Epitaxially strained ultrathin LaNiO$_3$/LaAlO$_3$ and LaNiO$_3$/SrTiO$_3$ superlattices: a density functional theory + $U$ study

TL;DR

This study uses density functional theory with a Hubbard U correction to explore how epitaxial strain and electronic correlations influence the magnetic and orbital order in ultrathin LaNiO3-based superlattices, revealing phase transitions between insulating and metallic states.

Contribution

It provides a detailed first-principles analysis of strain and correlation effects on nickelate superlattices, highlighting the dependence of their ground states on these parameters, which was less understood before.

Findings

Weakly correlated regimes favor charge-disproportionated insulating states.

Strong correlations or large tensile strain stabilize ferromagnetic states with Jahn-Teller orbital order.

Polar interfaces significantly influence the electronic structure in LaNiO3/SrTiO3 superlattices.

Abstract

By employing first-principles electronic structure calculations we investigate nickelate superlattices [LaNiO$_3$]$_1$/[LaAlO$_3$]$_1$ and [LaNiO$_3$]$_1$/[SrTiO$_3$]$_1$ with (001) orientation under epitaxial tensile strain. Within density functional theory augmented by mean-field treatement of on-site electronic correlations, the ground states show remarkable dependence on the correlation strength and the strain. In the weakly and intermediately correlated regimes with small epitaxial strain, the charge-disproportionated insulating states with antiferromagneitc order is favored over the other orbital and spin ordered phases. On the other hand, in the strongly correlated regime or under the large tensile strain, ferromagnetic spin states with Jahn-Teller orbital order become most stable. The effect from polar interfaces in LaNiO$_3$]$_1$/[SrTiO$_3$]$_1$ is found to be noticeable in our single-layered geometry. Detailed discussion is presented in comparison with previous experimental and theoretical studies.