Fig. 1. MBE growth of the Bi₂Te₃ and FeTe films. (a) The schematic crystal structure of Bi₂Te₃ and FeTe. (b) The RHEED pattern of the STO surface which shows that the substrate has a well-defined 2 × 1 surface reconstruction. (c) The RHEED pattern of the FeTe surface. (d) The RHEED pattern of the Bi₂Te₃ surface. The double-line structure shows two kinds of domains in the Bi₂Te₃ film. (e) Schematic of two types of Bi₂Te₃ crystal domains on FeTe.

Fig. 2. (a), (b) Photoemission intensity of the cut along the Γ–M direction of FeTe acquired on pure FeTe and 0.5 QL Bi₂Te₃/FeTe heterostructure, respectively. (c) Plot of EDCs of (b). (d), (e) Differential intensity maps of (a) and (b). (f) Photoemission intensity of the cut along the Γ–K direction of Bi₂Te₃ on 2 QLs Bi₂Te₃/FeTe sample.

Fig. 3. (a) An STM image of different sizes of 1 QL Bi₂Te₃ islands on the FeTe terrace. (150 × 150 nm², V_Bias = 200 mV, I_Tunnel = 50 pA). (b) STS curves taken over different positions on different size Bi₂Te₃ islands with Roman numbers indicating their positions (set point: V_Bias = 200 mV, I_Tunnel = 50 pA, modulation voltage: ΔV = 300 μV). (c) Zoom in image of an island in (a). (20 × 20 nm², V_Bias = 200 mV, I_Tunnel = 50 pA). (d) STS curves acquired over position IV in (c) under different tip states (set point: V_Bias = 200 mV, I_Tunnel = 50 pA, modulation voltage: ΔV = 300 μV).

Fig. 4. (a) A zoom in STM image showing the edge of a 1 QL Bi₂Te₃ island (32 × 32 nm², V_Bias = 2.5 mV, I_Tunnel = 50 pA). (b)–(d) dI/dV mappings over (a) at 0.5 mV, –0.5 mV, and 1.5 mV, respectively (32 × 32 nm², set points: V_Bias = 2.5 mV, I_Tunnel = 50 pA, modulation voltage: ΔV = 300 μV).

Fig. 5. (a) Zoom in atomic resolution STM images showing the top edge of the Bi₂Te₃ island in Fig. 4(a) between the Bi₂Te₃ island (bottom) and the FeTe terrace (top), respectively. Red points with numbers indicate positions where STS curves were taken (15 × 15 nm², V_Bias = 10 mV, I_Tunnel = 1.5 nA). (b) and (c) STS curves taken on the labeled positions in (a) on the FeTe terrace and the Bi₂Te₃ island (set points: V_Bias = 10 mV, I_Tunnel = 1.5 nA, modulation voltage: ΔV = 300 μV). All spectra are offset vertically for clarity with dotted lines indicating the 0 position before the offset. (d) ZBC of the spectrum in (b) and (c) vs. distance from the edge. Blue line indicates the edge position. Red numbers indicate spectra positions. Dashed lines below each spectrum indicate the respective zero dI/dV value. (e) STS spectra Nos. 4–6, taken on the Bi₂Te₃ island in (c) after the subtraction of the most inner No. 1 spectrum.