A characteristic property of the 1/f-noise is its apparent unboundedness. A way out of contradiction with finiteness of the total noise power is to admit frequency-odd contributions to the noise spectral density. This option is realized by quantum fluctuations of the electromagnetic field produced by elementary charge carriers. In the present talk, the main steps of the derivation of 1/f spectrum will be described first, followed by some applications. Open problems such as deviations of the frequency exponent from unity and the correct choice of observable will be also discussed.

A defining mechanical property of amorphous materials, which are abundant in daily life and nature, is the existence of a yielding threshold. In the case of soft materials, flow occurs only when the applied stress exceeds a threshold value. Understanding the mechanisms of yielding and subsequent flow is important for a variety of rheological applications and designing newer materials. During yielding, the glassy materials often respond via formation of inhomogeneous flow patterns. These transient heterogeneities have a finite lifetime depending upon the magnitude of applied shear. We will discuss the transient dynamics that emerge during this onset of flow for various imposed shear protocols. In particular, using extensive simulations for the case of imposed shear-rates, we will demonstrate the occurrence of a transition towards the formation of a percolating cluster of mobile regions. This occurs for all imposed shear-rates and only at low shear rates, these clusters subsequently evolve into a transient (but long-lived) shear band with a diffusive growth of its width, before steady flow is attained.

In this talk I will consider single particle Standard Model extensions in order to solve the discrepancy between the measured and the predicted value of the anomalous magnetic moment on the muon. After classifying all the scalar, fermionic and vectorial extensions, I will discuss in each case whether the new physics can solve the anomaly or not. I will give particular attention to vectorial extensions, which correspond to non-renormalizable models, and show how calculabitily can be recovered if the massive vectors are the gauge bosons of a broken enlarged gauge symmetry.

Depuis l’observation de l’émission de lumière des nanotubes de carbone (NTC) en 2002 par O’Connell et al., les propriétés optiques de ces nano-objets unidimensionnels ont fait l’objet d’un nombre considérable d’études de recherche reportées dans la littérature. Afin d’optimiser les fonctions optiques pour les réseaux de télécommunications optiques, et d’ouvrir la voie des composants optiques de nouvelle génération à base de NTC, nous étudions les propriétés optiques linéaires et non-linéaires des NTC, comparativement aux hétérostructures à semiconducteurs III-V conventionnelles (puits, fils et boîtes quantiques).
Je présenterai au cours de ce séminaire nos résultats sur les propriétés d’absorption non-linéaire des NTC pour les applications en tant qu’absorbants saturables ultra-rapides, puis nos études sur leur intégration dans un guide d’onde optique qui ont abouti à la 1ère observation de photoluminescence guidée des NTC à 1,55um. Ces études sur les composants optiques passifs à base de NTC, réalisés technologiquement au laboratoire FOTON, sont une étape nécessaire vers la fabrication et la démonstration de composants actifs performants tels que des sources de lumière à base de NTC (type DEL et lasers). Depuis la 1ère observation en 2010 du gain optique qui constituent toujours un challenge international.

Some remarkably universal empirical formulas are used to characterize the slow dynamics of disordered materials and imperfect crystals. Stretched-exponential relaxation is used for time-dependent response, non-classical critical scaling is used for temperature-dependent behavior, and 1/f noise is used for frequency-dependent fluctuations. I will describe a common physical foundation for all of these formulas. The behavior may be attributed to strict adherence to the laws of thermodynamics: energy is conserved using Hill’s subdivision potential for nonlinear terms, entropy is maximized using a local thermal bath, and similar states are treated using the statistics of indistinguishable particles. Alternatively, the mechanism may be interpreted using information theory for reversible fluctuations. I will emphasize how specific models based on these principles yield the empirical formulas, plus deviations from the formulas that often match the measured behavior. 

