Study of the ferromagnetic instability in a repulsive Fermi gas of ultracold atoms.

Valtolina G., Scazza F., Amico A., Burchianti A., Enss T., Inguscio M., Zaccanti M., Roati G.
  Mercoledì 28/09   10:00 - 13:00   Edificio Psicologia 2 - Aula 2B   II - Fisica della materia
Ferromagnetism is a clear manifestations of interactions in many-body fermion systems. It requires strong repulsion to develop, making its description notoriously difficult. It is still debated if, in the simplest case of a homogeneous Fermi gas with short-range repulsive interactions, ferromagnetism can be present all. We experimentally tackle this question by studying a clean model system consisting of a spin-mixture of ultracold ${}^{6}Li$ atoms, whose interactions are tuned via a Feshbach resonance. The ferromagnetic instability is revealed by observing the softening of the spin-dipole mode, directly linked to the increase of the spin susceptibility while approaching the ferromagnetic transition.