Origin of band inversion in topological Bi2Se3

Abstract

Topological materials and more so insulators have become ideal candidates for spintronics and other novel applications. These materials portray band inversion that is considered to be a key signature of topology. It is not yet clear what drives band inversion in these materials and the basic inferences when band inversion is observed. We employed a state-of-the-art ab initio method to demonstrate band inversion in topological bulk Bi2Se3 and subsequently provided a reason explaining why the inversion occurred. From our work, a topological surface state for Bi2Se3 was described by a single gap-less Dirac cone at k→ = 0, which was essentially at the Γ point in the surface Brilloiun zone. We realized that band inversion in Bi2Se3 was not entirely dependent on spin-orbit coupling as proposed in many studies but also occurred as a result of both scalar relativistic effects and lattice distortions. Spin-orbit coupling was seen to drive gap opening, but it was not important in obtaining a band inversion. Our calculations reveal that Bi2Se3 has an energy gap of about 0.28 eV, which, in principle, agrees well with the experimental gap of ≈0.20 eV-0.30 eV. This work contributes to the understanding of the not so common field of spintronics, eventually aiding in the engineering of materials in different phases in a non-volatile manner.