bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Electron‐Phonon Interaction on the Density‐of‐States Tails and Impurity Band Optical Absorption
Authors: Burbaeva N. V. 
Published: July 2007

AbstractThe effect is considered of the weak electron‐phonon interaction on the density‐of‐states tail and tail‐to‐band optical absorption in disordered semiconductors. The frequency dependence of the relevant absorption coefficient is discussed as well as the correlation between the coefficient and the density of states of the fluctuation level.
Collective Excitations in Charge‐Ordered Systems with Orbital Degeneracy
Authors: Lubimov V. S. , Mronov V. S. , Makarov E. F. , Ionov S. P. 
Published: July 2007

AbstractThe spectra of collective excitations in the charge‐ordered state with orbital degeneracy are considered. It is found that in such systems there are three branches, the energies of which are smaller than that ones of the edges of the corresponding bands. Possible instabilities of the charge‐ordered state are considered.
Spin–Phonon Excitations in Crystals Doped with Dilute Magnetic Impurities
Authors: Kokshenev V. B. 
Published: July 2007

AbstractAn analysis of the excitation conditions of coupled spin‐phonon excitations in crystals doped with dilute magnetic impurities is carried out. It is shown that the rearrangement of the vibrational spectrum followed by the excitation of a spin‐phonon mode occurs at a concentration above a critical one. In the case when the interaction between impurities is not small, the spectrum rearrangement of the crystal is characterized by a temperature phase transition. The expressions for the damping of a phonon‐like branch of spin‐phonon excitations are obtained.
Multiple Scattering in Disordered Materials. I. Theory of the Effective Medium for Homogeneous One‐Component Systems of Correlated Scatterers
Authors: Lenk R. 
Published: July 2007

AbstractMultiple scattering of scalar waves propagating in a macroscopic system composed of identic spherically symmetric nonoverlapping scatterers is treated theoretically for the general case of anisotropic scattering at correlated scatterers. A basic approximation is involved in the treatment of the back‐scattering of the wave going out from a fixed scatterer. The incident field within the homogeneous medium obeys a local wave equation with medium wave number k. The theory yields a system of equations for the relative strength coefficients of the angular momentum components of the incident field. The wave number has to be determined from this system of equations too. Back‐scattering itself cannot be treated correctly using a naive medium‐like approach.
Landau Model of a Spin Glass with Two Order Parameters: Stability and Derived Physical Properties. II. Comparison with Experimental Data
Authors: Deutges D. , Heber G. 
Published: July 2007

AbstractBased on the stability considerations, performed in part I, experimental data of zero field susceptibility of AuFe or EuSrS can be fitted relatively well over large temperature intervals By this fitting the magnetic field dependence of the susceptibility as well as the magnetization are obtained with the correct tendency. On the other hand, the resulting specific heat does not agree with the experimental data.
Thermodynamical Properties of the Electron–Hole System outside the Region of Droplet Formation in Germanium
Authors: Schweizer H. , Forchel A. , Klingenstein W. 
Published: July 2007

AbstractDetailed experimental and theoretical investigations of the electron‐hole system in germanium in the density range from 1015 to 1017 cm−3 and for temperatures between 15 and 60 K are reported. The theoretical part of the work is carried out using a homogeneous plasma theory which provided the ionization degree as a function of the total density and the temperature. Experimentally the ionization degree is obtained from luminescence measurements of the indirect transition in germanium, which are fitted under the assumption that only free charge carriers end free excitons contribute to the emission.
Double‐Beam Linear Dichroism Investigation of the Two‐Photon Absorption in InSb
Authors: Areshev I. P. , Gusseinaliev M. G. , Danishevskii A. M. , Kochegarov S. F. , Subashiev V. K. 
Published: July 2007

AbstractA double‐beam linear dichroism method is developed to determine the amplitude of the polarization dependent part (β∽) of the total TPA constant (β12) in crystals. This method allows to separate two‐photon processes via virtual states from attendant effects. Two‐photon absorption in some n‐type InSb samples is investigated by using CO2 laser pulse radiation (λ = 10.6 μm) at T = 300 K. The electron concentration dependence of β∽ is evidenced and explained by the increase of the conduction band population (Burstein‐Moss effect in the case of TPA). The results are in a good agreement with the theory used. In addition a double‐beam TPA constant β12 as well as a single beam TPA constant β are determined by using the measured value of β∽ and the theoretical relation between βl2, β, and β∽.
On the Pressure Derivatives of the Second‐Order Elastic Constants of Ionic Solids
Authors: Sharma U. C. , Verma M. P. 
Published: July 2007

