bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantum‐limit cyclotron resonance linewidth in semiconductors
Authors: Arora V. K. , Spector H. N. 
Published: July 2007

AbstractA quantum theory developed earlier is used to study the cyclotron‐resonance linewidth for the electron scattering via the acoustic phonon, the ionized‐impurity, and the piezoelectric scattering mechanisms. For the electron‐acoustic‐phonon scattering, the linewidth is found to increase linearly with the magnetic field, while the peak‐value decreases with the increasing magnetic field. For the electron‐ionized impurity scattering, the line width decreases with magnetic field, while the peak‐value increases. The linewidth and the peak‐value are independent of the magnetic field in the case of piezoelectric scattering. Under the combined effect of all three scattering mechanisms, a minimum of the linewidth as a function of the magnetic field is predicted. The critical magnetic field for which the linewidth is minimum and the minimum value of the linewidth are found to vary as the square‐root of the impurity concentration. Wherever possible, comparison is made with the existing experimental data.
Static magnetic properties of doped magnetic semiconductors mean field approach
Authors: Spałek J. , Tarnawski Z. 
Published: July 2007

AbstractThe magnetic field and temperature dependences of static magnetic characteristics: magnetization, susceptibility, and paramagnetic Curie temperature of doped ferro‐, antiferro‐, and ferri‐magnetic semiconductors, are investigated within the mean field approximation. The case of deep impurities is considered, i.e. kBTC,N≪ ϵa. The general behaviour of the results is in agreement with the experimental data for some chalcogenides with spinel structure and those of rare earths. On this basis general conclusions are drawn, concerning the distinction between space homogeneous and inhomogeneous magnetic ground states.
A study of the collective properties of the degenerate electronic gas in metals using the (e, 2e), (e, 3e), and (γ, 2e) processes at high energies 103 to 104 eV
Authors: Neudachin V. G. , Yudin N. P. , Zhivopistsev F. A. 
Published: July 2007

AbstractThe process of quasielastic knock‐out of an electron by the projectile electron (e, 2e) allows one to study the κ‐ and also ε‐dependence of the single‐particle spectral density A(κ, ε). The plasmaronhole excitations of the metal conduction band and the modification of Mahan‐Nozières singularities in the production of a deep hole in a metal are considered as examples. Depending upon the experimental procedure the (e, 3e) and (γ, 2e) processes of knocking out the electron pair provide direct information either about the two‐hole spectral density B(κ1, κ2, ε) or about the Fourier image fk1κ2 (q) of the electron‐electron correlator f(r2).
Non‐linear fluorescence quenching in molecular crystals II. Recombination of free excitons
Authors: Benderskii V. A. , Brikenshtein V. Kh. , Burshtein A. G. , Lavrushko A. G. , Prikhozhenko A. G. , Filippov P. G. 
Published: July 2007

AbstractThe decrease of quantum yield and the fluorescence decay time of naphthalene and anthracene crystals with increasing exciton concentration (non‐linear quenching) in the range from 10 to 80 K is measured. Rate constants of bimolecular recombination, γ, found from these data with regard to diffusional escape of excitons from the light absorption layer, are increased by the factor of 1.5 to 2.0 with the increase in temperature from 10 to 30 K. In the same temperature interval the diffusion coefficient of excitons is decreased. Free‐pass model explaining an increase of γ with temperature (by the increase in the mean thermal velocity of free excitons) is suggested. From the measurements of non‐linear quenching for different light absorption coefficients of pumping the diffusion coefficients of excitons along the c′‐axis at 10 K are found to be equal to (1.3 ± 0.5) and (3 ± 1.5) × 10−3 cm2s−1 in anthracene and naphthalene crystals, respectively.
Tunneling investigations on V3Si
Authors: Schumann J. , Elefant D. 
Published: July 2007

AbstractOn bulk single phase V3Si single crystals (residual resistivity ratio ϱ(293 K)/ϱ(17.5 K) = 15 to 30) tunnel junctions are prepared by different preparation methods. The tunnel characteristics obtained by means of modulation technique yield energy gap values in the range of δo = (1.93 to 2.66) meV on a lot of different tunnel junctions. The relation 2δo/kTc > 3.52 found on some junctions indicates strong electron‐phonon interaction. Above the energy gap phonon induced structures are found in some tunneling characteristics.
A quantitative study of excitonic polariton reflectance in CdS II. B‐exciton and κ‐linear term
Authors: Broser I. , Rosenzweig M. 
Published: July 2007

