  We report quantum oscillation measurements in SrFe2As2 - which is an
antiferromagnetic parent of the iron-arsenide family of superconductors - known
to become superconducting under doping and the application of pressure. The
magnetic field and temperature dependences of the oscillations between 20 and
55 T in the liquid helium temperature range suggest that the electronic
excitations are those of a Fermi liquid. We show that the observed Fermi
surface comprising small pockets is consistent with the formation of a
spin-density wave. Our measurements thus demonstrate that high Tc
superconductivity can occur on doping or pressurizing a conventional metallic
spin-density wave state.
