Electronic Structure of Ruddlesden-Popper Nickelates from First-Principles Calculations

High-critical temperature (T_c) superconductivity in the cuprates remains a defining problem in condensed matter physics. One strategy to tackle this problem has been the study of alternative transition metal oxides with similar structure and 3d electron count. With nickel situated immediately next to copper in the periodic table, nickelates have long been prime targets in this context. The realization of the promise of nickelates for superconductivity came in 2019 when superconductivity was observed in infinite-layer nickelates with a T_c ∼15 K. In these materials, Ni¹⁺ (d⁹) forms square planar NiO₂ layers, closely resembling the cuprates structurally and in terms of electron count. More recently, signatures of superconductivity have also been observed in the Ruddlesden–Popper bilayer (n=2) and trilayer (n=3) nickelates under pressure with much higher T_cs. Unlike the infinite-layer nickelates, the RPs have n-perovskite-like layers and a d^7+1/n electron configuration. Here, we analyze the electronic structure of the RP bilayer and trilayer nickelates in connection to superconductivity using first-principles calculations.