bluuebunny/crossref_metadata_2025_split huggingface dataset:
Compton profiles of FeAl
Authors: Podloucky R. , Neckel A. 
Published: July 2007

AbstractCalculations 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.
Raman scattering in red mercury iodide. New improved polarization spectra
Authors: Prevot B. , Biellmann J. 
Published: July 2007

AbstractThe room temperature Raman spectra of α‐HgI2 are re‐examined using the backscattering configuration on natural crystallographic faces. It is shown that the assignments of the symmetry species involved in the three Raman peaks is strongly dependent on the experimental procedure and that a great care is recommanded in choosing the scattering surface as well as in selecting the scattered radiations. By this method, the 18 cm−1 peak is attributed to a pure Eg‐type symmetry, the 29 cm−1 peak to both Eg and B1g‐type symmetries and the 114 cm−1 structure to mainly A1g and B1g species. These attributions are based on intensity measurements of the lines.
To what extent are the observed lifetimes of F‐centers intrinsic?
Authors: Bosi L. , Nimis M. 
Published: July 2007

AbstractNew measurements, performed at near 65 K, of the F‐center radiative lifetime τR in KBr samples containing α‐ and F'‐centers show a τR‐increase which is related to low and, in some cases, scarcely detectable, critical α‐center concentrations. Analysis of experiments known in literature reveals that a far from negligible quantity of α‐centers is always present in real crystals. These facts lead us to the stimulating hypothesis that the τR‐values might be incorrect because of the perturbation due to the interaction between F‐ and α‐centers.
Optical absorption of the layer antiferromagnet Rb2MnCl4
Authors: Popov E. A. , Kotlyarskii M. M. 
Published: July 2007

AbstractThe optical absorption spectrum of the quasi‐two‐dimensional (2D) antiferromagnet Rb2MnCl4 is investigated in the region of the 6A1g → 4T2g(4D) transition (D group bands). It is found that short‐range magnetic order strongly influences the absorption spectrum at temperatures T > TN. The spin‐flop phase transition is observed in a magnetic field of 56 kOe. Investigation of the Zeeman effect allows to conclude the spectrum in this region to consist of magnon and magnon–phonon sidebands of three different purely excitonic lines.
Random field parameters and pseudopotential
Authors: Bonch‐Bruevich V. L. , Karaivanov V. D. , Proykova Ya. G. 
Published: July 2007

AbstractBinary correlation functions are considered of the random fields produced by various types of atomic disorder in amorphous, liquid, and glassy semiconductors, both homopolar and heteropolar. Conditions are established under which the field may be considered as smooth, Coulombic or short‐ranged, depending upon the nature of the material. Parameters characterizing random fields in question are expressed explicitly in terms of directly observable material quantities with some numerical estimates included.
Temperature dependence of atomic core levels in solids I. Separation of the temperature dependence of conduction‐band and core‐exciton energies
Authors: Hübner K. , Bechstedt F. 
Published: July 2007

AbstractFor the first time an explicit investigation is made of the T‐dependence of atomic core levels in non‐metallic solids and shown that this dependence can be of the same order as that one of electronic energy bands. The basis for these investigations are models for the chemical and the relaxation shift of core levels, which lead to absolute core‐level energies and their shifts, in agreement with corresponding photoemission data. In the present part of this work the T‐dependence of conduction‐band and core‐exciton energies of GaP, Si, and SiO2 is separated, which is involved in the total T‐dependence of the corresponding core‐level to conduction‐band transitions. In the second part of this work it is shown that multiphonon and hydrostatic processes lead to large and different T‐coefficients of the Si2p level in Si and SiO2, whereas the different contributions to the T‐dependence of the Ga3d level in GaP give an almost vanishing total effect. Furthermore, it is shown that the main contributions to the T‐dependence of atomic core levels in semiconductors and insulators come from the electrostatic interaction of the core electrons with their environment, whereas the T‐dependence of relaxation energies is very small. The results are in agreement with data which are deduced from corresponding experiments performed by Aspnes et al.
Band structure of Hg1−xMnxSe from anomalous shubnikov‐de haas effect
Authors: Takeyama S. , Galązka R. R. 
Published: July 2007

