Maximal Rashba Splitting in GeTe/Bi₂Te₃ Heterostructures via Strong Band Bending

The Rashba effect has emerged as a pivotal phenomenon driving novel discoveries in condensed matter physics. Materials with large Rashba energy E_R, wavenumber offset k₀ and Rashba parameter α_R are prerequisites for spintronic devices operating above room temperature. While neither ultrathin GeTe films (<3.0 nm thickness) nor monolayer topological insulator Bi₂Te₃ (1 quintuple layer (QL) on Si(111)) manifest Rashba splitting, An unprecedented strength of Rashba effect with $E_R=\left(0.57\pm 0.03\right)\mathrm{eV}$ , $k_0=\left(0.16,\pm ,0.03\right){\AA }^{-1}$ and ${\alpha }_R=\left(6.86,\pm ,0.59\right)\mathrm{eV}·\AA$ in GeTe (1 nm)/Bi₂Te₃ (1 QL) heterostructure is achieved. The spin-momentum-locked bands resulting from the Rashba effect of GeTe /Bi₂Te₃ is confirmed by density functional theory (DFT) calculations. In GeTe (x nm)/Bi₂Te₃(10 QL), it is find that the values of E_R, k₀ and α_R significantly enhance as the thickness of GeTe decreases contrasting with GeTe films. By comparing the thickness dependence of GeTe with that of GeTe/Bi₂Te₃, it is determined that the enhanced Rashba parameter Δα_R is proportional to the electric field in the GeTe/Bi₂Te₃ heterojunction region. It is concluded that the origin of this huge Rashba effect is attributed to the strong band bending in the GeTe/Bi₂Te₃ heterojunction region, where the striking inversion-symmetry-breaking and significant bandgap difference result in a sharp potential gradient normal to the interface. This work opens an avenue to enhance the Rashba splitting by strong band bending and design spin field effect transistors with spin channel as short as several nanometer scales.