bluuebunny/crossref_metadata_2025_split huggingface dataset:
f‐Level Green's Function for an Intermediate‐Valence Impurity
Authors: Schlottmann P. 
Published: July 2007

AbstractMori's technique is used to rederive the f‐level Green's function of a mixed valence impurity with two arbitrary ionic configurations. The result agrees with the Brillouin‐Wigner resummation of Goldstone diagrams by Grewe and Keiter. The leading Brillouin‐Wigner approximation leads to an unphysical gap in the excitation spectrum of the impurity, which is closed in next leading order. The drastic change in the excitation spectrum is related to a violation of the fluctuationdissipation theorem. The consequences of a gap or continuous excitation spectrum are discussed. The advantage of the method is that only two commutators need to be evaluated in order to rederive the Brillouin‐Wigner results.
Optically Induced Potential Fluctuations in a‐Si:H Films
Authors: Hauschildt D. , Fuhs W. , Mell H. 
Published: July 2007

AbstractThe influence is studied of prolonged optical exposure on the properties of the current path in glow discharge deposited a‐Si:H films. Information on these properties is obtained from concomitant investigations of the conductivity σ and thermoelectric power S as a function of temperature. It is found that the activation energies of both quantities, Eσ and ES, increase appreciably upon light exposure. At the same time the difference Eσ — ES = EQ rises from ≈ 0.09 to 0.21 eV. The quantity EQ, which is an apparent mobility activation energy, is associated with spatial fluctuations of the mobility edge. The increase of EQ is attributed to the enhancement of potential fluctuations which is caused by inhomogeneously distributed charged centers generated during optical exposure.
Magnetization, Electrical Resistivity, Thermopower, and Neutron Diffraction in HoCu2
Authors: Gratz E. , Sechovsky V. , Sima V. , Smetana Z. , Ström‐Olson J. O. 
Published: July 2007

AbstractHoCu2 shows a Curie‐Weiss susceptibility above 15 K. The paramagnetic moment and the paramagnetic Curie temperture is (10.1 ± 0.1) μB/H0 and (4 ± 2) K, respectively. Two cusps (at about 7 and 10 K) are seen in the magnetization versus temperature curve. These cusps reflect a change of the magnetic structure and the Néel temperature. The influence of conduction electron scattering on the localized 4f moments is estimated for the resistivity and the thermopower. Neutron diffraction measurements show that the antiferromagnetic structure is incommensurate with the crystal lattice.
Ultrasonic Investigation of the Acceptor Ground State of Si(B) I. The Longitudinal and Transverse Relaxation Rates of the Strain‐Split Two‐Level System
Authors: Zeile H. , Harten U. , Lassmann K. 
Published: July 2007

AbstractThe “spin”‐lattice relaxation of the two‐level system of the strain‐split acceptor ground state of Si(B) is determined from the temperature dependence of the ultrasonic relaxation attenuation, around 10 K. It is found that Raman relaxation alone does not fit the results but that, in addition, an Arrhenius‐type of relaxation, possibly due to a Jahn‐Teller effect, is involved. The transverse relaxation is obtained from intensity‐dependent and hole‐burning measurements of the resonant attenuation. At small acceptor concentrations it is determined by “spin”‐lattice relaxation alone; for higher concentrations an additional temperature‐independent interaction term is found much smaller than expected for elastic dipole or exchange interaction.
Host‐Lattice Effects in the EPR Spectra of Gd3+ Doped Hydrated Single Crystals of Rare‐Earth Chlorides, Nitrates, and Sulphates
Authors: Misra S. K. , Mikolajczak P. , Jalochowski M. 
Published: July 2007

AbstractLarge amount of X‐band EPR data, for external field orientations in both, the zx and xy planes, are obtained for Gd3+ ion doped rare‐earth trichloride hexahydrate (RCH), rare‐earth trisulfate octahydrate (RSO), and rare‐earth trinitrate hexahydrate (RNH) single crystals. A rigorous least‐squares fitting procedure is used to evaluate the spin Hamiltonian parameters g‖, g⊥ and b (including those with negative m values). Approximate linear dependences upon the host rare‐earth ion radius is found on both, the parameters b and b within each family of the isostructural hosts investigated.
Calibration of the Isomer Shift for the 67.03 and 13.3 keV Transitions of 73Ge
Authors: Antoncik E. , Bing‐lin Gu 
Published: July 2007

