Spin oscillations of the normal polarized Fermi gas at unitarity

Using density-functional theory in a time-dependent approach, we determine the frequencies of the compressional modes of the normal phase of a Fermi gas at unitarity as a function of its polarization. Our energy functional accounts for the typical elastic deformations exhibited by Landau theory of Fermi liquids. The comparison with the available experiments is biased by important collisional effects affecting both the in-phase and the out-of-phase oscillations even at the lowest temperatures. New experiments in the collisionless regime would provide a crucial test of the applicability of Landau theory to the dynamics of these strongly interacting normal Fermi gases.

Figure 1

Frequency of the axial compressional mode as a function of the polarization $P$. Dashed line: the single-polaron-mode frequency. Solid line: the collisionless value of the mode frequency obtained via the variational principle described in the present work. Points: experimental data reported in [4].