Strain induced tuning and annihilation of Dirac point in the topological insulator Bi₂Se₃ (001) surface.

Engineering the band gap and tuning the Dirac point (DP) of (001) surface of the 8 quintuple layers (QLs) thick Bi₂Se₃ were investigated by varying the strain through first principle density functional theory calculations, with and without the presence of spin-orbit coupling (SOC). The strain on the Bi₂Se₃ (001) surface primarily varies the band width, which changes the orbital pupulation in the conduction and valence band. The tuning of the p_z - orbital population of Bi on the (001) surface of the Bi₂Se₃ froms the Dirac cone at the Γ point, which can be achieved under uniaxial, biaxial or volume conservation strain. Around 6% out-of-plane tensile strain annihilates the DP of the (001) surface of the Bi₂Se₃ which causes the loss of topological surface states. The anniliation of the DP occurs even at lower values of volume conservation strain. However, the DP feature is preserved for the entire range of biaxial strain. The DP moves towards the Fermi level for the increasing tensile strain under unixial and volume conservation configuration, but the similar displacement of DP occurs due to increasing compressive biaxial strain. The tuning of DP may provide a new pathway to control many physical properties of Bi₂Se₃ and shed light for its technological applications.