Figure 2: Spin-resolved DFT surface electronic structure calculations.

Band structure along of slabs of Bi1Te1 terminated by (a) 2QLs and (b,c) 1QL. The size of the symbols corresponds to the spin polarization in the first four layers of a slab, the colour (red/blue) indicates the orientation of the spins with respect to a direction perpendicular to the momentum and surface normal. The green circle marks the Dirac cone of the TCI. In c (QL′), the symmetry has been broken by strain along [1
00] direction, such that
is no longer a high-symmetry line and a gap opening can be observed (see inset).