorded are consistent with the present Mössbauer resülts. The inverse magnetic susceptibility versus temperature curves for the systems LaCo1−xZrxO3 (x = 0.3, 0.5) show different slopes in the 300 to 800 K temperature range. The higher slopes above ≈ 500 and ≈ 550 K for the system LaCo0.7Zr0.3O3 and LaCo0.5Zr0.5O3, respectively, indicate lower μeff which, in turn, suggests the generation of Co2+ ions at the cost of Co3+ ions. The generation of low spin CoII and CoIII at low temperatures is attributed to larger crystal field splitting Δcf compared to exchange energy Δex in the system as a result of tetravalent Zr ion substitution.
Ising Ferromagnet with Three‐Site Four‐Spin Interaction
Authors: Iwashita T. , Uryû N.
Published: July 2007

For Ising ferromagnets, the effects of the three‐site four‐spin interaction J′(Si · Sj) (Sj · Sk) on the magnetization 〈Sz〉 and the Curie temperature Tc are studied in the cases of large spin S = 2 and S = 5/2. Using the three‐spin model approximation, the temperature dependence of 〈Sz〉 is calculated numerically. The results show a first order phase transition for positive J′ larger than a certain critical value and show also an abnormal behavior for negative J′ smaller than another critical value.
Phase Transitions of Heisenberg Ferromagnetic Superlattices
Authors: Endo Y.
Published: July 2007

Static properties of a ferromagnetic superlattice made from alternating layers of strong and weak Heisenberg exchange interactions are theoretically studied at finite temperatures. Using the Green's function, magnetizations in each layer and transition temperatures are calculated, and their dependence on the thicknesses and strengths of interactions in both the materials is discussed.
Low‐Frequency SERS from Ag Colloids in Alkali Halide Crystals
Authors: Abel H.‐B.
Published: July 2007

Thermally and photochemically prepared Ag colloids in various alkali halides show a low‐frequency mode (LFM) between 3 and 8 cm−1. By stepwise annealing the crystal the LFM band maximum is shifted to lower wave numbers. The average size of the Ag colloids is determined from the LFM spectrum. The independence of the LFM on the polarization of the exciting laser light indicates predominantly spherically shaped Ag colloids. The influence of temperature on the LFM is investigated both, on Stokes and anti‐Stokes side. After dividing the LFM intensities by the Bose function the reduced SERS signal is found to be temperature independent and mirror symmetric concerning the Stokes shift.
Thermalized and Hot Interstitial Halogen Ions in Alkali Halides
Authors: Lushchik A. Ch. , Frorip A. G.
Published: July 2007

The efficiency of α, I pair creation at exciton decay is high at 4.2 K for KCl, KBr, and RbBr crystals for which H centers are oriented along 〈110〉. The efficiency of α, I pair creation by VUV‐irradiation at 4.2 K is extremely low for NaCl crystals for which H centers are oriented along 〈111〉. The process of mobile crowdion‐type interstitial halogen ion (I center) formation in KCl, KBr, RbCl, and RbBr (but not in NaCl) due to the tunneling recharge of primary F, H pairs is discussed. Such an I crowdion can shift by several interanion distances along [110] even at 4.2 K and, as a result, the system leaves the zone of spontaneous annihilation of α and I centers.
Inelastic Scattering of Low‐Energy Electrons by Electrons Localized in Surface Potential Wells
Authors: Strelniker Ya. M. , Zinets O. S.
Published: July 2007

Inelastic scattering of low‐energy electrons on the surface of a semi‐infinite crystal with excitation of electrons localized in a surface potential well is considered. The analytical expressions for the electron inelastic scattering cross‐section as a function of initial energy, incidence and scattering angles as well as potential well parameters are obtained. It is shown, that the peaks of the cross‐section angle dependence are determined by the energy spectrum of electrons localized in the potential well.
The Influence of Complex Luminescence Centres on the Luminescent Properties of CaS: Eu
Authors: Gruzintsev A. N. , Demishev S. V. , Nikiforova T. V.
Published: July 2007

Photoluminescence, cathodoluminescence, and excitation spectra of CaS: Eu phosphors with different activator concentrations (0.1 to 2 at%) are measured at 4.2, 80, and 300 K. Excitation and luminescence bands originating from the associate centres Eu‐VCa are observed in addition to those of a single Eu centre. Calculations by the method of linear combination of atomic orbitals (LCAO) allow to obtain a scheme of the electron terms of the associates which is in good agreement with the experiment.
Nonlinear Current—Voltage Characteristics of Ta2O5 and Nb2O5 Amorphous Oxides
Authors: Bryksin V. V. , Goltsev A. V. , Khanin S. D. , Novotelnova A. V. , Vasilev A. N.
Published: July 2007

