  We present a two-fluid description for iron-based superconductors, which
contains an itinerant electron Fermi-liquid and a local moment spin-liquid,
coupled together via an effective Hund's rule interaction. We examine the
low-energy collective behavior of such a system. We find that an
electron-spinon composite mode emerges in the intermediate coupling regime,
which may account for the hump-dip behavior observed in the resent scanning
tunneling spectroscopy experiments. The superconductivity and spin-density-wave
phases are consistently described within the same framework. Possible
experimental test is also proposed.
