bluuebunny/crossref_metadata_2025 huggingface dataset:
On the canonical transformation in the theory of exciton–phonon interaction
Authors: Davydov A. S. , Pestryakov G. M.
Published: July 2007

A canonical transformation which eliminates the trilinear exciton–phonon interaction and introduces new elementary excitations — “dressed” excitons — is proposed; it holds true both for the narrow and for broad exciton bands. The energy spectrum of the dressed excitons is investigated in detail for a one‐dimensional model of Frenkel excitons interacting with optical phonons.
On Certain Peculiarities of Electrical and Optical Properties of Many‐Valley Semiconductors
Authors: Dneprovskaya T. S.
Published: July 2007

A theoretical study of the effects of the light pumping on the conductivity of the multi‐valley n‐type semiconductors is presented. It is shown that the existence of the resonant impurity states associated with the secondary minima cause the peculiarities in the conductivity dependence on the pumping intensity. Under certain conditions this dependence should contain a hysteresis loop.
The Specific Heat of Terbium Arsenate
Authors: Berkhahn W. , Kahle H. G. , Klein L. , Schopper H. C.
Published: July 2007

Specific heat measurements on TbAsO4 were carried out in the temperature region between 0.8 and 30 K. They show that this compound undergoes two phase transitions; one at TD = (27.7 ± 0.5) K, which is caused by a crystallographic phase transition from tetragonal to orthorhombic symmetry and another, at TN = (1.50 ± 0.02) K, which has to be attributed to a magnetic phase transition from the paramagnetic to the anti ferromagnetic state. An effective exchange integral and critical parameters were determined and compared with theory. The contribution to the heat capacity associated with the crystallographic phase transition shows a typical molecular field behaviour; the experimental values and the data derived from a modified molecular field theory are in very good agreement.
Raman Spectrum of Polaritons in the Presence of Mass Defects
Authors: Ohtaka K.
Published: July 2007

In the low concentration limit of mass defects, the Raman spectrum is examined in the polariton region, i.e., in the small momentum transfer region. Expressions for the lifetime broadening and the frequency shift of the polariton peak are derived and the impurity‐induced continuous spectrum is also discussed. Calculations made so far for the localized mode polariton are improved in several respects. It is also shown that the electro‐optical coefficient derived from the PA type of the electron‐polariton interaction has only a apparent ω‐dependence to be eliminated in getting the proper Raman intensity.
Electron Paramagnetic Resonance (EPR) of Phosphorus in Silicon‐Rich Silicon–Germanium Alloys
Authors: Vollmer H. , Geist D.
Published: July 2007

g‐values, hyperfine splittings, and line widths of the EPR‐spectra of phosphorus substituted into Si1−xGex alloys were investigated at 9.3 GHz and 1.8 K in the range 1 ≧ (1 — x) ≧ 0.84 with phosphorus concentrations between 5 × 1015 and 1019 cm−3. The peculiar variation of the measured quantities with the silicon concentration is discussed with regard to band structure investigations and to the individual surroundings of each phosphorus atom.
Surface and Bulk Magnetic Exciton Resonance in a Thin Film of an Induced Ferromsgnet
Authors: Kowalewski L. , Popielewicz A.
Published: July 2007

Surface and bulk longitudinal magnetic exciton resonance is investigated in a thin film of an induced ferromagnet. Infrared absorption intensities in the low temperature range are calculated for a thin film with f.c.c. structure and for the singlet‐singlet molecular field level model. The calculations are made in the approximation of the pure 4fn configuration.
EPR and Spin–Lattice Relaxation of Mo3+ Ions in Corundum
Authors: Sharoyan E. G. , Torosyan O. S. , Markosyan E. A. , Gabrielyan V. T.
Published: July 2007

The EPR spectra of Mo3+ ions in corundum at v = 9.25 GHz and T = 77 °K were investigated. It is shown, that Mo3+ ions isomorphously replace Al3+ ions in the octahedral coordination. Due to the large zero‐field splitting, only the −1/2 ↔ +1/2 transition is observed. The zero‐field splitting constant 2D = (−49 ± 18) GHz, the spectroscopic splitting factor g⊥ = 1.968 ± 0.001, g ⊥ = 1.98 ± 0.01, and the hyperfine splitting constant A‖ = (119 ± 1) MHz, A⊥ = (121 ± 2) MHz are determined. It is shown that in the case of large zero‐field splitting 2D ≫ v the magnitude of 2D can be determined by measurements at a single frequency, using the value of geff at 35°2′ (cos2 θ = 2/3). The angular dependence of the hyperfine structure splitting due to the large zero‐field splitting is observed and good agreement with values calculated in first order of perturbation theory is obtained. The spin‐lattice relaxation times of Mo3+ ions in corundum are estimated from the magnitude of the broadening of the absorption curves with increasing temperature. In the temperature range of 77 to 500 °K the spin–lattice relaxation rate is τ1−1 ∼ T2.5.
Properties of type‐II superconductors with arbitrary impurity concentration near Hc2
Authors: Ovchinnikov Yu. N. , Brandt E. H.
Published: July 2007

The magnetic field distribution H and the magnetization 4πM are calculated by the method of energy‐integrated Green's functions near the upper critical field HC2 as a function of temperature, electron mean free path, and of the concentration of paramagnetic impurities. The field distribution of Delrieu and of one of the authors is thereby reproduced. The non‐linearity of the magnetization curve is investigated. At low temperatures and long mean free paths this non‐linearity becomes pronounced and leads to a logarithmically vanishing slope of the magnetization curve as the applied field approaches Hc2.
The dielectric function of GeS single crystals determined by electron energy loss spectroscopy
Authors: Venghaus H. , Büchner U.
Published: July 2007

