Electron microscopy and spectroscopy investigation of atomic, electronic, and phonon structures of NdNiO2/SrTiO3 interface

TL;DR

This study uses advanced electron microscopy and spectroscopy to analyze the atomic, electronic, and phonon structures at the NdNiO2/SrTiO3 interface, revealing elemental intermixing and strain effects crucial for understanding nickelate superconductivity.

Contribution

It provides detailed atomic and electronic insights into the NdNiO2/SrTiO3 interface, highlighting the roles of elemental diffusion and strain in influencing superconducting properties.

Findings

Sr atom diffusion causes hole doping at the interface.

Epitaxial strain leads to a redshift in optical phonons.

Interface effects are dominated by elemental intermixing and strain.

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 under atmospheric pressure has only been observed in thin films, indicating the heterointerface is essential. Here, we employed the advanced Scanning Transmission Electron Microscopy-Electron Energy Loss Spectroscopy (STEM-EELS) technique to thoroughly investigate the atomic configuration, layer-resolved electronic states and phonon across the NdNiO2/SrTiO3 interface. We found the Sr atoms diffusion at the interface, which results in hole doping into oxygen and nickel band to form a p-type interface. A pronounced redshift of the highest-energy optical phonon (HEOP) of NdNiO2 (~78 meV) is observed at the interface, which is primarily attributed to the epitaxial strain. Our work clarifies that the effects of the interface on electron and phonon states are mainly due to elemental intermixing and epitaxial strain, which could lay the foundation for future investigations into superconducting mechanisms of infinite-layer nickelates.