Collective modes of trapped Fermi gases with in-medium interaction
Résumé
Due to Pauli blocking of intermediate states, the scattering matrix (or T matrix) of two fermionic atoms in a Fermi gas becomes different from that of two atoms in free space. This effect becomes particularly important near a Feshbach resonance, where the interaction in free space is very strong but becomes effectively suppressed in the medium. We calculate the in-medium T matrix in ladder approximation and study its effects on the properties of collective modes of a trapped gas in the normal-fluid phase. We introduce the in-medium interaction on both sides of the Boltzmann equation, namely in the calculation of the mean field and in the calculation of the collision rate. With mean field inclusion, we can considerably improve the agreement with measured temperature dependence of frequency and damping rate of the scissors mode. In addition, we compute frequencies and damping rates of the radial quadrupole and compression modes.