bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the concept of cyclotron resonance in metals
Authors: Saermark K. , Lebech J. , Johansen H. 
Published: July 2007

AbstractExperimental evidence is presented, indicating that an impinging, high frequency electromagnetic wave penetrates to a considerable depth beneath the surface of a monocrystalline, metallic sample. It is shown, on the basis of a rigorous dispersion equation for cyclotron waves, that the attenuation length for these waves is γi = vgτ where vg is the group velocity and τ the relaxation time. The attenuation length varies in a characteristic way with the magnetic field and may become as large as the mean free path of the charge carriers. A possible relation to Azbel‐Kaner cyclotron resonance is pointed out.
Theory of resonance Raman scattering in disordered solids
Authors: Bechstedt F. , Enderlein R. 
Published: July 2007

AbstractA theory of the resonance Raman scattering from optical phonons is developed for disordered solids which can be described by the smooth random field (SRF)model. The disorder influences only the electronic subsystem but not the vibronic one. Despite the Q = 0 selection rule is broken, practically no change of the scattering spectrum due to disorder results within the SRF‐ model. The dispersion of the scattering cross‐section is calculated for the two cases of randomly fluctuating energy gap and of random electric field. The scattering cross‐section of the disordered system can be related to that of a crystal by means of an integral representation similar to the Redfield representation of the dielectric function.
Heterofission in pentacene‐doped tetracene single crystals
Authors: Burgos J. , Pope M. , Swenberg Ch. E. , Alfano R. R. 
Published: July 2007

AbstractThe magnetic field and the temperature dependence of both guest and host fluorescence in penta‐eene‐doped tetracene single crystals is studied. From an analysis of the experimental results it is concluded that pentacene enters substitutionally into the host lattice sites and that thermally activated heterofission is site‐dependent with activation energies ≈︁ (0.13 ± 0.01) e V and ≦ 0.06 eV. From a kinetic fit to the temperature dependence of the green and red fluorescence, a thermally activated host singlet exciton diffusion coefficient ≈︁ 2 × 10−2 cm2/s is inferred; its activation energy is estimated to be (0.018 ± 0.001) eV. The heterofission rate of ≈︁(4.7 ± 0.5) × l0−10 cm3 s−1 is determined and location of the pentacene triplet level is found to be at (0.86 ± 0.03) eV.
Electronic structure investigation of metallic vanadium by XS and XPS
Authors: Werfel F. , Dräger G. , Brümmer O. 
Published: July 2007

AbstractThe valence band of vanadium is investigated using X‐ray and X‐ray photoelectron spectro‐scopy. By XPS core level measurements the several spectra are correlated and drawn in unitary energy scale for comparison purpose. The spectra are compared with density‐of‐states functions from the literature and discussed in terms of electron states of different symmetry (s‐, p‐, d‐like). From the experimental spectra the widths of the occupied d‐band and s‐d band are estimated to 4.0 and 6.8 eV, respectively. The experimental results confirm the general accepted picture of the electron structure of 3d metals.
Specific features of many‐photon photoemission from metals and semiconductors in strong fields
Authors: Brodskii A. M. 
Published: July 2007

AbstractEquations are derived describing photoemission from metals and semiconductors in strong fields. A perturbation theory is advanced which, is valid even in the presence of resonance transitions. Threshold and resonance expressions for photocurrent are obtained. New strong field effects, dependent on band structure and collective excitation spectrum, are considered. A number of experimentally observed phenomena are explained in terms of the theory developed.
The elementary interaction force between the flux‐line lattice and precipitates
Authors: Fähnle M. 
Published: July 2007

AbstractThe elementary interaction force p between a precipitate and the flux‐line lattice is calculated by means of the Ginzburg‐Landau theory. It is shown that p depends on the shape and the extensions of the precipitate in a complicated manner. This gives rise to a modification of the field dependence of the interaction force, which had not been taken into account so far. As a consequence it is impossible to describe the field dependence of the volume pinning force by a simple scaling law.
The energy–angle distribution of heavy particles penetrating solids
Authors: Meyer L. , Klein M. , Wedell R. 
Published: July 2007

