Reversible giant out-of-plane Rashba effect in two-dimensional Ga$XY$ ($X$= Se, Te; $Y$= Cl, Br, I) compounds for persistent spin helix

TL;DR

This paper reports the discovery of a giant out-of-plane Rashba effect in 2D GaXY compounds with in-plane ferroelectricity, enabling non-volatile control of spin textures and potential applications in spintronics.

Contribution

First-principles calculations reveal a giant out-of-plane Rashba effect in 2D GaXY monolayers, linking ferroelectric polarization switching to spin texture reversal.

Findings

Giant out-of-plane Rashba effect observed in GaXY monolayers.

Out-of-plane spin textures can be reversed by switching ferroelectric polarization.

Potential for non-volatile spintronic device applications.

Abstract

The coexistence of ferroelectricity and spin-orbit coupling (SOC) in noncentrosymmetric systems may allow for a nonvolatile control of spin degrees of freedom by switching the ferroelectric polarization through the well-known ferroelectric Rashba effect (FRE). Although the FER has been widely observed for bulk ferroelectric systems, its existence in two-dimensional (2D) ferroelectric systems is still very rarely discovered. Based on first-principles calculations, supplemented with $\vec{k}\cdot\vec{p}$ analysis, we report the emergence of the FRE in the Ga$XY$ ($X$= Se, Te; $Y$= Cl, Br, I) monolayer compounds, a new class of 2D materials having in-plane ferroelectricity. Due to the large in-plane ferroelectric polarization, a giant out-of-plane Rashba effect is observed in the topmost valence band, producing unidirectional out-of-plane spin textures in the momentum space. Importantly, such out-of-plane spin textures, which can host a long-lived helical spin mode known as a persistent spin helix, can be fully reversed by switching the direction of the in-plane ferroelectric polarization. Thus, our findings can open avenues for interplay between the unidirectional out-of-plane Rashba effect and the in-plane ferroelectricity in 2D materials, which is useful for efficient and non-volatile spintronic devices.