Spin Hall effect in prototype Rashba ferroelectrics GeTe and SnTe

TL;DR

This study uses density functional theory to show that ferroelectric Rashba semiconductors GeTe and SnTe exhibit significant spin Hall effects, which could enable electric-field-controlled spintronics devices without magnetic fields.

Contribution

It demonstrates the presence of large spin Hall effects in GeTe and SnTe, explores doping effects on ferroelectricity and Rashba phenomena, and estimates spin Hall angles in these materials.

Findings

Large spin Hall effect can occur in both ferroelectric and paraelectric phases.

Doping levels affect ferroelectric displacements and Rashba effects.

Spin Hall angles are significant in doped polar phases.

Abstract

Ferroelectric Rashba semiconductors (FERSC) have recently emerged as a promising class of spintronics materials. The peculiar coupling between spin and polar degrees of freedom responsible for several exceptional properties, including ferroelectric switching of Rashba spin texture, suggests that the electron's spin could be controlled by using only electric fields. In this regard, recent experimental studies revealing charge-to-spin interconversion phenomena in two prototypical FERSC, GeTe and SnTe, appear extremely relevant. Here, by employing density functional theory calculations, we investigate spin Hall effect (SHE) in these materials and show that it can be large either in ferroelectric or paraelectric structure. We further explore the compatibility between doping required for the practical realization of SHE in semiconductors and polar distortions which determine Rashba-related phenomena in FERSC, but which could be suppressed by free charge carriers. Based on the analysis of the lone pairs which drive ferroelectricity in these materials, we have found that the polar displacements in GeTe can be sustained up to a critical hole concentration of over $\sim 10^{21}$/cm$^{3}$, while the tiny distortions in SnTe vanish at a minimal level of doping. Finally, we have estimated spin Hall angles for doped structures and demonstrated that the spin Hall effect could be indeed achieved in a polar phase. We believe that the confirmation of spin Hall effect, Rashba spin textures and ferroelectricity coexisting in one material will be helpful for design of novel multifunctional spintronics devices operating without magnetic fields.