Three-Dimensional Limit of Bulk Rashba Effect in Ferroelectric Semiconductor GeTe

Ferroelectric Rashba semiconductors (FERSCs) have recently attracted intensive attention due to their giant bulk Rashba parameter, α_R, which results in a locking between the spin degrees of freedom and the switchable electric polarization. However, the integration of FERSCs into microelectronic devices has provoked questions concerning whether the Rashba effect can persist when the material thickness is reduced to several nanometers. Here we find that α_R can keep a large value of 2.12 eV Å in the 5.0 nm thick GeTe film. The behavior of α_R with thickness can be expressed by the scaling law and provides a 3D thickness limit of the bulk Rashba effect, d_c = 2.1 ± 0.5 nm. Finally, we find that the thickness can modify the Berry curvature as well, which influences the polarization and consequently alters the α_R. Our results give insight into understanding the factors influencing α_R in FERSCs and pave a novel route for designing Rashba-type quantum materials.