bluuebunny/crossref_metadata_2025_split huggingface dataset:
Light Absorption in Semiconductors with Superlattice in Quantizing Magnetic Field
Authors: Chaikovskii I. A. , Shmelev G. M. , Enaki N. A. 
Published: July 2007

AbstractThe interand optical transition in semiconductors with superlattice (SL) in the presence of a quantized magnetic field are considered. Investigations are performed for two cases: H ∥ to the axis of SL, and H ⟂ to the axis of SL. In the first case the magnetic field affects the electron motion In the direction of the SL‐axis and the energy spectrum is determined in the effective‐mass approximation from the solution of Schrödinger equation which reduces to the Mathieu equation in the second case the energy spectrum is sufficiently anisotropic and has minibond character in the direction of the SL‐axis, but in the planes of layers an oscillatory structure. The selection rules for interband transitions are obtained for both cases. For H ∥ z the absorption coefficient has the form of a saw‐tooth curve; with increasing H the slope of the curve decreases, but the distance between peaks increases.
Refined Model of Exchange Inversion in Spontaneous Metamagnetism
Authors: Tuszyński J. A. , Cofta H. 
Published: July 2007

AbstractThe magnetic ions of an anharmonic crystal are assumed to interact through the Heisnberg exchange. In the temperature dependence of the exchange constants contributions from the lattice oscillations are included in addition to the usual exchange‐strictive term. The role of exchange‐striction in the metamagnetic transition is reexamined and a new eriterion for metamagnetism is formulated. An explanation for the lattice contraction of the Mn3GaC compound at the matamagnetic temperature is given and a paradox associated with previous theories is removed.
Localization of 3d‐Like Electrons in Cr‐Fe and V‐Fe Alloys
Authors: Szuszkiewicz M. , Rozenfeld B. , Chojcan J. 
Published: July 2007

AbstractLocalization of 3d‐like electrons at the atomic cores of the components of the b.c.c. alloys Cr1−xFex and V1−xFex is determined on the ground of positron annihilation and Mössbauer effect data and by taking into account certain assumptions concerning the interpretation of these results. For V1−xFex the electron transfer from Fe to V occurs in the whole concentration interval. In the case of Cr1−xFex the transfer from Fe to Cr takes place only for x < 0.65, whereas for x > 0.80 the opposite transfer (from Cr to Fe) occurs.
On the Polarization Dependence of Photoemission from Metals
Authors: Brodskii A. M. , Daikhin L. I. , Urbakh M. I. 
Published: July 2007

AbstractThe dependences of one‐and two‐photon photoemission currents from metal on angle of incidence and polarization of light are considered. They are found to be affected by the electric field intensity near the metal boundary. Unlike previous expressions for photocurrent, the formula derived includes an interference term between the amplitudes of probability of transition under the action of fields normal and parallel to the boundary. Experimental data on photoemission and electroreflectance of lead and indium are analyzed. Such a combined analysis may reveal certain essential electronic characteristics of the boundary, in particular, change in the phase of reflection of electrons on Fermi surface from the metal surface when its state changes. The effect of microroughness of the metal boundary on frequency and polarization dependences of photoemission is given special attention. The most significant effects arise in a frequency range where surface plasmons are created. The theory is consistent with experiments on photoemission from silver.
Soft X‐Ray Emission Spectra of Aluminium and Dysprosium from DyCo2–DyAl2 Intermetallic Compounds
Authors: Slebarski A. , Auleytner J. 
Published: July 2007

AbstractIt is shown that from the changes of the position and intensity of the L spectra of cobalt and aluminium and the NIV, V spectra of dysprosium in DyCo2‐DyAl2 alloys the following conclusions result: (1) cobalt is an acceptor of 3d electrons in the investigated compounds in agreement with the results of magnetic measurements, (2) the presence of the cobalt atoms does not change the character of the aluminium‐dysprosium bond, (3) on the high energy side of the Dy NIV, V spectrum the positive shift towards higher energy of the observed maxima which are connected with 4f → 4d transitions suggests a different band structure of DyAl2 in comparison to pure Dy.
Polarization‐ and Temperature‐Dependent Two‐Phonon Absorption Spectra in InSe
Authors: Riede V. , Neumann H. , Lévy F. , Sobotta H. 
Published: July 2007

