bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quasi‐Local Acceptor Levels and Electron Mobility in Hg1−xCdxTe
Authors: Mekhtiev M. A. , Seid‐Rzaeva S. M. 
Published: July 2007

AbstractThe scattering problems of conduction electrons by quasi‐local acceptor levels is considered. The relaxation time of electrons and the analytical expression for the ϵg‐dependence (ϵg is the energy gap between light‐carrier bands) of the energy of the quasi‐local acceptor level are determined for a more general form of the acceptor potential taking into account the contributions from three upper bands (the conduction band, and the bands of heavy and light holes) as well as the effects of non‐parabolicity. The calculated results for the ϵg‐dependence of the quasi‐local level energy and electron mobility are in good agreement with experimental data in the range of ϵg > 60 meV.
Hybrid Resonance in a Quantizing Magnetic Field in BiSb
Authors: Stegmann R. , Oelgart G. 
Published: July 2007

AbstractHybrid resonances are investigated in a quantizing magnetic field in semiconductive BiSb alloys. The measurements are carried out at 1.6 K at frequencies ranging between 120 and 70 GHz with the magnetic field being parallel to the binary axis. It is found that above a definite measuring frequency hybrid resonances can be detected, the occurrences and the field location of which are in effect determined by the redistribution of charge carriers between the component surfaces of the parted Fermi surface in the quantizing magnetic field. The discussion of the results allows the determination of the spin splitting parameter, which is found to be G2 = 0.9. A quadratic relation between energy and momentum gives good agreement between theory and experiment.
Crystal Field Levels of Pr3+ in PrAl3 Studied by Inelastic Neutron Scattering
Authors: Andreeff A. , Kaun L. P. , Lippold B. , Matz W. , Moreva N. I. , Walther K. 
Published: July 2007

AbstractThe crystal field splitting of the 3H4 ground multiplet of the Pr3+ ion in the intermetallic compound PrAl3 is investigated by inelastic scattering of thermal neutrons. At several temperatures crystal field transitions are measured by TOF and TAS methods for polycrystalline PrAl3. In order to decide between crystal field transitions and phonon scattering, the isostructural, nonmagnetic compound LaAl3 is also measured. The crystal field parameters and the energy level scheme for the ground multiplet splitting in PrAl3 are given.
Surface Phenomena in the Polarization‐Dependent Electroreflectance Spectra of Si
Authors: Tyagai V. A. , Snitko O. V. , Evstigneev A. M. , Krasiko A. N. 
Published: July 2007

AbstractThe polarization anisotropy in the longitudinal surface barrier electroreflectance (ER) of heavily doped Si (110) single crystal is measured as a function of the bias for the 3.4 eV peak (E′0). The ER anisotropy under depletion and weak accumulation conditions is found to be characterized by the usual polarization ratio signature of S = 1.35. Both, in the flatband and in the strong accumulation regions practically no polarization dependence is observed. The data obtained indicate that the surface‐related electrooptic effect contributes essentially to the isotropic behaviour of surface‐barrier ER of Si due to surface quantization (flatband region) and to surface amorphism (strong accumulation). The unusual lineshape of the ER spectra taken in the flatband region is shown to be due to the mixing of the depletion‐ and accumulation‐type spectra in the nondifferential ER measurement conditions.
The Dynamic Dielectric Function in HgSe and HgTe
Authors: Szuszkiewicz W. , Witowski A. M. , Grynberg M. 
Published: July 2007

AbstractAbsorption measurements in the infrared region from 5 to 30 μm for HgTe at 295 K and for HgSe at 10, 80, and 295 K are performed. On the basis of the observed interference phenomena the dependence of the refractive index on the wavelength is obtained. These results are analysed in terms of the dynamic dielectric function. The contribution of the Γ → Γ transitions is calculated in terms of Kane's band structure model. From the comparison of theoretical results and experimental data the value of ϵ′∞, treated as a fitting parameter, is determined. The relation ϵ′∞(T) determined for HgSe is somewhat different from that found for HgTe and differs from the value proposed earlier for HgSe.
Exciton Propagation and Memory Effect in Molecular Crystals at Low Temperatures
Authors: Šubrta V. 
Published: July 2007

