bluuebunny/crossref_metadata_2025 huggingface dataset:
Proton Spin‐Lattice Relaxation Time of TCNQ NH
Authors: Alizon J. , Berthet G. , Blanc J. P. , Gallice J. , Robert H.
Published: July 2007

Proton spin‐lattice relaxation time T1 of tetracyanoquinodimethan‐ammonium salt (TCNQ NH) has been studied as a function of temperature. In this material, the shape of the T1 curve is quite different of that observed in simple alkaline M‐TCNQ salts. It is shown that the reorientation of the NH4 ion must be taken into account.
Kondo‐Type Resistivity Anomaly in Noble Metal Alloys with 3d Metals
Authors: Inoue K. , Nakamura Y.
Published: July 2007

The electrical resistivities of the f.c.c. Au‐V, Au‐Mn, Au‐Fe, and Au‐Ni alloys with high concentration of 3d‐element impurities have been measured from 4 to 1000 K. The results were analyzed together with other data for Au‐Cr, Au‐Co, Ag‐Mn, Cu‐Mn, and Cu‐Ni alloys. At high temperatures, the decrease of magnetic resistivity with increasing temperature is observed for Au‐V, Au‐Cr, Au‐Mn, Au‐Fe, Au‐Co, Ag‐Mn, and Cu‐Mn alloys and is expressed empirically by the equation Rmag(T) = ‐ c (Y + Z c) ln (T2 + + X2 c2)1/2 + c (R1 + R2 c), except for Au‐Co alloys, where c is the concentration of 3d element, T the temperature, and X, Y, Z, R1, and R2 are constants. Yc coincides with the coefficient of ln T in each dilute alloy. R1, c coincides with the temperature independent term in each dilute alloy. Xc is nearly of the same order as the RKKY interaction strength. Au‐Ni and Cu‐Ni alloys do not show such a decrease. The maximum of magnetic resistivity observed for Au‐Cr, Au‐Mn, Au‐Fe, Ag‐Mn, and Cu‐Mn alloys is explained by the destruction of very short range ordering, such as pairs and triplets, remaining far above the Néel temperature.
Electronic Energy Loss of Ions in the Modified Firsov Theory
Authors: Komarov F. F. , Kumakhov M. A.
Published: July 2007

An analytical version is derived of the modified Firsov theory for the calculation of inelastic energy losses of ions traversing through crystalline and amorphous targets. Shell effects are included. The model describes correctly the dependence of the inelastic energy loss on the atomic number of the target atoms and incident ions and yields a fair agreement with experimental data.
Long‐Range Forces in the Dynamics of Crystals with Defect
Authors: Litzman O. , Rózsa P.
Published: July 2007

A point defect with long‐range interaction changes the dynamical matrix of the ideal crystal in infinitely many elements. The method for the evaluation of the local modes and of the Green's function of this problem proposed earlier is extended in order to apply it to the case when interstitials are present. The use of some more general formulae enables the final formulae to be stated in a surprisingly clear form.
High Field Transport in n‐InSb at 77 °K and the Solution of Boltzmann's Equation by Iteration
Authors: Stokoe T. Y. , Cornwell J. F.
Published: July 2007

The solution of Boltzmann's equation for n‐InSb at high fields and 77 °K is obtained by Rees' iterative method. The time independent solution obtained is in agreement with a recent Monte‐Carlo calculation by Fawcett and Ruch and experimental results by Neukerman and Kino. A comparison between the Boltzmann solution and the drifted Maxwellian approach previously discussed by the authors is also presented.
Dynamical Properties of the Singlet—Singlet Van Vleck Paramagnet
Authors: Cheung T. H.
Published: July 2007

The high temperature dynamical properties of the singlet—singlet model for the Van Vleck paramagnet is investigated. Such a system can be described by the Hamiltonian of the Ising model with a transverse field. Using the high temperature approximation of Mori's continued‐fraction representation, an approximate expression for the longitudinal relaxation function is derived. This leads to renormalized magnetic excitations and the appearance of a central peak for the corresponding spectral density. Its relevance to recent neutron scattering data is discussed.
Stress and Magneto‐Optical Studies of F‐Centres in SrCl2
Authors: Billardon M. , Duran J. , Lefrant S. , Taurel L.
Published: July 2007

Magneto‐optical and stress linear dichroism studies are made on the new F centre found in SrCl2 which belongs to Td symmetry group. The results have been analysed by the method of moments in order to determine a number of useful parameters. It is found that the excited state orbital Landé factor is close to zero. This is explained by taking into account an admixture of |p〉 and |d〉 type orbitals in the excited state. It is found that the spin—orbit splitting is about — 100 cm−1. A careful analysis of higher order moments of the magnetic circular dichroism and stress linear dichroism curves leads to a determination of the dynamic electron lattice coupling parameters which can in turn be compared to the static parameters determined from the first order moment of the stress linear dichroism curves. The dynamic electron lattice interaction is predominantly due to a trigonal vibrational mode whose mean frequency is about 100 cm−1.
Magnetic Properties of Manganese‐Doped Mercury Telluride
Authors: Savage H. , Rhyne J. J. , Holm R. , Cullen J. R. , Carroll C. E. , Wohlfarth E. P.
Published: July 2007

The inverse susceptibility—temperature curves of MnxHg1—xTe (x = 0.05, 0.11, 0.17, 0.235) showed a Curie‐Weiss behaviour at high temperatures and a downward deviation at low temperatures. The paramagnetic Curie temperatures and effective numbers of magnetic carriers also deviated from a linear dependence on x at low values of x. These results were explained in terms of a cluster model at low x values and a molecular field model at high x.
The Energy Bands and the Fermi Surface of β′AgZn
Authors: Skriver H. L.
Published: July 2007

