bluuebunny/crossref_metadata_2025 huggingface dataset:
Brillouin Scattering by Phonons Renormalized by Two‐Magnon Excitations in Ferromagnetic Dielectrics
Authors: Krishnasamy L. , Kumar N.
Published: July 2007

Brillouin scattering by one‐phonon‐two‐magnon interacting excitations in ferromagnetic dielectrics is discussed. The basic light scattering mechanism is taken to be the modulation of the density‐dependent optical dielectric polarizability of the medium by the dynamic strain field generated by the longitudinal acoustic (LA) phonons. The renormalization effects arising from the scattering of phonons by the two‐magnon creation‐annihilation processes have, however, been taken into account. Via these interactions, the Brillouin components corresponding to the two‐magnon excitations are reflected indirectly in the spectrum of the phonon scattered light as line‐broadening of the otherwise relatively sharp Brillouin doublet. The present mechanism is shown to be dominant in a clean saturated ferromagnetic dielectric with large magneto‐strictive coupling constant, and with the magnetic ions in the orbitally quenched states. Following the linear response theory, an expression has been derived for the spectral density of the scattered light as a function of temperature, scattering angle, and the strength of the externally applied magnetic field. Some estimates are given for the line‐width and line‐shift of the Brillouin components for certain typical choice of parameters involved. The results are discussed in relation to some available calculations on the ultrasonic attenuation in ferromagnetic insulators at low temperatures.
On Green's Tensor Funktion for a Hexagonal Crystal with Applications to Dislocation Theory
Authors: Chou Y. T. , Yang H. C.
Published: July 2007

Explicit expressions for the planar Green's tensor function defined on the basal plane of a hexagonal crystal are given. These expressions are functionally identical to those for an isotropic medium. Applications to the stress fields and energies of dislocation segments and curved dislocations are shown.
Radiative Decay of Electron‐Induced Surface Plasmons in Rough Surfaces
Authors: Sauerbrey G. , Woeckel E. , Dobberstein P.
Published: July 2007

Coupling between fast electron‐induced surface plasma waves in metals and an electromagnetic field was calculated for surfaces with statistical roughness. Measurements of electron‐induced surface plasmon radiation from evaporated silver targets (3.54 eV ≙ ≙ 350 nm peak wavelength) showed that a non Gaussian surface autocorrelation function must be assumed, which prefers medium spatial frequencies, and that the assumption of a plane surface for the surface plasmon excitation process is allowed if the surface is not too rough. With increasing roughness additionally lower frequency excitations take place. Agreement with the measured spectral distributions only could be obtained, if the optical constants of Philipp and Taft were used; from the optical constants of evaporated silver targets follows the peak intensity at 3.62 eV (λ = 342 nm), retardation taken into account.
Theory of Coupled Nuclear and Electronic Spin‐Wave Modes I. The Linear Approximation
Authors: Tucker J. W.
Published: July 2007

A quantum field theoretical perturbation method is employed in a study of the coupled nuclear and electronic spin‐wave modes that exist in magnetically ordered materials due to the hyperfine interaction. The calculation makes use of a diagrammatic technique in which the evaluation of the thermal averages of products of spin operators is facilitated by the use of the drone‐fermion representation. The dispersion relation for the undamped coupled nuclear and electronic spin‐wave modes is derived in linear theory and the contribution to the free energy from the spin‐flip part of the hyperfine interaction is found.
On the Quantum Theory of Spin Waves in an Electron Liquid
Authors: Okulov V. I. , Pamyatnykh E. A.
Published: July 2007

The basic relations of the quantum theory of the electron liquid of a metal in a magnetic field are formulated. On the basic of a proposed approximation for the kernel of the Fermi‐liquid interaction the quantum oscillations of the effective magnetic moment of the quasi‐particles are considered. Taking into account two constants of the Fermi‐liquid interaction and assuming them to be small, the frequencies of spin waves propagating across the direction of a magnetic field are obtained. The quantum oscillations of the frequencies and the spin magnetic susceptibility are discussed.
Characteristic Surfaces of Fluctuations and Critical Index for the Phase Transition in Uniaxial Ferromagnets
Authors: Klamut J. , Sznajd J.
Published: July 2007

Basing on Landau's theory which admits spatial inhomogeneities of the magnetization, the fluctuations near the ferro‐paramagnetic phase transition have been calculated. The magnetic anisotropy is shown to lead to anisotropic correlation functions which for a uniaxial ferromagnet lead to ellipsoidal isocorrelation surfaces with rotational symmetry, instead of the spherical symmetry assumed in the conventional Orstein‐Zernike theory. For the phase transition in the presence of an external magnetic field, the field and temperature dependence of the anisotropic correlation radii has been determined.
Valence Bands of Solid Hydrogen in H.C.P. Lattice
Authors: Parravicini G. Pastori , Piccini F. , Resca L.
Published: July 2007

The valence electronic states of ortho‐hydrogen crystals in h.c.p. lattice are calculated assuming space group Pca21 for the orientation of the molecules. The maximum and the minimum of the valence bands, whose width is found to be 0.080 Ryd, occur at the points X and Γ of the Brillouin zone. A detailed comparison with the energy bands of solid ortho‐hydrogen in f.c.c. lattice is considered. The modifications of the energy levels in the case of a h.c.p. disordered structure arc also discussed.
Variational Calculation of Electron‐Phonon Scattering in Heavily Doped n‐Ge
Authors: Singh D. P. , Verma G. S.
Published: July 2007

