bluuebunny/crossref_metadata_2025_split huggingface dataset:
Energy Levels of Sm2+ in BaClF and SrClF Crystals under Magnetic Field I. Theory
Authors: Kibler M. , Grenet G. , Gǎcon J. C. , Jacquier B. 
Published: July 2007

AbstractFrom an experimental as well as from a theoretical viewpoint the effects of a magnetic field on the low‐lying energy levels of Sm2+ in BaClF and SrClF crystals are studied. This first paper is devotedto the description of a 6‐parameter model and a more refined 14‐parameter model as well as of the accompanying procedures for the interpretation of the observed spectra.
Parametric Decay of a High‐Power Helicon Wave in to a Transverse Acoustic and Another Helicon Waves in Longitudinally Magnetised Cubic Piezoelectric Semiconducting Plasmas
Authors: Ghosh S. , Dixit S. 
Published: July 2007

AbstractA detailed analytical investigation is made of the parametric decay of a high‐power helicon into another helicon and an acoustic wave in a longitudinally magnetised n‐type cubic piezoelectric semiconducting crystal belonging to the class 43m. The dispersion relation is obtained by using a hydrodynamic model of an homogeneous, piezoelectric,one‐component (electron) semiconducting plasma, and the threshold value of pump electric field and the growth rate of unstable mode well above the threshold are discussed. The analysis is applied to a specific semiconductor, n‐InSb at 77 K duly irradiated by a high‐power heliconwave for numerical estimation. The laser wave intensities used are in the range of 109 to 1012 Wm−2 which is assumed to be less than the damage threshold of the InSb crystal. The order of waveamplitude is feasible presently. The growth rate is found to be of the order of 1010 s−1.
Pressure Study of Photoconductivity in Indium Antimonide I. Low‐Concentration n‐Type at 77 K. Pressure‐Dependent Capture Coefficient of a Hole‐Trapping Center
Authors: Piotrzkowski R. 
Published: July 2007

AbstractA strong increase of photoresponse and decay time constant is observed under hydrostatic pressure at 77 K in low‐concentration n‐InSb samples. A lowering of free‐electron concentration, possible in this material by application of the metastable states freezing technique, enhances this effect leading to an appearance of non‐linear photoconductivity. An analysis of the experimental dependences carried out on the basis of a two‐center recombination model deduced from the above data enables to conclude that the observed pressure effect is related to an exponential decrease of the capture cross‐section of the hole‐trapping center involved in the kinetics process.
Light Scattering from Surfaces near Phase Transition Points
Authors: Filho A. Ribeiro , Tilley D. R. , Albuquerque E. L. , Almeida N. S. , Oliveros M. C. 
Published: July 2007

AbstractA semi‐infinite medium with a one‐component order parameter η is considered. It is assumed that the free energy density is given by a simple Landau‐type expansion in η, that the boundary condition is linear in η and Δη, and that fluctuations in the dielectric function depend linearly on fluctuations in η. With the useof phenomenological equations of motion the order‐parameter Green function is derived. Expressions are given, and illustrated numerically, for the power spectrum of order‐parameter fluctuations and the cross section for inelastic light scattering.
Raman and Infrared Studies on Ag2HgI4 and Cu2HgI4 Superionic Compounds
Authors: Sudharsanan R. , Srinivasan T. K. K. , Radhakrishna S. 
Published: July 2007

AbstractRaman measurements between 77 and 340 K are reported for Ag2HgI4 and Cu2HgI4. Additively far infrared reflection and transmission spectra between 30 to 180 cm−1 are measured. Symmetrybased vibrational band assignments are given for both the internal and external optic modes. The conductivity in the region 30 to 150 cm−1 is calculated and the behaviour is explained using the jump diffusion model.
First‐Principles Thermal Expansion in Rb and Cs
Authors: Prasad B. 
Published: July 2007

AbstractThe thermal expansion of Rb and Cs is investigated using Toya's first‐principle approach with modified g‐function. The mode Grüneisen parameters γqj and the temperature dependence of both, the mean Grüneisen parameter γT and the thermal expansion coefficient βT are calculated and compared with the experimental data available up to the present time. The agreement obtained between theory and experiment is satisfactory.
The Influence of Many‐Body Interactions on the Speed of Sound in Liquid Metals
Authors: Kovalenko N. P. , Kuzmina L. M. 
Published: July 2007

AbstractA method is proposed for the calculation of compressibility of liquid metals using the longitudinal limit of the static structure factor. It is shown that the accurate determination of compressibility requires to take into account many‐ion interactions. The compressibility for alkali metals is calculated. The equality of static and dynamic compressibilities is proved.
On the Angular Dependence of the Effective Spin‐Pinning in Thin Insulator Film
Authors: Jirsa M. 
Published: July 2007

