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 Bi₂Se₂Te, Bi₂Te₂Se, and GeBi₂Te₄, exhibit a singly degenerate Dirac-like surface state, while Bi₂Se₂S is a fully gapped insulator with no measurable surface state. One of these compounds, Bi₂Se₂Te, shows tunable surface state dispersion upon its electronic alloying with Sb (SbₓBi_2-xSe₂Te series). Other members of the ternary family such as GeBi₂Te₄ and BiTe1.5S1.5 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 BiTe1.5S1.5. 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.