Doubling the critical current density in superconducting FeSe_0.5Te_0.5 thin films by low temperature oxygen annealing

Iron chalcogenide superconducting thin films and coated conductors are attractive for potential high field applications at liquid helium temperature for their high critical current densities J_c, low anisotropies, and relatively strong grain couplings. Embedding flux pinning defects is a general approach to increase the in-field performance of superconductors. However, many effective pinning defects can adversely affect the zero field or self-field J_c, particularly in cuprate high temperature superconductors. Here, we report the doubling of the self-field J_c in FeSe_0.5Te_0.5 films by low temperature oxygen annealing, reaching ∼3 MA/cm². In-field performance is also dramatically enhanced. Our results demonstrate that low temperature oxygen annealing is a simple and cost-efficient post-treatment technique which can greatly help to accelerate the potential high field applications of the iron-based superconductors.