We report on the first tunable resonant Raman scattering study performed on suspended isolated and coupled single-wall carbon nanotubes, unambiguously identified by electron diffraction. Besides the confirmation of the relation between the structural properties, the radial breathing frequency and the optical resonances for isolated metallic nanotubes, we evidence that interacting nanotubes experience drastic modifications of their resonance fingerprints. We first demonstrate a degeneracy lifting of an electronic level in a bundle of identical zigzag nanotubes. We then show the existence of a strong energy transfer mediated by a mechanical coupling between two nonidentical bundled nanotubes.

When a rotating rod is brought into a polymer melt or concentrated polymer solution, the meniscus climbs the rod. This spectacular rod climbing is due to the normal stresses present in the polymer fluid and is thus a purely non-Newtonian effect. A similar rod climbing of an interface between two fluids has therefore been taken as a signature that one of the fluids exhibits normal stress effects. We show here, however, that the effect can occur with simple Newtonian fluids: it occurs when a Taylor-Couette instability happens in the less viscous of the two liquids but not in the more viscous one.

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We study the evolution of the surface-plasmon resonances of individual ion-beam-shaped prolate gold nanoparticles embedded in a dielectric SiO 2 environment by electron-energy-loss spectroscopy mapping in a scanning transmission electron microscope. The controlled symmetric dielectric environment obtained through the ion-beam-shaping method allows a direct quantitative comparison with numerical results obtained through simulations (auxiliary differential-equation finite-difference time-domain and boundary-element method) and with theoretical results obtained through analytical models (quasistatic model for prolate nanoellipsoids and waveguide model for infinite one-dimensional plasmonic waveguides), with which our experimental results are in very good agreement. We confirm the accuracy of state-of-the-art numerical tools and analytical theories that establish ion-beam shaping as a very promising method to design metal-dielectric nanocomposites with well-predicted optical properties, and with many possible applications in surfaceenhanced Raman spectroscopy and second-harmonic generation, as well as in conventional applications of metamaterials like negative refraction, superimaging, and invisibility cloaking.

We have altered the superconductivity of a suspended rope of single walled carbon nanotubes, by coating it with organic polymers. Upon coating, the normal state resistance of the rope changes by less than 20 percent. But superconductivity, which on the bare rope shows up as a substantial resistance decrease below 300 mK, is gradualy suppressed. We correlate this to the suppression of radial breathing modes, measured with Raman Spectroscopy on suspended Single and Doublewalled carbon nanotubes. This points to the breathing phonon modes as being responsible for superconductivity in carbon nanotubes. PACS numbers:Carbon nanotubes have been heralded as model systems to explore one dimensionnal (1D) conductors, in which electron-electron interactions lead to a non conventional ground state, the Luttinger liquid [1]. In particular, the single particle density of states is depressed at low energy, with a power law whose exponent depends on the interaction strength. The experimental observation of the power law suppression of the tunnel conductance at low energy was therefore interpreted as a proof of this ground state and of the strength of repulsive electron electron interactions in Single Walled Carbon Nanotubes (SWNT). The discovery of superconductivity in suspended individual ropes of SWNT therefore came as a big surprise [2,3]. As for the case of metallofullerene molecules [6], the question of which phonon modes give rise to the attractive interaction leading to superconductivity is still unsettled. Whereas Sédéki et al.[10] and Gonzalez [11,12] consider the coupling to optical phonon modes, De Martino and Egger [13,14] conjecture that attractive interactions can be mediated by low energy phonon modes, and specifically the radial breathing modes (RBM), which are the compression and dilatation modes of carbon nanotubes. They find that the attractive interaction may be strong enough to overcome the repulsive interactions in SWNT, especially in ropes of SWNT where the Coulomb interaction can be screened because the SWNT are packed so closely together. Their theory [14] also could reproduce the temperature dependence of the superconducting transition observed in ropes.To experimentally test the role played by the phonon modes on superconductivity, we have gradually coated a suspended rope of SWNT with organic material. We show that superconductivity is gradually destroyed. Parallel Raman experiments show that the radial breathing modes are affected by coating, thereby hinting to these modes as playing a major role in the superconductivity of carbon nanotubes. The experiments described hereafter also help define the criteria required to observe a superconducting transition in carbon naotubes.The sample whose superconductivity we have altered is a rope containing roughly 40 SWNT, as determined from its diameter (10 nm) measured in a Transmission Electron Microscope. This rope is produced by the arc discharge method followed by purification [15,16]. The rope is suspended across a 1 µm wide slit etched in a suspended sili...

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International audienc

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