Electron Microscopy and Spectroscopy Investigation of Atomic, Electronic, and Phonon Structures of NdNiO₂/SrTiO₃ Interface

Abstract The infinite-layer nickelates, proposed as analogs to superconducting cuprates, provide a promising platform for exploring the mechanisms of unconventional superconductivity. However, the superconductivity has been exclusively observed in thin films under atmospheric pressure, underscoring the critical role of the heterointerface. Here, we employed the advanced scanning transmission electron microscopy-electron energy loss spectroscopy technique to thoroughly investigate the atomic configuration, layer-resolved electronic states and phonon modes across the NdNiO 2 /SrTiO 3 interface. Our findings reveal that interfacial Sr diffusion drives the formation of a p-type interface, thus facilitating hole doping into the oxygen and nickel bands. Notably, a pronounced redshift of the highest-energy optical phonon of NdNiO 2 (∼ 78 meV) is observed at the interface, predominantly induced by Sr diffusion and epitaxial strain. Our work demonstrates that interfacial Sr diffusion and epitaxial strain can reconfigure the electronic and phonon structures at the p-type interface, offering critical insights for elucidating the superconducting mechanisms in infinite-layer nickelates.