bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Optical Absorption Spectrum of Co2+ in CaF2
Authors: Alonso P. J. , Alcalá R. 
Published: July 2007

AbstractThe temperature evolution is measured of the absorption band centered at about 540 nm in the absorption spectrum of Co2+in CaF2 at temperatures in the range from 80 to 320 K in order to check previous designations of the transitions that produce the band. Four peaks at 19100, 18560, 18450, and 17800 cm−1 are observed. The peak at 18565 cm−1 is assigned to the 4A2g(4F) → 2T1g(2G) transition of the Co2+ in a cubic environment with values of Dq = 360 cm−1, B = 930 cm−1, and C/B = 4.47 for crystal‐field and Racah parameters, respectively. The other three peaks are assigned to transitions from the 4A2g(4F) ground state to the Jahn‐Teller split 4T1g(4P) triplet with the same Racah and crystal‐field parameters and with Jahn‐Teller parameters c2 = 0.42 eV, ħω = 247 cm−1, γ = 0.57. With these designations the temperature evolution of the peak positions and of the integrated intensity of the band are in good agreement with those predicted by the theory.
Pseudo‐Spin Motion in Solid Solutions of the Type of the Type K(H1−xDx)2PO4
Authors: Schreiber J. 
Published: July 2007

AbstractWithin the pseudo‐spin model which includes occupation dependent tunnelling frequencies Γi, dipole moments μi, and interactions Iij ∼ μitijμj, the dielectric susceptibility is obtained by a linearized Bloch equation for ferroelectric solid solutions of the type K(H1−xDx)2PO4. The single site and the Bethe‐Peierls version of CPA are used to solve the disorder problem. Using a suitable set of ingoing parameters the Curie temperature, the spontaneous polarization, the intensity of Raman scattering, and the static susceptibility are calculated for various deuterium concentrations, x, and discussed in relation to experiments.
Magnetic and Thermodynamic Properties of Heisenberg Open Finite Chains. I. Susceptibility in Zero Field
Authors: Rakitin Yu. V. , Kalinnikov V. T. , Hatfield W. E. 
Published: July 2007

AbstractCalculations of spin levels and effective magnetic moments as functions of reduced temperature, μeff(kT/J), are carried out for Heisenberg open finite chains with ion spins of 1/2 to 5/2 containing up to 11 subunits (N ≦ 11). Some relationships useful in interpretation of experimental results are considered. A detailed comparison of the results with literature data is given.
Lattice Dynamics of Rubidium Halide Crystals
Authors: Goel C. M. , Dayal B. 
Published: July 2007

AbstractPhonon dispersion curves of rubidium halide crystals are calculated in three principal symmetry directions on the basis of the three‐body force shell model by incorporating charge transfer effects in an appropriate manner. A comparison of the theoretical results with the neutron scattering measurements of Raunio and Rolandson exhibits very good agreement.
Two‐Photon Absorption by Envelope–Hole Coupled Exciton States in Cubic ZnSe. II. Polarization Dependence in the Case of Degenerate Valence Bands
Authors: Sondergeld M. 
Published: July 2007

AbstractThe general angular dependence of two‐photon absorption for elliptical polarization is given in terms of complex polarization vectors in the case of cubic and spherical symmetry. The two‐photon transition probability for p‐like envelope–hole coupled exciton states is treated within an extended two‐band model which, for the case of degenerate valence bands, includes Hd‐term contributions of the exciton Hamiltonian. By use of the effective Bohr radii, resulting from the envelope–hole coupled exciton wave functions, the experimental polarization ratios yield good quantitative agreement with the values predicted theoretically.
Polarons in the Degenerate‐Band Case. II. Weak to Intermediate Hole–Phonon Coupling
Authors: Trebin H.‐R. 
Published: July 2007

AbstractDue to the valence band degeneracy it is a special feature of the hole‐phonon interaction in cubic polar semiconductors that the holes cannot only be intraband but also interband scattered by virtual LO phonons. Within the k · p‐formalism this amounts to a change of the \documentclass{article}\pagestyle{empty}\begin{document}$ J = \frac{3}{2} $\end{document} spin component along the hole wave vector. It is shown that because of this spin scattering new correlations between the emission of successive phonons are introduced in addition to those caused by the hole recoil. A generalized Glauber‐state ansatz is made for the wave function of slowly moving hole polarons containing spin‐dependent displacement amplitudes. With the use of the Fröhlich interaction term renormalization relations for the band parameters γ1 and μ are established valid for weak to intermediate hole–phonon coupling.
Fluctuations of the Superconducting Order Parameter below Tc by Tunnel Effect
Authors: Burrafato G. , Giaquinta G. , Mancini N. A. , Pennisi A. , Simone F. , Troia S. O. 
Published: July 2007

