Figure 3: Band structure of Bi₂Te₃ and Bi₁Te₁.

Comparative wide energy range ARPES spectra along direction of thin films of (a) Bi₂Te₃ and (b) Bi₁Te₁ measured at T≈25 K using hν=21.2 eV. The colour code in the experimental spectra scales from bright=low to dark=high intensity. Superimposed are the results from the corresponding spin-polarized DFT calculations (1QL termination from Fig. 2 is used; red and blue dots mark opposite in-plane spin channels). (c,d) Energy distribution curves obtained along the dashed areas in a,b, respectively, at (c) k_||,x=0 Å⁻¹ and (d) 0.39 Å⁻¹ (black curve from Bi₂Te₃ and green curve from Bi₁Te₁). Black arrows mark prominent spectral differences. Magnified electronic structure close to the Fermi level along indicated crystallographic directions are shown in e for Bi₂Te₃ at hν=21.2 eV and in h for Bi₁Te₁ at hν=8.4 eV. Additionally, the corresponding calculations are shown in f for Bi₂Te₃, and in i–j for Bi₁Te₁ ((i) 1QL termination, (j) 2QL termination), and superimposed on the experimental spectra in g,k, respectively ((k) shows overlap with (i) and (j)). The Fermi energy in the calculated spectra was shifted up by 100 meV (200 meV) in the 1QL (2QL) Bi₁Te₁ case compared to Fig. 2, and by 250 meV for the Bi₂Te₃ case. Red arrows point to a single spin-polarized band in Bi₂Te₃ (f), and two overlapping bands with opposite spin polarization for Bi₁Te₁ (j).