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Résumé |
The frequencies and damping rates of collective oscillations in ultracold trapped Fermi gases contain a lot of information about the dynamical properties of the system which cannot be determined by measuring static density profiles. In the first part of the talk, I will discuss the transition from superfluid to normal collisionless behaviour of a Fermi gas in the BCS limit. Using the transport theory developed by Betbeder-Matibet and Nozieres, I will show that at finite temperature, but below Tc, the collective mode spectrum has a complicated structure, and that the modes are strongly damped when their character changes from that of a zero-temperature superfluid to that of a collisionless normal gas. In the second part of the talk, I will discuss the transition from the collisionally hydrodynamic to the collisionless regime of a normal-fluid (but still degenerate) strongly interacting Fermi gas in the framework of the Boltzmann equation. The influence of the in-medium T matrix in the mean field and in the cross section will be discussed. I will also show that the widely used relaxation-time approximation, neglecting the spatial dependence of the relaxation time, strongly overestimates the collisional effects. |
