bluuebunny/crossref_metadata_2025 huggingface dataset:
Zur Lösung des 2. Fickschen Gesetzes unter nicht‐isothermen Bedingungen in Gegenwart von äußeren Kräften
Authors: Kirchheim R.
Published: July 2007

Das zweite Ficksche Gesetz, das Konzentrationsänderungen für isotherme Systeme beschreibt, wird auf Systeme mit einem Temperaturgradienten erweitert. Dabei muß der Thermotransport mitberücksichtigt werden. Außerdem wird der Einfluß treibender äußerer Kräfte, die Funktionen der Temperatur, aber nicht der Konzentration sein dürfen, miterfaßt. Durch Variablensubstitution läßt sich das Problem durch eine einfache Differentialgleichung beschreiben. Außer in zwei Spezialfällen ist diese Gleichung nur numerisch zu lösen. Für das Randwertproblem bei abgeschlossenen, eindimensionalen Systemen werden Näherungsgleichungen nach dem Verfahren von Ritz und Galerkin und der quantenmechanischen Störungsrechnung für die Eigenwerte und Eigenfunktionen angegeben, die gut mit experimentellen Werten aus Thermo‐ und Elektrotransportuntersuchungen übereinstimmen. Für die Eigenwerte, die die Einstellung des stationären Zustandes beschreiben, lassen sich neben den Näherungswerten zudem obere und untere Schranken angeben.
Thermoelectric power near the atomic limit of the hubbard model
Authors: Ihle D. , Eifrig Th.
Published: July 2007

The thermoelectric power in the one‐dimensional Hubbard model near the atomic limit is calculated as function of temperature and electron density n. It is shown, that for low temperatures the calculation of the thermopower in the atomic limit by Bari and Beni is not justified. Taking into account a finite bandwidth by means of the alloy analogy approximation a vanishing zero‐temperature thermopower is obtained. For 0.5 ⪅ n < 1 the thermopower increases with increasing temperature, reaches a maximum, decreases, changes sign, and saturates at high temperatures.
Chemical shift of Si 2p core level in SiOx calculation of relaxation contribution
Authors: Bechstdt F.
Published: July 2007

Starting from the treatment of the electron self‐energy in the linear shielded potential approximation relaxation energies for the excitation of Si 2p‐electrons in SiOx compounds are calculated. It is shown that the differences ≈ 5 eV between one‐electron Hartree‐Fock values and binding energies found by means of XPS are caused by dynamical relaxation in the electronic system. The contribution of relaxation to the oxygen‐induced shift of the Si 2p core level is estimated. The total chemical shift with x can be explained in terms of variation of core‐level shift due to solid‐state effects and relaxation energy. The contribution of the Fermi level shift seems to be negligible.
Band parameters of CdS and CdSe single crystals determined from optical exciton spectra
Authors: Voigt J. , Spiegelberg F. , Senoner M.
Published: July 2007

An investigation is made of the energy spectra of A and B excitons in CdS by measuring the transmission and reflectivity of very thin highly perfect crystals at 1.8 K. The excited states of both series follow hydrogen‐like series in a good approximation yielding different Rydberg's R = (28 ± 0.4) and R = (31.3 ± 0.4) meV, whereas the ground states are shifted in opposite direction with respect to the series, δE = −2.2, δE = +0.5 meV, resulting in exciton binding energies E = 30.2 and E = 30.8 meV, which are different from the corresponding Rydberg energies. This effect could not be attributed to a single perturbation acting on the ground state in different ways. Moreover, oscillator strengths are determined. A discussion is given in terms of the quasi‐cubic model. For CdSe, the exciton‐LO‐phonon interaction is investigated using a line‐shape analysis of the absorption lines at different temperatures. Analogous to other II–VI compounds, at higher temperatures (T > 77 K) this interaction is the dominate one for the exciton absorption spectra.
On the dielectric response of solids I. New approximations for the treatment of local field effects
Authors: Schulze K.‐R.
Published: July 2007

Using a perturbation method in the self‐consistent Hartree approximation simple analytical formulae for the dielectric matrices both ε(q + K, q + K′) and ε−1(q + K, q + K′) are deduced, which depend on the crystalline potential only and do not require any knowledge about band structure or wave functions. Further it is shown how to account for exchange and correlation in the non‐diagonal formalism. Moreover, in particular for semiconductors a local‐density approximation is proposed to include local‐field effects within a diagonal treatment.
Contribution of resonant states to the conductivity of HgTe
Authors: Szlenk K. , Dziuba Z. , Galazka R. R.
Published: July 2007

Measurements of the Hall effect and conductivity are performed on HgTe in the temperature range 4 to 40 K and magnetic field up to 70 kG. The analysis of conductivity tensor versus magnetic field enables to establish the influence of different types of carriers on the total conductivity. The concentration of the conduction band electrons versus temperature is determined from the low magnetic field experimental data. By comparing this dependence with the theoretical one the position and concentration of discrete acceptor levels are determined. It is found that the energy of the acceptor level decreases from 2.3 to 1.7 meV when the acceptor concentration increases from 2 × 1018 to 7 × 1018 cm−3. A significant contribution of the low‐mobility electrons (μ < 5 × 103 cm2/Vs) to the conduction is established.
Bound excitons in local density Approximation
Authors: Wünsche H.‐J. , Henneberger K.
Published: July 2007

