Hierarchical structure of primary and hybridization-induced superconducting correlations in bilayer nickelates

TL;DR

This study uncovers a hierarchical pairing mechanism in bilayer nickelates, showing how orbital hybridization influences superconducting correlations and supports an $s_{\u2215}$ state robust to Fermi-surface changes.

Contribution

It reveals a hierarchical structure of pairing interactions and correlations in bilayer nickelates, emphasizing the role of orbital hybridization in shaping superconductivity.

Findings

Primary pairing from Ni $3d_{z^2}$ orbitals due to bonding--antibonding splitting

Orbital hybridization redistributes correlations to the $d_{x^2-y^2}$ channel

The $s_{}$ state remains stable despite Fermi-surface topology variations

Abstract

High-pressure superconductivity in the bilayer nickelate La$_3$Ni$_2$O$_7$, with a transition temperature approaching 80 K, has stimulated intense debate regarding its microscopic origin. Although an $s_{\pm}$ gap symmetry has been widely proposed, the electronic degrees of freedom responsible for pairing remain unsettled. Here we investigate a bilayer two-orbital Hubbard model using the variational Monte Carlo method and reveal a hierarchical pairing structure in bilayer nickelates. The primary pairing interaction originates from the bonding--antibonding splitting of the Ni $3d_{z^2}$ orbitals, while orbital hybridization redistributes superconducting correlations to the $d_{x^2-y^2}$ channel despite its weak intrinsic pairing interaction. This distinction between the origin of pairing and resulting superconducting correlations explains why the two orbital channels exhibit comparable long-range correlations. The resulting $s_{\pm}$ state is robust against changes in Fermi-surface topology. These results reconcile apparently competing theoretical scenarios and provide a comprehensive understanding, highlighting the distinctive role of orbital hybridization in multilayer correlated superconductors.