The simplified variational method has been extended to Ziman's electron‐phonon scattering and the results are applied to explain the phonon conductivity results of heavily doped n‐Ge, for which donor‐electron states merge with conduction states and phonons are scattered by donor electrons in the conduction state. The expressions for the scattering matrix elements for the electron‐phonon scattering are obtained and its contribution to the thermal resistivity is considered in the temperature range 2 to 10 °K in the presence of boundary scattering and isotopic scattering of phonons. The analysis of the thermal resistivity data reveals that the effective mass of the donor electron in the conduction state varies from 0.25 to 0.45 in the temperature range 2 to 10 °K.
Electronic Correlation Effects (Exciton Manifestation) in the Singl—Particle Band Structure of Nonmetallic Crystals I. General Theory
Authors: Stolz H. , Zimmermann R.
Published: July 2007

The effect of electron correlation on the single‐particle spectrum of electrons in nonmetallic crystals is investigated starting from the full Hamiltonian of the interacting electron system. By these effects excitons become manifest in the single‐particle spectrum entering Dyson's equation of the corresponding Green's functions via the screeningof the Coulomb potential in the self‐energy. Dyson's equation is solved to render the spectral function by a systematic perturbative approach recently introduced in connection with the electron gas problem. The single‐particle spectrum exhibits modified main bands accompanied by exciton satellites contributing remarkably to the density of states. This picture appears not to be fully obtained by the electronic polaron theory starting from a model Hamiltonian which is also investigated in this study.
Cyclotron Resonance and Quantum Oscillations of p‐Type Semiconducting Bi1−xSbx Alloys
Authors: Oelgart G. , Herrmann R.
Published: July 2007

Measurements of magnetic‐field‐dependent microwave absorption at a p‐type semiconductor, Bi0.92Sb0.08 within the frequency ranges around 35, 70, and 135 GHz are reported. The resultsof the diamagnetic resonance and the quantum oscillations of the surface impedance are discussed. Diamagnetic resonance was measured both for light holes at the point L of the Brillouin zone and for heavy holes at thepoint Tof the Brillouin zone. The light holes define three ellipsoidal Fermi bodies of relatively large prolateness. For different models the Fermi energy isdetermined from the obtained cyclotron masses and extreme cross‐sections of the Fermi surface.
Microwave Faraday Effect in Heavily Doped n‐Type Germanium
Authors: Haller H. O. , Kahlert H.
Published: July 2007

Measurements are reported of the microwave Faraday effect at a frequency of 33 GHz in samples of n‐type Ge with carrier concentrations ranging from 5 × 1015 to 3 × 1017 cm−3. From these results the anisotropy of the momentum relaxation time for pure ionized impurity scattering is found to have a value of Kτ(i) = 11 ± 1. This value is comparedwith results from previous experimental investigations and is in good agreement with theoretical predictions.
Theory of Raman Scattering from Excitons
Authors: Peuker K. , Enderlein R.
Published: July 2007

The scattering cross section for Raman lines due to the creation of excitons in the final state of the crystal is calculated. According to the selection rules Raman scattering by p‐exciton is possible for allowed interband transitions, while in the case of forbidden transitions Raman scattering will occur between the ground state of the crystal and s‐ and d‐exciton levels. Analytical expressions for the Raman cross section are derived using a Green's function formulation. In discussing the experimental prospects for the observation of Raman scattering from excitons resonance and non‐resonance scattering are distinguished. The appropriate scattering efficiencies are estimated for CdS and the yellow exciton series of Cu2O.
X‐Ray Photoemission Measurements of the Valence‐Band Density of States of Sb and InSb
Authors: Vesely C. J. , Kingston D. L.
Published: July 2007

The valence‐band density of states has been measured for both crystalline Sb and InSb by X‐ray induced photoemission using 1253.6 eV Kα X‐rays of Mg. The results are compared with theoretically determined band structure and density‐of‐states calculations. A peak observed in the InSb curve at −6 eV is interpreted as being due mostly to s—p‐like bands of the Sb.
Electronic Correlation Effects (Exciton Manifestation) in the Single‐Particle Band Structure of Nonmetallic Crystals II. Investigation of a Model
Authors: Zimmermann R.
Published: July 2007

The appearance of excitonic satellites is the most pronounced feature due to electron correlation in the band structure of nonmetallic crystals. The general theory presented in a foregoing paper [1] is applied to a model of an insulator with parameter values appropriate to the alkali halide CsI. Only four bands with tight‐binding energies and one exciton line are taken into account. Numerical results are given for self‐energy, spectral function, and density of states in the main bands and the satellite bands.
Evaluation of Acoustoelectric Wave Vectors and Amplitudes from X‐Ray Diffraction Experiments
Authors: Köhler R. , Möhling W. , Peibst H.
Published: July 2007

On the basis of a theory presented earlier [1] diffraction phenomena in CdS crystals with acoustoelectrically generated lattice vibrations are analyzed. Evidence for the generation of a second harmonic is given. Wave vectors and amplitudes of first and second harmonics are calculated from measured changes of reflection curves. The increase of the integrated intensities in dependence on the vibration amplitudes is evaluated, and a model for the transition from dynamical to kinematical diffraction behaviour is discussed.
Nernst‐Ettingshausen and Seebeck Effect of Pure and Electron‐Irradiated Tellurium at Low Temperatures
Authors: Saffert R. , Schapawalow J. , Landwehr G. , Gmelin E.
Published: July 2007