AbstractThe usual procedure using free‐atom/ion wave functions to calibrate the Mössbauer isomer shifts is modified in order to include solid state and band structure effects properly. To estimate the electron densities at the nucleus, self‐consistent‐field Dirac‐Fock‐Slater wave functions are calculated for several electronic configurations of germanium atoms and ions, taking into account the finite space allowed to these atoms (ions) in solids. Using experimental isomer shift (IS) values, the calibration constants for 73Ge both for the 67.03 and 13.3 keV transitions are calculated, giving the relative change of the nuclear‐charge radius ΔR/R = 0.5 × 10−3 and ΔR/R = 1.2 × 10−3, respectively. The accuracy of the calibration procedure is discussed.
The Bond‐Bending Force Model (BBFM) for Phonons in β‐SiC
Authors: Kushwaha M. S. 
Published: July 2007

AbstractThe normal modes of vibrations for cubic SiC are investigated on the basis of an eight‐parameter bond‐bending force model (BBFM). The model consists of short‐range (central + bond‐bending) forces and long‐range Coulombic interactions including up to second nearest neighbours. The results for phonon dispersion relations in the three highest symmetry directions [100], [110] and [111], phonon density of states, and Debye‐charcteristic temperatures are shown. The theoretical results compare well with available experimental data.
Influence of Electron Heating on Reflection and Attenuation Coefficients of Electromagnetic Waves in Semiconductors with Superlattice
Authors: Dykman I. M. , Prokhnitskii L. A. 
Published: July 2007

AbstractThe electromagnetic wave reflection from the surface of a semiconductor with a superlattice in a heating electric field is studied. The superlattice is formed by the periodic distribution of the electron density. Frequency dependences of the reflection and attenuation coefficients in the vicinity of the Bragg resonance are calculated, taking into account electron interaction with lattice vibrations. These dependences are shown to have maxima at the resonance frequency ωR. The shape and magnitude of the maxima depend significantly on the ratio |ξ| ωR/v0, where the amplitude of electron density modulation |ξ| and the effective collision frequency v0 are functions of the heating field. The field dependences of |ξ| and v0 show the possibility of controlling the Bragg reflection effects, which can be used, for example, to investigate v0.
Pseudo‐Exciton Effect in the Schottky‐Barrier Electroreflectance
Authors: Kiselev V. A. 
Published: July 2007

AbstractAn account of the nonhomogeneity of the electric field in the space‐charge region of a semiconductor is presented. It is shown that the nonuniform field can lead to a sharp feature in the reflection spectra in the vicinity of a direct gap. The behaviour of this new lineshape with varying surface potential reproduces closely the behaviour of the exciton lineshape in reflection for which the phenomenon of “rotation” is well known. This effect is determined by the nonuniform character of the joint density of states involved in the band‐to‐band transition in the direction normal to the surface. The modulated electroreflectance spectra obtained employing the theory that neglects exciton effects are in good agreement with literature results of measurements on GaAs with donor concentration of 4.5 × 1016 cm−3 at room temperature. A possible application of the observed phenomenon, as well as that of the exciton lineshape rotation, to investigate the energy and time characteristics of the space‐charge region and surface (interface) states is discussed.
On the Long‐Wavelength Plasmon in the Alkali Metals A Nearly‐Free‐Electron Pseudopotential Calculation
Authors: Oliveira L. E. 
Published: July 2007

AbstractThe nearly‐free‐electron pseudopotential theory is used to calculate the macroscopic dielectric function ε(O, ω) for Li, Na, and K in the long‐wavelength limit within the self‐consistent‐field approximation. The plasmon energies are obtained from the peak position of the energy loss function Im [–1/ε(O, ω)]. The results are compared with the experiment and the agreement is good provided that the effects of ion‐core polarization in the long‐wavelength plasmon energy are taken into account.
Raman Scattering from Nonfundamental States in Ammonium Chloride Crystals at Low Temperatures
Authors: Umarov B. S. , Gorelik V. S. , Sushinskii M. M. , Vetelino J. F. 
Published: July 2007

AbstractThe Raman spectra of the δ‐phase of ammonium chloride crystals at low temperatures are carefully investigated. Particular attention is focused on the Raman spectra in the region of the internal vibrations of the ammonium group. At liquid helium temperatures intense sharp lines of definite symmetry type are observed. These lines are identified as two particle bound states (biphonons) in agreement with theoretical predictions.
Electron–Molecular Vibration Coupling in Trimerized Organic Ion‐Radical Semiconductors
Authors: Yartsev V. M. 
Published: July 2007