AbstractA new method of theoretical low‐temperature calculation of the memory functions (MF) governing the exciton propagation in a model of a three‐dimensional perfect crystal with one molecule per elementary cell is presented. This method is suitable for all MF irrespective of distance between sites involved. The influence of initial condition on the exciton propagation is also tested.
Vibronic Spectra of Molecular Systems
Authors: Zgierski M. Z. , Henneker W. H. 
Published: July 2007

AbstractA model for investigation of the vibronic spectra of molecular crystals and polymers is presented. The model assumes that Frenkel excitons and intramolecular phonons (vibrational excitons) move independently and permits a study of two interacting Frenkel exciton bands in a crystalline system containing one molecule per unit cell. In particular the hypo‐ and hyperchromic effects on intensity distributions among different vibronic bands are investigated. A possible generalization of the model to crystalline systems of more than one molecule per unit cell is indicated.
A Kinetic Model of Triplet Exciton Dynamics in Organic Crystals with Discrete Trapping Levels
Authors: Zboiński Z. 
Published: July 2007

AbstractA simple kinetic model is developed to provide expressions for interpreting data from delayed fluorescence and phosphorescence experiments. The expressions for steady state, transient, and chopped light excitations are obtained for a system containing several triplet trapping levels which are well separated in energy. The interrelation of the experimental data obtained for the three modes of excitation enables the evaluation of depths, triplet lifetimes, and other parameters of the trapping levels.
EPR Investigations of ADP:Cr3+ above and below TC
Authors: Diemer H. K. , Bijvank E. J. , den Hartog H. W. 
Published: July 2007

AbstractCr3+ impurities in ADP crystals have been investigated employing the EPR technique. A detailed study has been made at temperatures higher than the Curie temperature; it is suggested that the Cr3+ impurities are located at an NH4+ site which is accompanied by two neighboring proton vacancies. This is concluded from the directions of the principal axes with respect to the crystal axes. In the paraelectric phase there is only one type of Cr3+ center but below TC there are two different centers probably due to different arrangements of the H+ vacancies.
Phenomenological Study of Vacancies in Aluminium within Density‐Functional and Second‐Order Perturbation Formalisms
Authors: Perrot F. 
Published: July 2007

AbstractThe vacancy‐formation energy in aluminium is calculated up to second order in electron–ion interaction within the density‐functional formalism, where the explicit gradient‐expansion of the kinetic energy is used. The ground state for the defect corresponds to an uniform positive background with a spherical hole and an electron density profile represented by an analytical (Gaussian) form which minimizes the total energy. An entirely analytical expression is obtained for zero‐and first‐order energies. The density induced by the perturbative ionic potential (superposition of pseudopotentials minus positive background) is calculated using a linear‐response function which, in the defect, takes into account the charge depletion around the vacancy. The following conclusions are drawn: the perturbation series is convergent, the vacancy‐formation energy is very sensitive to the choice of the (local) pseudopotential.
Chemisorption on a Model Transition Metal. Coverage Dependence of the Adsorption Behaviour
Authors: Masuda K. 
Published: July 2007

AbstractThe adsorption both of a single atom and a monolayer of atoms on the (001) surface of the model transition metal is investigated using the Green's function formalism and the phase shift technique. The electronic structure of the surface is obtained by the Kalkstein‐Soven method. For comparison, both the single‐ and two‐peaked models of the surface density of states (DOS) are used. The adatom charge, heat of adsorption, and the change in the DOS due to chemisorption are calculated within the Newns‐Anderson model and are compared with the available experimental results as well as with those of the previous chemisorption calculations. It is shown that the two‐peaked substrate DOS model can qualitatively account for the strong coverage dependence of the photoemission spectra observed in the system such as H/W(100). The present theory is also extended to the chemisorption system with general coverages.
Lattice Dynamics, Specific Heat, and Bulk Modulus of Scandium
Authors: Rao R. Ramji , Ramanand A. 
Published: July 2007

AbstractThe phonon dispersion curves for scandium along the symmetry directions are obtained using the nearest‐neighbour central‐force model for h.c.p. metals proposed by Srinivasan and Ramji Rao. The theoretical curves are in good agreement with experiment, except in the case of two transverse optic branches. The calculated lattice heat capacity is in good agreement with the Cvl‐ values estimated from the experimental Cp‐data of scandium. The theoretical third‐order elastic (T.O.E.) constants of scandium are used to determine its Anderson‐Grüneisen (A.G.) parameter and the temperature dependence of the bulk modulus of scandium is calculated using Anderson's theory. The calculated change in Bs from 300 to 0 K is in accord with that estimated from the measured elastic constants of scandium.
Higher Anharmonicities in the Improved Unsymmetrized Self‐Consistent Field Approximation for a Crystal. II. Comparison of Calculations with Experiment
Authors: Zubov V. I. 
Published: July 2007

