Electronic Structure of Higher-order Ruddlesden-Popper Nickelates

Nickelates have long been considered as cuprate analogs and have been extensively studied for their potential for high-temperature superconductivity. Indeed, the Ruddlesden-Popper nickelates (R_n+1Ni_nO_3n+1, R= rare-earth) have long been viewed as close cousins of the cuprates and it was recently found that the n = 5 compound (when chemically reduced into the square-planar form) exhibits superconductivity [1].  Here, we analyze the electronic structure of La-based higher-n (n=4-6) RP nickelates and scrutinize their similarities and differences with cuprates using first-principles calculations. Our results show large hole-like Fermi surfaces with dx²−y² character that closely resemble those of optimally hole-doped cuprates. For higher n values, extra bands with dz² orbital character appear and increase the 3D-like character of the electronic structure.  These aspects highlight that this RP series can provide a means to modify the electronic ground states of nickelates by tuning their dimensionality. With their similarities and differences with cuprates, this new family of materials can potentially shed light into the physics of copper-based oxides.