AbstractPolarization‐ and temperature‐dependent transmittance and reflectance spectra of InSe are measured in the wavenumber range from 200 to 500 cm−1. The absorption peaks observed are interpreted in terms of two‐phonon combination modes due to Γ point phonons considering the β‐, ϵ‐ and γ‐polytypes. It is concluded that the InSe crystals are of the γ‐polytype. Mode Grüneisen parameters are estimated for the intralayer modes.
Quantitative Analysis of the Nonresonant Interband Faraday Rotation in Ge and Si
Authors: Metzdorf J. , Kessler F. R. 
Published: July 2007

AbstractThe Kramers‐Kronig transform of the purely absorptive real part Re of the nondiagonal component of the complex dielectric tensor is applied for the first time to assign quantitatively the contributions from various individual interband transitions (≦ 4.6 eV) to the dispersive interband Faraday rotation (IFR) in Si and Ge. The data of Re needed are determined from measurements of Faraday ellipticity and complex Kerr effect, respectively. In particular, the following problems could be clarified: (i) the origin of the nonresonant change in sign of the rotation in Ge which is due to the competition mainly between negative contributions from E0, E1 + Δ′0 transitions and a positive contribution from E1 transitions; (ii) the relative contributions from indirect transitions in Si. (iii) The present results are generally useful for studying and interpreting the effect of doping and, moreover, give indication of a systematic trend in how various critical points may contribute to the nonresonant IFR in different semiconductors.
Radiation Damage of Ni2+‐Doped NH4MgPO4 · 6 H2O
Authors: Chowdari B. V. R. , Ravisekhar Y. , Muralikrishna C. 
Published: July 2007

AbstractAn optical absorption study of NH4MgPO4 · 6 H2O doped with Ni2+ shows that Ni2+ substitutes for Mg2+ in the lattice. This spectrum is fitted to the Liehr and Ballhausen scheme for a 3d8 ion in Oh surroundings. A correlated ESR and optical absorption study of these crystals on X‐ or γ‐irradiation at room temperature indicates the formation of Ni3+ and NH3+ radicals. The NH3+ center is found to have an isotropic g and AH and an anisotropic AN. This center is also produced in undoped crystals with lower yield. Ni3+ centers are found to be paramagnetic and exhibit their characteristic optical absorption bands.
Application of BBGKY Equations to the Study of Ordering in Alloys
Authors: Stark Yu. S. , Steinberg A. S. 
Published: July 2007

AbstractThe chain of the BBGKY (Bogolyubov‐Born‐Green‐Kirkwood‐Yvon) equations for lattice systems is obtained. These equations differ greatly from those for the continuous case and can be used in the theory of the Ising model. Different characteristics of ordering in alloys are computed using these equations: phase transition temperature, correlation parameter, correlation functions at great distances. The results obtained are in good agreement with other theories.
Evaluation of the Grüneisen Parameter for NaCl‐Structure Alkali Halide Crystals
Authors: Shanker J. , Singh K. 
Published: July 2007

AbstractThe Grüneisen parameters for sixteen alkali halide crystals with NaCl structure are calculated with the help of the model recently developed by Migault and Romain. This model takes into account the volume dependence of Poisson's ratio. The derivatives of pressure with respect to volume are estimated by adopting different potential functions suitable for ionic crystals. The results obtained in the present study are discussed and compared with experimental data and other recent investigations.
CPA Study of the Electrical Conductivity for Various Percolation Models
Authors: Kolley E. , Kolley W. , Fehske H. 
Published: July 2007

AbstractTransport properties are examined for randomly disordered systems comprising a mixture of conducting and insulating components. The tight‐binding models on a s.c. lattice are specialized to purely diagonal disorder, off‐diagonal disorder of the multiplicative and additive type, also in the presence of electron‐electron interaction; the percolation limits are reached by the breaking of inter‐ or intra‐species links. The effective medium is provided by the CPA (coherent potential approximation) and its extended version ODCPA, if necessary combined with the Hartree‐Fock approximation. The dc conductivity σ vanishes at a critical concentration xc of inaccessible sites at fixed Fermi energy. The ODCPA involving vertex corrections refers to localization in the middle of the band. Numerical σ(x)‐results are presented.
Electron Structure and X‐Ray Absorption Spectra of Potassium Chloride I. Band Structure Approach
Authors: Gegusin I. I. , Datsyuk V. N. , Vedrinskii R. V. 
Published: July 2007

