bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic Transitions in the Raman Spectra of FeCl2 · 2 H2O and FeCl2 · 2 D2O1
Authors: Graf L. 
Published: July 2007

AbstractRaman spectra in FeCl2 · 2 H2O (FC2) and FeCl2 · 2 D2O (FC2D) are observed at 2 K. The electronic transitions of the Fe2+−ion in a crystal field are identified after a thorough assignment of the phonon lines in the four isomorphic compounds to symmetry types, using backscattering and 90°‐scattering techniques. The lowest of these phonons is known to be coupled resonantly to the magnons below TN. This coupling and other important magnetic properties of the iron salts are determined by the influence of the crystal field. With the approach of a rhombic symmetry the crystal field parameters are evaluated directly from the observed electronic transitions and related to the single‐ion anisotropy and the g‐value of the iron salts. Also the reductions of spin—orbit couplings in FC2 and FC2D by covalency effects are discussed.
Spectroscopy of Mixed Alkali Halide Crystals Activated by Thallium
Authors: Kalnin A. E. , Trinkler M. F. 
Published: July 2007

AbstractSpectral, polarizational, and kinetic characteristics of mixed alkali halides KBr · KI—Tl and KCl · KI—Tl with three different iodine concentrations are investigated. The conclusion of a paramount role of Jahn‐Teller effect in relaxed excited 3T1u‐state formation is made. It is shown that A‐absorption subbands and shortwave emission bands correspond the five possible variants of coordinate wave function overlapping with four anions of nearest environment, rather than iso‐structures. The effect of preferential orientation of emitting oscillators in mixed crystals quenched at uniaxial compression, confirming the correctness of proposed interpretation, is discovered.
Magnetic Behaviour of the s—f Two‐Band Hubbard Model
Authors: Frauenheim Th. , Röpke G. 
Published: July 2007

AbstractThe magnetic phase diagram of a two‐band Hubbard Hamiltonian as proposed by Jullien and Coqblin in actinide metals is constructed using the functional integral technique. The direct exchange interaction between the localized electron states and the indirect one via the conduction electrons is considered.
Theory of Cyclotron Resonance of Two‐Dimensional Electrons Interacting With Surface and Volume Phonons
Authors: Dykman M. I. 
Published: July 2007

AbstractThe interaction between nondegenerate two‐dimensional electrons in a quantizing transverse magnetic field and volume phonons is shown to be weak for the majority of systems. The coupling to surface phonons often appears to be strong. To separate the contribution of the interaction with volume phonons the diagram technique is developed. The influence of strong and weak interaction with surface phonons on the shape of the absorption peaks near the cyclotron frequency and its overtones and on the dc conductivity is analysed. The dependence of parameters on temperature and magnetic field strength is considered. The transverse electric field is shown to affect the electron—phonon coupling in the case of two‐dimensional electrons near semiconductor surfaces.
Theory and Experiment of the Light Emission of Surface Plasmons Induced by Fast Electrons on Modulated Surfaces
Authors: Heitmann D. 
Published: July 2007

AbstractThe light emission of surface plasmons induced by fast electrons on periodically modulated surfaces by using a first order scattering theory is calculated. Experiments are made on sinusoidally modulated Ag‐surfaces with 80 keV electrons. Good agreement of experiment and calculation is found for the shape of the angular‐ and wavelength spectra, for the influence of the angle of electron incidence, the polarization of the light emission, and — for weakly modulated gratings — for the absolute intensity, too.
Propagation of Electromagnetic Waves in a Direction Parallel to the Magnetic Field in Semiconductive Bi—Sb Alloys
Authors: Oelgart G. , Stegmann R. , Herrmann R. 
Published: July 2007

AbstractMeasurements are carried out on the small‐gap‐semiconductor Bi—Sb at temperatures of liquid helium and in a frequency range between 9 and 70 GHz. Special attention is paid to the investigation of spatial resonances in a magnetic‐field range in the neighbourhood of cyclotron resonance. The anisotropy of the Fermi surface and the redistribution of charge carriers over the parted Fermi surface in a quantizing magnetic field have a great influence on the dispersion behaviour of the waves. A comparison between the experimental and the theoretical dispersion behaviour provides information about the cyclotron masses and the dispersion relation of the charge carriers for the alloy system investigated.
Polarization Properties of Biexciton Luminescence and Two‐Photon Raman Emission in CuCl
Authors: Hönerlage B. , Phach Vu Duy , Grun J. B. 
Published: July 2007

