bluuebunny/crossref_metadata_2025_split huggingface dataset:
Energy levels of A and B excitons in wurtzite‐type semiconductors with account of electron–hole exchange interaction effects
Authors: Flohrer J. , Jahne E. , Porsch M. 
Published: July 2007

AbstractThe effect of both the complexity of the two upper valence bands as well as the electron–hole exchange interaction on the exciton binding energies in wurtzite‐type semiconductors is studied. The energy level scheme and explicit expressions for the lowest exciton states of both A and B series are given. Using recent very accurate experimental data on exciton energies in CdS, the averaged B band hole mass is estimated to 1.6mo, and the position of the n = 1 B(Γ2) exciton level to about 0.2 meV below the transverse B(γ5) level. The longitudinal–transverse splitting of γ5 excitons is calculated from a microscopic approach in excellent agreement with experimental data taking into account an interband momentum matrix element P = 21 eV screened by a background dielectric constant ε' = 8. The exchange parameters introduced by Cho are determined for CdS to 3j0 ≈ 1 meV and 9j1 ≈ 2.1 meV.
Investigation of sulfur molecular paramagnetic centers in SrCl2
Authors: de Siebenthal J. M. , Bill H. 
Published: July 2007

AbstractS and S centers in SrCl2 single crystals are observed. The underlying experimental investigation is carried out by EPR, Raman, and optical absorption spectroscopy. The S centers show dynamical features in their EPR spectra. The temperature dependence of these spectra is compared with the results of the Kubo line shape theory. This enables to identify the motion as a thermally activated reorientation of the center between two equivalent equilibrium positions.
Electromagnetic absorption in antiferromagnetic chromium
Authors: Cuden C. B. , Guedes J. , Malbouisson J. M. 
Published: July 2007

AbstractThe inconsistencies between the theoretical and experimental predictions of the electromagnetic absorption in chromium, magnesium, and potassium are discussed. For the case of chromium, the absorptive part of conductivity as a function of frequency and temperature is calculated for the photon absorption by one‐electron, one‐hole, and electron–hole pair excitations. It is shown that the unphysical divergence of the absorptive part of conductivity for the photon frequency equal to twice the antiferromagnetic energy gap, found by Fedders and Martin, is removed by taking properly into account the statistical coherence effects.
A model theory of ferroelectric and other structural phase transitions of first and second order
Authors: Albers J. 
Published: July 2007

AbstractA model is presented in which the appearance of displacive phase transitions is explained by short‐range internal forces. Electrically charged or uncharged parts of the structure are squeezed out of symmetrical positions and thus lead to a symmetry‐lowering and to phase transitions of ferroelectric or pure structural types. A simple microscopic potential describes transitions of first and second order in good agreement with data of ferroelectric crystals. The Taylor series expansion of this potential allows the comparison with Devonshire's theory.
On the dielectric response of solids II. Local field effects in the phonon‐induced density change of a semiconductor
Authors: Schulze K.‐R. 
Published: July 2007

AbstractIt is examined in one important example how the recently developed approximations for the consideration of local‐field effects in solid‐state screening do work for semiconductor problems. While the perturbation‐theoretical formula for the dielectric matrix leads to a noticeable overestimation of the semiconductor screening, the proposed local‐density approximation results in an excellent agreement with „exact”︁ data from extensive calculations.
Anisotropic K absorption in gallium
Authors: Weber W. M. 
Published: July 2007

AbstractFor linearly polarized X‐rays, a marked orientation dependence of the extended K‐absorption fine structure of a single crystal of gallium is observed at 5 K. Spectra calculated from Kostarev's theory of K absorption of unpolarized and polarized X‐rays in single crystals are in good agreement with the experiment.
Scattering of phonons and ultrasonic attenuation by donors in doped diamond‐type semiconductors
Authors: Singh Mahiradhwaj 
Published: July 2007

AbstractThe relaxation rates for scattering of phonons by bound donor electrons in diamond‐type semiconductors whose conduction band minima are along [100] direction, are obtained in presence of internal static and dynamic strains and an external magnetic field. The coefficients of ultrasonic attenuation by bound donor electrons are also obtained for the above semiconductors in presence of strains and magnetic field. The expressions for electron–phonon relaxation rate are used in explaining the phonon conductivity results of P‐doped silicon at low temperatures. The present theory gives excellent agreement between theory and experiment.
Boundary conditions for polarization waves in spatially dispersive dielectrics
Authors: Stahl A. 
Published: July 2007

