At : Campus Jussieu, 4 pl. Jussieu, Paris 5è, Amphi 55A , on 14:00

The dynamical behavior of disk-like microparticles being transported and deformed by fluid flows is of crucial importance in various technological fields such as flow de-contamination, but more remarkably for the understanding of biological transport phenomena, such as Red Blood Cell transport, drug delivery systems or non-invasive diagnosis procedures. In this thesis, we systematically study the behavior of disk-like particles of different shapes and properties under different complex flow geometries. In order to do that, we make use of advanced microfluidic techniques for microparticle synthesis and microchannel fabrication. Our particles are made of polymerized polyethylene glycol diacrylate (PEGDA) and they are synthesized in the lab by means of a photolithography technique. On the one hand, we study the dynamics of rigid microdisks of different diameters as they are transported in a microchannel with hyperbolic geometry. Such a geometry produces regions of elongational and shear flow inside the channel, which give rise to interesting dynamics for the orientations of the particles. We build our study on top of that developed by Jeffery for ellipsoidal particles under simple shear flows. Jeffery developed the equations of motion describing the orientation of the particles, today known as Jeffery orbits. We complement our experimental observations of the same phenomenon with numerical simulations. On the other hand, we study the dynamics of microrings of fixed diameter and different thicknesses as they are flowing through a bifurcating microchannel. We are particularly interested in the events taking place at the bifurcation or apex, the passage time of the rings through this region, and how the particles’ parameters, such as their flexibility, and the geometry’s parameters, such as the opening angle of the bifurcation, will affect the dynamics of the particles. In all cases we make use of optimized observation techniques and flow control systems in order to carry out well- controlled experiments. The findings of this work contribute to the advance of the field of fluid-structure interactions in microfluidic environments and microparticle transport, and in particular they bring us towards a better understanding of the behavior of Red Blood Cells and other disk-like microparticles under complex flows.

At : Amphitéâtre Blandin, Laboratoire de Physique des Solides 1 rue Nicolas Appert, Bât. 510 91405 Orsay Cedex , on 14:00

La frustration magnétique est la propriété exhibée par certains matériaux lorsque les interactions magnétiques ne sont pas toutes minimisées: il en résulte une dégénérescence de l’état fondamental, pouvant mener à des propriétés exotiques de la matière, telles que les liquides de spin quantiques. Durant cette thèse, pour étudier ces propriétés, nous avons utilisé des méthodes de spectroscopie, notamment la diffusion des neutrons polarisés et non polarisés. La diffusion des neutrons est une sonde puissante pour observer les propriétés magnétiques. Contrairement aux rayons X, les neutrons sont porteurs d’un spin 1/2, ce qui les rend sensibles aux interactions magnétiques; il est ainsi possible de sonder spécifiquement les structures et les excitations magnétiques, notamment via la diffusion inélastique des neutrons. Dans la première partie de cette thèse, nous avons étudié le composé supraconducteur de fer BaFe2Se3 au moyen la diffusion inélastique des neutrons en temps de vol, et par des techniques numériques telles que les simulations Monte Carlo et les simulations d’ondes de spin. Dans la seconde partie, nous avons étudié le composé liquide de spin pyrochloreTb2Ti2O7, à partir de la diffusion inélastique des neutrons en temps de vol et en trois axes polarisés, que nous avons couplée à des analyses de symétries et des simulations numériques, afin de reproduire les données expérimentales.

