bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Biexciton in Polar Crystals
Authors: Bobrysheva A. I. , Vybornov V. I. 
Published: July 2007

AbstractThe effective Hamiltonian of electrons and holes interacting via the Coulomb law and through exchange by virtual longitudinal optical phonon is derived. On the ground of this Hamiltonian the correction to the biexciton dissociation energy is obtained. In GaAs the interaction of electrons and holes with the lattice affects favourably the biexciton stability.
The Motion of an Electron in One‐Dimensional Periodic Potential under the Influence of Uniform Electric and Magnetic Fields
Authors: Jannussis A. D. , Papatheou V. , Tsilimigras P. 
Published: July 2007

AbstractThe properties are discussed of an electron moving in one‐dimensional periodic potential in the presence of homogeneous mutual perpendicular electric and magnetic fields. The perturbation energy is shown, by two different methods, to be a periodic function of the ky quantum number, as required by Harper's conditions, and also a periodic function of the electric field. Furthermore the partition function is calculated to second order in perturbation. The free energy of the system is evaluated, the magnetic moment as well as the magnetic susceptibility and its dependence on the electric field.
Frequency Dependences of Conductivity and Dielectric Permeability of a One‐Dimensional Disordered Conductor
Authors: Gogolin A. A. , Melnikov V. I. 
Published: July 2007

AbstractThe frequency dependences of conductivity and dielectric permeability of a one‐dimensional disordered conductor were calculated by means of the numerical solution of the Berezinskii equations. The experimental results on the frequency dependences of conductivity and dielectric permeability in TTF‐TCNQ are analyzed and a free path time τi−1 ≈︁ 1000 cm−1 is found. In case of isotropic electron‐phonon scattering the temperature dependences of dc conductivity and dielectric permeability in a one‐dimensional disordered conductor is calculated numerically.
Host Nuclear Magnetic Resonance in Copper‐Based Magnetic Alloys
Authors: Thiemann J. 
Published: July 2007

AbstractThe lineshape of the bulk Cu63 NMR signal of the Kondo systems _Cu—Mn, _Cu—Fe, and _Cu—Co is investigated experimentally as a function of the temperature and of the concentration of the dilute magnetic impurities. The measurements are compared with Monte‐Carlo simulated line‐shapes broadened by charge density oscillations as well as spin density oscillations of the conduction electrons in the surrounding of the impurity atoms. The increasing coupling between the impurity and the conduction electrons with decreasing temperatures (T < TK) leads to a reduction in the amplitude of charge density oscillations in the range of the coherence length. The analysis of the experimental data gives the coupling constant |Jsd| of the different Kondo systems, showing the minimum value of |Jsd| in the middle of the 3d series for _Cu—Mn.
Many‐Electron Effects on the Characteristics of Short‐Range Order in the Pseudopotential Approximation
Authors: Khwaja Farid A. , Katsnelson A. A. , Silonov V. M. 
Published: July 2007

AbstractThe effect of the many‐electrons interaction on the local ordering energy and the short‐range order (SRO) parameter for the solid solutions is critically studied using various prevalent forms of exchange and correlation corrections in an electron gas. An estimate about the effect of these corrections on the ordering energy and the SRO parameter is made. Detailed calculations for Al—Zn and Ni—Pt alloys are carried out to investigate the influence of these corrections on the ordering energy and SRO parameter. It is concluded that the use of the incorrect correction for exchange and correlation may bring a disaggreement between calculated and experimentally measured values of α1 even in their signs. It is observed that the exchange and correlation correction of Vashista and Singwi yields the best agreement of the calculation with the experimental values of the SRO parameter α1 for Al—Zn alloys.
Complex Band Structure and Density of States for a One‐Dimensional Model of Transition Metal Alloys
Authors: Richter R. , Goedsche F. 
Published: July 2007

AbstractThe multiple‐scattering theory is applied to determine the electronic spectrum of a one‐dimensional binary alloy of spatially non‐overlapping randomly distributed scatterers. A general expression is derived for the alloy density of states using the average‐T‐matrix approximation (ATA). Within the framework of the ATA both the complex energy bands and the electronic density of states are calculated numerically for a transition metal like alloy.
Surface States in the (111) and (&1mcar;1&1mcar;1&1mcar;) Faces of Zincblende Compounds
Authors: Flores F. , Tejedor C. , Martín‐Rodero A. 
Published: July 2007

