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HL: Fachverband Halbleiterphysik

HL 41: Topological insulators: Theory (with DS/MA/O/TT)

HL 41.4: Vortrag

Mittwoch, 18. März 2015, 10:15–10:30, ER 270

Effect of Bi bilayers on the topological states of Bi₂Se₃: A first-principles study — Kirsten Govaerts¹, Kyungwha Park², Christophe De Beule¹, Dirk Lamoen¹, and •Bart Partoens¹ — ¹CMT-group and EMAT, University of Antwerp, Belgium — ²Virginia Tech, Department of Physics, USA

Bi₂Se₃ and vice versa, has not been explored much. Bi bilayers are often present between the quintuple layers of Bi₂Se₃, since (Bi₂)_n(Bi₂Se₃)_m form stable ground-state structures. Moreover, Bi₂Se₃ is a good substrate for growing ultrathin Bi bilayers. By first-principles techniques, we first show that there is no preferable surface termination by either Bi or Se. Next, we investigate the electronic structure of Bi bilayers on top of, or inside a Bi₂Se₃ slab. If the Bi bilayers are on top, we observe a charge transfer to the quintuple layers that increases the binding energy of the surface Dirac cones. The extra states, originating from the Bi bilayers, were declared to form a topological Dirac cone, but here we show that these are ordinary Rashba-split states. This result, together with the appearance of a new Dirac cone that is localized slightly deeper, might necessitate the reinterpretation of several experimental results. When the Bi bilayers are located inside the Bi₂Se₃ slab, they tend to split the slab into two topological insulators with clear surface states. Interface states can also be observed, but an energy gap persists because of strong coupling between the neighboring quintuple layers and the Bi bilayers.