Ternary tetradymite compounds as topological insulators

Ternary tetradymites Bi(2)Te(2)S, Bi(2)Te(2)Se, and Bi(2)Se(2)Te are found to be stable, bulk topological insulators via theory, showing band inversion between group V and VI p(z) orbitals. We identify Bi(2)Se(2)Te as a good candidate to study massive Dirac fermions, with a (111) cleavage-surface-derived Dirac point (DP) isolated in the bulk-band gap at the Fermi energy (E(f))-like Bi(2)Se(3) but with a spin texture alterable by layer chemistry. In contrast, Bi(2)Te(2)S and Bi(2)Te(2)Se (111) behave like Bi(2)Te(3), with a DP below E(f) buried in bulk bands. Bi(2)Te(2)S offers large bulk resistivity needed for devices.