bluuebunny/crossref_metadata_2025 huggingface dataset:
Concept of Force Variation Due to Charged Defects in Elemental and Compound Semiconductors
Authors: Vandevyver M. , Talwar D. N. , Plumelle P. , Kunc K. , Zigone M.
Published: July 2007

Green's function calculations of force variation due to charged impurities in elemental and compound semiconductors are analysed on the basis of simple physical arguments. It is strongly suggested that the trends of force variation may not be related with the long range Coulomb interactions, however, the important criteria should be the effect of electric field of charged impurity on its nearest neighbour bonds that mainly affects the short range couplings. Some new experimental results by i.r. method due to Si and Cl impurities in CdTe are also included that lend additional justification to the arguments.
Impurity Effects on Adatom Density of States
Authors: Ueba H.
Published: July 2007

The influence of both, impurity and surface states on the adatom electronic properties is studied using the Dyson equation approach. The surface Green function of a semi‐infinite crystal contaminated by a single impurity atom is calculated. It is found that the surface state energy depends on the location of the impurity atom. A similar calculation is performed for the case where an adatom interacts with the contaminated substrate and the energy Ea of an electron localized on the adatom is determined as a function of the impurity atom location and potential. The adatom density of states is also calculated to discuss the significant effect of the impurity near the surface.
Optical Orientation of the Carriers in an Electron—Hole Plasma in CdS Crystals
Authors: Gubarev S.
Published: July 2007

The degree of circular polarization of the electron—hole plasma recombination radiation is measured under high power excitation with circular polarized light. Depolarization of the radiation on the high‐energy edge of the spectrum is observed in the transverse magnetic field. The experimental results are explained in terms of different populations in the electron and hole spin subbands. The spin disorientation times for electron Tsc and hole Tsh systems and the life time of the carriers τ in the electron—hole plasma are defined from the Hanle effect and are equal to Tse = (3 to 5) × × 10−12 s, Tsh = (10 to 15) × 10−12 s and τ = (80 to 120) × 10−12 s.
Phenomenological Behaviour and Phase Transition Mechanism of the Layered Antiferroelectric Squaric Acid
Authors: Maier H. D. , Petersson J.
Published: July 2007

Usually it is assumed that the interactions between the protons within the molecular layers drive the phase transition of the antiferroelectric squaric acid. In the present work it is proposed that besides these interactions also the interlayer interactions play a central role for the phase transition mechanism. This assumption is discussed in relation to some well‐known properties of squaric acid above Tc. On these conditions a potential is developed describing the behaviour of the order parameter, and of the dielectric and elastic constants above and below Tc. Finally the dynamics is discussed on the assumption of a flipping motion of the protons.
First Plasmon Satellite in the (e, 2e) Process in Metals Temperature Dependent Theory
Authors: Zhivopistsev F. A. , Comas F. E.
Published: July 2007

Firstly, the plasmon satellite structure is discussed in the (e, 2e) reaction in metals when a core electron is excited from a localized state. Finitely temperature effects are considered by means of a certain generalization of Nozières‐de Dominicis' theory. A Gaussian broadening is predicted for (e, 2e) spectra. FWHM is computed for Li and Na. The results are compared with other theoretical data and with the data from photoemission experiments.
Polarizabilities of Donors in Elemental Semiconductors (II)
Authors: Palaniyandi E.
Published: July 2007

Using the multivalley effective mass equation and a variational method, an expression for the polarizability of donors in semiconductors is derived including the electron mass anisotropy in the Hamiltonian and using an improved trial function. Polarizability estimates of shallow donors in Si are made and these are compared with experimental results and the results of earlier calculations. The electron mass anisotropy contributes significantly to the polarizability values. Estimates of the polarizabilities of shallow donors in Ge are also presented.
The Theory of Paraelectric Induction and Echo Formation under Conditions of a Strong Inhomogeneous Broadening
Authors: Vagapova F. S. , Saburova R. V.
Published: July 2007