AbstractThe conduction band (CB) structure of potassium chloride in a rather wide energy region is calculated by means of the augmented plane wave (APW) method. The important features of CB are the hybridization and interaction of nearly free electron bands with K d‐ and Cl d‐bands. These effects lead to the appearance of many contrast peaks in the energy distribution of the density of K p‐and Cl p‐states. These distributions are compared with the experimental X‐ray K‐spectra in KCl. As a result of this comparison it is concluded that the band theory of an ideal crystal ground state is insufficient for an adequate quantitative explanation of the X‐ray absorption spectra in alkali halides. The assumption is made that one must take in account the deep core hole influence on the final‐states spectrum.
Integral Representation of the Incoherent Field in Disordered Matarials. I. Current Balance, Density‐of‐States Test, and New Mobility Formula
Authors: Lenk R. 
Published: July 2007

AbstractFor a disordered material composed of many point‐like single scatterers a representation considered first by Foldy for the autocorrelation function of the incoherent field guarantees in a general way a loss‐free total current which consists of a coherent and an incoherent part. This demand fixes uniquely the representation mentioned. An exact connection with the density of states allows for an additional test independent from the current balance. By the generalizing inclusion of a driving force into the coherent wave equation a non‐classical prescription for the calculation of the mobility is derived. In three as well as in one dimensions the new formula reproduces exactly the classical limit for a large mean free path. For a filled band it yields no current. In the case d = 1 for short mean free paths the conductivity departs significantly from its classical value, but not for d = 3.
Cyclotron Masses and Many‐Body Effects in Transition Metals
Authors: Schmidt B. , Antonov V. N. , Mrosan E. 
Published: July 2007

AbstractCyclotron masses for extremal orbits in Nb, Ta, W, Ir. Pt, and Au are calculated using a relativistic APW band structure. The integration along the extremal electron orbits over the Fermi surface is performed numerically using the well known tetrahedron method. Results are compared with experimental values obtained from the de Haas‐van Alphen investigations. The influence of manybody effects is discussed.
Experimental Check of Different Additional Boundary Conditions in Case of Spatial Dispersion
Authors: Skettrup T. 
Published: July 2007

AbstractReflection and transmission spectra are computed for the A‐ and B‐excitons in ZnO which exhibit spatial dispersion. The different additional boundary conditions are tested by comparison with the corresponding experimental spectra. Without exciton free surface layer the Pekar condition (perfect reflection and vanishing of excitonic wave function at the surface) yields the best fit to the experimental spectra. The agreement is improved if the damping is assumed k‐dependent. With exciton free surface layer included it turns out that the best agreement is obtained if only part of the excitonic wave function is reflected from the surface. Without k‐dependent damping about 50% must be reflected, and with k‐dependent damping about 70% of the excitonic wave function must be reflected from the surface. A simple method is also described from which the transmission spectra of spatially dispersive crystal slabs with exciton free surface layers can be computed.
Mixed Valence State and Metal–Non‐Metal Transition of KCP
Authors: Nagasawa H. 
Published: July 2007

AbstractOn the basis of the recent XPS results, which established the existence of Pt4+ ions in KCP at 153 K, a new model is proposed of platinum valence state in KCP, that is, a valence mixing state of 0.85 Pt2+ and 0.15 Pt4+ ions as a ground state and Pt3+ ionic state as an excited state. The experimental results of the conductivity, the spin susceptibility, the NMR relaxation, the EPR relaxation, and the neutron scattering are discussed according to the present model.
An Assessment of the High‐Energy Approximation in the Dynamical Theory of Electron Diffraction
Authors: Kim H. S. , Sheinin S. S. 
Published: July 2007

AbstractThe high energy approximation in the dynamical theory of electron diffraction is assessed for both the symmetrical Laue and non‐symmetrical Laue cases. In order to carry out this assessment an exact form of the theory, expressed as an eigenvalue equation, is first developed. The results obtained show that for the normal operating conditions which prevail in the electron microscope examination of crystals, the errors introduced by the high‐energy approximation in the symmetrical Laue case are small. In the non‐symmetrical Laue case, the errors obtained for strong beam diffraction conditions are also small. For weak beam diffraction conditions, however, significant errors can be obtained.
Temperature and Coupling Strength Dependence of Polaron Effective Mass and Radius
Authors: Fedyanin V. K. , Rodriguez C. 
Published: July 2007

