Magnetism and superconductivity in strongly correlated systems -- Magnétisme et supraconductivité dans des systèmes fortement corrélés

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Materials whose physical properties are dominated by particle-particle interactions are called strongly correlated. These interactions produce novel ground states at low temperatures among which superconductivity and magnetism are the most important. The competition, the coexistence and the interrelation between these states must be investigated experimentally to appreciate their potential in future devices. Among these materials, organic conductors with a low-dimensional character are particularly attractive because an unconventional superconducting state is in competition with magnetism. They are also considered as ideal systems because of energy scales (temperature, pressure, magnetic field) attainable in laboratories. Superconducting thin films which can be more easily incorporated in novel devices and magnetic materials showing simultaneously magnetism and electric polarization (multiferroics) will also be studied. We propose to perform ultrasonic and microwave experiments on these systems to address important issues related to the identification and characterization of the novel superconducting and/or magnetic states. Such experiments are essential to sustain the construction of theoretical models of these materials. These experiments will be performed as a function of temperature (low 2-300 K and ultra-low 20 mK), of magnetic field (18 Tesla as a function of orientation) and hydrostatic pressure (12 kbar). These measurements can potentially constitute key experiments to complete our understanding of the materials.