Collisionless collective modes of fermions in magnetic traps -: art. no. 063606

We present a random-phase-approximation formalism for the collective spectrum of two hyperfine species of dilute K-40 atoms. magnetically trapped at zero temperature and subjected to a repulsive s-wave interaction between atoms with different spin projections. We examine the density and the spin oscillation spectra, as well as the transition density profiles created by external multipolar fields. The zero sound spectrum is always fragmented and the density and spin channels become clearly distinguishable if the trapping potentials acting on the species are identical. Although this distinction is lost when these confining fields are different, at selected excitation frequencies the transition densities may display the signature of the channel.