The formation of paraelectric induction and echo is shown to be associated with the inhomogeneously broadened resonant line and excited pulse parameters. The exact times of coherent responses are calculated. The effects of the induction‐decay and echo retardation are predicted. To determine the form of the echo a numerical integration is made. It is shown that the interaction of the electric dipole moment of the paraelectric centers with external oscillating fields creates new signals with other conditions for the excitation wave vector and the generated pulses.
On Stochastic Models of the Excitation Transfer in Molecular Crystals The Lineshape of the Phononless Exciton Band
Authors: Rips I. B. , Čápek V.
Published: July 2007

In the Sumi model describing the effect of the exciton—phonon coupling on excitons in molecular crystals by a stochastic Markoff‐Gauss process with a site‐diagonal potential with a time‐dependent exponentially decaying correlation function, the phononless exciton lineshape is investigated. It is proved that in general, cumulants of all even orders contribute to the optical lineshape function due to non‐commutativity of relevant operators at different times. So the recent result by Blumen and Silbey is shown to be just an approximation neglecting all but second‐order cumulants. The fourth‐order correction is calculated and it is proved that starting from this order of approximation, the free‐exciton density of states does not give a sufficient information necessary to deduce the optical lineshape function.
Charge Density Fluctuations and the Dielectric Matrix in a Quasi‐One‐Dimensional CDW Distorted Solid
Authors: Heiner E. , Gasser W.
Published: July 2007

Using an extended RPA procedure and symmetry properties of the system, the macroscopic dielectric function, plasmon frequencies, and the dielectric matrix are calculated for an one‐dimensional CDW‐distorted electron system in the condensed phase. Thereby the Peierls charge‐density wave potential is treated for a general case. Real and imaginary parts of the macroscopic dielectric function are discussed in the limit of vanishing wave numbers for different values of the dynamical parameters.
Neutron Spectroscopic Study of Lattice Vibrations in NaClO3 and Specific Heat
Authors: Haugstuen W. , Grip J. , Fjaer E. , Samuelsen E. J.
Published: July 2007

The acoustic branches and one optic branch of phonons in cubic NaClO3 are studied at room temperature by inelastic neutron scattering. Sound velocities are deduced, and specific heat versus temperature calculated by incorporating also high energy branches from Raman scattering. Connection between the specific heat and a suggested order—disorder process in NaClO3 is discussed.
An Assessment of the Scattered‐Wave Cluster Technique by Considering the Internal Conversion of 99mTc in the Metal
Authors: Hartmann E. , Seifert G.
Published: July 2007

The electronic structure of a 13‐atom Tc cluster is obtained from Xα‐SW calculation. Comparing the data derived for the internal conversion (IC) of 99mTc in the metallic state with recent experimental findings an assessment is made of the scattered‐wave cluster technique for the study of short‐range phenomena in metals.
Polar Kerr Effect of Magnetite in the Visible and Near Infrared Spectral Regions
Authors: Šimša Z. , Legall H. , Široký P.
Published: July 2007

Polar Kerr rotation and ellipticity of the synthetic single crystal magnetite are measured at room temperature in the 400 to 2400 nm spectral region. Using these magnetooptical measurements together with the earlier optical data the diagonal and the off‐diagonal tensor elements of the dielectric function are deduced. In the infrared region the dependences are dominated by the presence of the charge carriers while the behaviour in the visible part of the spectra is mainly due to the 3d crystal field transitions of the tetrahedral and octahedral iron ions.
Partial Pressure Contributions to the Equation of State of Alkali Metals
Authors: López J. M. , In̄guez M. P. , Alonso J. A.
Published: July 2007

The density functional formalism is combined with the concept of ionic pseudopotential in the form proposed by Meyer, Umar, and Young, and the different contributions to the equation of state of alkali metals are analyzed. The inhomogeneity of the electron density is shown to play a major role. The theoretical compressibility shows good agreement with experiment.
Optical Properties of Ni+ Centres in CaF2:Ni and SrF2:Ni
Authors: Alonso P. J. , González J. Casas , Den Hartog H. W. , Alcalá R.
Published: July 2007