Using LDA for exchange and correlation contributions the binding energies for localized few particle complexes consisting of up to two excitons bound at a fixed coulomb centre are calculated. A simple isotropic two‐band structure is adopted. For the exciton bound at the ionized donor D+X good agreement is found with values obtained by elaborated variational ansatzes in the literature. Binding energies for the exciton bound at a neutral donor D°X in a wide range of electron to hole mass ratios are obtained for the first time, well reflecting the known limiting cases of H2 (s̀ → 0), H− (s̀ → ∞), and PsH (s̀ = 1). Furthermore, stability is predicted for the biexciton bound at the ionized donor D+X2 below s̀ ≦ 1.4. From all results it is concluded, that LDA is appropriate to describe excitonic complexes bound at shallow impurities.
On the possibility of hydrogen ordering in rare‐earth hydrides
Authors: Bashkin I. O. , Ponyatovskii E. G. , Kost M. E.
Published: July 2007

The region of f.c.c. solid solutions of the NdH system is investigated by DTA at temperatures from −140 to 100 °C. A phase transformation is revealed, its temperature depends on composition. On the basis of the shape of theT–Cdiagram, kinetics of transformation at low temperatures, weak dependence ofTcon pressure, and neutron diffraction data the conclusion is made that the phase transformation is induced by ordering of hydrogen in octahedral sites. The relationship between ordering and the metal‐to‐semiconductor transition is discussed.
First‐order NPO scattering in semiconductors drift mobility and hall factor
Authors: Heinrich A.
Published: July 2007

The drift mobility and the Hall factor are calculated for the nonpolar optical (NPO) scattering in first order of the phonon wave vector by the numerical solution of the linearized Boltzmann equation. This scattering mechanism was recently suggested to be the dominant lattice scattering in chalcopyrite semiconductors. The drift mobility shows a strong temperature dependence with a high temperature behaviour of T−5/2. The Hall factor r is approximately proportional to T0.53 over the whole considered temperature region. Consequently the usual approximation r = 1 is poor in the case of this scattering mechanism. For n‐ZnSiP2 an analysis is given of the lattice limited Hall mobility. The relevance of the first order NPO scattering in other than chalcopyrite semiconductors is discussed.
Modes of vibrations due to single ion substitutional impurities in alkali halides
Authors: Gupta R. K. , Singh A. K.
Published: July 2007

Modes of vibrations due to single ion impurities in alkali halides are studied by Green's function technique. The Green functions computed on the basis of shell model parameters fitted to the neutron data are used in the computation. The modes of vibrations are computed by considering the vibrations of the defect and its six nearest neighbour ions, having Oh symmetry. Using group theory symmetry coordinates are constructed for the seven‐atom defect space and analytical expressions are derived for various modes of vibrations, in terms of Green's functions of the perfect lattice and the perturbation matrix as a result of the defect. Mass changes at the defect site as well as the changes in the short‐range interaction due to the presence of the defect are taken into account. The change ΔA in the short range interaction parameter A is fitted to the observed single ion frequencies in various alkali halides. A considerable softening of the nearest neighbour short‐range interaction varying from 8% in KBr:Cl to 64% in KI:Na is found.
Theory of Raman scattering on polar phonons
Authors: Ovander L. N. , Tyu N. S.
Published: July 2007

Raman scattering (RS) on dipole‐active phonons in crystals of all kinds of symmetry is investigated for the case of arbitrary direction of a vibrational wave vector. The explicit form of RS tensor associated with electrooptic scattering mechanism is obtained. A comparison is made with the tensor obtained within the framework of polarizability theory. The electrooptic mechanism is shown to contribute to the scattering intensity on transverse phonons which is caused by local fields generated by dipole vibrations. The violation of selection rules due to the dipole vibration macroscopic field is investigated. It is shown how electrooptic mechanism contribution to scattering intensity can be separated in the explicit form in all anisotropic crystals.
Luminescence from anthracene single crystals with photoinduced local centres
Authors: Gaievskii A. S. , Lisovenko V. A. , Faidysh A. N. , Yankovskaya L. B.
Published: July 2007

A new series in the fluorescence spectra (4.2 K) red‐shifted by 32 cm−1 from bottom of the exciton band is found in anthracene single crystals irradiated by light with λ ≧ 320 nm at temperatures 353 K and higher. The intermolecular frequencies of this series coincide with those in the exciton fluorescence spectrum. The series is ascribed to the local states in an anthracene crystal (the L‐series). From a number of experiments it is concluded that the L‐series arises from the deformation of the lattice due to the formation of dianthracene from a photochemical reaction. The disappearance of the L‐series upon secondary irradiation with λ = 250 nm is believed to be a convincing argument for the above conclusion (dianthracene is known to decompose to anthracene upon irradiation with λ = 250 nm). The temperature dependence of the L‐series intensity is measured; the local centre concentration is estimated.
General theory of light scattering in solids
Authors: Enderlein R. , Peuker K. , Bechstedt F.
Published: July 2007

A theory of light scattering is developed which uses consequently the connection between the scattered light and the fluctuations of the electromagnetic field. A general formula is given expressing the scattering cross‐section in terms of the fluctuations of the electrical conductivity operator, and by applying the dissipation‐fluctuation theorem in terms of the conductivity operator itself. It is shown how the common representations of the scattering cross‐section can be derived from the general theory.
Spin‐wave instability theory in cubic single crystal magnetic insulators I. General theory
Authors: Patton C. E.
Published: July 2007