AbstractSpatial dispersion in bounded media affords so called additional boundary conditions (ABC) in order to match polarization waves. A method is described how these ABC can be found in the framework of phenomenological transport theory. The procedure is illustrated by two examples: a phononlike system and an electronic exciton system. The result is that without additional assumptions the gradient condition ΔP = 0 comes out as the preferred boundary condition. The commonly used Pekar condition, P = 0, is attributed to the case where the dynamical properties are disturbed in a boundary layer.
On the theory of resonant secondary radiation of excitons strongly interacting with phonons
Authors: Hizhnyakov V. V. , Sherman A. V. 
Published: July 2007

AbstractA theory of resonant secondary radiation of self‐trapped Frenkel excitons strongly interacting with phonons both in self‐trapped and band states is developed. The absorption and ordinary luminescence spectra of such excitons are shown to be close in form to those of the impurity centre. Formulae for partial spectra are found. The corrections taking account of the electronic excitation transfer from site to site cause the asymmetry of the absorption spectrum and the excitation profiles of partial spectra. The width and general form of the exciton band can be determined from the value and sign of the asymmetry.
Spin—lattice relaxation of 19F and magnetic couplings in rare‐earth fluorides
Authors: Svare I. 
Published: July 2007

AbstractMeasured relaxation times T1 and T1ρ of 19F in CeF3, PrF3, NdF3, and SmF3 from 100 to 400 K give information about electron magnetic moment correlation times. Exchange‐type couplings Ce3+F and Ce3+Ce3+ are larger than the corresponding dipolar couplings. Such couplings are less important in PrF3, and they do not influence T1 and T1ρ in NdF3 and SmF3. Raman electron spin—lattice relaxation ∼ T2 dominates over spin flips in SmF3, and direct relaxation ∼ T dominates in NdF3.
Theory of local electronic states in a semi‐infinite mixed crystal
Authors: Ueba H. , Ichimura S. 
Published: July 2007

AbstractA theory is presented to study the local electronic states in a semi‐infinite mixed crystal, by extending the coherent potential approximation developed in the study of an infinite bulk crystal to a suitable one for a semi‐infinite crystal. The effect of semi‐infinity of a crystal is taken into account by Sugakov's method in which the wave function of an electron is expressed in terms of a standing wave with nodes. The site‐dependent coherent potentials are introduced to calculate the local density of states in a semi‐infinite mixed crystal. The appearance of the localized surface state is also discussed.
Vacancy and interstitial configuration in hexagonal close packed metals
Authors: Tomé C. N. , Monti A. M. , Savino E. J. 
Published: July 2007

AbstractThe lattice static Green function and computer simulation methods are used in order to calculate the lattice distortion owing to a vacancy and a self‐interstitial in a hexagonal close packed lattice. A semidiscrete method is developed for the perfect lattice Green function evaluation. An empirical potential deduced by fitting magnesium parameters, and a pseudopotential, deduced for that metal, by Appapillai and Heine, are adopted for the calculation. The validity of using those potentials is discussed. An almost isotropic and very small lattice distortion is calculated for the vacancy, while a large and anisotropic lattice distortion calculated for an interstitial atom determines the trigonal (tetrahedral) configuration to be stable with respect to the hexagonal (octahedral) one.
Intraband absorption in lead chalcogenide mixed crystals
Authors: Kurowska A. 
Published: July 2007

AbstractFree carrier absorption due to the chemical disorder is calculated for lead chalcogenide mixed crystals, taking into account the actual band structure. It is found that in an alloy the absorption coefficient due to composition fluctuations may be comparable with the intraband absorption due to the LO polar scattering, at low temperatures.
Isomer shift and quadrupolar splitting of the Mössbauer spectrum of ferroelectrics
Authors: Bashkirov Sh. , Lebedev V. N. 
Published: July 2007

