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

The discovery of 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 ± 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 tendency originates from the bonding–antibonding splitting of the Ni 3d_z² 3 d z 2 orbitals, while orbital hybridization redistributes superconducting correlations to the d_x²-y² d x 2 − y 2 channel despite its weak intrinsic pairing tendency. This distinction between the origin of pairing and the resulting superconducting correlations explains why the two orbital channels exhibit comparable long-range correlations. The resulting s ± 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.