Active Materials consist of a collection of objects that self-propel by absorbing energy from either an internal reservoir or from their surroundings. Examples of these include swimming bacteria, while artificial microswimmers can be realised by active Janus colloids. In recent years, they have become a topical research direction in soft matter due to the possibility to realise self-controlling applications. In these materials, the building blocks can carry out tasks autonomously, without an outside intervention. Examples of these include active colloidal materials for both lab-on-chip and drug delivery applications in microscale and autonomous robotic applications in macroscale. A grand challenge in active matter research, is how to guide and control the self-motile building blocks. Understanding how to do this gives novel possibilities to design artificial materials with life like qualities for robotic (dry; macroscale) and novel colloidal (hydrodynamic; microscale) applications. One possibility is to use confining surfaces. Both, spherical self-propelling colloids and active granular rods have been shown to accumulate at surfaces. And various geometrical constructions can be used to guide them. Further, the confinement can become motile, due to aggregation of the self-motile objetcs. This can give a rise to novel applications in swarm-robotic applications, where a the collections of a simple non-communicating build blocks are used to create coherent collective motion. However, these approaches are inherently 2-dimensional. To realised guiding in the 3-dimensional bulk, the properties of the swimming media can be used. Recently, it has been shown that microswimmers can be guided using the broken orientational symmetry of nematic liquid crystals. Typically, rod like bacteria will align along the nematic director and they can be guided into complex paths by controlling the direction of the nematic order. This project deals with guiding artificial self-propelling particles It includes two distinctive branches: 3-dimensional guiding spherical microswimmers using fluid topology (liquid crystalline order) for microscale applications and granular active particles (self-propelling rods) in flexible containers for 2-dimensional robotic applications. In the first part, we will construct a complete hydrodynamic picture of spherical (colloidal) microswimmers in liquid crystals. In addition to classic nematic phase, we will consider both also chiral nematic and blue phases. We will interface state-of-the art simulations (lattice Boltzmann) with analytical calculations. We will study both the hydrodynamic alignment of the particles as well as the trapping and swimming along defect lines. In the second part, we will consider dry granular rods in a flexble container, which is rendered motile through the accumulation of the active rods in high curvature regions.

The RHEOLIFE project aims at elaborating a general time-frequency rheology framework for analyzing and modeling the non-stationary and multi-scale spatio-temporal dynamics of living systems. As the elementary building block of living systems, cells are active mechanical machines that, in contrast to amorphous materials, have the the fascinating property to constantly remodel their structural organization to withstand forces and deformations and to promptly adapt to their mechanical environment. We will revisit classical Fourier-based rheology formalism with wavelets for modeling the mechanical behavior of a unicellular organism, the budding yeast S. cerevisiae. We will use this new time-frequency rheology approach to perform a multi-scale analysis of experimental recordings (nanomechanical and optical devices) of living cell in vivo mechanical response to external strain or stress.

Superconductivity is a fascinating quantum state of condensed matter. Its study and understanding have always aroused immense interest in fundamental physics, but also in materials science and its exploitation leads to numerous technological applications: lossless current transport, energy storage, quantum computation or sensors with unprecedented resolution. In 1986, the discovery of high Tc superconductivity in cuprates allowed the acceleration of enormous progress, both experimentally and theoretically, in several areas of condensed matter physics. However, the origin of high Tc superconductivity is still an unresolved problem; One of the main reasons is the complexity of the physics of cuprates resulting from multiple interactions in competitions (magnetic fluctuations, strong electronic correlations, charge-network coupling, etc.) and nearby orders (charge density wave, antiferromagnetism, pseudo-gap, etc.). The emergence of superconductivity in nickelates, structural and electronic “cousins” of cuprates, was eagerly awaited, but only postponed in 2018 in LaNiO3 / (La, Sr) MnO3 superlattices and in August 2019 in thin layers of the “Infinite phase” Nd0.8Sr0.2NiO2 / SrTiO3, due to the inherently complex chemical processes to stabilize this phase. The SUPERNICKEL project will explore the chemical, structural, physical and electronic properties of new superconducting nickelates, using a transversal approach involving the synthesis of thin films, superlattices and massive materials, the crystallochemistry of the solid, a large battery of macroscopic probes. and experimental microscopic (magneto-transport, X-ray diffraction, photoemission spectroscopy, among others) and theory. Our objectives are to determine the nature and symmetries of the superconducting state, the origin of the interaction forming Cooper pairs, by clarifying the similarities and differences between nickelates and cuprates. Over the past few months, we have focused our efforts on mastering the complex protocol allowing to stabilize the phase of infinite layers and to synthesize the superconducting nickelate.We have already obtained samples with good nominal compositions and close to superconducting instability, and we are confident that very soon, after optimizing their synthesis, we will be one of the few groups in the world to have good quality superconducting nickelates. . In parallel, we will work on other nickelate phases. The possibility of synthesizing and studying in depth, in addition to thin films and superlattices, bulk nickelates will also be a unique approach of SUPERNICKEL. We expect from the thin film / solid material comparison essential and potentially unique information on the specificity of the thin film / substrate form in the emergence of superconductivity. Our multi-approach strategy integrates design, development, detailed crystallochemical characterization, exploration of the physical and electronic properties of normal and superconducting states and theoretical modeling. The SUPERNICKEL consortium thus covers a wide range of know-how in all the essential fields and techniques necessary to tackle this problem: oxide chemistry for the synthesis of massive and thin layers, crystallography, strong correlations, magneto-transport, structure. electronics, magnetism and superconductivity. We also hope that beyond the SUPERNICKEL consortium, the dynamics of this project will become a strong pillar to consolidate and revitalize the French community working in the wider field of new superconductors.

