Ab initio study of topological surface states of strained HgTe

Abstract: The topological surface states of mercury telluride (HgTe) are studied by ab initio calculations assuming different strains and surface terminations. For the Te-terminated surface, a single Dirac cone exists at the $\Gamma$ point. The Dirac point shifts up from the bulk valence bands into the energy gap when the substrate-induced strain increases. At the experimental strain value (0.3%), the Dirac point lies slightly below the bulk valence band maximum. A left-handed spin texture was observed in the upper Dirac cone, similar to that of the Bi$_2$Se$_3$-type topological insulator. For the Hg-terminated surface, three Dirac cones appear at three time-reversal-invariant momenta, excluding the $\Gamma$ point, with nontrivial spin textures.