Scissors mode in a superfluid Fermi gas - art. no. 023609

We evaluate the frequencies of scissors modes for density and concentration fluctuations in a vapor of fermionic atoms placed in two hyperfine levels inside a spherical harmonic trap. Both the superfluid and normal states are considered, with inclusion of the interactions at the random-phase level. Two main results are obtained: (i) the transition to the superfluid state i s signaled by the disappearance of soft transverse modes of the normal flui d in the collisionless regime; and (ii) the eigenfrequency of the density f luctuations in the superfluid coincides with that of the normal fluid in th e collisional regime. The latter property is related to the opening of the gap in the single-pair spectrum.