AbstractThe polarization properties of biexciton luminescence and resonant two‐photon Raman emission are studied. For the first time, direct evidence on the biexciton distribution function in momentum space is obtained. Raman lines are found to be due to a four‐particle process where all momenta are well defined. The origin of the biexciton luminescence lines is, on the contrary, a cold gas of biexcitons, which is subjected to elastic and inelastic collisions. Its distribution function is wide spread but not yet isotropic in the momentum space.
The Effect of Oxygen Impurities on the Electron Tunneling
Authors: Otschik P. 
Published: July 2007

AbstractThe effect of dissolved oxygen ions in the vicinity of the interface between tunnel barrier and superconductor on the tunnel density of states and on the parameters of the Eliashberg equations is investigated. Because of existing solvent profiles averaged quantities are measured, as the tunneled quasiparticle averages over the properties in the range of mean penetration depth. Therefore, the theoretical tunnel density of states and the Eliashberg equations are modified. Assuming a solvent profile and a reasonable Coulomb pseudopotential the effective phonon density of states α2F(b) of bulk material is obtained. The set of equations is applied to niobium.
On the Positron Localization in Ordered and Disordered Metallic Alloys
Authors: Koenig C. 
Published: July 2007

AbstractThe positron relative affinity for one of the components of a disordered binary metallic alloy is estimated within an ideal solid solution model. The calculation of the probability of finding the positron on each atomic site is reduced to the determination of a pseudo particle density in a tight binding model; these densities are then obtained in the coherent potential approximation (CPA). In the ordered alloy FeAl, the positron wave function is a Bloch wave function, and its relative amplitude on each of the two sublattices gives the positron density on the corresponding metal. The numerical results show that in each case, the inhomogeneities or structural defects must have an important effect on the experimental results.
Localized Vibrations of Substitutional Atomic Hydrogen in KCl and RbCl Studied by ENDOR
Authors: Hoentzsch Ch. , Spaeth J. M. 
Published: July 2007

AbstractThe superhyperfine (shf) interactions of atomic hydrogen trapped on a cation vacancy next to a Ca++ ion in [110] are measured by ENDOR. The shf interactions increase with increasing temperature. This is explained as due to the occupation of higher modes of the localized hydrogen vibrations. The thermal excitation energy is (17 ± 2) meV for RbCl and (25 ± 2) meV for KCl. A theoretical interpretation of the shf interactions is given including vibrational effects and the lattice distortion of the nearest neighbours.
Thermalization of the Electron—Hole Plasma in GaAs.
Authors: Goebel E. O. , Hildebrand O. 
Published: July 2007

AbstractThe band‐to‐band luminescence lineshape of the electron—hole plasma emission in GaAs is analyzed as a function of the excess energy of the photocreated electrons and holes. This yields experimental data for the dependence of the effective carrier temperature of the electron—hole plasma on the excess excitation energy for high electron and hole densities. Carrier temperatures as low as 5 K can be obtained in the case of resonant excitation. A discussion of these data in terms of the possible energy dissipation processes shows that hole—phonon interaction gives an important contribution to the cooling of the carrier system.
Stimulated Emission, Absorption Spectra, and Recombination in Epitaxial PbTe
Authors: Galeskii F. , Yunovich A. E. , Herrmann K. H. , Kostial H. , Rechenberg I. , Schäfer P. 
Published: July 2007

AbstractStimulated emission at temperatures up to 220 K is detected in epitaxial PbTe layers by means of a Q‐switched Nd3+:YAG laser. From an analysis of simultaneous measurements of the absorption edge, the conclusion is drawn that the emission is due to direct interband transitions with k‐conservation. A unique quantitative description of generation and radiative recombination at high levels of excitation is given. The role of nonradiative processes is outlined.
A Result Not Dependent on Rationality for Bloch Electrons in a Magnetic Field
Authors: Wannier G. H. 
Published: July 2007

AbstractThere are some facts known about the wave functions of a Bloch electron in a magnetic field. A great deal more is known for a special model. All results are restricted to rational fields and depend heavily on the denominator of the representative fraction. A result is described below which is independent of rationality. It is the statistical weight of identifiable regions in an energy versus field plot. In fact if one goes further and plots instead of the energy the integrated density of state versus field a set of computable polygons results for these regions.
Exciton Luminescence in Semiconductors. Surface Recombination and Space‐Charge‐Layer Effects
Authors: Sachenko A. V. , Tyagai V. A. , Kundzich A. G. 
Published: July 2007