At : Amphi BLANDIN, Laboratoire de Physique des Solides, 1 rue Nicolas Appert, Bât. 510, 91405, Orsay , on 14:00

Les ordinateurs numériques sont construits avec deux types d’éléments, des bits qui interagissent par l’intermédiaire de portes logiques. Les ordinateurs quantiques utilisent des qubits qui sont couplés par des portes quantiques. De même, un neuro-ordinateur nécessite deux éléments matériels : des neurones interconnectés par des synapses. Nous présentons une unité neuro-synaptique à pointes bio-inspirée construite avec des composants électroniques conventionnels. Notre matériel est basé sur un modèle théorique d’un neurone à pointes et de ses courants synaptiques et membranaires. Tous les paramètres du modèle sont réglables et les échelles de temps sont biocompatibles. Le neurone à pointes est entièrement analogique et son excitabilité est implémentée avec un memristor. Les courants synaptiques et membranaires sont à la fois excitateurs et inhibiteurs, avec une intensité réglable et une dynamique bio-mimétique. Nous démontrons diverses primitives neuro-informatiques de base, et comment combiner des motifs de réseau de base pour obtenir des fonctions neuro-informatiques plus complexes. L’unité neuro-synaptique peut être considérée comme la pierre angulaire de la construction de réseaux neuronaux de géométrie arbitraire. Sa conception compacte et simple, ainsi que la grande accessibilité des composants électroniques ordinaires, font de notre méthodologie une plateforme attrayante pour construire des interfaces neuronales pour les appareils médicaux, la robotique et les systèmes d’intelligence artificielle tels que l’informatique de réservoir. Nous discutons également d’autres extensions possibles de notre travail : (i) utiliser le circuit neuro-synaptique comme modèle pour incorporer des memristors d’oxyde qui font l’objet de recherches intensives en science des matériaux ; (ii) porter la conception à l’électronique d’intégration à très grande échelle (VLSI) pour mettre en œuvre des réseaux massifs qui peuvent être moins affectés par le problème d’inadéquation. Notre dispositif est un bloc de construction neuromorphique à usage général qui permet de mettre en œuvre un neuro-ordinateur fonctionnant en temps réel continu avec une mise à l’échelle parfaite. Il pourrait ouvrir la voie à l’exécution de modèles de réseaux neuroscientifiques théoriques, au-delà de ce qui est actuellement possible dans les simulations informatiques numériques, réalisant ainsi la suprématie de la neuro-informatique. Nous fournissons une nomenclature et des dessins de circuits imprimés pour la mise en œuvre du dispositif.

At : Coll , on 14:00

At : Campus Jussieu, 4 pl Jussieu, Paris5é, IMPMC, Salle de Conference , on 14:00

Since its discovery, the origin of the insulating ground state of Ba2IrO4 and Sr2IrO4 has been widely debated. Although the importance of the spin-orbit coupling (SOC) for the metal-insulator transition in these compounds has been universally recognized, yet it seems unclear whether the formation of the insulating gap is driven by the formation of magnetic moments (Slater) or by the Coulomb interaction (Mott). Regardless of the nature of the insulating phase, iridates have been vastly described within the single band jeff=1/2 model, triggering analogies with cuprate superconductors. However, the single-orbital nature of these compounds has been questioned both theoretically and experimentally. Aiming to elucidate these aspects, we study both compounds within the dynamical mean-field theory framework.Concerning Ba2IrO4, we focus on its paramagnetic phase, clarifying the role of SOC and investigating the validity of the single band picture. Then, we simulate antiferromagnetic order and systematically study the competition between Slater and Mott physics. We find that Ba2IrO4 lies in the crossover between the two regimes but with prominent Mott character, thus establishing Ba2IrO4 as a Mott insulator. We finally compare our calculations with angle-resolved photoemission and optical absorption spectra available in literature, providing an alternative explanation for the double peak structure of the optical spectrum.Shifting our focus to Sr2IrO4, we investigate the consequences of electron doping on the electronic structure. Our simulations yield a non-negligible effect on the jeff=3/2 bands upon charge variation, highlighting the multi-orbital nature of this compound.