The optical properties of X‐irradiated CaF2:Ni and SrF2:Ni are studied. An absorption band at 255 nm in CaF2 and 270 nm in SrF2 is created by X‐irradiation. It is concluded from optical bleaching experiments in low‐temperature X‐irradiated samples that those absorption bands are due to Ni+ ions. Optical dichroism experiments indicate that these Ni+ centres are oriented along the <100> directions. A comparison with previous EPR experiments of X‐irradiated CaF2:Ni indicates that the centres responsible for the 255 nm band in CaF2:Ni and the 270 nm band in SrF2:Ni are Ni+ ions displaced from the centre of the cube of fluorines toward one of the faces of that cube.
X‐Ray Spectroscopic Investigation of the Electronic Structure of AIIBIVCV2‐Type Semiconducting Phosphides
Authors: Gusatinskii A. N. , Bunin M. A. , Blokhin M. A. , Minin V. I. , Prochukhan V. D. , Averkieva G. K.
Published: July 2007

K‐bands and absorption spectra of phosphorus and emission L2, 3‐bands of silicon and phosphorus in MgSiP2, ZnSiP2, and CdSiP2 are obtained. From a comparison of the spectra of different series and components in these compounds the influence of metal d‐states on the valence band structure is studied. The admixture of phosphorus and zinc states to a metal d‐state is estimated from the ZnSiP2 spectra. Its smallness and the similarity of shape, position, and relative intensity of details of the corresponding spectra of all compounds are indicative of the fact that all metal d‐states are only slightly hybridized with other states and only weakly affect the valence band structure. A sufficiently fair correspondence is revealed between the calculated spatial charge density distribution of valence electrons and the data about the localization and symmetry of electron states obtained from X‐ray spectra. Good agreement between ΔE and Eg is found (ΔE is the energy gap between the emission ending and the onset of absorption of corrected P K‐spectra, Eg is the energy gap obtained by other physical methods).
Electrical Properties of Some TCNQ Complexes
Authors: Shaikh M. A. , Fleming R. J.
Published: July 2007

In order to have some insight into the conduction mechanism of TCNQ complexes, electrical resistivity and thermoelectric power of four TCNQ complexes, namely, methyltriphenylphosphonium (TCNQ)2, ethyltriphenylphosphonium (TCNQ)2, dibenzotetrathiofulvalinium (TCNA), and 1,2‐di (N‐ethyl‐4‐pyridinium) ethylene (TCNQ)4 are investigated in the temperature range 77 to 370 K. The results are presented and discussed on the basis of three models: a) metallic conduction, b) Hubbard model, and c) simple semiconductor band model.
Electrical Resistivity of Antiferromagnetic Chromium–Rhenium Alloys
Authors: Arajs S. , Moyer C. A. , Abukay D.
Published: July 2007

Electrical resistivity (ϱ) of Cr‐Re alloys containing 0.56, 2.45, 5.05, 6.57, 10.7, and 13.1 at% Re is studied as a function of temperature (T). The ϱ vs. T curves exhibit large anomalies at the Néel temperature (TN). The TN vs. at% Re curve has a maximum near 7 at% Re. The data of ϱ near TN and the behavior of TN with Re concentration are discussed from the viewpoint of Fermi surface nesting within the two‐band model.
Monte‐Carlo Calculation of the Electron Transmission, Reflection, and Absorption in Solids in the Energy Range up to 10 keV
Authors: Akkerman A. F. , Chernov G. Ya.
Published: July 2007

The Monte‐Carlo model of individual collisions is applied for low energy electron transport calculations. The applicability of this model is analyzed in detail with theoretically calculated cross sections. Some semiempirical relations for the most important characteristics of the transmission, backscattering, and absorbed energy distributions for C, Mg, Al, Si, Ge, Bi solid targets are obtained.
Peculiarities of the Magnetoresistance of Hg1−xMnxTe
Authors: Davydov A. B. , Ponikarov B. B. , Tsidilkovskii I. M.
Published: July 2007