AbstractPolaron effective mass and radius are investigated by using path integral methods. The calculations are performed in the framework of the variational principle for the free energy. At low temperatures, a generalization of Feynmans expression for the effective mass and an expression for the polaron radius at arbitrary coupling are obtained. It is shown that at low temperatures, the effective mass increases and the radius decreases with increasing temperatures. This behaviour of the effective mass agrees satisfactorily with cyclotron resonance experiments and is easily explained qualitatively.
Hyper‐Raman Scattering by Phonons and Mixed Polaritons in a Calcite Crystal
Authors: Denisov V. N. , Mavrin B. N. , Podobedov V. B. , Sterin Kh. E. 
Published: July 2007

AbstractThe polarized hyper‐Raman spectra of a calcite crystal in different scattering geometries are obtained. Two silent A1u‐vibrations at 227 and 1085 cm−1 as well as infrared active vibrations are found. The upper branch of mixed A2u‐polaritons and their resonance with Eu‐vibrations is investigated. The calculation of mixed polariton dispersion curves is presented.
Partial Structure of Liquid Sodium—Cesium Alloys
Authors: Rao R. V. Gopala , Satpathy B. M. 
Published: July 2007

AbstractThe partial structure factors defined by Ashcroft and Langreth and also the number–number, number–concentration, and concentration–concentration structure factors of Bhatia and Thornton are calculated for liquid sodium–cesium alloys at various concentrations with a square‐well potential. The total structure factor obtained from these partials compares very well with experimental results. Isothermal compressibilities obtained from the partial structures in the long wave limit are also found to compare satisfactorily with those calculated from sound velocity data.
On the Nature of the Oscillating Behaviour of the Free Induction Decay
Authors: Sabirov R. Kh. , Vinukhov I. A. 
Published: July 2007

AbstractEvans and Powles' theory is used for the investigation of the transverse autocorrelation and pair correlation functions for quantum spins with truncated dipolar interaction in a simple cubic lattice. It is shown that the oscillating behaviour of the free induction decay (FID) function is determined by the contribution of the pair correlation functions in the FID function describing the evolution of the transverse magnetization. The role of the orientational dependence of the dipolar interaction constants with the appearance of oscillations in the FID is investigated. Estimates of the FID function for a model Hamiltonian are made.
Bound Exciton Time Decay and the Auger Effect in Zinc Telluride
Authors: Schmid W. , Dean P. J. 
Published: July 2007

AbstractThe measured lifetimes for the decay of excitons bound to a variety of neutral acceptors in ZnTe reveal a complex trend with increase in the acceptor binding energy EA. The lifetimes increase with EA up to > 0.15 eV, in a manner expected for radiative transitions because of the decrease in the giant oscillator strength of the transition with increase in localisation of the electronic particles. Although rather few well‐identified acceptor species are available with EA > 0.15 eV, it is clear that this trend of lifetime is sharply reversed in this range, as expected if the Auger (non‐radiative) recombination rate overtakes the decreasing radiative rate near EA ≈ 0.15 eV. Comparisons with other available data from direct and indirect gap semiconductors support this relationship between the transition rates. Therefore, a much more significant role for Auger recombinations is found in bound exciton and other transitions involving more than two electronic particles than previously recognised for direct gap semiconductors.
Double Structure of AX and AT Emissions in Low‐Doped KI:TI+ Crystals
Authors: Benci S. , Fermi F. , Reverberi R. 
Published: July 2007

AbstractThe emission spectra of low‐doped crystals (up to 10 ppm) of KI:TI+ (as‐received, quenched and slowly cooled from 500 °C) show the presence of a center, probably a dimer center, that absorbs at λ > 2900 Å at LNT and emits in the range of the AT and AX emissions of the monomer. The emissions of this center affect the emission spectra at T > LNT also for excitation at λ < 2900 Å.
On the S‐Shaped Characteristic of Semiconductors at Low Temperature
Authors: Proctor W. G. , Lawaetz P. , Marfaing Y. , Triboulet R. 
Published: July 2007

AbstractIt is shown that when the energy level pattern of an impurity in a semiconductor is reduced to the ground state and one excited state, and when the occupation of this excited state is a necessary step for both impact excitation and relaxation, an S‐shaped dependence of the carrier density upon the electric field dependent impact parameters is obtained. Simple functions of the impact parameters are measured against electric field for ZnTe at 77 K using the above theory.
Conversion of Impurity—Vacancy Complexes under γ‐Irradiation and Subsequent F Band Bleaching in KCI:Eu2+
Authors: Mladenova M. , Malinovski A. , Georgiev M. 
Published: July 2007