The spin‐wave instability theory for magnetic insulators is extended to include the effect of magnetocrystalline anisotropy for any arbitrary microwave pumping configuration. The results are used to analyze previously published data for parallel pumping and subsidiary absorption. Part I presents the general theory. It is shown that previous effective field anisotropy for mulations, which are valid for the analysis of ferromagnetic resonance, are not valid for spin‐wave instability calculations if the microwave field has components transverse to the magnetizing field direction. General expressions are obtained for first‐order process in cubic single crystals magnetized in an arbitrary direction in a (110) plane, with a general microwave pump polarization.
Phonon dispersion in rare gas solids
Authors: Lehri S. , Verma M. P.
Published: July 2007

A many body potential is empirically derived in the case of rare gas solids by assuming a variable atomic polarizability, the variation of the polarizability depending on the proximity of neighbouring atoms. The van der Waals potential resulting from this polarizability involves a three body term in addition to the conventional potential. This potential added to a nearest neighbour repulsive potential is used to determine the elements of the dynamical matrix exactly. Expressions for the elastic constants derived from this dynamical matrix and the equilibrium condition determine the four potential parameters involved. The phonon dispersion curves of the rare gas solids Ne, Ar, Kr, and Xe derived from this dynamical matrix give a very good agreement with experimental curves. Correction for the zero point energy introduces minor changes in the theoretical results except in the case of neon.
Dynamical electron scattering by a layer structure geometrical resonances
Authors: Gerlach E. , Paier K.
Published: July 2007

It is shown that a layer structure due to precipitations or dislocations may lead to geometrical resonances in the dynamical scattering of carriers. Maximum scattering is obtained for frequencies, for which a multiple of the wavelengths of the plasmons and of the free carriers, respectively, is equal to the separation of the layers.
On the charge‐ordered solution of the half‐filled Hubbard model
Authors: Richter A. , Mizia J.
Published: July 2007

Within the functional integral treatment it is shown, that local magnetic moments for the conventional half‐filled Hubbard model with repulsive correlation correspond to charge densities for an attractive correlation. Inclusion of electron—phonon interaction leads to a renormalization of repulsion energy and to a charge‐ordered state for a negative effective Ũ. Fluctuations in the effective charge field turn out to be important in this region.
Lattice dynamics of Cd‐rich Cd1−xHgxTe alloys
Authors: Hoclet M. , Plumelle P. , Vandevyver M. , Triboulet R. , Marfaing Y.
Published: July 2007

An investigation is made of the lattice dynamics of low concentration of Hg atoms (x < 0.3) in Cd‐rich Cd1−xHgxTe mixed system. The vibrational mode frequency for the isolated Hg replacing Cd atoms in CdTe is observed at 131 cm−1. The impurity is described by a perturbation model that accounts for the change of mass at the impurity site as well as the local variation of nearest‐neighbour forces. A calculation based on the Green's function theory suggests stiffening in nearest‐neighbour forces (Δf/f = +0.25) due to isolated Hg in CdTe system.
A lattice dynamical study of potassium halide solids
Authors: Singh R. P.
Published: July 2007

The contributions of the van der Waal's interaction and the zero‐point energy are incorporated in the dynamical matrix of the three‐body force shell model. The modified model is applied to the study of the dispersion of phonons, Debye temperature, and Raman spectra in the case of potassium halides. The study shows excellent agreement between the theoretical and experimental values.
Luminescence induced by tunnelling recombination between neutral silver atoms and Vk centres in alkali halides
Authors: Tashiro T. , Takeuchi S. , Saidoh M. , Itoh N.
Published: July 2007

The decay curves of the tunnelling recombination luminescence between the neutral silver atom and the Vk centre in NaCl and KCl induced by irradiation with an electron pulse are obtained in the temperature range between 77 and 580 K. It is shown that the decay at 77 K follows a t−1 dependence for NaCl but a slower time dependence for KCl. The temperature dependence of the decay curve for NaCl is found to be such that the increase of temperature makes the decay slower at a delay time depending on temperature and enhances the decay rate at a longer delay time. On the other hand, the decay rate for KCl becomes faster with increasing temperature. The time dependence of the decay at 77 K and the temperature dependence of the decay are explained in terms of the anisotropic character of the tunnelling recombination.
Crystal‐field properties of Fe in brucite Mg(OH)2
Authors: Blaauw C. , Stroink G. , Leiper W. , Zentilli M.
Published: July 2007

Samples of brucite Mg(OH)2 containing iron are investigated using 57Fe Mößbauer spectroscopy. The values of the isomer shift and the quadrupole splitting, measured at room temperature, are IS = 1.15 mm/s relative to metallic iron and QS = 2.94 mm/s. From these values, iron is deduced to be in a high spin divalent state. From the magnitude of the QS it is inferred that the ground state associated with the crystal‐field splitting of the 3d levels for Fe2+ in the trigonally distorted oxygen octahedron is a singlet, in agreement with the results of calculations of this splitting. It is argued that this may lead to an increase of the trigonal distortion and provide an explanation of the anomaly in the c/a lattice parameter ratio observed in Fe(OH)2 in comparison with other compounds forming the brucite structure.
The Large Polaron Phase Transition in the Strong Coupling Limit
Authors: Mańka R.
Published: July 2007

