Correlated electronic structures and unconventional superconductivity in bilayer nickelate heterostructures

Abstract

ABSTRACT The recent discovery of ambient-pressure superconductivity in thin-film bilayer nickelates opens new possibilities for investigating electronic structures in this new class of high-transition-temperature ($T_\mathrm{c}$) superconductors. Here, we construct a realistic multi-orbital Hubbard model for the thin-film system based on structural parameters integrating scanning transmission electron microscopy measurements and ab initio calculations. The interaction parameters are calculated with the constrained random phase approximation (cRPA). Density functional theory (DFT) plus cluster dynamical mean-field theory (CDMFT) calculations, with cRPA-calculated on-site Coulomb repulsive $U$ and experimentally measured electron filling $n$, quantitatively reproduce Fermi surfaces from angle-resolved photoemission spectroscopy experiments. The distinct Fermi surface topology from simple DFT+$U$ results features the indispensable role of correlation effects. Based upon the correlated electronic structures, a modified random-phase-approximation (RPA) approach yields a pronounced $s^{\pm }$-wave pairing instability, due to the strong spin fluctuations originating from the Fermi surface nesting between bands with predominantly $d_{z^{2}}$ characters. Our findings highlight the quantitative effectiveness of the DFT+cRPA+CDMFT approach that precisely determines correlated electronic structure parameters without fine-tuning. The revealed intermediate correlation effect may explain the same order-of-magnitude onset $T_\mathrm{c}$ observed both in pressured bulk and strained thin-film bilayer nickelates.