Ordering and multiple phase transitions in ultrathin nickelate superlattices

We interpret via advanced ab initio calculations the multiple phase transitions observed recently in ultrathin LaNiO3/LaAlO3 superlattices. The ground state is insulating, weakly charge ordered, and antiferromagnetic due to concurrent structural distortion and weak valency disproportionation. We infer distinct transitions around 50 K and 110 K, respectively, from antiferromagnetic order to moment disorder, and from a structurally dimerized insulator to an undistorted metallic Pauli paramagnet (exhibiting a cupratelike Fermi surface). The results are in satisfactory agreement with experimental results.