Figure 3. Transport measurements on 20 QLs Bi₂Se₃, 20 QLs Bi₂Te₃ and 1 QL Bi₂Se₃/19 QLs Bi₂Te₃ heterosturcture films.

(a) Schematic structure of the TI films for transport measurements. The thickness is not to scale. (b) 2D sheet resistance (R_sq) vs temperature of 20 QLs Bi₂Se₃ and 20 QLs Bi₂Te₃ from room temperature to 2 K. (c) 2D sheet resistance (R_sq) as a function of temperature for 1 QL Bi₂Se₃/19 QLs Bi₂Te₃ heterostructure film. (d)–(f) The normalized resistance (R/R_min) of 20 QLs Bi₂Se₃, 20 QLs Bi₂Te₃ and 1 QL Bi₂Se₃/19 QLs Bi₂Te₃ as a function of temperature at different magnetic field, indicate that a logarithmic increase with decreasing T (the dashed lines are guides to the eyes). In the upper inset of (f), the slope defined as κ = (πh/e²)dσ_xx/dlnΤ is shown as a function of magnetic field. (g)–(i) The normalized MR (R(H)/R(0)) vs magnetic field of 20 QLs Bi₂Se₃, 20 QLs Bi₂Te₃ and 1 QL Bi₂Se₃/19 QLs Bi₂Te₃ at different temperatures. (j) and (k) Resistance vs tilt angle of 20 QLs Bi₂Se₃ and 20 QLs Bi₂Te₃ in a fixed magnetic field of 160 kOe at T = 2 K. The inset shows the rotation configuration. The magnetic field is always perpendicular to the current when the sample is rotating. (l) Resistance vs tilt angle of 1 QL Bi₂Se₃/19 QLs Bi₂Te₃ in a fixed magnetic field of 150 kOe at T = 2 K. The function |cosθ| fitting is shown as solid red lines in (j)–(l).