AbstractBy the method considered in the preceding papers the thermodynamic properties of strongly anharmonic crystals of Ar, Kr, and Xe are calculated in extensive temperature ranges. Various pair potentials are used and the three‐body interactions are taken into account. The thermal stability of strongly anharmonic crystals is discussed. The calculated thermodynamic properties of Ar, Kr, and Xe are compared with both the experimental data and Monte Carlo computations.
Study of the Ultraslow Critical Dynamics of the Order Parameter of the Ferroelectric AgNa(NO2)2 by the Spin Relaxation Times T1, T1ϱ, T2 of the 23Na Nucleus
Authors: Grossmann J. , Müller D. , Petersson J. 
Published: July 2007

AbstractMeasurements are made of the temperature dependences of the spin relaxation times T1, T1ϱ, and T2 of the 23Na nucleus in the uniaxial ferroelectric AgNa(NO2)2. Although none of these quantities shows an anomalous behaviour near Tc their temperature dependences can be ascribed to the dynamics of the electric dipoles which cause the ferroelectricity.
The Influence of Surface Layers on Photoreflectance in the Exciton Region of CdS
Authors: Risch L. 
Published: July 2007

AbstractChanges of exciton reflectance spectra by an intense light beam (photoreflectance) are used to investigate electric fields on the free, unprepared crystal surface, originating from surface states. There are two types of photoreflectance spectra in CdS at 105 K, which are associated to different crystal properties A and B. The electric field increases in type A crystals and decreases in the case of type B crystals. This mechanism produces the main contribution to photoreflectance; the screening of the Coulomb interaction of the excitons by free electrons is negligible.
Quasi‐Molecular Model Interpretation of the Resonances in the Fundamental Absorption Region of Valence Semiconductors
Authors: Shatalov V. M. 
Published: July 2007

AbstractAn interpretation of the two main maxima in the valence semiconductor optical spectra and an explanation of the shape of the dielectric constant curve are suggested using the quasi‐molecular model of these crystals suggested by Tolpygo. According to this model the resonances in the continuous spectrum are due to the transitions to the metastable Frenkel exciton states. The interband transitions give rise only to the background component of the spectrum. Estimates of the parameters of the theory are given and experimental sequences of the model are discussed.
Photoemission Studies of 2p Core Levels of Pure and Heavily Doped Silicon
Authors: Eberhardt W. , Kalkoffen G. , Kunz C. , Aspnes D. , Cardona M. 
Published: July 2007

AbstractThe energy distribution curves of the 2p core levels of pure and heavily doped Si are investigated using highly monochromatized (≈︁ 0.1 eV) synchrotron radiation (105 to 140 eV). Shifts and broadenings of the spectra with doping and with the energy of the exciting photons are observed and interpreted in terms of the electrostatic band bending at the semiconductor surface and, for pure Si, of surface core shifts. The “absorption” spectrum of the 2p → conduction band transitions is studied for the same materials with the partial yield technique. By combining the absorption spectra and the core level EDC's a value of EB = (0.18 ± 0.2) eV for the core exciton binding energy is determined. Small differences in the 2p → conduction edge both with doping and with the energy of the exciting photons are observed and discussed.
Hall Coefficient of Dilute Aluminum Alloys. I. Calculation by Four‐OPW Approximation
Authors: Yonemitsu K. , Takano K. , Matsuda T. 
Published: July 2007

AbstractThe Hall coefficients of dilute aluminum alloys are computed by 4‐OPW approximation. The Hall coefficient is found to be very sensitive to the scattering potential. By slight modification of the potential, the calculated results are fitted to the experimental values. Formulae to calculate the mean relaxation time for various parts of the Fermi surface from the measured values of the Hall coefficient and electrical resistivity are deduced.
Phonon Attenuation in n‐Type Semiconductors with ZB Structure in Presence of Internal Strains and Magnetic Field
Authors: Singh Mahiradhwaj 
Published: July 2007

