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Abstract Iron-based 1111-type superconductors display high critical temperatures and relatively high critical current densitiesJ_c. The typical approach to increasingJ_cis to introduce defects to control dissipative vortex motion. However, when optimized, this approach is theoretically predicted to be limited to achieving a maximumJ_cof only ∼30% of the depairing current densityJ_d, which depends on the coherence length and the penetration depth. Here we dramatically boostJ_cin SmFeAsO_1–xH_xfilms using a thermodynamic approach aimed at increasingJ_dand 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 quadrupledJ_dreaches 415 MA cm^–2, a value comparable to cuprates. Finally, by introducing defects using proton irradiation, we obtain highJ_cvalues in fields up to 25 T. We apply this method to other iron-based superconductors and achieve a similar enhancement of current densities. 

One of the most promising routes for achieving high critical currents in superconductors is to incorporate dispersed, non-superconducting nanoparticles to control the dissipative motion of vortices. However, these inclusions reduce the overall superconducting volume and can strain the interlaying superconducting matrix, which can detrimentally reduce Tc. Consequently, an optimal balance must be achieved between the nanoparticle density np and size d. Determining this balance requires garnering a better understanding of vortex–nanoparticle interactions, described by strong pinning theory. Here, we map the dependence of the critical current on nanoparticle size and density in (Y0.77, Gd0.23)Ba2Cu3O7−δ films in magnetic fields of up to 35 T and compare the trends to recent results from time-dependent Ginzburg–Landau simulations. We identify consistency between the field-dependent critical current Jc(B) and expectations from strong pinning theory. Specifically, we find that Jc ∝ B−α, where α decreases from 0.66 to 0.2 with increasing density of nanoparticles and increases roughly linearly with nanoparticle size d/ξ (normalized to the coherence length). At high fields, the critical current decays faster (∼B−1), suggesting that each nanoparticle has captured a vortex. When nanoparticles capture more than one vortex, a small, high-field peak is expected in Jc(B). Due to a spread in defect sizes, this novel peak effect remains unresolved here. Finally, we reveal that the dependence of the vortex creep rate S on nanoparticle size and density roughly mirrors that of α, and we compare our results to low-T nonlinearities in S(T) that are predicted by strong pinning theory.