AbstractThe angular dependence of the boundary conditions in a perfectly homogeneous insulator film with an uniaxial surface anisotropy is discussed with respect to the determination of the critical angle. The existence of two different critical angles and two different surface modes for each symmetry (symmetrical and antisymmetrical with respect to the central plane of the film) follows from this treatment for high negative values of the surface anisotropy constant Ks.
The Mixing of Frenkel and Charge‐Transfer Excited States I. General Treatment of Singlet and Triplet Excitations and Analytic Solutions of Simple Models
Authors: Reineker P. , Schmid B. J. 
Published: July 2007

AbstractThe mixing of Frenkel and charge‐transfer excitons in molecular crystals and dimers which may be formed by two identical or different molecules is discussed. The Hamiltonian takes into account the kinetic and potential energy of the electrons, their Coulomb and spin—spin interaction, and their energy in an external magnetic field. The resulting Hamiltonian consists of a part for singlet excitons which is diagonalized exactly for some special cases in an analytical manner and a part for triplet excitons. The fine‐structure tensor of the latter part is expressed explicitlyin terms of electronic matrix elements.
The Jahn‐Teller Effect in Layer Crystals
Authors: Lukiyanets B. A. , Tovstyuk K. D. , Boichuk V. V. , Danilevich‐tovstyuk K. K. 
Published: July 2007

AbstractThe adibatic potential in the layer semiconductor GaSe is considered taking into account the Davydov splitting of the bands. It is shown that in the case of electron—phonon interaction which is responsible for the Jahn‐Teller pseudoeffect, distortions are possible either normal to layers or along the layers, depending on the parameters of the electron and phonon subsystems.
Effects of the BijSxiSxj Interaction on the IMTF's Dynamics
Authors: Borges A. T. , Ribeiro L. A. Amarante 
Published: July 2007

AbstractAdditively to the Ising model in a transverse field (IMTF) an interaction BijSS is considered. For a S = 1/2 three‐dimensional cubic latticethe longitudinal relaxation shape function is calculated by means of Mori's continued‐fraction representation in a three‐pole approximation. The effects of this new term on the fluctuation spectra are studied for T > Tc and the results compared with those obtained for the pure IMTF.
Charge Transfer and Energy of Formation in Ordered Binary Alloys
Authors: Chakraborty S. , Manna A. , Ghosh A. K. 
Published: July 2007

AbstractThe study of charge transfer between constituents plays a central role in the study of alloy formation. So far it has been studied by the pseudopotential, self‐consistent KKR‐Xß. Thomas‐Fermi, and Thomas‐Fermi‐Dirac methods. Recently it is shown that the α‐expansion method of Löwdin, as adopted by Matheiss, can be successfully employed to derive electron density distribution in a solid from free atomic statefunctions, and hence charge transfer and energy of formation of ordered binary alloys can be calculated via Hodges and Stott mechanism as proposed by Alonso and Girifalco. Here a still simpler direct procedure is presented which yields equally good, if not better, results.
A Theoretical and Experimental Study of the Enthalpies of Formation of LaNi5‐Type Compounds
Authors: Pasturel A. , Colinet C. , Allibert C. , Hicter P. , Percheron‐Guegan A. , Achard J. C. 
Published: July 2007

AbstractThe heats of formation of LaNi5‐type compounds are computed within a tight‐binding scheme for the d‐band. It is shown that the relatively large difference between the energy levels of the two elements is a dominant factor in the determination of the formation energy. The evolution of the energy level of the rare‐earth metal can explain the experimental behaviour of the heats of formation of the RNi5 compounds along the rare‐earth series. In order to discuss the calculated results the enthalpies of formation of LaNi5, PrNi5, SmNi5, and YNi5 are determined by a calorimetric method.
Photostimulated Reorientation of H (Pb2+) Centres in a KCl:PbCl2 Crystal
Authors: Nagirnyi V. , Soovik T. , Zazubovich S. 
Published: July 2007

AbstractTemperature dependences of polarization and kinetic characteristics of luminescence are investigated for Pb2+ ions perturbed by a (nnn) cation vacancy and an interstitial chlorine atom (H(Pb2+) centres) in a KCl:PbCl2 crystal. At T > 110 K the reorientation of these centres in the triplet excited state of the Pb2+ ion stimulated by polarized UV radiation becomes evident in the polarization spectra and decay kinetics of the AT emission. It results neither in the depolarization of the emission nor in the „alignment”︁ of the centres. Most probably the effect can be explained by a strong covalent interaction between the excited Pb2+ ion and an interstitial, and it is caused by the dissociation of the two‐component defect near the Pb2+ ion and the following jump of the interstitial chlorine atom into one of the 〈100〉 directions perpendicular to the {Pb2+‐v} axis.
Evidence of Open 4f Shells in Rare Earth Compounds
Authors: Gupta S. N. , Shah S. 
Published: July 2007

