bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the Short‐Range Repulsive Potential in Alkali Halides
Authors: Kaur A. J. , Bhende W. N. , Bakhshi P. S. , Shanker J.
Published: July 2007

The applicability of the Woodcock potential form is considered for studying the crystalline properties of alkali halides. This potential form represents the composite form of the inverse power dependence and the exponential dependence of the repulsive energy on interionic distance. The cohesive energy, pressure derivative of bulk modulus, thermal expansion coefficient, and the Grüneisen‐Anderson parameters are calculated for sixteen NaCl‐structure alkali halide crystals. The results are discussed and compared with available experimental data. The corresponding values obtained from the Born‐Landé inverse power form and from the Born‐Mayer exponential form are also presented for the sake of comparison. The important contribution is the finding that the Woodcock potential is applicable to all the three states viz. molecular state, liquid or molten state, and crystalline state of alkali halides.
New Approach to the Theory of Hybrid Excitations in Magnetic Dielectrics
Authors: Škrinjar M. J. , Kapor D. V. , Šetrajčić J. P. , Ivić Z.
Published: July 2007

An analysis is made of the magnetic and optical properties of an antiferromagnetic dielectric (AFD) in constant magnetic field. Hybrid excitations appearing in AFD during the single‐particle transitions represent a mixture of magnetic excitons and photons. The direct relationship between the average magnetic and electric dipole moment of the crystal is a consequence of the hybridization of elementary excitations. This relationship is described by the magneto‐optical tensor, which is expressed through the microscopic features of the system, more precisely, through electric dipole and magnetic dipole moments of the transitions in the paramagnetic ions in AFD.
Biexciton Two‐Photon Absorption and Raman Scattering in CuBr
Authors: Bobrysheva A. I. , Baltaga V. V. , Grodetskii M. V.
Published: July 2007

The probabilities of the two‐photon absorption by a biexciton in the ground and the first vibrational states in CuBr and the probability of the two‐photon Raman scattering with the participation of the ground and the first vibrational states of the biexciton as intermediate states are calculated by perturbation theory method. Supposing that a Lorentzian distribution of frequencies ωi of the exciting light and a Lorentzian shape of the emission lines of the excition occur, the shape of the emission line at different values of the biexciton half‐width Γm is calculated. The dependence of the Raman scattering maximum position on ωi is obtained. At the condition 2Γ ≧ Γm; Γ Γm ≦ Γf the experimentally observed deviation of the Raman scattering maximum shifting from 2Δωi, is explained. The polarizational properties of the Raman scattering probability are obtained including the case when the intermediate states are the biexcitons Γ1, Γ5, Γ3.
Electron States and Conductivity of Size Quantized Systems with Rough Boundaries
Authors: Potapenko S. Yu. , Satanin A. M.
Published: July 2007

A new approach to the study of electron properties of the systems with rough boundaries is proposed. The boundary problem is reduced to the analysis of Schrödinger equation with effective Hamiltonian and boundary conditions for flat surfaces by using a curvilinear coordinate system. A criterion for existence of localized states is obtained and evaluation of the lifetime of resonance states arising near the bulges is presented. Asymptotic behaviour of the state density tails from the subbands of the size quantization, intraband and interband relaxation time, and conductivity of the film are estimated. The influence of the scattering by boundaries on the localization effects in two‐dimensional systems is investigated.
Pressure—Volume Relation in Intermediate Valence Compounds
Authors: Naudts J. , Werner A. , Hochheimer H. D.
Published: July 2007

Experimental p—V data of the compounds YbO, Sm4Bi3, and TmSe are analysed using a simple thermodynamic model. Acceptable values are obtained for the density of states of the conduction electrons, the volume at which the bandgap closes, and the pressure dependence of the bandgap.
Asymtotic Medium Concept Applied to Correlated Point Scatterers in the Weak‐Scattering Limit
Authors: Solbrig H.
Published: July 2007