The electronic energy band structure for the ordered alloy β′AgZn has been calculated by the augmented plane wave method. The bands obtained are similar to those of β′CuZn except for the d‐band parameters: width and position. Various density‐of‐states functions have been determined. The calculated ϵ2(ω) profile is in agreement with static reflectance measurements. A Fermi surface model has been derived. The angular dependence of various extremal cross sections agrees extremely well with existing de Haas‐van Alphen experiments. Cyclotron masses have been estimated and compared to the experimental values giving the apparent mass enhancement.
Nonlinear Heat Transfer in a Lattice Containing Impurities
Authors: Dubey K. S.
Published: July 2007

Nonlinear heat transfer in a lattice has been studied considering two scattering mechanisms, isotopic scattering and dislocation scattering as impurity scattering process. A sufficiently good agreement is observed between the experimental conductivity of NaF in the entire temperature range 2 to 10 °K.
On the Mechanism of Small‐Polaron Transport
Authors: Klinger M. I.
Published: July 2007

A model of the mechanism of (nonadiabatic) small polaron transport is considered for intermediate temperatures when the coherence of the Bloch band states is significantly destroyed but thermally activated hops still do not dominate. The mechanism of small polaron tunneling is studied at high temperatures when the scattering is fairly strong (quantum diffusive motion).
Considérations sur l'importance de quelques hypothèses physiques dans la théorie de l'émission électronique secondaire
Authors: Moulin B. , Ganachaud J.‐P. , Cailler M.
Published: July 2007

On propose un certain nombre de corrections à apporter au travail théorique d'Amelio ainsi qu'une nouvelle méthode de résolution plus rapide et moins contraignante. On considère ensuite l'influence de l'hypothèse restrictive de la constance du libre parcours moyen des électrons sur la distribution énergétique de l'émission électronique secondaire. On considère aussi l'influence de la fonction source.
Contributions to the hyperfine field at the 57Fe nucleus in crystals with garnet structure
Authors: Valentin R.
Published: July 2007

ENDOR measurements are performed on a number of Fe3+ doped crystals with garnet structure (YAIG, LuAlG, TmAlG, YGaG, LuGaG, TmGaG, and EuGaG) which enabled to determine the hyperfine field at the 57Fe nucleus. The Fe3+ ions occupy cation sites ((a)‐sites) which are surrounded by oxygen octahedra. It is found that the hyperfine field is linear dependent on the trigonal part of the crystal field at the (a)‐site, and thus on the field gradient Vzz. This dependence is attributed to the dipole‐dipole interaction between electron and nuclear spins which in higher order contributes to the hyperfine field.
A KKR approach to electronic spectra of amorphous semiconductors
Authors: Maschke K. , Overhof H. , Thomas P.
Published: July 2007

A new method is proposed to calculate the configurational averaged Green's function for amorphous semiconductors. In contrast to earlier work based on pseudopotentials this method is within the framework of the KKR approach. It, therefore, can avoid the approximations for the potential average necessary in the pseudopotential scheme. Some general properties of the resulting spectral function and density of states are discussed.
The influence of the short‐range order on the energy spectrum of disordered tellurium phases
Authors: Kramer B. , Maschke K. , Laude L. D.
Published: July 2007

The influence of different types of short range order on the density of states of tellurium is investigated. The results for usual trigonal short range order are compared to those for simple cubic short range order. The density of states for the corresponding systems without long range order is discussed within the framework of the complex band structure method. The results are compared to photoemission experiments for different modifications of disordered tellurium.
Theory of scattering yield in channeling
Authors: Ohtsuki Y. H.
Published: July 2007

Making use of the non‐local potential due to inelastic scattering, an expression for the transition probability of inelastic scattering in Channeling is introduced. The theory of back‐scattering yield oscillation is studied as a demonstration. Expressions for the blocking pattern and the star pattern are also presented in terms of the transition probability in channeling.
Mössbauer spectrum depending on the degree of spin‐system ordering
Authors: Selyutin G. Ya.
Published: July 2007

A theoretical investigation is made of the Mössbauer spectrum in crystals containing exchange coupled magnetic ions. It is shown that for a Lorentz shape of the Mössbauer line the line broadening, the Debye‐Waller factor describing the intensity of the Mössbauer spectrum, and the line shift depend on the value of exchange interaction of magnetic ions and on the degree of spin‐system ordering.
The hyperfine fields in ferromagnetically ordered cubic Laves phase compounds of gadolinium with non‐magnetic metals
Authors: Dormann E. , Buschow K. H. J.
Published: July 2007

By means of current zero‐field spin‐echo NMR technique the hyperfine fields at the Gd and X sites in the ferromagnetic cubic Laves phase compounds of the type GdX2 (X = Al, Pt, Ir, Rh) are derived. The easy direction of magnetization in GdIr2 is [100] in contrast to [111] in GdAl2.
On the theory of phonon‐like excitations in noncrystalline solids
Authors: Böttger H.
Published: July 2007

Phonon‐like excitations are studied on a monatomic spatially disordered system with pair interaction between the atoms. Dispersion and damping of phonon‐like excitations are governed by the self‐energy occurring in the Dyson equation of the ensemble averaged Green's function of the system. For the self‐energy a functional differential equation is derived and discussed.
Polariton line shape in two‐photon spectroscopy
Authors: Uihlein Ch. , Barentzen H.
Published: July 2007