AbstractA systematic temperature investigation of the Shubnikov‐de Haas effect in Hg1−xMnxSe is reported. Band parameters are determined including exchange parameters which are characteristic for semimagnetic semiconductors and responsible for the anomalous temperature dependence of spin split energy levels. The effective mass is determined from the ShdH amplitude in restricted higher temperature region. The exchange parameters are used as adjustable parameters to fit the observed ShdH peak positions at all measuring temperatures.
The lattice thermal conductivity of aluminium at low temperatures
Authors: Borchi E. , De Gennaro S. , Pelosi G. , Rettori A. 
Published: July 2007

AbstractStarting from the general theory, the lattice thermal conductivity of Al is evaluated at low temperatures. The calculation is carried out without free parameters using the complete lattice dynamics and the Ashcroft pseudopotential for Al. The results of the calculation are discussed in comparison with available experimental data.
Excition reflection spectra under high‐intensity excitation in CdS and CdSe
Authors: Kuroiwa A. , Saito H. , Shionoya S. 
Published: July 2007

AbstractExciton reflection spectra under high‐intensity excitation by a nitrogen laser are studied in CdS and CdSe at 4.2 K. With increasing excitation density, the reflection peak intensity decreases, simultaneously the spectral width becoming broader, and finally the reflection structure becomes very obscure. Shapes of observed spectra are analyzed in terms of the classical oscillator model using a phenomenological damping term. From the comparison of the results of the analysis with luminescence spectra simultaneously measured, it is concluded that the obscurity of the reflection structure is caused by the shortening of the transverse relaxation time of excitons due to the inelastic collision of excitons.
Untersuchungen zum elektrischen widerstand von versetzungen in metallen I. Allgemeine theorie
Authors: Rauh H. 
Published: July 2007

AbstractIm Rahmen der Einelektronennäherung und des Gültigkeitsbereichs der linearisierten Boltzmann‐Gleichung wird eine allgemeine Theorie für den elektrischen Restwiderstand geradliniger Versetzungen in Metallen gegeben. Sie ist der Translationsinvarianz der betrachteten Kristallfehler angepaßt und gilt sowohl für beliebige Fermi‐Flächen als auch für beliebige elastische Streumechanismen. Die verwendeten Formulierungen des Streu‐ und des Transportproblems führen auf Sätze linearer Gleichungen. Vereinfachungen, die sich aufgrund von Symmetriebeziehungen ergeben, werden diskutiert.
Mean field theory of a single fröhlich polaron possible existence of phase transitions
Authors: Lépine Y. , Matz† D. 
Published: July 2007

AbstractNew results for the free polaron ground state energy are presented, based on a non‐perturbative Fock approximation mean field theory. From variational calculations a new energy upper bound for all couplings is obtained, whose newness lies in its cylindrical symmetry, thu sbreaking the spherical symmetry of the Fröhlich Hamiltonian. For α (the electron–phonon coupling constant)≦3 a translational invariant state is found, for 3 ≦ α ⪅ 3.8 a two‐dimensional localized state while for α ⪆ 3.8, a three‐dimensional cylindrical localized state is obtained. By linking the variational approach to a dynamical approximation of the Fröhlich Hamiltonian, the possibility is suggested of second‐order phase transitions for the structure of the polaron, in the framework of the Fock approximation.
Classical Theory of a Metamagnet with Temperature‐Dependent Anisotropy
Authors: Michalski K. J. , Reich W. , Cofta H. 
Published: July 2007

AbstractThe collinear, two‐sublattice metamagnet with thermal dependence of the magnetic anisotropy parameter but with constant parameter of the inter‐sublattice isotropic exchange coupling is investigated in classical approximation. Using Pál's form of the phenomenological free energy, the magnetization curves for both mT(h) and mh(T) processes are derived. The possibility of occurrence of the spontaneous metamagnetism is demonstrated and its criterion is derived. Moreover, the stable oblique phase is studied, exhibiting new interesting abrupt magnetic transitions on its phase boundaries. Some rules for the accompanying volume jumps are established.
Dielectric Function of a Charge‐Density‐Wave Distorted Quasi‐One‐Dimensional Solid
Authors: Gasser W. , Heiner E. 
Published: July 2007