At : UFR de Physique, amphithéâtre Pierre-Gilles de Gennes, bâtiment Condorcet, 10 rue Alice Domon et Léonie Duquet, 75013 Paris , on 14:30

L’érosion due à la dissolution de roches solubles par des écoulements d’eau est à l’origine, dans la nature, d’une grande diversité de structures géomorphologiques. Parmi celles-ci existent des motifs réguliers, à des échelles typiques allant du millimètre à plusieurs mètres, auxquels cette thèse est particulièrement dédiée. Nous caractérisons d’abord sur le terrain deux de ces motifs, grâce à des reconstructions 3D précises : les karren linéaires -cannelures parallèles creusées dans des dalles calcaires- et les scallops -cavités concaves ornant les parois de grottes. Tous deux ont en commun de présenter des crêtes acérées pouvant être décrites comme des singularités de la surface. Grâce à des modèles numériques décrivant l’évolution non-linéaire de motifs de dissolution, nous interprétons l’émergence de ces singularités comme résultant d’un mécanisme géométrique très général. Ce mécanisme ne permet cependant pas d’expliquer tous les aspects de la morphologie des karren ou des scallops, ni leurs dimensions caractéristiques. Pour cela, il convient de s’intéresser plus précisément aux mécanismes hydrodynamiques susceptibles d’induire l’érosion différentielle à l’origine des motifs, ce que nous faisons, dans la suite de la thèse, dans des cas spécifiques. Nous nous intéressons d’abord expérimentalement au cas où des solides solubles se dissolvent sans écoulement imposé. Nous suspendons pour cela des blocs de sel, de sucre ou de plâtre dans des aquariums remplis d’eau et caractérisons leur évolution. Au contact de surfaces pointant vers le bas, la couche limite de concentration se déstabilise sous l’effet d’une instabilité de Rayleigh-Bénard solutale, entraînant un écoulement de convection. Il engendre l’apparition de motifs dont la forme évoque fortement les scallops observées dans la nature, et est cohérente avec les prédictions du modèle numérique. Nous décrivons aussi le cas plus complexe où le bloc est incliné. L’écoulement moyen a alors une composante le long du bloc, entraînant l’apparition de stries qui, dans certains cas, évoluent pour former un motif tridimensionnel. Motivés par le contexte des grottes, traversées de rivières souterraines, nous modifions ensuite le dispositif expérimental afin de pouvoir étudier la compétition entre convection solutale et convection forcée. Nous plaçons pour cela les blocs solubles dans un canal hydraulique, permettant d’imposer des vitesses allant jusqu’à 50 cm/s. Nous décrivons comment l’écoulement imposé modifie les taux de dissolution, la taille et la morphologie des motifs ; et tentons d’expliquer les observations en modélisant la couche limite de concentration cisaillée. Nous discutons ensuite de l’application potentielle de ces résultats au cadre naturel. Finalement, dans un dernier chapitre largement indépendant du reste, nous décrivons un mécanisme de propulsion engendré par la dissolution. Nous construisons pour cela des petits bateaux en caramel et expliquons comment, une fois placés dans l’eau, ils sont propulsés par l’écoulement de convection solutale résultant de leur dissolution.

