Stacking Defects

Three-dimensional topological insulators (TIs) of the Bi₂Se₃ family show a layered structure with hexagonally compact atomic planes. The stacking along the [0001] direction is analogous to that of the fcc structure along its (111) direction (AbCaB...).

Moreover, the primitive cell is composed of a quintuple layer (QL), within which interatomic interactions are strong, while QL-QL interaction is much weaker (mainly due to van der Waals interactions). Since the inter-QL coupling is weak, many experiments show defected samples of Bi₂Se₃-like compounds.

We investigated the energetics and the effect of different kinds of planar extended defects in Bi₂Se₃. We found that twin boundaries between QLs are the energetically most favourable kind of extended two-dimensional defects. Furthermore, these type of defects break the inversion symmetry of the crystal creating an electric dipole moment. We characterised different defect configurations and computed their spontaneous polarisation. We also related this polarisation to the doping induced in the topological surface states. By tailoring the defect position and density, the topological surface state doping is tunable in sign and magnitude.

For more details see:

Tunable Dirac Electron and Hole Self-Doping of Topological Insulators Induced by Stacking Defects, H. Aramberri, J.I. Cerdá, M.C. Muñoz, Nano Lett. 15 (6), pp 3840–3844 (2015).