J (4.2 K, 31.2 T) beyond 1 kA/mm of a ~3.2 μm thick, 20 mol% Zr-added MOCVD REBCO coated conductor.

A main challenge that significantly impedes REBaCuO (RE = rare earth) coated conductor applications is the low engineering critical current density J because of the low superconductor fill factor in a complicated layered structure that is crucial for REBaCuO to carry supercurrent. Recently, we have successfully achieved engineering critical current density beyond 2.0 kA/mm at 4.2 K and 16 T, by growing thick REBaCuO layer, from ∼1.0 μm up to ∼3.2 μm, as well as controlling the pinning microstructure. Such high engineering critical current density, the highest value ever observed so far, establishes the essential role of REBaCuO coated conductors for very high field magnet applications. We attribute such excellent performance to the dense c-axis self-assembled BaZrO nanorods, the elimination of large misoriented grains, and the suppression of big second phase particles in this ~3.2 μm thick REBaCuO film.