Effect of S doping on the critical current density and vortex dynamics in FeSe single crystal

We report a detailed study of the S doping effect on the critical current density, Jc, and vortex pinning in FeSe single crystal. The value of Jc for FeSe is found to be enhanced from ∼4 × 104 A/cm2 at 2 K under self-field to ∼6 × 104 A/cm2 after S doping. Similar field decaying rates of Jc and the absence of fishtail effect in both FeSe and FeSe0.86S0.14 single crystals indicate the similar pinning mechanism for both crystals, i.e., the dominance of strong point-like pinning from nanometer-sized defects or imperfections. On the other hand, vortex dynamics study manifests that the S doping reduces the size of flux bundle and enhances the effective pinning energy, which may come from the lattice distortion caused by S doping.