Observation of Single Dirac Cone Topological Surface State in Compounds TlBiTe2 and TlBiSe2 from a New Topological Insulator Family

TL;DR

This study uses ARPES to confirm the presence of a single Dirac cone surface state in TlBiTe2 and TlBiSe2, establishing their topological insulator properties and potential for superconductivity.

Contribution

It provides experimental evidence of topological surface states in TlBiTe2 and TlBiSe2, expanding the family of known topological insulators with detailed band structure analysis.

Findings

Single Dirac cone observed at the BZ center in both compounds

TlBiSe2 is a large gap topological insulator with a Dirac point at the valence band top

TlBiTe2 exhibits a semi-metallic band structure suggesting potential for topological superconductivity

Abstract

Angle resolved photoemission spectroscopy (ARPES) studies were performed on two compounds (TlBiTe$_2$ and TlBiSe$_2$) from a recently proposed three dimensional topological insulator family in Thallium-based III-V-VI$_2$ ternary chalcogenides. For both materials, we show that the electronic band structures are in broad agreement with the $ab$ $initio$ calculations; by surveying over the entire surface Brillouin zone (BZ), we demonstrate that there is a single Dirac cone reside at the center of BZ, indicating its topological non-triviality. For TlBiSe$_2$, the observed Dirac point resides at the top of the bulk valance band, making it a large gap ($\geq$200$meV$) topological insulator; while for TlBiTe$_2$, we found there exist a negative indirect gap between the bulk conduction band at $M$ point and the bulk valance band near $\Gamma$, making it a semi-metal at proper doping. Interestingly, the unique band structures of TlBiTe$_2$ we observed further suggest TlBiTe$_2$ may be a candidate for topological superconductors.