A route for a strong increase of critical current in nanostrained iron-based superconductors

The critical temperature T(c) and the critical current density J(c) determine the limits to large-scale superconductor applications. Superconductivity emerges at T(c). The practical current-carrying capability, measured by J(c), is the ability of defects in superconductors to pin the magnetic vortices, and that may reduce T(c). Simultaneous increase of T(c) and J(c) in superconductors is desirable but very difficult to realize. Here we demonstrate a route to raise both T(c) and J(c) together in iron-based superconductors. By using low-energy proton irradiation, we create cascade defects in FeSe(0.5)Te(0.5) films. T(c) is enhanced due to the nanoscale compressive strain and proximity effect, whereas J(c) 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 J(c) enhancement is achieved in both parallel and perpendicular magnetic fields to the film surface.