AbstractThe effect of surface conditions on excitonic luminescence of wide‐band gap semiconductors like CdS in a situation when excitons are created by the binding of electron—hole pairs is considered. The surface contribution is considered by the velocity of surface exciton annihilation, the effective rate of electron and hole surface recombination, and by surface band bending. The analysis of continuity equations for electrons, holes, and excitons in line with Poisson's equation is carried out. The above set of equations is found to have analytical solutions in the following simple situations: a) at low exciton concentrations when both transfer and annihilation of the excitation energy are determined by the motion and recombination of electrons and holes; b) intermediate exciton concentrations when excitation energy transfer is realized by electron—hole diffusion while its annihilation is due mainly to the excitonic channel; c) high exciton concentrations (in respect to the minor carrier concentrations) when the diffusion as well as the annihilation of a excitation energy is realized by the excitonic channel. A new physical picture of the appearence of “dead” layer in excitonic luminescence based on the enhanced electron—hole recombination near the semiconductor surface, particularly, in conditions of a strong tunneling ionisation of excitons in surface electric fields is proposed.
Theory of the Phononless High Frequency Hall Effect in Disordered Systems
Authors: Fishchuk I. I. , Rudko V. N. 
Published: July 2007

AbstractThe anti‐symmetrical phononless high frequency part of the conductivity tensor of disordered systems which determines the Hall effect in the low temperature region is calculated by Kubo formula. A general expression which takes into account the contribution to conductivity of both the diagonal and non‐diagonal (with respect to the site index) components of the dipole momentum operator of the electron is obtained. The frequency dependence of the anti‐symmetrical part of the phononless conductivity tensor is investigated for a particular form of the density curve of continuous distribution of electron levels of the atoms in the system. The calculations show that the relation between the noted contributions strongly influences the frequency dependence of the Hall effect.
Azbel‐Kaner Cyclotron Resonance as a Long‐Wavelength Limit of an Exact Expression for the Surface Impedance of a Metal in a Magnetic Field
Authors: Saermark K. 
Published: July 2007

AbstractA recently derived, rigorous expression for the surface impedance of a metal placed in a magnetic field is considered in a long‐wavelength approximation. The result is shown to be equivalent to surface impedance expressions used in the Azbel‐Kaner theory.
Vibrational Properties of the 〈001〉 Split Interstitial in Silicon
Authors: Wruck D. 
Published: July 2007

AbstractA theoretical investigation is made of the vibrational behaviour of the 〈001〉 split interstitial in silicon using the Green's function formalism. In particular, the cases of the Si‐Si, C–C, and C–Si dumbbell are discussed. For the numerical calculation of the vibrational frequencies a modified Keating force model is used, in which the coupling of the dumbbell stoms each with another and to the four nearest‐neighbour atoms as well as the changes in the force constants between these four neighbours are described in terms of the ratio d/x (2d separation of the dumbbell atoms,4a lattice constant). The calculations are performed with d/a as parameter using a perfect crystal Green's function determined from neutron scattering data. The results show for reasonable values of d/a (0.5 ≦ d/a ≦ 1) in the case of the equiatomic dumbbell (D2d symmetry) the existence of two high‐frequency localized vibrations (an A1 ‐ and a B2 ‐ mode) and of two doubly degenerate (E ‐ type) resonance modes or localized modes near the maximum lattice frequency. In the case of the mixed dumbbell (C2v symmetry) also two high‐frequency localized modes (both of A1 ‐ type) and four resonance or low‐frequency localized modes (two of B1 and two of B2 ‐ type) are obtained. On the basis of the above calculations, an interpretation of the C(I) infrared absorption bands observed in carbon‐doped electron‐irradiated silicon crystals as the two A1 ‐ modes of the C–Si〈001〉 dumbbell can be made on the basis of the absolute values of the frequencies and the relative line intensities but becomes difficult when considering also the separation of the two modes and its isotopic shift with respect to carbon.
The Influence of Internal Strain on Bound Hole–Phonon Interaction in p‐Type Semiconductors with Zincblende Structure
Authors: Singh Mahiradhwaj 
Published: July 2007

