Static dipole polarizabilities of Scn （n ≤15） clusters

The static dipole polarizabilities of scandium clusters with up to 15 atoms are determined by using the numerically finite field method in the framework of density functional theory. The electronic effects on the polarizabilities are investigated for the scandium clusters. We examine a large highest occupied molecular orbital --- the lowest occupied molecular orbital (HOMO--LUMO) gap of a scandium cluster usually corresponds to a large dipole moment. The static polarizability per atom decreases slowly and exhibits local minimum with increasing cluster size. The polarizability anisotropy and the ratio of mean static polarizability to the HOMO--LUMO gap can also reflect the cluster stability. The polarizability of the scandium cluster is partially related to the HOMO--LUMO gap and is also dependent on geometrical characteristics. A strong correlation between the polarizability and ionization energy is observed.     

Theory of distinct crystal structures of polymerized fullerides AC60, A = K, Rb, Cs: the specific role of alkalis

The polymer phases of AC60 form distinct crystal structures characterized by the mutual orientations of the (C( -)(60))(n) chains. We show that the direct electric quadrupole interaction between chains always favors the orthorhombic structure Pmnn with alternating chain orientations. However, the specific quadrupolar polarizability of the alkali metal ions leads to an indirect interchain coupling which favors the monoclinic structure I2/m with equal chain orientations. The competition between direct and indirect interactions explains the structural difference between KC60 and RbC60, CsC60.     

The determination of a temperature-dependent tilt angle in a smectic C liquid crystal by electron resonance spectroscopy

A method used by Steiner to simplify the calculation of the hydrogen atom static dipole polarizability is applied to the frequency-dependent dipole and quadrupole polarizabilities.     

Modification of the Xe 4d giant resonance by the C60 shell in molecular Xe@C60

It is demonstrated that in photoabsorption of the 4d ¹⁰ subshell of a Xe atom in molecular Xe@C₆₀, the 4d giant resonance that characterizes the isolated Xe atom is distorted significantly. The reflection of photoelectron waves by the C₆₀ shell leads to profound oscillations in the photoionization cross section such that the Xe giant resonance is transformed into four strong peaks. Similarly, the angular anisotropy parameters, both dipole and nondipole, are also modified. The method of calculation is based on the approximation of the C₆₀ shell by an infinitely thin bubble potential that leaves the sum rule for the 4d-electrons almost unaffected, but noticeably modifies the dipole polarizability of the 4d-shell. The text was submitted by the authors in English.     

On the dipole moment of three identical spherical atoms

Martin's perturbation theory result [2] for the dipole moment of three identical spherical atoms at large separations is shown to simplify: There are two contributions to this three-atom dipole and the strength of each factors into a product of the dipole polarizability of one atom and a two-atom average of dipole and quadrupole matrix elements. The simplified results are used to obtain an improved evaluation of the three-atom dipole of three He atoms, employing extensive pseudo-spectral representations of the dipole and quadrupole excitations.     

Molecular beam deflection experiments on mixed clusters

Gas phase Ti-C₆₀ clusters are studied by molecular beam electric deflection. The permanent dipole moment of the TiC₆₀ molecule is determined. It is equal to 8.1±1.5 D. This dipole is due to a transfer of electron from the transition metal atom to the C₆₀ cage. No dipole is observed for Ti(C₆₀)₂ molecules. This is in agreement with the symmetrical dumbbell-like structure that has been previously proposed. Received 22 November 2000     

Structure of nano-objects through polarizability and dipole measurements

The electric polarizability and the electric permanent dipole are important quantities for understanding the electronic properties of a cluster. Experimental techniques, the simulations necessary to interpret the experimental results, and a review of measurements on atomic and mixed clusters are presented. For atomic clusters, the polarizability is related to the type of bonding. In simple metal clusters such as alkali clusters, the results are well interpreted by the electron delocalization characteristic of the metallic bonding. In other metal clusters, the polarizability reflects the difficulty of establishing a clear and regular picture of the size evolution of electronic properties. The size evolution observed for covalent and semiconductor clusters is different from the evolution for metal clusters, and the influence of the geometry is preponderant, as demonstrated in the case of fullerenes. For mixed clusters, the measurements of the electric dipole allows one to deduce the charge transfers and the geometric arrangement. This is illustrated in the case of the metal-fullerene system and alkali halide clusters. To cite this article: M. Broyer et al., C. R. Physique 3 (2002) 301–317.     