For the first time experimental data of the Nernst‐Ettingshausen effect at low temperatures in tellurium are reported. Measurements of resistivity, Hall coefficient, Seebeck coefficient, and Nernst‐Ettingshausen coefficient on the same sample allow to deduce directly the scattering exponent r, which characterizes the energy dependence of the relaxation time τ. The results clearly reveal a strong anisotropy in the scattering factor r. This is explained by the presence of dislocations. Irradiations with 1 MeV electrons at low temperatures confirm earlier results on the recovery stages I and II in tellurium. It is demonstrated that the Nernst‐Ettingshausen effect is a very useful tool to decide whether recombination or only rearrangement of radiation induced defects occurs during sample recovery.
On Variable Range Hopping near the Fermi Energy One‐Dimensional Systems
Authors: Maschke K. , Overhof H. , Thomas P.
Published: July 2007

Model calculations on variable range hopping conduction in quasi‐one‐dimensional systems are presented. It is shown that the temperature behaviour of the conductivity depends strongly on the geometry of the sample consisting of 1D strands. Comparison with an analytical theory is made. Careful numerical evaluation of an integral in the latter approach is necessary to obtain reasonable agreement with the results of the model calculation.
Nuclear Magnetic Resonance in IB–III–VI2 Semiconductors
Authors: Spiess H. W. , Haeberlen U. , Brandt G. , Räuber A. , Schneider J.
Published: July 2007

Nuclear magnetic resonance spectra of Cu63 and Al27, Ga69 and In115 have been recorded in ternary IB–III–VI2 semiconductors, which crystallize in the tetragonal chalcopyrite structure. Nuclear electric quadrupole coupling constants have been determined and are discussed in connection with the structural parameters of these compounds, which were determined by X‐ray diffraction.
Electron and Mössbauer Spectra of M2SbxSn1−xCI6 Mixed Crystals
Authors: Ionova G. V. , Makarov E. F. , Ionov S. P. , Aleksandrov A. Yu.
Published: July 2007

On the basis of MSössbauer spectra, a packing and nearest neighbour arrangement model is proposed in M2SbxSn1−x Cl6 mixed crystals. The electron spectra of the pure (x = 1) and mixed crystals are discussed in terms of this model.
Core Transitions from the Al 2p Level in Amorphous and Crystalline Al2O3
Authors: Balzarotti A. , Bianconi A. , Burattini E. , Grandolfo M. , Habel R. , Piacentini M.
Published: July 2007

The soft‐X‐ray spectra of aluminium oxide in the polycrystalline γ and amorphous forms have been investigated in detail with improved resolution using the synchrotron radiation of the Frascati electron synchrotron. In contrast to a previous measurement, it is found that the L2,3 threshold starts at almost the same energy in both forms. The sharp peaks observed at the absorption edge are interpreted as excitons. This picture fits well both with ESCA results and with the optical spectra at the fundamental edge in the ultraviolet. It is suggested that metastable excitons are responsible for the intense structure observed at (82.6 ± 0.3) eV in the ordered phase and lacking in the amorphous phase. The spectral features of crystalline alumina are analyzed on the basis of the band structure. The modifications induced by the lack of long‐range order in the amorphous samples are discussed thoroughly.
Isotope Effect in Self‐Diffusion of Cs in Single Crystals of CsI
Authors: Klotsman S. M. , Polikarpova I. P. , Tatarinova G. N. , Timofeev A. N.
Published: July 2007

The simultaneous diffusion of Cs‐131 and Cs‐137 has been measured over the temperature range 470 to 600°C. The isotope effect was measured by the method of separation of the radiations of the two isotopes. The strength of the isotope effect is E = ∫ δK = (0.54 ± 0.02) and is independent of temperature within the experimental error. This indicates that the contribution of divacancies (cation‐anion vacancy pairs) to the selfdiffusion in CsI is small and the predominant mechanism of self‐diffusion in these crystals s the diffusion via free monovacancies.
The Magneto‐Seebeck Coefficient of Bismuth Single Crystals
Authors: Uher C. , Goldsmid H. J.
Published: July 2007

The magneto‐Seebeck Coefficients α11 (B3) and α33 (B1) have been measured for pure bismuth crystals between about 20 K and room temperature in magnetic fields of up to 5.5 T. The observed behaviour has been compared with a theory due to Korenblit. It appears that a phonon‐drag component of the Seebeck coefficient at very high fields persists up to well above liquid nitrogen temperature. However, some features of the results are not in accordance with theory.
The Fermi Surface of White Tin from RF Size Effect Measurements
Authors: Matthey M. M. M. P. , Devillers M. A. C. , de Vroomen A. R.
Published: July 2007

Extensive results of RF size effect measurements on the Fermi surface of white tin are presented. The data are interpreted for the larger part and a set of unambiguously determined points on the Fermi surface is given.
Optical Pumping and Transverse Magnetic Field Effect for Excitation above the Band Edge in p‐Type Semiconductors
Authors: Fishman G. , Hermann C.
Published: July 2007

