# Ferroelectricity with Asymmetric Hysteresis in Metallic LiOsO3 Ultrathin Films

## TL;DR

This study demonstrates that ultrathin LiOsO3 films can exhibit switchable ferroelectricity with asymmetric hysteresis, challenging the belief that ferroelectric metals cannot have switchable polar states.

## Contribution

The paper reveals that a two-unit-cell LiOsO3 film can have a switchable out-of-plane polarization and introduces an extension of Born effective charge to metallic systems.

## Key findings

- Ultrathin LiOsO3 films show switchable out-of-plane polarization.
- Hysteresis loop is asymmetric due to surface ion displacement.
- Extension of Born effective charge concept to metals.

## Abstract

Bulk LiOsO3 was experimentally identified as a "ferroelectric" metal where polar distortions coexist with metallicity [Shi et al., Nature Materials 12, 1024 (2013)]. It is generally believed that polar displacements in a "ferroelectric" metal cannot be switched by an external electric field. Here, via comprehensive density functional theory calculations, we demonstrate that a two-unit-cell-thick LiOsO3 thin film exhibits a ferroelectric ground state having an out-of-plane electric dipole moment that can be switched by an external electric field. Moreover, its dipole moment-versus-electric-field hysteresis loop is asymmetric because only surface Li ions'displacements are reversed by external electric field whereas the field-induced force on inner Li atoms are nearly fully screened by itinerant electrons. As a relevant by-product of our study, we also extend the concept of "Born effective charge" to finite metallic systems, and show its usefulness to rationalize the observed effects.

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Source: https://tomesphere.com/paper/1904.01247