AbstractParticles of definite initial energy and direction penetrating into a solid have, in a given depth, a certain distribution with respect to energy loss and scattering angle. This energy‐angle distribution is calculated in small angle approximation for heavy low energy particles, taking scattering and nuclear stopping into account on the basis of a Thomas‐Fermi potential and electronic stopping with a definite dependence on scattering angle. Introducing redviced values of energy loss, scattering angle, and thickness of the penetrated layer, it is found, that it is possible to get a general solution independent of particle and target type and of energy. The result is given by a combination of two functions which are tabulated. The most probable energy losses of the total energy distribution and of the distribution of the particles scattered in forward direction as well as the half‐widths of these distributions are given. The results show, that stopping and scattering cannot be considered independently for heavy low energy particles. In particular the conception of ‘stopping cross section’ at low energies essentially looses its meaning.
Radiative electron capture by backscattered ions from solid surfaces
Authors: Koyama K. , Kaneko T. 
Published: July 2007

AbstractRadiative electron capture by heavy ions scattered at grazing incidence on solid surfaces is investigated. Remarkable oscillations in cross‐sections of the process versus the distance of ions from the surface are found. This behaviour is ascribed to the correlation between the ion velocity and electronic states near the surface. The dependence of the cross‐sections on the incidence angle is calculated for the several primary energies. The possibility of the surface structure analysis by a measurement of the radiative electron capture is discussed.
The lattice dielectric constant in Bi100–xSbx as a function of x
Authors: Oelgart G. , Herrmann R. , Meschter U. 
Published: July 2007

AbstractThe dielectric constant of the lattice, ε1, is determined in semiconductive bismuth–antimony alloys (7 at% < x < 22 at%). For measuring ε1 the effect of the displacement current on the wave propagation in a direction parallel and perpendicular to the magnetic field is utilized. The measurements are carried out at helium temperatures and within a frequency range from 9 to 70 GHz. Thus the effect of the displacement current can be experimentally separated. The dielectric constant exhibits a strong dependence on x, which indicates a pole for the disappearing gap.
The phonon spectra of β‐CuI. II. The numerical evalutaion
Authors: Haxton M. B. 
Published: July 2007

AbstractThe phonon spectra of β‐CuI is numerically evaluated using the second neighbor ionic model of Banerjee and Varshni. The short‐range parameters are evaluated by correcting the parameters of the ideal wurtzite lattice, found by transformation of zinc blende parameters previously calculated, for the nonideal nature of β‐CuI. Dispersion curves are drawn in the [100], [110], and [001] directions and a crude estimate of the density of states is found.
Low‐temperature thermal conductivity of pure and impure niobium and tantalum single crystals
Authors: Wasserbäch W. 
Published: July 2007

AbstractThe thermal conductivities of niobium and tantalum single crystals of different impurity contents are measured between 0.3 and 20 K. Below about 1 K the thermal conductivities of all specimens vary with temperatures as T3, but the magnitude of the thermal conductivity decreases with increasing impurity content. A careful investigation of the defect structure of the specimens leads to the conclusion that interstitial and substitutional impurities give rise to a thermal resistance even at low temperatures.
The influence of fast neutron irradiation on the critical current densities in Nb3Sn I. Low neutron doses (Φ < 2 × 1018 neutrons/cm
Authors: Fähnle M. 
Published: July 2007

AbstractBy irradiation with fast neutrons the critical current densities Jc of Nb3Sn are modified in a characteristic manner depending on the irradiation dose. A short survey is given of the experimental work on this subject. By a model calculation it is shown that the modification of the critical current densities after low‐dose irradiation (Φ < 2 × 1018 neutrons/cm2) may be explained by a modification of the density of pinning centres and not by an influence on the intrinsic superconducting parameters, as assumed by other authors.
Electron spin–lattice relaxation measurements in a two‐dimensional crystal
Authors: Giordano M. , Martinelli M. , Pardi L. , Santucci S. 
Published: July 2007

AbstractThe spin relaxation times T1 and T2 are studied in a two‐dimensional magnetic system by varying the angle between the anisotropy axis and the external magnetic field. Measurements are done on the Mn2+ ions in a single crystal of (C2H5NH3)2MnCl4, using the new technique of longitudinal detection of electron spin resonance (LODESR). The angular dependence of T1 is explained by taking into account an isotropic interaction besides the exchange modulated dipolar interaction. The theoretical curves are in fair agreement with experiments.
Electrical conductivity of two‐band models for disordered binary substitutional alloys theory
Authors: Kudrnovský J. , Petrů J. 
Published: July 2007

