Polarization switching induced by domain wall sliding in two-dimensional ferroelectric monochalcogenides

TL;DR

This paper investigates the microscopic mechanism of polarization switching in two-dimensional ferroelectric materials by analyzing domain wall migration, providing insights that align well with experimental coercive fields and revealing optical property changes due to domain walls.

Contribution

It offers a first principles approach to calculate domain wall energies and migration barriers, linking these to coercive fields and optical properties in 2D ferroelectrics, which was previously not well understood.

Findings

Calculated coercive fields match experimental data.

Domain wall migration explains polarization switching.

Presence of domain walls causes a red shift in optical absorption.

Abstract

The ability to switch between distinct states of polarization comprises the defining property of ferroelectrics. However, the microscopic mechanism responsible for switching is not well understood and theoretical estimates based on coherent monodomain switching typically overestimate experimentally determined coercive fields by orders of magnitude. In this work we present a detailed first principles characterization of domain walls (DWs) in two-dimensional ferroelectric GeS, GeSe, SnS and SnSe. In particular, we calculate the formation energies and migration barriers for 180 and 90 DWs, and then derive a general expression for the coercive field assuming that polarization switching is mediated by DW migration. We apply our approach to the materials studied and obtain good agreement with experimental coercive fields. The calculated coercive fields are up to two orders of magnitude smaller than those predicted from coherent monodomain switching in GeSe, SnS and SnSe. Finally, we study the optical properties of the compounds and find that the presence of 180 DWs leads to a significant red shift of the absorption spectrum, implying that the density of DWs may be determined by means of simple optical probes.