AbstractThe macroscopic dielectric function is calculated for a quasi‐one‐dimensional charge‐density‐wave distorted solid described by a half‐filled one‐band tight‐binding model with weak electron‐electron interaction and a charge‐density‐wave potential due to electron—phonon interaction. The Green function formalism is used treating the electron correlation by a modified RPA whereas the charge‐density‐wave potential is taken into account exactly. The real and the imaginary part of the dielectric function are discussed in the limit of vanishing wave numbers.
Energy Bands of the Copper Halides
Authors: Overhof H. 
Published: July 2007

AbstractThe energy bands of CuCl, CuBr, and CuI in the zincblende modification are calculated using the relativistic KKR method. The resulting bands confirm qualitatively the empirical band model derived from photoemission and ESCA data. A tentative interpretation of the optical absorption spectra is made in terms of critical points of this band model.
Hot Electrons in Semiconductors in Longitudinal Quantizing Magnetic Fields
Authors: Pinchuk I. I. 
Published: July 2007

AbstractA method for calculating the power transferred to the lattice by electrons in longitudinal quantizing magnetic fields is developed without restriction on the degree of quantization. Both, the inelasticity of scattering and the spreading of Landau levels are taken into account. The quantizing magnetic field appears to eliminate the heating of the electron gas. Electron temperature oscillations due to energy losses through optical phonon emission are studied.
Collective Excitations in Dipole Pseudo‐Spin Glasses
Authors: Akhmadullin I. Sh. , Saburova R. V. 
Published: July 2007

AbstractExcitations are considered in a system of tunneling dipoles randomly distributed over the host with electric dipole—dipole interaction. It is shown that excitations with small damping can exist in both a paraelectric phase and a dipole pseudo‐spin glass one. The phase transition can be a first—order or second—order depending upon the dipole concentration.
Auger Recombination with Traps
Authors: Haug A. 
Published: July 2007

AbstractAuger recombination in semiconductors involving traps is calculated taking into account the statistics of the traps. The results are valid for different traps and different cases of ionization and excitation. In particular, localized traps (δ‐potential model) and non‐localized traps (hydrogen model) are compared with the result that the depth of the traps is essential for Auger recombination, but not their localisation.
Micromagnetic Theory of Phase Transitions in Inhomogeneous Ferromagnets. I. Basic Equations
Authors: Kronmüller H. , Fähnle M. 
Published: July 2007

AbstractLandau's theory of second‐order phase transitions is applied for an investigation of inhomogeneous ferromagnetic materials near the Curie temperature. Using micromagnetic concepts it is shown that fluctuations of the Landau parameters as well as magnetostrictive and dipolar interactions lead to deviations from the so‐called linear Arrott plots. In addition it is found that these latter interactions give rise to transversal components of the spontaneous magnetization.
Theory of AC and DC Conductivity in Disordered Hopping Systems
Authors: Movaghar B. , Pohlmann B. , Sauer G. W. 
Published: July 2007

AbstractA self‐consistent theory is given of ac and dc transport in disordered hopping systems. The method is an extension of an effective medium approximation and a Cayley tree formalism. The calculated dc and ac conductivity are compared with the results of computer simulations of R‐hopping networks and data of amorphous germanium. The agreement is very satisfactory. The exponent s of the ωs component decreases with temperature in the way observed experimentally.
Interstitial Motion During Radiation Damage and Sputtering Processes
Authors: Agullo‐Lopez F. , Townsend P. D. 
Published: July 2007

AbstractThere are two major models for the mechanism of interstitial motion away from the F centre during photon or low energy electron excitation of alkali halides. Previously these models of a focussed replacement collision sequence of halogen ions or a thermally activated H centre diffusion are considered to be alternatives. Some new detailed data on halogen ejection from alkali halides during low energy irradiation are reported which are relevant to this problem. A model is presented which offers an explanation for the data on halogen ejection: the energy spectrum, temperature dependence, and presence of molecular emission. Experiments which would further clarify the model are proposed.
Influence of the Quasi‐Local Acceptor Levels on the Kinetic Properties of Hg1−xCdxTe Type Semimetallic Materials
Authors: Mekhtiev M. A. , Mustafaev N. B. 
Published: July 2007