AbstractA forbidden transition 2P3/2–4f (unoccupied) is detected in the L‐absorption spectra of compounds of rare earth metals Tb and Dy, indicating the presence of an open 4f shell in these compounds. the location of these 4f shells is found to shift towards the high‐energy side when these metals form compounds.
Anomalous Radiation of Fast Channeled Electrons in Optically Transparent Crystals
Authors: Popov D. E. , Rozum E. I. , Uglov S. R. , Vorobiev S. A. 
Published: July 2007

AbstractThe spectral and angular characteristics of radiation of channeled electrons in the mean energy region for optically transparent crystals are calculated. An anomalous radiation is shown to be generated in the ultraviolet, visible, and infrared ranges of the spectrum. Peculiarities of the experimental observations and investigation of the anomalous radiation are discussed.
The First Born Approximation in Estimates of the Threshold Anomalies in the X‐Ray Spectra of Simple Metals
Authors: Leiro J. A. 
Published: July 2007

AbstractThe XPS core line asymmetries and the XAS threshold singularities of Zn, Cd, In, Mg, and Na metals are considered. The singularity indices and threshold exponents, calculated by using the “Z + 1” approximation are compared with experimental values. Furthermore, the results obtained by a partial‐wave method are compared with those estimated by the first Born approximation. It is found that the Born approximation values are in agreement with those within the partialwave method.
Shallow Impurity States in Strong Magnetic Field
Authors: Gawron T. R. , Mycielski J. 
Published: July 2007

AbstractAssuming that the shallow‐impurity wave function is composed of the states of a single Landau subband, an effective one‐dimensional wave equation is derived and discussed in detail, allowing for the band anisotropy. The optical transitions from the bound impurity states to both, bound and free‐carrier states are considered. For strong effective‐mass anisotropy, e.g. for acceptors in semimagnetic semiconductors, the energies and wave functions are explicitly given for all impurity states.
Mössbauer Conversion Electron Spectra at Total Reflection
Authors: Andreeva M. A. , Kuzmin R. N. 
Published: July 2007

AbstractA theory of the secondary processes at total reflection of Mössbauer radiations from a flat surface containing resonant nuclei is developed. It is shown that the Mössbauer spectrum of the conversion electrons has a sufficiently broadened two‐hamped shape instead of a simple Lorentzian lineshape. Direct calculations are performed for the case of resonant 57Fe films of different thicknesses and different substrates.
Far‐Infrared and Submillimeter Dielectric Response of Sodium Nitrite
Authors: Wyncke B. , Brehat F. , Sherif M. El , Kozlov G. V. 
Published: July 2007

AbstractThe far infrared and submillimeter dielectric function of sodium nitrite single crystal are determined by means of precise transmission spectroscopy (8 to 17 cm−1) and reflection spectroscopy (10 to 600 cm−1) over the temperature range 20 to 230 °C for the a and c crystallographic directions. All the infrared active lattice modes are observed and their parameters calculated using the factorized form of the dielectric function. A low‐frequency excitation of relaxation type is introduced to explain the low‐frequency dielectric function (< 100 cm−1) in each a‐ and c‐directions.
On the Formation of Large Clusters of Recombining Particles of One Kind in Solids during Reaction A + B = 0. Two‐ and Three‐Dimensional Discrete Models
Authors: Antonov‐Romanovskii V. V. 
Published: July 2007

AbstractOn the basis of two‐ and three‐dimensional models an investigation is investigation is made of the concentration dependence of recombination on the average group size of one‐kind immobile particles arising during a prolonged excitation as a result of the reaction type A + B = 0.
ENDOR Investigation of H(Li) Centres in KCl
Authors: Heder G. , Spaeth J. M. 
Published: July 2007