The polarization of the luminescence light shows the importance of the thermalization time for electrons, excited in the conduction band by circularly polarized light of energy larger than the band gap. The influence of the thermalization time on the oscillations of the light polarization as a function of the excitation energy is discussed and applied to GaSb and GaAs. Besides, the effect of a transverse magnetic field (”︁Hanle effect„) in a three level atomic system is extended to a semiconductor. This allows to explain the Hanle effect that had not yet been interpreted for such an energy of excitation in a semiconductor. A new form of Hanle line is predicted and the experimental conditions to observe it are specified.
An Exact Solution of a New Superconducting State
Authors: Fink H. J. , Poulsen R. S.
Published: July 2007

An exact solution of a new superconducting state is obtained which exists for DC currents larger than the critical current in thin wires. The order‐parameter is zero at all times at certain points in the whisker, thereby permitting the phase to slip at a constant rate, a consequence of which is a de potential difference between the separate singly‐connected superconducting regions. These solutions are periodic in space and lead to voltage steps in the do voltage‐current characteristic. It is proven in the limit when the zeros of the order‐parameter are far apart that these solutions are stable.
State Equation of the Ising Model in the Ladder Approximation
Authors: Sadreev A. F.
Published: July 2007

The three‐dimensional Ising model for the case S = ½ in an external magnetic field is considered by the diagram expansion of the Green temperature function. The state equation of the Ising model is proposed in the ladder approximation. The calculation of the state equation is given as magnetization curves for the temperature region T ⪆ Te and for magnetic fields H = 18 and 5 kOe. Also the Tyablikov equation is solved for the same temperatures and magnetic fields. The comparison shows a better agreement of the ladder approximation with the experimental data than the molecular field approximation or the Tyablikov equation.
The Influence of “Rotational” Lattice Deformation States on the F Center Emission
Authors: Ascarell G.
Published: July 2007

Recent ENDOR measurements of the relaxed excited state of the F center indicate that this state is p like. Previous theories of the temperature dependence of the radiative lifetime of the F center and of the Stark effect in emission are based on the assumption that the excited state is s like with an admixture of the p like states produced by the interaction with Γ modes. The present model supposes instead an extended p like excited state and a large lattice relaxation of Γ symmetry. The electronic state and the associated lattice are described by an appropriate vibronic state. It is assumed that a series of rigid rotator “rotational” states can be associated with each of the forementioned vibronic states. These “rotational” states are interpreted as describing the rotation of the center of mass of the nearest neighbour ions around the geometrical center of the vacancy. The Stark effect can be explained as having both an electronic and an ionic component. The latter is very much enhanced by the local electric field produced by the change of the electronic charge distribution resulting from the applied field. The ionic contribution to the Stark effect is larger than the electronic one. The changes of lifetime produced by the applied field do not depend on the direction of polarization of the emitted light in agreement with the experimental result. The major difficulty of the model is that it predicts no polarization of the emission. This is contrary to the experimental result. To explain the observed effect a selective population of some of the pi states must be assumed during lattice relaxation in a crystal subject to an external electric field.
Temperature Dependence of the Nuclear Spin Relaxation Rate of Liquid l15In
Authors: Halder N. C.
Published: July 2007

Temperature dependence of the atomic structure and self diffusion coefficient have been considered to predict the temperature dependence of the nuclear magnetic relaxation rate W1m and the nuclear quadrupolar relaxation rate W1q. The present calculation indicates that substantical a mount of the relaxation rate comes from the nuclear quadrupolar interaction. While Wlm increased from 3.677 to 6.894 ms−l, W1q, decreased from 0.276 to 0.070 ms−1 in the temperature range 170 to 650 °C.
On the Theory of Rate Processes in Condensed Media
Authors: Fain V. M.
Published: July 2007

A general theory of electronic transitions in condensed media is developed which describes in particular various possible chemical reactions in condensed media. The approximations used are: the Born‐Oppenheimer adiabatic approximation, the Condon approximation to describe the dependence of the matrix elements of the electron transition, and the harmonic approximation to describe the nuclear motion in the initial and final electronic states. In the framework of these approximations general expressions are obtained for the rate constants of the corresponding reactions. In a certain approximation these constants can be reduced to the form given by the Eyring theory of rate processes. In the other region the expressions for the rate constants are obtained which are of an essentially different character and are interpreted in terms of the theory of the multiphonon transitions. Reactions are considered which occur only with a conformation transition of the system as well as those which are accompanied by conformation transitions and by breaking of a chemical bond.
Far‐Infrared and Raman Studies on (NH4)Cl1−xBrx Mixed Crystals in the Cubic Phases β and δ
Authors: Bauhoper W. , Genzel L. , Jahn I. R.
Published: July 2007

The lattice modes in the cubic phases β and δ of the mixed crystal system (NH4)Cl1−xBrx are investigated by far ir and Raman spectroscopy. The system (NH4)Cl1−xBrx shows an optical one‐mode behavior. Therc is sonie evidence for a two‐mode behavior in the acoustical frequency region.
Piezoelectricity of the Cuprous Halides
Authors: Lawaetz P.
Published: July 2007

Recent data on the elastic and piezoelectric constants of the cuprous halides are analysed by a method previously proposed by the author. The results confirm that the same constant ratio between polar quadrupole and dipole strengths applies to the whole family of tetrahedrally coordinated semiconductors.
Atomistic Formulation for the Melting Point of Metallic Elements
Authors: Plendl J. N.
Published: July 2007

