Breathing distortions in the metallic, antiferromagnetic phase of LaNiO$_3$

TL;DR

This study investigates the structural and magnetic properties of LaNiO$_3$ using density functional theory, revealing near-degenerate structures, breathing distortions, and antiferromagnetic order consistent with experimental observations of coexistence of magnetism and metallicity.

Contribution

It provides a detailed theoretical analysis of the structural and magnetic instabilities in LaNiO$_3$, highlighting the role of breathing distortions and proximity to a structural quantum critical point.

Findings

Multiple structures with different Glazer tilts are nearly degenerate.

Breathing distortions significantly lower the energy, favoring antiferromagnetic order.

The phases are semimetallic with small Fermi pockets, matching experimental data.

Abstract

I study the structural and magnetic instabilities in LaNiO$_3$ using density functional theory calculations. From the non-spin-polarized structural relaxations, I find that several structures with different Glazer tilts lie close in energy. The $Pnma$ structure is marginally favored compared to the $R\overline{3}c$ structure in my calculations, suggesting the presence of finite-temperature structural fluctuations and a possible proximity to a structural quantum critical point. In the spin-polarized relaxations, both structures exhibit the $\uparrow\!\!0\!\!\downarrow\!\!0$ antiferromagnetic ordering with a rock-salt arrangement of the octahedral breathing distortions. The energy gain due to the breathing distortions is larger than that due to the antiferromagnetic ordering. These phases are semimetallic with small three-dimensional Fermi pockets, which is largely consistent with the recent observation of the coexistence of antiferromagnetism and metallicity in LaNiO$_3$ single crystals by Li \textit{et al.} [arXiv:1705.02589].