AbstractThe surface states in the (111) faces of zincblende compounds are studied within the pseudopotential approach, by introducing surface self‐consistency. The surface state occupation and its energy levels are determined and compared with available experimental results.
Search for Anisotropy of Mössbauer Absorption in Biotite
Authors: Chandra R. , Tripathi R. P. , Lokanathan S. 
Published: July 2007

AbstractA search for anisotropy of Mössbauer factor ƒ in biotite single crystal is made by observing the angular variation of Mössbauer γ‐absorption directed at various angles to the normal to the plane of the sheet and also by looking for the Goldanskii‐Karyagin effect in the powdered specimen. It is suggested that the absence of any detectable anisotropy of the ƒ‐values in biotite, and indeed in other Fe containing compounds, in general, is possibly due to the large value of the ƒ‐fraction. This is in contrast to tin‐ and rare‐ earth compounds where such anisotropy is detectable even at room temperatures.
Polariton Dispersion and Crystal Optics in Monoclinic Materials
Authors: Claus R. 
Published: July 2007

AbstractA dispersion relation for long‐wave phonons and phonon‐polaritons in monoclinic polyatomic crystals is derived. It can be brought in the form of a generalized Fresnel equation for the wave normal referring to the principal dielectric axes at a fixed frequency in the visible. Angular dispersion of coupled phonon‐ and polariton‐modes in the crystallographic plane with directional dispersion of the dielectric axes, and the possibility of experiments are discussed.
the Mixing between Frenkel Excitons and Charge Transfer States on Charge Carrier Transfer in Molecular Crystals. II. Physical Consequences
Authors: Petelenz P. 
Published: July 2007

AbstractThe effect of mixing between Frenkel excitons and CT states on the transfer of charge carriers in molecular crystals is considered according to the theory presented in the recent paper. The numerical estimates of the exponential narrowing factors, polaron binding energies, and CT state populations are given for some model cases. Based on these results, the possible methods of experimental verification are suggested.
Higher‐Order Corrections to the Spectrum of the Easy‐Axis Heisenberg Ferromagnet
Authors: Nawrocka W. , Zossel R. 
Published: July 2007

AbstractThe method of thermodynamic two‐time retarded Green functions is applied to calculate the energy spectrum of the easy‐axis Heisenberg ferromagnet. The Dyson‐Maleev transformation is applied what limits the results to the low‐temperature region. The connection of the two‐spin Green function with the scattering matrix is essentially exploited.
Lattice Thermal Conductivity of Solid Neon in the Temperature Range 0.5 to 10 K
Authors: Gupta I. J. , Trikha S. K. 
Published: July 2007

AbstractThe thermal conductivity of neon samples from 0.5 to 10 K is analysed on the basis of Holland's formulation. Fairly good agreement is found between the theoretical and the experimental results of Clemans. It is found for neon samples that longitudinal phonons carry only 15 to 30% of heat, as was shown for argon. The values of the dislocation densities and the average grain sizes of the polycrystalline neon samples are also determined.
Phonon Relaxation in One‐ and Two‐Dimensional Displacive‐Type Ferroelectrics
Authors: Kashcheev V. N. 
Published: July 2007

AbstractThe dampings and frequency shifts (one‐dimensional case) for acoustic phonons as well as for the soft mode due to cubic and quartic anharmonism are derived for the Silverman model of one‐and two‐dimensional displacive‐type ferroelectrics. Contributions from the various phonon–phonon interactions to the phonon dampings are considered and the damping critical exponents are found. In the calculations a self‐consistent formalism in the hydrodynamical limit is used.
Extended‐Hückel‐Theory Calculations for the Positive Divacancy in Silicon
Authors: Ammerlaan C. A. J. , Wolfrat J. C. 
Published: July 2007

AbstractCalculations are carried out for the positive divacancy in silicon using the extended Hückel theory. These are non‐iterative calculations in the molecular unit cell approach for various sizes of the unit cell and for various points in the Brillouin zone. The effects of two symmetry‐allowed distortion modes of the six nearest‐neighbour atoms of the divacancy are investigated. The parameters for stable Jahn‐Teller distortion are determined by minimizing the extended‐Hückel‐theory energy. A second minimum with slightly higher energy is a saddle point with respect to distortions corresponding to other Jahn‐Teller configurations. The energy barrier for reorientation between these configurations is obtained. From the wavefunction of the unpaired electron the hyperfine interaction with 29Si nuclei in the two nearest‐neighbour shells are calculated. For suitable distortions the results compare favourably with existing experimental data. A large discrepancy is found between the distortion parameters for minimum energy and for optimum match of the hyperfine constants.
Electron Spin Transfer in Alkali Chlorides and Alkali Bromides Doped with Divalent Vanadium
Authors: Vanhaelst M. , Matthys P. , Boesman E. 
Published: July 2007

