Quantum oscillations in the parent magnetic phase of an iron arsenide high temperature superconductor

We report measurements of quantum oscillations 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 T-c superconductivity can occur on doping or pressurizing a conventional metallic spin-density wave state.