On semimetallic Hg1−xMnx Te samples with 0.02 ≦ x ≦ 0.06 the dependences of the Hall constant‐RH and longitudinal, ϱZZ, and transverse, ϱxx, magnetoresistances are investigated on the induction of magnetic field B in the region of 0 ≦ B ≦ 50 kG at temperatures 1.6 ≦ T ≦ 40 K. A maximum of ϱxx(B) observed in 5 to 7 kG fields at helium temperatures is accounted for by the contributions which both, conduction band electrons and impurity acceptor band holes, make to the transport processes. The decrease in magnetoresistance in fields B > 7 kG is attributed to the increase of the mobility of carriers in the impurity band due to the ordering of magnetic moments of manganese ions in the magnetic field. It is proved that the maximum ϱxx(T) at 7 ≦ B ≦ 12 kG occurring at temperatures between 2.5 and 5 K is not a thermooscillation peak.
Optical Transitions at Ag Centers in ZnS Crystals
Authors: Schwenkenbecher K. , Boyn R. , Resagk H.
Published: July 2007

An experimental study is made of transitions occuring at the centers responsible for the blue emission band of Ag‐doped ZnS crystals. Excitation and infrared quenching spectra of this emission and of photoconductivity are measured. The results are consistent with the pair‐transition model proposed by Shionoya and coworkers. A discussion is given of the transition energies in this system, taking account of lattice relaxation and using data on electron‐lattice coupling which are deduced from the temperature dependence of the emission band width.
Application of ENDOR‐Induced Electron Spin Resonance to the Study of Point Defects in Solids
Authors: Niklas J. R. , Spaeth J. M.
Published: July 2007

The technique of ENDOR‐induced ESR (EI‐ESR) is applied to the investigation of several point defects in insulating crystals. It is shown that the lineshape of the EI‐ESR spectrum depends on the ENDOR line used for the experiment. The EI‐ESR technique allows the separation of overlapping ESR spectra in the presence of several defects. New applications are the selection of spin states and the determination of relative signs of spin‐Hamiltonian parameters, the selection of centre orientations and the assignment of nuclei in complex ENDOR spectra, and the determination of quadrupole interactions which are not resolved in the ENDOR spectrum.
Recalculations of Madelung Potentials and Polarisabilities of Ions in Stoichiometric Rutile (TiO2)
Authors: Iguchi E. , Sawatari H. , Tilley R. J. D.
Published: July 2007

The Madelung potentials in stoichiometric rutile (TiO2) are calculated and found to be 29.53 eV at the Ti4+ site and −41.20 eV at the O2‐ site. These potentials lead to the value of 141.5 eV for the Madelung energy per TiO2 “molecule” and also the value of 4.810 for the Madelung constant. Using the Madelung potential at the Ti4+ ion, the electronic polarisability of the Ti4+ ion is estimated to be 0.368 Å3. This result is used to determine the ionic polarisability of the Ti4+ ion and the electronic and ionic polarisabilities of the O2‐ ion. The electronic polarisability of the O2‐ ion is found to be large in value compared with that in other oxides. The possible connection between polarisability and defect structure formation in nonstoichiometric rutile is discussed.
Theory of Optical Bistability of Excitons
Authors: Goll J. , Haken H.
Published: July 2007

The saturation behaviour of excitons driven by an impinging electromagnetic plane wave is investigated. The nonlinear absorption coefficient and the nonlinear refractive index are determined. Taking care of the boundary conditions at the end faces of the crystal, the nonlinear transmissivity of the crystal is determined. The phenomenon of optical bistability is investigated taking into account standing wave effects and the influence of the detuning is discussed.
A First‐Principles Model of Energetical Trap Distributions in Solids II. The Finite Defect Chain of Uniform Curvature
Authors: Hamann C.
Published: July 2007