AbstractCalculations are made of all the kinetic coefficients for semimetallic materials of Hg1−xCdxTe type related with resonance electron scattering at the quasi‐local acceptor levels. The results are compared with experiments. It is shown that at low temperatures all the characteristic features of kinetic coefficients are explained satisfactorily on the basis of the considered mechanism. It is also shown that this scattering mechanism gives a change of sign of the thermo‐electromotive force versus pressure and temperature.
A New Approach to Auger Recombination. Application to Lead Chalcogenides
Authors: Ziep O. , Mocker M. 
Published: July 2007

AbstractThe Auger transition rate derived by means of Green's functions is formulated in terms of exchange of energy and wave vector of the corresponding transitions. Hereby the transition probabilities are modified by dynamical corrections. This treatment allows to calculate the Auger coefficient in lead chalcogenides with sufficient accuracy. As a consequence Auger recombination in PbSe has to be considered.
Anisotropie des seebeck‐koeffizienten, der lorenz‐zahl und des hall‐koeffizienten von halbleitern, verursacht durch anisotrop gemischte streuung
Authors: Stordeur M. 
Published: July 2007

AbstractDer Seebeck‐Koeffizient, die Lorenz‐Zahl und der Hall‐Koeffizient werden in halbleitenden Kristallen selbst bei nichtkubischer Symmetrie und anisotroper Standard‐Bandstruktur nur unter speziellen Bedingungen anisotrope Größen. Wenn nur eine Trägersorte am Ladungs‐ und Wärme‐transport partizipiert, führt eine anisotrop gemischte Streuung zur Richtungsabhängigkeit dieser Transportkoeffizienten. Für diesen Fall werden die Koeffizienten in Abhängigkeit vom reduzierten Ferminiveau und den Mischungsparametern für Streuung an akustischen Phononen und ionisierten Störstellen bzw. an akustischen Phononen und optischen Phononen (T > TD) jeweils approximiert durch die entsprechenden Relaxationszeiten berechnet. Die numerischen Resultate zeigen, daß die Transportkoeffizienten im Unterschied zur reinen Streuung deutliche Anisotropien aufweisen.
Crystal Field Investigation on PrMg3
Authors: Andreeff A. , Goremychkin E. A. , Griessmann H. , Lippold B. , Matz W. , Chistyakov O. D. , Savitskii E. M. 
Published: July 2007

AbstractThe results are given of crystal field investigations on the cubic intermetallic compound PrMg3 by inelastic neutron scattering and specific heat measurement. From the neutron spectra measured at T = 8 and 80 K the following crystal field parameters are obtained: B = −34.7 × 10−4 meV and B = −89 × 10−6 meV. The crystal field ground state of Pr3+ is the non‐magnetic doublet Γ3.
Calculation of Jahn‐Teller Coupling Constants of 3d Transition Metal Ions in Crystals. II. RbMnF3
Authors: Nikiforov A. E. , Shashkin S. Yu. , Krotkii A. I. 
Published: July 2007

AbstractIn the LCAO‐MO scheme using semiempirical approximations the first‐ and second‐order Jahn‐Teller coupling constants for the interaction of 4T1, 4T2 terms of the Mn2+ ion in RbMnF3 crystal with a1, e, and t2 vibrations are calculated. The problems of covalency and configuration interaction influence upon the Jahn‐Teller constants are considered.
Quantum Effects in the Plasticity of Crystals
Authors: Feltham P. 
Published: July 2007

AbstractBelow about a quarter of the Debye temperature the rate processes controlling creep and plastic yielding in crystalline materials are found to be increasingly less temperature dependent as T → 0. These observations, and the occurrence of creep down to helium temperatures, are not encompassed by classical rate‐theory. The effects are shown to be explicable in terms of the contribution of the zero‐point energy to the vibrational spectrum of the lattice: below a certain temperature this necessitates replacing kT in the classical Arrhenius rate‐equation τ−1 = v exp (−u/kT) by k(T0 + AT2), where T0 and A are constants.
Internal Stark Effect on Impurity States in Germanium
Authors: Ohyama T. 
Published: July 2007

AbstractEffects of the Coulomb field by ionized impurities on the acceptor as well as on the donor states in germanium are studied by low‐temperature magneto‐absorption measurements. The broadening of the representative acceptor transition is roughly proportional to the two‐third power of the ionized impurity concentration. It is attributed to the Stark effect by ionized impurities which removes the degeneracy of the excited states. The effect is smaller for the donor state in which the level splitting by magnetic field is larger.
Effect of Spin–Lattice Relaxation on the Dependence of the Triplet Exciton Annihilation Rate on the Strength of Magnetic Field
Authors: Lesin V. I. , Sakun V. P. 
Published: July 2007