AbstractTunnelling anomalies in Al–formvar–Sn junctions operated at temperatures slightly below the transition temperature of the Al arm, are detected as function of externally applied magnetic fields. Evidence is given to interpret these anomalies as due to the thermodynamic fluctuations of the superconducting order parameter in the Al side. A transverse fluctuation mode appears to be present, in good agreement with the theoretical model proposed by Simanek and Hayward.
Enhancement Effect on Positron Annihilation with Tightly Bound Electrons
Authors: Chiba T. , Dürr G. B. , Brandt W. 
Published: July 2007

AbstractCoulomb correlation is taken into account in the annihilation process of positrons in solids with tightly bound electrons by first‐order perturbation theory. A momentum‐dependent enhancement formula is derived which is applicable to insulators with high electron density. With the use of the Thomas‐Fermi approximation the formula is reduced to give an annihilation rate depending solely on the overlap density of electrons and a positron. It is shown that the annihilation rates in insulators follow an enhancement curve different from that for metals.
Optical Constants of GaSe at the Fundamental Absorption Edge
Authors: Antonioli G. , Bianchi D. , Canevari V. , Emiliani U. , Podini P. 
Published: July 2007

AbstractThe three‐dimensional mechanical character of GaSe single crystals makes it very difficult to study the optical properties along the c‐axis. A technique is developed based on the analysis of the interference pattern as a function of the wavelength. Using the envelope of maxima or minima it is possible to normalize the data in respect to the intensity of the incident light so to have an absolute measurement. The fit of the experimental normalized data gives the index of refraction n and the extinction coefficient k with an error of the order of 1\documentclass{article}\pagestyle{empty}\begin{document}$ {\raise0.7ex\hbox{$0$} \!\mathord{\left/ {\vphantom {0 {00}}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${00}$}} $\end{document} for n ⟂ c and 3\documentclass{article}\pagestyle{empty}\begin{document}$ {\raise0.7ex\hbox{$0$} \!\mathord{\left/ {\vphantom {0 {00}}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${00}$}} $\end{document}, for n ∥ c. An error ten times greater is obtained for k⟂ and k∥. It must be emphasized that in the presence of a variation of the refractive index as small as 1\documentclass{article}\pagestyle{empty}\begin{document}$ {\raise0.7ex\hbox{$0$} \!\mathord{\left/ {\vphantom {0 {00}}}\right.\kern-\nulldelimiterspace} \!\lower0.7ex\hbox{${00}$}} $\end{document} between two neighbouring maxima or minima the more traditional methods based only on the determination of the position of extrema are quite inconsistent. On the contrary the envelope method proposed can be used on a wider range. Moreover this method allows to determine k also in a region of low absorption, where 4πk/λ ≪ 1/z0. The transmission between 8000 and 5900 Å is measured and n⟂ land k⟂ are obtained on the entire region while for n∥ and k∥ the determination is possible only in the exciton tail. In this region a ratio k∥/k⟂ ≈ 3 is found.
Structure of the Thermomagnetic Tensor in Semiconductors of n‐Ge Type
Authors: Baranskii P. I. , Buda I. S. , Shcherbina L. A. 
Published: July 2007

AbstractUsing the anisotropic scattering theory the general expression of the components of the thermomagnetic tensor α(H) is obtained for semiconductors of n‐Ge type for arbitrary Orientation of the magnetic field vector H with respect to crystallographic axes. The formulas obtained can be generalized to the case of crystals with non‐cubic symmetry. The structure of thermomagnetic tensor α(H)in n‐Ge is studied in detail for the three most typical cases of orientation of the “laboratory” coordinate system with respect to crystallographic axes. The expressions found allow to compare the theoretical conclusions with the experimental data.
Calculation of the Energy Flows between Subsystems by Means of the Non‐Equilibrium Statistical Operator
Authors: Skrebnev V. A. 
Published: July 2007

