Nodal superconductivity in FeS: Evidence from quasiparticle heat transport

Abstract

We report low-temperature heat transport measurements on superconducting iron sulfide FeS with ${T}_{c}\ensuremath{\approx}5$ K, which has the same crystal structure and similar electronic band structure to the superconducting iron selenide FeSe. In zero magnetic field, a significant residual linear term ${\ensuremath{\kappa}}_{0}/T$ is observed. At low field, ${\ensuremath{\kappa}}_{0}/T$ increases rapidly with increasing field. These results suggest a nodal superconducting gap in FeS. We compare it with the sister compound FeSe and other iron-based superconductors with nodal gaps.