AbstractThe parameters of the Mössbauer spectrum of Fe3+ ions in ferroelectrics are considered. It is shown that the internal electric fields in ferroelectrics cause the strong polarization of the—covalency occupied 4s shell of Fe3+. This gives the significant contribution to the isomer shift and quadrupolar splitting of the Mössbauer spectrum. For BaTiO3, this contribution determines both sign and magnitude of the observed discontinuous change of the shift at Tc. It is also shown that the structure reconstruction of BaTiO3 decreases the isomer shift at the transition in the ferroelectric phase. The contribution of the electrically polarized 4s shell of Fe3+ ion to the quadrupolar splitting of the Mössbauer spectrum for BaTiO3 gives more than a half of the observed value of the quadrupolar splitting.
Correlation of zero‐field splittings and site distortions I. MnCl in approximately trigonal symmetry
Authors: Sachs H. , Lehmann G. 
Published: July 2007

AbstractEPR parameters for Mn2+ in single crystals of (CH3NH2)2ZnCl4 and (enH2)2ZnCl6 (en = ethylene diamine) are reported. The axial splitting parameter B for these and two other systems from the literature are approximately proportional to the size of the trigonal site distortion. The rhombic parameter B also correlates well with the amount of deviation from true C3 symmetry. For large distortions the z‐axes of the EPR parameters are close to the direction of the longest ZnCl bond. Thus the distortion of the first coordination sphere of the paramagnetic ion appears to determine the size of the second order fine structure parameters if the bond lengths differ by at least 1 pm.
Spin wave stiffness constant of narrow‐band ferromagnetic alloys with random hopping
Authors: Kolley E. , Kolley W. 
Published: July 2007

AbstractThe spin wave stiffness constant D of ferromagnetic binary metallic alloys is derived at zero temperature from a random Hubbard model including diagonal and off‐diagonal disorder. The fluctuations of the hopping integrals are restricted to the additive limit. Vertex corrections to D due to the randoness of the transverse spin current are calculated in an extended CPA. D is renormalized by electron‐electron correlations within the coherent horizontal ladder approximation. Stability and damping of the spin waves, Ward relations, and the electrical conductivity are discussed.
Impurity scattering effect on the cyclotron resonance of carriers in Cu2O
Authors: Goltzené A. , Schwab C. 
Published: July 2007

AbstractCyclotron resonance is made on purest and deliberately Fe‐doped Cu2O to assess the extrinsic origin of one of the two polaron masses previously reported (0.58m0 and 0.69m0). Only one mass is observed, which shifts to higher values with doping and is excitation wavelength dependent, except for the best undoped material. The latter shows the lowest mass, ascribed therefore to the uppermost valence band. Material improvements are discussed with respect to the carrier lifetimes.
Certain features of semiconductor behaviour in strong parallel magnetic and electric fields I. Effect of electric field on the magnetic moment of a specimen
Authors: Berezhkovskii A. M. , Ovchinnikov A. A. 
Published: July 2007

AbstractIt is shown that the spin contribution to the magnetic moment of a semiconductor specimen placed in strong parallel magnetic and electric fields becomes zero when the energy of spin splitting in magnetic fields is a multiple of the energy difference between adjacent Wannier‐Stark levels in electric fields.
On the static conductivity of a heavily doped semiconductor
Authors: Arbuzov Yu. D. , Evdokimov V. M. 
Published: July 2007

AbstractIt is shown that the static conductivity of a heavily doped semiconductor may be obtained in terms of a transport relaxation time. Not only the term of Born's approximation is regained in the framework of the assumptions made but as well the terms associated with the scattering by two impurities are taken into account. The relevant correction to the static conductivity is calculated.
Eigenoscillations of Hot Electrons in an Inhomogeneous Semiconductor under Classically Strong Magnetic Field
Authors: Dykman I. M. , Prokhnitskii L. A. 
Published: July 2007

AbstractAn extrinsic semiconductor with periodic impurity distribution is studied. The distribution function in such a semiconductor applied to a mutually perpendicular heating electric field and a classically strong magnetic field is determined. The spectrum of electron gas eigenoscillations is calculated. The frequencies of eigenoscillations are proved to be considerably sensitive to the electric field strength. The spatial periodicity of the semiconductor changes the number of vibrational modes. Similarly to other works, semiconductor inhomogeneity results in resonance‐type dependencies for some modes. The magnetic field is also found to be the factor changing significantly the spectrum of eigenoscillations.
Some Special Models of the Spatial Theory of Dispersion
Authors: Litzman O. , Holý V. 
Published: July 2007