The two‐photon absorption line of a polariton is derived by means of linear response theory. The shape is determined by the imaginary part of the polariton Green's function. The Green's function can be related to the complex dielectric function. The two‐photon absorption line is thus completely determined by the linear optical properties of the crystal. This is confirmed for the second exciton in CuCl were we succeeded in fitting the two‐photon line shape by means of the dielectric function known from one‐photon measurements.
Magnetoemission of GaSb: Free and bound excitons
Authors: à la Guillaume C. Benoîa , Lavallard P.
Published: July 2007

The free exciton g factor is measured to be equal to −9. An analysis of the magneto‐absorption and magneto‐emission data shows that the lower energy level of the bound exciton γ has Γ6 (J = 1/2) symmetry. A Jahn‐Teller effect on the acceptor site may explain this result. The bound hole g factor is evaluated to be equal to 0.3.
On the theory of the domain structure and the elastic properties of the orthorhombic weak ferromagnets
Authors: Mitsek A. I. , Kolmakova N. P. , Sirota D. I.
Published: July 2007

The possible magnetic states of orthorhombic weak ferromagnets and rare‐earth orthoferrites (REOF), the change of the magnetic state with the change of the temperature, and the mechanism of the formation of a new magnetic phase nucleus from a 180° domain wall for the first‐order phase transition are considered. The ΔE‐effect for both the first order phase transition and the transition by the reversible rotation of the antiferromagnetic vector and the magnetic susceptibility tensor, connected with the displacement of 90° domain walls, are calculated.
Interaction of plasma and lattice waves in piezoelectric semiconductors
Authors: Robson R. E. , Paranjape B. V.
Published: July 2007

The interactions between collective excitations of free electrons and holes with the lattice vibrations are investigated. Detailed calculations presented are valid in materials having piezoelectric properties. The dispersion relation is found using Boltzmann's equation for the plasma rather than the hydrodynamic equations previously used. The method followed is quite general, but is concentrated on the case where there is collisionless damping in the plasma. The case where damping of plasma waves is through collisions has been treated by Hutson and White [6]. The general formula gives their results in the limit of collision‐dominated plasma. In the collisionsless limit, it is shown that there is attenuation of lattice waves and that this reaches a maximum at a certain frequency. For frequencies slightly greater than the plasma frequency, it is shown that there can be a resonance between the optical vibrations of the plasma and the lattice waves, provided the temperature is low enough.
Calculation of nuclear quadrupole relaxation times in NaI on the basis of breathing shell model
Authors: Ray D. K. , Sangster M. J. L.
Published: July 2007

In order to test the accuracy of the eigenvectors associated with the ionic motions which one gets from the Breathing Shell Model (BSM) of Schröder in NaI the nuclear quadrupole relaxation times have been calculated as function of temperature at both Na23 and I127 sites and these are compared with the experimental results.
Temperature dependence of the hyperfine structure coupling parameters of CO and AsO molecule ions in γ‐irradiated single crystal calcite
Authors: Chan S. S. , Marshall S. A. , Serway R. A.
Published: July 2007

The hyperfine structure coupling parameters of CO and AsO molecule ions in γ‐irradiated single crystal calcite have been measured from 4.2 to 325 K. For Co, the data suggest that the fractional electron spin density at the carbon atom increases by about 1% on raising the temperature from 4.2 to 200 K. For the AsO molecule ion, the fractional electron spin density on the arsenic atom decreases by about 7% on raising the temperature from 4.2 to 325 K.
Variational method in the theory of reciprocal electron and phonon drag in semiconductors
Authors: Pinchuk I. I. , Ya. Luste O.
Published: July 2007

A variational method of the anisotropic scattering theory is used to analyse the drag effect of electrons by phonons and of the reciprocal drag effect on the kinetic properties of semiconductors. The role of various phonon scattering mechanisms and their effect on the thermo‐e.m.f. of the drag are discussed. The temperature dependence of thermo‐e.m.f. is obtained taking into account various phonon and electron scattering mechanisms.
Binding of an exciton to a donor‐acceptor pair in a semiconductor ii. binding energy and critical separation in the case of a coulomb interaction – influence of the polarization effects
Authors: StÉabEá B. , Munschy G.
Published: July 2007

The binding energy of an exciton to a donor–acceptor pair is calculated in the approximation of Coulomb interactions. Haken's potential is also considered to take into account the electronic and ionic polarization effects. To this aim, the variation method is applied to an electron‐hole product wave function with two adjustable parameters. The computations are made for both equal and unequal electron and hole effective masses. The results obtained compare favourably to the experimental data in ZnSe. Haken's potential is found to be suitable for donor‐acceptor separations close to the critical length, in which case the polarization effects are still important.
Rapid variation of the superconducting transition temperature in the Al12Mg17 phase
Authors: Claeson T. , Granqvist C. G. , Ivarsson J.
Published: July 2007

The superconducting transition temperature decreases from about 0.7 to less than 0.03 K. as the Mg content is increased within the Al12Mg17 phase. The rapid variation is correlated with an increasing tendency for the electrons to participate in covalent and ionic bonds.
M‐Center singlet to triplet excitation in KCl
Authors: Schneider I. , Keller F. J.
Published: July 2007

