Quadrupling the depairing current density in the iron-based superconductor SmFeAsO1–xHx

Iron-based 1111-type superconductors display high critical temperatures and relatively high critical current densities Jc. The typical approach to increasing Jcis to introduce defects to control dissipative vortex motion. However, when optimized, this approach is theoretically predicted to be limited to achieving a maximum Jcof only ∼30% of the depairing current density Jd, which depends on the coherence length and the penetration depth. Here we dramatically boost Jcin SmFeAsO1–xHxfilms using a thermodynamic approach aimed at increasing Jdand incorporating vortex pinning centres. Specifically, we reduce the penetration depth, coherence length and critical field anisotropy by increasing the carrier density through high electron doping using H substitution. Remarkably, the quadrupled Jdreaches 415 MA cm–2, a value comparable to cuprates. Finally, by introducing defects using proton irradiation, we obtain high Jcvalues in fields up to 25 T. We apply this method to other iron-based superconductors and achieve a similar enhancement of current densities.