Spatial variations of the order parameter around a Kondo impurity for T ⩽ Tc

Analytic expressions for the spatial variations of the order parameter around a Kondo impurity are obtained. The oscillatory contribution due to impurity scattering is calculated using the t-matrix of Matsuura which conveniently yields the general results below T_c. Differences between our values and those of Schlottmann are reported.     

Magnetic properties of intermetallic ruthenium compounds with the CsCl structure

Magnetization measurements on six ruthenium compounds with the CsCl structure (B2-compounds) are reported. The magnetic properties can be described in terms of a temperature independent Pauli susceptibility and a contribution of localized moments of about 4μ_B which are very likely connected with magnetic centers consisting of one ruthenium atom which substitutes for an X-atom in an otherwise ordered compound RuX and its eight nearest neighbours. The results show that a weak antiferromagnetic coupling exists between these moments of which the concentration is about 0.003 per ruthenium atom.     

InSe electrical characterization by means of transport parameters

SCLC measurements in single crystals of the layered semiconductor n-type InSe are reported. The measurements were carried out at various temperatures and on samples grown with indium added in excess (from 5 to 10%). The experimental results suggest that the trapping levels location and the charge transport are dependent on the indium excess. Only the samples grown with an indium excess of about 5% show the features typical of intrinsic semiconductors. The anomalous behaviour of samples grown with indium excess between 6 and 10 is explained by means of scattering mechanisms between charge carriers and ionized impurity centers.     

Theoretical investigations on the formation of wurtzite segments in group III-V semiconductor nanowires

Structural trends in group III-V semiconductor nanowires (NWs) are systematically investigated based on Monte-Carlo simulations using our empirical potential calculations. The calculated NW stacking sequences for the selective area growth demonstrate that the averaged periodicity between wurtzite segments, which is independent of the NW size, decreases with increasing ionicity of semiconductors f_i. It is also found that the periodicity is affected by the nucleus size of NWs: The calculated periodicity in InP (InAs) NWs with the nucleus size consisting of ∼ 10 atoms are 0.76 (0.86) nm, reasonably consistent with the experimentally reported one. On the other hand, the nucleus size to reproduce the experimentally reported periodicity in GaAs NWs is estimated to be more than 70 atoms. These results thus imply that the nucleus size as well as f_i is of importance in determining the averaged periodicity between wurtzite segments.     

Infrared reflectance spectrum of BN calculated from first principles

Using the linear response theory, vibrational and dielectric properties are calculated for c-BN, w-BN and h-BN. Calculations of the zone-center optical-mode frequencies (including LO-TO splittings) are reported. All optic modes are identified and excellent agreement is found between the theory and experimental results. The static dielectric tensor is decomposed into contributions arising from individual infrared-active phonon modes. It is found that all the structures have a smaller lattice dielectric constants than those of the electronic contributions. Finally, the infrared reflectance spectrums are presented. Our theoretical results indicate that w-BN shows a similar reflectivity spectrum as c-BN. It is difficult to tell apart the wurtzite structure from the zinc blende phase by IR spectroscopy.     

Positron annihilation in gamma irradiated crystals

The angular correlation between the two gamma-quanta arising from positron annihilation in untreated and gamma-irradiated alkali halides is reported. For low level gamma irradiation the percentage of positrons annihilating with F-centre electrons is not very significant. When the F-centre concentration is increased to as much as 1.5 × 10¹⁷ per cm³, about 15 per cent of positrons annihilate with F-centre electrons. The angular correlation curve becomes progressively narrower with increase in F-centre concentration. Positrons annihilating in gamma-irradiated crystals reduce the F-centre considerably. The results of a systematic investigation on F-centre bleaching by positron annihilation are reported.     

Non-grey radiative heat transfer in the picket-fence approximation

The radiative heat transfer between parallel plates separated by an absorbing gas with a “picket-fence” absorption coefficient is treated by a variational technique. For the heat transfer, a simple rational algebraic expression is obtained and the variational results are found in excellent agreement with the numerically “exact” results reported recently by Reithet al.(⁸) An expression for the extrapolation distance is also deduced and the results are compared with the values reported earlier by Bond and Siewert.(⁵)     

Particle correlations in e + e − → W + W − events

Preliminary results are reported on the two-particle correlation function R(Q) in hadronic Z decays, fully hadronic WW decays, and mixed hadronic-leptonic WW decays using data collected by the DELPHI detector at LEP at energies between 189 and 206 GeV. Evidence for Bose-Einstein correlations was observed in all three cases. The event mixing technique was used to determine correlations between particles arisingfrom different W bosons in fully hadronic WW decays. An excess of like-sign particle pairs with low four-momentum difference in fully hadronic WW events is observed, consistent with the effect expected from correlations between identical particles from different W bosons.     