The model of the finite defect chain is used to calculate the trap distributions caused by a defect chain with a uniform curvature. For spherical potentials not belonging to the Coulomb‐type analytical solutions are obtained. This paper shows that any spatial defect chain causes essentially trap distributions with exponential characteristics in the solid.
Short‐Range Order Modelling and Bonding in Metal–a‐Ge Systems
Authors: Manaila R. , Devenyi A.
Published: July 2007

A structural model is proposed for the metal‐amorphous Ge systems, based on the filling of the inner voids by the metal in a tetrahedral CRN. This starting model is relaxed under a set of bond‐stretching, bond‐bending, and Me‐Ge interaction potentials, for the specific case of the Cux(a‐Ge)1−x alloys (x = 0.22 and 0.40). A good agreement between the calculated and an experimental interference function is obtained by assuming an alteration of the bonding character in the a‐Ge matrix towards a more metallic one.
On the SD Model for Coexistence of Ferromagnetism and Superconductivity
Authors: Tonchev N. S. , Brankov I. G.
Published: July 2007

The Vonsovskii‐Zener model for a superconductor with regularly positioned magnetic impurities is considered. Two theorems are given which prove the exact solubility of the thermodynamic problem by the approximating Hamiltonian method. Exact analytical solutions for the zero‐temperature order parameters and the ground state energy of the mixed phase are derived. A comparison of the energies of the different phases confirms the known result that ferromagnetism and superconductivity cannot coexist in the ground state of the model.
Effect of Electron‐Phonon Interaction on the Density‐of‐States Tails and Impurity Band Optical Absorption
Authors: Burbaeva N. V.
Published: July 2007

The 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

The 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

An 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

Multiple 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

Based 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

Detailed 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

A 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

A 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

Comparative 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

The 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

Gigantic 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

The 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

It 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

The 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

An 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

An 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

The 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

In 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

It 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

Simple 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

A 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

Theoretical 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

It 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

Some 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

The 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

An 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

ESR 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

The 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

The 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

Computed 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

The 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

Using 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

The 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.
Theory of Secondary Electron Emission. I. General Theory for Nearly‐Free‐Electron Metals
Authors: Rösler M. , Brauer W.
Published: July 2007

A detailed theory of secondary electron emission (SEE) for nearly‐free‐electron (NFE) metals is developed. The creation of secondary electrons (SE) by primary electron (PE) collisions with metal electrons in core states and in the Fermi sphere is considered. Especially a calculation is given of SE production by plasmon decay on the basis of a general model potential. Both, elastic and inelastic collisions of internal secondaries are taken into account. Primary energies are limited to 1 to 2 keV. General formulas regarding excitation functions, mean free paths, and scattering functions, necessary for the computation of the energy angular distribution of SE and secondary yield, are derived.
The Electron–Hole Plasma in a Strong Electromagnetic Field. Optical Properties in a Simplified Model
Authors: Harbich Th. , Mahler G.
Published: July 2007

An electron–hole plasma in the presence of a high‐intensity laser field is considered in the quasienergy picture. Using a two‐band model it is shown that the gain spectrum depends on the strength of the laser field in a characteristic way, provided the frequency of transitions between the conduction and the valence band is at least of the order of the inverse collision time.
Nearest‐Neighbour Poisson Approximation to a Functional Approach for the Hubbard Model
Authors: Behn U.
Published: July 2007

In the framework of the Poisson approximation to a functional scheme for the Hubbard model the effect of the spatial correlation of the discrete stochastic potential Uvi(t) simulating the spin‐↓ subsystem is considered. For a half‐filled band in the paramagnetic case at zero temperature the density of states is calculated in a nearest‐neighbour approximation. For strong Coulomb repulsion the subbands occur sharper and the minimum in between is deeper compared with the single‐site approximation. The influence of the spatial correlation on the possible appearance of a gap within a dynamic approximation is discussed.
Composition Dependence of the Maximum Cyclotron Mass m in n‐Type Semiconducting Bi1–xSbx
Authors: Fellmuth B. , Krüger H. , Rudolph R. , Herrmann R.
Published: July 2007

