The ferroelectric transition in YMnO$_3$ from first principles

TL;DR

This study uses first-principles calculations to analyze the structural phase transition in YMnO$_3$, revealing a zone-boundary instability that couples with polarization, indicating it is an improper ferroelectric.

Contribution

It provides a detailed first-principles analysis of the ferroelectric transition mechanism in YMnO$_3$, highlighting the role of a zone-boundary instability.

Findings

Identified a single zone-boundary instability

Coupling between instability and polarization is strong

YMnO$_3$ is an improper ferroelectric

Abstract

We have studied the structural phase transition of multiferroic YMnO$_3$ from first principles. Using group-theoretical analysis and first-principles density functional calculations of the total energy and phonons, we perform a systematic study of the energy surface around the prototypic phase. We find a single instability at the zone-boundary which couples strongly to the polarization. This coupling is the mechanism that allows multiferroicity in this class of materials. Our results imply that YMnO$_3$ is an improper ferroelectric. We suggest further experiments to clarify this point.