Quadrupolar contributions to the atom-surface Van Der Waals interaction

The problem of the quadrupolar contribution to the atom-surface Van der Waals interaction, as discussed by Jiang et al. [Surface Sci. 145 (1984) 281; 148 (1984) 21], is re-examined. It is shown that this earlier work neglects an important contribution associated with quadrupolar fluctuations in the solid. A simplified treatment demonstrates how these contributions are expected to arise in a more general theory.     

Multipole contributions to atom-surface scattering potential

We calculate multipole corrections to the standard van der Waals (dipole) potential in atom-surface scattering. The quadru- and octupoles give at most a 15% deeper potential at relevant physisorption distances, and the degree of metal screening is shown to have very little effect on this conclusion.     

The role of ionic quadrupolar deformation in atom-surface potential

We show that the quadrupolar deformation of surface ions gives appreciable contribution to the potential energy between the atom and an ionic surface. Calculations are presented for a number of alkali halides. The validity of Fumi and Tosi crystal radii in the surface region is discussed in connection with the depth and the corrugation parameter.     

Semiempirical determination of the atom-surface interaction

We discuss three methods of determining V(z), the lateral average (G = 0 Fourier component) of the atom-surface interaction, from the bound state spectrum found in beam scattering. One method uses the Rydberg-Klein-Rees technique, which yields the width of the potential (i.e., separation of classical turning points) as a function of energy. This method incorporates also the known asymptotic form V ～ ?C₃z^?3, whereC₃ is derived from the polarizability and dielectric function of atom and solid, respectively. The second method uses a hybrid potential, constructed from a Morse potential with shifted zero of energy connected to the asymptotic form,?C₃z^?3, requiring continuity of V and $\text{d}\text{V}\text{d}\text{z}$. The third potential is a Lennard-Jones 3–9 interaction. Results are presented for H and He scattering from LiF and NaF.     

Multiphonon contributions to diffracted intensities and resonance profiles in atom-surface scattering

In this Letter, multiphonon contributions to the elastic diffracted intensities and resonance profiles are considered in atom-surface scattering within the close-coupling formalism. Application to the scattering of He atoms from the corrugated Cu(110) and Cu(113) surfaces is shown.     

Electromagnetic contributions to the nucleon-nucleon interaction

The helicity amplitudes of the nucleon-nucleon one-photon exchange interaction are calculated. The anomalous magnetic moments of the proton and neutron are included in the calculations. The formalism is especially suitable for the small angle proton-proton interaction at intermediate energies. The electromagnetic phase shifts in the Born approximation are defined and calculated. The three cases of the proton-proton, the neutron-proton and the neutron-neutron interactions are dealt with separately. Analytic expressions are given for sums defined by divergent partial waves. We indicate the pecularities of the neutron-proton interaction: the singlet-triplet transitions and the t⁻¹ singularity in the differential cross section. These peculiarities require an improved treatment of the neutron-proton interaction. A modified formalism is suggested.     

Atom interferometry measurement of the atom-surface van der Waals interaction

Using a nano-scale grid as a phase-shifting component, an atom interferometer has been utilized to study atom-surface van der Waals (VdW) interactions. We report phase shifts on the order of 0.2 rad, with a few percent uncertainty. We also report the velocity-dependent attenuation of atomic de Broglie wave amplitude that occurs in conjunction with the observed phase shifts. From these data we deduce the strength of the VdW potential and its dependence on the atom-surface separation. We discuss how our measurements can be used to set limits on the strength of non-Newtonian gravity at short length scales and we discuss the possibility of measuring the atom-surface interactions over a larger range of atom-surface distances. We also compare our results to several theoretical predictions for the VdW potential of Li near a variety of surfaces.     

Higgs-boson two-loop contributions to electric dipole moments in the MSSM

The complete set of Higgs-boson two-loop contributions to electric dipole moments of the electron and neutron is calculated in the minimal supersymmetric standard model. The electric dipole moments are induced by CP-violating trilinear couplings of the `CP-odd' and charged Higgs bosons to the scalar top and bottom quarks. Numerical estimates of the individual two-loop contributions to electric dipole moments are given.     

Separation of quadrupolar and magnetic contributions to spin-lattice relaxation in the case of a single isotope

We present a NMR pulse double-irradiation method which allows one to separate magnetic from quadrupolar contributions in the spin–lattice relaxation. The pulse sequence fully saturates one transition while another is observed. In the presence of a Δm = 2 quadrupolar contribution, the intensity of the observed line is altered compared to a standard spin-echo experiment. We calculated analytically this intensity change for spins I = 1, , , thus providing a quantitative analysis of the experimental results. Since the pulse sequence we used takes care of the absorbed radiofrequency power, no problems due to heating arise. The method is especially suited when only one NMR sensitive isotope is available. Different cross-checks were performed to prove the reliability of the results obtained. The applicability of this method is demonstrated by a study of the plane oxygen ¹⁷O (I = ) in the high-temperature superconductor YBa₂Cu₄O₈: the ¹⁷O spin–lattice relaxation rate consists of magnetic as well as quadrupolar contributions.     