AbstractA formula for the triplet exciton annihilation rate in molecular crystals is obtained with taking into account spin–lattice relaxation of the excitons. Using this formula, some experimentally observed peculiarities in the dependence of the annihilation rate on the magnetic field may be explained at least qualitatively.
EPR Investigation of Stabilized ZrO2 Single Crystals Doped with Chromium and Manganese
Authors: Zhilinskaya E. A. , Lazukin V. N. , Chepeleva I. V. , Osiko V. V. 
Published: July 2007

AbstractEPR of Mn2+ and Cr3+ impurity ions in cubic single crystals of (ZrO2)0.9(Y2O3)0.1 solid solutions is studied in X‐ and Q‐bands at 300 and 77 K. A set of Mn2+ centres differing by coordination, value, and symmetry of the crystalline field as well as trigonal Cr3+ centres with considerable zero‐field splitting are found. For the Cr3+ centres and some of Mn2+ centres charge compensation by anion vacancies (main lattice defect) exists. Considerable linewidths are an indication of pronounced lattice distortion about the impurity centres.
Energy Spectrum of Thin Film Heterostructure
Authors: Gasparyan V. M. , Kasamanyan Z. A. 
Published: July 2007

AbstractUsing the Green's function method the charge carrier energy spectrum in a thin film heterostructure is studied taking account of the surface states. The density of states in various parts of the heterostructure is calculated. It is shown that their ratio may vary within large limits. This may lead to the appearance of a negative conductivity in presence of a longitudinal electric field.
Energy Bands and Optical Properties of HgTe and CdTe Calculated on the Basis of the Tight‐Binding Model with Spin–Orbit Interaction
Authors: Czyżyk M. T. , Podgórny M. 
Published: July 2007

AbstractIt is shown that inclusion of spin–orbit interaction and omission of the usual two‐center approximation in the second neighbour Slater‐Koster tight‐binding method leads to an improved interpolation formula for the energy bands of II–VI semiconducting compounds such as CdTe. Due to the inclusion of spin–orbit interaction it is possible to obtain the inverted band structure of HgTe. Reflectivity spectra are computed in fairly good agreement with experiment, up to 5 eV. A detailed discussion of critical points contributed to E1, E1 + Δ1 and E2, maxima is carried out. Moreover, the local properties near the γ point (e.g. effective mass, g factor, Kane's matrix element P, nonparabolicity, warping) of the valence and conduction bands are found to be in excellent agreement with experimental data.
Giant Oscillations of Intensity and the Lineshape of Secondary Cyclotron Emission in Polar Semiconductors
Authors: Goltsev A. V. , Lang I. G. , Pavlov S. T. 
Published: July 2007

AbstractSecondary emission at the cyclotron frequency of a polar semiconductor located in an external homogeneous constant magnetic field and stimulated by monochromatic light of frequency within the region of fundamental absorption is discussed. Analytical expressions of the cross‐section at the cyclotron frequency as a function of the excitation frequency ω1 are obtained, and the shape of the line of cyclotron radiation (LCR) is studied. Giant oscillations of the LCR intensity under changes of ω1 are predicted. This effect is determined by the complete filling of the energy states in the Landau zones by electrons. It is shown that the shape of the LCR is not the result of a overlapping of Lorentz lines, and that it is determined to a high degree by a new type of quantum interference processes in which LO phonons take part. The contribution of these interference processes to the cross‐section may be positive or negative and is responsible for the difference in the shape of the LCR and the Lorentz line.
Electronic Spectrum of Wannier Excitons in Quasi‐Two‐Dimensional Structures
Authors: Kolychev N. N. , Tarasov G. G. , Yaremko A. M. , Sheka V. I. 
Published: July 2007

AbstractThe discrete energy values of excitons in uniaxial crystals are calculated in adiabatic approximation. A model adiabatic potential is discussed for the case of the intermediate anisotropy. It is shown that for the ground state the adiabatic approximation yields the results not worser than the variational ones in the actual range of the anisotropy constant.