Interlayer hybridization promotes superconductivity in bilayer nickelates.

Abstract

Ruddlesden-Popper nickelates offer a route to high-temperature superconductivity beyond cuprates and iron pnictides. However, the electronic reconstruction enabling superconductivity in bilayer nickelates remains unresolved, largely due to the difficulty of directly probing superconducting samples. Here we stabilize superconducting (La,Pr)3Ni2O7 thin films with a protective capping layer, enabling direct X-ray absorption and resonant inelastic X-ray scattering measurements. Across insulating, superconducting and metallic samples, we track the evolution of in-plane and out-of-plane electronic states, spin and orbital excitations, and spin-density-wave order. Combined with theoretical analysis, our results show that itinerant d x 2 - y 2 states form the in-plane electronic backbone, whereas superconductivity emerges with coherent d z 2 -pz- d z 2 interlayer hybridization, together with suppressed static spin order and strongly damped spin excitations. Oxygen stoichiometry and epitaxial strain both tune this interlayer channel, placing superconductivity within a narrow regime of interlayer coherence and establishing a multiorbital picture of superconductivity in bilayer nickelates.