Superconductivity in singlet La-Pr and in nonmagnetic La-rare earth alloys

We show that concentration dependence of the superconducting transition temperature of d.h.c.p. $\text{La}$Pr alloys is almost identical to that of $\text{La}$Y and $\text{La}$Lu alloys. This suggests that Pr is in a singlet ground state and that lifetime broadening caused by the 4? electrons of Pr have little effect on the superconducting process in $\text{La}$Pr. The depression of the transition temperature arises largely from pair weakening (or possibly crystal field effects) rather than pair breaking effects.     

Deconvolution method for composition profiling by Auger sputtering technique

Some of the sputter broadening effects on profile measurements using the Auger sputtering technique have been quantitatively investigated for $\text{Ag}\text{Au}$ and $\text{Cu}\text{Ni}$ systems. Two methods have been used to measure the resolution function as a function of the sputter distance for these two systems. The broadening can be separated into contributions from original surface roughness and sputtering effects, the latter amounting to about 7% of the sputter depth for $\text{Cu}\text{Ni}$ and 14% for $\text{Ag}\text{Au}$ interfaces. Based on the measured resolution function, a deconvolution method has been developed to facilitate the retrieval of the actual profile from the observed profile by reducing the sputter broadening. Using this method, we found that the measured interfacial profile can be substantially sharpened. The implications of using the deconvolution method for interdiffisuion studies in thin films are discussed.     

Hall effect in dilute magnetic alloys

We review the theory and the experimental results on the Hall effect in noble metals containing magnetic impurities of transition metals. In order to illustrate the various types of observed effects, we focus succesively on selected systems: $\text{Cu}$Mn, with only enhancement of the ordinary Hall effect due to the existance of different spin-up and spin-down currents; $\text{Au}$Fe and $\text{Au}$Cr, with skew scattering by magnetic impurities; $\text{Cu}$MnT ternary alloys (where T is a non-magnetic impurity), with skew scattering effects due to combined spin—orbit scattering by non-magnetic impurities and spin scattering by Mn impurities. The skew scattering in $\text{Au}$Fe and $\text{Au}$Cr can be ascribed to the orbital character of the impurity moments and accounted for in an orbitally degenerate virtual bound state model. However, the anomalous temperature dependence of the skew scattering in Kondo alloys at low temperature is not well understood. We also present some magnetoresistance data in order to describe the links between the Hall effect and the magnetoresistance in magnetic alloys. In particular, we relate the skew scattering and the magnetoresistance anisotropy observed in $\text{Au}$Cr alloys.     

The quark sea and the ΔI = 12 rule

The effect on nonleptonic processes of quark-antiquark pairs due to quantum chromodynamics is studied. Their presence improves agreement between theory and experiment for hyperon decays. In kaon decays a new $\text{ΔI =}\text{1}\text{2}$ contribution is found, but $\text{Δ =}\text{3}\text{2}$ effects are still large to to be in agreement.     

Higgs production and decay into heavy flavours with the gluon fusion mechanism

We consider the reaction $\text{gg}\text{→}\text{H}\text{→}\text{Q}\text{Q}$ and find that there are interference effects with the pure QCD process $\text{gg}\text{→}\text{Q}\text{Q}$. These effects as well as the large QCD background make it unlikely that this reaction is a good candidate for the study of Higgs-boson production, unless the Higgs boson couplings differ very much from their values in the standard model.     

Polarization effects for W± and Z0 production in pp collisions

Polarization effects for the leptonic decays of W^± and Z⁰ are calculated and discussed in $\text{p}\text{p}$ collisions with longitudinally polarized proton beams. Numerical examples are given for the CERN $\text{p}\text{p}$ collider and Fermilab Tevatron.     

Orbital classical solutions,non-perturbative phenomena and singularity at the zero coupling constant point

We try to extend previous arguments on orbital classical solutions in non-relativistic quantum mechanics to the $\text{1}\text{4}\text{λ|φ|}{}^4$ complex relativistic field theory. The single valuedness of the Green function in the semiclassical $\text{(}\text{h}\text{?}\text{→ 0)}$ limit leads to a Bohr-Sommerfeld quantization. A path integral formalism for the Green functions analogous to that in non-relativistic quantum mechanics is employed and a semiclassical approach which uses our classical solutions indicates non-perturbative effects. They reflect and $\text{e}{}^{\mathrm{<mtext>1</mtext><mtext>\lambda </mtext>}}$ singularity at the zero coupling constant point.     