Nonlinear current‐voltage characteristics of Ta2O5 and Nb2O5 amorphous oxides are studied in the temperature range from 213 to 363 K. The data give an evidence for the polaron mechanism of charge transport in these materials. A theoretical treatment of data is presented that gives a critical hopping lenght and a critical index.
Concentrated Kondo Systems in Solid Solutions on the Base of Europium Ternary Compounds
Authors: Levin E. M. , Kuzhel B. S. , Bodak O. I. , Belan B. D. , Stets I. N.
Published: July 2007

The experimental results of the components substitution effect on crystal structure, electronic transport properties, and Eu effective valence in solid solutions based on EuCu2Si2 and EuPd2Si2 ternary compounds are presented. It is shown, that when the Eu effective valence reaches the critical value v = 2.1, corresponding to degeneration of the 4f7 and 4f6 configurations, the condition of the concentrated Kondo system and an essential perturbation of the band electron spectrum near the Fermi level occur.
Exact Relations and Galvanomagnetic Properties of the Inhomogeneous Two‐Dimensional Medium
Authors: Arkhincheev V. E.
Published: July 2007

A two‐dimensional randomly inhomogeneous two‐composite medium in a magnetic field is considered. The exact relations for the effective characteristics of the system are found. The linear isomorphism between the galvanomagnetic and the conductivity problem is established. On the basis of these results the galvanomagnetic properties are studied.
An ESR Study of Li+ Impurity Ion Deformational Fields in KTaO3
Authors: Pechonyi A. P. , Antimirova T. V. , Glinchuk M. D. , Smolyaninov I. M.
Published: July 2007

From a study of the influence of uniaxial pressure on the ESR spectrum of “cubic” paramagnetic Fe3+ centres in KTaO3, their spin—phonon coefficients G11 = 1.28 × 10−3 eV and G44 ⪅ 0.74 × 10−4 eV are determined. The dilatation part of the deformation tensor Ω1 = 1.4 eV of the Li+ off‐centre ion in KTaO3 is obtained as a result of the study of the elastic broadening of the ESR line caused by the deformation fields of the Li+ ions. It is shown that the deformation mechanism makes a substantial contribution to the ESR linewidth of these centres in K1−xLixTaO3.
A Study of the White Lines Associated with the Rare Earth LII and LIII Absorption Discontinuities in Some Oxides and Tungstates
Authors: Vishnoi A. D. , Sapre V. B. , Mande C.
Published: July 2007

The intensities are studied of the white lines associated with the LII and LIII absorption discontinuities of the rare earth elements in their oxides RE2O3 (RE = La, Ce, Pr, Nd, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) and some tungstates RE2(WO4)3 (RE = La, Ce, Nd, Sm, Gd and Dy). These white lines correspond to the absorption transitions from the 2p1/2 to the 5d3/2 and from the 2p3/2 to the 5d5/2 levels. It is observed that the intensities of the white lines depend upon the filling of the 4f levels, which partially overlap the 5d levels.
Structural Modelling of Low‐Symmetry Phases of Spinels. I. Phases with 1:1 Octahedral Order
Authors: Talanov V. M.
Published: July 2007

The structural ordering mechanism of cations in octahedral positions of spinels of the type 1:1 is discussed using group‐theoretical methods of phase transition research. The structure of ordered phases is deduced theoretically from that of disordered phase. Qualitative pictures of possible displacements of atoms near phase transition temperatures are given. The experimental data are discussed.
Mean Square Displacement (MSD) of Neighbours around a Vacancy in Some Zinc Based Tellurides
Authors: Madhavan Y. , Ponnammal K. , Ramachandran K. , Haridasan T. M.
Published: July 2007

The mean square displacements (MSD) of neighbours around anion and cation vacancies in the systems ZnTe, ZnxCd1−xTe, and ZnxHg1−xTe are worked out for different values of x giving an active role for the vacancy following the theory of Maradudin et al. The results are compared with available experimental values and discussed.
Envelope Equation and Wave Function Matching for Narrow‐Gap Semiconductors
Authors: Paasch G. , Nguyen P. H. , Gobsch G.
Published: July 2007