Heavy fermion contributions to the anomalous magnetic dipole and quadrupole moments of theW-boson

The contribution of a massivet-quark to the anomalous magnetic moment (Δκ) and the quadrupole moment (ΔQ) of theW-boson is calculated. An upper bound of Δκ=1.5×10^?2 and ΔQ=2.5×10^?3 for the standard model is obtained. Additional contributions from extraE ₆ fermions is also discussed.     

Bound state vibrational spectrum of the 3–9 atom-surface interaction

The potential $\text{V(z) =}\text{C}{}_9\text{z}{}^9\text{?}\text{C}{}_3\text{z}{}^3$ is a reasonable parametrization of the atom-surface interaction. We evaluate the discrete spectrum E_n of bound states for this potential with arbitrary coefficients C₉ and C₃. The resulting form in the WKB approximation is $\text{E}{}_{\mathrm{n}}\text{= ?D [1 ?}\text{(n +}\text{l}\text{2}\text{)}\text{L}\text{]}{}^6$, where L depends on the mass and D is the well depth. We find that the exact solution of the Schrödinger equation can be written in the same form, with n shifted slightly by an amount δ_n, which we calculate. The results are applied to the case of He near a NaF surface, in which the calculated eigenvalue spectrum agrees well with experimental values.     

The absence of surface dipole contributions to metal work functions

A simple model, derived from a linear approximation to the ionization potentials of atoms, is used to compute the work functions of some 43 metals, mostly within their experimental uncertainties. The computation does not make use of a surface dipole contribution. In this respect, it departs from the current literature of many-body theoretical calculations in which the surface dipole plays a major role. Even without the use of surface dipoles, the model can still count for small differences observed on different crystal faces. The model also accounts for the experimental correlations of work functions with half the ionization potential and yields a simple formalism for computing the work functions of metallic clusters. Finally, the model yields the work functions of ions in terms of the same parameter used for the work functions of electrons.     

Classical and quantum interaction of the dipole

A unified and fully relativistic treatment of the interaction of the electric and magnetic dipole moments of a particle with the electromagnetic field is given. New forces on the particle due to the combined effect of electric and magnetic dipoles are obtained. Several new experiments are proposed, which include observation of topological phase shifts.     

Induced dipole contributions to the potential in the surface region of an ionic solid

The theory of the electric potential near the surface of an ionic solid is extended to include induced dipolar effects. Numerical results are given for the {100} and {110} faces of several solids having the NaCl structure. General matrices are given which allow the determination of the dipolar contribution for any ionic solid of the NaCl type. It is shown that the contribution is small for the two surface planes considered.     

Fluxon interaction with the finite-size dipole impurity

Interaction of the fluxon with the finite size dipole impurity in the long Josephson junction is investigated. The impurity has polarity and will be referred to as a dipole impurity because it also has a direction and, consequently, changes its sign under the space inversion transform $x\to ?x$. Such a model is used to describe the inductively coupled to the Josephson transmission line qubit and the misaligned Abrikosov vortex that penetrates into the long Josephson junction. We derive the approximate equations of motion for the fluxon centre of mass and its velocity. With the help of these equations we demonstrate that pinning and scattering of the fluxon on the impurity differs significantly from the case of the point impurity which is modelled by the derivative of the Dirac's δ-function.     

Electron-correlation third-order contributions to the electric dipole transition amplitudes of rare earth ions in crystals

In ab initio studies of the impact of electron correlation effects of f ? f transition probabilities much numerical work is concerned with evaluating radial factors. These terms are expressed as products of the radial integrals summed over all excited orbitals including those in the continuum. To simplify the evaluation of these sums, for the first time in f ? f transition theory, the perturbed-function approach has been applied. The detailed analysis of numerical results obtained for the radial factors contributing to the transition amplitudes for Pr³⁺ are presented. Special attention is paid to studying the impact of the incompleteness of the radial basis set upon the radial factors occurring in f ? f electric-dipole transition theory.     

Temperature dependence of the hyperfine quadrupolar interaction in K2ZrF6

The thermal dependence of the hyperfine quadrupolar interaction of¹⁸¹Ta at Zr sites in K₂ZrF₆ has been studied by TDPAC between RT and 511 °C. Four phases of ever increasing symmetry have been found in the range RT-437 °C. The possible existence of a healing mechanism with an activation energy of 0.187±0.040 eV is discussed for the lattice recovery in the range 270 °C–335 °C. The results at temperatures above 437 °C can be understood assuming a thermal decomposition of the compound.     

Evaluation of thesscf andpy approximations for quadrupolar fluids

Two approximations, the single super chainf-expansion (sscf), and Percus-Yevick (py) approximation, are evaluated for a molecular fluid in which the molecules interact with a pair potential, that is the sum of Lennard-Jones and quadrupole-quadrupole parts at two values of reduced quadrupole moment. These results are compared with Monte-Carlo results. Except for the harmonic coefficienth (222;r), thesscf approximation seems to be quite accurate for the lower value of quadrupole moment but at higher valuespy approximation produces much better results except forh(220;r).