Static electric dipole polarizabilities of Na clusters

The static electric dipole polarizability of Na _N clusters with even N has been calculated in a collective, axially averaged and a three-dimensional, finite-field approach for , including the ionic structure of the clusters. The validity of a collective model for the static response of small systems is demonstrated. Our density functional calculations verify the trends and fine structure seen in a recent experiment. A pseudopotential that reproduces the experimental bulk bond length and atomic energy levels leads to a substantial increase in the calculated polarizabilities, in better agreement with experiment. We relate remaining differences in the magnitude of the theoretical and experimental polarizabilities to the finite temperature present in the experiments. Received 8 November 1999     

Electric dipole moments and conformations of isolated peptides

The electric dipole moments of the isolated amino acid tryptophan and small glycine-based peptides (WG_n, n = 1-5, W = tryptophan, G = glycine) have been measured by deflection of a molecular beam in an inhomogeneous electric field. The measurements are compared to the results of ab initio calculations and Monte-Carlo simulations. The conformation and the flexibility of the peptides, at different temperatures, are discussed. The WG_n peptides are much more floppy than an isolated tryptophan, even a single glycine is enough to make the peptide floppy on the timescale of the electric deflection measurements. Received 4 January 2002 Published online 13 September 2002     

Ab initio calculations of the second dynamic hyperpolarizability of LiH by means of Floquet theory approach

Floquet theory is used to describe the response of a molecule to applied radiation electric field. The method of ab initio calculation of frequency dependent (hyper)polarizabilities based on combination of perturbation theory with the finite field method has been developed. Electron correlation is taken into account by means of the CIPSI algorithm. The total wave function expansion involves spectral, pseudo-spectral states and polynomial terms. The developed approach is applied to the calculation of the second hyperpolarizability of the lithium hydride molecule subjected to the superposition of harmonic and static electric fields. The method can be used to calculate the higher order nonlinear properties of molecules. Received 23 November 2000 and Received in final form 25 March 2001     

Percolation with constraints in the highly polarizable oxide KTaO<Subscript>3</Subscript>:Li

Experimental data on the temperature and electric field dependence of the Second Harmonic Generation Intensity in the solid solution KTaO₃:Li is analyzed in the framework of a new percolation-type approach which considers the history of cluster formation averaged over a large number of samples. In order to take into account that two cluster dipole moments turn when joining clusters together, a constraint is imposed on the cluster growth. This constraint leads to cluster-size saturation just after the percolation threshold. Owing to this circumstance, the connected cluster coexists with free clusters in some range of the impurity concentration and temperature. There is qualitative agreement between the computational results and experiments on Second Harmonic Generation intensities. The algorithm was written in C++ which allowed realistic computations to be performed on a standard PC. Received 26 August 1999 and Received in final form 27 December 1999     

Functional renormalization description of the roughening transition

We reconsider the problem of the static thermal roughening of an elastic manifold at the critical dimension d=2 in a periodic potential, using a perturbative Functional Renormalization Group approach. Our aim is to describe the effective potential seen by the manifold below the roughening temperature on large length scales. We obtain analytically a flow equation for the potential and surface tension of the manifold, valid for low temperatures. On a length scale L, the renormalized potential is made up of a succession of quasi parabolic wells, matching onto one another in a singular region of width for large L. For strong periodic potential, the perturbation theory breaks down, and we argue, based on a variational calculation, that the transition becomes first order. We also obtain numerically the step energy as a function of temperature, and relate our results to the existing experimental data on ⁴He. Finally, we examine the case of a non local elasticity which is realized physically for the contact line. Received 16 April 1999 and Received in final form 11 October 1999     

Phase transitions in generalized chiral or Stiefel's models

We study the phase transition in generalized chiral or Stiefel's models using Monte Carlo simulations. These models are characterized by a breakdown of symmetry O(N)/O(N-P). We show that the phase transition is clearly first order for when P=N and P=N-1, contrary to predictions based on the renormalization group in expansion but in agreement with a recent non perturbative renormalization group approach. Received 7 October 1999     

Kosterlitz-Thouless vs. Ginzburg-Landau description of 2D superconducting fluctuations

We evaluate the charge and spin susceptibilities of the 2D attractive Hubbard model and we compare our results with Monte Carlo simulations on the same model. We discuss the possibility to include topological Kosterlitz-Thouless superconducting fluctuations in a standard perturbative approach substituting in the fluctuation propagator the Ginzburg-Landau correlation length with the Kosterlitz-Thouless correlation length. Received 30 June 1999     

Nuclear spin conversion in CH F induced by an alternating electric field

The nuclear spin conversion in CH₃F molecules subjected to an alternating electric field was investigated experimentally. The conversion rate was found to be almost unaffected by low electric fields ( V/cm) but sharply increased tenfold when the electric field amplitude exceeds the values ( V/cm) sufficiently high to produce crossings of the ortho and para states of the molecule. A theoretical model for the molecular conversion in alternating electric field was developed. The results of the experiment were found to be in a good agreement with the theory. Received 23 July 1999 and Received in final form 7 September 1999     

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     

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.     

Classical study of the rovibrational dynamics of a polar diatomic molecule in static electric fields

We study the classical dynamics of a polar diatomic molecule in the presence of a strong static homogeneous electric field. Our full rovibrational investigation includes the interaction with the field due to the permanent electric dipole moment and the polarizability of the molecule. Using the LiCs molecule as a prototype, we explore the stability of the equilibrium points and their bifurcations as the field strength is increased. The phase space structure and its dependence on the energy and field strength are analyzed in detail. We demonstrate that depending on the field strength and on the energy, the phase space is characterized either by regular features or by small stochastic layers of chaotic motion.     

