bluuebunny/crossref_metadata_2025 huggingface dataset:
Valence Band Structure of Tellurium from Shubnikov‐de Haas Experiments
Authors: Braun E. , Neuringer L. J. , Landwehr G.
Published: July 2007

Measurements of Shubnikov‐de Haas (SdH) oscillations in tellurium were carried out on doped, single crystals with hole concentrations of 5.9 × 1016 ≦p0 ≦ 5 × 1018 cm−3. Experiments were performed using static magnetic fields up to 15 T at several temperatures in the liquid helium range. The observed angular dependence of the periods were analysed by a method due to Mueller which yields the shape of the constant energy surfaces independent of assumptions as to the specific analytical form of the E(k)‐function. The dumb‐bell shape of the constant energy surfaces, and the small trigonal warping about the kz‐axis at the highest concentrations which were found are in agreement with the predictions of existing theories about the upper valence band of tellurium. Values are given for terms of higher order than k2 in the E(k)‐function of the upper valence band. Using the temperature and field dependence of the oscillation amplitudes the cyclotron masses and Dingle broadening temperature were determined at various carrier concentrations.
Etude de la structure électronique de de l'antimoniure d'indium de type n par une méthode de battement hyperfréquence
Authors: Ferre D. , Castelain M. , Dubois H.
Published: July 2007

Dans cet article, nous montrons que, moyennant un choix convenable de la puissance de deux hyperfréquences irradiant un cristal d' InSb n, on peut utiliser le battement qui prend naissance pur étudier la distribution électronique du cristal lorsque la température de celle‐là s'écarte pas trop de celle du réseau cristallin et en conclure à l'existence d'une bande d'impureté complètement séparée de la bande de conduction pour des concentrations inférieures à 1014 cm−3 en champ magnétiquenul. Cette interprétation est confirmée par les études réalisées en fonction du champ magnétique et de la concentration en impuretés.
Mixing of 3d and Excited Orbitals of an Iron Group Ion in a Tetrahedral Field and Its Effect on Orbital Momentum and Spin‐Orbit Coupling Coefficient
Authors: Basu C. , Majumdar D. , Ghosh U. S.
Published: July 2007

Mixing of 3d and excited orbitals such as 4p, 4d, and 4f of an ion via crystal field and the effect of this mixing on the orbital moment and the spin‐orbit coupling coefficient have been discussed for the case of iron‐group complexes of tetrahedral coordination. It has been shown that the admixture of excited orbitals to the 3d orbitals effectively reduces the orbital moment and S—O coefficient with respect to the values corresponding to pure 3d orbitals. These reductions have been estimated for different ions of tetrahedral coordination within the framework of crystal field theory. The reduction of the S—O coefficient is found to be larger than that of the orbital moment. It has been inferred that in some of the ions the reductions due to the admixture of excited metal orbitals may not be negligible when compared with those produced by the covalency effect although the latter, in general, causes a larger reduction of the two parameters.
Anisotropy of Cyclotron and Spin Mass of n‐ and p‐Type PbSe
Authors: Kästner P.
Published: July 2007

The variation of the spin splitting of Landau levels as a function of the angle between magnetic field and crystallographic axes of n‐ and p‐type lead selenide was investigated by observing magnetoacoustic quantum oscillations at 1.5 K. The main result is that within experimental error the spin mass shows the same anisotropy as the cyclotron mass. The ratio K of longitudinal to transverse mass presented in this paper is 1.70 for n‐ and 1.87 for p‐PbSe in good agreement with values reported by other authors.
High‐Frequency Conductivity of Hot Carriers in Semiconductors with Non‐Parabolic Dispersion Law in the Presence of a Magnetic Field
Authors: Almasov L. A.
Published: July 2007

The conductivity of semiconductors with respect to a weak alternating electric field in the presence of applied stationary electric and magnetic fields has been calculated. The energy band of free carriers is supposed to be isotropic but, in general case, non‐parabolic. Different special and limiting cases are considered. It is shown that the non‐parabolicity of the energy bands leads to qualitatively new results in the infrared range.
Enhancement of the Capture Rate of Excess Carriers Due to Acousto‐Electric Amplification
Authors: Nimtz G.
Published: July 2007

The recombination behaviour of excess carriers was investigated during the process of acousto‐electric amplification. The experiments were carried out with the piezoelectric semiconductor tellurium. A decrease of the lifetime of the excess carriers was observed up to four orders of magnitude depending on the intensity of the amplified acoustic flux. The new recombination effect is explained by about 1018 states/cm3 in the forbidden band. These states are a consequence of the random nature of the carrier potential energy in the acousto‐electrically amplified flux, as was shown by Bonch‐Bruevich quite recently. The high intensity flux gives rise to a density of states in the band gap analogous to disordered semiconductors.
Lattice Dynamics of Cadmium at 88 K
Authors: Toussaint G. , Champier G.
Published: July 2007

Phonon‐dispersion curves along the [0110], [1120], and [0001] symmetry directions of the h.c.p. metal cadmium have been measured by diffuse scattering of X‐rays at 88 K. A general interatomic force‐constant model has been used to fit the phonon frequencies and interactions up to at least sixth neighbours have to be taken into account. A frequency‐distribution function has been calculated and used to calculate the specific heat and anisotropic Debye‐Waller factor. Finally, by identifying the calculated frequency dispersion curves to the curves obtained from X‐ray scattering experiments, the parameters of a pseudopotential model are calculated.
Electron Paramagnetic Resonance Spectra of Ti3O5 Crystals
Authors: Schlenker C. , Buder R. , Schlenker M. , Houlihan J. F. , Mulay L. N.
Published: July 2007

