Topological Surface States and Dirac point tuning in ternary Bi2Te2Se class of topological insulators

TL;DR

This study uses angle-resolved photoemission spectroscopy to analyze the electronic structures of various ternary topological insulators, revealing tunable surface states and topological classifications relevant for device applications.

Contribution

It provides detailed experimental insights into the surface states and topological properties of several ternary topological insulators, including tunability via alloying and identification of different topological classes.

Findings

Bi2Se2Te exhibits tunable Dirac surface states with alloying.

Bi2Se2S is a fully gapped insulator with no surface states.

GeBi2Te4 and BiTe1.5S1.5 show in-gap Dirac points and different topological invariants.

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 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 (SbxBi2-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.