AbstractA method of direct differentiation is proposed for obtaining expressions for the first‐ and secondorder pressure derivatives of the second‐order elastic constants (SOEC) from the expressions for the SOEC and the equilibrium condition corresponding to a state of the solid under a hydrostatic pressure. The method is simple and straightforward and can be used effectively as a check on the correctness of the expressions for the third‐ and fourth‐order elastic constants. An application of the corrected expressions for the fourth‐order elastic constants of CsCl structure solids gives the values of the second‐order pressure derivatives of the SOEC in much better agreement with the experimental values than those obtained from the erroneous expressions.
57Fe Absorption and Emission Mössbauer Spectroscopy in Hydrated and Anhydrous Iron(II) and Cobalt(II) Acetylacetonates
Authors: De Jesus Filho M. F. , Sanchez J. P. , Friedt J. M. 
Published: July 2007

AbstractComparative 57Fe Mössbauer absorption and emission data are reported for the anhydrous and hydrated Fe(II) and Co(II) acetylacetonates in the temperature range from 1.5 to 300 K. The results concern the structural, electronic, and paramagnetic relaxation properties of the Fe2+ ions in these hosts. The 57Fe emission data of the 57Co electron capture decay products show that a fraction of the decayed atoms occupies unperturbed substitutional sites whereas another part stabilizes in perturbed ferrous sites and as ferric ions.
Multiple Scattering in Disordered Materials. II. Limits and Special Cases
Authors: Lenk R. 
Published: July 2007

AbstractThe theory developed in a preceding paper is evaluated for relatively simple special cases. Physically sensible results and agreement with prior work is found for long medium waves and for weak scatterers. In the second case especially the kinematic result for the attenuation of the wave is reproduced. For point‐like scatterers and for higher partial waves anomalies in the back‐scattering occur which are caused by centrifugal effects and which could be avoided only by cluster calculations beyond the present scheme.
Giant Spin Splitting of Exciton States in ZnSe with Mn and Fe Impurities
Authors: Komarov A. V. , Ryabchenko S. M. , Terletseii O. V. 
Published: July 2007

AbstractGigantic magnetofield splitting of the 1s exciton reflection spectrum is observed in ZnSe:Mn and ZnSe: Fe crystals. The effects are attributed to the exchange interaction between the carriers which enter in the free exciton and the magnetic impurity ions. The effects are qualitatively and quantitatively similar to the earlier one reported for ZnTe:Mn and CdTe:Mn. The exchange interaction of the c‐band electron with impurity 3d ions is ferromagnetic while for the v‐band electron it is antiferromagnetic. The values of intraexciton electron‐hole exchange interaction in magnetodoped crystals under investigation are found to be different from the reported'ones in nondopedc ZnSe crystals. The peculiarities of the effects in ZnSe:Mn and ZnSe:Fe are discussed.
Model Pseudopotentials of Some Noble and Transition Metal Atoms
Authors: Yamada Y. 
Published: July 2007

AbstractThe model pseudopotentials for Ag, Au, Ni, Co, Fe, Mn, and Cr atoms are calculated from the band calculation of the metals. The model pseudopotential is expressed as a summation of the local and nonlocal parts, which predominantly work on s‐ and d‐electrons, respectively. The electronic configuration of the valence electrons is discussed. In the transition metals, the parameters are determined following an electronic configuration of (3d)n(4s)1.
g‐Factor Anisotropy and Charge Transfer in Three Complex TCNQ Salts
Authors: Kürti J. , Menczel G. 
Published: July 2007

AbstractIt is found that the principal axes of the g‐tensor of the three complex TCNQ salts Qn(TCNQ)2, NPQn(TCNQ)2, and TEA(TCNQ)2 correspond to the geometry of the TCNQ molecules, known from crystal structure analysis, and the corresponding diagonal g‐values, calculated for B TCNQ molecule, are the same within an accuracy of 5 × 10−5. This points to the fact that the ESR signal in these materials arises from electrons of the TCNQ molecules, that is–as all three donors have closed shells after ionization–the donor‐acceptor charge transfer is complete. At the same time the measurements give evidence that the g‐tensor in these salts is unaffected by the intrachain delocalization, which is different for these materials.
Effect of Neutron Irradiation on NMR Properties of Single‐Crystalline V3Si
Authors: Skripov A. V. , Stepanov A. P. , Pan V. M. , Shevchenko A. D. , Michailov I. G. 
Published: July 2007