It is shown that Zawadzki's equation for the conduction band envelope in a narrow‐gap semiconductor can be derived from the Ben Daniel‐Duke equation containing a position dependent effective mass if the position dependence of the band edge is taken into account in the Kane type energy dependence of the effective mass. Contrary to the original derivation of Zawadzki generalizations to other types of band structures are easily possible. As examples envelope equations are derived for an anisotropic Kane band structure and for the case of different conduction and valence band masses. In addition, the procedure presented here leads also to the conclusion that the envelope matching condition used till now has to be replaced by a more general and energy dependent one.
Optimization of Spin‐Hamiltonian Parameters by the Method of Non‐Linear Least‐Squares Fitting
Authors: Hrabański R. , Lech J.
Published: July 2007

A non‐linear iterative least‐squares fitting procedure for the analysis of EPR spectra is presented. In this method the line positions obtained for a given orientation of the external magnetic field are fitted to evaluate the spin‐Hamiltonian parameters. The procedure is illustrated by an application to the X‐band room temperature EPR data obtained for Mn2+ doped single crystals of [Mg(H2O)6]SnCl6.
Investigation of the Thermodynamic Properties of Anharmonic Crystals by Momentum Method. IV. The Limiting of Absolute Stability and the Melting Temperature of Crystals
Authors: Tang Nguyen , Van Hung Vu
Published: July 2007

On the basis of results obtained earlier the equation for the limiting of absolute stability in the crystalline state with f.c.c. structure is found. Using this the limiting temperatures of absolute stability and the melting temperatures of inert gas crystals at various pressures (including of very high pressures) are determined. Besides, the nearest neighbour distances and the Grüneisen constants at these temperatures are obtained. In comparison with the experimental data the calculated results deviate only by some per cent.
Lattice Dynamics of Sulphur Dioxide
Authors: Binbrek O. S. , Anderson A.
Published: July 2007

A simple force constant model is developed and applied to the vibrations of solid sulphur dioxide. Eight parameters (two intra‐ and six inter‐molecular force constants) are adjusted to obtain the best fit to the 15 lattice and internal mode frequencies observed by Raman and infrared spectroscopy. The calculated eigenvectors are used to assign the frequencies and to estimate the degree of translationallibrational mixing.
Potential Energy of an Argon Atom Adsorbed on the Stepped and Kinked Surfaces of a Sodium Chloride Crystal
Authors: Yanagihara T. , Yomogita K.
Published: July 2007

The potential energies of an Ar atom adsorbed on flat, stepped, and kinked NaCl crystal surfaces are calculated by using dispersion, electrostatic, and Born‐Mayer repulsive potentials. They have a minimum value (−10.1 kJ/mol) above each Na+ ion site in the flat surface and a minimum (−15.0 kJ/mol) in the vicinity of each Na+ ion site on the lower terrace along a step in the stepped surface. In the kinked surface they have a minimum value (−21.9 kJ/mol) in the vicinity of a kink on the lower terrace. Furthermore, on those sites the isosteric heats of an Ar adatom at zero coverage are calculated and discussed in comparison with experimental results.
Structural Classification of AB‐Type Binary Compounds
Authors: Walzer U.
Published: July 2007

At first, a review is given on how structure maps for the prediction of the space group and structure type of AB‐type binary compounds can be designed with the help of semiempirical theories. Then, two ab‐initio pseudopotential theories are compared in detail. The all‐electron single‐particle equation and the spin‐density‐functional formalism form the starting point for both theories. While transferability is aimed at in both theories, the conditions imposed differ in some respects. Theory A uses the Schrödinger equation as starting point. The crossing points of a screened pseudopotential are employed as characteristic quantities. The structure energy is dominated by s‐p electrons, even in the case of the compounds of two transition metals. Theory B is based on the Dirac equations and takes into account spin–orbit effects which are relevant for heavier elements. The coordinates of the minima of the bare‐ion potentials serve as characteristic radii and energies. In both cases, a good separation of the structure types is achieved. For theory B, in addition, a few predictions concerning lattice constant a and the melting temperature are represented graphically.
Low Temperature Specific Heats of AgSb Alloys
Authors: Al‐Shibani K. M. , Sacli O. A.
Published: July 2007

Low temperature specific heats of AgSb alloys of concentrations 0.89; 2.67; 3.7, and 4.72 at% are measured between 0.4 and 4.2 K. Experimental results for pure Ag and AgSb alloys obey the relation C=γT + βT3 with an experimental error of 2%. It is observed that the electronic specific heat coefficient, γ, increases linearly with the impurity concentration while the Debye temperature, θD, decreases linearly with the concentration. It is established that the change of γ on alloying can be expressed as Δγ=1/3 c(Z – 1) by modifying the free electron result. Variation of the Debye temperature, θD, is believed to result from the change of mechanical properties of Ag. By employing Lindeman's melting theory it is shown that (θD)alloy=(1 – 0.63c) (θD)Ag which agrees satisfactorily with the experimental results.