Spin Hall effect in prototype Rashba ferroelectrics GeTe and SnTe

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 Rashbarelated 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 ∼ 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.

Atomic and Electronic Structure of a Multidomain GeTe Crystal

“…This value of a R is close to the one predicted in recent bulk structure calculations. 49 In Figs. 9c-e, it is seen that the spin vector component of the surface state along the x direction is negligible, while along the y direction it is oriented counterclockwise (clockwise) for the inner (outer) surface band, in agreement with the Rashba-type spin texture.…”

Nonreciprocal charge transport up to room temperature in bulk Rashba semiconductor α-GeTe

“…Although the carrier concentration shows anomalous temperature dependence from 3 to 300 K, its absolute change in the magnitude remains weak, revealing a negligible shift of Fermi level with temperature. According to previous reports, the metallic resistivity and high P-type carrier concentrations are ascribed to the natural tendency for Ge deficiency in α-GeTe films [28][29][30][31] . However, the anomalous temperature-dependent carrier concentration remains puzzling, which will be discussed later.…”

Dynamical amplification of electric polarization through nonlinear phononics in 2D SnTe

“…This intensified repulsion between Sn and Te results in the increase in-plane displacement, which eventually results in an enhanced responses of the E u,x amplitude with a given Q Au . The effect of doping on polar distortions has also discussed previously for bulk SnTe 33 . We expect that the modified Coulomb interaction by doping not only alters the ground state configuration but modifies the lattice dynamics and the interaction strength between phonons for both bulk and monolayer SnTe.…”