Minimal two-band model of the superconducting iron oxypnictides

Following the discovery of the Fe-pnictide superconductors, local-density approximation (LDA) band structure calculations showed that the dominant contributions to the spectral weight near the Fermi energy came from the Fe 3d orbitals. The Fermi surface is characterized by two hole surfaces around the Gamma point and two electron surfaces around the M point of the two Fe/cell Brillouin zone. Here, we describe a two-band model that reproduces the topology of the LDA Fermi surface and exhibits both ferromagnetic and q=(pi,0) spin-density wave fluctuations. We argue that this minimal model contains the essential low energy physics of these materials.