AbstractThe influence of κ‐linear terms on the reflectivity spectra of excitonic polaritons is discussed for the case of the Γ5‐states of the B‐exciton of CdS. Using Pekar's abc and a dispersion relation consisting of three transverse and two longitudinal modes an effective index of refraction n* for oblique incidence of light is calculated. Spatial dispersion, the damping constant, the surface layer thickness, and the κ‐linear term are considered simultaneously. The energy parameters of the B‐exciton, especially the κ‐linear term, are deduced from the lineshape analysis of carefully measured reflectivity spectra. The structured spectra of the double resonance allow the more distinct investigation of the small discrepancies between theory and experiment still existing in the model of excitonic polaritons.
Reststrahlen spectra of PbSe1−xTex)
Authors: Finkenrath H. , Franz G. , Uhle N. 
Published: July 2007

AbstractThe TO‐ and LO‐modes of PbSe1−xTex mixed crystals are determined from optical measurements in the frequency range 660 to 10 cm−1 at 300, 100, and 8 K. The results for polycrystalline bulk samples as well as for thin films, prepared by hot‐wall epitaxy, show a two‐mode behaviour. This conclusion is in contrast to a number of criteria which permit a prediction of the mode behaviour.
Effect of second‐order spin–orbit coupling λ′ (L · S)2 on electronic spin relaxation of paramagnetic Fe2+ in CaCO3 and CdCO3
Authors: Srivastava K. K. P. , Singh H. C. 
Published: July 2007

AbstractAt low temperatures the Mössbauer spectra of paramagnetic Fe2+ (3d6, 5D) ions in CaCO3 and CdCO3 show magnetic hyperfine structure due to slow spin relaxation only in the presence of an applied magnetic field whereas no magnetic field is needed to observe the same in rhombohedral MgCO3 and ZnCO3. This field dependent magnetic relaxation behaviour of Fe2+ ions in CaCO3 and CdCO3 has earlier been explained by assuming a small rhombic distortion of Fe2+ substitutional sites from the trigonal symmetry of host cation sites. It is shown how the presence of second order spin–orbit coupling of the type λ′(L · S)2 for Fe2+ ions in CaCO3 and CdCO3 produces new ground states which can explain the observed magnetic relaxation properties and there is no need to artificially lower down the trigonal symmetry around Fe2+ ions. It appears that the perturbations due to the rhombic crystalline electric field and the second order spin–orbit coupling are very similar in nature.
On the X‐ray plasmon scattering from small particles of graphite at κ =0
Authors: Priftis G. D. , Boviatsis J. , Vradis A. , Kountouris K. 
Published: July 2007

AbstractThe inelastically scattered X‐ray radiation from small particles of graphite is investigated at zero scattering angle. It is established that there is no measurable intensity corresponding to either surface or volume plasmon excitation in agreement with the theory.
Effect of controlled defects on the microwave transport and dielectric constant of tetrathiofulvalene–tetracyanoquinodimethane
Authors: Gunning W. J. , Heeger A. J. 
Published: July 2007

AbstractThe introduction of controlled disorder in TTF‐TCNQ through irradiation provides information on the transport mechanism. The large changes in the magnitude and temperature dependence of the conductivity in the conducting regime are consistent with either 1d localization or pinning of CDW fluctuations by impurities. However, studies at low temperatures appear to be inconsistent with the localization ideas. Furthermore, the frequency dependence in the conducting regime at microwave frequencies suggests a substantial contribution of fluctuating CDW's to the low frequency transport. The introduction of controlled defects allows a separation of the low temperature conductivity into an intrinsic contribution plus a second contribution of impurity origin. Information on the frequency dependence of the intrinsic conductivity is obtained from comparison of the dc and microwave data. The results are interpreted in terms of soliton transport inhibited by the Larkin‐Lee tunneling.
Band structure of rhodium and photoemission from its low index surfaces
Authors: Borstel G. , Braun W. , Neumann M. , Seitz G. 
Published: July 2007

AbstractPhotoelectron spectra are given of the low index surfaces of rhodium together with band structure calculations which are extended up to 40 eV above the Fermi level. The photoelectron spectra are strongly dependent upon photon energy and crystal orientation. The spectra can be explained reasonably well within the direct model in terms of the band structure calculation using nonrelativistic dipole selection rules. Some features observed in the spectra of the Rh(110) surface indicate that relativistic dipole selection rules may have to be considered.
Magnitude of localized magnetic moments in metals
Authors: Kiwi M. , Pestana E. , Ramírez R. 
Published: July 2007