The formulation for the melting point of metallic elements, derived from relations recently deduced from an analysis of the infrared spectra of solids, involves three atomic characteristics which decisively determine the melting point. They are: the critical amplitude of the thermal vibrations, the atomic coordination valency and a structural parameter, the reciprocal of which is proportional to the atomic packing density. The higher the bond strength of the atonis within the atomic coordination in the lattice (atomic coordination valency) and the lower the collision frequency of the vibrating atoms (proportional to the atomic packing density and to the eigen frequencies), the higher a temperature is required to produce the critical amplitude of the atomic vibrations, which eventually causes the breakdown of the lattice bonds, and so starts the melting process. The formulation has been verified by the agreement obtained between experimental and calculated data of 20 metallic elements with strong bondings. In relating the critical amplitude of the atomic vibrations with the data of full‐range thermal expansion up to the melting point, an atomistic explanation of the phenomenon of thermal expansion has been developed, without recourse to asymmetrical vibrations, nonexistent in metallic elements with cnbic structures.
Polarization of the Luminescence of Cubic ZnS:Mn Single Crystals
Authors: Scharmann A. , Schwabe D.
Published: July 2007

The polarization of the visible luminescence of cubic ZnS:Mn single crystals under excitation with light has been investigated. The influence of birefringence of faulted ZnS on the polarization results has been calculated. The 585 nm emission band, attributed to Mn as impurity, is never polarized, whereas other emission bands at 700, 475, 410, and 385 nm show polarization under polarized excitation. The experimental results exclude band‐models. The 585 nm emission probably originates from a Mn‐center with symmetry Td. The other emission bands can only originate from centers having symmetry C3v, C2v or Cs.
Contribution of Plasmon and Quasi‐Elastic Scattering to the Kikuchi Structures of Si Measurement and Comparison with the Dynamical Theory
Authors: Meyer‐Ehmsen G. , Siems A.
Published: July 2007

Absolute intensity measurements of the Kikuchi structures in the electron diffraction diagram (75 keV) of a thin Si single crystal have been carried out. The contributions of plasmon and quasielastic scattering have been measured separately by energy analysis. The measured line profiles and band edges are compared with the theory. From the intensity distribution due to plasmon scattering the structure potential V220 and the absorption potentials P000 and P220 could be determined. From the shape of the band edges it can be deduced that the contribution of Umklapp processes to the plasmon scattering is less than 5%. The intensity profile of the quasielastic scattering can mainly be interpreted by phonon scattering.
Luminescence and Optically Detected EPR of Close F‐Center Pairs in KCl
Authors: Schnegg P. A. , Jaccard C. , Aegerter M.
Published: July 2007

By an appropriate optical treatment at RT the distance separating the members of F‐center pairs can be decreased, giving rise to different optical and magnetic properties, revealed by the existence of a spin dependent non‐radiative disexcitation mechanism. A model with an exchange spin‐spin interaction is analyzed and compared with experiments at LHeT (variation of the luminescence with an applied magnetic field, optical detection of the EPR, and relaxation processes). The observed effects are related with population changes in the ground state caused by optical pumping and they are sensitive to the mixing of the states produced by the different interactions. The average exchange energy is found to range between the hyperfine and the Zeeman energy depending of the state of aggregation. The paramagnetic resonance occurs in the ground state (g = 1.998, linewidth 52 G) and the relaxation times range between 25 and 250 ms, depending of the optical pumping rate. The relation predicted by the model between the luminescence variation and the relaxation rate agrees with the experiments.
Phonon Dispersion Relations in Copper and Silver by a Modified Sharma‐Joshi Model
Authors: Goel C. M. , Pandey B. P. , Dayal B.
Published: July 2007

The Sharma and Joshi model has been modified by substituting an exact expression for Bardeen's G‐function in the electron‐ion interaction term and to include angular forces, in addition to usual central forces, proposed by Clark, Gazis, and Wallis, up to the second neighbours. The modified model has been applied to study the phonon dispersion relations in copper and silver. The results obtained show an excellent agreement with experimental data.
Optical Modulation Spectra of CdP2 Crystals and Ni‐CdP2 Schottky Barriers
Authors: Radautsan S. I. , Syrbu N. N. , Kiosev V. K.
Published: July 2007

The relative photosensitivity spectra of Ni‐CdP2 Schottky barriers have been investigated experimentally; in these spectra a structure consisting of nine maxima has been observed in the intrinsic absorption region. The anisotropy of the observed transitions has been investigated using electroabsorption or spectral distribution of the photoelectromotive force or photoconductivity. The splittings of the bands responsible for the observed transitions have been determined. The fine structure of photoelectromotive force caused by high‐frequency phonons involved in the transitions at K = 0 is considered.
On a Self‐Consistent Approximation Procedure with Application to the Hubbard Model
Authors: Elk K.
Published: July 2007

Considering a very general derivation of Dyson's equation an approximation procedure is discussed, which exhibits a summary of different known methods. Concerning the Hubbard model a generalization of Roth's procedure follows. In particular it is possible to obtain a self‐consistent method.
Inelastic Neutron Scattering by Cerium Hydrides I. Experimental
Authors: Vorderwisch P. , Hautecler S.
Published: July 2007

