Theoretical investigation of superconductivity in trilayer square-planar nickelates

The discovery of superconductivity in Sr-doped NdNiO₂ is a crucial breakthrough in the long pursuit for nickel oxide materials with electronic and magnetic properties similar to those of the cuprates. NdNiO₂ is the infinite-layer member of a family of square-planar nickelates with general chemical formula Rₙ₊₁NiₙO₂ₙ₊₂ (R = La, Pr, Nd, n=2,3,...∞). In this Rapid Communication, we investigate superconductivity in the trilayer member of this series (R₄Ni₃O₈) using a combination of first-principles and t-J model calculations. R₄Ni₃O₈ compounds resemble cuprates more than RNiO₂ materials in that only Ni-d_x²-y² bands cross the Fermi level, they exhibit a largely reduced charge transfer energy, and as a consequence superexchange interactions are significantly enhanced. We find that the superconducting instability in doped R₄Ni₃O₈ compounds is considerably stronger with a maximum gap about four times larger than that in Sr0.2Nd0.8NiO₂.