Electron energy loss spectra were taken with 50 keV electrons on GeS single crystals for 0 < E < 40 eV and with different orientations of transferred momentum. No anisotropy of the energy loss functions Im (–1/ϵii) (i = x, y, z) could be observed indicating ϵxx ≈ ϵyy ≈ ϵzz for E 3 eV. ϵxx is calculated from Im (–1/ϵxx) by Kramers‐Kronig analysis. Our results indicate that the dielectric function of GeS is, to a good approximation, isotropic for E > 3 eV despite the layer type structure of the compound.
Group Theoretical Analysis and Phonon Modes of V3Si
Authors: Achar B. N. N. , Barsch G. R.
Published: July 2007

The group theoretical analysis of the dynamical matrix has been carried out for the A15 structure by using the irreducible multiplier representations of the point group of the wave vector. Numerical results are presented for the complete set of phonon dispersion relations in V3Si along the principal symmetry directions calculated from a microscopic model given earlier.
A simple phenomenological model for the lattice dynamics of B. C. C. metals
Authors: Raiand R. C. , Hemkar M. P.
Published: July 2007

A simple phenomenological model is developed for b.c.c. metals which considers ion‐ion interaction up to second neighbours and electron‐ion interaction on the lines of Bhatia theory using an appropriate value for the screening parameter. The volume force is averaged over the whole Wigner‐Seitz sphere. In the present model the ionic lattice is in equilibrium in a medium of electrons. The theory is satisfactorily applied to the computation of phonon dispersion curves and Debye characteristic temperatures for four alkali metals, lithium, sodium, potassium, and rubidium.
Theory of axial dechanneling
Authors: Ōmura T. , Kitagawa M. , Ohtsuki Y. H.
Published: July 2007

Making use of the generalized Fokker‐Planck equation, and the diffusion coefficients for the many‐phonon excitations and the single electron excitation, the dechanneled fractions for 1.6 MeV H+ in the Si [110] axis are calculated numerically. The temperature dependence of the calculated results is stronger than that of the Lindhard model. Comparison between the present results and the experiments is also made.
Quadratic electronic polarizability of the interacting electron gas
Authors: Paasch G. , Rennert P.
Published: July 2007

The quadratic electronic polarizability of the interacting electron gas is calculated with a self‐consistent method. It can be expressed by the dielectric function and by the quadratic response function of non‐interacting electrons. It is shown that this result is correct in the sense of many‐body perturbation theory within the RPA. As the simplest application the asymptotic behaviour of the total potential is considered which is caused by an additional point charge in the electron gas.
Biexciton resonant two‐photon absorption in CuCl
Authors: Phach Vu Duy , Bivas A. , Hönerlage B. , Grun J. B.
Published: July 2007

In studying the two‐photon absorption (TPA) of the biexciton in CuCl by using two different light sources, interesting information is obtained. The biexciton ground‐state energy is determined accurately; its symmetry is experimentally verified; a value for the TPA coefficient is deduced and compared with a theoretical evaluation; a lineshape analysis enables us to discuss the damping constants of the exciton and biexciton states involved.
Resistivity and thermoelectric power of liquid lithium and sodium from Harrison's first principle
Authors: Mitra N. R. , Thakur J. , Srivastava P. L.
Published: July 2007

The nonlocal pseudopotential formalism of Harrison is applied to the problem of resistivity and thermoelectric power of liquid metals, lithium and sodium. Slater's recent value of α in the Xα‐exchange is used. Exchange and correlation between the conduction electrons are taken into account using the modified dielectric function proposed by Vashishta and Singwi. The results agree well with the experimental values.
Exciton emission of ytterbium‐implanted cadmium telluride
Authors: Nahum J. , Bryant F. J.
Published: July 2007

Luminescence measurements show that implantation of cadmium telluride with ytterbium (followed by a suitable annealing treatment) produces an ytterbium defect capable of binding an exciton. Annihilation of the exciton bound to this defect produces a sharp emission at 1.5850 eV. Preliminary studies show that the emission does not split if the crystal is subjected to uniaxial stress. The temperature dependences of these and other excitons are studied and compared with the temperature dependences obtained for Yb3+ emissions in ytterbium‐implanted cadmium telluride.
Theory of the thermomagnetic effects in thin films in a magnetic field of arbitrary magnitude
Authors: Askerov B. M. , Kuliev B. I. , Figarova S. R. , Ya. Shteinshraiber V.
Published: July 2007

Thermomagnetic effects of a thin film in a magnetic field normal to the film surface are studied for an arbitrary value of specularity parameter p. Using the solution of the Boltzmann equation for an arbitrary film thickness and magnetic field strength the basic thermomagnetic coefficients are calculated, the Nernst‐Ettingshausen coefficient (N‐E) Q, the thermopower in a magnetic field α(H), and the thermal conductivity in a magnetic field χ. A detailed analysis is given of their dependences on the thickness, magnetic field strength, and the parameter p. It follows from the analysis that in a weak magnetic field the thermopower α and the N‐E coefficient Q are practically p‐independent. The computer calculations show that α and Q oscillate as functions of the magnetic field strength, the oscillations of Q being more pronounced than those of the electronic thermal conductivity. χ varies monotonically with the magnetic field.
H2O Related Centers in Potassium Chloride
Authors: Kuczynski G. C. , Dietz P. E. , Hamill W. H. , Jischke J. H.
Published: July 2007