AbstractThe Knight shift, quadrupole interaction, spin‐lattice, and spin‐spin relaxation times for51V and magnetic susceptibility are measured as functions of temperature in a single crystal of V3Si in the unirradiated state and after neutron irradiation up to a fluence of 8.6 × 1018neutrons/cm2. In irradiated V3Si the temperature‐dependent distribution of electric field gradients at vanadium sites is observed. After the neutron irradiation the signs of tetragonal deformation appeared already at ≈︁ 35 K though only part of the irradiated sample exhibit the structural transformation. The Knight shift is found to be almost unaffected by the irradiation, in contrast to magnetic susceptibility and spin‐lattice relaxation time. The peculiarities of analysis of experimental data in homogeneous and inhomogeneous compounds are discussed.
X‐Ray Bond Charge in GaAs and InSb
Authors: Pietsch U. 
Published: July 2007

AbstractAn X‐ray bond charge model is presented for the reevaluation of quasiforbidden reflections from InSb and GaAs. The bond charge is assumed to be an additional scattering centre. The matrix atoms remain spherical, but the valence orbitals are reduced by the bond charge amount. The reconstruction of the experimental structure factors measured by Bilderback is established in the same quality as his semiempirical deformation model. Further the position and the form of the bond charge can be deduced with respect to the distance between next neighbours.
Exactly Solvable Model of Amorphous Ferromagnets
Authors: Bobák A. 
Published: July 2007

AbstractAn exactly solvable model for amorphous ferromagnets is presented. The model shows that random fluctuations of the exchange integral around its crystalline mean value cause an increase of the Curie temperature. In addition to the influence of fluctuations of the exchange integrals on the magnetization σ(T), the susceptibility χ(T), and the magnetic part of the specific heat Cv(T) is investigated. The results correspond to those obtained by the mean field approximation.
Polarization Phenomena for Inhomogeneous Waves in Mössbauer Optics
Authors: Andreeva M. A. , Kuzmin R. N. 
Published: July 2007

AbstractThe anomalous behaviour of the refracted waves near grazing incidence is considered for an anisotropic case. It is shown that the damping and phase shifts of the eigen refracted waves essentially alter its value in comparison with the case of normal incidence. This result is not obtained in framework of index‐of‐refraction formalism, introduced in Mössbauer optics by Blum and Kistner. For the extremely asymmetric diffraction an additional difficulty arises due to the refraction effect. In this case the refraction dependence of dynamical coefficients has to be taken into account. Using the covariant method the behaviour of inhomogeneous refracted waves is considered for the case of a single Zeeman line of Mössbauer spectrum.
Band‐to‐Band Recombination via Spontaneous Emission of Phonon–Plasmon Coupled Modes in Lead Chalcogenides
Authors: Ziep O. 
Published: July 2007

AbstractIn lead chalcogenides with degenerate statistics the small‐signal lifetime for spontaneous emission of phonon–plasmon coupled modes is calculated in dependence on temperature. The results are compared with corresponding data concerning Auger recombination. Within the approximation of undamped collective modes plasmon emission dominates as compared to Auger recombination for doping levels ND > 1019 cm−3 in PbSnSe at sufficiently low temperatures.
On the Concentration Dependence of the Thermal Impurity‐to‐Band Activation Energies in Semiconductors
Authors: Monecke J. , Siegel W. , Ziegler E. , Kühnel G. 
Published: July 2007

AbstractIt is proved by Hall effect measurements on Te‐doped GaP and on ZnSiP2 that the thermal activation energies of the majority impurities depend on the minority impurity concentrations. A new theoretical explanation for this concentration dependence is presented.
Evaluation of Susceptibility Functions
Authors: Hill R. M. 
Published: July 2007

