Thickness-Dependent Interface Polarity in Infinite-Layer Nickelate Superlattices
Chao Yang, R. A. Ortiz, Yi Wang, Wilfried Sigle, Hongguang Wang, E. Benckiser, B. Keimer, Peter A. van Aken
Abstract
High Resolution Image Download MS PowerPoint Slide The interface polarity plays a vital role in the physical properties of oxide heterointerfaces because it can cause specific modifications of the electronic and atomic structure. Reconstruction due to the strong polarity of the NdNiO 2 /SrTiO 3 interface in recently discovered superconducting nickelate films may play an important role, as no superconductivity has been observed in the bulk. By employing four-dimensional scanning transmission electron microscopy and electron energy-loss spectroscopy, we studied effects of oxygen distribution, polyhedral distortion, elemental intermixing, and dimensionality in NdNiO 2 /SrTiO 3 superlattices grown on SrTiO 3 (001) substrates. Oxygen distribution maps show a gradual variation of the oxygen content in the nickelate layer. Remarkably, we demonstrate thickness-dependent interface reconstruction due to a polar discontinuity. An average cation displacement of ∼0.025 nm at interfaces in 8NdNiO 2 /4SrTiO 3 superlattices is twice larger than that in 4NdNiO 2 /2SrTiO 3 superlattices. Our results provide insights into the understanding of reconstructions at NdNiO 2 /SrTiO 3 polar interfaces.