Impact of Polarity Mismatch in Infinite-Layer Nickelates.

The recent discovery of superconductivity in infinite-layer Sr-doped NdNiO grown on SrTiO(001) provides a new platform to explore the conducting mechanism of unconventional superconductors. However, the electronic structure of infinite-layer nickelates remains controversial. In this paper, we systematically compare the structural and electronic properties of NdNiO films grown on SrTiO and LaAlO substrates using first-principles calculations. Our results show that the lattice reconstruction accompanied by electronic reconstruction occurs in nickelate films on both substrates. Although both heterostructures (HSs) are conducting at the interface, the SrTiO-based HS shows distinct atomic displacement in the interfacial TiO layer and significant electron accumulation deep into three SrTiO layers below the interface, while the LaAlO-based HS shows negligible atomic displacement and electron localization in the interfacial AlO layer, reflecting the impact of polarity mismatch on the electronic structure. Further, Wannier function calculations reveal that the interface stress has no obvious effect on the splitting energy and hopping integral between Ni 3 and Nd-layer orbitals. Although the hybridization between Ni 3 and Nd 5 orbitals is tiny, the hybridization between the Ni 3 orbital and an itinerant interstitial (IIS) orbital is significantly strong in both cases, suggesting that the IIS orbital may play a critical role in the superconductivity of nickelates.