AbstractA comparative theoretical analysis of the covalent electron transfer in various alkali chlorides and bromides, doped with V2+, is presented. Using previously studied EPR and optical measurements, it is found that, in spite of the striking difference in spin‐Hamiltonian parameters, the spin density (fractional electron transfer) is of the order of 3% in both the chlorides and bromides which were studied. More systematic differences in the normalized admixture coefficients are observed when, for the same ligand, the interionic distance is increased.
On the Electronic Properties of Disordered Quasi‐One‐Dimensional Systems with Electron Correlation
Authors: Eifrig Th. 
Published: July 2007

AbstractThe one‐dimensional disordered Hubbard model is investigated in alloy analogy and coherent potential approximation. The temperature dependence of the static susceptibility and the dc conductivity is calculated. The numerical investigation shows that especially at low temperatures the results are strongly influenced by disorder. The application of this approximation to the substance NMP‐TCNQ is discussed.
Lifetime of Color Centers in NaBr
Authors: Bosi L. , Longoni A. , Nimis M. 
Published: July 2007

AbstractNew results on the temperature‐dependence of the lifetime of the F‐center in NaBr are obtained by luminescence measurements. The disexcitation energy is evaluated to (0.078 ± 0.006) eV. A fast component ((22.9±1)ns) of the decay spectra is attributed to the M‐center. The data are discussed in respect of previous photoconductivity measurements and of the criterion of occurrence of F‐center luminescence in ionic crystals.
Positronium in Mixed Molecular Crystals
Authors: Goworek T. , Rybka C. , Wawryszczuk J. 
Published: July 2007

AbstractPositronium formation in mixed organic crystals is investigated. The size of the free volume in the neighbourhood of the strange molecule influences the lifetime of the ortho‐positronium and the width of the momentum distribution of the para‐positronium. A systematic change of positronium formation probability with the position of the substituted group in naphtalene derivatives is observed. In pyrene host crystals it is found that after addition of guest molecules a distortion of the whole momentum spectrum appears.
A Study of Excitonic Spectra in CdSxSe1−x Mixed Crystals
Authors: Kozanecki A. , Werner Z. , Rzewuski H. , Loferski J. J. 
Published: July 2007

AbstractCathodoluminescence and reflectivity spectra are studied in homogeneous CdSxSe1−x mixed crystals with x = 0.85, 0.64, 0.47, 0.29 over the temperature range 7 to 110 K. It is found that the luminescence at 7 K is dominated by bound exciton emission. The binding energies of exciton complexes are deduced from the spectra and found to decrease linearly with the increase of selenium content in the crystals. It is concluded that excitons in different CdSxSe1−x mixed crystals are bound to the same impurity or defect.
Theoretical Investigations of Haynes' Rule
Authors: Atzmüller H. , Schröder U. 
Published: July 2007

AbstractIn a variety of semiconductors the binding energy EBX of excitons bound to ionized or neutral impurities shows a linear dependence on the ionization energy EIof the corresponding defect. This variation is described in the form of a generalized Haynes' rule,E EBX = A + BAI, and follows from first‐order perturbation theory with a short‐range potential. The constants A and B are calculated for ionized and neutral complexes as a function of σ = m/m. Good agreement of the theoretical results with experimental data is obtained.
Molecular Vibrations in a Polymethine Dye Layer Studied by Inelastic Electron Tunneling Spectroscopy
Authors: Ewert S. , Heiland G. , Lüth H. , Roll U. , Sander W. 
Published: July 2007

AbstractInelastic electron tunneling spectroscopy (IETS) at liquid He temperature is used to study the vibrational spectrum of the polymethine dye NH‐rhodanine merocyanine (NH‐RMc). The dye interlayers are prepared by in situ sublimation of the molecules onto the Al2O3layer of (AlAl2O3Pb) tunneling sandwiches. An interpretation of the most prominent vibration bands is given. By comparison with infrared data it is concluded that the dye molecules are arranged in the film with their polymethine chain parallel to the substrate.
Impurity Interaction on Excited Acceptor States in GaP
Authors: Senske W. , Sondergeld M. , Queisser H. J. 
Published: July 2007

