Trapped Phase-Segregated Bose-Fermi Mixtures and their Collective   Excitations
  Recent progress in the field of ultracold gases has allowed the creation of phase-segregated Bose-Fermi systems. We present a theoretical study of their collective excitations at zero temperature. As the fraction of fermion to boson particle number increases, the collective mode frequencies take values between those for a fully bosonic and those for a fully fermionic cloud, with damping in the intermediate region. This damping is caused by fermions which are resonantly driven at the interface. 
Bert Van Schaeybroeck and Achilleas Lazarides