AbstractThe static electrical conductivity for a two band S–D matrix generalization of the Shiba model is determined for a disordered binary substitutional alloy within the single‐site approximation. Unlikely the previous works, the conductivity is expressed in an analytic form allowing for an interpretation of the Boltzmann equation limit in terms of the scatterings in complex, hybridized bands.
The magnetic susceptibility of antimony and bismuth chalcogenides in the liquid state
Authors: Uemura O. , Satow T. 
Published: July 2007

AbstractThe magnetic susceptibilities of liquid SbTe, BiTe, SbSe, and BiSe systems are measured by the Faraday method using a torsion balance. The decrease in diamagnetic susceptibility at the melting point is relatively large in liquid Bi2Te3 and Sb2Te3. On the other hand, it is considerably small in liquid Sb2Se3. This corresponds to the temperature change in the electrical conductivity reported previously. The value of susceptibility for liquid SbTe alloys is considerably different from the data measured by a previous author. It is clarified from the composition dependence of susceptibility that both liquid Te systems behave like metals rather than semiconductors in a wide range of composition. The composition dependence of susceptibilities in the liquid Se systems showes that in the Se‐rich region the short‐range bonding remains unchanged when melting, and these alloys take rapidly a metallic character with increasing metal content beyond the composition of Sb2Se3 or Bi2Se3. These experimental results are discussed using the bond orbital approximation.
Reaction yield detected magnetic resonance spectra of intermediate pairs of triplet excitions evolution of spectra during degeneracy of energy levels
Authors: Lesin V. I. , Sakun V. P. , Pristupa A. I. , Frankevich E. L. 
Published: July 2007

AbstractThe changes in reaction yield for the reaction of equivalent triplet excition annihilation under the action of a resonant microwave power are studied both theoretically and experimentally. The resonant effect is shown to vanish when energy levels of the intermediate double–triplet complex are degenerated.
Auger lifetimes for excitons bound to neutral donors and acceptors in Si
Authors: Schmid W. 
Published: July 2007

AbstractThe lifetimes of excitons bound to the neutral donors Li, P, and As and neutral acceptors B, Al, Ga, and In in silicon are determined by time‐resolved photoluminescence measurements at 4.2 K and a strong dependence on the binding energy of the donor or acceptor is found. This dependence can be understood assuming a localized phononless Auger‐process to be the main recombination mechanism. A theoretical calculation using approximate wavefunctions is presented and leads to a very good agreement with the experimental results.
Evidence of coulomb interaction at the e1 interband transition of hexagonal CdSe
Authors: Lange H. , Iliev I. A. 
Published: July 2007

AbstractTransmission and reflection spectra are measured on CdSe single crystals in the region 3.6 to 5.9 eV at 109 K and RT and the absorption coefficient, refractive index, and real and imaginary part of the DF are calculated from these data. The line shape of ϵ2 around the E1(B) peak indicates a strong influence of electron–hole interaction. A comparison with Kane's theory gives a binding energy of the two‐dimensional exciton of 0.23 eV. In thermally modulated transmission spectra a new structure is observed which is attributed to the M1 edge of the E1(A2) exciton yielding a binding energy of the same magnitude.
Dispersion relation of phonon‐like excitations in a simple model of a noncrystalline solid
Authors: Leihkauf R. , Böttger H. 
Published: July 2007

AbstractThe dispersion relation of phonon‐like excitations in a solid with structural disorder is calculated using a simple model system. The dispersion curve for the disordered system shows a disorder induced roton‐like minimum. The frequency gap connected with this minimum increases with increasing disorder. In the frequency spectrum of the disordered system are also frequencies above the maximum frequency of the corresponding crystalline system.
On the density of states at the fermi level for normal systems
Authors: Behn U. , Zinke H. 
Published: July 2007