AbstractThe totally‐symmetric (ag) internal molecular vibrational excitations in a trimer are considered. The mode corresponding to the charge transfer (CT) between non‐centric molecules is shown to be responsible for the indirect IR activity. The trimer MO calculations in the site occupation representation are simplified and the symmetry of the basis states is taken into account. Eigenstates and eigenvalues of the molecular trimer with two radical electrons are calculated as a function of the transfer integral, t, and the Coulomb „on‐site”︁ repulsion, U. The following interpretation of the absorption spectrum of the cesium salt of tetracyanoquinodimethane Cs2(TCNQ)3 is given: the 1.4 eV peak is attributed to intratrimer charge transfer excitation, the less than 0.6 eV peak corresponds to the electronic transition between neighbouring trimers. The electron–molecular vibration coupling constants and Hubbard parameters U and t are evaluated for Cs2(TCNQ)3.
The Theory of the Strain Effects in the Crystals Described by the s (d)‐f Model
Authors: Stasyuk I. V. , Grigorchuk R. A. 
Published: July 2007

AbstractIn the framework of the s(d)‐f model taking into account the hybridization of localized and band states, the relative shift of the band and its broadening at strain, the possibility of the jump‐like change of unit‐cell volume and the localized state filling under external pressure is investigated. The phase diagrams in the pressure‐averaged total electron number plane are obtained. The behaviour of the crystal compliance at the phase transition induced by pressure is studied.
Metamagnetoelastic and Metamagnetoelectric Behaviour of the Jahn‐Teller Antiferroelastics
Authors: Kaplan M. D. 
Published: July 2007

AbstractIt is shown, that the magnetic field induced structural phase transition from the antiferrodistortional to the ferrodistortional phase is possible in Jahn‐Teller antiferroelastics. The phase transition under consideration is simultaneously the crystal transition from the ferroelectric into the antiferroelectric state. The anomalously sharp change of the crystal strain and polarization is realized in the range of the critical magnetic fields. Such a behaviour of crystal strain and polarization is named metamagnetoelasticity and metamagnetoelectricity, respectively. The properties of the ESR spectra of the system under consideration are analysed. The possibilities of experimental observation of the predicted effects are discussed.
An Interatomic Pair Potential for Copper Calculation of Stacking Fault Energy
Authors: Rautioaho R. H. 
Published: July 2007

AbstractTwo potential functions, V2(R) and Veff(R) are derived for Cu from phonon dispersion curves. V2(R) is fitted to the phonon frequencies without considering possible multi‐ion effects, whereas Veff (R) is constructed by including dominant multi‐ion interactions in the potential. V2(R) is in relatively close agreement with more fundamental potentials at short distances, whereas Veff(R) appears to give a somewhat better representation of the long‐range interactions. Both of these potentials are used in a calculation of the energies of intrinsic and extrinsic stacking faults. This calculation gives reasonable results, 30 mJ/m2 for γintr and 35 mJ/m2 for γextr.
Correlation of Transition Frequencies in Impurity Spectra of Inhomogeneous Solids
Authors: Kikas J. , Rätsep M. 
Published: July 2007

AbstractA statistical theory is developed to obtain the joint distribution function for frequencies of different transitions in impurities affected by matrix imperfections. The results are specified in the case of an inhomogeneous broadening caused by an elastic interaction of impurities with point defects and applied to axially symmetric impurities in cubic crystals to study the correspondence between ransition frequencies in different orientations of the impurity.
Magnetic Relaxation of Ideal Superparamagnets Studied by Monte‐Carlo‐Simulation
Authors: Kostinek J. , Markum H. , Rauch H. 
Published: July 2007

AbstractThe local and total magnetization of small magnetic particles are calculated using a Monte‐Carlo‐procedure and assuming a Heisenberg nearest‐neighbor interaction. The ideal magnetic system relaxes from a non‐equilibrium to an equilibrium state and the observed time constant is obtained in units of Monte‐Carlo steps for various temperatures. Further calculations deal with a system having an antiferromagnetic coupling for the spins within the surface layer. Such systems may simulate superparamagnetic particles with an oxide layer on their surfaces.
Influence of Secondary Excitons in Intensity and Decay of Phosphorescence in Doped Benzophenone Single Crystals
Authors: Melnik V. I. , Nelipovich K. I. , Faidysh A. N. , Shpak M. T. , Yankovskaya L. B. 
Published: July 2007

AbstractSpectroscopic and kinetics data for the phosphorescence of benzophenone crystals doped with deuteronaphthalene, naphthalene, and α‐bromonaphthalene are analyzed. It is established that the duration of the delayed excitonic phosphorescence depends substantially on τ of the impurity triplet states at T > 170 K. The results obtained are treated in terms of the thermal detrapping of impurity molecule excitation to the triplet excitonic band of the host.
Thermo‐ and Photostimulated Recombinations of F–HA and α–IA Centres in KBr with Large Na Concentration
Authors: Dauletbekova A. , Akilbekov A. , Elango A. 
Published: July 2007