M centers are transformed to a triplet state either through the capture of an electron by an M+ center or through the optical bleaching of an M′ center. Using a technique similar to one previously developed by Schneider, Keller, and Klick, it is found that about four times as many triplets are produced through the M+ mechanism than through the M′. In these experiments, bleaching is produced with intense infrared excitation of short duration absorbed in the F′ or M′ bands for crystals which contain either M+ or M′ centers. Evidence is also presented which indicates that the M+ mechanism might be predominant at low temperatures for continuous excitation in the F‐spectral region.
Decoupling of correlation functions in calculating the transport coefficients
Authors: Dudkin S. I.
Published: July 2007

A method of calculating the transport coefficients based on the Kubo formula [1] is presented. The complex admittance is calculated by setting up and solving the equations for the mass operators. A procedure for decoupling the correlation functions is proposed.
Study of broadening of the NMR line due to dislocations by the monte carlo method
Authors: Plishkin Yu. M. , Greenberg B. A.
Published: July 2007

By the method of statistical tests (Monte Carlo) investigations were made on a digital computer of the resonance line (satellite and central line) in a crystal of the NaCl type containing edge line dislocations uniformly distributed over the volume. The expression for the frequency shift due to quadrupole interactions in the crystal containing dislocations was obtained within the framework of anisotropic elasticity. Statistical calculation of the shape of the line is made for Na23Cl and KBr81 crystals for different orientations of the magnetic field. The elementary statistical test consists in calculation of shift of frequency of a certain nucleus due to n randomly distributed dislocations. The repetition of computer experiments is carried out N times after which the whole series of experiments is subjected to statistical processing. On the basis of statistical processing of the computer experimental curves are plotted of the integral distribution function and of histograms of the probability density and calculations are made of the first moments of the resonance curve. Investigations were made of the change of the broadening of the line with the change of the orientation of the external constant magnetic field relative to the crystal having a given distribution of dislocations.
A Quantitative Study of the Stabilization Field for 180° Walls in Iron Single Crystal Sheets Containing Solute Nitrogen
Authors: Tahara Y. , Sugeno T.
Published: July 2007

The strength of the stabilization field for 180° walls in [100] (011) iron single crystal sheets is derived theoretically and compared with experimental results. An initial magnetization curve after the stabilization of domain walls has taken place is derived using a model in which the reversible and irreversible magnetization processes are separately taken into account. The theoretical maximum value of the stabilization field is shown to be equal to the magnetic field at which the initial magnetization curve shows a first sudden discontinuous increase in induction. Effects of domain wall orientation and magnetostriction on the strength of the stabilization field are calculated. Calculations show that the 180° walls parallel to the (011) plane can be displaced irreversibly at the weekest magnetic field. These theoretical results are satisfied by experiment. A breakaway motion of domain walls is proposed for the sudden discontinuous increase in induction in the stabilized initial magnetization curves. The flexibility of domain walls contributes to the breakaway motion of domain walls.
Density of states and conductivity in highly impure semiconductors
Authors: Lukes T. , Rogers B. A.
Published: July 2007

The evaluation of the density of states of a semiconductor disordered by a high density of impurities is considered by path integral methods. An effective momentum approximation and a cumulant approximation in momentum space are both used and graphical results for the density of states are presented. The results are applied to the evaluation of the static electrical mobility. It is found that this can be described by a Boltzmann like and non‐Boltzmann like term and graphical results for the variation with Fermi energy of both these terms are given.
A model of the electrical transport phenomena in imperfect crystals of copper phthalocyanine II. Surface States of Phthalocyanine Single Crystals
Authors: Hamann C. , Lehmann G.
Published: July 2007

Starting from real grown crystals and their habit the binding energies of a molecule for different crystal directions are estimated and some ideas about the electronic surface morphology are given. The high concentration of lattice defects on the surface causes their interaction which leads to a quasicontinuous energetic distribution of traps. The microstructure of the distribution can be referred to the geometry of the crystal lattice. The theoretical results agree excellently with the experiments.
Relaxation and Formation Energy of Vacancies in Metals
Authors: Augst G. R.
Published: July 2007

An expression for the vacancy formation energy in metals is obtained taking into account the associated lattice distortions. For the purpose of finding the electrostatic energy Ewald's method was generalized specially for a lattice with a vacancy. Equations are found for the calculation of the displacements around the vacancy.
On the Theory of the Dynamic Stark Effect and Franz‐Keldysh Effect in a Resonant Electromagnetic Radiation Field
Authors: Becker L. , Enderlein R. , Peuker K.
Published: July 2007

The influence of the electric field of a resonant laser radiation on the dielectric function of a three‐band semiconductor model is investigated theoretically. The laser radiation is assumed to be in resonance with the transition between the two unoccupied bands of the model. The relative contributions of the dynamic Stark effect due to the interband coupling caused by the laser field and of the Franz‐Keldysh effect due to the intraband coupling are discussed. The laser‐radiation‐induced change of the real part of the dielectric function is calculated. The corresponding result for the imaginary part is in agreement with an earlier result of other authors. Explicit line shapes for the change of the real and imaginary part of the dielectric function are given with parameter values chosen close to those of GaAs.
Influence of the Size of the Precipitates in NaCl:Pb2+ Crystals on Rayleigh Scattering and UV Absorption
Authors: Fayet‐Bonnel M.
Published: July 2007

