Geometric effects in the infinite-layer nickelates
Fabio Bernardini, Andrea Bosin, A. Cano
Abstract
Geometric effects in the infinite-layer nickelates $R{\mathrm{NiO}}_{2}$ associated with the relative size of the $R$-site atom are investigated via first-principles calculations. We consider, in particular, the prospective ${\mathrm{YNiO}}_{2}$ material to illustrate the impact of these effects. Compared to ${\mathrm{LaNiO}}_{2}$, we find that the $\text{La}\ensuremath{\rightarrow}\text{Y}$ substitution is equivalent to a pressure of 19 GPa and that the presence of topotactic hydrogen can be precluded. However, the electronic structure of ${\mathrm{YNiO}}_{2}$ departs from the cupratelike picture due to an increase in both self-doping effect and ${e}_{g}$ hybridization. Furthermore, we find that geometric effects introduce a quantum critical point in the $R{\mathrm{NiO}}_{2}$ series. This implies a $P4/mmm\ensuremath{\leftrightarrow}I4/mcm$ structural transformation associated to an ${A}_{3}^{+}$ normal mode, according to which the oxygen squares undergo an in-plane rotation around Ni that alternates along $c$. We find that such an ${A}_{3}^{+}$-mode instability has a generic character in the infinite-layer nickelates and can be tuned via either the effective $R$-site atom size or epitaxial strain.