Statics and dynamics of a single ferrofluid-peak

We consider a single peak of a ferrofluid resulting from the Rosensweig instability for a small fluid container. Minimizing the total energy of the system by a variational method we determine the shape of the peak in a static field as well as the characteristics of the subcritical bifurcation leading to its formation. The latter are in very good agreement with experiment. Generalizing the approach to dynamic situations we qualitatively reproduce the complicated subharmonic response of the peak to an oscillating part in the external magnetic field found in recent experiments. Received 14 December 1999 and Received in final form 31 May 2000     

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     

Transport properties of high temperature air in local thermodynamic equilibrium

In the paper new calculated transport coefficients of air in the temperature range 50-100 000 K are presented. The results have been obtained by means of the perturbative Chapman-Enskog method, assuming that the plasma is in local thermodynamic equilibrium (LTE). The calculations include viscosity, thermal conductivity, electric conductivity and multicomponent diffusion coefficients. For the calculation, a recent compilation of collision integrals obtained by Capitelli et al. [1] has been utilized. Analytical expression for all transport coefficients and thermodynamic parameters of the air plasma are also reported. Received 17 November 1999     

Electrodynamic trap for neutral atoms

An electrodynamic trap is proposed that stores cold neutral atoms or nonpolar molecules in their ground state as well as in excited states by means of the quadratic Stark effect. The trap uses an oscillating hexapole field and a superposed static homogeneous field. The dynamics of an atom in this trap can be described as a harmonic oscillation in a static pseudopotential. Stability criteria and sample parameters for a number of atomic species are given. Received: 7 August 1998 / Received in final form: 7 January 1999     

Diamagnetic interactions in disordered suspensions of metastable superconducting granules

The simulation of the transition sequence of superheated Type I superconducting granules (SSG) in disordered suspensions when an external magnetic field is slowly increased from zero has been studied. Simulation takes into account diamagnetic interactions and the presence of surface defects. Results have been obtained for the transition sequence and surface fields distribution covering a wide range of densities. These results are compared with previous analytical perturbative theory, which provides qualitative information on transitions and surface magnetic fields during transitions, but with a range of validity apparently limited to extremely dilute samples. Simulations taking into account the complete diamagnetic interactions between spheres appear to be a promising tool in interpreting SSG experiments, in applications such as particle detectors, and in some fundamental calculations of Solid State Physics. Received 6 April 2001 and Received in final form 15 October 2001     

The Bethe lattice spin glass revisited

So far the problem of a spin glass on a Bethe lattice has been solved only at the replica symmetric level, which is wrong in the spin glass phase. Because of some technical difficulties, attempts at deriving a replica symmetry breaking solution have been confined to some perturbative regimes, high connectivity lattices or temperature close to the critical temperature. Using the cavity method, we propose a general non perturbative solution of the Bethe lattice spin glass problem at a level of approximation which is equivalent to a one step replica symmetry breaking solution. The results compare well with numerical simulations. The method can be used for many finite connectivity problems appearing in combinatorial optimization. Received 27 September 2000     

All-dielectric left-handed metamaterial based on dielectric resonator: design, simulation and experiment

Dipoles with Lorentz-type resonant electromagnetic responses can realise negative effective parameters in their negative resonant region. The electric dipole and magnetic dipole can realise, respectively, negative permittivity and negative permeability, so both the field distribution forms of electric and magnetic dipoles are fundamentals in designing left-handed metamaterial. Based on this principle, this paper studies the field distribution in high-permittivity dielectric materials. The field distributions at different resonant modes are analysed based on the dielectric resonator theory. The origination and influence factors of the electric and magnetic dipoles are confirmed. Numerical simulations indicate that by combining dielectric cubes with different sizes, the electric resonance frequency and magnetic resonance frequency can be superposed. Finally, experiments are carried out to verify the feasibility of all-dielectric left-handed metamaterial composed by this means.     

Large parity violating effects in atomic dysprosium with nearly degenerate Floquet eigenvalues

In this article we study effects of parity nonconservation in atomic dysprosium, where one has a pair of nearly degenerate levels of opposite parity. We consider the time evolution of this two-level system within oscillatory electric and magnetic fields. These are chosen to have a periodical structure with the same period, such that a Floquet matrix describes the time evolution of the quantum states. We show that, if the states are unstable, the eigenvalues of the Floquet matrix may have contributions proportional to the square root of the parity violating interaction matrix element while they are almost degenerate in their parity even part. This leads to beat frequencies proportional to which are expected to be larger by several orders of magnitude compared to ordinary P-violating contributions which are of order . However, for the simple field configurations we considered, it still seems to be difficult to observe these P-violating beat effects, since the states decay too fast. On the other hand, we found that, within only a few Floquet cycles, very large parity violating asymmetries with respect to experimental setups of opposite chirality may be obtained. The electric and magnetic fields as well as the time intervals necessary for this are in an experimentally accessible range. For statistically significant effects beyond one standard deviation a number of about 10⁷ atoms is required. Our ideas may be applied directly to other 2-level atomic systems and different field configurations. We hope that these ideas will stimulate experimental work in this direction. Received 16 September 1999 and Received in final form 10 March 2000     

Multiscaling and localized instabilities in fracture, fragmentation, and growth processes

It is shown that localized instabilities can be an origin of log-normal and power-law statistical distributions in fracture, fragmentation and island growth processes. Results of laboratory experiments and numerical simulations performed by different authors are used to demonstrate the applicability of this approach. Received 2 September 1999