Pyridine intercalated Bi$_2$Se$_3$ heterostructures: controlling the topologically protected states

TL;DR

This study uses ab initio simulations to demonstrate how intercalating pyridine molecules in Bi$_2$Se$_3$ can control its topological states, enabling switching between topologically protected metallic states and trivial insulators via external pressure.

Contribution

It introduces a method to tune topological states in Bi$_2$Se$_3$ by intercalation and pressure, revealing controllable topological phase transitions at heterojunctions.

Findings

Intercalation increases layer separation and suppresses parity inversion.

A heterojunction with topologically protected states forms at the interface.

External pressure can revert the system to a trivial insulator by shifting metallic states.

Abstract

We use ab initio simulations to investigate the incorporation of pyridine molecules (C$_5$H$_5$N) in the van der Waals gaps of Bi$_2$Se$_3$. The intercalated pyridine molecules increase the separation distance between the Bi$_2$Se$_3$ quintuple layers (QLs), suppressing the parity inversion of the electronic states at the $\Gamma$-point. We find that the intercalated region becomes a trivial insulator. By combining the pristine Bi$_2$Se$_3$ 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 Bi$_2$Se$_3$, 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.