Topological surface states and Dirac point tuning in ternary topological insulators

Using angle-resolved photoemission spectroscopy, we report electronic structure for representative members of ternary topological insulators. We show that several members of this family, such as Bi ₂Se ₂Te, Bi ₂Te ₂Se, and GeBi ₂Te ₄, exhibit a singly degenerate Dirac-like surface state, while Bi ₂Se ₂S is a fully gapped insulator with no measurable surface state. One of these compounds, Bi ₂Se ₂Te, shows tunable surface state dispersion upon its electronic alloying with Sb (Sb _xBi _2-xSe ₂Te series). Other members of the ternary family such as GeBi ₂Te ₄ and BiTe _1.5S _1.5 show an in-gap surface Dirac point, the former of which has been predicted to show nonzero weak topological invariants such as (1;111); thus belonging to a different topological class than BiTe _1.5S _1.5. The measured band structure presented here will be a valuable guide for interpreting transport, thermoelectric, and thermopower measurements on these compounds. The unique surface band topology observed in these compounds contributes towards identifying designer materials with desired flexibility needed for thermoelectric and spintronic device fabrication.