AbstractSimple algebra is sufficient to show that all the commonly accepted, empirical susceptibility relationships exhibit power laws as functions of frequency, in the limits of both low and high frequencies. The exponents of these power law relationships are presented and it is shown that simple relationships exist between them. It is established that the Debye relationship is unique. By means of Cole‐Cole presentation comparison is made between the susceptibility functions. As it has been established that in order to characterise the large bulk of experimental data on solids and liquids functions requiring two characteristic parameters are required comparison is made between the Havriliak‐Negami and Dissado‐Hill expressions, which are of this form, and typical experimental results. It is concluded that the latter expression is more applicable.
Energy Band Structure and Electronic Properties of NiAs Type Compounds. I. Ferromagnetic Manganese Arsenide
Authors: Sandratskii L. M. , Egorov R. F. , Berdyshev A. A. 
Published: July 2007

AbstractA first calculation of the electron energy spectrum of ferromagnetic MnAs is made using the Green's function method. A potential model with variable occupation numbers determined from the condition of magnetic moment self‐consistence is employed. Strong hybridization of manganese 3d‐states and arsenic 4p‐states is obtained. In accordance with the experiment the conductivity has metallic character. The spin‐polarisation is shown to affect the electron structure formation considerably. The principal cross‐sections of the Fermi surface are plotted and discussed. The joint density of states and magnetic form factors are calculated and compared with the experiment.
Scattering on Short‐Range Potentials in InSb. A Pseudopotential Calculation
Authors: Gorczyca I. 
Published: July 2007

AbstractTheoretical results are presented for the parameters of electron scattering on short‐range potential centres associated with ionized impurities in InSb. The calculations are based on the pseudopotential formalism. In order to perform that calculation, the pseudowave functions previously obtained are used. Values of the short‐range interaction parameters obtained for Te‐, Se‐, and S‐doped InSb are in good agreement with the empirical estimates.
Urbach's Rule and Phase Fluctuations of the Transmitted Light
Authors: Skettrup T. 
Published: July 2007

AbstractIt is shown that both Urbach's rule (exponentially increasing absorption edge) and the large fluctuations of the phase of transmitted light observed in depolarization experiments can be derived from the same phenomenon, namely the fluctuating exciton resonance energy caused by the fluctuations in the phonon number in thermal equilibrium. A simple layer model is applied in order to derive quantitative results for absorption and phase fluctuation. The comparison of these results with experimental values for ZnO yields a good agreement. A coherence length of the LO phonons interacting with excitons is also obtained.
Phase Transition in the Extended Falicov‐Kimball Model With Finite f‐Bandwidth
Authors: Sharma H. V. , Singh I. 
Published: July 2007

AbstractSome actinide compounds, which have non‐zero f‐bandwidth, are found to exhibit mixed‐valence behaviour for a certain range of composition and temperature. The effects are studied of finite f‐bandwidth on the semiconductor–metal transition and the existence of a mixed‐valence phase using the extended Falicov‐Kimball model.
On the Peierls Transition in the Strong Correlation Limit of the Hubbard Chain
Authors: Gasser W. , Heiner E. 
Published: July 2007

AbstractThe wave number kp of the Peierls distortion is determined for the Hubbard chain in the strong correlation limit at arbitrary electron occupation numbers n. Using approximations it is shown that kpa = 2π(1 – α)/(1 + α) holds, where α is given by α = 1 – n for n < 1 and by α = n – 1 for n > 1.
Effect of Three‐Body Potential on the Dielectric Behaviour and Optic Mode Grüneisen Parameters of Alkali Halide Crystals
Authors: Singh A. V. , Shanker J. 
Published: July 2007

AbstractAn analysis of the effect of Lundqvist's three‐body potential on the strain derivatives of the dielectric constants and optic mode Grüneisen parameters is performed for alkali halide crystals. Modified relations are used to obtain the values of the low frequency and high frequency polarizabilities and their volume derivatives. The calculated values of transverse and longitudinal optic mode Grüneisen parameters are found to compare well with recent experimental data. The potential parameters used are consistent with the elastic properties as well as with the dielectric behaviour of crystals under investigation.
Guest Donor Arrangement in CT Crystals
Authors: Möhwald H. , Erdle E. 
Published: July 2007