EPR spectra have been recorded at 77 °K on Ti3O5, crystals which were found to be twinned by X‐ray characterization. The spectra show several weak lines and two intense lines with anisotropic g‐factors. The presence of the two main lines has been attributed to the twinning. The line intensity corresponds to a spin concentration of the order of 10−4 of the Ti3+ ions. The spectra are believed to be due to Ti2+ ions and related to the breaking of some covalent metal‐metal bonds involving the localization of come 3d electrons on one of the three different Ti sites. The line anisotropy has been ascribed to the distorted octahedral crystal field.
Quasi‐Elastic Neutron Scattering on Hydrogen in Niobium Single Crystals
Authors: Stump N. , Gissler W. , Rubin R.
Published: July 2007

Quasi‐elastic neutron scattering experiments on the system NbH0.07 have been performed with Niobium single crystals at T = 235 and 256 °C. The width of the quasi‐elastic line has been measured 1) for fixed momentum transfer |x|, changing the angle between x and a reference plane of the crystal, and 2) dependent on |x|, the x‐vector parallel to three symmetry directions. The results have been compared with theoretical half widths corrected for experimental resolution. They favour the tetrahedal site model assuming simple jump diffusion. However, in the (001) direction deviation from the predicted behaviour occurs and the obtained value of the mean residence time differs by a factor of two from that derived from the macroscopic diffusion constant assuming tetrahedral sites.
Allowed and Forbidden Hyperfine Transitions in the Electron Paramagnetic Resonance of Mn2+ Doped in Ferroelectric NaNO2
Authors: Upbeti G. C.
Published: July 2007

Some interesting observations have been made on the allowed and forbidden hyperfine transitions in the electron paramagnetic resonance of Mn2+ doped in single crystals of ferroelectric NaNO2. The observed field dependence of the spacings of hyperfine lines in the M = + 1/2 ↔ − 1/2 transition for H∥Z is related to the zero‐field splitting parameter D. An interesting result is the observation of forbidden hyperfine transitions along the Y and Z principal axes of the Mn2+ complex. The observed doublet separations are unusual and highly anisotropic necessitating the inclusion of the anisotropic term I. R. H in the spin‐Hamiltonian. The parameters for the best fit of the forbidden doublets are Q′ = −3.18 G, Q″ = +0.53 G, Rx = + 1.65 × 10−3, Ry = + 1.19 × 10−3 Rz = −0.93 × 10−3.
Monte Carlo Calculations on Electron Transport in CdTe
Authors: Borsari V. , Jacoboni C.
Published: July 2007

A theoretical analysis of high‐field electron transport in CdTe has been performed with the Monte Carlo technique for different temperatures and ionized impurity contents. The negative differential mobility is due to the combined effect of the increasing population of the low‐mobility satellite valleys and of the intervalley scattering on the mobility of the electrons in the central valley. Which of the above mechanisms is predominant depends on the particular values of physical parameters which, in the case of CdTe, are not yet well known. Ionized impurity scattering maintains its influence on the electron drift velocity also at very high applied fields, above the threshold value (around 10.5 kV/cm at 77 °K). At these fields the electron mean energy is very high. and one would expect the effect of such scattering to be negligible. This feature must not be attributed to an effect of the ionized impurities on very fast electrons but rather to the larger number of electrons that ionized impurity scattering keeps in the more randomized low energy part of the distribution function. The present theoretical results are discussed and compared with recent experimental data.
Annealing Effects on the Thermoelectric Power and a Model for Low‐Field Conduction in Amorphous Germanium
Authors: Vescan L. , Telnic M. , Popescu C.
Published: July 2007

New measurements of the temperature dependence of conductivity σ and thermopower Q in a‐Ge at different annealing stages are reported and a previous model for the low‐field conduction is developed in order to account for experimental data. The model explains the T1/4 law of the conductivity, σ = σ0exp (– M T−1/4), gives concrete expressions for σ0 and M and accounts for the small negative values of Q in the T1/4 region. An explanation for the annealing effects is sketched.
On the Theory of the Electron States and the Surface Conductivity of a Semiconducting Slab
Authors: Dimitrov H. D. , Grânǎarova E. I.
Published: July 2007

The surface electrical conductivity of a thin semiconductor film with electric dipoles on the surface is calculated. Surface electron states connected with the semiconductor–dielectric interface are investigated and the influence of the image forces on the surface conductivity is evaluated. In some cases these forces give rise to two‐dimensional surface energy bands at a depth of about 0.01 eV in the energy gap, so that they must be taken into consideration.
New Types of Superdislocations in Ordered L10 Structure
Authors: Gbeenberg B. A.
Published: July 2007

A new type of glissile superdislocations in an ordered L10 structure is proposed. Such superdislocations can arise from known glissile superdislocations with a (2 a/2) 〈110〉 Burgers vector either as a result of their dissociation, or as a result of their interaction with ordinary dislocations. Sessile dislocation configurations are discussed which arise as a result of definite transformations from superdislocations and are barriers hindering the movement of dislocations. Studies were made of specific configurations of dislocation dipoles and nodes in a given alloy, as well as some peculiarities of interaction of superdislocations with domain boundaries.
Surface Impedance of Type I Superconductors in a Weak Magnetic Field
Authors: Kaner E. A. , Yampolskii V. A.
Published: July 2007