Application of the nuclear liquid drop model to atomic and molecular physics problems

The liquid drop model is applied to describe some basic properties of atoms, homoatomic molecules, metallic clusters of atoms and fullerene molecules. Equilibrium atomic size, energy and polarizability of the atom are calculated. Collective modes of oscillations (dipole, quadrupole and monopole, or breathing, ones) are regarded. Electromagnetic radiation by an atom, passing through a barrier is studied. Equilibrium volume of a homoatomic molecule of two atoms, axes ratio, dissociation energy and the frequencies of the dipole oscillations are calculated. Models to describe some properties of clusters and fullerene molecules are proposed. The size of the metallic cluster, its energy and the frequency of dipole oscillations are calculated. The frequencies of the dipole and breathing mode oscillations of the fullerene molecules are obtained. The calculated frequency of the dipole oscillations was found to be in a rather good accord with the experimental one.     

Susceptibility and electric dipole in metal C 60 compounds

The permanent electric dipole moment of metal atom-C₆₀ compounds is measured. A column (alkali) and a row (transition metals) of the periodic table are systematically investigated. Most of the experimental results are obtained at high temperature when the atom is mobile on the C₆₀ cage. For a given example (NaC₆₀), the dipole moment is also measured by a different method at low temperature and both results are consistent. For alkali, the results are compared to ab initio calculations. A good agreement is obtained, both for absolute values and for the evolution of the bonding in the alkali column. For transition metals, the relative values of the dipole moments are in qualitative agreement with the ionic character of the compounds.     

On the effects on a Landau-type system for an atom with no permanent electric dipole moment due to a Coulomb-type potential

We analyse the bound states for a Landau-type system for an atom with no permanent electric dipole moment subject to a Coulomb-type potential. By comparing the energy levels for bound states of the system with the Landau quantization for an atom with no permanent electric dipole moment (Furtado et al., 2006), we show that the energy levels of the Landau-type system are modified, where the degeneracy of the energy levels is broken. Another quantum effect investigated is a dependence of the angular frequency of the system on the quantum numbers associated with the radial modes and the angular momentum. As examples, we obtain the angular frequency and the energy levels associated with the ground state and the first excited state of the system.     

[二苯并18冠醚6]KC60里C60的取向有序与磁相关的13C NMR研究

报道了超分子材料[二苯并18冠醚6]KC₆₀是一种具有奇异磁特性的富勒烯衍生物,经¹³C NMR研究发现,C₆₀的取向有序与磁性之间存在着很强的相关性.     

Experimental and theoretical study of the quantum-confined Stark effect in a single InGaN/GaN quantum dot under applied vertical electric field

We present a study of the effect of externally applied vertical electric field on the optical properties of single InGaN/GaN quantum dots via microphotoluminescence spectroscopy. This is achieved by incorporating the quantum dot layer in the intrinsic region of a p–i–n diode structure. We observe a large blue energy shift of 60 meV, which is explained by the partial compensation of the internal piezoelectric field. The energy shift dependence on the applied field allows the determination of the vertical component of the permanent dipole and the polarizability. We also present theoretical modelling of our results based on atomistic semi-empirical tight-binding simulations. A good quantitative agreement between the experiment and the theory is found.     

Mesoscopic fluctuations of the dipole moment and the electric polarizability

We consider mesoscopic fluctuations of the dipole moment and the electric polarizability of a disordered thin film in the diffusive regime. It is shown, that the requirement of a fixed particle number is crucial for obtaining finite fluctuations at low temperatures. For systems with sufficient disorder and a long screening length a spontaneous dipole moment should be observable with an atomic force microscope.Dedicated to Prof. H. Wagner on the occasion of his 60th birthday     