Multiphoton excitation of visible emission in Y2O2S: Er,Yb phosphors by 810 nm excitation

During investigations of anti-Stokes effects in erbium—ytterbium doped yttrium oxysulphide phosphors we have found an excitation of the erbium green emission due to 810 nm radiation (⁴I$\text{15}\text{2}$ → ⁴I$\text{9}\text{2}$ transition), the effect being of a two-photon type. There is also a two-photon excited blue emission (²H$\text{9}\text{2}$ → ⁴I$\text{15}\text{2}$ transition) due to the same radiation. Introduction of ytterbium impurity has a deleterious effect on the above 810 nm excitation, in contrast to its sensitization of the 1000 nm anti-Stokes excitation. To distinguish between various excitation schemes a two-beam excitation technique has been used. Results show that ytterbium inclusions lead to loss of energy from the 810 nm excitation by increasing the probability of downward transitions from the ⁴F$\text{9}\text{2}$ level to ⁴I$\text{11}\text{2}$ and ⁴I$\text{13}\text{2}$ states, reached after onephoton absorption. This effect is indicated by an increase in 1500 nm emission (⁴I_{$\text{13}\text{2}$} → ⁴I_{$\text{15}\text{2}$} with ytterbium concentration.     

Relativistic Hartree-Fock oscillator strengths for the lowest s→p and p→d transitions in the first few members of the Ag(I) and Au(I) isoelectronic sequences,with allowance for cope polarization

Relativistic, single-configuration Hartree-Fock oscillator strengths for the lowest ns²S_{$\text{1}\text{2}$}→np²P_{$\text{1}\text{2}$$\text{3}\text{2}$} and np²P_{$\text{1}\text{2}$$\text{3}\text{2}$}→nd²D_{$\text{3}\text{2}$$\text{5}\text{2}$} transitions in the first few members of the silver (n = 5) and gold (n = 6) isoelectronic sequences have been studied, both with and without allowance for core polarization. Core polarization is included by introducing a polarization potential in the one-electron Hamiltonian and by employing the corresponding correction for the dipole-moment operator in the transition matrix element. The results obtained are compared with available experimental data and the influence of core-polarization effects on oscillator strengths is discussed.     

The rotational bands 12+[411]and 12−[541]in 175Lu

In a study of the γ-radiation emitted in the reaction ¹⁷⁶Yb(p, 2n) excited states of the nucleus ¹⁷⁵Lu up to spin I = $\text{13}\text{2}$ have been investigated. The main results concern the rotational bands $\text{1}\text{2}$⁺ [411]and $\text{1}\text{2}$^? [541]with the corresponding band heads found at 626.60 and 370.88 keV, respectively. The half-life of the $\text{1}\text{2}$⁺[411] level has been determined to be $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 10.7±0.5}\text{ns}$. Furthermore, the band heads $\text{3}\text{2}$^?[532]and $\text{3}\text{2}{}^{\mathrm{+}}$[411]are proposed at energies of 999.0 and 1150.8 keV, respectively. Experimental E1 transition probabilities between both $\text{K =}\text{1}\text{2}$ bands are compared with calculations including the Coriolis and pairing effects, as well as theoretically deduced quadrupole deformation parameters.     

Three- and five-quasiparticle isomers,rotational bands and residual interactions in 175Hf

Two 3-quasiparticle isomers with spins, parities and half-lives of $\text{19}\text{2}$⁺, 1.1 μs and $\text{23}\text{2}$^?, 1.2 ns have been identified at 1433 and 1766 keV in ¹⁷⁵Hf. A third isomer, possibly $\text{35}\text{2}$^? with a 1.2 μs half-life, is found at 3015 keV. The first two are characterised as a $\text{7}\text{2}$⁺ [633] neutron coupled to the known 6⁺ and 8^? 2-proton isomers of the core nuclei. Rotational bands based on the 3-qp isomers are highly perturbed, due to Coriolis mixing, and their structure is reproduced in a band mixing calculation. The energy depression of the 3-quasiparticle states relative to the 2-quasiproton core states is attributed mainly to the residual proton-neutron interaction, and possibly also to blocking effects through neutron admixtures.     

Electronic structure of the (111) and (111) surfaces of GaAs

Inward relaxation effects of the outermost Ga layer on the electronic structure of GaAs (111) Ga and outward expansion effects of the outermost As layer on that of GaAs ($\text{111}$) As are studied by extended Hückel theory. Three different surface geometries are examined for the respective surfaces. It is shown that upon relaxation on GaAs (111) or upon expansion on GaAs ($\text{111}$) new surface states associated with dangling- and back-bonds are revealed. The character and dispersion behaviour of strongly localized surface states are described.     