AbstractIn KCl doped with Li+ recently a new paramagnetic hydrogen centre has been observed. From the ESR spectrum it was described to be a (LiH)+ molecule occupying a cation site with a Li+–H0 separation of 1.44 Å. Below 70 K it is frozen‐in along [111], at higher temperatures it undergoes a rapid reorientational motion. Using ENDOR now the shf interactions of the hydrogen electron with three equivalent Cl and one Li neighbour nuclei are determined precisely at 25 and 41 K and the ESR analysis essentially is confirmed. A theoretical calculation of the shf interactions shows, however, that the centre is not a (LiH)+ molecule. It is rather a perturbed interstitial atomic hydrogen centre (H(Li) centre) with a Li+–H0 separation of 2.17 Å, where the hydrogen atom is displaced from the interstitial site by about \documentclass{article}\pagestyle{empty}\begin{document}$ (1/4)\sqrt 3 d_0 $\end{document} d0 (d0 lattice spacing) towards the cation site.
The Incommensurate CDW Phase of a Quasi‐One‐Dimensional Peierls‐Fröhlich System with a Nearly Quarter‐Filled Band. I. Analytical Treatment
Authors: Fischbeck H. J. 
Published: July 2007

AbstractThe continuum limit of the Peierls‐Fröhlich model with a nearly quarter‐filled band is considered in the mean‐field approximation. The incommensurate state is described by a complex order parameter Δ and a further real order parameter called Δ2. The original 4 × 4 Schrödinger equation is reduced to a standard 2 × 2 problem by a low‐energy approximation. The latter involves the electronic gap function θ(x) which is given in terms of Δ and Δ2. It is shown that the self‐consistency condition for θ(x) can be satisfied by a „single‐kink‐band function”︁ if the commensurability mediated by Δ2 dominates. The corresponding electronic energy spectrum is calculated in close analogy to a previous paper on commensurability 3.
Excited States and Collective Excitations in a Dense Gas of Excitons
Authors: Manzke G. , May V. , Henneberger K. 
Published: July 2007

AbstractFollowing the concept of Hanamura the Bose formalism of Usui is used to investigate the collective properties of a dense gas of excitons. The correlation self‐energy for excitons is calculated with the help of a special concept of pure excitonic screening. The dielectric function and the collective modes are studied in detail. It is shown, that the consideration of excited exciton states leads to a lowering of the 1s exciton level with increasing exciton density. Furthermore the damping of the 1s exciton due to exciton–exciton collisions is investigated.
States of Thermal Equilibrium in β‐Rhombohedral Boron and Their Alteration by Optical Excitation
Authors: Werheit H. , Franz R. 
Published: July 2007

AbstractIt is shown that β‐rhombohedral boron has different states of thermal equilibrium at T ⪅ 150 and ⪆ 180 K. These states can be distinguished by their optical absorption spectra showing electronic transitions into a bound state at 0.4 eV at low temperatures, and transitions into an energy continuum at higher temperatures. By steady state optical excitation the transition temperature is lowered indicating a kind of Mott transition. This phase transition is assumed to be the reason for the discontinuity of numerous physical properties of β‐rhombohedral boron in this range of temperature.
A Study of the Reflection Spectra of Surface Exciton–Impurity Complexes
Authors: Ermakov V. N. , Korbutyak D. V. , Litovchenko V. G. , Mikityuk O. Yu. , Nitsovich V. V. 
Published: July 2007

AbstractAn experimental and theoretical study is made of the reflection spectra of surface excitons and exciton–impurity complexes. The conditions for the localization of the excitons near the CdS surface are fulfilled experimentally by low‐energy argon ion bombardment (E ⪅ 1 keV). The binding energy of the surface excitons at impurities of small effective charges is calculated theoretically. It is shown that the binding of the surface excitons at an impurity center is possible both, for positive and negative effective charges. Satisfactory agreement is observed between the theoretical calculation of the reflection spectrum within the frequency range of the surface excitons and the experimental data for Ar‐ion bombarded CdS surface.
Dielectric Dispersion and Dynamics of Nitrite Ions in K2Ba(NO2)4
Authors: Unruh H.‐G. 
Published: July 2007

AbstractDielectric measurements reveal Debye‐like dispersions of the main permittivities below room temperature at audio‐frequencies, the activation energy of the corresponding motions of nitrite ions being 0.5 eV. The role of the three non‐equivalent NO2 groups in the phase transition at about 203 K is investigated using Raman‐spectroscopic results on internal NO2 modes. A model is proposed that includes freezing of certain NO2 groups with static disorder.
Soliton Solution for the Excited State in the Spin‐Peierls S = 1/2 Antiferromagnetic Chain
Authors: Dassen G. L. M. , de Moura M. A. 
Published: July 2007

AbstractThe ground‐state and low energy excitation spectrum of the spin‐Peierls S = 1/2 antiferromagnetic chain is studied in the adiabatic limit. It is shown that this model corresponds to the semiclassical Gross‐Neveu model with only one kind of Fermion and that the lowest excited state corresponds to the usual‐kink‐soliton of the Φ4‐theory. Its energy is approximately one‐third of the singlet‐triplet excitation gap.
Some Critical Properties of the s‐d Model
Authors: Wesselinowa Julia M. 
Published: July 2007