Using the Mie theory the extinction cross‐sections of PbCI2 spheres embedded in NaCl are calculated for various radii between 1 and 46 nm, in the wavelength region 220 to 400 nm. These calculations allow to propose a model with two types of spherical precipitates — the concentrations and the radii of which depend on the heat treatments — that fits the experimental results of UV absorption and Rayleigh scattering by NaCI:Pb2+ after different heat treatments.
Anomalous Temperature Dependence of Charge Carrier Density and Mott Transition in Ferromagnetic Semiconductors
Authors: Grigin A. P. , Nagaev E. L.
Published: July 2007

The temperature dependence of the conductivity of ferromagnetic semiconductors is theoretically investigated for both the non‐degenerate and degenerate case with allowance of the exchange interaction between moveable electrons and localized magnetic moments. For the former the temperaturedependence of the charge carrier density is found.
Charge Transfer in Some Transition‐Metal Semiborides
Authors: Kohm A. , Merz H.
Published: July 2007

High‐resolution bremsstrahlung isochromats of the semiborides (FeCo)B, Co2B, (CoNi)B, Ni2B are presented. A systematic difference between the isochromats of the borides and those of the corresponding metals can be understood in a simple charge transfer model. Boron acts as donor and supplies (1.6 ± 0.5) electrons per boron atom.
Statistical Theory of the Interaction between Point Defects and Flux Lines
Authors: Schmucker R. , Kronmüller H.
Published: July 2007

Under special consideration of the magnetic terms, the micromagnetic theory of super‐conductivity is employed to calculate the interaction between flux lines and elastic dipoles. The interaction force between one flux line and one elastic dipole with cubic symmetry is given analytically. The average pinning force due to the interaction with many point defects isobtained by a statistical treatment which considers the spatial fluctuations in the dipole density and the flexibility of the flux lines.
Mean‐Square Ionic Displacements and Force Constants of Crystals with the CsCl Type Structure
Authors: Jex H. , Müllner M. , Dyck W.
Published: July 2007

Mean‐square vibrational amplitudes of ions in the diatomic lattices of crystals with the CsCl type structure have recently been determined in the high temperature region by elastic scattering of neutrons. An evaluation of mean‐square displacements in terms of frequency moments is derived and connections with the force constants of the crystals are worked out. The difference of the vibrational amplitudes of the two ions is calculated from the experimental data and by means of force constants derived from phonon measurements.
On the Equivalence of the Kubo Formalism and a Transport Equation Approach
Authors: Van Keer R. , Phariseau P.
Published: July 2007

From an analysis on the equivalence of the Kubo formula for electrical conductivity and a transport equation approach for electrons in disordered systems, it is made clear that the decoupling assumptions, involved in the derivation of the macroscopic equations, are justified if Taylor's conditions are satisfied.
Galvano‐ and Thermomagnetic Phenomena in n‐InSb‐Type Semiconductors at Inelastic Optical Scattering
Authors: Tolpygo H. I.
Published: July 2007

Following a previous work [1] the temperature and field dependence of the transport coefficients are calculated for non‐degenerated n‐InSb taking intoaccount Kane's dispersion law, inelastic optical scattering, and the temperature dependence of the band structure parameters. Preliminary calculations based upon the relaxation time approximation confirmed the conclusion [1] about the dominant role of the optical and impurity scattering (including that of electrons by holes) in a broad temperature interval (50 to 400 °K). The Boltzmann equation for this scattering mechanisms using the method developed in [2] is solved. The electron distribution functions were found for the cases of the electric and magnetic fields and the thermal flow being present. Theoretical results for the mobilities and the Nernst‐Ettingshausen (NE) coefficients are compared with the experiment. This comparison shows that the theory overestimates somewhat the role of the optical scattering. Both the absolute values and the temperature dependence of the NE coefficients turn out to be only in a rough correspondence with the observed ones. The possible reasons of discrepancies are discussed.
Herzberg‐Teller Interaction and Vibronic Coupling in Molecular Crystals I. The Simple Model
Authors: Zgierski M. Z.
Published: July 2007

The vibronic absorption spectrum of a molecular crystal, corresponding to the formation of an exciton in a state forbidden by the intramolecular symmetry, is investigated. It is assumed that intensity is borrowed from a higher electronic state with help of the Herzberg‐Teller mechanism. Non‐totally and totally symmetric intramolecular vibrations are included into this consideration. Formulae for relative intensities of different vibronic lines in the spectrum are obtained. The one‐ and two‐phonon regions of the spectrum are discussed.
Elastic Interaction of Small Defects and Defect Clusters in Hexagonal Crystals
Authors: Yoo M. H.
Published: July 2007

An analysis is given of the elastic interaction between small defects and/or defect clusters in hexagonal crystals. Simple explicit expressions for the interaction energy are obtained directly from the Green's function given by Kröner. Some typical calculated results are presented for various combinations of axially symmetric defects, e.g., a pair of point defects, a pair of dislocation loops, and a point defect and a dislocation loop. Applications to a study of Frenkel defects recombination processes in irradiated hexagonal crystals are discussed.
Anisotropy of Electron and Hole Masses and g‐Factors for PbSe by k · p Calculation
Authors: Bangert E. , Kästner P.
Published: July 2007

An ellipsoidal non‐parabolic k · p model (enp‐model) is used to calculate the anisotropy constant K = ml/mt and der transverse g‐factor g ⟂ for n‐ and p‐type lead selenide. These quantities are fitted to the experimental values by variation of only one parameter. For the anisotropy constants an excellent agreement could be achieved, whereas the computed transverse g‐factor turns out to be too large by about 30%.
Electric‐Field‐Modulated Reflectance on Tellurium
Authors: Herwig R. , Stuke J. , Weiser G.
Published: July 2007