AbstractExpressions for the resonance scattering of phonons by bound holes are obtained for semiconductors with zincblende structure for the situation when the degeneracy of the acceptor ground state belonging to J = 2/3 which is a fourfold degenerate state, is split into two doublets namely M1 = ± 2/3 and M1 = ± 2/1 besides the usual valley‐orbit splitting of the sixfold state into one doublet state belonging to J = 2/1 and one fourfold state belonging to J = 2/3. These expressions are used in the analysis of the unexplained asymmetric nature of the resonance dip in the phonon conductivity of Mn‐doped GaAs at low temperatures. The agreement between the theory and the experimental results is excellent.
A Quantum Mechanical Approach to the Velocity of Dislocations in Ice
Authors: Forouhi A. R. , Bloomer I. 
Published: July 2007

AbstractA quantum mechanical formulation is used to calculate the velocity of a kink on an otherwise straight dislocation line in ice. Treating the kink as a quasi‐particle there exists the probability that it can tunnel through the potential barrier caused by unfavorable positions of the protons on the site jute ahead of it. By unfavorable it is meant that the protons arrre arranged such that point defects occur if the kinkk proceeds. When an external stress is applied to the system there will be a net drift of the kink which advances the dislocation. The velocity thus calculated is in agreement with experimental evidence.
Dipole Barriers at Structured Metal Surfaces
Authors: Fritsche L. , Gollisch H. , Noffke J. 
Published: July 2007

AbstractMattheiss' successful method of approximating the electronic charge distribution in crystals by superposing the charge densities of free atoms is used to calculate dipole barriers at metal surfaces. Low index surface planes are studied for five simple metals and eleven transition metals of either f.c.c. or b.c.c. structure. Some of these metals are also studied by other authors with different methods. The agreement with the results obtained is fairly good. In addition, the differences in the work function obtained from the calculated dipole barriers for different surface planes of a specific metal agree surprisingly favourable with the majority of the respective experimental data.
Polarization Dependence of the Photoelectron Energy Distribution Curves of Cesium
Authors: Humberg H. , Merz H. 
Published: July 2007

AbstractThe energy distribution curves of photoelectrons, emitted from compact cesium films by linearly polarized light in oblique incidence, are measured for photon energies between 3.0 and 4.9 eV. s‐polarization and p‐polarization give different results: the relative contribution of primary electrons is more prominent for p‐polarization than for s‐polarization; only for p‐polarization a weak maximum occurs 1.2 eV below the Fermi energy.
Drift Mobility and Photoconductivity in Amorphous Silicon
Authors: Fuhs W. , Milleville M. , Stuke J. 
Published: July 2007

AbstractDrift mobility and photoconductivity are studied on amorphous silicon (glow discharge type) by conventional time‐of‐flight technique as well as measurements of the response time. The time‐of‐flight experiments yield dispersive transients which do not allow the definition of a transit time. The drift mobility obtained from steady‐state photoconductivity and response time is thermally activated with an energy of 0.13 to 0.16 eV. No indication for a change in transport mechanism is found in the investigated temperature range (100 K < T < 500 K). Longer exposure to light leads to a decrease of the response time, enhancing the recombination via deep lying centres.
Dynamic Dielectric Function in the Three‐Band Model for Zero‐Gap Semiconductors in a Magnetic Field
Authors: Kacman P. , Blinowski J. , Grynberg M. 
Published: July 2007

AbstractThe energies of the magnetic subbands associated with conduction and valence Γ8 bands in zero‐gap semiconductors are calculated analytically in the three‐band model corrected by first‐order perturbation theory to account for the effect of higher bands. Based on the obtained eigenvalues and eigenfunctions both, the imaginary and real parts of Γ8→Γ8 intra‐and interband contributions to the dynamic dielectric function (DDF) are evaluated in collisionless approximation. The influence of frequency and magnetic field dependence of DDF on the reflection coefficient in intrinsic and n‐type samples at T = 0 is presented.
An Exactly Soluble Model of Singlet‐Ground‐State Ferromagnetism
Authors: Kventsel G. F. , Katriel J. 
Published: July 2007