The electromagnetic absorption is investigated theoretically in type I superconductors placed in a weak magnetic field parallel to the surface of the specimen. A shallow potential box has been considered which contains a single magnetic surface level. The energy of the surface state is calculated. At zero temperature the electromagnetic absorption threshold decreases. At temperatures of the order of the energy gap the surface impedance possesses a logarithmic singularity at the frequency corresponding to the excitation transition from the magnetic surface level into continuum. The temperature dependence of the electromagnetic absorption has been derived also.
The Band Structure of Rhodium and Its Relation to Photoemission Experiments
Authors: Christensen N. E.
Published: July 2007

The band structure of Rh has been calculated by means of the relativistic augmented plane wave method. The density of states, the joint density of states, and the energy distribution curves (EDC's) for photoemitted electrons were computed using the Gilat‐Raubenheimer integration technique. It is demonstrated that final‐state velocity modulation influences strongly the calculated EDC's through the mean free path of the excited electrons. Although this improves the agreement between theory and experiment the experimental lineshapes cannot be satisfactorily explained within the applied models. The results indicate that the present band calculation does not disagree with the optical experiments, but the photoemission process is too complex to be described in terms of the simple direct or non‐direct model.
Theory of Resolved and Unresolved Crystal Field Structure of ESR Spectra in Dilute Magnetic Alloys
Authors: Plefka T.
Published: July 2007

The influence of crystal fields on the dynamic transverse susceptibility of localized spin moments coupled to the conduction electrons in a metal is investigated. In Liouville‐space, the projector onto the subspace is introduced which is spanned by the transverse component of the conduction electron magnetization and the transition operators of the crystal field energy levels. Within the framework of projector formalism, the susceptibility is expressed in terms of a transition matrix which is then calculated in lowest order perturbation theory. The found explicit expression of the susceptibility is valid for the isothermal case as well as for the bottleneck one. The theoretical predicted resolved and unresolved ESR spectra are discussed for high and low temperature. For the bottleneck and the isothermal case, a resolved spectrum is expected when crystal field splittings are greater than the Korringa relaxation rate.
Optical Properties of CuGaS2 near the Fundamental Absorption Edge
Authors: Regolini J. L. , Lewonczuk S. , Ringeissen J. , Nikitine S. , Schwab C.
Published: July 2007

The absorption and reflection spectra of “green” and “orange” CuGaS2 crystals, prepared by chemical transport reaction, have been studied at low temperatures. The “orange” crystal presents an excitonic spectrum characteristic for intrinsic material. The triplet structure can be explained by comparison with CuCl. This configuration involves that the upper valence band, as in the case of cuprous halides, is formed by a mixing of p‐ and d‐like wave functions. The observation of a n‐ S h e by a wavelength modulation technique permits the calculation of the binding energy of the free exciton. The spectrum of the “green” sample, shifted towards the low‐energy side, is much more complicated. It is characteristic for a compound strongly perturbated by defects.
Spin Wave Spectrum and Magnetization of Magnetic Thin Films with a Rough Surface
Authors: Freese H. , Krey U.
Published: July 2007

The influence of the surface roughness on the low energy spin wave properties is treated within a quantized phenomenological spin wave theory. Up to second order in the roughness amplitude, the surface roughness can be replaced for thin films by a non‐local scattering Hamiltonian acting in two dimensions. For a surface with a random “mosaic structure”, results are obtained for the self‐energy of the magnons, for the density of states g(E), and for the magnetization as function of the temperature T. For rough films, due to the properties of g(E), the magnetization decreases faster with T than for a smooth film of equal thickness.
New Color Centers in KCl Crystals
Authors: Matsumura G. , Kuczynski G. C.
Published: July 2007

New absorption centers giving bands with maxima at 555 nm (Y) and 625 nm (Y′) at liquid‐nitrogen temperature, were observed in OH–containing KCl single crystals annealed in vacuum a t 600 °C and subsequently uv irradiated. The thermal bleaching of these bands yields F centers. Optical bleaching of Y′ yields increase of intensity of Y and F bands and vice versa. The Y and Y′ centers can be converted into F centers by compressing the crystal. This reaction is accompanied by emission of 460 nm light. Study of the effect of ambient atmospheres upon formation of these centers suggests the involvement of oxygen molecule ions present in the crystals.
Interband and Exciton Effects on Faraday Rotation near the Absorption Edge of CuCl
Authors: Suga S. , Koda T. , Mitani T.
Published: July 2007

The oscillatory behaviour of the Faraday rotation spectra near the absorption edge of CuCl is interpreted in terms of the interband and exciton effects. According to this interpretation, the positive Faraday rotation in low energy regions is predominantly due to the interband effect, while the large negative rotation a t energies just below the exciton absorption band is ascribed to the non‐rigid shift contribution of the exciton effect. Calculation based on this model is in satisfactory agreement with experiment. It is further suggested that the same effect will be also responsible for the similar oscillatory behaviour of the Faraday rotation observed in several semiconductors such as GaSb, GaAs, and CdTe.
Hyperfine Fields in Ferromagnetic Rare‐Earth Alloys
Authors: Guimaraes A. P. , Gomes A. A.
Published: July 2007

The hyperfine fields in ferromagnetic rare‐earth alloys are discussed assuming that the impurity concentration affects only the transferred hyperfine field, the effects on the band susceptibility being assumed to be small. The slope of the hyperfine field versus average spin in these alloys can be analysed in terms of this model; intermetallic systems like GdxY1−xAl2 are also considered. It is observed that the dominant contribution to the magnetization is due to d electrons, whereas the hyperfine field slope arises mostly from the interaction with the s electrons.
Temperature Dependence of Magnetoconductivity Tensor Coefficients in Pure Antimony Single Crystals at Low Temperatures
Authors: Bansal S. K. , Duggal V. P.
Published: July 2007