The concept of an asymptotic medium with a superimposed inhomogeneity shell about the source point is employed as an interpretation scheme for multiple‐scattering approximations to the averaged Green function. Including third‐order scattering (finite‐ranged pair correlation), analytical expressions are obtained for the index of refraction of the asymptotic medium and the reflection and transmission coefficients of the inhomogeneity shell as well as for the electronic density of states.
Impurities and Charge Compensation in Some Molybdenium Oxides
Authors: Grunin V. S. , Patrina I. B.
Published: July 2007

The role of impurities in the defect formation in MoO3 and Na2Mo2O7 crystals is discussed. The EPR spectra of the X‐ray and uv‐irradiation centres are investigated. The constants of the appropriate spin‐Hamiltonians are obtained. It is shown that the localization radius of an electron (or a hole) exceeds the interatomic distances, therefore the EPR spectra have a low symmetry with noncoincident axes of the A‐ and g‐tensors. The unpaired density distribution depends on the characteristics of the lattice and impurity cations such as the electronegativity, the coordination number, and the degree of the local environment symmetry distortion.
Theory of the Power Spectrum and Scattering Properties of Three‐Dimensional Disordered Systems Having a Variable Degree of Short‐Range Order. II. Line Spectrum and Cross‐Relation Technique
Authors: Celasco M. , Mazzetti P. , Stepanescu A.
Published: July 2007

A new approach to the power spectrum calculation of the three‐directional distribution of physical events characterized by a variable degree of order, ranging from a perfect long‐range order to a complete disorder, including short‐range order properties, is given in Part I of the paper. In this second part simple analytical expressions of the line component of the power spectrum are obtained. The scattering properties of disordered or partially ordered atomic or molecular structures (like for instance, liquid crystals) are considered, concerning both, the diffuse and the line component of the spectrum. The case when in the local order different types of sublattices can still be identified is also considered. Applications of the above results include X‐ray and neutron scattering properties of disordered or partially ordered atomic or molecular structures concerning both, the line and diffuse component of spectrum, excess energy and power loss calculation in ferromagnets and superconductors, and physical properties of amorphous materials. Some of these applications will be discussed in a forthcoming paper.
Phonon‐Polaritons in Bilayer Systems. p‐Polarized Guided Wave Phonon‐Polaritons and Guided Wave Surface Phonon‐Polaritons
Authors: Wendler L.
Published: July 2007

In a bilayer system consisting of two dielectric media with local, frequency‐dependent dielectric functions in addition to the surface phonon‐polaritons other types of p‐polarized phonon‐polaritons, guided wave phonon‐polaritons and a new type guided wave surface phonon‐polaritons, can exist. These phonon‐polaritons are associated with electromagnetic fields having standing wave character in one or in both layers in the direction normal to the surfaces. The regions in the ω — k‖ plane where the different types of phonon‐polaritons of a bilayer system occur are discussed for the three physically different possibilities of combining two dielectric media. The dispersion curves and electric fields of guided wave phonon‐polaritons and guided wave surface phonon‐polaritons are calculated and presented in graphical form.
Role of the Excess Volume of Formation on Alloying
Authors: Alonso J. A. , González D. J. , Iñiguez M. P.
Published: July 2007

It is found that the virtual crystal model of a disordered binary alloy (in which the alloy is considered as an effective monatomic solid with atoms of intermediate characteristics between those of the two component metals) explains the tendency for a negative deviation of the alloy volume with respect to the volume predicted by Vegard's law. These volume deviations constitute an effective way of lowering the heat of formation of the alloy.
First‐Order Raman Scattering in RbCl Containing F‐Centres
Authors: Negi B. B. S. , Ram P. N.
Published: July 2007

