Abstract
Iron-based 1111-type superconductors display high critical temperatures and relatively high critical current densities J(c). The typical approach to increasing J(c) is to introduce defects to control dissipative vortex motion. However, when optimized, this approach is theoretically predicted to be limited to achieving a maximum J(c) of only ∼30% of the depairing current density J(d), which depends on the coherence length and the penetration depth. Here we dramatically boost J(c) in SmFeAsO(1-x)H(x) films using a thermodynamic approach aimed at increasing J(d) and 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 J(d) reaches 415 MA cm(-2), a value comparable to cuprates. Finally, by introducing defects using proton irradiation, we obtain high J(c) values in fields up to 25 T. We apply this method to other iron-based superconductors and achieve a similar enhancement of current densities.