Optimization for epitaxial fabrication of infinite-layer nickelate superconductors

The discovery of nickelates superconductor creates exciting opportunities to unconventional superconductivity. However, its synthesis is challenging and only a few groups worldwide can obtain samples with zero-resistance. This problem becomes the major barrier for this field. From plume dynamics perspective, we found the synthesis of superconducting nickelates is a complex process and the challenge is twofold, i.e., how to stabilize an ideal infinite-layer structure Nd _0.8Sr _0.2NiO ₂, and then how to make Nd _0.8Sr _0.2NiO ₂ superconducting? The competition between perovskite Nd _0.8Sr _0.2NiO ₃ and Ruddlesden‑Popper defect phase is crucial for obtaining infinite-layer structure. Due to inequivalent angular distributions of condensate during laser ablation, the laser energy density is critical to obtain phase-pure Nd _0.8Sr _0.2NiO ₃. However, for obtaining superconductivity, both laser energy density and substrate temperature are very important. We also demonstrate the superconducting Nd _0.8Sr _0.2NiO ₂ epitaxial film is very stable in ambient conditions up to 512 days. Our results provide important insights for fabrication of superconducting infinite-layer nickelates towards future device applications.