Fig. 4 The degree to which bands are inverted M 0 is tracked against the lattice constant of (a) SnTe and (b) Bi 2 Te 3 . The M 0 value is calculated at the L-point for SnTe and at the Γ-point for Bi 2 Te 3 . Since band inversion is primarily driven by atomic orbital interactions in the rock-salt family, the band inversion M 0 of SnSe and SnTe follow the same trend. On the other hand, since spin-orbit coupling prompts band inversion in tetradymite systems, M 0 of Bi 2 Se 3 is far from the trend of Bi 2 Te 3 .