Signatures of ambient pressure superconductivity in thin film LaNiO.

Recently, the bilayer nickelate LaNiO has been discovered as a new superconductor with transition temperature T near 80 K under high pressure. Despite extensive theoretical and experimental work to understand the nature of its superconductivity, the requirement of extreme pressure restricts the use of many experimental probes and limits its application potential. Here we present signatures of superconductivity in LaNiO thin films at ambient pressure, facilitated by the application of epitaxial compressive strain. The onset T varies roughly from 26 to 42 K, with higher T values correlating with smaller in-plane lattice constants. We observed the co-existence of other Ruddlesden-Popper phases within the films and dependence of transport behaviour with ozone annealing, suggesting that the observed low zero resistance T of around 2 K can be attributed to stacking defects, grain boundaries and oxygen stoichiometry. This finding initiates numerous opportunities to stabilize and study superconductivity in bilayer nickelates at ambient pressure, and to facilitate the broad understanding of the ever-growing number of high temperature and unconventional superconductors in the transition metal oxides.