The electroreflectance spectrum of tellurium single crystals (MOS structure) has been studied in the energy range between 0.3 and 3.2 eV and compared with the spectrum of selenium. Three transitions are observed below 0.5 eV which correspond to the threefold split valence band at point H of the Brillouin zone. The sequence of these energy bands is the same as in selenium and also the temperature shift of the gap shows a similar behaviour for both materials. At higher energies (ℏω > 1 eV), the spectrum of tellurium is much more complicated than that of selenium and a correlation to bandstructure calculations is only partially possible. The dependence of the electroreflectance response on a dc bias points to the existence of slow surface states at the interface tellurium–tellurium dioxide.
Magneto‐Microwave Kerr Effect in Semiconductors
Authors: Srivastava G. P. , Kothari P. C.
Published: July 2007

A theoretical and the experimental study of magneto‐microwave Kerr effect has been done in terms of R, the amplitude ratio of the two orthogonal elliptically polarized components of the reflected wave and δ, the phase difference between them. A double microwave bridge technique (X‐band) has been employed for the experimental measurements. The magnetic field has been applied both parallel (Faraday configuration) and perpendicular (Voigt configuration) to the direction of propagation. The experimental results for R, in the Faraday configuration, on two n‐type germanium and two n‐type silicon samples compare well with the theory, while in the Voigt configuration, there is a discrepancy in the theoretical and experimental results. The probable reasons for this discrepancy have been discussed.
Temperature Dependence of the Specific Heat of Superconductors
Authors: Nowotny H. , Grau D. , Hittmair O.
Published: July 2007

A dynamic one‐parameter model discussed in a previous paper is used to calculate the temperature dependence of the electronic specific heat of superconductors from the grand canonical potential. Deviations from the law of corresponding states are obtained and the numerical results show that the experimentally measured electronic specific heats of superconductors with strong or intermediate electron‐phonon interaction are very well reproduced. In particular the predictions of the model for the strong‐coupling superconductor lead are discussed.
Bound Electron States in the Strain Field of a 60° Dislocation in Germanium
Authors: Claesson A.
Published: July 2007

Dislocations in a crystal have a great influence on the states of electrons and phonons. As to electrons the effect of the dislocations is especially noticeable in semiconductors where the number of charge carriers normally is very small. The aim of the present paper is to find the potentials which describe the interaction between electrons and the strain field of a 60° dislocation in germanium. These potentials give rise to bound states with localized electrons.
A Theoretical Estimate of Acoustic‐Emission Stress Amplitudes
Authors: Malén K. , Bolin L.
Published: July 2007

A theoretical estimate is made of the stress amplitude for acoustic emission due to the sudden local change of an inelastic strain. The source may thus be e.g. dislocation motion, crack propagation, twinning or martensitic transformation. The dynamic aspect of the acoustic emission event is emphasized. The estimates have been compared with some experimental results reported in the literature and a reasonable agreement is found.
Electronic Properties and Defect Structure of Ti407: Correlation of Magnetic Susceptibility, Electrical Conductivity, and Structural Parameters via EPR Spectroscopy
Authors: Houlihan J. F. , Mulay L. N.
Published: July 2007

Variable temperature EPR studies of polycrystalline Ti4O7 and preliminary single crystal studies have been interpreted in relation to the static magnetic susceptibility, electrical conductivity and X‐ray diffraction data obtained on Ti4O7 samples from the same chemical run. This has facilitated the calculation of the mobility, the electrical conductivity, and the electronic effective mass in both the metallic and semiconducting regions of Ti4O7. Below ≈ 149 K a hopping mechanism dominates the conduction properties and at ≈ 120 K, μhop ≈ 4 × 10−6 cm2/Vs and σcal ≈ 1.49 × 10−3 (Ω cm)−1. This latter value is in good agreement with σmeas ≈ 3 × 10−3 (Ω cm)−1 obtained experimentally. An electronic effective mass of 5.6 me has been obtained for the semiconducting region and is consistent with a value of ≈ 5 me determined from thermoelectric and Hall effect data for the low temperature phase of Ti2O3. Above 149 K optical mode phonon scattering and ionized defect scattering combine to yield a total mobility of μT ≈ 0.6 cm2/Vs and σcal ≈ 1.43 × 103 (Ω cm)−1 which is in excellent agreement with the electrical conductivity results at 295 K.
Theory of Raman Scattering by Polaritons Due to Spatial Dispersion
Authors: Sindeev Yu. G. , Granovskii V. G.
Published: July 2007

The theory of Raman scattering (RS) by polaritons in the infrared range of frequencie‐when the optical nonlinearity of the crystal is due to spatial dispersion (SD) is develop ed. It is demonstrated that the RS in centrosymmetric crystals may be observed due to this nonlinearity. The RS cross section due to SD by the phonons and polaritons of lower and upper branches is calculated by a Green's function method. Anumerical estimate of the RS cross section due to SD is given for the case of sodium chloride.
The Polarised Raman Spectra of Ferroelectric and Non‐Ferro‐electric Potassium Lithium Niobate
Authors: Siapkas D. , Clarke R.
Published: July 2007