AbstractThe ESR signal from I‐V complexes in KCI:Eu2+ is found to decrease markedly as a result of γ‐irradiation and to vary swing‐wise on subsequent F band bleaching at RT. The main bleaching process is explained by the superposition of Z1 centre formation and the revival of I‐V complexes following photostimulated recombination of F centres with I‐V‐trapped interstitials. Evidence seems also to be obtained for Eu+ formation at the initial bleaching stage.
X‐Ray Spectroscopic Study of Rare Earth‐Gallium Intermetallics RGa2
Authors: Prabhawalkar V. , Padalia B. D. 
Published: July 2007

AbstractRare earth‐gallium, RGa2 (R = La, Ce, Pr, Nd, Sm, Tb, Ho, Er, and Tm) intermetallic compounds are prepared and checked for single phase formation. The K‐absorption spectrum of Ga and the L3‐absorption spectrum of R in RGa2, are recorded photographically. A forbidden transition, 2P3/2 4f (unoccupied) is detected for TbGa2, DyGa2, HoGa2, and TmGa2 indicating the presence of a open 4f shell in these compounds. The measured chemical shifts exhibit linear relationship with theoretically estimated values ofeffective charges on the absorbingions. An attempt is made to calculated the edge shifts theoretically. The R‐Ga and Ga‐Ga bond lengths estimated using EXAFS methods show reasonable agreement with crystallographic data. The parameter, α, which is a measure of chemical bonding in the system, is evaluated using the graphical methodof Lytle, Sayers, and Stern.
Entropy of Mixing of Liquid Alloys
Authors: Singh P. , Khanna K. N. 
Published: July 2007

AbstractAn analysis of the concentration dependence of the entropy of mixing, based on the idea of excess volume formation on alloying the hard spheres of different diameters, is presented. Flory's formula for the entropy of mixing provides unsatisfactory results also due to incorrect estimation of excess volume formation in the theory.
Contributions to “Crystal Fields” from Electron Kinetic Energy Terms
Authors: Dixon J. M. , Chatterjee R. , McInnes J. A. 
Published: July 2007

AbstractThe magnitude of contributions to the B crystal field coefficient, from second‐order kinetic energy terms, is estimated and compared with the value from other sources. Its relative value is small and never greater than approximately 10%. If the parameters chosen in the paper for the 3s oxygen state are used, the contributions to B, B, and B are 1 to 2 cm−1.
Electrodynamics of a Spatially Dispersive Medium with Spherical Cavity
Authors: Kryuchenko Yu. V. , Sugakov V. I. 
Published: July 2007

AbstractThe exact solution of the problem of electromagnetic wave scattering by a spherical inclusion in a spatially dispersive medium is obtained. In comparison with well‐known results of the Mie theory of a medium without spatial dispersion the main new features are: (i) the frequency dependence of the scattering cross‐section is changed; (ii) the transformation of normal waves from one type into another takes place at the inclusion; (iii) the states bound to the spherical inclusion have finite lifetimes even in the absence of usual dissipative mechanisms. For some physical systems (excitons in CdS) the numerical calculations of scattering cross‐sections are performed. The frequencies and lifetimes of states bound to the spherical inclusion are also determined.
The Excitation Map of Surface Barrier Resonances III. Resonances at Tilted Incidence on the Ni(001) Surface
Authors: Solbrig H. 
Published: July 2007

AbstractThe excitation map (|det (I – RphS+−)| as a function of E, k|; Rph, S+− reflection matrices of the substrate and the barrier, respectively) is used for qualitatively treating the following aspects of surface barrier resonances: decomposition of complex resonance states with respect to their source effects (beam emergences), ground resonance and Bragg effects, resonance profile and resonance energy, and interaction and superposition of resonance processes.
Polarization Dependence of Two‐Photon Magnetoabsorption of the 1S Exciton in Cu2O
Authors: Fröhlich D. , Kenklies R. 
Published: July 2007

AbstractThe formalism for the two‐photon polarization dependence of a Γ state (Oh symmetry) in a magnetic field is developed. Experiments on the 1S exciton (yellow series) in Cu2O yield an unambiguous assignment of magnetic quantum numbers, thus allowing to determine g‐values.