AbstractA classical system of dipoles is investigated interacting via retarded dipole‐dipole and nonretarded “mechanical” forces. On the basis of formulae deduced in previous papers two models of mechanical forces (exponential model and next‐nearest neighbour model) are investigated. After evaluating of refraction indices and reflexivity for both the models it is shown that the results are comparable with those of the continuous model dielectric.
An Improved Molecular Field Approach to the Triangular Ising Antiferromagnet
Authors: Doman B. G. S. 
Published: July 2007

AbstractThe phase transitions are examined of a triangular lattice with Ising model interactions which are antiferromagnetic for nearest neighbours and ferromagnetic for second neighbours. It is assumed that the ferromagnetic interaction is much smaller than the nearest‐neighbour interaction. The average spin is worked out on a given site for all possible spin configurations of the neighbours. This is then weighted according to the neighbours' probabilities of being up or down. Several possible states of the system are found. The stable state is selected by using the free energy.
Fluorescence of Interstitial Atomic Hydrogen in Alkali Halides Doped with I−
Authors: Lohse F. , Spaeth J. M. 
Published: July 2007

AbstractIn KCl and RbCl doped with I− interstitial atomic hydrogen shows fluorescence emission if one of the four chlorine neighbours is replaced by an I−. In KCl one emission band at 2.84 eV with a radiative decay time of 14 ns and two overlapping bands at 1.97 eV with decay times of 34 ns and 720 ns (at 4 K) are observed. Similar results are found for RbCl. The results are interpreted as due to two charge transfer type relaxed excited states, one of which is a spin quartet and responsible for the long radiative lifetime.
On the Interaction between F‐ and α‐Centres in KBr
Authors: Bosi L. , Nimis M. 
Published: July 2007

AbstractLuminescence measurements show an increase in the F‐centre lifetime in KBr, corresponding to a critical α‐centre concentration after F→F′ conversion. An inhibition of the luminescence quenching effect, related to the F‐centre density, is also observed. The results are discussed in respect of the Crandall photoconductivity data and explained on the basis of an interaction mechanism that involves the electron capture cross‐section by α‐centres and the mean distance between F‐centres.
Magnetopolaritons in Wurtzite‐Type Crystals
Authors: Röseler J. , Henneberger K. 
Published: July 2007

AbstractThe influence of a magnetic field on the polariton dispersion resulting from the An = 1 excitons in wurtzite‐type crystals is calculated by the diagonalization of the Hamiltonian describing magnetoexciton–photon interaction. Remarkable changes compared with the field‐free dispersion are obtained: Beside energy shifts, new branches and crossing points arise due to the field‐induced mixing of exciton states. The results should be interesting also with respect to final states of the radiative decay of biexcitons in crystals like CdS and CdSe.
Chemical Shifts of the L3‐Absorption Edge of Pt in the Rare Earth–Platinum Intermetallic Compounds
Authors: Koul P. N. , Hatwar T. K. , Ghatikar M. N. , Padalia B. D. 
Published: July 2007

AbstractChemical shifts of the L3‐absorption edges of Pt in RPt2 and RPt5 compounds are measured and correlated with the effective charges calculated using Siegbahn's method. It is found that the L3‐edge shifts towards the lower‐energy side of the Pt metal edge in RPt2 compounds, while in the case of RPt5 the shifts are in opposite direction. An attempt is made to explain the behviour of these chemical shifts.
OOn the Origin of Localized Magnetic States in Transition Metal Alloys II. Doubly Degenerate Orbitals
Authors: Oleś A. M. , Morkowski J. 
Published: July 2007

AbstractA doubly degenerate model of transition metal impurities is solved in a hierarchy of approximations which conserve up to first four moments of the spectral density function. It is shown that the Hund's rule plays a crucial role in the local moment formation stabilizing configurations with more than one electron (hole) per impurity. The present model is qualitatively consistent with available experimental data and explains why magnetic moments are formed on Fe or Co atoms while they cannot be stabilized on Ni.
Theoretical Calculation of the Absorption Energy of the F‐Centre in Alkali Halides
Authors: Dochy F. 
Published: July 2007

AbstractThe absorption energy of the F‐centre in all 20 alkali halides are calculated in a pseudopotential theory developed by Bartram, Stoneham, and Gash, using a point‐ion lattice with an ion‐size correction. Polariztion and lattice distortion effects are included. Different anlaytical forms for the trial pseudo‐wave functions are investigated. It is found that the empirical reduction factor, introduced by Bartram, Stoneham, and Gash depends strongly on the type of wave function used.
The Electron Structure of 3d Metals
Authors: Ksendzov Ya. M. 
Published: July 2007

