Fig. 4.

Model analysis results and TSS dominated SOT in 5–8 QL Bi₂Se₃. a Sheet carrier concentration of topological surface states (TSS), two-dimensional electron gas (2DEG) and bulk channels. b The location of the Fermi level relative to Dirac point (E _F – E _DP) and Fermi vector (k _F) of TSS. c Ratio of charge currents in the TSS on the top surface and total currents in Bi₂Se₃. d Interface SOT efficiency, λ _TSS (blue squares), as a function of t _BiSe at room temperature. The amended interface SOT efficiency from TSS after excluding the opposite 2DEG contribution is shown for 7, 8, and 10-QL Bi₂Se₃ in d with red circles. The factor of 2 in a arises due to the consideration of both the bottom and the top TSS in Bi₂Se₃. The error bars in d are the standard deviation from three devices at each Bi₂Se₃ thickness