The insertion of defect operators of various types can change the Hilbert space of a quantum field theory. Surface defects in 4d N=2 theories introduce a class of ”2d-4d” BPS states which the original 4d theory does not possess. For theories of class S spectral networks count 2d-4d BPS states, and through the 2d-4d wall-crossing phenomenon the 4d BPS spectrum can be obtained. In this talk I will give a brief introduction to spectral networks, with an emphasis on their physical interpretation. Some of their applications and extensions will then be illustrated.

Les expériences (e,2e) et (e,3e) constituent un outil privilégié pour étudier la dynamique de la simple et la double ionisation de petits systèmes par impact électronique, et plus généralement pour contribuer à la compréhension du problème de l’interaction à N-corps.
Dans ce travail, nous avons réalisé de telles expériences dans un domaine cinématique resté quasi-inexploré, où le transfert de moment à l’ion résiduel est important, de sorte que l’ion joue un rôle majeur dans le processus d’interaction projectile - cible. Les résultats expérimentaux sont comparés à ceux des modèles théoriques les plus sophistiqués.
Je vous montre les sections efficaces triplement différentielles (SETD) de simple ionisation de He et H2, ce qui a permis de mettre en évidence la présence pour la molécule H2 d’effets d’interférences quantiques de type fentes d’Young.
Nous discutons ensuite des mesures de SETD de Ne et N2, ionisés sur une orbitale externe ou interne. Nos résultats ont permis de montrer l’importance des interactions post-collisionnelles et du rôle joué par le noyau.
La compétition entre différents processus d’ionisation de l’argon sera aussi discutée : d’une part, simple ionisation (e,2e) en couche interne 2p, et d’autre part, double ionisation (e,3e) directe (3p-2) ou indirecte via le processus Auger impliquant la couche 2p. Dans les conditions cinématiques choisies, ces processus peuvent entrer en compétition ou interférer entre eux. L’accent est mis sur leur contribution respective, en particulier pour l'effet Auger. Diverses structures observées dans la distribution angulaire des sections efficaces (e,3e) sont attribuées à différents mécanismes d’ionisation.

Mechanical forces can be utilized to distort the shape of biomolecules, thereby explore their elastic properties. Furthermore, mechanical forces can be used to alter the rate of biochemical transitions, thereby access energetic and kinetic parameters of reactions. We use optical tweezers and scanning probe microscopies to investigate various biomolecular systems ranging from cytoskeletal filaments to nucleic acids and supramolecular complexes. Force-driven unfolding and refolding of the giant muscle protein titin provides a unique insight into how this molecule may be involved in the mechanics and regulation of muscle contractility. Nanomanipulation of methylated DNA allows us to dissect possible epigenetic mechanisms. Finally, the mechanical manipulation of bacteriophages gives a glimpse at the mechanisms of viral capsid architecture and the triggering of viral DNA ejection.

A major obstacle of using graphene for nanoelectronic applications is its significant vulnerability of contamination by adsorbed molecules. Various polymers commonly used for device processing leave residual traces on graphene, leading to doping effects and band structure modifications. We present an experimental study of time dependent ozone treatment on post-process epitaxial graphene using both electron transport measurements and resonant micro-Raman spectroscopy. We focus on a systematic analysis of residual polymer decomposition on the epitaxial graphene on SiC substrate. It was found that graphene could be effectively cleaned by ultraviolet (UV)/ozone treatment after nanofabrication from residual lithographic polymers. This procedure improves the charge carrier mobility, almost by a factor of two for strongly contaminated samples, decreases the doping level and does not introduce defect inside the graphene lattice. It was found that epitaxial SiC graphene is extremely stable when exposed to radical oxygen atoms. We ascribe this effect to the substrate topography, which significantly affects the graphene stability under UV/ozone treatment. Our calculations reveal that surface roughness of the SiC substrate can change the energy gain from epoxy group adsorption by a few tenths of electron volts.

Référence : V.S. Prudkovskiy, K.P. Katin, et al., Carbon, 109, 221 (2016) http://dx.doi.org/10.1016/j.carbon.2016.08.013