AbstractIn KBr:Na (1 mol%), containing only FHA and α–IA pairs of radiation defects when X‐rayed at 80 K, the thermo‐ and photostimulated (by illuminating with light corresponding to the maxima of F or HA absorption bands) recombinations of these pairs are investigated. The recombination of α and IA centres takes place without emission. In the course of the recombination of HA centres with F centres excited by light there occurs an emission with the maximum at about 2.8 eV. It arises from the relaxation of a tunnelling‐created (HA + e)* centre. The luminescence, accompanying the recombinations of F and H centres (occurring during HA illumination) is very weak and no so‐called π‐emission (at 2.3 eV) is observed. It is concluded that the creation of a self‐trapped exciton by F–H recombination is not efficient.
Far‐Infrared Reflection Spectra, Optical and Dielectric Constants, Effective Charges, and Lattice Dynamics of the Skutterudites CoP3, CoAs3, and CoSb3
Authors: Lutz H. D. , Kliche G. 
Published: July 2007

AbstractFrom the far‐infrared reflection spectra of the skutterudite type compounds CoP3, CoAs3, and CoSb3 the TO and LO phonon frequencies at wave vector |q| ≈ 0 are determined by both Kramers‐Kronig analysis and classical oscillator fit method. In the case of CoP3 large free carrier contributions (plasma resonance frequency ω′p ⩽ Ω+ ≈ 800 cm−1) with strong plasmon–phonon interactions are observed. Attempts to calculate the decoupled phonon frequencies of CoP3 using a three and a four parameter model of the dielectric function failed. Lattice dynamical calculations are done by setting up a valence force field consisting of M–X, two X–X and X4–X4, and M–M stretching constants. The obtained force constants, e.g. f(CoSb): 85, f(SbSb): 87 and 59 N m−1, respectively, and also the calculated effective dynamical charges (from TO/LO splittings) show the mainly covalent character of the skutterudites under consideration. The lattice modes of CoSb3 are found to be both mainly internal vibrations of the planary Sb4‐units, v4 and v5, at 174 and 144 cm−1, respectively, and external ones, v1–v3 and v6–v7, at higher and lower wavenumbers than v4 and v5.
On the Electric Subbands in n‐Inversion Layers on (111) Ge
Authors: Germanova K. , Marinova K. , Trayanov A. 
Published: July 2007

AbstractSelf‐consistent results on the subband energy structure of n‐inversion layers on (111) Ge in the effective‐mass approximation at T = 4.2 and 77 K are presented. The nonequilibrium case with a bias voltage, applied between the inversion layer and semiconductor bulk, is described.
Superionic Conductivity versus Ionicity
Authors: Ogorelec Z. 
Published: July 2007

AbstractSome arguments given suggest that a group of ANB8–N solid electrolytes with monovalent cations may have a superionic phase only if its permittivities satisfy the equation (ε ∞ ‐ l)/(l/ε ∞ – l/ε0)2 ≈ 1000. There are indications of a wider validity of this equation.
Heat Pulse Diffusion in TEA(TCNQ)2
Authors: Grassi H. , Brau A. , Farges J. P. 
Published: July 2007

AbstractMeasurements of the thermal diffusivityDon crystals of the highly anisotropic organic semiconductor TEA(TCNQ)2are reported. These measurements are made using a heat pulse method. For the crystal axis 1 parallel to the TCNQ columns and associated with the largest component σ1of the electrical conductivity,D1is 1.6×10−3cm2s−1at 300 K increasing to 2.7×10−3cm2s−1at 200 K. The thermal conductivityk1is evaluated to 4 mW cm−1K−1at 300 K with an estimated electronic contribution of only 1%. The phonon mean free path at 300 K is extremely small l1≈ 2 Å, of the order of the shortest distance between the TCNQ molecules in a column. It is thus expected to be almost constant at this temperature, a result which is also suggested from the observedTdependence ofD1. For the crystal axis 2 associated with the intermediate component σ2of the electrical conductivity,D2is 2.3×10−3cm2s−1at 200 K. From these results it appears that the thermal diffusivityDis not markedly anisotropic in TEA(TCNQ)2, as it may be expected from a phonon contribution only.
First Principles Calculation of the Energy Band Structure of Diamond
Authors: Persson A. , Jones R. 
Published: July 2007

