Solid foams are complex networks of bubbles tightly packed in a solid material. These bubbles can be interconnected, like in sponge (opened cells), or separated by a solid film (closed cells), giving very different properties for applications. Despite its importance, the pore connectivity of today’s materials tends to be controlled thanks to several decades of experience, rather than by scientific understanding of the governing processes. The aim of the project is to contribute to that fundamental understanding by investigating the properties of the initially liquid foam template and its behaviour under solidification. For this purpose, it is crucial to elucidate the competition between several mechanisms taking place at different timescales and controlling the dynamics and rupture of the thin liquid films separating bubbles. More specifically, foam generation has to be faster than solidification, which in turn has to be slower (or faster) than film rupture to obtain open (or closed) cells, respectively. To compare these different time scales, we will perform experiments to determine the time for the rupture of a single film during generation and drainage. Even though the opening time of a hole inside a static soap film is at this stage well characterized, it is indeed not clear what controls the rupture time of a film, especially under dynamic conditions. Some of our preliminary results show that this rupture time is critically linked to the thinning time. It is therefore crucial to first understand the generation and drainage of a thin film, which is controlled by the hydrodynamic boundary condition at the liquid/air interface. This boundary condition is intrinsically viscoelastic and determines the mobility of the interface, ranging from fully mobile to rigid, depending on the specific surfactant properties. Several descriptions exist in the literature that parameterize the interfacial mobility in a way that is either ad-hoc (such as the slip length) or incomplete (such as the interfacial rheology). The main objective of this project is therefore to combine theory and experiments in order to propose a complete and coherent description of this boundary condition, in which the interfacial mobility is directly related to the specific nature of the surface-active agents. Since this is a complex task, we will start with the investigation of simplified model systems. We ultimately intend to predict the rupture time during generation and drainage of a polymer film and to compare it to its solidification time (by reticulation). Since this project is very ambitious, E. Rio, the coordinator has chosen to gather a team with complementary skills. Having both a solid education in hydrodynamics and 5 years’ of experience in physical-chemistry, she noticed how important it is, for such a project, to put together people from both communities. E. Rio is perfectly placed in this respect, being presently part of D. Langevin’s team, who popularized the importance of physical-chemistry to understand foam physics. At the same time, leading the project would be a great opportunity for her to create an independent team around a subject, where she is already internationally recognised. The project will have a crucial need for a theoretician to elaborate models that are consistent with the various experimental conditions considered in this project. That is why the team will include B. Scheid (ULB, Brussels), who is a specialist in modelling thin film dynamics with both elastic and viscous interfaces and is used to work in close interaction with experimentalists. F. Restagno, who is a specialist of friction at interfaces, will also be involved in the project. For film solidification, in the last part of the project, W. Drenckhan, who is already part of the same team as E. Rio, will be a precious advisor and collaborator. Finally, with a PhD student funded by the ANR, the team will be complete allowing great progress in this project.

Contrary to received wisdom, conventional superconductors out-of equilibrium (NECSs) can be good ferromagnets and also excellent spin-dependent thermoelectric materials, and the superconducting wavefunction can be composed of spin-aligned pairs of electrons. My recent experiments demonstrating out-of-equilibrium magnetism, spin-charge separation and quasiparticle spin resonance in superconducting aluminium revealed that the magnetic properties of NECSs depend strongly on voltage- and magnetic-field-induced spin/charge currents and can thus be finely tuned. This work has motivated theoretical studies of the thermoelectric properties of NECSs, which are expected to show similar sensitivity to accessible experimental parameters. Thus, out-of-equilibrium spin currents and distributions in superconductors promise enhanced versatility and novel concepts for spin- and heat-based electronics – respectively spintronics and caloritronics – in particular through spin-sensitive distribution-function engineering. Building on my previous work, I propose to demonstrate, and establish techniques to finely control, the inter-conversion of non-equilibrium spin currents with both heat and charge currents in superconductor and topological-insulator-based devices. In doing so, I shall close the heat-spin-charge current triangle of mutual conversion and control in superconductors. This will in turn bring new techniques to bear on fundamental, long-standing problems in superconductivity, including the mechanisms of spin relaxation and decoherence; and the manipulation of the constituent electron spins in Cooper pairs to generate triplet superconductivity or spin-filtered, spatially-separated entangled electrons.

