Search

In this work we investigate the properties of elastic waves propagating in gyroid lattices. First, we rigorously characterize the lattice from the point of view of crystallography. Second, we use Bloch&ndash, Floquet analysis to compute the dispersion relations for elastic waves. The results for very long wavelengths are then compared to those given by classic elasticity for a cubic material. A discrepancy is found in terms of the polarization of waves and it is related to the noncentrosymmetry of the gyroid. The gyroid lattice results to be acoustically active, meaning that transverse waves exhibit a circular polarization when they propagate along an axis of rotational symmetry. This phenomenon is present even for very long wavelengths and is not captured by classic elasticity.

International audience; Self-sustained all-optical poling second-harmonic generation (SHG) experiments are conducted in single-core and multicore dye-doped poly(methyl methacrylate) optical fibers. By tuning the polarization of the fundamental beam, the SHG signal is degraded and is reconstructed spontaneously up to its initial level. We found a new situation in which the photo-induced self-organization of azo polymers creates a well-ordered periodic structure.

International audience; The noncentrosymmetric p-carboxybenzenesulfonate anion afforded, in electro-oxidation experiments with bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), the low-gap semiconductor (room-temperature conductivity: 18 S cm–1) mixed-valency salt BEDT-TTF2[O3S-C6H4-CO2H], which is noncentrosymmetric due to head-to-tail arrangement of the anions, whereas EDT-TTF-CONHMe (EDT-TTF = ethylenedithiotetrathiafulvalene) afforded the fully oxidized centrosymmetric salt [EDT-TTF-CONHMe+][HO2C-C6H4-SO3–] in which the driving force for the crystal packing is the existence of strong hydrogen-bonding interactions between the anions and the amido groups of the cations.