AbstractThe magnitude of the localized magnetic moment of a transition or rare earth element impurity in a metal is evaluated within the framework of the Anderson model. Rotational invariance is preserved throughout. Graphs of the magnitude of the magnetization as a function of the relevant darameters of the model are provided and discussed.
Density of valence states of the superionic conductor AgI
Authors: Ostrow M. , Goldmann A. 
Published: July 2007

AbstractTemperature dependent photoelectron spectra of AgI are measured between room temperature and 251°C for photon energies hω = 21.2 and 40.8 eV. The spectra are decomposed into approximate partial p and d densities of valence states by using atomic cross sections for the corresponding partial photoexcitation probabilities. Significant abrupt reversible changes are observed in the partial p density of states at Tc = 147°C, where the crystal structure changes from the wurtzite (β) phase to the superionic “disordered” α‐phase. In contrast, the partial d density of states, except for a slow continuous broadening with temperature, shows no sudden change at Tc. The results strongly support the model, that in the α‐phase the Ag+ ions occupy lattice sites with tetrahedral symmetry for a large fraction of the time.
Electronic properties of n‐type (Bi1−xSbx)2Te3 from magneto‐quantum oscillations
Authors: Köhler H. , Weidner R. 
Published: July 2007

AbstractThe magnetoresistance of n‐type (Bi1−xSbx)2Te3 mixed crystals is investigated in quantizing magnetic fields (B ≦ 10 T) between 1.6 and 4.2 K. Up to x = 0.3 Shubnikov‐de Haas oscillations can be observed on samples with electron concentrations between 7.8 × 1017 and 4.4 × 1018 cm−3, allowing the evaluation of electronic mass parameters and g‐factors. The six‐ellipsoid non‐parabolic model for the lowest conduction band of Bi2Te3 can be shown to apply up to about 15% Sb content with unvariable mass parameters but a decreasing tilt angle ζ0(x) of their principal axes relative to the crystal axes within the mirror planes of the Brillouin zone. Starting from x = 0.2 the Shubnikov‐de Haas patterns are changed drastically due to a cross‐over of two different types of conduction band minima.
Elliptical spin precession correction factor in the theory of spin‐wave resonance
Authors: Puszkarski H. 
Published: July 2007

AbstractEllipticity of spin precession is analysed for its relevance to the microscopic theory of spin‐wave resonance. Applying the surface inhomogeneity model of a thin film with surface anisotropy described in terms of an effective pinning field, it is shown that elliptical spin precession gives rise to a correction factor in the resonance line intensity formula dependent only on the frequency of the microwave field and the orientation of the static field with respect to the film surface.
Phonon diffusion with frequency down‐conversion
Authors: Kazakovtsev D. V. , Levinson Y. B. 
Published: July 2007

AbstractIn most of the experiments with heat pulses the frequency spectrum of the nonequilibrium phonons does not differ very much from the equilibrium one. In this case nonequilibrity evolves only due to propagation in space (ballistic propagation, diffusion, second sound). But if the injected non‐equilibrium phonons are superthermal (i.e. have frequencies much higher than the bath temperature T), nonequilibrity also evolves in the frequency domain – the spectral distribution due to the phonon decay shifts toward lower frequencies. The frequency down‐conversion influences the propagation, since all the scattering rates strongly depend on frequency. A theory of phonon diffusion accompanied by spontaneous phonon decay is presented. The phonon occupation numbers are supposed to be small and the bath temperature is supposed to be zero.
Optical properties of manganese ferrites
Authors: Šimša Z. , Široký P. , Lukeš F. , Schmidt E. 
Published: July 2007

AbstractThe near normal reflectance spectrum together with the data on the index of refraction and the extinction coefficient are combined in a Kramers‐Kronig analysis to obtain the spectral dependences of the real and the imaginary parts of the diagonal elements of the dielectric function of the single crystal series MnxFe3−xO4 for 0 ≦ x ≦ 1.6. One‐oscillator fit to optical constants is used to show that the main rise in absorption at about 2 eV is due to the 3d‐crystal field transitions of the Fe3+ and/or Mn2+ ions in tetrahedral sites. The anomalous behaviour of optical constants below 1 eV in iron rich Mn‐ferrites is ascribed to the presence of charge carriers (Fe2+) in octahedral sites.
Fine structure of P excitons in CuBr
Authors: Mattausch H. J. , Uihlein Ch. 
Published: July 2007