Vacuum annealing of crystals of KCl at 600 °C produces stable defect centers which trap electrons during uv or γ irradiation as well as during additive coloration. When vacuum annealed crystals are exposed to 2 atm H2O at 200 °C prior to γ irradiation, coloration is suppressed, including the F band. This may be due to displacement of an electron from F by interstitial H2O which occupies V. When previously untreated crystals are exposed to 0.25 atm of HCl at 200 °C and γ‐irradiated, only one of the color centers previously mentioned is observed. The same center is produced in crystals grown from aqueous KCl containing HCl. The center is attributed to H3O+F. Precursor H3O+ (and OH−) is produced by heating in vacuum at 600 °C. Additional chemical reactions are required to account for the other bands.
Electron Paramagnetic Resonance of Mn2+ in Guanidinium Aluminium Sulfate Hexahydrate
Authors: Milsch B. , Windsch W.
Published: July 2007

The electron paramagnetic resonance (EPR) spectrum of Mn2+ ions in ferroelectric guanidinium aluminium sulfate hexahydrate is analyzed. It turned out that these impurity ions enter into regular Al3+ lattice sites forming two non‐equivalent magnetic hexaquo‐manganese (II) complexes of axial symmetry. The hyperfine lines of several fine‐structure transitions exhibit a hidden “spin‐flip” satellite structure. It results from the proton ligand hyperfine interaction in the magnetic hexaquocomplexes. A strong dependence on temperature and uniaxial stress is found for the zero‐field splitting parameter D. Its variation with temperature is discussed in terms of thermal lattice expansion and local lattice vibration effects.
IR Absorption of OH and OD Centres and OH/OH, OD/OD, and OH/OD Complexes in Cu‐Doped ZnO Single Crystals
Authors: Gärtner F. G. , Mollwo E.
Published: July 2007

With ZnO:Cu:H, ZnO:Cu:D, and ZnO:Cu:H:D IR‐active absorption line spectra composed of 20 absorption bands are observed. Regarding the values of the absorption coefficients one of the 20 absorption bands is prominent (“main peak”), 18 absorption bands lie on the high energy side of the main peak (“side bands”). Measurements with the main peaks and the side bands are represented.
Theoretical and experimental study of X‐ray acoustic resonance in perfect silicon crystals
Authors: Entin I. R.
Published: July 2007

An experimental investigation of Borrmann effect resonance suppression by transverse ultrasonic vibrations with wavelengths, approximating the extinction length is carried out. A theory of this phenomenon is developed. It is shown that X‐ray acoustic resonance allows to measure the X‐ray atomic scattering factor with a relative accuracy of ≈ 1%, as well as to investigate the shape of the dispersion surface of X‐ray dynamical diffraction.
The frequency spectra of solid neon and xenon
Authors: Kushwaha M. S. , Kushwaha S. S.
Published: July 2007

The phonon frequencies of normal modes of vibration in solid neon and xenon are calculated at all the irreducible points of the first Brillouin zone with finer subdivisions (1000), using the unpaired‐elastic‐force model (EFM) recently developed. This is used to calculate the phonon densities of states. The calculated frequencies are compared in the highest symmetry directions [100], [110], and [111] with the recent available experimental data. It is observed that the theoretical results show a fairly good agreement with the neutron scattering measurements.
Excitons bound to neutral donor impurities in CuCl
Authors: Sauder T. , Certier M. , Stébé B.
Published: July 2007

Magneto‐optical studies as well as theoretical results, allow us to attribute the group of lines v3 (25 533 cm−1 at 4.2 K) of CuCl optical spectra to excitons bound to neutral donors.
A Critical Study of Dynamical Properties of Ionic Crystals
Authors: Gupta H. N. , Upadhyaya R. S.
Published: July 2007

The basic differences among the three most popular extensions of the shell model i. e. the breathing shell model (BSM), the deformable shell model (DSM), and the three‐body force shell model (TSM) are sought out by applying their nearest‐neighbour versions to some representative rocksalt type ionic crystals. The phonon dispersion curves are determined by each model for each of the crystals and compared with the experimental phonons which forms perhaps the best test for this purpose. The same number (eight) of parameters of each model are determined by using the same set of input data. The results and degrees of agreement obtained in each case show clearly the superiority of the “charge‐transfer mechanism” for representing the deformations of electron shells, used in the TSM, over the “breathing” and “deformation mechanism” used in the BSM and DSM, respectively, for the same purpose. The study also shows that the TSM, DSM, and BSM form a series of descending order according to their relative degrees of agreement, obtained in explaining the lattice dynamical behaviour of these crystals.
Analytical theory of crystal growth of two‐component systems I. Basic features and equilibrium properties
Authors: Pfeiffer H. , Haubenreisser W.
Published: July 2007

The basic features of an analytical theory of crystal growth for two‐component systems with atomically rough interfaces are developed in the framework of a multi‐layer SOS‐interface model using the concept of the theory of elementary rate processes. Attachment, detachment, and diffusional processes of the species are taken into account as interfacial elementary rate processes. Rate equations for these elementary rate processes are formulated. The rates are determined in terms of the change of the system free energy due to each specific elementary process using the principle of detailed balance. Especially, the equilibrium properties (interface profile, concentration profiles of the components, phase diagram) are described analytically and evaluated approximately in the continuous Bragg‐Williams approximation (CBWA) for ideal mixtures. The results of the interface model are discussed in comparison with those of the phenomenological theory.
Jahn‐Teller Coupling of Cr2+ Ion with Degenerate Modes in ZnS, ZnSe, and ZnTe Crystals: Microscopic Treatment
Authors: Natadze A. L. , Ryskin A. I.
Published: July 2007

