Robust Surface Doping of Bi$_2$Se$_3$ by Rb Intercalation

TL;DR

This study demonstrates that intercalating Rb atoms into Bi$_2$Se$_3$ surfaces reduces reactivity and preserves electronic properties, offering a promising approach for stable topological insulator surface modifications.

Contribution

It introduces a method of Rb intercalation into Bi$_2$Se$_3$ that maintains electronic structure while enhancing surface stability against oxidation.

Findings

Intercalation reduces surface reactivity significantly.

Rb intercalation preserves the 2DEG electronic structure.

Intercalation occurs above room temperature and is influenced by Coulomb interactions.

Abstract

Rubidium adsorption on the surface of the topological insulator Bi$_2$Se$_3$ is found to induce a strong downward band bending, leading to the appearance of a quantum-confined two dimensional electron gas states (2DEGs) in the conduction band. The 2DEGs shows a strong Rashba-type spin-orbit splitting, and it has previously been pointed out that this has relevance to nano-scale spintronics devices. The adsorption of Rb atoms, on the other hand, renders the surface very reactive and exposure to oxygen leads to a rapid degrading of the 2DEGs. We show that intercalating the Rb atoms, presumably into the van der Waals gaps in the quintuple layer structure of Bi$_2$Se$_3$, drastically reduces the surface reactivity while not affecting the promising electronic structure. The intercalation process is observed above room temperature and accelerated with increasing initial Rb coverage, an effect that is ascribed to the Coulomb interaction between the charged Rb ions. Coulomb repulsion is also thought to be responsible for a uniform distribution of Rb on the surface.