Energy dependence of the reaction mechanism of 11B induced single nucleon transfers on 26Mg

Angular distributions for elastic scattering and for single nucléon stripping reactions induced by a 31 MeV ¹¹B beam on ²⁶Mg have been measured. The DWBA calculations provide a good account of the shape and magnitude of the proton transfer data and of the neutron transition to the $\text{j-}\text{favoured}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ level in ²⁷Mg, but fail to reproduce the features of the $\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and $\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ transitions to ²⁷Mg. The j-dependent effects and l-matching conditions are investigated as a function of beam energy and their role in determining the reaction mechanism is examined.     

Photoemission of Xe and Kr adsorbed on the W(110) plane

The UPS and XPS spectra of Xe adsorbed on clean, O, CO, and Xe covered W(110) surfaces and the UPS spectrum for Kr on clean and O covered W(110) surfaces have been investigated. On clean W, Xe and Kr show a splitting of the $\text{5p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ and $\text{4p}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ hole states respectively. For Xe the coverage dependence of this splitting was investigated in detail; neither the positions nor the intensity ratio of the substates are coverage dependent for θ ? 0.04, suggesting that splitting is due to differences in the image interaction of the $\text{m}{}_{\mathrm{j}}\text{= ±}\text{3}\text{2}$ and $\text{m}{}_{\mathrm{j}}\text{= ±}\text{1}\text{2}$ components. For Xe equal shifts, relative to vacuum, of ~1.0 eV were observed for 5p, 4d, and 3d levels, suggesting that initial state effects are small. Image interaction for Xe and Kr on clean W could best be fitted by assuming an increase, rather than a decrease in the effective hole-image separation from the nominal value, suggesting that the image plane is moved back into the metal by a screening length. For Xe adsorbed on $\text{Xe}\text{W}$(110), or on virgin-$\text{CO}\text{W}\text{(110)}$ polarization of the intermediate layers was found to contribute significantly to relaxation. Coadsorbed oxygen broadened Xe 5p and Kr 4p peaks. There was an almost linear relation between O 2p UPS intensity at the energies of the various peaks and the amounts of broadening, suggesting that the latter results from resonance neutralization by electrons from the O 2p states.     

Odd-even features in 3He + 3H scattering

The single-channel resonating-group method is used to study effects of the Pauli principle on ³He + ³H scattering. Comparison is made with previous similar calculations for d + ³He scattering, and it is found that the Pauli principle affects the s = 0 state of the ³He + ³H system rather similarly to the way it affects the s = 1 state, whereas the Pauli principle affects the $\text{s =}\text{3}\text{2}$ state of the d + ³He system quite differently from the way it affects the $\text{s =}\text{1}\text{2}$ state. Mention is made of the possibility of observing similar effects of the Pauli principle in other nuclear systems.     

Photoemission from single crystal xenon

Normal exit photoemission spectra from the (111) surface of a xenon single crystal indicate that the valence level emission is considerably broader than expected on the basis of band structure calculations. Similar observations from polycrystalline samples have lead Parrinello $\text{et al}$ to propose an excitonic screening mechanism which would cause an apparent increase in the spin-orbit splitting at the Γ point. The details of the spectra reported here show, however, that the effect could simply be due to a dispersion of the bands stronger than that predicted theoretically. Anomalous intensity effects at $\text{h}\text{?}\text{ω = 21.2}\text{eV}$ are explained in terms of electron-electron scattering.     

Adsorbate-induced surface resonances observed in photoemission from a (2 × 2)R45° sulphur layer on Pd(100)

Angular-resolved photoemission spectra from a $\text{(}\text{2}\text{×}\text{2}\text{)R45°}$ sulphur layer on Pd(100) reveal peaks independent of photon energy, which show strong dispersion in the electron energy range 3…9 eV relative to the vacuum level. The appearance of these levels can be correlated with absolute gaps in the projected bulk band structure of palladium. We interpret these features, which are also observed in secondary electron emission, as adsorbate-induced surface resonances above E_F. The sulphur 3p-derived levels below E_F show strong dispersion effects in the [110] but not in the [100] crystal azimuth. The projected band structure also shows that $\text{sd}$ hybridisation gives rise to an absolute gap at approximately this energy in the [110] $\text{(}\text{ΓX}\text{)}$ direction.