The Jahn‐Teller (JT) interaction energy is calculated for 5T2 and 5E states of the Cr2+ ion in ZnS, ZnSe, and ZnTe crystals. The calculations are made within the framework of a particular microscopic model of the crystal field in the distorted crystal (model of point‐like exchange charges), the multimode interaction is taken into account. For the 5T2 term the energies of interaction with tetragonal and trigonal modes are of the same order of magnitude. This circumstance results in a small height of the barriers that separate various minima of the adiabatic potential and is responsible for the dynamic aspect of the static JT effect in these systems.
On the Dispersion Relation of Carriers in Semimetallic BiSb Alloys
Authors: Jung Th. , Braune W.
Published: July 2007

An investigation is made of the descriptive power of the semi‐empirical k · p models and of the deformation models of the band structure of semimetallic BiSb alloys. Using simple k · p models it can be shown that for x > 3 (x in at% Sb) the Fermi surface of the electrons assumes an ellipsoidal shape, whereas for the concentration dependence of the energy gap EgL one obtains a result which appears unrealistic. An application of models of the band structure on the basis of the deformation theory shows that if more than two bands are taken into account it is possible to obtain a concentration dependence of EgL, the essential properties of which are in agreement with the hitherto existing concepts.
Electronic Structure of Sb and Its Dependence on Hydrostatic Pressure
Authors: Pospelov Yu. A.
Published: July 2007

High‐accuracy computer calculations of the electronic structure of Sb and of its pressure dependence up to 20 kbar are reported. Calculations are performed in the framework of the Falicov‐Lin pseudo‐potential method. Accuracies of calculations of cross sections of the energy surface and of corresponding energy levels are improved up to few per cents and 10−4 to 10−5 Hartrees, respectively. This results in a coincidence between the calculated and observed pressure dependences of the electronic structure of Sb. Basic results of calculations, comparison with experimental data, and a discussion are presented.
A Co‐Ordinated Approach to the Calculation of Lattice Parameter and Heat of Formation for Alkali Halide Solid Solutions
Authors: Maity S. N. , Roy D. , Sengupta S.
Published: July 2007

Experimentally observed deviations of the lattice parameter from Vegards' law in alkali halide solid solutions are predicted from the boundary condition on the equation for the heat of formation. This also simultaneously makes the latter consistent with experimental results. The theory uses no experimental information of the solid solution and only the perfect crystal information is sufficient. The model is employed here to calculate the lattice parameter and heat of formation of ten alkali halide solid solutions over the entire concentration range. The agreement with the experimental results is quite satisfactory.
Theory of Planar Channeling of Relativistic Protons in Bent Crystals
Authors: Taratin A. M. , Filimonov Yu. M. , Vyatkin E. G. , Vorobiev S. A.
Published: July 2007

Dechanneling of relativistic protons in planar channels of bent crystals is examined on the basis of the Fokker‐Planck equation. The dependence of the dechanneling half‐length x1/2 in a curved channel of (110) Si on the particle energy E and the bending radius R is found. It is shown that in the bent crystal the dechanneling lengths are considerably reduced and the proportionality between the x1/2 value and the particle energy E is violated. The optimum conditions for deflection of a proton beam at the definite angle by a bent crystal are considered.
The Interaction of Surface Excitons
Authors: Bobrysheva A. I. , Zyukov V. T. , Beryl S. I.
Published: July 2007

The Fourier transform v(p) of the exciton–exciton interaction energy is derived. The excitons are situated in a semiinfinite polar crystal near the surface. The character of the interaction depends essentially on the symmetry of the spin functions under the permutation of identical particles. On the base of v(p) the shift of the surface excitons level with increasing exciton density nex is obtained. The numerical value is listed for GaAs. The effective Hamiltonian of surface excitons interacting through exchange by virtual surface longitudinal optical phonons is derived.
Some Evidence for the High Density Phase of Excitons in CdS
Authors: Rückmann I. , May V. , Voigt J.
Published: July 2007

Reflection spectra without and with additional pumping are measured in CdS at 1.8 and 77 K, respectively, starting from very low pump intensities. At low pump intensities a special behaviour of the reflection minimum is found indicating the importance of an exciton dead layer. The experimental spectra up to the highest pump intensities can be fitted very well taking into account spatial dispersion, exciton dead layer, and density dependent excitonic parameters. Polarizability, damping, and layer thickness change continuously in the whole range of excitation intensities. On the other side, the transverse dielectric function of a high density gas of interacting Is excitons is calculated. A comparison between theoretically and experimentally obtained excitonic parameters at different densities shows good agreement. Hence, the importance of many‐exciton interaction for the reflection spectra up to vanishing at highest pump intensities is concluded.
A Comparative Study of Dynamical Behaviour of Ionic Lattices
Authors: Gupta H. N. , Upadhyaya R. S.
Published: July 2007

A critical study of all the three extensions of the shell model i.e. the breathing shell model (BSM), the deformable shell model (DSM), and the three‐body force shell model (TSM) is further carried out for cesium chloride type ionic crystals on the similar pattern as reported earlier. These models are applied to study comparatively the dynamical behaviour of cesium chloride (CsCI) and thallous bromide (TIBr). The results so obtained, again confirm the superiority of TSM over DSM and BSM, not only in explaining the phonon dispersion curves but also for interpreting the infrared (IR) and Raman spectral peaks and Debye temperature variations.
On the Influence of the Polariton Effect on Excitonic Molecules
Authors: May V. , Röseler J.
Published: July 2007