AbstractThe exchange of energy between subsystems in the case when there is a great difference in the frequencies at which this exchange is possible, is treated by non‐equilibrium statistical operator method. It is shown that agreement with the experiment can be achieved taking into consideration only pair correlations when calculating the streams of energy. This fact is discussed from the viewpoint of the ergodic theory. A thermodynamic parameter is juxtaposed to the interaction between the subsystems which results in regarding interaction as energy capacity and in the Gibbs' distribution with establishment of equilibrium in the system.
Scattering of Electrons by the Deformation Potential in Doped InSb
Authors: Demchuk K. M. , Tsidilkovskii I. M. 
Published: July 2007

AbstractAn analysis of the experimental data for InSb and of the theoretical considerations used for the determination of the deformation potential constant of the conduction band ϵl is made. It is shown that the correctly calculated value of |ϵ1| is about 30 eV. The small values of |ϵ1| obtained in some works by observing transport phenomena in the hot electron region at lattice temperatures of 4.2 K in samples with electron densities n from 1015 to lo17 cm−3 for which the Boltzmann transport equation is valid, are caused by a distortion of the bottom of the conduction band due to fluctuations of the impurity potential.
Luminescence of Ph2+ and Bi3+ Centres in Alkali‐Earth Sulphides and Oxides
Authors: Ellervee A. F. 
Published: July 2007

AbstractLuminescence centres connected with Bi3+ and Pbz+ ions are investigated in CaO, SrO, CaS, and SrS crystals at 5 to 300 K. It is found that the ground state and the two lowest excited states of the Bi3+ as well as the Pb2+ centres correspond to the energy levels of the free impurity ions and have A1g, 3A1U, and 3T1u, symmetries, respectively. Emission is observed which is caused by electronic transitions from both the excited states. The 3A1u, → Alg transition becomes slightly allowed due to the interaction of an electron with the vibrations of T1u, symmetry. The anti‐Stokes and zero‐phonon lines are observed in the vibronic structure of spectra. The main series of lines are caused by the interaction of electrons with the totally symmetric Alg, vibrations. In the emission spectra of CaS: Bi and SrS: Bi electronic transitions in the host lattice perturbed by impurities are also evident besides intra‐centre electronic transitions.
Carrier Concentration and Magnetic Susceptibility of Doped Ferromagnetic Semiconductors with Application to EuO: Eu
Authors: Spalek J. , Lubecka M. , Węrzyn A. 
Published: July 2007

AbstractSlightly oxygen deficient crystals of EuO exhibit a metal‐semiconductor transition below the Curie temperature accompanied by a strong temperature dependence of the carrier concentration in the conduction band. For the description of this case a model is proposed which takes into account two donor levels: the first one is localized near an oxygen vacancy, and the other one is connected with other impurities or with conduction band tails formed by disorder in heavily doped samples. For such a general case the temperature dependence of carrier concentration is discussed. To get some information about the magnetic state of localized pairs of electrons near an oxygen vacancy the static magnetic susceptibility in the paramagnetic regime for the triplet state is calculated. It depends on carrier concentration and thus a correlation between transport and magnetic properties is obtained. The correspondence with the concept of the molecular magnetic polaron is briefly discussed.
Quadratic Jahn‐Teller Effect and Tunneling Splitting in Octahedral Clusters
Authors: Bacci M. 
Published: July 2007

AbstractThe tunneling splitting due to transitions between coexisting minima of different symmetry is considered and approximate expressions for this splitting are given. The contemporary presence of quadratic Jahn‐Teller terms and anharmonic restoring forces is also discussed. The results are a.pplied to the rase of MgO:V2+ and an hypothesis for the origin of the strirctrrre of the no‐phonon line (4A2g → 4T2g) in the absorption spectrum is proposed.
Channel Model in Isotropic Exchange Theory (II)
Authors: Eremin M. V. , Kakitin Yu. V. 
Published: July 2007

AbstractAn extension is made of the exchange channel model suggested in previous communications. The relationships between exchange parameters are derived that take into account configuration interactions and are applicable to various pairs of ions in excited as well as ground states and with nonquenched as well as quenched orbital moments. Good agreement of the semiempirical theory developed with experiment is demonstrated for a number of solids with perovskite and rock‐salt‐type structures containing bivalent ion pairs. The theory is used to predict spin exchange parameters for various homo‐ and heteronuclear ion pairs linked by 180° bridges in perovskite and rock‐salt structures.
Recombination in Tellurium at High Optical Excitation
Authors: Galkin G. N. , Bobrova E. A. , Herrmann K. H. 
Published: July 2007