AbstractThe available data on the electron energy losses in 3d metals from Sc to Cu are analyzed, and the energy loss maxima corresponding to plasmons are isolated. The number of plasmons changes from one in the beginning of the 3d series to three starting with Fe. This implies that the 4s + 3d electrons can be hybridized in one band or distributed over two or three bands separated by gaps. Taking into account the field acting on the core electrons (the Ar shell) makes it possible to obtain a refined formula for the effective plasma frequencies, which is used to calculate the electron concentration in the conduction and valence bands of the 3d metals. A proper consideration of the conditions at which the electrons of the valence bands, similar to those of the conduction bands, can be regarded as a quantum plasma permits to construct a diagram of distribution for the electron and spin densities of states as a function of energy. The electron density distribution in the 3d metals differs from that for the 3d atoms as well as from the one calculated for metals in recent theoretical works. The diagram of the electron and spin densities of states thus obtained is compared with other experimental data, viz. the X‐ray and neutron form factors, Hall effect, optical, photoemission, and X‐ray emission spectra.
Stress‐Induced Alignment of Jahn‐Teller Centres Cr2+ in ZnSe Crystals. Optical Study
Authors: Ryskin A. I. , Vasilev A. V. , Natadze A. L. 
Published: July 2007

AbstractUniaxial compression of ZnSe–Cr crystals along the fourth‐order axis results in shift and splitting of the zero‐phonon lines of the absorption band, connected with the 5B̂2(5T2) → (5Â1 + 5B̂1) (5E) transition of the impurity Cr2+ ions, and in dichroism, which is caused by the reorientation of the Jahn‐Teller centres Cr2+ along the stress direction. Spectra of stressed crystals are calculated on the base of the exchange‐charge model. In imperfect (twinned) ZnSe crystals two types of Cr2+ centres are observed. These centres are identified as Cr2+ ions in the interlayers of a twin structure.
Reflections of a New Type in the Mössbauer Diffraction Pattern
Authors: Kolpakov A. V. , Ovchinnikova E. N. , Kuzmin R. N. 
Published: July 2007

AbstractA new type of the Bragg reflections in the Mössbauer diffraction pattern, apart from the well‐known magnetic and quadrupole ones, is discussed. These reflections may be observed in the Mössbauer diffraction pattern only in the case when there are both the magnetic field and the electric field gradient at nuclei of Mössbauer isotope, i.e. two static internal fields with symmetries described by the ∞/m and ∞/mmm groups. The Mössbauer diffraction pattern of a KFeF4 single crystal is considered in detail.
One‐ and Two‐Phonon Raman Scattering in Ternary Phosphides ZnSiP2, ZnGeP2, CdSiP2
Authors: Gorban I. S. , Gorynya V. A. , Lugovoi V. I. , Krasnolob N. P. , Salivon G. I. , Tychina I. I. 
Published: July 2007

AbstractOne‐ and two‐phonon Raman scattering (RS) of orientated single crystals of ZnSiP2, ZnGeP2, and CdSiP2 are investigated. For the first time in ZnSiP2 the lattice vibrations B2(L/T) 146/145 and B1 466 cm−1 are observed, and the values of L–T splitting of polar modes are determined. It is concluded that in crystals of ZnGeP2, ZnSiP2, and CdSiP2 a completely symmetric component of the second‐order RS spectra is formed by overtones and gives the distribution of the phonon state density of the lattice of these compounds. This distribution is determined in the main by the points Λ, T, N of Brillouin zone and has the general form for all compounds investigated. An estimation is given of the frequencies ofinactive A2‐phonons in ZnGeP2, ZnSiP2, and CdSiP2.
Certain Features of Semiconductor Behaviour in Strong Parallel Magnetic and Electric Fields III. Interband Absorption
Authors: Berezhkovskii A. M. , Ovchinnikov A. A. 
Published: July 2007

AbstractIt is shown that under certain conditions the absorption spectrum of a semiconductor placed into strong parallel magnetic and electric fields transforms from a continuous into a discrete and equidistant form with energy intervals between the adjacent absorption maxima equal to the energy of a Wannier‐Stark ladder step.