Transition energies, wavelengths, oscillator strengths and transition probabilities between 1s, 1sns and 1snp (2?n?9) states for He-like Silicon

Multiconfiguration Hartree-Fock calculations with Breit-Pauli relativistic corrections are reported for electric dipole transition (E1) energies, wavelengths, weighted oscillator strengths and transition probabilities between all of the 1s², 1sns and 1snp (2?n?9) states for He-like silicon. The results are found to compare very well with available other results except Δn=0 due to differences in the calculated excitation energies.     

XPS and auger spectroscopy studies on mixtures of the oxides SiO2, Al2O3, Fe2O3 and Cr2O3

X-ray photoelectron Spectroscopy (XPS) and X-ray-induced Auger Spectroscopy were utilized to examine qualitative and quantitative aspects involved in the surface analysis of mechanical mixtures of the title oxides. Consideration of O1s and OKVV bands of the mixtures makes it possible to distinguish between the single oxide components. The energy shift between the Fe₂O₃ and SiO₂ (or Al₂O₃) components is about twice as large in the OKVV region as in the O1s region. By way of contrast, Auger Spectroscopy analysis of the mixtures does not appear to enable a quantitative distinction between the constituent oxides to be made. Conversely, XPS analysis provides instead quantitative results, although these are affected by a relative error of ± 10%. A simple approach, based on intensity ratio measurements of the single O1s components, enables relatively accurate quantitative results to be obtained.It is shown that analysis of appropriate mixtures is a useful case study for investigations on surface and interface properties of real materials. Argon ion etching effects on the mixtures and on the title oxides analyzed separately are reported.     

Magnetoreflectance of the Γ6 – Γ8 exciton ground state in cubic ZnSe

Magnetoreflectance measurements on the ground state of the Γ₆ – Γ₈ free exciton in cubic ZnSe in magnetic fields up to 18 T are reported. The splitting between the |1, ±1〉 states was derived from the measured difference spectrum between σ⁺ and σ^--polarized reflectance in Faraday configuration. The splitting between the two states corresponding to |2, 0〉 and |1, 0〉 at B = 0 was determined by means of a lineshape analysis. We derive an electron g-factor g = 1.48 ± 0.25, in reasonable agreement with existing k · p calculations, and obtain an effective hole g-value $\text{K}\text{?}\text{= -0.26±0.06}$. In addition, we find an upper limit for the short range electron-hole spin exchange energy Δ ? 0.1 meV, which is considerably smaller than values, which is considerably smaller than values reported in the literature, but agrees with recent results on ZnTe obtained by uniaxial stress and also magnetoreflectance measurements.     

The electronic structures of some aromatic sulfinylamines

He(I) and He(II) photoelectron spectra of some sulfinylamines are reported and assignments made on the basis of CNDO/S LCAO MO calculations. Insight into the effects of several substituents on the electronic structures of the compounds is obtained. The difference between the actual electronic structure of o,o′, p-trimethyl sulfinylaniline and that interpolated from other molecules in the series is assumed to reflect a different conformation for this compound.The results of the MO calculations agree fairly well with the experimental data, although some discrepancies occur, concerning especially the π-donating capacity of a Cl substituent, and ionizations from chlorine lone pair orbitals.     

On the induced cobalt moment in RCo4 B-type compounds

The results of magnetic measurements performed on (Gd_xY_1-x)Co₄B compounds in the temperature range 4.2 and 900 K are reported. The compounds with x ⩾ 0.2 are ferrimagnetically ordered. The mean cobalt moment is dependent on composition. Above the Curie temperatures, the reciprocal susceptibilities obey a non-linear dependence as function on temperature. By using a two sublattices model, the mean values of the molecular field coefficients, characterizing the magnetic interactions inside and between sublattices are determined. The mean cobalt moments are linearly dependent on the exchange fields acting on these atoms.     