An analogue of the molecular field approximation for the polaron in the strong coupling limit is constructed. It is shown for the large polaron that a spontaneous coherent state transition (SCS‐transition) occurs.
Scaling Hypothesis with a Finite Correlation Length at the Phase Transition Point
Authors: Mrygoń B. , Wojtczak L.
Published: July 2007

A generalization of the scaling hypothesis is given for the case when the correlation length is finite at the phase transition point. In the presented approach the correlation functions are generalized homogeneous functions with respect to the correlation length of the reduced temperature variable. The results following from the presented approach are compared with previous results based on the master equation in connection with the Rayleigh linewidth. It is assumed that the generalized scaling procedure can be treated as a more useful tool for the description of phenomena observed in real systems.
Transport Properties of CdvHg1–vSe Crystals
Authors: Stankiewicz J.
Published: July 2007

Hall coefficient and mobility of electrons are measured in CdvHg1–vSe in the temperature range 4.2 to 300 K and for compositions 0.035 ≦ v ≦ 0.05. The temperature and composition dependence of energy gaps and interband momentum matrix element is obtained by fitting the Hall coefficient data calculations based on Kane's full model. Numerical calculation of electron mobility is also performed with temperature and composition dependence of band parameters. The results of these calculations are in good agreement with the experiment.
Luminescence of Free and Relaxed Excitons in MgO
Authors: Rachko Z. A. , Valbis J. A.
Published: July 2007

The vacuum ultraviolet luminescence of pure and doped MgO crystals excited by 10 keV electrons is studied in the temperature region 80 to 450 K. At 80 K the narrow edge luminescence band at 7.65 eV due to radiative decay of free excitons dominates in the emission spectrum of undoped crystals. At thermal quenching of this luminescence with an activation energy of (0.037 ± 0.005) eV, another luminescence band with maximum at 6.9 eV increases. The activation energy of this increase is (0.039 ± 0.005) eV. No relation of the 6.9 eV luminescence band with the presence of impurities and defects could be established and it is suggested to be due to radiative decay of relaxed (self‐trapped) excitons.
Stimulated Raman Effect in Piezoelectric Cubic Crystals
Authors: Wenk J. , Merten L.
Published: July 2007

It is shown that the problem of anharmonic coupling of polariton, Stokes, and anti‐Stokes waves in simple piezoelectric cubic crystals leads to a system of three linear equations (basic equations) if the parametric approximation is used for the pump wave. The solutions of these basic equations are six coupled plane waves, each consisting of a polariton, Stokes, and Anti‐Stokes wave component. The dispersion functions of the six coupled waves are the roots of the corresponding secular equation. Also the coupling factors of the wave components can be derived form the basic equations. The coupled waves very sensitively depend on three dielectric functions. These dielectric functions can be transformed into the alternative form of Kurosawa relations which are useful for the interpretation and for applications.
Approximate Technique in ESR Transition Probability Treatments
Authors: Mialhe P.
Published: July 2007

A review of transition probability determination in ESR is discussed from a theoretical point of view and from a confrontation with experimental results. The spin Hamiltonian formulation and treatment are then considered through the hyperfine interaction that enables one to determine the limitation of each approximate method.
Phonon Scattering at a Low‐Angle Grain Boundary in Silicon
Authors: Roth E. P. , Anderson A. C.
Published: July 2007

The propagation of ballistic thermal phonons through a single low‐angle grain boundary in pure silicon is observed at equivalent temperatures of 2 to 20 K. No scattering of phonons by the boundary can be detected.
Theory of Broadening in X‐Ray Diffraction Peaks Caused by Substitutional Disorder
Authors: Arias A. González
Published: July 2007

In a preceding paper the diffraction theory on this subject has been worked out by using far less approximations than those which had been involved in earlier tratments, arriving at more general and exact results. The approach used to obtain the expressions for the variance and integral breadth of reflections differs from another one which sometimes had been used in the literature. It is shown fthe equivalence of both approaches by genralizing that of Wilson. The connetion betwen diferent probilistic concepts and order parameters used in those treatments is elucidated as well. It is also shown the equivalence with some diffraction theories on layer structures with mistakes. The expression for the variance, as well as their relation with the integral breadths, are obtained in detail in order to facilite the selection between two probable domain size distributions in crystals.
Analysis of Resonant Brillouin Scattering in GaAs
Authors: Itoh Y. , Adachi S. , Hamaguchi C.
Published: July 2007

The dispersion curves of the resonant Brillouin scattering cross sections in GaAs measured by Garrod and Bray are analyzed on the basis of the resonant Brillouin scattering theory and piezobirefringence theory. The resonant enhancement and cancellation are found to be well interpreted in terms of the sign reversal of the Brillouin amplitude (or photoelastic constant). A good agreement is found between the experimental data and the present analysis. In addition the present analysis predicts a cancellation of the Brillouin scattering at Λ = 0.976 μm for the scattering by the slow transverse (Tl) acoustic phonons. This prediction is supported by the analysis of the photoelastic constant made by using piezobirefringence theory.
Precision Investigations of the Fermi Surface of Molybdenum
Authors: Gasparov V. A. , Harutunian M. H.
Published: July 2007

