Electronic structure, magnetic correlations, and superconducting pairing tendencies in the Ruddlesden-Popper layered nickelates

Nickelates have continued to surprise due to the discovery of superconductivity in some nickelates under pressure. Here, using density functional theory (DFT) and random phase approximation (RPA) techniques, we found that Ruddlesden-Popper layered nickelates La_𝑚+1Ni_𝑚O_3𝑚+1 (𝑚=1 to 6) display many similarities, but they also show differences [1]. Similar to bilayer and trilayer nickelates [2,3], in-plane interorbital hopping of e_g orbitals was also found to be large in high-order nickelates, and it will increase as the layer number m increases. In contrast to the dominant 𝑠±-wave state driven by spin fluctuations in the bilayer La₃Ni₂O₇[4] and trilayer La₄Ni₃O₁₀[3], both 𝑠±-wave and 𝑑𝑥2−𝑦2-wave channels are strongly competing in the high-order nickelates [1]. In general, at the level of the random-phase approximation treatment, the superconducting transition temperature 𝑇𝑐 decreases in stoichiometric bulk systems from the bilayer La₃Ni₂O₇to the six-layer La₇Ni₆O₁₉, despite the 𝑚-dependent dominant pairing. Moreover, we also found quite interesting and complex magnetic correlations in those layered nickelates by studying magnetic susceptibility. Finally, we will briefly introduce our recent results related to the newly reported single-layer bilayer stacking nickelate La₅Ni₃O₁₁ superconductor [5].