Coexistence of low-moment magnetism and superconductivity in tetragonal FeS and suppression of T_c under pressure

The family of iron-based superconductors has recently acquired a new member material, FeS. Theoretically, this compound has been shown to have electronic structure similar to that of the superconducting FeSe. However, contradictory ground states have been predicted for FeS. In this work, a collaboration of authors from Switzerland and Germany use muon spin rotation and relaxation to show that weak-moment magnetism microscopically coexists with bulk superconductivity. Additionally, in contrast with some earlier studies, the results suggest a fully gapped superconducting state of FeS.