The Fermi surface (FS) of molybdenum is investigated with high precision ±;(0.2 to 0.5%) by means of the radio‐frequency size effect (RFSE) on thick samples. The anisotropy of extremal dimensions of all sheets of the FS of molybdenum in the {100} and {110} planes is measured. High precision of the measurements allows to separate effectively RFSE lines stipulated by the FS sheets with close dimensions, and to measure reliably the gaps between the tightly situated FS pieces of molybdenum. With the aid of computer calculations the analytical description of the FS is obtained in form of a series in spheric and cubic harmonics. The derivatives ∂S/∂kz for various directions kz are calculated with a computer according to these data. The extreme values of these derivatives are in good agreement with the RFSE experiments in the inclined magnetic field and with dopplerons experiment. The comparison is done of the analytical model with theoretical calculations and other experiments.
Electron Scattering by a Layer of Dislocation Lines in a Semiconductor
Authors: Gerlach E. , Kluttig H.
Published: July 2007

If dislocation lines are arranged periodically in a plane, the dc and the dynamical transport properties may become anisotropic around a single dislocation. The ratio of the resistivities for transport parallel and perpendicular to the plane are calculated using the energy loss method. Geometrical resonances appearing in the plasmon and in the power law regime are explained in terms of Bragg reflections by the periodic arrangement.
Use of the Symmetry‐Adapted Atomic Orbitals in the Large Unit Cell Approach to Solids
Authors: Evarestov R. A. , Lovchikov V. A.
Published: July 2007

The use of symmetry‐adapted linear combinations (SALC) of atomic orbitals in large unit cell (LUC) calculations of solids is considered. A procedure is proposed of SALC generation being convenient for the automation in computer calculations. It is shown that the use of the SALC in the semiempirical LUC calculations has advantages in essential computer time and memory savings and in simple distinction of the infinite crystal band states from the molecular orbitals obtained. The results of complete neglect of differential overlap (CNDO) calculations of LiF crystal LUC's in Li8F8 and Li32F32 are discussed.
A Phonon Dispersion Calculation of Silicon in the Dielectric Screening Theory a Closure Approximation
Authors: van Camp P. E. , van Doren V. E. , Devreese J. T.
Published: July 2007

The phonon dispersion curves of silicon are calculated based on the dielectric screening approach. Electron wave functions and energies are obtained from a Hamiltonian matrix with a pseudo‐potential which is self‐consistent with the electron‐ion potential. A direct summation of up to 40 conduction bands in the polarizability matrix yields a negative square of the TA mode. Positive frequencies are obtained if closure over all conduction states is used by treating the energy denominator as a constant. The results are in reasonable agreement with experiment.
Calculation of Soft X‐Ray Emission Spectra by the Relativistic APW Method: Lutetium
Authors: Nemoshkalenko V. V. , Antonov Vl. N. , Antonov V. N. , John W.
Published: July 2007

Starting from the Dirac equation an expression for the intensity of the X‐ray emission spectra is derived in the one‐electron approximation. As an example the OIII‐emission spectrum of lutetium is calculated by the relativistic APW method. The numerical results, which are obtained by using alternative dipole matrix elements are in reasonable agreement with the measured X‐ray emission spectrum.
Influence of Dislocations on the Cyclotron Resonance Absorption in Tellurium
Authors: Gerstenhauer E. , Bauer G. , Grosse P. , Doukhan J. C.
Published: July 2007

In tellurium a‐glide dislocation systems are activated by uniaxial compression experiments at T = 300 and 77 K. The dislocation substructures, chosen with respect to their elastic strain field, are characterized by etch pit counting and X‐ray topography. Optical transmission experiments performed under cyclotron resonance conditions in the submillimeter wavelength region (Λ = 337 and 311 μm) show a considerable effect of the dislocation density and configuration on the observed spectra. The appearance of CRI mode absorption is accounted by a change of the dielectric tensor in the basal plane, as caused by the dislocation strain field.
X‐Ray Spectra and Electronic Structure of Some CsCl‐Type Transition Metal‐Aluminium Alloys
Authors: Blau W. , Weisbach J. , Merz G. , Kleinstück K.
Published: July 2007

The aluminium Kβx emission spectra and transition metal L2,3 emission and self‐absorption spectra of the alloys VAl, FeAl, CoAl, and NiAl are measured by the use of a primary Bragg‐Soller spectrometer. Emission spectra and absorption spectra are converted into differential emission probabilities. Therefore, their height relations are significant. The spectra and the integral intensities are discussed in terms of free electron‐d‐resonance and charge transfer. A detailed comparison with bandstructure calculations will be presented in a second paper.
Luminescence of KBr:In+
Authors: Casalboni M. , Crisanti F. , Grassano U. M. , Manfroncelli C. , Scacco A. , Tanga A.
Published: July 2007

The temperature dependence of the luminescence spectra and of the emission lifetimes are measured in KBr:In+. From these results detailed information is obtained on the adiabatic potential energy surface of the relaxed excited state.
Electronic Structure of a Neutral Phosphorus Vacancy in GaP and InP
Authors: Srivastava G. P.
Published: July 2007

An empirical pseudopotential for a neutral phosphorus vacancy is used to calculate, employing the Green's function method, electronic states in the gaps of GaP and InP. An analytic form of the vacancy wave function is determined. The results are compared with previous available calculations.
Thermoreflectance of CdCr2S4 near the Curie Point
Authors: Iliev M. , Pink H.
Published: July 2007