At : Amphi Blandin, Bâtiment 510, 1 rue Nicolas Appert, Orsay, 91400 , on 14:00

Two pillars of contemporary condensed matter physics research are correlated matter and topological matter, with its underlier quantum geometry. The physics of materials whose properties are governed electronic correlations as a research domain has taken shape around the midth of the 20th century with the discovery of Mott insulators and the Kondo effect. In contrast, the field of topological matter is more recent as it originated from the integer quantum Hall effect in the 1980s, and has largely taken shape in the 2000s. Quantum geometry relies on band theory, which describes materials in terms of single-particle excitations. The fields of topological matter and correlated matter are thus significantly different fields that have mostly evolved separately. A contemporary research effort is underway to bring these two pillars of condensed matter physics closer. As part of that effort, this PhD thesis explores interplays between quantum geometry and electronic interactions. In the first part of the manuscript, we extensively review the foundations of band theory and its geometrical and topological extensions. We do so to argue that the single-particle excitations described by band theory are quasiparticles, dubbed Bloch fermions, whose emergence endows them with properties not shared with elementary electrons, one notable example being quantum geometry. We argue that the latter quantifies the non-locality of the Bloch fermion that arises from virtual interband transitions. We additionally discuss the fundamentals of BCS theory and of Green’s functions. Motivated by the apparent difference between Cooper pairs formed by Bloch fermions and by elementary electrons, the second part of the manuscript is devoted to the study of the relation between the normal state quantum geometry and the superconducting state. Our findings show that this relation is ambivalent, and can largely be understood using the non-locality argument. On one hand, the non-locality of the Bloch fermions allows for zero-point motion-driven supertransport. On the other hand, their non-locality weakens the pairing interaction through an emergent Darwin term. Lastly, in the third part of the manuscript we investigate interplays between quantum geometry, topology and Green functions. We show that in non-interacting systems the analytic properties of the Green’s function can be used to extract the value of $\mathbb{Z}_2$ topological invariants. Finally, we propose a generalization of quantum geometry beyond the free-fermion limit using Green functions.

At : Amphitheatre du C2N , on 10:00

The measurement of entropy in a highly correlated system cannot simply be interpreted as counting the accessible microstates of its ground state. It offers crucial insights into the nature of the system when conventional observables, such as conductance, fall short. This is especially true when the system hosts anyonic particles, whose entropy is fractional and whose conductance derivation is extremely complex. However, entropy measurements typically rely on bulk properties, which lack sensitivity for systems comprising only a few particles. Here, I will present the entropy evolution of a single Kondo impurity as it is progressively screened by an electron bath. This process results in a highly correlated system where the local impurity mediates electron-electron interactions, forming a flourishing basis for understanding a wide variety of intricate many-body problems. Our charge Kondo circuit employs a metallic island with two degenerate charge states to emulate a Kondo pseudospin, measured non-invasively via a capacitively coupled charge sensor. By connecting charge and entropy through a Maxwell relation, we establish the reduction of the impurity’s residual entropy due to its screening by the electron bath by a factor of up to 2. This reduction follows the universal renormalization flow from a single free spin with an entropy of

At : Campus Jussieu, 4 place Jussieu, 75005, Paris, Tour 22-23 Etage 3 Salle 317 , on 10:00

Although much heavier than electrons, light nuclei, mainly hydrogen, exhibit Nuclear Quantum Effects, such as tunnelling and zero-point energy, that can have a large impact on the structure and the dynamics of materials. The standard method to account for them when simulating the static properties at equilibrium is the use of path integrals. This method considerably increases the number of degrees of freedom with a consequent enlargement of the parameter space to study; moreover, extracting the partition function and other statistical quantities, such as the density of states (DOS) using path integrals is computationally prohibitive. In this thesis, we present a new formulation of nested sampling (a method that relies on Bayesian statistics), which reduces the multi-dimensional problem into a one-dimensional integral on the energy and directly provides the DOS. Firstly, we implement and test new algorithms in nested_fit - a program that is based on the nested sampling approach. Secondly, we compute the thermodynamic properties of clusters/aggregates with hundreds degrees of freedom within classical statistical mechanics. Finally, we merge the nested sampling and path integral approaches into a new method that provides the quantum partition function and the related thermodynamic quantities at a reasonable computational cost. As a test, we compare the classical and quantum behaviour of clusters where the atoms interact via a Lennard-Jones pairwise potential and discuss the impact of nuclear quantum effects on the thermodynamics of the clusters.

