L'auteur n'a pas fourni de résumé en français / The superconductivity had been thought to be incompatible with the magnetism, because the former originates from the weak attractive leading to the formation of Cooper pairs, whereas the latter is based on the strong Coulomb repulsive force, leading also to strong electronic correlations. Unconventional superconductors,which include heavy fermion systems, high-Tc cuprates, organic superconductors, and iron-pnictides, is a major topic of condensed matter physics. In all these systems, it has been understood that magnetism can even plays an important role for the pairing mechanism, so that both phenomena can coexist and even favour each other.Our target is on heavy fermion systems, namely uranium and rare earth compounds, where the 5f or 4f electrons which have a dual nature (itinerant/localized), play an important role. More precisely, we will focus on the ferromagnetic superconductors and their quantum criticality. In this field, new materials open new frontiers of research. The student will participate in this stream. He will learn and develop the fundamental crystal growth techniques, such as Czochralski, flux, and Bridgeman method. Since high quality single crystals are essential to elucidate the superconducting properties, a lot of efforts will be devoted to improve the quality of the samples. The next target is the quantum oscillation measurements, which allow a detailed microscopic observation of the heavy electronic state and of the topology of the Fermi surface. They require both very low temperature and high fields, like the study of the field induced superconducting phases in these compounds (like URhGe or UCoGe). The student will perform the measurements under extreme conditions, namely high fields up to 15T in SPSMS, or up to 30T in LNCMI, at low temperatures down to 30 mK, and high pressure up to 3 GPa.From the educational point of view, it is ideal that the student starts to synthesize a material, characterizes it, performs the low temperature measurements by him/herself throughout the PhD period, and get used to the exciting measurements under extreme conditions in a large scale facility like the LNCMI. Such a wide spectrum is rather rare in Europe, but our group („SPSMS/LNCMI) can provide such a unique opportunity, helping the student to become an independent researcher. It should be noted that the experiments in SPSMS and LNCMI are quite complementary each other. For quantum oscillation study, high fields, low temperatures and high quality singles are inevitably important. In general, the precise measurements at high fields up to 15T would be enough in order to determine the Fermi surface topology and the effective mass, which canbe done in SPSMS. However, the specific case, such as Lifshitz transition, field induced quantum critical phenomena, requires higher fields than 15T, which can be achieved by the resistive magnet in LNCMI.This project is supported by the ANR (CORMAT, SINUS) and the ERC starting grant “NewHeavyFermion”.Recently in SPSMS we purchased a top-loading dilution refrigerator for the quantum oscillation measurements, and started the installation. By the end of this summer, hopefully we detect the first de Haas-van Alphen signal at high fields up to 15T and at temperatures down to 30mK. Furthermore, we started to install the flux crystal growth equipment this month, involving the reconstruction of the room for the safe treatment of uranium compounds.

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Le projet de thèse s’inscrit dans la continuité de l’étude pilote développée dans le cadre du programme Doremi (Consortium européen de programmes de recherche portant sur les effets des faibles doses). En partant des résultats préliminaires déjà obtenus sur ce projet, l’objectif est d’approfondir les études sur les effets d’une contamination chronique à l’uranium via l’eau de boisson sur le processus de neurogénèse au cours du développement cérébral mais également au stade adulte. La première partie du projet de thèse consiste à comparer la prolifération, la survie et le potentiel de différentiation des cellules des zones neurogéniques (dans l’hippocampe principalement) à l’aide de marqueurs spécifiques de chaque stade de différentiation chez des rats contaminés ou non à l’uranium dès le stade in utero. Cette étude in vivo sera entreprise à différents stades : pendant le développement cérébral embryonnaire et post natal et à l’âge adulte. Cette première partie donnera des pistes pour étudier plus en détails les mécanismes d’action. La deuxième partie du projet de thèse vise donc à étudier comment l’uranium agit sur la neurogénèse à l’aide de modèles in vitro et ex vivo. Des cultures primaires de neurosphères seront utilisées afin d’étudier l’effet de l’uranium sur les capacités de multipotentialité des cellules souches neurales. En parallèle, un modèle de culture organotypique d’hippocampe sera développé. Ce modèle est particulièrement intéressant car il permet de réaliser des expositions aux radionucléides « à façon », d’en étudier les mécanismes d’action dans des aires cérébrales ayant une cytoarchitecture préservée et mettant en jeu différents types cellulaires, tout en combinant des méthodes d’analyse en histologie et en biologie moléculaire. / The PhD project is a continuity of the Doremi program (European Consortium of research programs on low doses effects). The objective is to assess the effects a chronic uranium contamination via drinking water on neurogenesis during brain development and in adult rats. The first part of the project will evaluate proliferation, survival and cell differentiation in neurogenic zones (in particular in the hippocampus) using specific markers for each differentiation stage in control and contaminated rats from the in utero life. This in vivo study will be performed at different stages: during embryonic and postnatal brain development and at the adult age. This part of the project will provide some clues on the potential mechanisms of action that we aim to study more in details. For this purpose, the second part of the project will be performed on in vitro and ex vivo model. Neurosphere primary cultures will be performed to assess uranium effects on the multipotential properties of neural stem cells. We also plan to use a model of hippocampal organotypic culture which will allow the study of the mechanisms of action in a preserved ex vivo structure in terms of cytoarchitecture, cell interactions, and being able to test different uranium concentrations and combine multiple analyses methods (histology, molecular biology…).