AbstractA Green's function technique is developed to study the critical behaviour of the s‐d model. The temperature and the magnetic field dependence of the spin magnetization are determined. The critical exponents β and δ are numerically calculated. Applying the scaling laws γ and γ2 are obtained. The critical exponents are in very good agreement with the experimental data and with other theoretical results.
The Width of the Energy Gap of TlBvC‐Type Compounds
Authors: Čermák K. 
Published: July 2007

AbstractThe Tl3BC4 (B  V, Nb, Ta; C  S, Se) compounds satisfy the 8N valence rule of Mooser and Pearson and belong to semiconductors. An increase in the value of energy gap Eg with the substitution of V by Nb or Ta in these compounds can be ascribed to the increasing bond ionicity due to the increasing difference of electronegativity of the anionic and cationic part of the compounds.
Partial Structure Factors and Self‐Diffusion in Liquid Copper‐Lead Alloys
Authors: Palchaudhuri S. , Joarder R. N. , Rao R. V. Gopala 
Published: July 2007

AbstractThe three partial structure factors, S11(k), S22(k) and S12(k) and also the Bhatia‐Thornton structure factors, SNN(k), SCC(k) and SNC(k) are computed for liquid copper‐lead alloys at various concentrations and at different temperatures with a square‐well potential. The total structure factor obtained from these partials compares satisfactorily with the experimental results. The isothermal compressibilities have been calculated from the partial structures in the long wave limit. The self‐diffusion coefficients Di have also been calculated at those concentrations of Cu for this alloy in the linear trajectory approximation of Helfand. From the self‐diffusion coefficients, an estimate of the mutual diffusion coefficients is made to a good approximation.
The Parisi‐Sompolinsky Solution for an Infinite‐Ranged Spin Glass Model with m‐Component Spins
Authors: Goltsev A. V. 
Published: July 2007

AbstractThe Parisi‐Sompolinsky solution is considered for the m‐component Sherrington‐Kirkpatrick model in the general case H > 0 and J0 > 0. Self‐consistent equations are derived which determine the free energy, the magnetization, and the functions q(x) and Δ(x). The stability problem is discussed.
Electronic Structure of V3Si and V3Ge. Comparison of NMR Data with Band‐Structure Calculations
Authors: Skripov A. V. , Stepanov A. P. 
Published: July 2007

AbstractThe parameters of electronic structure near the Fermi energy obtained from 51V NMR measurements in V3Si and V3Ge are compared with the results of band‐structure calculations. It is found that the band‐structure calculations of Klein et al. combined with the model of electron lifetime broadening can satisfactorily describe the experimental temperature dependence of spin‐lattice relaxation rate in V3Si and V3Ge. For both the compounds the experimental values of the electronic density of states at the Fermi level, N(EF), are about twice the theoretical ones. The d‐orbital content of N(EF) in V3Si derived from the experiment is consistent with the predictions of Mattheiss and Weber.
One‐ and Two‐Photon Luminescence Excitation of Eu3+ in a LaF3 Monocrystal
Authors: Kholodenkov L. E. , Makhanek A. G. , Kaminskii A. A. 
Published: July 2007

AbstractFor the first time results are given of a comparative study of the 5D2 manifold Stark components of Eu3+ in a LaF3 monocrystal by the polarization diagram method under one‐ and two‐photon luminescence excitation. As a whole, the experimental results are in agreement with the theoretical approach under consideration and comply with the case of C2v → C2 symmetry distortion. Stark components are identified by one‐ and two‐photon polarization diagrams. It is shown that two‐photon diagrams are much more informative in this respect.
Thermal Evolution of Low‐Temperature Manganese Centers in X‐Irradiated CaF2:Mn
Authors: Jahan M. S. , Cooke D. W. 
Published: July 2007

AbstractThermal evolution of the radiation‐induced defects in CaF2:Mn (0.1% by weight) are investigated by ESR techniques. The Mn+ resonance is found to decay at 200 K with an activation energy of 0.44 eV and frequency factor 2.8 × 108s−1 which agree with previous luminescence and optical absorption measurements. This activation energy and decay temperature also agree with that of the previously described H center. It is concluded that the luminescence in CaF2:Mn results from thermal release of holes at H centers with ultimate recombination at Mn+ ions producing excited state Mn2+(*). Relaxation yields the observed 500 nm emission characteristic of Mn2+. A second defect which decays at 150 K is observed but not identified.