AbstractThe lowest excited donor–acceptor pair states in GaP are monitored as a function of the pair separation R by luminescence excitation spectroscopy. They are interpreted in terms of the excited acceptor states 2P3/2, 2P5/2(Γ7) perturbed by the Coulomb field of the donor. The impurity interaction causes an increase ΔE(R) of the corresponding binding energies in the relevant range of R < 30 Å following the empirical law ΔE ∝ exp (−R/R0). The theoretical interpretation of the impurity interaction is based on the Coulomb overlap between the donor ground and acceptor excited states. Within a perturbational scheme hydrogen‐like wave functions are used with modified effective Bohr radii included. The first‐order calculations reflect the main features of the experimental results.
Magnetoresistance and de Haas‐van Alphen Effect in LaAl2
Authors: Reichelt J. , Winzer K. 
Published: July 2007

AbstractMeasurements of the transverse magnetoresistance and the de Haas‐van Alphen effect in LaAl2 are presented for the first time. The results are compared with a theoretical band structure calculation. Several features are in surprisingly good correspondence. Based upon these ones a model of the Fermi surface is proposed. Additionally a few representative cyclotron masses are given.
New Colour Centres in KCl: (Tl+ + Ca2+) and KCl: (Tl+ + Sr2+) Crystals
Authors: Ioan A. , Topa V. , Giurgea M. 
Published: July 2007

AbstractElectrolytic colouring under unusual conditions (low temperature and high voltage) gives rise to the appearance of three new absorption bands peaking at 3.2, 2.5, and 1.7 eV and at 2.8, 2.1, and 1.5 eV in KCl: (Tl+ + Ca2+) and in KCl: (Tl+ + Sr2+) single crystals, respectively. The modifications of the absorption spectra of the coloured crystals induced by the application of a reversed electric field at the colouring temperature or by heat treatment are investigated. It is likely that the colour centre responsible for the new absorption bands is an aggregate centre which, besides an Tl− complex, contains also at least an Ca(Sr) ion, a trapped electron, and an anionic vacancy.
Dipolar Relaxation Induced by an AC Field in Various Crystallographic Directions of Me2+‐Doped Alkali Halide Crystals. I. Nearest‐Neighbour Approach
Authors: Poźniak J. 
Published: July 2007

AbstractTheoretical analysis of the relaxation of Me2+–cation vacancy dipoles in NaCl‐type alkali halide crystals in an ac electric field acting along 〈110〉 or 〈111〉 crystallographic direction is carried out. There is also analyzed the possibility of calculating the rotational jump probabilities for lattice cation‐cation vacancy (ω1) and for direct exchange Me2+‐cation vacancy (ω2), on the basis of the experimental data of tan δ = F(ω) measurements.
Temperature and Frequency Dependence of the Dielectric Constant and Proton NMR near the Structural Phase Transition of Squaric Acid
Authors: Maier H.‐D. , Müller D. , Petersson J. 
Published: July 2007

AbstractThe frequency‐and temperature‐dependent dielectric constant is measured in directions parallel to the molecular layers of squarie acid crystals. There is a monodispersive relaxational dispersion step in the low‐frequency regime Which is ascribed to a thermally activated diffusional motion. The dielectric constant, which is the high‐frequency limit of this dispersion step, is influenced by the 100°C structural phase transition in a characteristic manner. In order to account for the observed behaviour different models are discussed. The measured orientational dependence of the proton NMR spectrum is related to the structural data.
On the Electronic Structure of As2O3, Sb2O3, and As2S3
Authors: Wimmer E. , Weinberger P. , Kosakov A. , Leonhardt G. 
Published: July 2007

AbstractThe AsKβ band in As2O3 and the X‐ray photoelectron spectra of crystalline As2O3 and Sb2O3, and amorphous As2S3 are interpreted by means of the SW method in terms of simple solid state clusters using energy dependent transition probabilities. Considering the simplicity of the applied models the theoretical results agree well with experiment.
On the Theory of Resonance Raman Scattering in Disordered Semiconductors
Authors: Esser B. 
Published: July 2007

AbstractUsing the Green's function technique a general expression of the one‐phonon resonance Raman scattering cross‐section is derived. This expression may be used to calculate the influence of a slowly varying random field present in the electronic subsystem on the resonance dependence. The theory is applied to the case of a fluctuating gap and internal random electric field. Local scattering amplitudes are obtained and the configurational average of the product of the scattering amplitudes is investigated. It is shown that this two point average effectively reduces to the averaging of the scattering amplitudes with one point distribution functions.
Exchange Interaction of Manganese 3d5 States with Band Electrons in Cd1−xMnxTe
Authors: Gaj J. A. , Ginter J. , Gałązka R. R. 
Published: July 2007