The polarised Raman spectra of two potassium lithium niobate compositions are presented. The first, a nearly stoichiometric ferroelectric version, K5.9Li3.8Nb10O30, exhibits a strongly temperature dependent A1(z) spectrum near the Curie point. This is held to be indicative of soft mode behaviour. The relationship between structural, dielectric and Raman measurements in this material is discussed. Measurements of the integrated intensity of the A1(z) modes, as a function of temperature, are presented and an estimation of the room‐temperature spontaneous polarisation is deduced. The A1(z) modes persist for tens of degrees above the Curie point indicating that there are regions of non‐zero polarisation within the crystal above the Curie point. No temperature dependence of the A1(z) mode frequencies is observed in K5.0Li2.4Nb10O30, a closely related non‐ferroelectric composition.
Herzberg‐Teller Interaction and Vibronic Coupling in Molecular Crystals. II. The Simple Model with Inclusion of a Frequency Change in the Non‐Totally Symmetric Vibration
Authors: Zgierski M. Z.
Published: July 2007

The simple model introduced in part I of this work, allowing for a theoretical investigation of symmetry‐forbidden vibronic absorption bands of molecular crystals, is extended in order to include the possibility of a frequency change of the non‐totally symmetric vibration which couples two molecular states with help of the Herzberg‐Teller mechanism. A formula for the absorption coefficient in the zero‐phonon approximation is derived and discussed. One‐ and two‐phonon regions of the spectrum are investigated.
Relativistic Theory of Low Energy Electron Diffraction: Application to the (001) and (110) Surfaces of Tungsten
Authors: Feder R.
Published: July 2007

A relativistic theory for calculating low energy electron diffraction intensities and spin polarization properties is applied to the (001) and (110) surfaces of tungsten for several angles of incidence. Intensity‐energy profiles are obtained in generally good agreement with experimental data. Relativistic effects on intensities are found to be noticeable, and appreciable spin polarization features are predicted. In particular, large degrees of spin polarization in conjunction with sizeable intensities are found in the specular beam for large angles of incidence on W(001).
Perturbation Theory with a Non‐Complete Set of Hamiltonian Eigenstates
Authors: Potapkov N. A.
Published: July 2007

A method is proposed of constructing a perturbation theory in which a non‐complete set of eigenstates of the non‐perturbated Hamiltonian is used. The expansion of the expectation value of the energy and magnetization of an anisotropic ferromagnet at T = 0 in powers of Ia/I is obtained. In this expansion the zero order, the first, and the second‐order terms are completely taken into account.
The Influence of Plasmon Damping on the Mean Free Path of Electrons for Plasmon Excitation
Authors: Ashley J. C. , Ritchie R. H.
Published: July 2007

Many‐body theory is used to calculate the inverse mean free path for plasmon excitation by an electron in a free‐electron gas with damping of the plasmon states included. The theory is applied to the special case of Al for which experimental data on damping of the plasmons are available. Numerical calculations indicate an appreciable probability for exciting plasmons by incident electrons with energies below the threshold energy predicted by “no‐damping” theories.
Elastic Constants and Lattice Stability of Quantum Crystals
Authors: Plakida N. M. , Aksienov V. L.
Published: July 2007

On the basis of the self‐consistent theory the elastic constants are calculated and the region of lattice stability of quantum crystal is found for a simple model with a f.c.c. lattice. It is shown that the second order terms in the self‐consistency equation play an essential role and should be taken into account for the correct description of the quantum crystals.
Mössbauer Spectra of (NH4)2SbxSn1−xCl6 Crystals
Authors: Yu. Aleksandrov A. , Ionova G. V. , Ionov S. P. , Baltrunas D. A. , Makarov E. F.
Published: July 2007

Mössbauer spectra of mixed (NH4)2SbxSn1−xCl6 crystals with x = 0.02, 0.06, 0.08, 0.19, 0.24, and 0.28 were investigated in the temperature range 77 to 150 K. On the basis of the obtained data a packing model of the mixed crystals is proposed. A transition is found in the crystal with x = 0.28: below a critical temperature region Sb3+ and Sb5+ ions are ordered and above they have the average valence of Sb4+. This transition is interpreted on the basis of the co‐operative interaction of electron pairs.
Optical Constants and Electronic Structure of Crystalline and Amorphous As2S3 in the 3 to 35 eV Range
Authors: Perrin J. , Cazaux J. , Soukiassian P.
Published: July 2007

By Kramers‐Kronig analysis, the complex dielectric constant tensor of monocrystalline As2S3 is deduced from energy losses in the 3 to 35 eV range suffered by a 40 keV electron beam. The weak optical anisotropy observed in this spectral range is explained and the results are discussed in terms of a valence bonding model with two groups of valence bands. Upon the amorphous to crystalline transition it is the optical transitions originating in the resonance bonds which are only influenced.
Optical Effective Mass of Holes in p‐Type AIIIBV Compounds
Authors: Filipchenko A. S. , Nasledov D. N. , Radaikina L. N.
Published: July 2007

A comparative study is made of the concentration dependences of the optical effective masses of holes in a series of p‐type AIIIBV compounds. It is shown that in all compounds studied the optical effective mass of holes begins to increase under high concentrations of carriers. A qualitative explanation is given of such increase. The comparison of the concentration dependences of mp for various compounds shows that the valence bands are similar in various AIIIBV compounds. The structure of the valence bands in AIIIBV compounds is substantially different from the structure of the conductivity bands. Therefore in theoretical calculations of different effects it is necessary to distinguish quite distinctly the dependences on the density‐of‐states effective mass and on the conductivity effective mass, i.e. to be very cautions in the use of the quasiisotropic band approximation.
Long‐Wavelength Optical Phonons in K1−xTlxCl and K1−xTlxBr Mixed Crystals
Authors: Bauhofer W. , Genzel L.
Published: July 2007

