Topological surface states and Dirac point tuning in ternary topological insulators

Abstract

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${}_{2}$Se${}_{2}$Te, Bi${}_{2}$Te${}_{2}$Se, and GeBi${}_{2}$Te${}_{4}$, exhibit a singly degenerate Dirac-like surface state, while Bi${}_{2}$Se${}_{2}$S is a fully gapped insulator with no measurable surface state. One of these compounds, Bi${}_{2}$Se${}_{2}$Te, shows tunable surface state dispersion upon its electronic alloying with Sb (Sb${}_{x}$Bi${}_{2\ensuremath{-}x}$Se${}_{2}$Te series). Other members of the ternary family such as GeBi${}_{2}$Te${}_{4}$ and BiTe${}_{1.5}$S${}_{1.5}$ 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${}_{1.5}$S${}_{1.5}$. 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.