Renormalization and damping of excitonic molecules due to their coupling to the radiation field is theoretically investigated within a picture of interacting polaritons and excitonic molecules. Numerical results are given for some cubic and wurtzite‐type materials. For CdS the renormalization reaches nearly 20% of the binding energy of the excitonic molecule.
Low‐Temperature Properties of an Anisotropic Heisenberg Ferromagnet
Authors: Škrinjar M. J. , Kapor D. V. , Šetrajčić J. P.
Published: July 2007

The low‐temperature properties of the anisotropic Heisenberg model proposed by Belorizky et al. are discussed in the approximation of small anisotropy J′/J ≪ 1. The closed set of self‐consistent equations for the magnetization and the energy of elementary excitations is obtained by the application of Zubarev's double‐time temperature dependent Green's functions. Magnetization is calculated in the approximation linear in J′/J, up to terms of order T9/2. All the coefficients of the low‐temperature expansion are renormalized (compared to Dyson's results), while a new term proportional to T3 appears due to anisotropy only. Zero‐point deviations are shown to be proportional to (J′/J)2.
Bound Magnetic Polaron in Europium Chalcogenides. Magnetic Properties
Authors: Kuivalainen P. , Sinkkonen J. , Stubb T.
Published: July 2007

The effect of shallow‐donor impurities and the bound magnetic polaron (BMP) formation on the magnetic properties of some Eu chalcogenides is considered. The contribution of the inhomogeneous spin polarization around the donors to the magnetic susceptibility and the total magnetization is calculated. It is shown that due to the donors a maximum of the zero‐field differential susceptibility shifts to a higher temperature as the donor concentration increases. Also the magnetization is non‐zero far above the Curie temperature when the donors are present. The results agree with the experimental data obtained in low‐conducting EuSe samples with various donor concentrations. Moreover, the calculated results indicate that the donors must form clusters with large unperturbed parts of the crystal between the clusters in order to explain the details in the experimental susceptibility.
Optical Absorption Spectrum of Cr3+ Ions Doped in CsCl
Authors: Trappeniers N. J. , Stibbe F. S. , Rao J. L.
Published: July 2007

The optical absorption spectrum of Cr3+ ions doped in CsCl is studied at room and liquid nitrogen temperatures. Assuming tetragonal site symmetry for the Cr3+ ion, the band maxima are successfully fitted with the theoretical energy equations of a d3 configuration immersed in a tetragonal ligand field, including full configuration interaction but neglecting spin—orbit perturbation.
Free‐Carrier Doping and Many‐Body Effects in Crystal Dynamics of Lead Sulphide Semiconductors
Authors: Singh R. K. , Singh K. P.
Published: July 2007

The effects of free‐carrier doping and many‐body interactions are thoroughly investigated on the crystal dynamics of lead sulphide semiconductors. The model used for such investigations is developed by incorporating the doping effect of free‐carriers in the framework of a well known extended three‐body force shell model. The importance of these effects in predicting the phonon dispersion curves, two‐phonon Raman, and infrared spectra of the solid under consideration is briefly discussed.
Reflectivity of Uniaxial Antiferromagnetic and Ferrimagnetic Crystals
Authors: Merten L. , Lehmeyer A.
Published: July 2007

Formulae for the reflectivity of uniaxial antiferromagnetic and ferrimagnetic crystals are derived for normal incidence parallel to the optical axis. The formulae show that in general the reflected waves are elliptically polarized. In particular, they can be used to fix the zeros of the off‐diagonal elements of the permeability tensor. Besides, the formulae are suitable to determine the properties of magnons from reflectivity spectra of uniaxial antiferromagnetic and ferrimagnetic crystals.
The FA(II) Center Relaxed Excited State and Models of FA(II)‐Like Defects in Alkali Halide Crystals
Authors: Parfianovich I. A. , Salomatov V. N.
Published: July 2007

In the second order perturbation theory the FA(II) center is considered as the F center in the field of a defect with excess dipole moment due to off‐center position of a small‐radius impurity cation. In such a model, the properties of the FA(II) center may be explained in terms of the wave‐function of greater spatial distribution for the F‐center relaxed excited state. The F‐center perturbation caused by the defect having its own small electric dipole moment (molecules of the type NO2−, OH−, CN−) is also discussed.
ESR Studies of Manganese Centres in LiH X‐Rayed at Low Temperature
Authors: Ikeya M.
Published: July 2007

ESR studies of the Mn2+ centre in LiH are made in X‐rayed LiH. No spectrum of the Mn2+‐vacancy complex is detected with ESR before irradiation in LiH though mass spectroscopic analysis indicates the presence of 1 to 10 ppm of Mn2+. The signals at g = 4.56, g = 2.057, and g = 2.0014 are produced by X‐irradiation at 20K. The signals are changed into the spectrum of Mn2+ with g = 1.991, A = 71.5 × 10−4 cm−1 and the axial field D = (450 ± 5) G with [100] symmetry at the temperature above 50K reversibly. The spectra are tentatively ascribed to Mn2+‐H− interstitialhydrogen complex with the thermal motion of H− around Mn2+.
Elastic behaviour of mixed alkali halide crystals of rocksalt structure
Authors: Basu C. , Kanrar A. , Ghosh U. S.
Published: July 2007