The q ≈︁ 0 lattice vibrations of mixed crystals of K1−xTlxCl and K1−xTlxBr have been observed by far infrared reflectivity measurements. Contrary to the existing assumption, the system K1−xTlxCl clearly shows a mixed‐mode behaviour similar to that of K1−xRbxI. K1−xTlxBr is either a mixed‐ or a two‐mode system. The experimental results are in good agreement with a modified version of the REI‐model.
Magnetische Bereichsstrukturen in Typ‐I‐Dünnschichtsupraleitern. I. Der Zwischenzustand
Authors: Kunze U. , Lischke B. , Rodewald W.
Published: July 2007

Die magnetflußerfüllten Bereiche in dünnen supraleitenden Schichten (Pb, In) in senkrechten Magnetfeldern wurden durch die Dekoration mit Eisenteilchen sichtbar gemacht. Die Abhängigkeit dieser Zwischenzustandsstrukturen von der Schichtdicke wurde mit theoretischen Modellen verglichen. Unterhalb einer kritischen Schichtdicke von etwa dc ≈︁ 0,1 μm wird ein Übergang von den Strukturen des Zwischenzustandes zum zweidimensionalen Mischzustand beobachtet.
Effects of Doping on the Condensed Electron–Hole State in Germanium and Silicon
Authors: Martin R. W. , Sauer R.
Published: July 2007

Radiative recombination in electron‐hole drops has been investigated for doping levels up to ≈︁1018 cm−3 in Ge and Si. It was found that the energy of the condensed state and the density of electrons and holes become dependent on excitation and on impurity concentration above 1016 cm−3. Characteristic differences of the lineshapes for the case of Ge and Si are discussed.
EPR of BaCl2:Gd3+
Authors: Oosterhoff T. , Den Hartog H. W.
Published: July 2007

The g‐value and the most important crystal field parameters of Gd3+ in orthorhombic (D) BaCl2, are determined at room temperature: g = 1.994 (isotropic), b = ± 90 × × 10−4 cm−1, and b = ∓444 × 10−4.cm−1. The corresponding theoretical values are g = 1.993, b = 85 × 10−4 cm−1, and b = −324 × 10−4 cm−1. A comparison of the results with values for Eu2+ and Gd3+ ions at Pb2+ sites in PbCl2, and PbBr2, is made.
Quantum‐Mechanical Study of Rosette‐Motion Channeling
Authors: Tamura A. , Ohtsuki Y. H.
Published: July 2007

Quantum mechanical treatment of the “Rosette‐Motion” channeling of energetic electron beams is developed. Energy levels and scattering angles corresponding to channeling are determined. Detailed calculations are performed for W〈111〉 for various energies. The lifetime of such quantum states is discussed making use of the mean free path due to lattice vibrations.
Shape of the Cyclotron Resonance Absorption Line of Polar Semiconductors: n‐InSb at 337 μm
Authors: Palmetshofer L. , Kranzer D.
Published: July 2007

The shape of the cyclotron resonance absorption line of n‐InSb samples is investigated. Experiments were carried out using a HCN laser beam. The temperature range considered being 77 to 150 K. According to the preparation of the sample surface different shapes of the absorption line are observed. Additionally a theory is worked out which is based on an exact numerical solution of the time‐dependent Boltzmann equation. The theoretical results are compared with the experiment.
Obtaining a Consistent Set of Thermodynamic Variables for Real Superconductors
Authors: Bostock J. , Mathews W. N. , Gregory W. D.
Published: July 2007

A method is presented for obtaining a consistent set of thermodynamic parameters and temperature‐dependent thermodynamic variables for a real superconductor. The method depends upon determining a temperature‐dependent effective interaction strength for the particular material. Conversely, given the effective interaction strength for the superconductor, the thermodynamic variables as functions of temperature can be obtained. The method is illustrated for Al, V, Ta, Nb, and Pb. The results of this approach and the McMillan theory of the critical temperature are compared for Nb, Pb, and the In‐Tl alloy system.
On the Existence of Antiferrormagnetism in Half‐Filled Narrow Energy Bands
Authors: Lindner U. , Hewson A. C.
Published: July 2007

It is shown that the spin‐dependent shift of the subbands considered by Roth for the treatment of ferromagnetic solutions of the Hubbard model plays a decisive role in making antiferromagnetism possible on this model. A relation is given which allows to calculate the Néel temperature TN for a simple cubic lattice and a half‐filled band in dependence on the parameters of the Hubbard model and which includes in the limit a criterion formerly obtained by the simple Hubbard decoupling.
Resonant States in III–V Semiconductor Compounds
Authors: Iadonisi G. , Zucchelli G. P.
Published: July 2007

A realistic model to discuss resonant states in semiconductors as GaAs and InP is developed. Analytic expressions for the energies and the widths of the resonant states are found and compared with recent experimental optical results in InP.
Effect of a Brownian Sublattice on Polariton Dispersion
Authors: Merten L. , Andrade P. Da R.
Published: July 2007

A set of coupled equations describing the effect of a disorder mechanism on polariton dispersion is given. The treatment differs from that one finds in the literature because the disorder mechanism is not taken as a second‐order perturbation. A particular solution of these coupled equations shows that all originally undamped polaritons become damped waves. They all shift in frequency. Physical properties of different wave types in an order‐disorder crystal are discussed. For the complex frequencies of the coupled waves a modified Kurosawa relation and a modified LST relation is valid. Numerical evaluations of this model shall be given in a forthcoming paper.