Surface plasmon polaritons and surface phonon polaritons on metallic and semiconducting spheres: Exact and semiclassical descriptions

We study the interaction of an electromagnetic field with a non-absorbing or absorbing dispersive sphere in the framework of complex angular momentum techniques. We assume that the dielectric function of the sphere presents a Drude-like behavior or an ionic crystal behavior modelling metallic and semiconducting materials. We more particularly emphasize and interpret the modifications induced in the resonance spectrum by absorption. We prove that "resonant surface polariton modes" are generated by a unique surface wave, i.e., a surface (plasmon or phonon) polariton, propagating close to the sphere surface. This surface polariton corresponds to a particular Regge pole of the electric part (TM) of the S matrix of the sphere. From the associated Regge trajectory we can construct semiclassically the spectrum of the complex frequencies of the resonant surface polariton modes which can be considered as Breit-Wigner-type resonances. Furthermore, by taking into account the Stokes phenomenon, we derive an asymptotic expression for the position in the complex angular momentum plane of the surface polariton Regge pole. We then describe semiclassically the surface polariton and provide analytical expressions for its dispersion relation and its damping in the non-absorbing and absorbing cases. In these analytic expressions, we more particularly exhibit well-isolated terms directly linked to absorption. Finally, we explain why the photon-sphere system can be considered as an artificial atom (a ``plasmonic atom" or "phononic atom") and we briefly discuss the implication of our results in the context of the Casimir effect.Comment: v2: Typos corrected; v3: Paper extended to absorbing media, references added and title change

Weyl formulas for annular ray-splitting billiards

We consider the distribution of eigenvalues for the wave equation in annular (electromagnetic or acoustic) ray-splitting billiards. These systems are interesting in that the derivation of the associated smoothed spectral counting function can be considered as a canonical problem. This is achieved by extending a formalism developed by Berry and Howls for ordinary (without ray-splitting) billiards. Our results are confirmed by numerical computations and permit us to infer a set of rules useful in order to obtain Weyl formulas for more general ray-splitting billiards

The decay law can have an irregular character

Within a well-known decay model describing a particle confined initially within a spherical $\delta$ potential shell, we consider the situation when the undecayed state has an unusual energy distribution decaying slowly as $k\to\infty$; the simplest example corresponds to a wave function constant within the shell. We show that the non-decay probability as a function of time behaves then in a highly irregular, most likely fractal way.Comment: 4 pages, 3 eps figure

Resonant Magnetic Vortices

By using the complex angular momentum method, we provide a semiclassical analysis of electron scattering by a magnetic vortex of Aharonov-Bohm-type. Regge poles of the $S$-matrix are associated with surface waves orbiting around the vortex and supported by a magnetic field discontinuity. Rapid variations of sharp characteristic shapes can be observed on scattering cross sections. They correspond to quasibound states which are Breit-Wigner-type resonances associated with surface waves and which can be considered as quantum analogues of acoustic whispering-gallery modes. Such a resonant magnetic vortex could provide a new kind of artificial atom while the semiclassical approach developed here could be profitably extended in various areas of the physics of vortices.Comment: 6 pages, 7 figure

Magnetic Screening of NbN Multilayers Samples

6 pagesInternational audienceIn 2006 Gurevich proposed to use nanoscale layers of superconducting materials with high values of Hc > Hc^Nb for magnetic shielding of bulk niobium to increase the breakdown magnetic field inside SC RF cavities [1]. We have deposited high quality "model" samples by magnetron sputtering on monocrystalline sapphire substrates. A 250 nm layer of niobium figures the bulk Nb. It was coated with a single and multi-stacks of NbN layers (25 or12 nm) separated by 15 nm MgO barriers, and characterized by X-Ray reflectivity and DC transport measurements. DC or AC measurement of HC1 is an important goal for multilayer evaluation during the sample evaluation phase. A clear increase of HC1 at low frequency is promising indication since HC1 is expected to increase with frequency (see e.g. [2] and references therein). We have measured the first penetration field (HP~HC1) on DC magnetization curves in a SQUID system. HP of NbN covered sample is increased compared to Nb alone. We have also developed a set-up that allows measuring a large range of field and temperature with a local probe method based on 3rd harmonic analysis. We have confirmed the screening behavior of a single 25 nm NbN layer placed on the top of a Nb Layer