The dependence of the elastic constants on the relative concentration of the constituents of mixed alkali halide crystals of rocksalt structure is investigated using the pseudo‐unit cell model for the mixed crystal as illustrated by Chang and Mitra and the deformable shell model for the lattice dynamics as developed by Basu and Sengupta. Expressions are derived for the three independent elastic constants C11, C12, and C44 of the mixed system in terms of the relative concentration of the constituents and certain parameters pertaining to the terminal crystals. The theory thus developed is applied with remarkable success to the case of the mixed crystal KCl–KBr for which detailed experimental data are available.
Effect of ultraviolet irradiation on Se2−‐anion vacancy dipoles in potassium iodide
Authors: Prakash J.
Published: July 2007

The absorption bands due to an isolated Se2−‐anion vacancy dipole in KI are located at 275, 291, 371, and 395 nm. It is observed that the irradiation in the 275 and 291 nm absorption bands results in a photo‐chemical reaction. Irradiation in the 395 nm absorption band in the presence of an electric field creates a situation in which more dipoles are aligned along the electric field direction whereas such an irradiation in the absence of the electric field destroys the preferred orientation of the frozen‐in polarized dipoles. The effect of UV irradiation is studied as a function of electric field strength, irradiation temperature, and irradiation time.
Electron hopping energy influence on the specific heat of phosphorus‐doped silicon
Authors: da Silva A. Ferreira , Fabbri M. , da Cunha Lima I. C.
Published: July 2007

The specific heat of doped semiconductors is shown to be very sensitive on the choice of the model that provides the electron hopping energy. The one‐band model of Matsubara and Toyozawa developed for impurity bands by including the effect of a stronger electron correlation via a Heitler‐London two‐particle wave function is applied in order to calculate the specific heat of Si:P. It shows a reasonable agreement with the experimental data. The results of the AMO‐MT, the highly‐correlated‐electron‐gas, and the inhomogeneity models are shown for comparison.
Thermodynamics of strongly anharmonic crystals
Authors: Malinowska‐Adamska C. , Owsiejczyk M. , Wojtczak L.
Published: July 2007

A self‐consistent phonon theory of lattice dynamics based on the thermodynamic double‐time Green's function method is applied to the investigation of the thermal properties of the anharmonic face‐centred and body‐centred cubic crystals with the Morse potential as a model for nearest‐ neighbour central force interaction. The temperature and pressure dependence of the thermodynamic functions of cubic metals in the high and low temperature limits are given and compared with experimental data.
Highly localized donor states in InSb and their pressure dependence
Authors: Kończewicz L. , Trzeciakowski W.
Published: July 2007

Some experimental results are given of the pressure dependence of Hall and Shubnikov‐de Haas effects in InSb doped with S and Se. For T = 4.2, 300, and 519 K a decrease of the free‐carrier concentration is observed due to the filling of the resonant impurity states lying highly in the conduction band. Interpreting the data with the simple Koster‐Slater model good agreement of the theory with experiment is obtained. More accurate conclusions could be drawn from such fits if the density of states in the conduction band and its dependence on pressure and temperature were better known.
Theoretical investigation of resonant magnon‐phonon interaction in FeF2 in high magnetic field
Authors: Bancewicz M. , Stasch A.
Published: July 2007

The experimental verification of van Vleck's model for FeF2 by using neutron and Raman spectroscopy and applying strong magnetic fields is discussed theoretically. The possibility of measuring the k‐dependence of the magnon‐acoustical phonon interaction parameter using the magnetic field‐induced splitting of antiferromagnon branches is analyzed. It is shown that for a field in the 0 to 200 kG range this effect can be observed by neutron spectroscopy for values of k from an area covering about 40% of the Brillouin zone. Moreover, the calculations of the magnon‐acoustical phonon interaction parameter proposed for H = 0 by Lovesey are extended to the case of coupling between magnons and optical phonons of Eg and B1g symmetry as well as to high magnetic fields. The values of the Eg phonon‐one magnon and B1g phonon‐two magnon coupling parameter, calculated on the basis of the van Vleck model, amount to 9.9 and 6.3 cm−1, respectively. It is also shown that in a magnetic field of the order of 100 kG two magnon‐B1g phonon hybridization can occur manifesting itself as a splitting of the Raman line.
Defect states in amorphous silicon
Authors: Ishii N. , Kumeda M. , Shimizu T.
Published: July 2007

The nature of defects in amorphous silicon is calculated by using several methods for clusters with varying size. The wave function of the dangling bond state has an approximately exponential decay with a decay length of about 0.2 nm. The correlation energy of electrons and the hyperfine structure constant with 29Si for the dangling bond state are evaluated. The correlation energy and the g‐values are calculated both for a weak bond and for a two‐fold coordinated defect and are compared with experiments.
A localized orbital description of Ge and α‐Sn
Authors: Smith P. V.
Published: July 2007

In previous work an accurate description of the band structure and the valence electron pseudocharge density of Si is given in terms of a small set of well localized basis functions comprising only ten states of s, p, d, and f symmetry per atomic site. Now this work is extended to the case of Ge and α‐Sn and it is shown that this localized orbital approach also provides an excellent representation of the electronic structure of these other diamond elemental semiconductors. Moreover, the resulting basis functions are again very well localized about their respective lattice sites. The implications of this work in relation to semiconductor impurity problems are also briefly discussed.
The influence of the surface barrier on the trajectory of sputtered particles
Authors: Abdel‐Malik T. G. , Aly A. A. , Abdeen A. M. , Motaweh H. A.
Published: July 2007

