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

TL;DR

This study demonstrates that introducing surface irregularities in Fe-based superconductors significantly enhances their critical current, especially near the irreversibility field, aligning with theoretical predictions for vortex surface currents.

Contribution

It provides experimental evidence that surface irregularities can increase critical current in Fe-based superconductors, supported by theoretical estimates.

Findings

Surface irregularities significantly increase critical current near H_irr.

The enhancement aligns with Mathieu-Simon theory for vortex surface currents.

Surface roughness can be used to optimize superconductor performance.

Abstract

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.