The thermoreflectance (TR) spectrum of the ferromagnetic semiconductor CdCr2S4 (Tc = 86 K) is measured between 24 and 330 K at photon energies ranging from 1. 5 to 3. 2 eV. A magneticorder‐induced band splitting associated with the earlier observed anomalous C‐band (Ec = = 1. 87 eV at 4. 2 K) is found below the Curie‐Weiss temperature as well as an additional “red shifting” structure at higher photon energies. The results support the assumption of a strong coupling between the electron and spin subsystems in ferromagnetic spinels. The mechanism of the spin‐dependent electronic processes seems to be more complex than predicted by the simplest models.
On the Renormalization of Collective Excitations in Intermediate Valence Metals
Authors: Barabnov A. F. , Tsvelik A. M.
Published: July 2007

The experimentally known minimum of the longitudinal sound velocity in the vicinity of the electronic phase transition is explained for metals with intermediate valence. It is shown that the density of states on the Fermi surface increases due to s‐fhybridization. This increase givesrise to screening of the electron‐ion interaction and hence the longitudinal sound velocity is reduced. The theoretical calculation is compared with experimental data for the γ‐α transition in Ce. It is also shown that the hybridization does not reproduce the existence of the recently proposed acoustic plasmon branch in intermediate valence metals.
Electron‐phonon and electron Raman scattering in polar semiconductors in high magnetic fields
Authors: Goltsev A. V. , Lang I. G. , Pavlov S. T.
Published: July 2007

Resonant electron‐phonon and electron Raman scattering are investigated in direct‐band polar semiconductors in high magnetic fields. The secondary radiation cross‐section is calculated as a function of the incident and emitted light frequencies ω1 and ωs, the magnetic field H and the direction of the emitted light. It is shown that for arbitrarily high magnetic fields, the appearance of sharp peaks in the cross‐section as a function of ω1 and ωs is due to electron and hole transitions into states kz = 0, kz being the projection of the electron or hole wave vector on the direction of H. Sharp maxima are also found at the cyclotron frequencies of electrons and holes. A study of the secondary radiation polarization suggests that the polarization is determined by the energy of the secondary radiation quantum and its direction of propagation as well as by the electron‐hole effective mass ratio.
Correlated pairs and a mass action law in two‐component Fermi systems excitons in an electron‐hole plasma
Authors: Stolz H. , Zimmermann R.
Published: July 2007

In an electron‐hole (or electron‐proton) plasma the density of either species is calculated from the single particle Green's function including ladder type diagrams. The density can be decomposed into contributions of uncorrelated quasiparticles and particles in correlated pairs, the latter referring to both, bound and scattering states. No discontinuity occurs at the Mott criterion. In the non‐degenerate limit a mass action law is obtained which is illustrated by a simple model calculation.
Nonlinear transport in Qn(TCNQ)2
Authors: Mihály G. , Jánossy A. , Kürti J. , Forrö L. , Grüner G.
Published: July 2007

A nonlinear electric field dependence is found in the quasi‐one‐dimensional organic conductor Qn(TCNQ)2. The non‐Ohmic behaviour sets in at electric fields as low as 2 V/cm and it is observed to temperatures above 100 K. Results obtained on a series of crystals with different lengths show that in defect‐free crystals the nonlinearity is intrinsic. Microscopic breaks enhance while chemical impurities depress the nonlinearities. The observations are in contradiction with a simple band semiconductor model and also with models where transport properties are assumed to be determined by short localization lengths.
Quantum‐limit magnetoresistance for impurity scattering
Authors: Arora V. K. , Spector H. N.
Published: July 2007

The theoretical formalism for calculating the magnetotransport effects developed by Arora and Peterson is extended to include the effects of anisotropic screened ionized impurity scattering in nondegenerate semiconductors in the quantum limit when ħωc ≫ kBT. Screening is found to be negligible at high magnetic fields for the transverse magnetoresistance. It is found that for point defect scattering, both the longitudinal and transverse magnetoresistance are linear in the magnetic field, whereas the Hall coefficient differs from its high field value 1/encc by a temperature dependent factor which is found to be close to unity. For ionized impurity scattering, the longitudinal magnetoresistance is found to be independent of the magnetic field, whereas the transverse magnetoresistance and the Hall coefficient decrease with magnetic field, the former as B−1, where B is the magnetic field. For combined acoustic phonon and ionized impurity scattering, the acoustic phonon scattering is found to dominate at very high magnetic fields giving rise to the ex‐perimentally observed linear magnetoresistance. The combination of acoustic phonon and point defect scattering also yields similar results.
Investigation of n‐Pb1−xSnxSe absorption spectra
Authors: Luchytskii B. M. , Manzhara V. S. , Staryk P. M.
Published: July 2007

The long‐wavelength edge of fundamental absorption and absorption by free carriers of Pb1−xSnxSe (x = 0.06) single crystals with free electron concentration 1.0 × 1017 ≦ N ≦ 5.0 × 1018 cm−3 is investigated. The absorption coefficient within 10 to 1500 cm−1 is shown to be exponentially dependent on photon energy. In samples with N > 5.0 × 1017 cm−3 the absorption edge is described by the Urbach rule only at high temperatures. At T < TU the Burstein‐Moss effect dominates the shape of the absorption edge. A correlation between the calculated electron‐phonon coupling parameters γ and the experimental (2/3) σ values is found. The temperature dependence of light absorption at λ = 14 μ by free carriers is investigated. Manifestation of the conduction band non‐parabolicity in the considered phenomena as well as the scattering mechanism of free electrons are discussed.
Iterative EHT calculations for the positive divacancy in silicon
Authors: Weigel C. , Ammerlaan C. A. J.
Published: July 2007

