Topological Dirac surface states in ternary compounds GeBi₂Te₄, SnBi₂Te₄ and Sn_0.571Bi_2.286Se₄ *

Abstract

Using high-resolution angle-resolved and time-resolved photoemission spectroscopy, we have studied the low-energy band structures in occupied and unoccupied states of three ternary compounds GeBi 2 Te 4 , SnBi 2 Te 4 and Sn 0.571 Bi 2.286 Se 4 near the Fermi level. In previously confirmed topological insulator GeBi 2 Te 4 compounds, we confirmed the existence of the Dirac surface state and found that the bulk energy gap is much larger than that in the first-principles calculations. In SnBi 2 Te 4 compounds, the Dirac surface state was observed, consistent with the first-principles calculations, indicating that it is a topological insulator. The experimental detected bulk gap is a little bit larger than that in calculations. In Sn 0.571 Bi 2.286 Se 4 compounds, our measurements suggest that this nonstoichiometric compound is a topological insulator although the stoichiometric SnBi 2 Se 4 compound was proposed to be topological trivial.