Abstract

The critical temperature Tc and the critical current density Jc determine the limits to large-scale superconductor applications. Superconductivity emerges at Tc. The practical current-carrying capability, measured by Jc, is the ability of defects in superconductors to pin the magnetic vortices, and that may reduce Tc. Simultaneous increase of Tc and Jc in superconductors is desirable but very difficult to realize. Here we demonstrate a route to raise both Tc and Jc together in iron-based superconductors. By using low-energy proton irradiation, we create cascade defects in FeSe0.5Te0.5 films. Tc is enhanced due to the nanoscale compressive strain and proximity effect, whereas Jc is doubled under zero field at 4.2 K through strong vortex pinning by the cascade defects and surrounding nanoscale strain. At 12 K and above 15 T, one order of magnitude of Jc enhancement is achieved in both parallel and perpendicular magnetic fields to the film surface.

Highlights

  • The critical temperature Tc and the critical current density Jc determine the limits to large-scale superconductor applications

  • Transmission electron microscopy (TEM) cross-sectional images along the ion traces in 230 MeV Au-irradiated Bi2Sr2CaCu2Ox single crystals showed several types of morphology of defects from parallel columnar defects to disordered cascade defects, as the ion energy is decreased in the crystals[22]

  • In single crystals of ironbased superconductors, it has been found that ion irradiations, as a whole, improve Jc and its Jc enhancements persist up to much higher fluencies than in cuprate superconductors, Tc is suppressed with increasing irradiation doses[27,28,29]

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Summary

Introduction

The critical temperature Tc and the critical current density Jc determine the limits to large-scale superconductor applications. The irradiated iron-based superconducting films have not shown as positive effects as found in single crystals[30,31]. Through extensive TEM characterization, we found nanoscale strain modulations in FST films irradiated with 1 Â 1015 p cm–2 dose of 190 keV proton.

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