Nodal Superconductivity Coexists With Low-Moment Static Magnetism In Single-Crystalline Tetragonal Fes: A Muon Spin Relaxation And Rotation Study

We report muon spin relaxation and rotation (mu SR) measurements on hydrothermally grown single crystals of superconducting tetragonal FeS, which help to clarify the controversial magnetic state and superconducting gap symmetry of this compound. mu SR time spectra were obtained from 280 K down to 0.025 K in zero field (ZF) and applied fields up to 75 mT. In ZF, the observed loss of initial asymmetry (signal amplitude) and increase of depolarization rate Lambda(ZF) below 13 K indicate the onset of static magnetism, which coexists with superconductivity below T-c. TF mu SR results indicate a linear temperature dependence of the superfluid density at low temperature, consistent with nodal superconductivity. The s+d-wave model gives the best fit to the observed temperature and field dependencies, and yields an in-plane penetration depth value lambda(ab) (T=0) = 241(3) nm.