Thermal expansion of CuInSe2 in the 11–1,073 K range: an X-ray diffraction study

Structural and elastic properties of chalcopyrite-type CuInSe₂ are determined in almost full stability range of temperature from 11 to 1,073 K, by in situ X-ray diffraction, employing a synchrotron-radiation source. The studied polycrystalline sample was prepared from a stoichiometric single crystal. Phase analysis reveals the formation of a trace amount of indium oxide impurity phase at the highest temperatures studied. From the obtained smooth lattice-parameter dependencies on temperature, the temperature dependencies of thermal expansion coefficients are derived. These coefficients are found to follow the trends previously reported for narrow temperature intervals. The present results provide a clear experimental evidence that the linear expansion coefficient is slightly negative below 47 K in both, a and c, directions; this temperature limit is in between the previously reported theoretical value (35 K) and the experimental ones (60 and 80 K) of such limit.     

Attachment and motion of hydrogen in hydrogen (deuterium) molybdenum bronzes,DxMoO3

Ambient temperature ²D NMR spectra are reported for powder samples of the single phase hydrogen (deuterium) molybdenum bronzes, D_xMoO₃, with x=0.36 (blue orthorhombic), x=0.90 (blue monoclinic), x=1.68 (red monoclinic) and x=2.0 (green monoclinic). Spectra over a range of temperatures are also reported for the red monoclinic and green monoclinic phases. Translation of H-atoms between magnetically inequivalent sites leads to narrowed spectra for all four phases. A consistent interpretation of results from a range of experimental techniques can be given in terms of H-atom sites corresponding to attachment to O-atoms as part of coordinated-OH (hydroxyl) and/or -OH₂ (water) groups.     

The nature of percolation ‘channels’

A relation is found between the percolation probability, P^(s)(x), for site percolation, the conductance, G(x), of certain random networks, and the spin-stiffness coefficient, D(x), of dilute Heisenberg ferromagnet. Numerical results and critical exponents for these quantities near their common threshold are reported. These results demonstrate that the percolation ‘channels’ in which spin waves occur cannot be regarded as one or two dimensional.     

Equilibrium properties of the cubic phases of cobalt

Lattice constants and magnetic moments of face-centered cubic (fcc) and body-centered cubic (bcc) phases of cobalt obtained from self-consistent spin-polarized total-energy calculations by the augmented spherical wave method are compared to measurements. The calculated lattice constants fit the measured values of both phases to about 1%, but favor one of the two reported results on the newly-synthesized bcc phase. However the reported magnetic moments are substantially lower than the theoretical value for the bcc phase. We show that bcc cobalt is metastable up to 400 kbars pressure and, like fcc cobalt, is a strong ferromagnet. The magnetic moment of fcc cobalt is shown to collapse at a 5% lattice compression.     

Zero-temperature equation of state of metals in the statistical model with density gradient correction

The density gradient correction to kinetic energy (nine times smaller than the original von Weizsäcker correction) has been used within local density formalism to calculate the cold compression curve of metals. Numerical results are reported for Li, Be, Al and Cu. The modifications to the Thomas-Fermi-Dirac (TFD) results strongly depend, in the low compression range (?/?₀ ? 5), on the electron density of the material. The relative difference between the pressures in the present model and the TFD model regularly decreases with increasing compression, suggesting that TFD is reliable for ?/?₀ ? 50 in Li, ??₀ ? 20 in Be and Al and ?/?₀ ? 10 in Cu.     

N-dependence of the lineshape in nonlinear radiation phenomena

Preliminary experimental results are reported on the investigation of the dependence of the intensity of the second harmonic generated by paramagnets on the number N of spins. A qualitative argument in terms of correlation effects among the spins is tentatively put forward to interpret the results.     

Angular distributions of penning electrons

Angular distributions of electrons ejected in thermal collisions of He(2¹ S, 2³ S)-metastables with Ar, Kr, Xe, Hg, CO, N₂ are measured with respect to the vector of relative velocity of the colliding particles. Except for preliminary results on the He(2₁S, 2³ S)-/Ar-system, these are the first such distributions reported. They are found to be strongly anisotropic and asymmetric in some cases, and approximately isotropic in those cases where the interaction potential between the metastable- and the target particle is strong. For the cases of weak interaction potential, the connection between the “internal” angular distribution in the frame fixed to the internuclear axis and the laboratory angular distribution, has been derived. Calculations of laboratory angular distributions involving an assumed “internal” distribution and the kinematics of a hard core collision show good qualitative agreement with the experimental results.