Density response of a trapped Fermi gas: a crossover from the pair   vibration mode to the Goldstone mode
  We consider the density response of a trapped two-component Fermi gas. Combining the Bogoliubov-deGennes method with the random phase approximation allows the study of both collective and single particle excitations. Calculating the density response across a wide range of interactions, we observe a crossover from a weakly interacting pair vibration mode to a strongly interacting Goldstone mode. The crossover is associated with a depressed collective mode frequency and an increased damping rate, in agreement with density response experiments performed in strongly interacting atomic gases. 
A. Korolyuk, J. J. Kinnunen, P. T\"orm\"a
cond-mat.quant-gas cond-mat.str-el cond-mat.supr-con