Orbital Polarization in Strained LaNiO$_{3}$: Structural Distortions and Correlation Effects

TL;DR

This paper theoretically investigates how epitaxial strain influences orbital polarization in LaNiO3 films, considering structural distortions and electron correlations, and compares findings with recent experimental results.

Contribution

It combines electronic structure and dynamical mean-field theory to analyze the effects of strain and correlations on orbital polarization in LaNiO3, highlighting the role of Hund's coupling.

Findings

Hund's rule coupling reduces orbital polarization

Tensile strain induces sizable orbital polarization

Full orbital polarization remains challenging in LaNiO3

Abstract

Transition-metal heterostructures offer the fascinating possibility of controlling orbital degrees of freedom via strain. Here, we investigate theoretically the degree of orbital polarization that can be induced by epitaxial strain in LaNiO$_3$ films. Using combined electronic structure and dynamical mean-field theory methods we take into account both structural distortions and electron correlations and discuss their relative influence. We confirm that Hund's rule coupling tends to decrease the polarization and point out that this applies to both the $d^8\underline{L}$ and $d^7$ local configurations of the Ni ions. Our calculations are in good agreement with recent experiments, which revealed sizable orbital polarization under tensile strain. We discuss why full orbital polarization is hard to achieve in this specific system and emphasize the general limitations that must be overcome to achieve this goal.