Few of the galvancmagnetic measurements, at low magnetic fields, as a function of temperature in the interval 4.2 to 30 °K in single crystals of pure antimony are presented. The temperature dependence of anisotropy of magnetoresistance is discussed within the framework of two‐carrier multivalley band model of the Fermi surface. The temperature dependence of mobility of electrons and holes concluded from the low field measurements is in agreement with the results of strong field measurements.
Transverse Dember Effect and Anisotropy of Carrier Mobilities in Tellurium Single Crystals
Authors: Genzow D.
Published: July 2007

Neasurenients have been made of the transverse Dember effect, photoelectromagnetic effect, Hall effect, and electrical conductivity of tellurium single crystals in the temperature range from 80 to 300 K. From this data information about magnitude and anisotropy of electron and hole mobilities have been deduced. The relaxation time for scattering of holes and electrons in tellurium single crystals without structure defects is nearly isotropic. The relaxation time for scattering by dislocations is characterized by the relation .
A Model of the Electrical Transport Phenomena in Imperfect Crystals of Copper Phthalocyanine. I. Basic Ideas and Treatment of Bulk Defects
Authors: Lehmann G. , Hamann C.
Published: July 2007

Starting from the needed simplification of the problem a model is proposed, approximating the real crystal by molecule stacks, consisting of perfectly conducting molecule discs. In this way a band scheme is found, very similar t o the observed one. On the understanding that molecule stacks break off within the crystal and considering the molecule spatial extent and molecule orientation in CuPc, the perturbation levels in the crystals are computed. They are found in a good agreement with experimentally determinedtrap levels for electrons. The geometrical extent of the perturbation justifies the neglect of the perturbation interaction between adjacent piles.
The Diffusion of Mercury in Purified KCl and the Effect of OH− on Diffusion
Authors: Allen C. A. , Fredericks W. J.
Published: July 2007

The diffusion of mercury into both purified and hydroxide doped Kci was studied. The high vapor pressure of HgCI2 required modification of the usual technique to assure constant boundary conditions. The very low solubility of mercury made accurate determination of diffusion parameters difficult. Mercury diffuses into purified KCI over the temperature range from 449 to 549 °C in accordance with the relation Ds = 8.18 × 10−5 exp (−0.57 eV/kT). Over this same temperature range the free energy of association for the mercuric ion‐cation vacancy complex varies from 0.75 to 0.80 eV, an abnormally large value for this type of association. The presence of OH‐ causes extreme distortion of the concentration‐distance curve by forming a maximum in mercury concentration well away from the surface of the crystal. The maximum is thought to arise from the formation of the mercuric ion‐hydroxide ion compound identified optically in earlier studies.
Equivalent Quantum States in dn and d5+n Electronic Configurations
Authors: Langer J. M.
Published: July 2007

It is shown that for ligand fields in which the symmetries are subgroups of the full rotational group, the sequence and relative energies of the states with maximum spin are the same for dn and d5+n (n ≦ 5) configurations. Possibility of the generalization of this theorem t o other 1n and 121+1+n configurations is discussed. As an example, wave functions and relative energies for the crystal field d‐states in a tetrahedral environment are given.
Analysis of Uniaxial Stress Effect on the Free Exciton Line in GaAs
Authors: Lavallard P.
Published: July 2007

Photoluminescence from free excitons in GaAs has been studied by Gilleo et al. [4] for [100] stresses up to 500 kp cm−2. An analysis of their results is presented taking into account the spin‐exchange splitting of the exciton states and the variation with stress of the enveloppes functions of the exciton states. It is shown that the quasi‐cubic model can well explain the observed intensities of the lines.
Properties of Extraordinary Polaritons in LiNbO3
Authors: Posledovich M. , Winter F. X. , Borstel G. , Claw R.
Published: July 2007

On the basis of corrected assignments of the optical phonons in LiNbO3 the dispersion branches of extraordinary polaritons have been calculated for different wave vector directions with respect to the optic axis of the material. A fundamental feature of extraordinary polaritons is the lifting of crossing points between dispersion branches for wave vector directions different from the principal directions. A first experimental observation of this effect is presented and has been compared with theoretical data. Furthermore the experiments allow a simultaneous observation of the lowest frequency ordinary and extraordinary polariton branches.
Multiple Scattering Theory and Pseudogaps in Amorphous Covalent Semiconductors
Authors: John W.
Published: July 2007

The electronic density of states of amorphous covalent semiconductors is investigated using the multiple scattering theory of nonoverlapping muffin‐tin potentials. In the nearest neighbour approximation an expression is derived for the density of states which relates it to the density of states of a simple tight‐binding Hamiltonian. Numerical calculations for amorphous sps‐bonded C and amorphous Si show the existence of a pseudogap which is determinated by short‐range order.
Influence de la direction de propagation, par rapport au champ magnétique, sur l'atténuation d'ondes ultrasonores dans l'antimoniure d'in dium dégénéré
Authors: Prieur J.‐Y.
Published: July 2007