Iterative EHT calculations are carried out for the positive divacancy in silicon with an improved set of EHT parameters for silicon. The nearest neighbours of the divacancy are systematically displaced in the symmetry‐allowed distortion modes until an acceptable agreement between calculated and experimentally derived wave function coefficients is reached for the nearest neighbours. At this particular distortion, the agreement for several shells of next‐nearest neighbours also appears reasonable.
On the theory of absorption and luminescence spectra in amorphous semiconductors
Authors: Sprenger D.
Published: July 2007

Optical transitions in a system of randomly distributed localized electron states coupled to the phonon system are considered. A general expression for the spectral dependence of the absorption coefficient and the luminescence intensity is derived. This expression is applied to the uncorrelated case where the spectral dependences are determined by a density‐of‐states model. Various types of optical transitions within a density‐of‐states model are considered and the corresponding spectral dependences discussed. The derived spectral representation allows the direct calculation of the temperature dependent moments for the various bands.
Fast radiationless recombination in amorphous silicon
Authors: Rehm W. , Fischer R.
Published: July 2007

The luminescence of armorphous silicon is excited by intense dye laser pulses of different energies. The variation of luminescence intensity with excitation intensity follows a square‐root law at high intensities. This indicates that here the recombination kinetics is governed by a bimolecular non‐radiative recombination process.
Stimulated brillouin scattering of helicon waves in a semiconductor
Authors: Sodha M. S. , Sharma R. R.
Published: July 2007

A right‐handed circularly polarised helicon wave decays resonantly into a low‐frequency acoustic wave and a scattered helicon wave in a piezoelectric semiconductor. The low‐frequency nonlinearity arises through the parallel ponderomotive force on electrons whereas the high‐frequency nonlinearity arises through the equation of continuity. The growth rate of instability turns out to be ≈︁ 103 s−1 for 1 to 10 MHz acoustic perturbations when a microwave of 20 kW/cm2 propagates through n‐InSb.
Central peak in ising model with transverse field
Authors: Kashcheev V. N.
Published: July 2007

The momentum and temperature dependence of the central peak (CP) width is found for the Ising model with a transverse field in the right neighbourhood of the Curie point. The width of CP in the critical and hydrodynamic limits is described by a scaling‐type relation. During deuteration the width of CP diminishes as a squared tunneling frequency.
Pb2+ and Bi3+ impurity centres in alkali‐earth oxides vibronic spectra, lattice dynamics, and electron‐phonon interaction
Authors: Zavt G. S. , Ellervee A. F.
Published: July 2007

The vibrational structure in the emission spectra of Pb2+‐ and Bi3+‐doped CaO and SrO single crystal is studied at 4.2 K. The emission spectra are caused by the forbidden 3A1u → 1A1g transition which is initiated by the mixing of 3A1u and 3T1u states by T1g lattice vibrations. A theory is given which takes into account, within the Cochran‐Cowley shell model, a linear vibronic coupling to A1g modes and a change of force constants in the final electronic state. In most cases the main source of the electron‐phonon interaction is found to be the coupling of the transition with the electronic polarization of the nearest anions. The T1g‐symmetry‐projected phonon density of states is shown to be concentrated within a narrow interval of the order of 10 cm−1. An estimate is presented showing that the hyperfine interaction can be responsible for the appearance of the weak zero‐phonon lines observed in the emission spectra.
Energy band structure of Cd3P2 for real D symmetry II. Symmetry properties
Authors: Plenkiewicz P. , Dowgiallo‐Plenkiewicz B.
Published: July 2007

The fundamental symmetry properties of the D space group, necessary in determining the band structure of Cd3P2 are studied in detail. The SCPW for all points and axes of high symmetry, and the compatibility relations for this group are constructed. The selection rules for double‐valued representations are calculated. Finally, the consequences of including spin to the calculated band structure of Cd2P2 are discussed.
Pressure dependent conductivity in InSb
Authors: Lam H. Y. , Jones R. E. , Keeler W. J. , Paranjape V. V.
Published: July 2007

The pressure dependent conductivity of n‐type InSb at 81 K is investigated theoretically and experimentally up to 10 kbar. In the calculations, the mobility is assumed to be dominated by ionized impurity scattering. An expression for the pressure dependent conductivity is obtained by considering the pressure dependence of the non‐parabolic conduction band, the dielectric constant, and the effective mass. The theoretical analysis, in spite of its simplicity, does explain the variation of conductivity with pressure up to 5 kbar although some deviation occurs at higher pressures.
Magnetic susceptibility of the A‐15 compound system (V1−xCrx)3Si
Authors: Handstein A. , Pietrass B. , Behr G.
Published: July 2007

The magnetic susceptibility of single and polycrystalline samples of the A‐15 compounds (V1−xCrx)3Si (0 ≦ x ≦ 1) is measured at temperatures between 4.2 and 320 K. The magnitude and the temperature dependence of the susceptibility diminish with increasing Cr concentration. Applying a peak model for the density of electronic states it is found that the change of the temperature dependence of the susceptibility with increasing Cr concentration is caused mainly by broadening of the peak in the density of electronic states.
The adsorptive chemostress effect
Authors: Ciftan M. , Ruck V.
Published: July 2007