The spin-valley physics in transition metal dichalcogenide two-dimensional monolayers has attracted attention due to its possible application in quantum information processing. Two distinct spin-split valleys occur due the non-centrosymmetric structure and spin-orbit coupling. Excitations in each valley can be created by circularly polarized laser and may be sufficiently long-lived to be manipulated. The role of atomic defects and confinement in excitation decay is under intense debate. Understanding decay is hindered by the spatial resolution limit of optical techniques. SpinE will fill this critical gap by designing new spectroscopy approaches coupling electron and photon techniques in an electron microscope. Laser pulses will be used to selectively create excited states, which will be detected using time-resolved electron spectroscopy. The atomic resolution of the electron microscopes will allow the study of the role of defects, interfaces and confinement in excitation decay.

Harvesting of photo-excitations in organic solar-cells is fundamentally governed by the quantum mechanical property of spin. Indeed, spin determines the generation and recombination pathways for a particular species, which ultimately determines device performance. Crucial to solar cell operation are spin-triplet excitons, which have the potential to overcome conventional efficiency limits through the singlet fission mechanism in which two triplet excitons can be generated from a single singlet exciton. The unique spin signatures of triplet excitons makes them ideally suited for investigations using spin-resonance techniques. We propose to study the interaction between spin dynamics and transport properties using a novel technique where triplet excitons are coupled to a microwave superconducting resonator which can simultaneously probe transport and spin-resonance signals. Performing measurements at sub-Kelvin temperatures, we will search for new quartet states created through spin-locking of fission generated excitons by the electromagnetic field in the resonator. This experiment will extend the concept of Majorana-Brossel resonances developed in atomic physics and that we recently demonstrated in an organic context by showing the formation of an overall spin S = 1 from two S = 1/2 polarons due to a strong interaction with the electromagnetic field in a superconducting cavity. Since exction fission strongly depends on the local molecular environment, we also propose a combination of optical and microwave techniques to study exciton fission in the limit of a small number of triplet pairs. This will enable quantitative investigations on the influence of molecular packing and morphology. Triplet excitons are neutral spin carriers, they can thus provide a perfect spin current source without associated charge transport. We describe several device architectures that can be used to harness spin current from triplet-excitons, starting from inverse-spin Hall effect geometries to mesoscopic devices where mesoscopic superconductivity and carbon nanotube quantum dots can be very sensitive probes of their local magnetic environment. We show preliminary results from devices using an inverse-spin Hall effect geometry suggesting spin-transfer between triplet excitons and a platinum thin film. In an attempt to bridge the gap between our fundamental results and the problem of photovoltaic energy generation we will start investigations on dielectric whispering mode gallery resonators that should allow to extend our experimental techniques all the way to room temperature. As an application of his approach we plan to study the problem of energy and charge transfer between triplet excitons and semiconducting nanocrystals which is very important for photovoltaic devices taking advantage of exciton fission. Spin properties are also actively investigated in the context of quantum information processing where long coherence times are essential. The spin of electrons trapped on a liquid helium 4 surface are expected to show record coherence times due to the complete absence of hyperfine interactions and magnetic impurities. We propose to couple electronic spins on liquid helium and photo-excited spins in organic conductors. Electronic spins can then form an ultra-sensitive probe for the spintronics in organic conductors, while the optical manipulation of spin processes in the organic materials will allow to achieve a better control of the spins of electrons on helium.

Electronic correlations are at the origin of many remarkable properties in solid state physics. In some materials several orders can coexist, couple or compete, giving rise to new properties. The case of the 123 family of compounds, embodied by BaFe2Se3, is one of these. It is multiferroic close to room temperature (256K) and described as a special Mott insulator. Under pressure, it undergoes an insulator-to-metal transition to become a superconductor. This project proposes to study all these orders and their interdependence in order to derive general information on highly correlated systems, multiple orders and their evolution according to various parameters: pressure, fields, temperature and doping.