Electronic Structures across the Superconductor-Insulator Transition at La2.85Pr0.15Ni₂O₇/SrLaAlO₄ Interfaces

Interfacial superconductivity discovered in bilayer nickelate heterostructures opens new avenues for effective tunability and control. Here, we report the superconductor-insulator transition in La2.85Pr0.15Ni₂O₇/SrLaAlO₄ interfaces, with corresponding electronic structures revealed using synchrotron low-temperature X-ray absorption spectroscopy (XAS) and X-ray linear dichroism (XLD). In addition to the valence states of each element within the films determined by XAS, XLD at the O K edge pre-peak reveals hybridizations involving both 2pz and 2pₓ/2py orbitals, which are concomitantly suppressed upon oxygen loss. Intriguingly, such oxygen loss that eliminates superconductivity, induces a qualitative XLD change at the Ni L₂ edge, implying significant transformations among 3d_x² _-y² and 3d_z² energy bands near the Fermi level. Our findings establish an element- and orbital-resolved electronic framework for the origin of superconductivity.