Inelastic neutron scattering measurements have been performed on polycrystalline samples of the cerium hydrides CeH1.98and CeH2.72at 70 °C in order to study their lattice dynamics. For the data analysis the spectrometer resolution has been carefully taken into account. A qualitative interpretation of the results clearly shows the importance of hydrogen‐hydrogen interactions. A diffusive motion of hydrogen could not be observed for both samples.
The Propagation of Strong Electromagnetic Waves under Conditions of Mutual Drag of Carriers and Phonons in Semimetals
Authors: Gasymov T. M. , Katanov A. A.
Published: July 2007

The effect of mutual drag of hot carriers and acoustical phonons on the propagation of strong electromagnetic waves in semimetals (Bi, Sb) with equal electron and hole concentrations is investigated. In the presence of a high magnetic field the frequencies of the plasma—phonon waves are shown to depend on the amplitude of the incident wave E, through the temperatures of the heated carriers and phonons. The frequencies of these waves decrease with increasing E0. It is shown that under the action of the incident wave a semimetal becomes optically non‐uniform, i.e. the refractive index is changed from point to point. Expressions for the damping of the field and for the temperature of the carriers have been established under the conditions of a non‐linear normal skin‐effect. The ohmic and Hall static conductivities depend on E0 both in weak and strong magnetic fields. The basic characteristics of the field and temperature are calculated.
Molecular Cluster Approach to Small‐Radius Impurity Centres in Solids
Authors: Bandura A. V. , Evarestov R. A.
Published: July 2007

The molecular cluster approach to the problem of small‐radius impurity centres in solids is discussed. It is shown that the molecular orbitals obtained for the cluster of host atoms can be connected with the crystalline states only for clusters having the form of a large unit cell. In this case the molecular orbitals of the cluster have the sense of Wannier functions, the appropriate one‐electron energies the sense of mean values of the band energies in the large unit cell scheme of the crystalline state classification. It is found that the cluster model is realistic for solids with narrow (1 to 5 eV) energy bands. The convergence of the results with increasing cluster size is shown for lithium chloride ([LiCl6]5− [Li14Cl13]+, and [Li18, Cl18]0 are considered), the molecular cluster calculations are performed for some alkali halides and the results are compared with those obtained using band structure calculations.
On Lattice Dynamics of Substrate‐Thin Film Systems
Authors: Karasová I.
Published: July 2007

A general method for the determination of localized modes of the substrate‐thin film system is derived. The method is applied for a computation of the mean‐square amplitudes of the film atoms at the free surface and on the film‐substrate boundary, if the substrate and the film have the structure of a simple cubic lattice.
Longitudinal Magnetoresistance and Hall Effect of CdxHg1−x Te in Strong Magnetic Fields
Authors: Tsidilkovskii I. M. , Giriat W. , Kharus G. I. , Neifeld E. A.
Published: July 2007

The results of measurements of the Hall coefficient and longitudinal magnetoresistance of CdxHg1−xTe (0.1 ≦ × ≦ 0.2) in the temperature range 1.8 to 300 K and in magnetic fields up to 300 koe are reported. The analysis of the data for zero‐gap semiconductors (x = 0.1) based on the two‐band model shows that hole‐like conduction in an impurity band, imposed on the conduction band, takes place. The strong rise of magnetoresistance observed in magnetic field for semiconducting compounds (x = 0.175 and x = 0.20) is attributed mainly to variation of the scattering probability at low temperatures and to the shift of the band edges in the magnetic field at higher temperatures.
Non‐Ideal Exciton Gas in Silicon and Its Condensation into Electron‐Hole Plasma Drops
Authors: Vavilov V. S. , Nolle E. L. , Fazilov A.
Published: July 2007

Experimental data on the kinetics of the recombination via exciton states are presented for pure Si excited by a pulsed electron beam in the temperature region 4.2 to 300°K. The energy spectrum of the exciton gas is discussed as a function of the exciton concentration Δnex and exciton radius rex. It is shown that for T ⪅ 77 °K at Δnexz ⪆ 1.5 × 10−2 r the exciton gas becomes non‐ideal, and must be regarded in the limiting case, near Δnex ⪆ r as an electron‐hole plasma. At T ⪅ 20°K and Δnex ⪆ 1.5 × 10−2r in the luminescence spectrum a new band appears with a maximum at hvmax = 1.088 eV. It corresponds to the exciton condensation into electron‐hole plasma drops. The nature of an other line with a maximum at hvmax = 1.081 eV is discussed in connection with the possibility of exciton molecular complex formation.
Static Field Splitting of Zero‐Phonon Lines in Jahn‐Teller Systems
Authors: Polinger V. Z. , Rosenfeld Yu. B. , Vekhter B. G. , Tsukerblat B. S.
Published: July 2007

The zero‐phonon line structure of the singlet‐doublet transition in systems with a static Jahn‐Teller effect is investigated; the perturbation splitting of the zero‐phonon lines is supposed to be small. The results obtained can be used for the interpretation of optical spectra in tetragonal systems and dimer molecules.
Quasi‐Localized Electronic States in the Model Pseudopotential Theory of Disordered Alloys of Simple Metals
Authors: Belenkii A. Ya. , Krasko G. L.
Published: July 2007