Characterization of superconducting multilayers samples

Best RF bulk niobium accelerating cavities have nearly reached their ultimate limits at rf equatorial magnetic field H 200 mT close to the thermodynamic critical field Hc. In 2006 Gurevich proposed to use nanoscale layers of superconducting materials with high values of Hc > HcNb for magnetic shielding of bulk niobium to increase the breakdown magnetic field inside SC RF cavities [1]. Depositing good quality layers inside a whole cavity is rather difficult but we have sputtered high quality samples by applying the technique used for the preparation of superconducting electronics circuits and characterized these samples by X-ray reflectivity, dc resistivity (PPMS) and dc magnetization (SQUID). Dc magnetization curves of a 250 nm thick Nb film have been measured, with and without a magnetron sputtered coating of a single or multiple stack of 15 nm MgO and 25 nm NbN layers. The Nb samples with/without the coating clearly exhibit different behaviors. Because SQUID measurements are influenced by edge and shape effects we propose to develop a specific local magnetic measurement of HC1 based on ac third harmonic analysis in order to reveal the screening effect of multilayers

Concentration and purification by magnetic separation of the erythrocytic stages of all human Plasmodium species

International audienceBackground : Parasite concentration methods facilitate molecular, biochemical and immunologicalresearch on the erythrocytic stages of Plasmodium. In this paper, an adaptation of magnetic MACS®columns for the purification of human Plasmodium species is presented. This method was useful forthe concentration/purification of either schizonts or gametocytes.Results and conclusions : The magnetic removal of non-parasitized red blood cells (in vivo andin vitro) using magnetic columns (MACS) was evaluated. This easy-to-use technique enrichedschizonts and gametocytes from Plasmodium falciparum in vitro cultures with a very high degree ofpurity. In addition, all haemozoin-containing stages (schizonts and/or gametocytes) from theperipheral blood of infected patients could be concentrated using this method. This method isparticularly useful for the concentration of non-falciparum species, which do not grow in cultureand are otherwise difficult to obtain in large amounts

Science with the space-based interferometer LISA. V Extreme mass-ratio inspirals

The space-based Laser Interferometer Space Antenna (LISA) will be able to observe the gravitational-wave signals from systems comprised of a massive black hole and a stellar-mass compact object. These systems are known as extreme-mass-ratio inspirals (EMRIs) and are expected to complete $\sim 10^4$-$10^5$ cycles in band, thus allowing exquisite measurements of their parameters. In this work, we attempt to quantify the astrophysical uncertainties affecting the predictions for the number of EMRIs detectable by LISA, and find that competing astrophysical assumptions produce a variance of about three orders of magnitude in the expected intrinsic EMRI rate. However, we find that irrespective of the astrophysical model, at least a few EMRIs per year should be detectable by the LISA mission, with up to a few thousands per year under the most optimistic astrophysical assumptions. We also investigate the precision with which LISA will be able to extract the parameters of these sources. We find that typical fractional statistical errors with which the intrinsic parameters (redshifted masses, massive black hole spin and orbital eccentricity) can be recovered are $\sim 10^{-6}$-$10^{-4}$. Luminosity distance (which is required to infer true masses) is inferred to about $10\%$ precision and sky position is localized to a few square degrees, while tests of the multipolar structure of the Kerr metric can be performed to percent-level precision or better.Comment: 13 figures, 22 pages; updated to match published versio

Orbital Magnetism in the Ballistic Regime: Geometrical Effects

We present a general semiclassical theory of the orbital magnetic response of noninteracting electrons confined in two-dimensional potentials. We calculate the magnetic susceptibility of singly-connected and the persistent currents of multiply-connected geometries. We concentrate on the geometric effects by studying confinement by perfect (disorder free) potentials stressing the importance of the underlying classical dynamics. We demonstrate that in a constrained geometry the standard Landau diamagnetic response is always present, but is dominated by finite-size corrections of a quasi-random sign which may be orders of magnitude larger. These corrections are very sensitive to the nature of the classical dynamics. Systems which are integrable at zero magnetic field exhibit larger magnetic response than those which are chaotic. This difference arises from the large oscillations of the density of states in integrable systems due to the existence of families of periodic orbits. The connection between quantum and classical behavior naturally arises from the use of semiclassical expansions. This key tool becomes particularly simple and insightful at finite temperature, where only short classical trajectories need to be kept in the expansion. In addition to the general theory for integrable systems, we analyze in detail a few typical examples of experimental relevance: circles, rings and square billiards. In the latter, extensive numerical calculations are used as a check for the success of the semiclassical analysis. We study the weak-field regime where classical trajectories remain essentially unaffected, the intermediate field regime where we identify new oscillations characteristic for ballistic mesoscopic structures, and the high-field regime where the typical de Haas-van Alphen oscillations exhibit finite-size corrections. We address the comparison with experimental data obtained in high-mobility semiconductor microstructures discussing the differences between individual and ensemble measurements, and the applicability of the present model.Comment: 88 pages, 15 Postscript figures, 3 further figures upon request, to appear in Physics Reports 199