At : Amphithéâtre Pierre Gilles de Gennes - Bâtiment Condorcet-4 Rue Elsa Morante, 75013 Paris , on 15:30

As with the study of electronic circuits, the study of complex systems is often facilitated by breaking them down into simpler sub-systems. Two sub-problems then arise: 1) the study of each sub-system separately; 2) the emergence of new behaviours when they are reassembled. The theory of non-equilibrium circuits is best understood for a single pair of current (electric) and conjugate thermodynamic force (voltage), as is the case in electronics. Each subsystem is then described by a current-voltage characteristic, summarised in the concept of scalar impedance. The current-voltage characteristic of the whole system is then obtained using the conservation laws within and at the interface of each subsystem (for example, Kirchoff’s laws). The aim of this thesis is to pave the way for the generalisation of stationary electronics to non-equilibrium stationary thermodynamic machines with an arbitrary number of currents and conjugate forces subject to different couplings (e.g. thermoelectric). To do this, we identify tools for treating conservation laws within a complex network. We replace the notion of scalar impedance by a matrix object, the non-equilibrium conductance matrix, which takes into account the coupling between the different types of currents flowing through the system. In particular, we show that the law of addition of resistances (resp. conductances) for series (resp. parallel) associations remains valid in the context of non-equilibrium thermodynamic machines. We illustrate this general result for a wide class of systems (thermoelectric converters, chemical reaction networks, energy conversion models with Markov jump processes).

At : Amphithéâtre du Centre de Nanosciences et de Nanotechnologies, 10 Bd Thomas Gobert, 91120 Palaiseau , on 10:00

Quantum technologies promise to bring several improvements in the fields of sensing, communication and computing. Single-photon-emitting devices are a promising platform for quantum applications, having already demonstrated an advantage over their classical counterparts. The highest-quality emitter for the purpose are epitaxial quantum dots (QD) made of III-V semiconductors. To reach the best performances the QDs are embedded in microcavities and are electrically controlled and stabilized. In this thesis are described the basics of QDs properties and the processes to transform them into efficient sources. This includes multiple advancements toward more functional sources with broader applications, requiring standardization to efficiently scale the fabrication yield. Major advancements have been taken on two key parts of the process, controlling the spatial and spectral density of QDs, and improving the deterministic fabrication by in-situ lithography. Motivated by simplifying the use of these devices, the development of directly fiber coupled sources of single photon is presented. This is a crucial step toward plug and play devices, allowing a simpler and more reliable operation. The fiber pigtailed devices are shown to conserve the state-of-the-art performances over months of operation. In parallel, a different type of QDs have been developed based on droplet-etching epitaxy. This unlocks the expansion of the wavelength range of available single-photon emitters. The first deterministic devices are fabricated based on the new droplet-etched QDs.

At : campus jussieu, amphithéâtre à préciser , on 14:00

During morphogenesis, bio-chemical signaling and mechanical cues are at play in order to give rise to shape and function to future formed tissues, influencing each other through a dynamic feedback loop. Still, the role of such mechanical cues on the emergence of structure is not well understood. In particular, in the context of adhesive tissues or cell aggregates, it is known that the hierarchy of cell-cell adhesion, together with cellular motility, can lead to the self-organization of identified structures, a phenomenon described within the framework of the differential adhesion hypothesis. Nevertheless, these kinds of processes have been mainly studied in biological systems in vivo or in vitro where deciphering the exact influence of individual factors like cell-cell adhesion or forces remain challenging. In order to tackle this problem, we choose to work in a simplified framework. We use adhesive emulsions as a biomimetic system of epithelial tissues, in which each oil droplet mimics a cell in the tissue and we introduce differentials of adhesion using palindromic DNA sequences as the binders between the droplets. The obtained “proto-tissues” are then flowed in micro-channels of various geometry that directly define the stress field. We seek to experimentally and theoretically elucidate the influence of local droplet deformations and T1 events on the global behavior of the emulsion flow. Next, we try to correlate those observations to the evolving structure of the emulsion along the channel as a function of the interdroplet adhesion hierarchy. By comparing our findings with structural features described in biological tissues we will thus be able to infer a potential role of adhesion regulations to facilitate the emergence of structure in developing tissues.