AbstractIn the single‐site and the nearest‐neighbour approximation, respectively, the density of electronic states at the Fermi level for normal systems at T = 0 is considered as a functional of the unperturbed density of states. For electron–hole symmetric systems, e.g. the half‐filled‐band Hubbard model, the density of states at the Fermi level in a normal single‐site approximation is either equal to the unperturbed value or vanishes. The expected gradual change in the density of states can be obtained in the nearest‐neighbour approximation.
The multimode Jahn‐Teller coupling for an orbital triplet in cubic crystals
Authors: Biernacki S. W. 
Published: July 2007

AbstractAn investigation is made of the properties of an iron group ion which has an orbital triplet ground state and which interacts with the lattice vibrations of its nearest neighbours. The interaction with e‐type vibrations is considered only. For the phonon spectrum of the host crystal the Debye and Einstein approximations are used. Explicit formulae are obtained for the Jahn‐Teller energy, the displacements of the neighbours nearest to an impurity, and for the first‐order reduction factor of orbital angular momentum in terms of the phonon spectrum parameters. All cubic coordinations are considered: fourfold, sixfold, and eightfold.
Indirect exchange in europium chalcogenides
Authors: Mauger A. 
Published: July 2007

AbstractThe indirect exchange in heavily doped europium chalcogenides is calculated in the mean field approximation. The finite width of the conduction band and carrier statistics (splitting of spin subbands, non‐thermal degeneracy) are taken into account. The model is applied to Gd‐doped EuO and EuS for which magnetic properties are derived. The predictions agree with experimental data both in the para‐ and ferromagnetic configurations. Statistical effects lead to a renormalization of the paramagnetic Curie temperature. Its variations with electron concentration are in good agreement with experiments. Moreover, the model accounts for some particular properties, such as a Curie constant a few per cent below the theoretical one and the systematic deviation of the magnetization curve with respect to the classical Brillouin law in the ferromagnetic configuration. The stability of the ferromagnetic order is also discussed.
Response of metal electrons to local fields of holes arising in X‐ray processes
Authors: Grebennikov V. I. , Sokolov O. B. , Turov E. A. 
Published: July 2007

AbstractX‐ray spectra computation methods are developed enabling allowance for metal valence band readjustment (extra‐atomic relaxation) caused by the field of a suddenly appearing finite‐lifetime hole. Allowance for the finite lifetime of the hole necessitates the introduction of a non‐hermitian perturbation Hamiltonian into the theory and, as a consequence, modification of Keldysh's technique of calculating nonequilibrium processes. The technique developed is illustrated with reference to an example of calculating the variation in time of the number of valence electrons on the site after the local field has switched on suddenly. Studying the asymptotic behaviour of that quantity allows one to determine the intensity of the satellite structure of inner‐level X‐ray photoelectron spectra.
A study of the kinetics of recombination radiation of CdS and CdSe crystals
Authors: Boiko G. A. , Dneprovskii V. S. , Kraevskii M. V. , Marinova K. , Oak S. M. , Silina E. K. , Fokin V. S. 
Published: July 2007

AbstractThe characteristic decay times of recombination radiation (P‐band) in CdS (2 × 10−11 to 2.7 × 10−9 s) and CdSe (1.7 × 10−10 to 3.7 × 10−9 s) monocrystals under different exitation levels, obtained by powerful picosecond light pulses, are measured with the help of a special laser spectrochronograph with a time resolution of 2 × 10−11 s (sample temperature 77 K). A comparison of the curves obtained for the rise and decay of the intensity of luminescence with the solutions of the system of rate equations for the exciton—exciton scattering processes makes it possible to estimate the values of rate constants of exciton—exciton interaction and of binding of carriers to excitons.
On the thermal broadening of core levels in metals due to many‐electron effects
Authors: Almbladh C.‐O. , Minnhagen P. 
Published: July 2007

AbstractFerrell's expression for the XPS lineshape is derived in a formalism which explicitly takes the electron—electron interaction into account. Also the corresponding expression for X‐ray absorption is given. In the presence of other broadenings, which are comparable or larger than kT, the electronic part of the core‐level broadening in XPS is indistinguishable from a Gaussian. This Gaussian broadening is of the same order as the expected phonon broadening for Al at room temperature and above, but it is of little importance for Li and Na. In X‐ray absorption, the effect seems in some cases to be important when extracting phonon broadenings from experimental data.
Transient photoconduction in a polydiacetylene single crystal determination of transit time, free lifetime, and recombination time of charge carriers
Authors: Reimer B. , Bässler H. 
Published: July 2007

