Inelastic neutron scattering study on Co-doped LiFeAs

We performed inelastic neutron scattering on Co-doped LiFeAs material. In 12{\%} Co doped LiFeAs, where Tc is dramatically suppressed, the low energy spin excitation is commensurate at (pi,0) point which is different from pure LiFeAs case. Based on the fact that in this material the perfect nesting exists between outer hole pocket and electron pocket and is dominated by dxy orbital, we argue that the superconductivity is actually associated with electron scattering from dxz/dyz orbital and the dxy orbital barely contributes to the superconducting pairing.