AbstractA first principles calculation of the energy band structure of diamond is performed using a muffin tin potential constructed from atomic functions and including the parametrized exchange term due to Slater. The crystal wave functions are expanded in 2s and 2p like functions obtained by integrating the Schrödinger equation for a single atom with a potential equal to the muffin tin potential inside the muffin tin radius and a constant elsewhere. The method gives a good valence band but a poorer conduction band. Excluding three centre integrals, varying the parameter in the exchange term and altering the electron configuration of the carbon atom does not appreciably change the band structure. Finally, including non muffin tin parts of the crystal potential improves the conduction band.
On the Theory of a Heisenberg Impurity Ferromagnet
Authors: Dyakin V. V. , Karpenko B. V. 
Published: July 2007

AbstractUsing the resolvent method a complete solution of the Wolfram‐Callaway problem for a Heisenberg ferromagnet with a single magnetic impurity atom is obtained. The spectrum of the system is determined and the exact wave functions of the continuous and discrete spectra of the system with a unit spin deviation are found. The theorem of completeness for eigenfunctions is proved. The treatment is performed with reference to the example of an infinite crystal with a simple cubic lattice.
A Pseudopotential Calculation of Phonons in Copper
Authors: Kumar B. , Sharma K. S. 
Published: July 2007

AbstractThe pseudopotential theory of d‐band metals is used for the calculation of phonons in copper by employing a linear form of the model pseudopotential for representing the electron—ion interaction and Moriarty's form for the overlap interaction of d‐bands. The computed frequencies compare well with the experimental data. The validity of the approach is further confirmed through a satisfactory representation of binding energy, compressibility, and elastic constants.
Magnetic Properties and Resonance Study of Gd (CoxAl1−x)3 Compounds
Authors: Burzo E. , Seitabla D. , Chiparǎ M. 
Published: July 2007

AbstractGd(CoxAl1–x)3 compounds with x ≧ 0.2 are ferrimagnetic. The mean cobalt moments decrease as the aluminium content is larger. The reciprocal susceptibility for ferrimagnetic compounds follows a hyperbolic law of Néeltype. The electron paramagnetic resonance measurements on GdAl3 show that g = 1.959 and the slope of the linewidth is DH/T = 2.8 G/K. For ferrimagnetic compounds the g and DH/T values are temperature dependent. The data are analysed in a model which uses the two—sublattices molecular field approximation. Finally, the magnetic behaviour of cobalt atoms in Gd(CoxAl1–x)3 compounds is analysed.
Magnetic Relaxation Effects in the Mössbauer Spectrum of Fe2+ in Gillespite
Authors: Srivastava K. K. P. , Mishra S. N. 
Published: July 2007

AbstractThe Mössbauer spectrum of paramagnetic 57Fe2+(3d6,5D) ions of the mineral gillespite (BaFeSi4O10) is found to show the effect of magnetic relaxation (i.e. relatively slow electronic spin relaxation rate) from 4.2 to 300 K. It is widely believed that ferrous ions are strongly coupled to lattice vibrations and consequently any spin relaxation effect on their Mössbauer spectra may be observed at very low temperatures only when the spin—lattice relaxation rates will be relatively small. In view of this the observed electronic spin relaxation behaviour of Fe2+ in gillespite is very unusual and rather surprising. A theoretical analysis is made to identify the dominant relaxation mechanism. A detailed analysis of the electronic eigenstates and their relaxation properties shows that in the case of gillespite the spin—spin relaxation is more dominant than the spin—lattice relaxation, which is rather unusual for Fe2+ ions. On this basis the observed magnetic relaxation behaviour of the Mössbauer spectra is consistently explained. It appears that the spin—lattice relaxation rate depends as much on the magnitude of the crystal field splitting as on the symmetry of the crystal field interaction itself as earlier suggested from the study of the low temperature Mössbauer spectra of Fe2+ in various carbonates.
UV Absorption and Electro‐Optical Alignment Behavior of Off‐Center AG+ in RbI
Authors: Kapphan S. E. 
Published: July 2007

AbstractThe polarization of four uv‐absorption bands due to Ag+ in RbI can be determined from the sign of the zero‐moment absorption change under applied electric field. The oscillator strength of these bands shows a temperature dependence very much like that of Ag+ in RbCl and RbBr, with a minimum around 150 K. Assuming fully polarized uv‐transitions the electro‐optical behavior can be fitted to a dipole alignment model with electric dipole moment values (uncorrected for local fields) of p = 1.6 or 2 eÅ. Two models, suggested earlier by Jimenez et al., a 〈111〉 dipole model and a restricted 〈110〉 model with 90° transitions only, allow a quantitative fit. Polarization and form of the uv‐spectra point to the 〈111〉 model.