AbstractESR experiments on triplet states in donor‐doped naphthalene‐TCNB crystals are reported. The phase transition of the crystal at 62 K, due to the freezing‐in of a librational motion, is observed from a change in ESR linewidth or signal intensity. Data obtained on the orientation and dynamics of the guest donors pyrene, phenanthrene, and anthracene are compared with corresponding values of the host donor. The donors differ drastically with respect to the orientation of symmetry axes, and to the frequencies and activation energies of librations. Of special importance is the finding that two sites observed in the low‐temperature phase differ also in the orientation of the plane normals (by 0° to 20°). This necessitates a review of the determination of the CT character from measured zfs parameters.
Luminescence Properties of Terbium‐Activated Rare‐Earth Oxyhalides
Authors: Hölsä J. , Leskelä M. 
Published: July 2007

AbstractThe luminescence properties of Tb3+ activated rare‐earth oxyhalides (REOX, RE = Y, La, Gd, and Lu; X = F, Cl, Br, and I) are studied mainly by UV excitation. The intensities of 5D3,4 → 7FJ transitions and thus the emission colour are observed to depend strongly on the matrix. In addition, the energies of 5D3,4 → 7F4–6 transitions increase with increasing ionic radius of the host cation within the isomorphous REOBr series. The fine structure of the Tb3+ spectrum is used as a structural probe on the RE oxyiodides. The energies of strong 4f → 5d absorption bands generally increase with the electronegativity of the host anion. According to the excitation spectra, efficient energy transfer occurs from the Gd3+ ion to the Tb3+ ion in GdOX matrices.
Temperature‐Dependent Surface Magnetization and Critical Temperature of Ferromagnetic Thin Films
Authors: Diep‐The‐Hung  
Published: July 2007

AbstractThe critical temperature Tc and temperature‐dependent surface magnetization μs(T) of ferromagnetic thin films are calculated as a function of surface exchange integrals J and J, by a Green's function method. It is found that Tc depends strongly on both J and J. The curvature of μs(T), on the other hand, depends essentially on J. These results are interpreted and discussed from the surface spin waves point of view.
An Ising Model Analysis of Dielectric Polarization. II. Computations of Dynamic Susceptibility and Comparison with Experimental Observations
Authors: Bozdemir S. 
Published: July 2007

AbstractComputed results for the previous theoretical analysis of infinite and finite dynamic molecular chains containing both parallel and perpendicular components of dipoles (to be referred to as I) are presented. The analysis shows good qualitative agreement with the data observed in polymers above their glass transition temperature, Tg, polymer solutions, hydrogen bonding systems in crystalline form or solutions, and also in order‐disorder ferroelectric substances. Double peaks, broadened symmetric or asymmetric peaks with significant shift in frequency below the one free particle loss peak‐frequency are obtained.
The Theory of the Electron Spin–Lattice Relaxation in Zincblende Semiconductors
Authors: Bogusławski P. 
Published: July 2007

AbstractThe spin–lattice relaxation time of conduction electrons is calculated for III–V and II–VI zincblende semiconductors, where the conduction band is of Γ6‐symmetry. The electronic states are described within the Kane three‐level model of band structure. Deformation potential interaction with acoustic and optical phonons, together with the piezo‐acoustic and polar optical scattering modes are considered. The spin‐flip transitions occur due to spin mixing in the electron wavefunctions (Elliott‐Yafet mechanism). Numerical calculations show that the electron–phonon interaction provides an important channel of the spin relaxation at high temperatures.
Reflection of Light on a Spatially Dispersive Crystal
Authors: Dub P. 
Published: July 2007

AbstractUsing the classical microscopic model of a crystal the problem of reflection of P‐polarized light incident on a semiinfinite dielectric with spatial dispersion is solved and the formula for the reflectivity is given. A comparison is done of the dispersion relations following from a microscopical model and from Pekar's theory. Using the formulae following from the microscopic model the frequency dependences of refractive indices and of reflectivity are computed.
Assignment of the Optical Absorption Bands in CsI:Tl and CsBr:Tl by Application of High Pressure
Authors: Asami K. , Naka T. , Ishiguro M. 
Published: July 2007

AbstractThe assignment of the absorption bands in cesium halide thallous phosphors (CsI:Tl and CsBr:Tl) is performed by making use of the phase transition from NaCl‐type to CsCl‐type under high pressures. It is concluded that the longest wavelength band corresponds to the A band in alkali halide thallous system and the origin of the next wavelength one is the A‐like transition, that is, the transition to the excited state similar to that in the case of the A band which has two relaxed excited states.