Orbital hybridization and its impact on superconductivity in infinite-layer nickelates

Infinite-layer nickelates have long been viewed as cuprate analogues, yet whether the Ni-d_x²-y² orbital hybridizes with other orbitals has been under intense debate, and if the hybridization exists, its impact on superconductivity in infinite-layer nickelates has received little attention. Building upon recent photoemission spectroscopic measurements, we combine ab initio and many-body calculations to show that infinite-layer nickelates have a three-dimensional (3D) Fermi surface, where the k_z dispersion arises from hybridization between Ni-d_x²-y² orbital and an interstitial-s orbital. This hybridization enforces van Hove singularities (VHS) on the Fermi surface and places infinite-layer nickelate in the “overdoped” regime relative to cuprates. By developing a random-phase-approximation plus dynamical-mean-field-theory approach (RPA+DMFT), we solve the superconducting gap equation across a wide range of interaction strengths. We find that in infinite-layer nickelates, at the “overdoped” concentration relative to cuprates, the observed 3D Fermi surface enhances superconductivity compared to a 2D single-orbital Fermi surface lacking VHS. The enhancement arises from the proximity to an antiferromagnetic instability driven by VHS, which amplifies spin fluctuations. Our work not only provides a beyond RPA-based weak-coupling approach for calculating superconductivity, but also highlights the critical role of VHS in infinite-layer nickelates. Reference: arXiv 2504.18778.