bluuebunny/crossref_metadata_2025_split huggingface dataset:
Second‐order Raman spectra of LiH
Authors: Laplaze D. 
Published: July 2007

AbstractThe outlines are summarized of the model for LiD and LiH crystals in which long‐range three‐body forces are included, and applied to the calculation of second‐order Raman scattering which is very strong for these crystals. This first approach made with simplifying hypothesis shows that both the interionic interactions between second‐neighbour hydrogen ions and deformation of H− ions must be taken into account to obtain the principal peaks of experimental Raman spectra.
Burstein‐Moss effect and near‐band‐edge luminescence spectrum of highly doped indium arsenide
Authors: Vilkotskii V. A. , Domanevskii D. S. , Kakanakov R. D. , Krasovskii V. V. , Tkachev V. D. 
Published: July 2007

AbstractThe shape of near‐band‐edge luminescence spectrum is studied and a quantitative analysis of the Burstein‐Moss shift in the three band approximation of Kane's theory is carried out. It is shown experimentally that with increasing electron concentration the spectrum maximum is shifted towards the high‐energy region up to 0.7 eV. At the high‐energy side of spectrum a kink is observed, and at the low‐energy side, an emission maximum at 0.39 to 0.40 eV. The calculations show that the spectrum shape may be described by indirect transitions: band–band and band–shallow acceptor. The narrowing of the optical band gap is accounted for a better agreement between the experimental and theoretical spectra.
Zur Lösung des 2. Fickschen Gesetzes unter nicht‐isothermen Bedingungen in Gegenwart von äußeren Kräften
Authors: Kirchheim R. 
Published: July 2007

AbstractDas 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

AbstractThe 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

AbstractStarting 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

AbstractAn 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

AbstractUsing 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

AbstractMeasurements 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

AbstractUsing 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

AbstractThe 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

AbstractThe 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

AbstractModes 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

AbstractRaman 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

AbstractA 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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractIt 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

AbstractWithin 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

AbstractAn 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

AbstractThe 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

AbstractThe 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

AbstractSamples 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.
Scaling Hypothesis with a Finite Correlation Length at the Phase Transition Point
Authors: Mrygoń B. , Wojtczak L. 
Published: July 2007

AbstractA 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

AbstractHall 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

AbstractThe 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

AbstractIt 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.
Theory of Broadening in X‐Ray Diffraction Peaks Caused by Substitutional Disorder
Authors: Arias A. González 
Published: July 2007

AbstractIn 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.