The parameters of a spherical surface barrier with refraction for the particles sputtered from Cu single crystals are computer calculated. Use is made of the method of straightforward simulation of the surface atom ejection in the field of the near‐surface block of atoms. The interactions of the atoms are described by a Morse potential.
Excitation of magnetoacoustic waves by two microwave beams in InSb
Authors: Maheshwari K. P. , Tarey Ganesh
Published: July 2007

An investigation is made of the resonant excitation of magnetoacoustic wave at the difference frequency of two microwave beams propagating in a magnetoactive solid state plasma viz. n‐InSb. Due to the interaction of the two waves in the semiconductor the ponderomotive force at the difference frequency becomes finite and generates a magnetoacoustic wave if the dispersion relation corresponding to magnetoacoustic wave is satisfied. The analysis shows that there is a finite probability of excitation of an acoustic wave alongwith the magnetoacoustic wave. The excited acoustic and magnetoacoustic waves couple at magnetic fields when the thermal pressure is equivalent to the magnetic pressure. The propagation characteristics of the coupled wave are also studied. The results show that microwave beams of power densities 1 MW cm−2 excite magnetoacoustic wave of power density 0.04 kW cm−2 when ωc/ω = 0.1. The increase in magnetic field increases the power density of the excited magnetoacoustic wave whereas it tends to reduce the refractive index and attenuation constant of the coupled wave.
Photo‐chemical reaction and photo‐induced polarization studies in sulphur‐doped potassium bromide
Authors: Praksh J.
Published: July 2007

The absorption bands of S2−‐anion vacancy dipoles in KBr lie in the ultraviolet range. Irradiation in the short‐wavelength absorption bands results in a photo‐chemical reaction. It is observed that the irradiation in the presence of an electric field in the long‐wavelength absorption band creates a situation in which more dipoles are aligned along the electric field direction. Irradiation in absence of the electric field in the long‐wavelength absorption band is found to destroy the frozen‐in alignment of polarized dipoles.
Effects of a transition layer on slab polaritons
Authors: Wendler L.
Published: July 2007

Dispersion relations are derived for polaritons in a dielectric slab, coated with a transition layer (thickness 20 to 150 Å), on a substrate. If \documentclass{article}\pagestyle{empty}\begin{document}$ \[{\tilde \varepsilon }\] $\end{document} 1(ω) is the dielectric function of the transition layer a splitting of the dispersion curves occurs for resonances of the form \documentclass{article}\pagestyle{empty}\begin{document}$ \[{\tilde \varepsilon }\] $\end{document}(ω ⟂) = ∞ and \documentclass{article}\pagestyle{empty}\begin{document}$ \[{\tilde \varepsilon }\] $\end{document}(ω∥︁) = 0 in the case of p‐polarized polaritons. In the case of s‐polarized polaritons the splitting is obtained only for resonances of the form \documentclass{article}\pagestyle{empty}\begin{document}$ \[{\tilde \varepsilon }\] $\end{document}(ω ⟂) = ∞.
Anisotropy of transport properties due to direction‐dependent band nonparabolicity
Authors: Stordeur M. , Langhammer H. T.
Published: July 2007

In addition to two‐band conduction or the action of an anisotropic‐mixed scattering mechanism a further possibility is proposed for the interpretation of the anisotropy of the Seebeck coefficient, the Hall coefficient, and the Lorenz number of semiconducting crystals with noncubic symmetry. In the band model a nonparabolicity is considered which depends on the crystal direction. For acoustic mode scattering the expected anisotropy of these effects is calculated in dependence on the reduced Fermi level with the nonparabolicity as the parameter. The numerical results show that in contrast to the isotropic nonparabolicity the model used here predicts distinct anisotropies.
Ground state and effective field distribution of ising and heisenberg disordered antiferromagnets
Authors: Petrakovskii G. A. , Aplesnin S. S.
Published: July 2007

Ground state of disordered antiferromagnets (AFM) is investigated by the Monte Carlo method for the case of simple cubic lattices of Ising and classical Heisenberg models. The sublattice magnetization and spin—spin correlation function and phase boundary between AFM and spin glass are calculated at various values of concentration v of the ferromagnetic I‐bonds and the parameter λ == J/|K| (K < 0, antiferromagnetic bonds). The upper bound of degeneracy of random AFM is evaluated and the distribution of effective fields is presented.
Phonon Relaxation Due to Anharmonism and Central Peak in Structural Phase Transitions I. Soft Optic Modes and Acoustic Phonons in Cubic Crystals
Authors: Kashcheev V. N.
Published: July 2007

In the mode–mode coupling approximation the critical exponente (CE) are calculated for the damping and frequency shift of soft optic modes and acoustic phonons at the structural transition point for crystals with dimensions d = 1, 2, 3. The CE are traced back to the anharmonic interaction of phonons taking into account the intrinsic dynamic central peak of any nature. Anharmonisms of all order are considered.
EXAFS Study of Crystalline Cu, Ni, and Fe
Authors: Ershov N. V. , Babanov Yu. A. , Galakhov V. R.
Published: July 2007

The X‐ray absorption K‐spectra of copper, nickel, and iron are registered at nitrogen and room temperatures using synchrotron radiation. The experimental conditions and the experimental data of the preliminary‐processing procedure are described. The radial atomic distribution functions of copper, nickel, and iron are obtained from the analysis of the extended X‐ray absorption fine structure by the regularization method.
Decomposition of SiOx Films Due to Internal Stress
Authors: Hübner K. , Shendrik A. V. , Praulinsh A. M.
Published: July 2007