Nous présentons des résultats expérimentanx sur la variation de l'atténuation ultrasoliore avec l'angle entre le vecteur d'onde et le champ magnétique dans des cristaux d'antimoniure d'indium dégénérés. Nous montrons que les oscillations de Haas et van Alphen doivent ětre associées à celles u temps de relaxation. Une mesure du temps de relaxation eut proposée.
The Spin‐Wave Contributions to the Low‐Temperature Specific Heats of MnPt3 and FePd3
Authors: Anderson D. A. , Cragknell A. P.
Published: July 2007

Using the published results of inelastic neutron scattering experiments on MnP3 and FePd, we have calculated the spin‐wave contribution to the specific heat of each of these materials. While the results show aT3/2 temperature dependence at low temperatures. substantial deviations from this law were obtained for temperatures above about 10 K.
Unified Perturbation Treatment for Phonons in Metallic Covalent and Ionic Crystals
Authors: Eschrig H.
Published: July 2007

An interpolation formula which interpolates the exact Hartree expression for the electronic part of the dynamical matrix between the limits of strong and weak crystal potentials and which becomes rigorous in the zero wave vector limit is used to avoid to the problems connected with the inversion of the screening tensor. In the ionic part of the dynamical matrix the Gaussian charge densities of the usual Ewald technique are replaced by the true charge densities around each ion in the unperturbed crystal. The arising expressions are transformed in such a way that the compensation with the corresponding terms in the electronic part can be done explicitely. As a result one gets an alternative formula for the dynamical matrix of simple metals, a practicable formula for transition and noble metals and covalent crystals, and a rather simple expression for ionic crystals which has some link to the physical picture of a shell model. It is shown that the given theory describes the qualitatively correct pressure dependence of the phonon frequencies.
Vibronic Interactions and Magnetic Dipole Effects in the Polarized Crystal Spectra of Diaquobismethoxyacetato Co (II)
Authors: Hu P. D. , Companion A. L.
Published: July 2007

Polarized absorption spectra of single crystals of diaquobismethoxyacetato Co(II) hare been measured at room and liquid nitrogen temperatures. The temperature dependence of oscillator strengths indicates that both vibronic and magnetic dipole transition mechanisms are operative. Selection rules within the C2t, point group permit assignment of major absorption peaks to transitions from a 4Bg ground state.
Pseudopotential and Lattice Vibrations of Simple Metals
Authors: Prasad B. , Srivastava R. S.
Published: July 2007

The phonon dispersion curves and binding energies of Rb, Cs, and Ba have been calculated using Harrison's modified point ion pseudopotential with two adjustable parameters. The exchange and correlation effects in the Hartree dielectric function have been adequately considered. The theoretical results are found to be in good qualitative agreement with the experimental results.
On the Theory of Phonon Electroreflectance of Light from Semiconductors
Authors: Dmitruk N. L.
Published: July 2007

The influence of a non‐uniform electric field on the reflectance of light by a semiconductor in the reststrahlen band (phonon electroreflectance) is considered. The calculation is carried out using the phenomenological model in which only the linear term of frequency and oscillator strength expansions in the local electric field is used for bulk phonons. The integral and differential phonon electroreflectance (PhER) are calculated for an arbitrary relation between wavelength λ and thickness I of the surface space charge region (SCR). The spectral and field dependence of the PhER is analysed.
Elektronenstruktur und Oberflächeneigenschaften von Übergangsmetallen
Authors: Goryachev Yu. M. , Podchernyaeva I. A.
Published: July 2007

Nit dem GO LCAO‐Verfahren (tight‐binding‐Näherung) wird das Energiespektrum der Valenzelektronen für die 〈111〉‐ und (110)‐Flächen von Mo‐, W‐ und Re‐Kristallen (mit hypothetischer k.r.z.‐Struktur) für die Analyse der Größenund der Elektronenbesetzung ders‐ und d‐Zustande der Oberflächenatome berechnet. Es wird gezeigt, daß die Anisotropie der Elektronenaustrittsarbeit mit der Besetzung der Elektronenzustände der Oberflächenatome zusammenhängt.
Energy Band Structure for Si and Ge from a Nonlocal Separable Potential Model
Authors: Fock H.
Published: July 2007

If the local potential at each lattice site is replaced by a nonlocal projection operator, the eigenfunctions of the electrons can be eliminated from the Schrödinger equation. The method of Green's functions is utilized and calculation of the energy bands is done assuming projection potentials, which are formed by s‐ and p‐symmetrical Gauss functions. Quantitative agreement is obtained between calculated and observed transition energies, but no parallel bands over a larger range along the A‐axis can be produced. So the curvature of this energy band model which contains four parameters differs from other band calculations.
Application of Vibronic Model to Stress‐Induced Polarization of F‐Centre Emission
Authors: Muramatsu S.
Published: July 2007

A vibronic model is applied to the stress‐induced polarization of the F‐center emission, and a comparison of calculations is made with experimental results by Hetrick and Compton [2]. A value obtained for a stress coupling constant with Eg, symmetry is consistent with parameters previously estimated from comparison of a model to experiments of magneticfield induced circular polarization and Stark effect. The temperature dependence of the stress‐induced polarization can be explained by assuming that an odd‐parity internal field changes with temperature.
Effect of Dislocations on Perturbed Angular Correlations in Paramagnets
Authors: Denisenko G. A. , Khaimovich E. P.
Published: July 2007

The effect of the elastic fields of dislocations on γ‐ray perturbed angular correlations in paramagnets has been investigated. The γ‐ray directional correlations are perturbed by magnetic hyperfine and nuclear Zeeman interactions. The crystal imperfections cause the hyperfine splittings to vary from ion to ion. The frequency‐averaged perturbation factor taking into account these variations is obtained. For obtaining the frequency distributions a statistical method is used. Numerical calculations are performed for the case of the Er3+ion in CaF2.
The Application of Perturbation Theory and Pseudo Alloy Atom Model to the Cs–Rb and K–Rb Systems
Authors: Tanigawa S. , Doyama M.
Published: July 2007

