Gold cluster carbonyls: vibrational spectroscopy of the anions and the effects of cluster size, charge, and coverage on the CO stretching frequency

We report the vibrational spectra of the carbonyl complexes of anionic gold clusters in the range of the CO stretching frequency as measured in the gas phase using IR multiple photon dissociation spectroscopy. The investigated complexes contain between 3 and 14 Au atoms and up to 7 CO ligands. Special attention is given to the complexes that exhibit saturation CO coverage as well as to the monocarbonyl species. In conjunction with data from the corresponding cationic complexes we quantify how the CO stretching frequency varies with the charge state of the gold cluster. Our results provide a size- and charge-dependent basis to interpret values of the CO stretching frequency measured for CO on deposited gold clusters in terms of the charge states of the clusters.     

Fluorescence lifetime enhancement of organic chromophores attached to gold nanoparticles

We present for the first time experimental evidence of fluorescence lifetime enhancement of organic chromophores attached to metal nanospheres via radiative decay engineering. The hybrid system (HS) was a modified "diconjugated" molecular probe, 4-acetamido-4'-maleimidylstilbene-2,2'-dithiol (AMDT), covalently bound to the surface of 5-nm-diameter Au nanospheres by its two sulfur atoms, at a distance d < 1 nm and with its molecular axis parallel to the surface of the nanoparticle surface. We measured a fluorescence lifetime increase of a factor of 2 at room temperature (tau(AMDT) = (4.32 +/- 0.10) ns and tau(HS) = (8.73 +/- 0.23) ns) and a factor of 3.4 at 4.2 K (tau(AMDT) = (2.64 +/- 0.07) ns and tau(HS) = (7.96 +/- 0.14) ns). We also found that the fluorescence quantum yield of this hybrid system is not reduced, proof of a weak energy transfer between the molecular probe and the nanoparticle. These results demonstrate that a molecular dipole oriented parallel to the metal surface tends to be reduced by the coupling with its image.     

Hydrogen burning of 17O in classical novae

We report on the observation of a previously unknown resonance at E(lab)(R)=194.1+/-0.6 keV in the 17O(p,alpha)14N reaction, with a measured resonance strength omegagamma(palpha)=1.6 +/- 0.2 meV. We studied in the same experiment the 17O(p,gamma)18F reaction by an activation method and the resonance-strength ratio was found to be omegagamma(palpha)/omegagamma(pgamma) = 470 +/- 50. The corresponding excitation energy in the 18F compound nucleus was determined to be 5789.8 +/- 0.3 keV by gamma-ray measurements using the 14N(alpha, gamma)18F reaction. These new resonance properties have important consequences for 17O nucleosynthesis and gamma-ray astronomy of classical novae.     

Deroughening of domain wall pairs by dipolar repulsion

As a magnetic domain wall propagates under small fields through a random potential, it roughens as a result of weak collective pinning, known as creep. Using Kerr microscopy, we report experimental evidence of a surprising deroughening of wall pairs in the creep regime, in a 0.5 nm thick Co layer with perpendicular anisotropy. A bound state is found in cases where two rough domains nucleated far away from one another and first growing under the action of a magnetic field eventually do not merge. The two domains remain separated by a strip of unreversed magnetization, characterized by flat edges and stabilized by dipolar fields. A creep theory that includes dipolar interactions between domains successfully accounts for (i) the domain wall deroughening as the width of the strip decreases and (ii) the quasistatic and dynamic field dependence of the strip width s.     

High harmonic XUV spectral phase interferometry for direct electric-field reconstruction

We demonstrate the first experimental complete temporal characterization of high-harmonic XUV pulses by spectral phase interferometry, with an all-optical setup. This method allows us to perform single-shot measurements of the harmonic temporal profile and phase, revealing a remarkable shot-to-shot stability. We characterize harmonics generated in argon by a 50 fs 800 nm laser pulse. The 11th harmonic is found to be 22 fs long with a negative chirp rate of -4.8 x 10(27) s(-2). This duration can be reduced to 13 fs by modulating the polarization of the generating laser. The technique is easy to implement and could be routinely used in femtosecond XUV pump-probe experiments with harmonics.     

Theory of mesoscopic magnetism in photonic crystals

We provide a rigorous theoretical basis for the artificial magnetic activity of metamaterials near resonances. Our approach is a renormalization-based scheme that authorizes a completely general theory. The major result is an explicit expression of the effective permeability, in terms of resonant frequencies. The theoretical results are checked numerically, and we give applications of our theory to left-handed media and to the solution of the Pokrovski-Efros paradox.     

Evidence for high-m secondary islands induced by large low-m islands in a tokamak plasma

Small-scale structures with high poloidal mode numbers (m=10-20) have been observed in the TEXTOR tokamak plasma with pulsed radar reflectometry and an electron cyclotron emission diagnostic, in conjunction with large 2/1 and 1/1 islands. The small islands have a peaked density profile, similar to that of the simultaneously observed large-scale 2/1 islands. This together with the observation that high-frequency density and temperature fluctuations are very pronounced near the X points of the large islands hints to a strongly perturbed magnetic topology around the X points.     

Closed hypersurfaces of S4(1) with constant mean curvature and zero Gauß–Kronecker curvature

We consider a closed hypersurface $M^3?{\mathbb{S}}^4(1)$ with identically zero Gauß–Kronecker curvature. We prove that if $M^3$ has constant mean curvature H, then $M^3$ is minimal, i.e., $H=0$. This result extends Ramanathan's classification (Math. Z. 205 (1990) 645–658) result of closed minimal hypersurfaces of ${\mathbb{S}}^4(1)$ with vanishing Gauß–Kronecker curvature. To cite this article: T. Lusala, A. Gomes de Oliveira, C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

Teleportation of electronic many-qubit states encoded in the electron spin of quantum dots via single photons

We propose a teleportation scheme that relies only on single-photon measurements and Faraday rotation, for teleportation of many-qubit entangled states stored in the electron spins of a quantum dot system. The interaction between a photon and the two electron spins, via Faraday rotation in microcavities, establishes Greenberger-Horne-Zeilinger entanglement in the spin-photon-spin system. The appropriate single-qubit measurements, and the communication of two classical bits, produce teleportation. This scheme provides the essential link between spintronic and photonic quantum information devices by permitting quantum information to be exchanged between them.