AbstractThe influence of a system of magnetic‐field‐aligned paramagnetic ions on the conduction and valence band electron states is studied. A model applicable to large‐gap semiconductors is presented, in which the direct influence of a magnetic field on the band electron states is neglected. This assumption allows to calculate the E(k) dependence in the presence of a magnetic field. The calculations are performed in the Kohn‐Luttinger model producing a strongly anisotropic and nonparabolic structure. As an illustration of the obtained results measurements of the exciton reflection structure in a magnetic field are presented on the ternary semiconductor CdMnTe. The ratio of the exchange integrals of conduction band electrons and valence band electrons to manganese ions is estimated to α/β = −0.25.
A quantitative study of excitonic polariton reflectance in CdS
Authors: Broser I. , Rosenzweig M. , Broser R. , Richard M. , Birkicht E. 
Published: July 2007

AbstractA careful quantitative analysis of the reflectance of CdS crystals in the spectral range of the A‐exciton is presented. Measured spectra for the isotropic and the mixed‐mode orientation of the crystal are fitted by calculations based on the model of excitonic polaritons. Spatial dispersion and Pekar's abc, damping, exciton‐free surface layers, and oblique incidence of light are considered simultaneously. The good agreement between theory and experiment confirms the model, the still existing discrepancies are due to the simplifying assumption of a homogeneous surface layer. The formulae needed are summarized, and the influence of the different polariton parameters on the calculated reflectivity spectra are discussed.
Optical anisotropy of highly oriented pyrolytic graphite. Effect of surface preparation
Authors: Zanini M. , Grubisic D. , Fischer J. E. 
Published: July 2007

AbstractPolarized reflectivity spectra are obtained at near normal incidence from highly oriented pyrolytic graphite surfaces which contain the c‐axis (i.e. normal to the cleavage surface). Comparison of spectra from polished and sputter‐etched surfaces leads to conclude ϵ∥ ≦ 3.4, consistent with previous determinations by oblique incidence reflectivity and by ellipsometry but substantially lower than recent values based on normal incidence spectra from polished surfaces. The nature of the polish‐induced damage is studied by RHEED, and explains the difference between our data and previous results.
On the quantitative characterization of chemical disorder of In1−xGaxP from wavelength‐modulated No‐phonon absorption
Authors: Strehlow R. , Kühn W. , Friedrich H. , Lange H. 
Published: July 2007

AbstractWavelength‐modulated transmission spectra of the no‐phonon structure of In1−xGaxP are quantitatively analysed on the basis of a recently developed theory. From this comparison the Koster‐Slater parameter J characterizing the magnitude of chemical disorder is determined. The theory also well accounts for the experimentally observed lineshape of the no‐phonon structure. From the intensity ratio of the no‐phonon and LA‐phonon‐assisted transitions the quantity J/C is estimated where C is the deformation potential constant for lattice deformation by LA phonons.
Clebsch‐Gordan coefficients of symmetry groups
Authors: van Den Broek P. M. , Cornwell J. F. 
Published: July 2007

AbstractA method is given for the determination of Clebsch‐Gordan coefficients of finite groups. The Clebsch‐Gordan coefficients may be arranged into vectors which are eigenvectors of certain projection matrices. It is shown how an appropriate set of orthonormal eigenvectors of these matrices may be obtained; this set gives then a unitary matrix of Clebsch‐Gordan coefficients. The symmetry properties of these Clebsch‐Gordan coefficients are studied with special emphasis on the crystallographic space groups.
Electron states below the conduction band in Germanium originating from dissociated 60°‐dislocations
Authors: Winter S. 
Published: July 2007

AbstractElectron states due to the strain field from dissociated 60°‐dislocations in Germanium are calculated using effective mass methods. The strain field is found to give rise to states with energies down to (Ec − 0.08) eV.
Fading memory as insufficient condition for the exciton diffusion
Authors: Šubrta V. , Čápek V. 
Published: July 2007

AbstractIt is argued that in contrast to the usual opinion, the decreasing character of memory functions (with increasing time) in the generalized master equation describing the exciton propagation in molecular solids is not yet a sufficient condition for the exciton propagation to be diffusion‐like.