The pseudopotential theory of metals is applied to the Cs–Rb and K–Rb alloy systems using the pseudo alloy atom model. The total binding energies, bulk moduli, and heats of solution were calculated as a function of alloy compositions. The calculated values of the total binding energies showed reasonable agreement with experimental data. The results predict the presence of a mixture of two phases at low temperatures. It is found that previous pseudopotential approaches are justified only for an alloy in which the electron density is nearly uniform. The present model is not subject to such a limitation.
Pulse Saturation of the O EPR Signal in Some Potassium Halides
Authors: Cornelis E. , Boesman E.
Published: July 2007

The results of spin–lattice relaxation (SLR) measurements of the O oxygen centre in KCl, KBr, and KI are given. The pulse saturation method was used. The results are compared with those of Castner, who used a different experimental technique, and the causes of the differences are briefly analysed. A theoretical calculation of the direct process, different in some respects from previous ones, is also summarized. The results of a numerical calculation for the angular variation of the SLR are given and discussed.
Single‐Phonon Contribution to the Hopping Low‐Field Magnetoresistance of Amorphous Semiconductors and Glasses
Authors: Čáapek V.
Published: July 2007

The change of sign of the low‐field hopping magnetoresistance at low temperatures is shown to be compatible with a previously reported theory of the hopping conduction in magnetic fields. When limiting to the low‐temperature single‐phonon contribution the longitudinal and transversal magnetoresistances are found to be the same in accordance with the experiment.
M center reorientation in CaF2
Authors: Collins W. C.
Published: July 2007

The reorientation efficiency of M centers in CaF2 is found to be directly proportional to the M+ center concentration. The wavelength dependence of the efficiency for optically induced reorientation is also found to agree with the M absorption rather than the MF. We propose that the M centers in CaF2 reorient under ultraviolet excitation by first photoionizing, i.e., becoming an M+ center; this M+ center then absorbs light in the same spectral range and reorients during a nonradiative transition from the excited state. This agrees with the mechanism found previously in the alkali halides.
Magnetic field dependence of the electron‐phonon correlation effects in polar crystals
Authors: Kaetheuser E. P. , Negrete P.
Published: July 2007

Polaron properties in magnetic fields of arbitrary strengths are studied in the framework of an improved Landau‐Pekar approach. General expressions of the ground state energy and longitudinal effective mass are given. It is shown that the introduction of the electron‐phonon correlation effects in Landau‐Pekar's approximation leads to a 10% lower value of the longitudinal effective mass. The correlation effects are reduced when a high magnetic field is switched on.
Spin wave amplification in ferromagnetic semiconductors
Authors: Coutinho Filho M. D. , Miranda L. C. M. , Rezende S. M.
Published: July 2007

The damping coefficient of magnons interacting ‐with drifting carriers in ferromagnetics semiconductors for both k l > 1 and k l < 1 regimes is calculated. It is shown that for CdCr2Se4 the amplification factor can be of the order or greater than the losses of spin waves due to other effects.
Dielectric susceptibility of 〈100〉‐type paraelectric defects in varying static bias fields and simulated random stress
Authors: Minor P. C. , Dick B. G.
Published: July 2007

The effect of simulated random stress on the static dielectric susceptibility of 〈100〉‐type paraelectric defects with varying bias electric fields is investigated. The results are applied to the interpretation of measurements of dielectric loss due to OH − defects in K Br by Reymann and Lüty.
Atomistic expression of thermal expansion of metallic elements
Authors: Plendl J. N.
Published: July 2007

As it was shown very recently, the coefficient of the thermal expansion of metallic elements is proportional to the valency which is effective between any two next neighbor atoms within the atomic coordination of crystalline structure, at ambient conditions of pressure and temperature. Presently, the Grueneisen parameter γ is shown to be a function of the atomic coordination number. Combining the two results leads to an expression for the thermal expansion based entirely on absolute constants and atomic parameters. Seventy percent of 48 elements, examined in this way, obey a single atomistic expression. The remaining thirty percent, belonging to group II, subgroup IVB, and to the lanthanides, have, in principle, the same expression, however, with different numerical factors, indicating a relative reduction of the thermal expansion, which increases in that order.
Self‐diffusion in silver at low temperatures
Authors: Lam Nghi Q. , Rothman S. J. , Mehrer H. , Nowicki L. J.
Published: July 2007

Self‐diffusion in silver single crystals was measured at temperatures between 270 and 500 °C. The diffusion coefficients were in the range of 3×10−18 to 2×10−13 cm2/s. The results indicate that the Arrhenius plot is curved owing to a large divacancy contribution and that the activation energy for diffusion by divacancies is temperature dependent due to a partial dissociation of the divacancies. The best values of the parameters for diffusion by monovacancies are Do= 0.041 cm2/s, Q = 1.76 eV.
Effective charges and lattice dynamics of zincblende structure crystals
Authors: Mani K. K. , Singh R. P.
Published: July 2007

