Effect of strain and doping on the polar metal phase in LiOsO$_3$

TL;DR

This study uses first-principles calculations to show that strain and doping can control the polar metal phase in LiOsO$_3$, revealing a strain-driven quantum phase transition and robustness of polar metallicity against doping.

Contribution

It demonstrates that biaxial strain can tune the polar metal phase in LiOsO$_3$, and that this phase remains stable under significant charge doping, which is a novel insight.

Findings

Compressive strain stabilizes the polar R3c phase.

Tensile strain favors the centrosymmetric R-3c structure.

Polar metal phase is robust against large charge doping.

Abstract

We systematically investigate the effect of strain and doping on the polar metal phase in lithium osmate, LiOsO$_3$, using first-principles calculations. We demonstrate that the polar metal phase in LiOsO$_3$ can be controlled by biaxial strain. Based on density functional calculations, we show that a compressive biaxial strain enhances the stability of the polar $R3c$ phase. On the other hand, a tensile biaxial strain favors the centrosymmetric $R\overline{3}c$ structure. Thus, strain emerges as a promising control parameter over polar metallicity in this material. We uncover a strain-driven quantum phase transition under tensile strain, and highlight intriguing properties that could emerge in the vicinity of this polar to non-polar metal transition. We examine the effect of charge doping on the polar metal phase. By means of electrostatic doping as well as supercell calculations, we find that screening from additional charge carriers, expected to suppress the polar distortions, have only a small effect on them. Rather remarkably, and in contrast to conventional ferroelectrics, the polar metal phase in LiOsO$_3$ remains robust against charge doping up to large doping values.