AbstractExpressions for the attenuation coefficient of phonons by donor electrons are obtained in presence of internal strains for n‐type semiconductors with ZB structure for the situations when besides the usual spin‐orbit splitting of the six degenerate states into a quartet and a lower lying doublet, the quartet further splits into two doublets due to internal strains present in the crystal. Similarily the expression for ultrasonic attenuation is also obtained in presence of a magnetic field for the most general case when the degeneracy of both the doublets is removed. These expressions are used in explaining the magnetic dependence of ultrasonic attenuation in Ge doped n‐type InSb. Good agreement between theory and experiment is observed.
Susceptibility Calculations on Spin‐Doped Crystals
Authors: Fakioǧlu S. 
Published: July 2007

AbstractThe susceptibilities of some transition elements, Fe3+ and Gd3+, in various crystals are calculated using the known crystal field parameters. These parameters are used in crystal field theory with the correlation of effective spin Hamiltonian. Two different methods, namely the density matrix formalism and van Vleck's momentum expansion, are utilized to calculate the susceptibilities. It is possible to see the effect of host crystals, and the temperature dependence of susceptibilities of such salts.
X‐Ray K‐Absorption Structure of Zirconium Metal and Its Compounds
Authors: Agarwal B. K. , Johri R. K. 
Published: July 2007

AbstractThe K‐absorption spectra of zirconium are studied in the following substances: Zr, ZrO2, ZrC, ZrBr4, Zr(SO4)2 · 4 H2O, Zr(NO3)4 · 5 H2O, ZrOCl2 · 8 H2O, and K2Zr(C2O4)3. The fine structure within the main edge is discussed on the basis of band structure and is in general accordance with the overlap of d‐ and sp‐bands in transition metals. The observed extended fine structure is analysed in each case to give information on the bond length.
Effect of Pressure on Hole Effective Masses in GaAs
Authors: Alekseeva Z. M. , Vyatkin A. P. , Karavaev G. F. , Krivorotov N. P. 
Published: July 2007

AbstractThe effect of pressure on light and heavy hole masses in GaAs is studied. A theoretical calculation of the dependence of the hole masses on pressure is carried out taking into account the influence of the lowest conduction band levels Γ and Γ. The experimental values are obtained from the change of the tunnel diode characteristics with pressure. The agreement of the calculated values with the experimental data is good for the light holes.
Thermoreflectance of PbTe
Authors: Baleva M. 
Published: July 2007

AbstractTwo groups of p‐type PbTe grown by direct synthesis and Bridgman methods are investigated. The thermoreflectance spectra at room and liquid nitrogen temperature are measured over the energy range from 1.0 to 4.6 eV. The spectra are found to be different for both the groups of samples. Quantitatively the results obtained are interpreted on the basis of theoretical and experimental information. The spectral positions are determined of the energy transitions, the values of dEg/dT for the different critical points and the dependence of dν/dT on the growth method and the temperature. The difference in the spectra for both the groups of crystals is explained.
Boundary Effects on the Transition into Excitonic Phase
Authors: Lozovik Yu. E. , Nishanov V. N. , Kaminskaya E. P. 
Published: July 2007

AbstractThe boundary influence on the transitions of semiconductors or semimetals into the excitonic phase is considered. Proximity effects lead to a decreasing of the dielectric gap in the excitonic phase near the boundary with vacuum or an insulator. In the case when two contacting materials have different critical transition temperatures (T and T) in the excitonic phase, the sample with the low critical temperature becomes insulator for temperature T > T > T. On taking into account the hybridization and interband transition the Ginzburg‐Landau equation for the effective order parameter describing the semimetal–“excitonic insulator”; phase transition is derived. The equation describing the proximity effects in the transition semiconductor‐“excitonic insulator” is equivalent to the equation for Wannier‐Mott excitons near the boundary.
Reaction Rate Constants of Triplet Excitons in Naphthalene Single Crystals
Authors: Asami H. , Nakayama T. , Chong T. , Itoh N. 
Published: July 2007

AbstractThe temperature dependence of the decay of the delayed fluorescence in a naphthalene crystal doped with β‐chloronaphthalene is measured. The results are analyzed in terms of the reaction kinetics comprising a term for the collision of a free exciton with an exciton trapped by β‐chloronaphthalene (X‐trap). The reaction rate constant between the free and trapped excitons is obtained and found to be larger than the reaction rate constants of the triplet exciton with another triplet exciton, a radical, and a guest anthracene molecule in naphthalene crystals. Assuming that the reaction rate constant between the free and trapped excitons is the value at the diffusion limit, the transition probabilities from the neighbouring pair of an exciton and an energy acceptor to the excited state of the energy acceptor are obtained and compared with the results of the analysis using Dexter's theory.
Pressure Dependence of the Electron—Phonon Coupling in Lanthanum
Authors: Glocker R. , Fritsche L. 
Published: July 2007

