Probing the many body dynamics of ultracold repulsive Fermi gases of lithium atoms

Itinerant ferromagnetism describes systems comprising microscopic magnetic moments which are not localized in space but are instead mobile. This concept was introduced back in the thirties by the British theoretical physicist Edmund Clifton Stoner, who first devised a minimal model to describe a ferromagnetic instability in a homogeneous Fermi gas driven by short-range repulsive interactions: in a free electron gas, the competition be- tween the kinetic energy, given by the Pauli pressure, and the interaction energy, given by the screened Coulomb potential, drives a paramagnetic to ferromagnetic phase transition, leading the development of a finite magnetization. This model is crucial to understand the magnetic properties of everyday life magnets, made of common metals like iron, nickel or cobalt in which the carriers of magnetism are the unsaturated d-band electrons, which are extremely mobile and can be thought as a free gas. The possibility that pure short-range repulsive interactions suffice to sustain ferromagnetism is still nowadays de- bated. It is in fact experimentally extremely challenging to isolate the problem from many additional ingredients typically present in solid-state physics such as flat dispersion bands, multi-orbital exchange, or the presence of disorder. In this thesis, I report our experimental investigations on the repulsive Fermi gas, studied exploiting a mixture of ultra-cold Li-6 atoms interacting through a Feshbach resonance.