Using the double‐time Green's function formalism of quantum‐statistical mechanics, it is shown that the chemical potential of an adatom, for the van der Waals interaction of the adatom with the solid substrate, can change significantly when the substrate is subjected to mechanical stress.
Optical‐acoustic two‐phonon relaxation in spin systems
Authors: Singh A. , Shrivastava K. N.
Published: July 2007

The two phonon Raman process of spin–lattice relaxation is investigated in spin systems having electronic properties appropriate to both optical and acoustic branches of phonon spectrum. Apart from exponential temperature dependence of relaxation times for resonance processes, T−3‐, T−4‐, T−5, and T−6‐processes are found for both branches under several conditions. However, when the Debye energy is very high, the T−2‐dependence dominates with corrections of T−3 and T−4. The level structure of the spin system is found to be important for the temperature dependence of relaxation times.
Self‐trapped exciton and F centre formation by picosecond laser pulses in alkali bromides and iodides
Authors: D'Hertoghe J. , Jacobs G.
Published: July 2007

Single crystals of NaBr, RbBr, KBr, CsBr, NaI, KI, RbI, CsI are excited by two‐photon absorption of the second harmonic of a mode‐locked ruby laser at room temperature and/or below. Induced absorption is measured at the wavelength of the first harmonic. The measured absorption is interpreted in terms of the formation of the lowest triplet state of the STE or of F centre formation depending on the case and the temperature.
Energy levels at Γ‐point in Hg1−xMnxTe in intense magnetic fields
Authors: Byszewski P. , Szlenk K. , Kossut J. , Gała̧zka R. R.
Published: July 2007

Measurements of Shubnikov‐de Haas effect in Hg1−x, MnxTe for x = 0, 0.02, 0.04, 0.09 in magnetic fields up to 30 T are reported. The experiments are interpreted within a model which takes into account the exchange interaction of mobile electrons and 3d localized electrons of Mn. At very low temperatures the freeze‐out effect is also observed.
Theory of nonradiative multiphonon transitions in impurity centers with extremely weak electron‐phonon coupling
Authors: Pukhov K. K. , Sakun V. P.
Published: July 2007

The nonradiative multiphonon (NMP) electron transition rate in impurity centers in ionic crystals is calculated taking into account high‐order anharmonicity terms in expansion of the electronphonon (EP) interaction in atomic displacements. In the extremely weak coupling limit the traditional potential energy surface displacement relaxational mechanism is shown to be inefficient and NMP relaxation is caused mainly by high anharmonicity of the EP interaction. For this limit a new formula is obtained, which may be applied, e.g., in analysing the NMP relaxation of RE ions in ionic crystals.
Multimode Jahn‐Teller effect for an E term with strong vibronic coupling I. Local and resonant states
Authors: Polinger V. Z. , Bersuker G. I.
Published: July 2007

The multimode Jahn‐Teller (JT) effect problem for an impurity orbital doublet strongly linearly interacting with lattice vibrations is solved. Within the adiabatic approximation the behaviour of the system is reduced to its collective rotation along and to small harmonic vibrations near the bottom of the circular trough of the potential surface. The JT interaction induces JT local and resonant states essential in the interpretation of the fine structure of vibronic spectra. The conditions of their occurrence are discussed.
The electronic theory of SiGe solid solutions
Authors: Soma T.
Published: July 2007

The pseudopotential theory of covalent crystals is applied to Si1−xGex systems using the virtual crystal approximation, the pseudo alloy atom model, and the ordered zinc‐blende‐type lattice (Si0.5Ge0.5). Calculated values of the equilibrium point are in good agreement with the experimental lattice constants. But, at the low temperatures, the phase mixture Si1−x + Gex is favourable compared with the disordered solid solution.
Isotope effect on the Verwey transition temperature of magnetite
Authors: Terukov E. I. , Reichelt W. , Ihle D. , Oppermann H.
Published: July 2007

Electrical resistance and DTA measurements on single crystals of Fe3O4, in which the oxygen is partially replaced by the stable isotope 18O, show a positive isotope shift in the Verwey transition temperature TV of δTV = (6.1 ± 0.05) K for the 18O concentration of 43%. This result can be qualitatively explained by a theory which is based on the concept of the condensation of a coupled charge density–phonon mode at TV and takes into account both the electron–phonon and the electron–electron interactions.
Spontaneous polarization of NH4Cl at the order–disorder phase transition
Authors: Kessler A. , Koreng B.
Published: July 2007

Measurements of the spontaneous polarization of doped and undoped NH4Cl at the order‐disorder phase transition are carried out. It is found that the cause of the polarization is an off‐centre position of divalent impurities. The transition into the polarized state is of first order and is most probably caused by a coupling between aligned dipole moments of the centers and a distortion of the lattice due to the reverse piezoeffect.
Compton profiles of FeAl
Authors: Podloucky R. , Neckel A.
Published: July 2007

Calculations of directional Compton profiles of FeAl are reported. The scattering matrix elements are treated within the impulse approximation using electron wave functions, which are obtained from a quasi‐self‐consistent APW band structure calculation. For an analysis of the Compton profiles at q = 0 an approximation is developed, which only needs the electron momentum distributions of the three cubic main directions. The convoluted differences of the Compton profiles in the three special directions show remarkable anisotropies which should be stimulating for the performance of Compton experiments on single‐crystal specimens of FeAl.