Critical current density and vortex pinning in tetragonal FeS1-xSex (x=0,0.06)

We report critical current density (J(c)) in tetragonal FeS single crystals, similar to iron-based superconductors with much higher superconducting critical temperatures (T-c). The Jc is enhanced three times by 6% Se doping. We observe scaling of the normalized vortex pinning force as a function of reduced field at all temperatures. Vortex pinning in FeS and FeS0.94Se0.06 shows contribution of core-normal surfacelike pinning. Reduced temperature dependence of J(c) indicates that dominant interaction of vortex cores and pinning centers is via scattering of charge carriers with reduced mean free path (delta l), in contrast to KxFe2-ySe2 where spatial variations in T-c (delta T-c) prevails.