The energy of disordered alloys with different ion valencies apparently cannot be described in the framework of the pseudopotential perturbation theory because of the strong electron scattering on the long wavelength concentration fluctuations. A model is suggested which provides for the existence of quasi‐localized (virtual) electronic states in alloys. A variational procedure of energy calculation is considered to modify the pseudopotential method. The concrete calculations are performed for the LiMg system. The two‐phase equilibrium, predicted by the theory is discussed.
Magnetic Susceptibility of UP and UAs
Authors: Troć R. , Lam D. J.
Published: July 2007

The magnetic susceptibility of UP and UAs have been measured as a function of temperature from 4.2 to 1000 K and the results are compared with published results in the literature. From the temperature dependence of the magnetic susceptibility, the most likely 5f3 electronic configuration of the uranium ion in these two compounds are deduced using a nonperturbative (full J‐mixing) crystal‐field theory.
Proton Spin–Lattice Relaxation Study of NH4+ Motion in Ammonium‐Doped Ferroelectric RbH2PO4
Authors: Blinc R. , Lahajnar G. , Levstik A. , Osredkar R. , Shuvalov L. A.
Published: July 2007

The temperature dependences of the proton Zeeman and dipolar spin–lattice relaxation rates have been measured in a Rb1–x(NH4)xH2PO4 mixed single crystal both in the paraelectric and the ferroelectric phase. The correlation time for ammonium ion reorientation has been determined and it is found that ultraslow reorientational motion of the H2PO4 groups exists above room temperature.
Electron Diffraction Study of the Local Atomic Arrangement in Amorphous TlCl and CuCl Films
Authors: Ichikawa T.
Published: July 2007

Thin films of amorphous TlCl and CuCl have been prepared by low temperature condensation in high vacuum, and a transmission electron diffraction study of them has been undertaken. A radial distribution analysis from the diffuse halo patterns obtained has been made and the local atomic arrangements in amorphous TlCl and CuCl are discussed by comparison of the experimental W(r) (=ϱ(r)/ϱ0) with W(r)'s calculated from disordered crystalline models.
Screening, Instability of the Uniform State, and Charge Carrier Scattering in Heavily Doped Ferromagnetic Semiconductors
Authors: Nagaev E. L. , Grigin A. P.
Published: July 2007

A calculation of the static dielectric function ε(q) and the magnetic response function to an electrostatic perturbation χ(q) is carried out for heavily doped ferromagnetic semiconductors. Due to the spin polarization of the charge carrier a strong correlation exists between the fluctuations of electron density and magnetization. This leads to diminishing screening length and the appearance of local magnetic moments near impurities, which, in turn, causes a strong magnetic field and temperature dependence of the resistivity. On further temperature increase, the screened potential becomes oscillating, and the screening length increases, going to infinity at a temperature which corresponds to the absolute instability of the uniform state. But still earlier a first order phase transition should occur into a nonuniform state, the nonuniform state being metastable in some temperature range. It may be responsible for the resistivity hysteresis observed in some ferromagnetic semiconductors.
Linearized Effective Exchange and Correlation Potentials for One‐Particle Property Calculations in Simple Metals
Authors: Dagens L.
Published: July 2007

The effective potential method of Sham and Kohn, which allows an exact calculation of one‐particle properties in an interacting electron gas of slowly varying density, is extended to the case of an arbitrary varying density. Assuming a static approximation for the mass operator, it is shown that the elastic scattering cross section can be calculated exactly from an effective scattering potential Ṽ which takes into account all vertex and self‐energy corrections. The same potential leads also to the exact Fermi surface, at least to the lowest non trivial order in the density fluctuation n(q). The matrix element of its indirect part Ṽxc = Ṽ – VH (VH is the Hartree part of the potential) is linearized as X̃(q, k) n(q) and the properties of the effective interaction X̃ are studied in great detail. The long wavelength limit X̃(0, k) is related to the linearized Sham‐Kohn one‐particle effective potential. The behaviour of X̃ in the whole range of q values is studied by means of numerical estimations, assuming a simple Thomas‐Fermi screening approximation. X̃(q, k) is found to be highly angular dependent (i.e., non local) and contact is made in this respect with a recent work of Yasuhara and Watabe. The simpler local interaction X̃(q) (equal to X̃(q, k) with k = kF = |k + q|) which is required for electronic transport property calculations is also discussed and compared to the Kohn‐Sham density‐response effective interaction.
Critical Investigation of Potentials for Band Structure Calculations
Authors: Paasch G. , Woittennek H.
Published: July 2007

The non‐selfconsistent calculation of potentials for band structure calculations is critically investigated. As essential properties of the potential the d‐resonance of the phase shifts and the lower band edge of the s‐band are used. The former characterizes the energy of the d‐bands. For the latter an approximate expression is given in terms of phase shifts. The influence of the atomic wave functions, configuration, and exchange on the potential is investigated. In addition the Mattheiss‐potential is compared with the renormalized atom. The possibility to obtain absolute band energies is discussed.
Cyclotron Waves in Silver – Interference Effects
Authors: Saermark K. , Lebech J.
Published: July 2007

A discussion is given of experiments on the transmission of cyclotron waves through a thin single‐crystalline sample of silver at a frequency of 44.86 GHz. From the data information is obtained on the oscillatory dispersion relation for the extraordinary wave, i.e. turning points, slope, and width of the branches of the dispersion relation.
Estimate of the d–d Overlap of V2O5 from ESR Measurements
Authors: Sperlich G. , Lazé W. D.
Published: July 2007