AbstractA multiplet structure of the 2P, 3P, and 4P exciton of the Z1,2‐series is observed in the two‐photon absorption spectrum of CuBr. It is shown that the P‐exciton fine structure results from a coupling between the angular momentum of the P exciton and the hole quasi‐spin associated with the Γ8 valence band. For the first time the energies of higher excited P excitons (3P) are compared with the theory of Baldereschi and Lipari. Therefore, the binding energies of the 3P excitons for a representative set of parameters μ and δ is calculated. Numerical calculations are performed using the “finite‐element method” (FEM). From the energy positions of nine excitons the effective Rydberg, the gap, and the parameters μ and δ of CuBr are determined with high accuracy. These data and the static dielectric constant are used to evaluate the reduced mass parameter γ1 and the Γ8 valence band parameters γ2 and γ3. The 3P exciton wave functions, calculated also with the FEM, are shown in addition.
Excitation and recombination of donor–acceptor pairs in ZnTe
Authors: Nakashima S. , Yasuda S. 
Published: July 2007

AbstractThe photoluminescence spectra and its excitation spectra of the donor‐acceptor pairs are observed in ZnTe crystals doped with Li and As in the region below the bandgap energy. The relaxation of electrons and holes into the first excited state of d‐a paris is studied for the three excitation processes: (1) bound‐to‐bound transitions, (2) bound‐to‐free transitions, and (3) free‐to‐free transitions. It is concluded that most of the electrons and holes at the excited states of each impurity level are relaxed rapidly into their ground states before the occurrence of the recombination involving the excited states. For the excitation process (2), conduction electrons are preferentially trapped by positively charged pairs. The redistribution of bound holes by hopping is suggested to explain the broad d– a emission band observed for the bound‐to‐free excitation for very distant pairs.
Diamagnetic band structure up to second order in the crystal potential
Authors: Neumann H.‐W. , Rauh A. 
Published: July 2007

AbstractThe energy spectrum is calculated of a crystal electron in the presence of a magnetic field by using the Landau functions as basis with the periodic potential treated perturbatively. In contrast to the prevailing opinion which is based on first‐order effects only, our second‐order calculation predicts an observable broadening of the lower Landau levels. Furthermore, our quantum mechanical treatment gives a similar magnetic breakdown condition as the well‐known semiclassical considerations. Also the optical transition probability is determined approximately and from this an expression for the cyclotron mass is derived.
Chemical shifts of the K‐Absorption edge of Mn in some mixed oxidic spinels
Authors: Nayak R. M. , Padalia B. D. 
Published: July 2007

AbstractChemical shifts of the K‐absorption edge of Mn in some mixed oxidic spinels of composition (AMn2O4)1−x(MgAl2O4)x, where A refers to Mg, Mn, Zn, or Cd and 0 < x < 1, are measured. Valence states of Mn in these mixed spinels are determined. Effective charges on Mn ions are estimated using Gianturco and Coulson's method. An attempt is made to interpret the chemical shifts in the light of the available data from other studies on the same samples.
On the low‐temperature resistivity of ferromagnetic transition metal alloys
Authors: Goedsche F. , Richter A. 
Published: July 2007

AbstractThe electrical resistivity of a disordered ferromagnetic alloy is estimated in terms of the two‐current model. Besides the residual resistivity due to spin dependent potential scattering a spin‐disorder residual resistivity is obtained. A significantT3/2term associated with incoherent electron magnon collisions and representing large deviations from Matthiessen's rule dominates the temperature dependence of the resistivity below about 10 K. Deviations from Matthiessen's rule arising from the two‐current conduction are discussed.
Debye‐waller factors for rare gas solids
Authors: Kushwaha M. S. 
Published: July 2007

AbstractMean‐square displacements of the rare gas solids (Ne, Ar, Kr, and Xe) are calculated as a function of temperature, using eigenvalues as obtained from the unpaired elastic force model, recently developed. The present results are compared with the theoretical results of Goldman, because of the paucity of experimental results. Lindemann's melting criterion is tested by evaluating the ratio of the root‐mean‐square displacement to the nearest neighbour distance. It is observed that this ratio is almost constant for all rare gas solids.
Non‐linear optical properties of band charge carriers due to scattering by lattice defects
Authors: Fomin V. M. 
Published: July 2007