AbstractPhotoconductivity (p.c.) and photomagnetoelectric effect (p.m.e.) are observed in tellurium at high levels of optical excitation by means of a Q‐switched ruby laser. The characteristics observed for the stationary case are analysed in terms of a spatial distribution of carriers governed by diffusion and interband Auger recombination. The coefficient of Auger recombination in tellurium C = 1.5 × 10−28 cm6 s‐l is obtained.
On the Ground State Energy of a Gas of Interacting Polarons
Authors: Lemmens L. F. , Brosens F. , Devreese J. T. 
Published: July 2007

AbstractUsing a canonical transformation the Hamiltonian of a gas of interacting polarons is studied. After elimination of the phonons the reduced Hamiltonian describes a system of charged particles interacting through an effective interparticle potential. The Hartree‐Fock ground state of the reduced system is analysed.
X‐Ray Spectroscopical Investigation of the Electronic Structure of Fe—Cr
Authors: Niederlag W. , Blau W. , Kleinstück K. 
Published: July 2007

AbstractFe‐ and Cr‐L2,3 emission and self‐absorption spectra of the disordered alloy Fe70Cr30 are measured using a Bragg‐Soller spectrometer in primary excitation. The intensities are corrected and both, the emission and the absorption spectra are converted into absolute emission probabilities. The results are inconsistent with the rigid band model and are interpreted on the basis of a dilute alloy model. The existence of unoccupied virtual bound states at chromium sites as demanded from theory is experimentally proved.
Soft X‐Ray Spectra of A1 and the Laves Phase CaAl2
Authors: Taut M. , Radwan A. M. 
Published: July 2007

AbstractBased on previous band structure calculations, the soft X‐ray spectra of pure Al and CaAl2, are calculated for transitions to Al core states. Pseudo‐wave functions (without orthogonalization correction to the core states) are used for the calculation of the transition probability. The orthogonalization correction is unimportant for the K‐spectra and doesn't produce any additional peak structure in L‐spectra.
Influence of Surface Carriers upon the Gralvanomagnetic Effects in Slightly Doped Tellurium Samples at Low Temperatures
Authors: Czaya C.‐P. , Keck K. , Rüthlein H. 
Published: July 2007

AbstractThe measured temperature dependence of the Hall coefficient of slightly Sb‐doped tellurium samples at low temperatures (T < 5K) is interpreted in light of surface carriers using a kind of two‐carrier‐model. By application of Fermi statistics the position of acceptor states in slightly Sb‐doped tellurium crystals can be determined from the temperature dependence of the bulk Hall coefficient.
On the Heating of Ultracold Neutrons
Authors: Blokhintsev D. I. , Plakida N. M. 
Published: July 2007

AbstractThe probability of ultracold neutron heating by inelastic scattering in neutron “bottles” is calculated by van Hove's method. The probability is low (⪅ 10−5) for pure substances but is greatly enhanced if light impurities with large incoherent cross‐section (like hydrogen) are present in the surface layers of the “bottle”.
Effective Electron‐Hole Interaction for Intermediate and Strong Electron‐Phonon Coupling A Comment
Authors: Bajaj K. K. , Aldrich C. 
Published: July 2007

AbstractThe values are calculated of the binding energy of a Wannier exciton in several polar crystals including thallous halides and cuprous chloride using both the potential derived by Barentzen and Haken's potential. It is found, contrary to what is claimed by Barentzen, that the values of the binding energy obtained from these two different effective interaction potentials hardly differ from each other. The reason why this is so is discussed.
Vibrational Spectrum of InSe
Authors: Belenkii G. L. , Alieva L. N. , Nani R. Kh. , Salaev E. Yu. 
Published: July 2007

AbstractReflection and absorption of light by InSe single crystals are investigated in the range of wave numbers 500 to 100 cm‐1. The measurements are carried out at room temperature in E ⟂ C orientation of the electric vector. The linear chain model is used for calculating the phonon frequencies at k = 0. The phonon energies at the edge of the Brillouin zone (M point) are calculated by means of the force constants model including the atoms of a single layer.
A classical analysis of the resonance modes in a randomly disordered chain
Authors: Chen G. L. , Wu Shi‐Yu , Schwartz M. 
Published: July 2007