A matter-wave interferometer based on the dc-Stark effect

We present a new separated beam atom interferometer in which the recombination of the atomic wave packet is due to the dc-Stark interaction of an induced atomic dipole with a cylindrically symmetric electric field of a charged wire. The fringe period shows a weak power-law dependence on the de Broglie wavelength and the polarizability of the particles. We present a semiclassical theoretical model for this interferometer which resembles the measured performance of the interferometer without free parameters. A discussion of possible applications of this interferometer for atoms and molecules is given. Received: 20 November 1998 / Published online: 8 September 1999     

Search for electric dipole moment in 129Xe atom using a nuclear spin oscillator

We aim to measure the electric dipole moment (EDM) of a diamagnetic atom ¹²⁹Xe using an optical-detection nuclear spin maser technique. The relation of EDM in a diamagnetic atom to nuclear Schiff moment and fundamental sources generating it is discussed, and the present status for the development of our experimental setup is presented.     

Concept of dipole polarizability matrices for a system of wires and examples of their calculations and variational estimates

The concept of dipole polarizability matrices for a system of wires is introduced that generalizes the wellknown concept of the dipole polarizability for a separate wire. Examples of calculations of the dipole polarizability matrices and variational estimates of these matrices are given.     

An algorithm for the calculation of the net induction energy and induced multipole tensors in a set of charge distributions with non-linear contributions of all potentials of external fields and both permanent and induced multipoles

This algorithm for the calculation of the induced multipole tensors in a set of charge distributions includes the contributions of partial derivatives of arbitrary order of the potentials defined by both induced and permanent multipoles as well as non-uniform external fields of arbitrary strength. Specific equations are given for both systems with and without translational order. The algorithm, which is based on the Maxwell invariant form, uses direct extensions of algorithms previously developed and tested for the calculation of permanent multipole energies and induced dipole vectors (when the non-uniformity of the field is neglected). The induced tensor components are calculated iteratively. The first approximation, which gives the components as the solution of a set of simultaneous linear equations, includes all nonlinear, non-uniform contributions of permanent multipoles and external fields as well as all contributions linear in derivatives of the induced potentials. The induced tensor components are then used to calculate the net induction energy. The general relations between the polarizability tensors with respect to a centre and the moments of the polarizability densities about the centre are derived.     

Electric field influence on spin polarization vector behaviour of the negative muon in silicon

When a negatively charged muon is captured by a silicon atom, the atom is transformed into a solitary acceptor center similar to an Al atom. An external electric field influences the formation process of the neutral acceptor center (A.C.). It is shown in this article that the behaviour of the muon polarization vector changes appreciably in electric fields with intensities E\,\gtrsim\,10 V/cm. We estimate the muon spin relaxation rate \varLambda_μ in the so‐called “dirty limit”; for example, interaction between an internal electric field from charged impurities and a nonzero dipole moment of the A.C. is taken into account. A phonon mechanism is proposed to explain the temperature dependence of \varLambda_μ. We also estimate the value of the paramagnetic shift of the muon spin precession frequency \delta\omega/\omega₀ which is also temperature dependent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Optical polarizabilities of large molecules measured in near-field interferometry

We discuss a novel application of matter wave interferometry to characterize the scalar optical polarizability of molecules at 532 nm. The interferometer presented here consists of two material absorptive gratings and one central optical phase grating. The interaction of the molecules with the standing light wave is determined by the optical dipole force and is therefore directly dependent on the molecular polarizability at the wavelength of the diffracting laser light. By comparing the observed matter-wave interference contrast with a theoretical model for several intensities of the standing light wave and molecular velocities, we can infer the polarizability in this first proof-of-principle experiment for the fullerenes C₆₀ and C₇₀, and we find a good agreement with literature values. PACS 03.75.Dg; 03.65.-w; 33.15.Kr     

Plasmonic modes in periodic metal nanoparticle chains: a direct dynamic eigenmode analysis

We demonstrate an efficient eigendecomposition method for analyzing the guided modes in metal nanoparticle chains. The proposed method has the advantage of simultaneously showing the dispersion relation and the mode quality. It can also separate the material properties from the geometrical properties. Its efficiency therefore does not depend on the complexity of the material polarizability. We used the method to analyze the guided modes of a single and a pair of metal nanoparticle chains. The rigorous dynamic dipole polarizability typically gives a redshift compared with the results obtained from the broadly used quasi-static dipole polarizability with radiation correction.