Pyridine intercalated Bi₂Se₃ heterostructures: controlling the topologically protected states

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We use ab initio simulations to investigate the incorporation of pyridine molecules (C₅H₅N) in the van der Waals gaps of Bi₂Se₃. The intercalated pyridine molecules increase the separation distance between the Bi₂Se₃ quintuple layers (QLs), suppressing the parity inversion of the electronic states at the Γ-point. We find that the intercalated region becomes a trivial insulator. By combining the pristine Bi₂Se₃ region with the one intercalated by the molecules, we have a non-trivial/trivial heterojunction characterized by the presence of (topologically protected) metallic states at the interfacial region. Next we apply an external compressive pressure to the system, and the results are (i) a decrease on the separation distance between the QLs intercalated by pyridine molecules, and (ii) the metallic states are shifted toward the bulk region, turning the system back to insulator. That is, through a suitable tuning of the external pressure in Bi₂Se₃, intercalated by pyridine molecules, we can control its topological properties; turning-on and -off the topologically protected metallic states lying at the non-trivial/trivial interface.