  We derive the coherent state representation of the integrable spin chain
Hamiltonian with non-compact supersymmetry group G=SU(1,1|1). By passing to the
continuous limit, we find a spin chain sigma model describing a string moving
on the supercoset G/H, H being the stabilizer group. The action is written in a
manifestly G-invariant form in terms of the Cartan forms and the string
coordinates in the supercoset.
  The spin chain sigma model is shown to agree with that following from the
Green-Schwarz action describing two-charged string spinning on AdS_5 x S^5.
