Critical current density and vortex pinning in tetragonal   FeS$_{1-x}$Se$_{x}$ ($x=0,0.06$)
  We report critical current density ($J_c$) in tetragonal FeS single crystals, similar to iron based superconductors with much higher superconducting critical temperatures ($T_{c}$'s). The $J_c$ is enhanced 3 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 FeS$_{0.94}$Se$_{0.06}$ shows contribution of core-normal surface-like 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$$l$), in contrast to K$_x$Fe$_{2-y}$Se$_2$ where spatial variations in $T_{c}$ ($\delta$$T_{c}$) prevails. 
Aifeng Wang, Lijun Wu, V. N. Ivanovski, J. B. Warren, Jianjun Tian,   Yimei Zhu and C. Petrovic
cond-mat.supr-con cond-mat.mtrl-sci cond-mat.str-el