In an earlier paper (referred to as I) effective charges for a number of II‐VT and III‐V compounds have been obtained from a model of the chemical bond in these crystals. In the present paper, the dynamics of GaAs is studied using a variety of rigid‐ion models and some empirical rules are deduced regarding their accuracy. These rules are used to evaluate the zone‐boundary phonon frequencies for CdTe, InSb, and AlSb, which have nearly the same effective charges (in the scheme of the present work) as GaAs. Phonon frequencies have also been calculated for ZnS, which is more ionic than the crystals mentioned above. The two and three phonon spectra of AlSb are calculated in order to show a possible way of refining lattice dynamical calculations.
Etude des transitions optiques dans MgO:Ni2+ par dichroïsme circulaire magnétique
Authors: Régis M. , Farge Y. , Fontana M.
Published: July 2007

Circular magnetical dichroism experiments, performed in the near infra‐red absorption spectrum of the Ni2+ ion in MgO crystals, at temperatures between 1.8 and 4.2 °K, show that the F3, F4 components of the 3T2g level are split. The presence of a dynamic Jahn‐Teller effect on the F4 component is also deduced.
Intra‐band electron pairing in the presence of a radiation field
Authors: Shankar R. K. , Sinha K. P.
Published: July 2007

A semiconductor with almost overlapping conduction bands b and c is considered. It is found that an attractive interaction leading to superconductivity can be induced between electrons in the conduction band b by a strong radiation field of monochromatic photons whose energy differs slightly from the band gap Ebc. The mechanism is the exchange of a photon and a phonon between the interacting electrons and the interaction is found to be proportional to the photon density.
Thermoreflectance spectra and energy band structure of ZnGeP2 crystals
Authors: Raudonis A. , Grigoreva V. S. , Prochukhan V. D. , Šileika A.
Published: July 2007

The thermoreflectance spectra of ZnGeP2 chalcopyrite crystals have been investigated with polarized light in the spectral region 2.0 to 5.0 eV at 120 and 320 °K. Three structures (2.46, 2.53, and 2.59 eV at 120 °K) due to the optical transitions derived from T15 — T1 transitions in sphalerite have been observed by 0.4 eV above the fundamental absorption edge. Crystal‐field and spin‐orbit splittings of the valence band were found to be 0.084 and 0.075 eV, respectively. At higher energies eight thermoreflectance peaks strongly dependent on polarization of light were observed. They were attributed to optical transitions derived mainly from transitions responsible for E1 E1 + Δ1, E0 and E2 structures in the optical spectrum of GaP, the closest binary analogue of ZnGeP2.
Kinetic Phenomena in Semiconductors with Narrow Forbidden Gaps at Resonance Scattering
Authors: Geigin A. P.
Published: July 2007

The scattering of current carriers in degenerate semiconductors with narrow forbidden gap has been considered for the case when the scattering at the ion core potential predominates. To obtain the scattering probability the Green's function method has been used. The calculation of relaxation time due to the narrow forbidden gap and the short range nature of the potential has been carried out in a two‐band model. It is shown that taking into accound the second band leads to the renormalization of the ion core potential. The resonance scattering of carriers at small width virtual level has been discussed. Conductivity, thermopower, and longitudinal magnetoresistance have been calculated. It is shown in particular that the magnetoresistance in the case of resonance scattering is negative and anomalously great.
Properties of CsBr Derived from the Phonon Density of States
Authors: Daubeet J. , Jex H. , Müllner M.
Published: July 2007

Detailed calculations are presented for the one‐ and two‐phonon density of states in CsBr. These densities are based on models fitted to phonons determined by inelastic neutron scattering. Most of the 800 phonons are in off‐symmetry directions. The densities and physical properties of CsBr derived from integrals over the frequency distribution are compared with optical measurements (infrared absorption, Raman scattering, infrared absorption from U‐centers) with caloric data (specific heat, frequency moments), and with elastic scattering experiments (Debye‐Waller factors, Debye temperatures).
Einfachgleitung in Natriumchlorid auf {110}‐ und {100}‐Ebenen
Authors: Franzbecker W.
Published: July 2007

Eine Schubapparatur wurde entwickelt zur Verformung von NaCl‐Kristallen mit konstanter Geschwindigkeit. Es wurden quantitative Schubverfestigungskurven auf (110)‐Ebenen aufgenommen. Bei Fassungsabständen Δ < 3 mm erfolgte bis 25% Einfachgleitung. Die Verfestigung war nur wenig geringer als im Bereich I druckverformter Proben. Ebenso konnte die Schubverfestigung auf (100)‐ (aber nicht auf (111)‐)Ebenen bei verschiedenen Temperaturen gemessen werden. Die Gleitebenen wurden durch Elektronen‐mikroskopie von Oberflächenabdrücken ermittelt. Die Ergebnisse werden im Zusammenhang mit Verfestigungstheorien von Hesse und Frank diskutiert. τ0auf (100) wird mit elektrostatischer Wechselwirkung zwischen (100)‐Versetzungen und Ca2+‐Verunreinigungen erklärt. Fur τ0 auf (111) wird aus Druckverformungen eine untere Grenze angegeben.
NMR and NQR Properties of Liquid In
Authors: Halder N. C.
Published: July 2007

The pseudopotential method in the theory of liquid metals and the experimental atomic interference functions have been used to investigate the temperature dependence of the Knight shift Ks and nuclear spin relaxation rate 1/T1 in liquid In. From this study, a value for the uniform exchange enhancement factor η = 1.65 has been predicted which agrees well with that estimated by Dupree and Seymour η = 1.58. With this η, K have been determined which are found to be in good agreement with the experimental data of Warren and Clark. These results seem to suggest that the core polarization contribution to Ks could be 25% of the direct shift and the exchange enhancement could be as large as 39% of Kstheo. From the present study the magnetic and quadrupolar contributions to Tl turn out to be T1 m = 0.538ms and T1 q = 0.960 ms, respectively, at 170°C.
Optical Absorption and Luminescence of I‐Centers in KBr
Authors: Takahashi M. , Saidoh M. , Itoh N.
Published: July 2007