AbstractA classical analysis of the resonance modes in a linear configuration composed of two light impurity atoms in the sea of heavy atoms is carried out for the purpose of understanding the underlying reason for the existence of the resonance peaks in the main band of a randomly disordered chain. The study leads to the conclusion that the peaky resonance modes in the main band of a randomly disordered chain are pseudolocalized modes and that the condition for the existence of the resonance peaks is closely related to the condition for total transmission.
Optical absorption in non‐crystalline semiconductors
Authors: Tripathi R. S. , Moseley L. L. , Lukes T. 
Published: July 2007

AbstractThe density of states is calculated near the band edges for amorphous semiconductors and insulators assuming that these can be described by the model Anderson Hamiltonian in single band approximation. It is shown that the transition matrix element which appears in the interband optical absorption, cannot be treated independent of photon frequency. These are used to calculate the absorption coefficient above the exponential tail in an amorphous material. Also the role of extended to extended transitions is considered, and found that this is smaller than the contribution coming from the extended‐localised absorption. The theory is compared with the experimental data of Greaves et al. on a‐As and good agreement is found between theory and experiment.
A layer summation for electrostatic surface problems. Application to the classical cleavage energy
Authors: Paasch G. , Hietschold M. 
Published: July 2007

AbstractA rather general method is given for calculating the electrostatic potential due to a half‐infinite 2D‐lattice periodic charge distribution. Such kind of potentials arises in the Coulomb integrals of the classical cleavage energy (a contribution to the surface energy) or in calculating ionic lattice relaxation near metal surfaces. For the former quantity numerical results are presented here. It is found that the contribution due to bulk electron density oscillations must be taken into account even for simple metals to get results for the total surface energy comparable with experimental ones (rather than with experimental surface tensions). Taking into account these density oscillations the anisotropy ratios are markedly improved, too. The calculation is made for all simple metals in terms of pseudopotential theory.
Electric field dependence of the electron mobility in tellurium at 77 K
Authors: Behrendt H. , Hoeestel W. 
Published: July 2007

AbstractThe field dependence of the electron mobility is measured in Te at 77 K using an electron drift technique. In the range up to 80 V/cm the electron mobility is nearly field‐independent. In the range from 100 to 400 V/cm the mobility lowers with E−0.6. At fields above 600 V/cm only a weak field strength dependence is observed. The zero field mobility ratio of electrons and holes at 77 K is about (3.55 ± 0.25) independently of the hole mobility of the samples.
On a variational procedure for obtaining the thermodynamic properties of statistical models
Authors: Ferreira L. G. , Salinas S. R. , Oliveira M. J. 
Published: July 2007

AbstractA procedure is developed for obtaining approximate thermodynamic properties of statistical models, based on a well known variational principle for the free energy. The procedure involves the choice of a suitable parametrized trial Hamiltonian which contains some elementary interactions. The free trial Hamiltonian leads to the usual mean‐field approximation. When the trial Hamiltonian includes a certain number of pair interactions only, the results are regained of the constant‐coupling approximation for the Ising model if the number of interacting pairs is conveniently chosen by a comparison with the first few terms of the exact high‐temperature expansion. This procedure is simpler than existing approximations and can be easily generalized. Besides treating the Ising model, some applications are presented to the spin‐1/2 antiferromagnetic Heisenberg model, and to the spin‐1 Heisenberg model with uniaxial anisotropy.
Electron energy loss studies of direct nonvertical interband transitions in silicon
Authors: Chen C. H. 
Published: July 2007

AbstractDirect nonvertical interband transitions in single‐crystal silicon of {001} orientation are detected in the electron energy‐loss spectra for the momentum‐transfer q in the directions of 〈100〉 and 〈110〉. The dependence of the transition energies as a function of q is measured and possible correlations with the energy band structure are discussed.
Off‐stoichiometry effects in the antiferromagnetic ferh alloy
Authors: Khwaja Y. , Nauciel‐Bloch M. 
Published: July 2007

AbstractA model is developed for the band structure of the Fe0.5Rh0.5 antiferromagnetic ordered alloy, and the local effects are studied of a substitutional impurity on the electronic and magnetic properties of the host. It is found that an Fe impurity substituted for Rh creates a perturbation extending at least to the nearest neighbours of the impurity, and a total ferromagnetic moment close to 3.5μB A Rh impurity substituted for Fe has a localized and less important effect. The influence of the magnetic state of the host and the case of other impurities substituted for Rh are also investigated.