AbstractA system of “atoms”, each one of which can be in one of two spin states, is considered. On the assumption that in one of the two atomic states a ferromagnetic interaction exists, the magnetic properties of the system are investigated. Various types of magnetic behaviour and phase transitions are found. Over a certain reasonable range of model parameters heat magnetization is obtained.
Positron thermalization as quantum statistical process
Authors: Mokrushin A. D. , Sabirov R. Kh. 
Published: July 2007

AbstractThe positron thermalization process is considered by the non‐equilibrium statistical operator method. Kinetic equations describing the slowing‐down of the fast positrons are given in the second order of the positron–medium interaction. Thermalization with account of the positron–phonon scattering is analyzed in detail in that case when the phonon subsystem may be in the non‐equilibrium state. Estimations show that in metals the positrons can be completely thermalize ed due to positron–phonon interaction even at very low temperatures – up to liquid helium temperature.
Dynamical screening and self‐energy of excitons in the electron–hole plasma
Authors: Zimmermann R. , Kilimann K. , Kraeft W. D. , Kremp D. , Röpke G. 
Published: July 2007

AbstractThe dependence of two‐particle energies on plasma density is investigated using Green's functions. An effective exciton equation is derived taking into account dynamically screened potential and one‐particle self‐energies. A variational calculation shows that the bound state levels (exciton energies) remain practically constant whereas the continuum edge (band gap) shifts to lower energies with increasing density, which is in accordance with experimental observations.
Kinetics of the intraband absorption and magnetoabsorption coefficients in mixed semiconductors with composition fluctuations
Authors: Flatau P. J. 
Published: July 2007

AbstractThe influence of short‐range ordering in a mixed semiconductor on the intraband absorption and magnetoabsorption coefficients is determined. The coefficients are shown to be temperature‐dependent. Their time‐evolution after changing the temperature is calculated. An experiment, permitting measurements of the degree of ordering (non‐ideality) in alloys is proposed, and a numerical example for HgTe–CdTe is given.
Dipolar relaxation induced by an AC field in various crystallographic directions of Me2+‐doped alkali halide crystals. II. Next‐nearest neighbour approach
Authors: Poźniak J. 
Published: July 2007

AbstractTheoretical analysis of the dipolar relaxation in Me2+‐doped f.c.c. alkali halide crystals is performed by considering the action of an ac electric field acting parallel to 〈100〉, 〈110〉, and 〈111〉 crystallographic directions of the crystals. The possibility of the existence of impurity dipoles in both n.n. and n.n.n. states is taken into account and the difference explained in theoretical results obtained by Lidiard and Dreyfus. The possibility of evaluating the jump probabilities w1 (lattice cation → cation vacancy), w2 (Me2+ → cation vacancy), w3 (n.n.n. state → n.n. state), and w4 (n.n. state → n.n.n. state) on the basis of experimental tan δ = F(ω) curves is analyzed.
Consequences of the linear part of the specific heat of dilute magnetic alloys
Authors: Freudenhammer A. 
Published: July 2007

AbstractFor large but finite systems the density of energy states can be obtained uniquely from the specific heat as a function of temperature. In a dilute magnetic alloy with linear dependence of the specific heat on the temperature T (at low T) the density of energy states in the lower energy region is given by a modified Bessel function.
Calculation of the g‐tensor and 29Si hyperfine tensors of the E′1 centre in silicon dioxide
Authors: Gobsch G. , Haberlandt H. , Weckner H.‐J. , Reinhold J. 
Published: July 2007

AbstractBoth the g‐tensor and the tensors of 29Si hyperfine interactions are calculated for the model of an O− vacancy in α‐quartz with asymmetric lattice distortion proposed by Yip and Fowler to explain the E′1 centre in SiO2. The extended Hückel theory (EHT) is applied to an α‐quartz cluster. The dangling bonds of the outer atoms are saturated by hydrogen. Theoretical and experimental results agree quantitatively well. Similar calculations are performed for the analogous model in β‐cristobalite. Computations with and without consideration of Si3d functions are compared.
Influence of band‐tail parameters on electronic specific heat and transport coefficients in heavily doped semiconductors
Authors: van Cong H. 
Published: July 2007

AbstractThe high density and low temperature dependences of the electronic specific heat and of the electronic and thermal transport coefficients are investigated for a simplified model of heavily doped semiconductors. The theoretical treatments are based on a Green's function method which was developed in preceding paper. A brief comparison with existing experiments on n‐Ge, n‐Si, and n‐GaAs is made and discussed.