Figure 1: Bulk band structures of Bi₁Te₁.

(a) Simple sketch of the crystal structure of Bi₁Te₁. The unit cell consists of 1Bi BL and 2QLs. (b,d) The bulk band structure calculation in the structurally relaxed geometry (c) and with artificially expanded distances between the BL and the QLs (d), respectively. States localized mostly in the BL are marked in green, while the states localized mostly in the 2QLs are shown in red. In d, the band structure of the BL shows an inverted gap about 0.2 eV above the Fermi level (E_F marked with a dashed line). (c) Bulk and surface Brillouin zone with parity product of the TRIM points for the relaxed structure resulting in +1 (red ‘+’) or −1 (blue ‘−’). The k_z direction corresponds to the stacking direction. ΓAML, that is, (k_x,k_z)-plane, marks a mirror plane.