Electronic structure of square planar nickelates revisited: relationship to cuprates*

Based on ab initio calculations, a close connection between the Ruddlesden Popper layered nickelates and high temperature superconducting cuprates is established. The electronic structure of La$_4$Ni$_3$O$_8$ and La$_3$Ni$_2$O$_6$ is similar to that of cuprates not only in terms of filling of $d$-levels (close to $d^9$) but also because they show Ni$^{1+}$(S=1/2)/Ni$^{2+}$(S=0) stripe ordering. The Ni$^{2+}$ ions are in a low-spin configuration (S=0) yielding an antiferromagnetic arrangement of Ni$^{1+}$ (pseudo Cu$^{2+}$) S=1/2 ions like the long-sought spin-1/2 antiferromagnetic insulator analog of the cuprate parent materials. The analogy extends further with the main contribution to the bands near the Fermi energy coming from hybridized Ni-$d_{x^2-y^2}$ and O-$p$ states [1]. These results bring renewed justification that layered nickelates of this type are cuprate analog systems that are promising for studying the interplay between structure, magnetism, and superconductivity. [1] A. S. Botana, V. Pardo, W. E. Pickett and M. R. Norman. Phys. Rev. B 94, 081105(R)(2016)