Zero-sound density oscillations in Fermi-Bose mixtures

Within a mean field plus random-phase approximation formalism, we investigate the collective excitations of a three-component Fermi-Bose mixture of K atoms, magnetically trapped and subjected to repulsive s-wave interactions. We analyze both the single-particle excitation and the density oscillation spectra created by external multipolar fields for varying fermion concentrations. The formalism and the numerical output are consistent with the generalized Kohn theorem for the whole multispecies system. The calculations give rise to fragmented density excitation spectra of the fermion sample and illustrate the role of the mutual interaction in the observed deviations of the bosonic spectra with respect to Stringari's rule.