ESR spectra are given of d electrons which are localized in the randomly arranged Coulomb fields of Li+ and Cu+ ions in single crystals of LixV2O5 and CuxV2O5 (x ⪅ 0.01). A localization within four vanadium 3d orbitals is derived from the hyperfine spectra. A resolved hyperfine splitting disappears at temperatures below about 15 K. The corresponding variation of the nonperiodic Coulomb field allows a rough estimate of the d‐overlap integral.
A Study of the Exchange‐Determined Absorption Lineshape Outside the Lorentzian Region
Authors: Cusumano C. , Troup G. J.
Published: July 2007

The wings of the EPR absorption line of an exchange narrowed spin system have been studied experimentally and theoretically. Solid solutions of DPPH in polystyrene with spin concentrations about 3 × 1020 spins/cm3 show an exponential rather than the often assumed Gaussian behaviour in the wings. The appropriate portion of the spectrum of the random frequency modulation causing the narrowing is recovered. The steepness of the exponential decrease is shown to be proportional to the exchange frequency. This result is in reasonable agreement with the high‐temperature spin correlation functions for a Heisenberg ferromagnet, obtained by some theoretical works on this subject.
Relativistic Symmetries and Lower Bounds for the Magneto‐Electric Susceptibility and the Ratio of Polarization to Magnetization in a Ferromagneto‐Electric Crystal
Authors: Ascher E.
Published: July 2007

A definition of the relativistic symmetry of a polarized crystalline medium is proposed. The requirement of invariance of the susceptibility under this group gives rise to relations between the components of the tensor which then are used in the case of orthorhombic boracite to obtain lower bounds for the magneto‐electric susceptibility and for the ratio of the spontaneous polarization to magnetization.
Effect of Core Structure on the Determination of the Stacking‐Fault Energy in Close‐Packed Metals
Authors: Cockayne D. J. H. , Vitek V.
Published: July 2007

The influence of dislocation core structure upon the relationship between the separation of Shockley partial dislocations and the stacking‐fault energy (γ) of materials crystallising with a close‐packed structure is investigated. It is shown that for the same separation of the partial dislocations a wide range of values of γ can be obtained assuming various core models. The relevance of these conclusions to measurements of the separations of partial dislocations using high resolution electron microscopy is discussed, and the importance of the various core parameters in the interpretation of the microscope images is considered.
Interserial Phototransitions of Excitons in Semiconductors
Authors: Khadshi P. I. , Moskalenko S. A.
Published: July 2007

Light absorption in semiconductors due to interserial transitions of excitons has been investigated. Analytic expressions for the spectral and temperature dependence of the absorption coefficient have been obtained for the allowed and forbidden transitions of the exciton from one series into arbitrary discrete states of the other series, for various ratios of the translational masses of the excitons in these series. The absorption of light has a threshold or boundary frequency ω0, depending on the mass of the excitons before and after the transition. With the increase of |ω – ω0|, the absorption coefficient increases and then decreases. For the allowed transition from the Is‐exciton state of one series into the nl‐state in the other series, the oscillator strength is proportional to Tl, whereas the maximum value of the absorption coefficient is proportional to Tl–1. The temperature ignition of the absorption bands at l >1 has been predicted, which is not related to the change of the level population.
The Stress Field near the Dislocation Pile‐Up Type Defects in Anisotropic Elasticity
Authors: Solovev V. A.
Published: July 2007

A general expression is obtained for the stress field at any point of infinite anisotropic crystals containing defects of the dislocation pile‐up type (e.g. pile‐ups, deformational twins, cracks, thin crystals of martensite). The stresses are expressed in form of an analytic continuation of the density of dislocations from the line of the pile‐up into the complex plane. The formulas obtained are valid for any geometrical arrangement of the defects, taking into account their non‐zero Burgers vectors and giving stresses due to the defects only. The interaction of a line source (i.e. a line force and a dislocation simultaneously) with the mentioned defects is investigated. The results may be used for an unified description of the adhesion forces, non‐linearity of the media, and plastic zone near the defects in terms of some integral coefficients. The concrete calculations are mainly reduced to the evaluation of the complex constants determining the stress field near a single dislocation. The constants are expressed and the stresses written in terms of elastic moduli for the defects lying in the direction of the orthotropic symmetry of the crystal. As a limiting case the general formulas for stresses near dislocation pile‐ups in isotropic media are found.
Influence of Magnetic Field on Polaritons in Uniaxial Polar Semiconductors
Authors: Gurevich L. E. , Arkhazian R. G. T.
Published: July 2007

The influence of a magnetic field on polaritons in uniaxial polar semiconductors is investigated. Faraday and Voigt configurations are considered in various cases of the magnetic field orientation with respect to the crystal axis. It is found that the influence of the magnetic field is very essential; for example, the number of branches and of transparency regions are changed and the resonance frequencies become dependent on the magnetic field in the Faraday configuration.
On the Static Approximation for the Hubbard Model. I. General Considerations
Authors: Puff H. , Weller W.
Published: July 2007

Starting from the functional‐differential equation for the self‐energy, a static approximation is introduced which is shown to be equivalent to the replacement of the Hubbard model by an alloy model. By means of the single‐site coherent potential approximation an equation is derived which determines the distribution function, characterizing this alloy model self‐consistently by the Green's function. The procedure avoids shortcomings of other methods, as ad‐hoc assumptions on the distribution function or non‐unique decompositions of the interaction term.