to an enhancement of the particle-hole susceptibility. This suggests that FS nesting among those pockets could induce spin-density-wave (SDW) order at the in-plane AF wavevector ${\bf Q}_{AF} = (1,0)$ with a collinear spin structure (Fig. 1b) [@dong], much like the FS-nesting induced SDW in pure chromium [@fawcett]. Neutron scattering experiments on LaFeAsO [@cruz], BaFe$_2$As$_2$ [@qhuang], and NaFeAs [@slli09] have reported results compatible with the theoretically predicted AF spin structure, albeit with an ordered magnetic moment smaller than expected from first-principles calculations [@mazin08]. In addition, quasiparticle excitations between the hole and electron FS can induce $s^{\pm}$-wave superconductivity [@mazin2011n; @hirschfeld; @kuroki08; @chubukov; @fwang09]. One of the consequences of this superconducting state is that the imaginary part of the dynamic susceptibility, $\chi^{\prime\prime}(Q,\omega)$ should have a sharp peak, termed spin resonance in copper oxide superconductors [@eschrig], at ${\bf Q}_{AF} = (1,0)$ below $T_c$ [@maier; @korshunov]. This prediction is also confirmed by inelastic neutron scattering (INS) experiments in iron-based superconductors such as hole-doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$ [@christianson; @chenglinzhang; @castellan], electron-doped BaFe$_{2-x}T_x$As$_2$ ($T=$Co, Ni) [@lumsden; @schi09; @dsinosov09; @jtpark; @clester; @hfli; @hqluo12], and FeTe$_{1-x}$Se$_x$ [@hamook; @qiu09; @lumsden2]. Finally, angle resolved photoemission spectroscopy (ARPES) experiments find that the general characterization of the FS and the superconducting order parameter are consistent 