Ordering and multiple phase transitions in ultra-thin nickelate superlattices

We interpret via advanced ab initio calculations the multiple phase transitions observed recently in ultra-thin LaNiO${}_3$/LaAlO${}_3$ superlattices. The ground state is insulating, charge-ordered, and antiferromagnetic due to concurrent structural distortion and weak valency disproportionation. We infer distinct transitions at 40 K and 150 K, respectively, from antiferromagnetic order to moment disorder, and from structurally-dimerized insulator to an undistorted metallic Pauli paramagnet (exhibiting a cuprate-like Fermi surface). The results are in satisfactory agreement with experiment.