Absence of Critical Thickness in an Ultrathin Improper Ferroelectric Film

TL;DR

This study uses density functional theory to explore the stability and surface properties of ultrathin improper ferroelectric YMnO3 films, revealing they can maintain ferroelectricity without a critical thickness, unlike conventional ferroelectrics.

Contribution

It demonstrates that improper ferroelectric ultrathin films can sustain ferroelectric states without a critical thickness, highlighting their unique properties.

Findings

Ferroelectric state remains metastable despite depolarizing field.

Connection established between improper ferroelectric transition and stability.

Ultrathin improper ferroelectric films exhibit distinctive properties.

Abstract

We study the ferroelectric stability and surface structural properties of an oxygen-terminated hexagonal YMnO$_3$ ultra-thin film using density functional theory. Under an open circuit boundary condition, the ferroelectric state with the spontaneous polarization normal to the (0001) surface, is found to be metastable in a single domain state despite the presence of a depolarizing field. We establish a connection between the result and the role of improper ferroelectric transition. Our results imply that improper ferroelectric ultrathin films can have rather unique properties that are distinctive from those of very thin films of ordinary ferroelectrics.