Superconductivity in trilayer Nickelates*

Infinite-layer NdNiO₂ has recently been shown to exhibit superconductivity upon Sr-doping [1].
For doped NdNiO₂, it is believed that pairing in the superconducting phase occurs mainly in the Ni d_x²-y² band [2]. In contrast to the Cu-based high-T_c superconductors, the parent RNiO₂ (R=La, Nd) phases are not insulating-in spite of containing Ni¹⁺: d⁹ ions-due to the appearance of rare-earth 5d-bands in the Fermi surface (FS) [2]. RNiO₂ materials are members of a larger family of layered nickelates R_n+1(NiO₂)_nO₂ with n= 2, 3, ... ∞ determining the number of NiO₂ planes along the c-axis. Here, we consider alternate trilayer compounds [3] where the rare-earth bands are pushed away from the FS which only includes three Ni- d_x²-y² sheets. We study superconductivity in these compounds in several doping regimes using a t-J model. We compare and contrast the pairing instabilities in the tri- and infinite-layer cases.

[1] D. Li, K. et al, Nature 572, 624 (2019).
[2] X. Wu et al, arXiv:1909.03015.
[3] J. Zhang et al, Nature Physics 13, 864 (2017).