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Abstract

Bi2Se3 and related compounds are prototype three-dimensional topological insulators with a single Dirac cone in the surface band structure. While the topological surface states can be characterized with surface-sensitive methods, the underlying bulk energy band inversion has not been investigated in detail. Here, a study is presented that combines density-functional theory and nuclear magnetic resonance to explore the nontrivial band edge of Bi2Se3 and Bi2Te3. It is found that the topological band inversion is not a discrete reversal of the order of the valence and conduction band at the Γ point. Rather, the bands closest to the Fermi level become well mixed and spread evenly below and above the band gap, such that the characters of the valence- and conduction-band edges become indistinguishable. Beside those bands relevant for the band inversion, i.e., Bi and Se pz, also Bi px and py states are involved. As a part of this mixture of states, the band inversion shows no edges in k space. © 2024 authors. Published by the American Physical Society.