The first‐order Raman spectra due to F‐centre in RbCl are calculated using a Green's function method. A simple impurity model including changes in nearest neighbour force constants is employed to calculated the Raman spectra in the A1g, Eg, and F2g modes and the results are compared with available experimental data. A 50% reduction in central force constants gives good account of the experimental values.
Spin‐Glass Behaviour in Disordered Hubbard Alloys
Authors: Fehske H. , Kolley E. , Kolley W.
Published: July 2007

The paramagnetism to spin glass transition in concentrated itinerant alloys AcB1‐c is studied on the basis of the random Hubbard model. Kakehashi's treatment of nonlocal spin fluctuations mapped onto an effective random‐site Ising model is combined with Nambu's Landau‐type order parameter expansion of the quenched averaged free energy based on the replica method. The temperature‐ and concentration‐dependence of the exchange couplings is determined by a self‐consistent CPA calculation. Numerical results are presented for nearest‐neighbour pair interactions, freezing temperature, specific heat, single‐site distribution functions, densities of states, and spin glass order parameters.
On the Fluctuations and Phase Transitions in Dicke‐Like Models
Authors: Loos J.
Published: July 2007

The fluctuation theory based on the functional integration method is developed for a multimode Dicke‐Hamiltonian with arbitrary spins and with antiresonant terms included. The effective classical Hamiltonian of the fluctuations is deduced and the equilibrium phase transition, the existence of soft modes as well as the general equations of state are discussed in this unified approach. The consequences of the rotating‐wave approximation are clearly distinguished. The solid state phenomena of the cooperative Jahn‐Teller effect and of spin‐reorientation are implied in these considerations.
Ultrasound Attenuation and Quantum Oscillations in BiSb Alloys
Authors: Dominec J. , Misek K. , Kraak W. , Herrmann R.
Published: July 2007

The attenuation of ultrasound is measured in Bi100−xSbx alloys (x = 0, 1.2, 4, 4.5, 5, 6.4) in an experimental arrangement, where the wave vector and the magnetic field are parallel to the trigonal axis of the sample. The period and the amplitudes of the quantum oscillations, analogous to the Shubnikov‐de Haas ones, are discussed.
The Effect of Temperature on the Optical Absorption Edge of Amorphous Thin Films of Silicon Monoxide
Authors: Al‐Ani S. K. J. , Hogarth C. A. , Waters D. N.
Published: July 2007

The analysis of the optical absorption edge as a function of temperature is discussed with particular reference to amorphous silicon monoxide films. The validity of the Urbach rule is investigated and the respective parameters are estimated. Experimental measurements on thin SiO films of the optical energy gap as the temperature is varied in the range 100 to 474 K, are reported and the results are discussed in terms of current theory.
Optical Properties of Bielectron—Impurity Complexes
Authors: Kovarskii V. A. , Sinyavskii E. P. , Chernysh L. V.
Published: July 2007

A calculation of the energy spectrum of the bielectron‐impurity complex is performed. If the energy of relative motion of the two electrons which form the bielectron is much greater than the energy of the bielectron‐impurity interaction, the problem may be solved in the adiabatic approximation for the separation of “rapid” (bielectron) and “slow” motion of the bielectron as a quasiparticle in the field of the impurity potential. It is shown that the bielectron‐impurity complex spectrum has the form of an inverted hydrogenic series and near each line of the inverted hydrogenic series from the long wavelength region, the lines of the forward hydrogenic series are located. The intensities of phototransitions on the bielectron‐impurity complex levels are calculated, too. The dependence of the absorption light coefficient versus the main quantum number of the inverted hydrogenic series is investigated. The theory developed is compared qualitatively with experimental data.
Lattice Dynamics of Tetrahedral Compounds with the Local Heine‐Abarenkov Model Potential
Authors: Kagaya H.‐matsuo , Soma T.
Published: July 2007