Despite the tremendous interest of the scientific community in the dissymmetrization of metal oxide semiconducting nanoparticles (NPs), very few methods can produce efficiently highly dissymmetric systems at the nanoscale, especially metal oxide nanocatalysts for photocatalytic water splitting. The OSCARE project intends to introduce a new strategy to synthesize such dissymmetrical oxide heteronanostructures efficient for O2 (OER) and H2 (HER) evolution reactions by using a laser deposition method. Exploiting focused laser in millichannels, the strategy involves the asymmetric photodeposition of oxidation and/or reduction cocatalysts on metal oxide NPs exposing well-defined facets obtained by hydro/solvothermal routes under non-conventional activation methods. A full set of advanced characterizations will be implemented to study the morphology, optical and electronic properties of these nanosystems, and their ability to promote OER and HER reactions under sunlight illumination. The influence of both the type and size of the co-catalyst deposits on the photocatalytic activities will be thoroughly studied to determine the main factors ruling these properties. This project will thus make it possible to develop heterostructures with optimized charge carrier separation properties for applications in the field of solar energy conversion to produce solar fuels.

Levitated nanomechanical oscillator presents some advantages with respect to its clamped optomechanical counterparts, as e.g. its ability during free-fall and coherent evolution to expand its wavefunction up to overlap the particle’s size. Wave-matter interference are expected to test the fundations of quantum mechanics through collapse models and to verify the role of gravity as a fundamental limit in the coherence of a macroscopic quantum superposition. With its extreme isolation from environment and the highest recorded mechanical quality factor, levitated particles are also ultra-sensitive force sensors with the ability to test the existence or not a fifth force, arising from beyond standard models. A prerequisite for carrying out theses studies is to ground state cool the centre-of-mass motion of the optically trapped particle. There are several types of cooling schemes, such as parametric and linear feedback, as well as, cavity-based side-band and coherent scattering cooling. The latter enabled to achieve ground state cooling for only one vibrational degree of freedom. LOMA is a pioneer in France in the study of optical vacuum trapping of dielectric nanoparticles. To go further in this field, it is desirable to cool the particle in the three directions of space in a completely optical manner. Our all-optical cooling protocol will enable to directly measure in real-time weak vectorial forces. The QleviO project proposes to ground state cool all vibrational degrees of freedom of a nanoparticle by radiation pressure without requiring an optical resonator or a cryostat. Up to now, optical trapping in high vacuum restricts nanoparticle materials to silica because of its efficient heat dissipation by emitted black body photons. To extend to other materials, the quality of the material and the laser sources are of the utmost importance. To control the particle motional state with light, the refractive index should be high and the light absorption should be weak, while mitigating the heat excess in high vacuum. It turns out that the only laboratory that best meets all of these conditions is the ICMCB that produces core@shell Si@SiO2 particles. The core has a high index and the silica shell efficiently dissipate the heat excess due to its higher emissivity. This now requires to trap and cool such particles to the most favorable wavelength, 1550 nm. Futhermore, the intensity noise of the laser source has to be specifically minimized at the oscillator frequencies. The experts in high-power ultra-low intensity noise laser sources are in LP2N and will develop such sources : one for trapping (and detecting the particle’s motion) and one source dedicated to cool the center-of-mass motion. The interactions between partners will be strong and the consortium strategy will be to work in parallel in the material side, the optomechanical setup and the laser sources. Remarkably, almost all position information is carried by the backscattered photons, facilitating a homodyne measurement operating close to the Heisenberg limit. Thus, to reach the ground state in the three dimensional space of an optically tweezed particle, we will use measurement-based quantum feedback. This is based on the fact that we can resolve the zero point motion in the decoherence scale time and implement a measurement-based feedback control to cool the oscillator towards its ground state. In other words, the real-time feedback anticipates and cancels the disturbance due to backaction-induced motion.