Insulating Pockets in Metallic LaNiO3

LaNiO3 is locally distorted to orthorhombic at room temperature, and further to monoclinic at 200 K from globally rhombohedral structure. Such local rhombohedral phase hosts uncorrelated singlets, resulting in a pseudogap. Consequently, a crossover emerges at the rare earth nickelates phase diagram from fully gapped monoclinic long-range order to pseudogap monoclinic short-range order, as the radius of rare earth ions increases.