Optical absorption and luminescence of interstitial ion centers, the I‐, IA(Na), and IA(Li) centers in KBr are studied. Two optical absorption bands associated with each center are identified around 230 nm and the separations of the two bands for the I‐, IA(Na), and IA(Li) centers are 0.31, 0.39, and 0.35 eV, respectively. These two bands are ascribed to the transition to the spin‐orbit doublet, E5/2 and 63/2, and the increase in the width of the lower energy band in the order of the I‐, IA(Na), and IA(Li) centers is ascribed to the removal of the degeneracy of G3/2 in the C3 v symmetry. On the basis of the similarity of the I‐center luminescence and recombination luminescence, it is suggested that the I‐center luminescence is essentially caused by the recombination of (Br + e)*. The relaxation processes from the excited Br− at the interstitial site to the (Br + e)* at either the singlet or triplet states are discussed.
Ferroelectric Transitions in KH2PO4 and KD2PO4 Studied by Infra‐Red Polarized Reflection
Authors: Levin S. , Pelah I. , Wiener‐Avnear E.
Published: July 2007

The polarized infra‐red reflection spectra (250 to 4000 cm−1) of single crystals of KH2PO4 and KD2PO4 were measured at various temperatures above and below the ferroelectric Curie temperature. The results were compared with previous absorption measurements and allow better assignment of the infra‐red active modes. The existence of strong coupling between certain PO4 modes and low frequency hydrogen modes is deduced from the abrupt spectral changes on crossing the ferroelectric phase transition. This coupling results from the extremely anharmonic nature of the potential wells along the hydrogen bonds, as is also demonstrated by the KD2PO4 results. The build‐up of the line strength of the transverse hydrogen mode was related to the establishing of the spontaneous polarization below Tc. The two phase transitions observed in the KD2PO4 reflection spectra lead to the conclusion that KH2PO4 crystalline nucleation exists on the surface of KD2PO4 single crystals.
Photoelectric Properties of the Lead Chalcogenides
Authors: Cardona M. , Langer D. W. , Shevchik N. J. , Tejeda J.
Published: July 2007

The energy distribution spectra of electrons photoemitted from the lead chalcogenides by 48.4, 40.8, and 21.2 eV photons have been measured. Both the valence band and the 5d electrons of Pb are observed in these spectra. The valence band portions exhibit considerable structure which is compared with theoretical calculations and with recent X‐rays photoemission work. The d‐electrons spectra are extremely sharp (line width 0.5 eV). They are also compared with theoretical predictions (OPW, KKR, and pseudopotential calculations), with the result of X‐ray photoemission, and with the corresponding spectra of pure Pb. A discussion of the relative intensities of the valence and d‐electron energy distribution spectra is presented.
High‐Field Transport: Collision Integrals for Small Band Gap Semiconductors
Authors: Stokoe T. Y. , Cornwell J. F.
Published: July 2007

Collision integrals are derived for polar optical, acoustic, and intervalley phonon scattering, ionised impurity scattering and carrier—carrier scattering. The full effects of band structure non‐parabolicity are taken into account.
Anisotropic Spin‐Orbit Coupling Contribution to the Zero‐Field Splitting of 3d5 Ions
Authors: Lowther J. E.
Published: July 2007

The crystal field potential contributes directly to the spin‐orbit interaction. Effective Hamiltonians describing this interaction are used to calculate the magnitude of this effect in the ground state splitting of 3d5 ions. Numerical results are given for ZnF2:Mn2+.
NMR Study of the Low‐Temperature Insulating State in the One‐Dimensional “Conductor” K2Pt(CN)4Br0.3·3H2O
Authors: Niedoba H. , Launois H. , Brinkmann D. , Brugger R. , Zeller H. R.
Published: July 2007

NMR experiments from 1.2 to 110 °K in the one‐dimensional conductor K2Pt(CN)4Br0.3·3H2O are presented. The observation of a single quite narrow NMR line, with a temperature independent position that is typical for chemical shifts of such compounds suggests that the compound is a band insulator in its ground state. The T1 data obtained at liquid helium temperature support this hypothesis. This insulating state would be due to a Peierls instability.
An EPR Study of Divacancy Centres in CaWO4
Authors: Weightman P. , Henderson B. , Dugdale D. E.
Published: July 2007

Two paramagnetic defects with spin S = 1/2 have been identified in CaWO4 after neutron irradiation. The EPR spectra of these defects fit the spin‐Hamiltonian ℋ = β S g̃ B + SÃ (I1 + I2) with g1 = 1.811, g2 = 1.785, g3 = 1.497 and g1 = 1.766, g2 = 1.774, g3 = 1.429. The hyperfine structures for both centres are identical, arising from the 14% abundant 183W isotope at two equivalent sites. The hyperfine tensors have components A‖ = 167.4 × 10−4 cm−1 and A⊥ = 87.4 × 10−4 cm−1 with I1 = ±1/2 or 0 and I2 = ±1/2 or 0. The detailed analysis of the spectra, magnitude of the spin‐Hamiltonian parameters and tensor axes are consistent with the two spectra arising from different charge states of oxygen divacancy centres located on adjacent WO complexes.