AbstractPhotocurrent transients in polydiacetylene‐bis(toluenesulfonate) single crystals are investigated under 1060, 694, and 347 nm laser excitation and different sample geometry. With thick samples pulse decay is controlled by electron—hole recombination, the recombination coefficient being γ = (4 ± 1) X 10−6 cm3 s−1. Under 1060 nm irradiation silver‐contacted sandwich samples, typically 100 μm thick, show transit signals originating from injected carriers. The mobility is (4.8 ± 1.5) cm2/Vs. It varies as T0.5 as expected for carrier transport in a one‐dimensional band if scattering is by acoustic phonons. The carrier free lifetime depends on crystal preparation. For sandwich samples furnished by polishing monomer crystals it can be as low as 35 ns at 298 K.
Rayleigh wing scattering in disordered sodium nitrate
Authors: Neumann G. , Vogt H. 
Published: July 2007

AbstractThe temperature dependence of the Raman spectrum of NaNO3 is measured with special emphasis on those scattering configurations neglected in previous works. A Rayleigh wing of exponential lineshape is found arising from the increasing mobility of the NO3− ions in approaching the order—disorder phase transition and the nearby melting point.
Temperature dependences of the nonradiative multiphonon carrier capture and ejection properties of deep traps in semiconductors. I. Theoretical results
Authors: Pässler R. 
Published: July 2007

AbstractProceeding from the recently developed semiempirical theory of Shockley‐Read processes a short survey of theoretical predictions is given on the temperature dependences of the nonradiative multiphonon carrier capture ejection properties of deep traps in semiconductors. At low temperatures the corresponding capture cross‐sections are but weakly dependent on temperature and vary in the cases of attraction, neutrality, and repulsion as T−1, T−1/2, and T−7/6× × exp {−3[θ/T]1/3}, respectively, where the parameter θ depends on the magnitude of the centre charge. At high temperatures, activation‐type dependences exp {− U/kT} play an important part where the activation energies U depend on the actual structure of the given traps. On the basis of the complete theory the temperature dependences of the capture cross‐sections and ejection frequency factors in the range of intermediate temperatures are visualized graphically.
Deformation effects on exciton excitation spectra in CdS
Authors: Goede O. , Krug H.‐J. , Horst A. 
Published: July 2007

AbstractThe deformation effects for free excitons in CdS were studied by measuring the excitation spectra of the edge emission at 77 K for uniaxial stress parallel or perpendicular to the c‐axis. The stress‐induced shift of the A and B exciton peaks is in good agreement with the corresponding results of previous piezoreflection and piezoemission experiments. Moreover, the C exciton shift could be measured which enables a more precise determination of the deformation potential constants. For the first time a piezospectroscopy of excited states of free excitons could be carried out showing the exciton binding energy to be stress‐independent. The observed stress dependence of the excitation probability ratios for various excitons can be attributed to the stress‐controlled thermal exciton dissociation.
Electronic structure of dilute α‐phase AgCd alloys from thermoreflectance and XPS measurements
Authors: Rosei R. , Colavita E. , Modesti S. , Nisticò N. 
Published: July 2007

AbstractThe position of the s, p, and d‐like levels (at L) in four different silver—cadmium dilute α‐phase alloys is determined with respect to the Fermi level, using thermoreflectance and XPS measurements. The use of an analytical model, previously developed, to fit the thermoreflectance data, allows to determine, with substantially increased accuracy over previous alloy work, the dependence of the relevant optical gaps versus solute concentration. Of particular relevance is the behaviour of the L3L′2(EF) gap which shows at first a slight decrease versus solute concentration. XPS measurements on the same samples are consistent with this behaviour which is the opposite of what is predicted by the rigid band model.
Bound states of electrons and optical phonons under conditions of one‐dimensional quantizing
Authors: Sardaryan V. S. , Arakelyan M. M. 
Published: July 2007

AbstractIt is shown that there exist bound states of electrons and optical phonons in a film stipulated by the electron‐phonon interaction, quadratic in the displacement of the lattice. The full solution of the problem for the model Hamiltonian, in which the interaction is determined only by the momentum transfer is obtained. The existence of the bound states is also proved for a more realistic description of the polarization electron‐phonon interaction.