AbstractThe influence functionals of point, linear, and plane defects in an electron density matrix represented by functional integrals are obtained. A non‐liner polarization due to the interaction of band carriers with the lattice defects is found. The dependence of the shape of the absorption coefficient non‐linearity on the dimension and nature of scatterers is analyzed. Orientations of the laser field polarization are ascertained, which are optimum for evidencing the non‐linearity of the absorption coefficient. The possibility of effectively identifying the deformation interaction with dislocations from the dependence of the laser radiation absorption coefficient on its intensity is established.
The optically detected magnetic resonance of nickel‐doped silver chloride
Authors: Marchetti A. P. , Scozzafava M. 
Published: July 2007

AbstractOptically detected magnetic resonance is observed in nickel‐doped AgCl at liquid‐helium temperatures. The species found is thought to be [(NiCl6)5−Ag+vac], indicating that [(NiCl6)4−Ag+vac] traps electrons at low temperatures. The signals due to [(NiCl6)5−Ag+vac] are weak and represent a decrease in light emission upon microwave absorption in accord with a simple model for radiative recombination.
Model pseudopotential for elementary semiconductors
Authors: Mašović D. R. , Zeković S. 
Published: July 2007

AbstractA simple model pseudopotential, particularly suitable for energy band calculations in elementary semiconductors, is presented. It includes the Veljković‐Slavić's general model pseudopotential and phenomenological correction. This correction represents a sum of spherical Bessel functions of higher order with the coefficients obtained by fitting the form factor of the pseudopotential to the experimental values of the transition energies around the energy gap. The band structures of Si, Ge, and α‐Sn are calculated and agree well with the experimental data. This pseudopotential is tested by calculating the resistivity of liquid Si, Ge, and Sn.
Excitonic magnetoabsorption in Cd1−xMnxTe mixed crystals
Authors: Twardowski A. , Nawrocki M. , Ginter J. 
Published: July 2007

AbstractResults of magnetoabsorption measurements for CdMnTe mixed crystals on extremely thin samples (≦ 1 μm) are presented. The complex structure of the exciton transition is observed. The qualitative interpretation of the full spectrum and quantitative theory of the ground state splitting is presented.
The calculation of the electronic structure of a vacancy by the green's function theory
Authors: Reifman S. P. , Shulichenko B. V. 
Published: July 2007

AbstractThe Green's function theory in a non‐orthogonal basis of atomic orbitals is used to consider the problem of the electronic structure of the vacancy in non‐polar crystals. With certain assumptions relative to the perturbation a simple expression is obtained for the Green's functions of a crystal with a vacancy. A numerical calculation is carried out for the influence of the vacancy on the valence band of Ne and Ar crystals.
On the lattice dynamical background of optical activity in crystals
Authors: Claus R. 
Published: July 2007

AbstractThe lattice dynamical theory of crystal optical activity developed by Born is discussed in the view of polariton dispersion. Three major difficulties occur: 1) For large wave vectors k no continuous connection with the phonon dispersion branches as recorded by neutron scattering is found. 2) There are spectral regions in which two left‐ or two right‐circularly polarized waves with different k are expected. 3) Polariton group velocities in the Γ‐point remain undefined when time reversal is required. An alternative model omitting these difficulties is proposed. It is based on the assumption of the existence of anharmonic resonance coupling between orthogonally polarized polariton waves with degenerate dispersion branches.
Electron–phonon versus coulomb interaction effects at the verwey transition of Fe3O4
Authors: Lorenz B. , Ihle D. 
Published: July 2007

AbstractThe Verwey transition in Fe3O4 is treated as the condensation of a coupled charge density‐phonon mode with q = (0, 0, 2π/a) (a lattice constant of the cubic unit cell) and Δ(1)5 symmetry on the basis of a model for the extra electrons at the Fe ions taking into account the electron correlation due to the electron‐phonon and the Coulomb interaction between nearest (U1) and next‐nearest neighbours (U2). Within the model three charge ordered phases are possible: besides the Verwey order and the Δ(1)5 Yamada order (along the orthorhombic a‐axis), a new ordering scheme, the ab‐order (combination of Δ(1)5 order and charge order along the b‐axis due to U2) accompanied by a doubling of the primitive cell along the c‐axis, is obtained. In the phase diagram the various phases are separated by first‐order transition lines.