Antiferromagnetic spin fluctuations in LiFeAs observed by neutron scattering

We report neutron inelastic-scattering measurements on the stoichiometric iron-based superconductor LiFeAs. We find evidence for (i) magnetic scattering consistent with strong antiferromagnetic fluctuations and (ii) an increase in intensity in the superconducting state at low energies, similar to the resonant magnetic excitation observed in other iron-based superconductors. The results do not support a recent theoretical prediction of spin-triplet $p$-wave superconductivity in LiFeAs but instead suggest that the mechanism of superconductivity is similar to that in the other iron-based superconductors.