AbstractOn the basis of self‐consistent band calculations for f.c.c. lanthanum the first moment of the Eliashberg function and its dependence on hydrostatic pressure is evaluated. The formula of Allen and Dynes is used to connect it to the critical temperature of superconductivity, Tc, and the mean phonon frequency Ω. On adjusting Ω for each pressure p such that Allen and Dynes' value of Tc coincides with the respective experimental transition temperature, it is concluded that Ω is lowered with increasing pressure up to 35 kbar reflecting a phonon softening under pressure. Following an ensuing pressure interval of relatively little variation of Ω(p) there is a marked upward bending beyond 53 kbar suggesting restored lattice stability after a passage through (possibly isostructural) phase transitions at 35 and 53 kbar. The results substantiate identical conclusions of Wittig and collaborators drawn from pressure experiments on superconducting lanthanum.
Electron Spin Resonance of Mobile Electrons in AgCl
Authors: Eachus R. S. , Graves R. E. , Olm M. T. 
Published: July 2007

AbstractDivalent cationic impurities such as Cd2+ and Pb2+ and low levels of Br− ions extend the photo‐electron lifetime in silver chloride. The free carrier is observed by conventional ESR in the doped solid, and a free‐electron g‐value of 1.8775 ± 0.0005 is obtained. A careful correlation of kinetic data obtained by ESR and the ac microwave photoconductivity technique leads to a reasonable mechanism to explain the photoinduced decomposition of the doped material.
Binding of an Exciton to a Neutral Acceptor
Authors: Stébé B. , Munschy G. 
Published: July 2007

AbstractThe binding energy of the exciton—neutral acceptor complex is calculated by means of an atomic‐like variational wave function, suitable for not too large electron‐to‐hole mass ratios σ = m/m. The results obtained with a 46‐term trial function do not disagree with previous deductions stating that there is a σ‐region of instability. Further, the empiric “Haynes rule” is not well verified in the limited region (σ ≦ 0.431), where the stability can be achieved by means of our trial function. The computed energies are in good agreement with the experimental data relative to GaAs.
A Note on the Polarization Dependence of the Two‐Photon Absorption Coefficient in Crystals. Extension to Circularly Polarized Light
Authors: Doni E. , Girlanda R. , Parravicini G. Pastori 
Published: July 2007

AbstractThe two‐photon absorption coefficient in crystals is discussed for the case, where one or both exciting beams are circularly polarized. The procedure previously used for linearly polarized light is extended to include circularly polarized photons, and also in this case the absorption coefficient is factorized into dynamical factors containing matrix elements of the momentum operator, and into geometrical factors which depend on the polarization directions of the linearly polarized beams, and on the propagation vectors of the circularly polarized beams. Detailed tables of the geometrical factors are given in the case of cubic crystals. For crystals with tetragonal, trigonal, and hexagonal symmetry, the geometrical factors are given in the case of light propagating along the anisotropy axis. The dynamical selection rules are also reported. It is indicated how the two‐photon spectroscopy, using circularly polarized photons too, is able to lead to a complete experimental determination of the symmetry properties of the excited states in crystals.
X‐Ray Emission Spectrum of Metallic Lithium
Authors: Mgbenu E. N. , Maduemezia A. 
Published: July 2007

AbstractUsing improved wave functions, the X‐ray K‐emission spectrum of metallic lithium is computed in the one‐electron band approximation. An adaptation of the multi‐Lagrangian formula is employed in the interpolation required in the density of states evaluation. The shape of the transition probability curve and the gradient of the intensity spectrum at the Fermi energy are investigated in detail. The conclusion is that self‐consistency in the wave functions has a dramatic effect on the X‐ray transition probability. Nozières and de Dominicis' singularity is applied at the threshold to obtain agreement between the experimental and computed spectra. It is found that the value of the cut‐off energy ξ0 required for correspondence between the two spectra in the threshold region, is of the order of the Fermi energy. This confirms predictions obtained analytically.