Spin-wave excitations in the spin-density wave state of doped iron pnictides

We investigate spin-wave excitations in the spin-density wave state of doped iron pnictides within a five-orbital model. We find that the excitations along ($\pi ,0$)  →  ($\pi ,\pi$) are very sensitive to dopings whereas they do not exhibit a similar sensitivity along ($0,0$)  →  ($\pi ,0$). Secondly, the ellipticity of the elliptical ring-like excitations around ($\pi ,0$) is also very much dependent on doping. Thirdly, the spin-wave spectral weight shifts towards the low-energy region as it moves away from zero doping. We find several features to be in qualitative agreement with the inelastic neutron-scattering measurements for the doped pnictides. (paper)