The lattice dynamics of III—V and II—VI tetrahedral compounds is investigated using a recently presented binding force and the local Heine‐Abarenkov model potential. Numerical calculations on the phonondispersion curves are performed for GaP, GaAs, GaSb, InP, InAs, InSb, ZnS, ZnSe, ZnTe, and CdTe. The resulting ones especially for TA modes are in good agreement with the observed data of the neutron scattering, contrary to those using the Ashcroft‐type potential.
Nonlinear Absorption in III—V Semiconductors
Authors: Sen P. K.
Published: July 2007

A coherent radiation‐exciton interaction model is employed to study analytically the phenomenon of nonlinear absorption in important III—V semiconductors (viz., GaAs, GaSb, InSb, InAs), the crystals being irradiated by suitable lasers with energies (hω) nearly equal to the band gap energies (hωg). The nonoptical processesare accounted for phenomenologically by introducing a damping parameter into the equation of motion of the probability amplitude of the excited electron—hole pair state. The Wannier‐Mott type of exciton wave function is found to be responsible for the giant nonlinearity of the crystal absorption coefficient in the near resonant optical interband transition regime with h | ω ‐ ωg | of the order of the crystal exciton binding energy. The effect of renormalization of the crystal band gap in the presence of Coulomb interaction and Starkbroadening is also discussed.
Self‐Consistent Field Theory Applied to the Semiconductor Band Edge
Authors: Huhn W. , Stahl A.
Published: July 2007

The electrodynamics of a two‐band semiconductor with a direct gap is governed by a set of non‐linear constitutive equations which are an appropriate generalization of the Maxwell‐Bloch equations for two‐level atoms. The following quantities are connected by these equations: density matrices for electrons and holes, coherent exciton amplitudes, and self‐consistent fields. The equations are derived from a standard two‐band Hamiltonian by a thorough analysis of localization properties of electromagnetic quantities. As limiting cases the theory comprises: linear exciton polariton theory, self‐consistent field theory ofthe electron gas, Maxwell‐Bloch treatment of two‐level atoms.
On the Possibility of Bose‐Einstein Condensation and the Superfluidity of Frenkel Excitons
Authors: Šetrajčić J. P. , Kapor D. V. , Mirjanić D.
Published: July 2007

The characteristic time of exciton relaxation due to phonons is estimated, and as it turns to be smaller than the exciton lifetime, it is concluded that Bose‐Einstein condensation is possible in the system of Frenkel excitons. It is further shown that kinematical interaction obtained in the Boson representation due to the Paulionic character of the excitonic operators, causes the superfluid excitation transfer through the crystal.
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

From 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

A 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

A 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

A 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

Raman 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

The 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

A 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

The 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.
Positronium Spin Rotation and Time Oscillation of the Normal to the Three‐Photon Positronium Decay Plane in Magnetic Field
Authors: Baryshevskii V. G.
Published: July 2007

It is shown that in magnetic fields the angular distribution of the normal to the three‐photon positronium decay plane oscillates as a function of time.
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

The 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

The 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

Additively 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

The 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

The 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

Temperature 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.
Two‐Soliton Solution in a Modified Hubbard Chain
Authors: Lindner U. , Scherf S.
Published: July 2007

In the case of constant electron density along the chain the two‐soliton solution is given explicitly. For simplification the coupling between electronic system and lattice is neglected.
Evidence of Open 4f Shells in Rare Earth Compounds
Authors: Gupta S. N. , Shah S.
Published: July 2007

A 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

The 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

The 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

Assuming 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

A 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

The 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

On 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

In 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

The 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

Following 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

It 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

An 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

Dielectric 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

The 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

A 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

The 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

The 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

The 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

The 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

For 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

Thermal 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.
Calculation of Phonon Dispersion Curves for AlP, AlAs, and AlSb
Authors: Kagaya H.‐Matsuo , Soma T.
Published: July 2007

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

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

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

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

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

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

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

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

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

The spin‐wave spectra of simple cubic ferromagnets with single and few impurities are investigated via a continuum model. Using the Green's function technique, it is shown that only the s‐like localized impurity state exists, in consistency with the experimental results.