Results of optical absorption, reflectance, and ESR measurements are presented, which demonstrate that SiOx films characterized originally by a random‐bonding structure reveal after aging at room temperature a partial decomposition to Si and SiO2, i.e. a transition to a mixture structure. This decomposition is explained with the help of a model for the internal mechanical stress of SiOx films due to the large difference between the expansion coefficients of their Si and SiO2 constituents.
Theorie des durch das äußere Magnetfeld induzierten Jahn‐Teller‐Effektes in orthorhombischen J = 1‐Paramagneten
Authors: Ulner J.
Published: July 2007

Es wird eine Theorie des durch das äußere Magnetfeld induzierten Jahn‐Teller‐Effektes in orthorhombischen J = 1‐Paramagneten formuliert, die die Rotationsinvarianz der magnetoelastischen Wechselwirkungen mit einbezieht. Mit Hilfe einer Greenfunktionsmethode, die die Eigenschaften des Gesamtdrehimpulses exakt berücksichtigt, werden die elementaren Anregungen des Systems ermittelt. Es wird die Temperatur‐ und Magnetfeldabhängigkeit der Schallgeschwindigkeiten bestimmt und diskutiert. Bei Abwesenheit der Rotationsinvarianz der magnetoelastischen Wechselwirkungen korrespondieren die untersuchten Schallgeschwindigkeiten mit den elastischen Konstanten c55 und c66.
Incomplete Gamma Functions and Lattice Sums for B.C.C. Structures
Authors: Gupta K. C. , Agrawal R. M. , Rathore R. P. S.
Published: July 2007

Certain wave vector dependent lattice sums which extend over the entire lattice are computed for b.c.c. structures by the method of Born and Bradburn. These lattice sums are of general importance in the studies of some thermodynamical properties of lattices particularly the vibrational studies. All the needed values of incomplete gamma functions are also presented since they are required in the evaluation of the lattice sums in general.
Quasi‐Classical Quantization for Potentials with an Infinite Surface Barrier. Subbands in Inversion Layers
Authors: Paasch G. , Fiedler T. , Klář M. , Bartoš I.
Published: July 2007

For potentials with a high surface barrier, quasi‐classical quantization schemes are investigated. WKB and other previous approximations provide good results for the lower eigenvalues in special cases only. Here a modified local density approximation is used for the calculation of the density of states. From the integral density of states a quantization expression is derived where the ground state constant depends explicitly on the shape of the potential. It yields the whole eigenvalue spectrum very precisely for quite different potentials with surface barrier. The application to subband energies in inversion layers is discussed.
Some remarks on the theory of the dielectric response of crystals and on the lorentz‐lorenz formula
Authors: Fiorino E. , Del Sole K.
Published: July 2007

An investigation is made of the macroscopic dielectric function of a model insulator including local field effects and treating exchange by (i) the many‐body perturbation technique, (ii) the mean field, and (iii) excitonic approximations. The different methods yield similar results, showing the reliability of approximations (ii) and (ii) in most cases. Also the validity of the Lorentz‐Lorenz formula is discussed, showing that it is always valid in cubic crystals, if the “atomic” polarizability is suitably defined as the limit of the crystal polarizability for vanishing dipole—dipole interaction.
Magneto‐optical properties of RbMnF3 in the paramagnetic state
Authors: Malakhovskii A. V. , Morozova T. P. , Yuzvak V. I.
Published: July 2007

The spectrum of the Faraday effect (FE) in the range of 9000 to 37000 cm−1 and its temperature dependence in the range of 90 to 570 K are investigated in RbMnF3. The absorption spectrum in the range of 19000 to 60000 cm−1 and the magnetic circular dichroism spectrum in the range of 19000 to 36000 cm−1 are also obtained at room temperature. FE is decomposed to the following components: A0, the frequency‐independent FE, A, the diamagnetic FE, and C, the temperature‐dependent paramagnetic FE which are found to be commensurate in value with each other. It is shown that: 1. the paramagnetic magneto‐optical activity for the majority of d—d transitions in RbMnF3 is close to the maximum possible one in spite of the lack of orbital moment in the ground state of the Mn2+ ion and due to the spin—orbit interaction in the excited states; 2. C, the term of FE is caused by the highest frequency d—d transition 6A1g → 4T2g(4F) at ω = 51000 cm−1; 3. the diamagnetic FE is caused by the wide band of strong absorption at ω > 60000 cm−1.
Semiempirical theory of shallow short‐range electron traps in silicon in a magnetic field
Authors: Arkhincheev V. E. , Savvinikh S. K.
Published: July 2007

A theoretical investigation is made of the intervalley multiplet of electron states localized at short‐range traps in silicon placed in a magnetic field using an approximation of the zero‐short‐range potential. To describe the electron‐impurity interaction the intervalley and intravalley scattering lengths are introduced. They are considered as empirical parameters. It is shown that in crossed constant electric and magnetic fields the electric dipole transitions between multiplet states became available. The formulae describing the dependence of the probability of electric dipole transitions on the field strengths, on their orientation relative to crystallographic axes, and on the polarization of the variable electric field causing transitions, are derived.
Correlation energy from compton scattering and positron annihilation data
Authors: Das G. P. , Chaddah P.
Published: July 2007

The second moments of Compton profiles are used to obtain electronic energies. It is proposed that the second moment of a line‐slit positron annihilation angular correlation curve, in comparison with the second moment of Compton profiles, can yield the correlation energy contribution to the cohesive energy of a material. The need for correcting the PAAC data for the positron enhancement factor and thermalization effects is examined. Numerical estimates of the errors involved are given for sodium and lithium and the possible applicability of the proposal is shown.