Enhancement of the critical current by surface irregularities in Fe-based superconductors

The critical current \(I_c\) of single crystals of the iron pnictide superconductor BaFe\(_2\)(As\(_{1-x}\)P\(_x\))\(_2\), has been studied through measurements of magnetic hysteresis cycles. We show that the introduction of surface irregularities in the \(\mu\)m scale significantly increase \(I_c\), primarily near the irreversibility magnetic field \(H_{irr}\), where the surface currents are the main contribution to \(I_c\). Such an increase is consistent with a theoretical estimate for the maximum non-dissipative current that a rough surface can sustain, based on Mathieu-Simon continuum theory for the vortex state.