a first-principles study*

In this work, we elucidate how the most common non-magnetic intrinsic defects, Se vacancies, perturb the topologically protected states of Bi₂Se₃, and further explore a method to quench these defects by ambient gases. Our study shows that Se vacancies don’t merely n-dope the system but give rise to a vacancy induced non-linear band pinned near the Fermi level, in addition to splitting the Dirac cone into the valence and conduction bands. These non-trivial features protecting the topological nature of Bi₂Se₃ emerge from the hybridization between the surface, defect, and quantum well states, which we confirm using a numerical model [1]. Furthermore, we show that these effects are reversible, i.e. the Dirac cone can be reverted back to the Fermi level by the adsorption of ambient gases that are either isoelectronic to Se or highly electronegative to counter-dope the slab. We distinguish the possible features of the adsorbates that can be used to a priori predict their effects on the electronic structure of the Bi₂Se₃ slab after adsorption [2]. Our results provide a foundation for a general strategy to in situ engineer the band structure of the Bi₂Se₃ family of topological insulators by healing chalcogen vacancies.

References

[1] Sharmila N. Shirodkar and Pratibha Dev, “Nonlinear Hybrid Surface-Defect States in Defective Bi₂Se₃”, J. Phys. Chem. C  2022 126 (28), 11833-11839.

[2] Sharmila N. Shirodkar, Gregory M. Stephen, Aubrey T. Hanbicki, Adam L. Friedman, and Pratibha Dev, “Healing Se Vacancies in Bi₂Se₃ by Ambient Gases”, J. Phys. Chem. C 2022, 126, 39, 16877–16884.