Ferroelectricity in strained Hf$_2$CF$_2$ monolayer

TL;DR

This paper predicts that a functionalized Hf$_2$CF$_2$ monolayer can exhibit unconventional out-of-plane ferroelectricity induced by biaxial strain, with potential for manipulating metallic domain walls.

Contribution

It introduces a novel ferroelectric mechanism in Hf$_2$CF$_2$ monolayer driven by strain, expanding understanding of ferroelectricity in 2D materials.

Findings

Strain induces nonpolar to polar transition in Hf$_2$CF$_2$ monolayer.

Ferroelectricity involves out-of-plane polarization from fluorine layer shifts.

Metallic domain walls can be controlled via ferroelectric domain reshaping.

Abstract

Low dimensional ferroelectrics are highly desired for applications and full of exotic physics. Here a functionalized MXene Hf$_2$CF$_2$ monolayer is theoretically studied, which manifests a nonpolar to polar transition upon moderate biaxial compressive strain. Accompanying this structural transition, a metal-semiconductor transition occurs. The in-plane shift of unilateral fluorine layer leads to a polarization pointing out-of-plane. Such ferroelectricity is unconventional, similar to the recently-proposed interlayer-sliding ferroelectricity but not identical. Due to its specific hexapetalous potential energy profile, the possible ferroelectric switching paths and domain walls are nontrivial, which are mediated via the metallic paraelectric state. In this sense, the metallic walls can be manipulated by reshaping the ferroelectric domains.