Superconductivity in infinite-layer nickelate La 1-x Ca x NiO 2 thin films.

We report the observation of superconductivity in infinite-layer Ca-doped LaNiO ₂ (La _{1- x} Ca _x NiO ₂ ) thin films and construct their phase diagram. Unlike the metal-insulator transition in Nd- and Pr-based nickelates, the undoped and underdoped La _{1- x} Ca _x NiO ₂ thin films are entirely insulating from 300 K down to 2 K. A superconducting dome is observed at 0.15 < x < 0.3 with weakly insulating behavior at the overdoped regime. Moreover, the sign of the Hall coefficient R _H changes at low temperature for samples with a higher doping level. However, distinct from the Nd- and Pr-based nickelates, the R _H -sign-change temperature remains at around 35 K as the doping increases, which begs further theoretical and experimental investigation to reveal the role of the 4f orbital to the (multi)band nature of the superconducting nickelates. Our results also emphasize a notable role of lattice correlation on the multiband structures of the infinite-layer nickelates.