The propagation of magnetoplasma waves in the configuration B‖C2‖k is measured for a number of n‐type semiconducting Bi1–xSbx alloys (0.07 < x < 0.14) at frequencies of 41 and 70 GHz and helium temperatures. The attenuation behaviour and a comparison between the experimental and the theoretical dispersion of the waves yield a rapid increase of the maximum cyclotron mass m1c with increasing x, which by far exceeds the variation of the low cyclotron mass m2c. Under the given conditions, the results obtained are largely independent of the dispersion relation of the electrons, which is used in the description of the wave dispersion in a quantizing magnetic field.
Polarized TiKβ Valence Band Spectra of TiO2 (Rutile)
Authors: Dräger G. , Brümmer O. , Heera V. , Seifert G. , Ziesche P.
Published: July 2007

The TiKβ valence band spectra of a TiO2 (rutile) single crystal are measured polarized parallel and perpendicular to the tetragonal c‐axis. The shape of the spectra shows a strong anisotropy giving more information on the electronic structure of this substance than the corresponding unpolarized spectrum of a polycrystalline sample. Theoretical spectra are calculated for a TiO6 cluster with D2h symmetry on the basis of the results of a SW Xα cluster calculation. The agreement between the theoretical and experimental spectra is very good with respect to the calculated orbital energies and measured peak positions and is qualitatively satisfying regarding the intensities. For the last case, however, a cluster–cluster interaction along the c‐direction of rutile must be taken into consideration.
The Influence of Far‐Band k · p Interaction on Carrier States in Lead Chalcogenides
Authors: Mironov A. G. , Ziep O.
Published: July 2007

Statements of the Dimmock model with respect to dispersion relation und wave functions are discussed within the framework of the k·‐matrix of Mitchell and Wallis. The eigenvalues obtained are compared with the exact secular equation of a six‐band model which neglects the interaction between far bands. With respect to the dependence on the Fermi energy of carrier concentration and density of states predictions of the Kane model, of a recent developed multiband model, and of the Dimmock model are compared.
The Luminescence Properties of Alkaline‐Earth Oxides Activated with 6s2 Ions
Authors: van der Steen A. C. , Dijcks L. T. F.
Published: July 2007

The luminescence spectra of CaO and SrO activated with Pb2+ or Bi3+ ions show vibrational structure. The features in the spectra are discussed by considering the PbO (BiO) octahedron as an isolated unit in the rocksalt lattice. The luminescence spectra of Tl+‐activated CaO and SrO do not show vibrational structure. Comparisons are made with other s2 ion‐activated systems.
Pressure Derivatives of Elastic Stiffness Constants under Pressure of Si and Ge
Authors: Soma T.
Published: July 2007

The bulk modulus B, the shear elastic constants C44 and C′ = (C11 – C12)/2 under pressure of Si and Ge are studied theoretically using the presented local Heine‐Abarenkov model potential and the higher order perturbational formalism. The pressure‐derivatives dB/dP, dC44/dP, and dC′/dP decrease under compression from the experimental data at low pressures, and dC44/dP and dC′/dP tend to become negative below about 100 kbar.
On the Magnetism in Narrow‐Band Conductors
Authors: Karpenko B. V.
Published: July 2007

The problem of the double exchange interaction mechanism in narrow‐band magnetic conducting crystals in terms of the Vonsovskii s‐f exchange model is considered taking into account the Coulomb interaction between conduction electrons, using Hubbard approximation. The values of the Néel paramagnetic temperature and of effective paramagnetic moment, as function of concentration of current carriers, are determined. A comparison of the theoretical expressions with the experimentally found Gd concentration dependence of the Curie paramagnetic temperature of solid solutions Eu1–xGdxSe helps to obtain a correlation between the conduction band width, the magnitude of the intraatomic exchange integral, and the value of the Coulomb interaction of electrons on a site. The variation of the effective magnetic moment value in the Eu1–xLaxS series, as a function of La concentration is discussed.