Topological Surface State Evolution in Bi$_2$Se$_3$ via Surface Etching

TL;DR

This study introduces a controlled surface etching technique on Bi$_2$Se$_3$ to manipulate and track the evolution of its topological surface states, revealing their robustness and relocation during surface modifications.

Contribution

It presents a novel method for gradually removing surface layers of Bi$_2$Se$_3$ and monitoring the topological surface state evolution with high precision.

Findings

Topological surface states remain robust during surface layer removal.

The Dirac cone relocates in real and momentum space as surface layers change.

Charge transfer occurs among surface layers during etching.

Abstract

Topological insulators are materials with an insulating bulk interior while maintaining gapless boundary states against back scattering. Bi$_2$Se$_3$ is a prototypical topological insulator with a Dirac-cone surface state around $\Gamma$. Here, we present a controlled methodology to gradually remove Se atoms from the surface Se-Bi-Se-Bi-Se quintuple layers, eventually forming bilayer-Bi on top of the quintuple bulk. Our method allows us to track the topological surface state and confirm its robustness throughout the surface modification. Importantly, we report a relocation of the topological Dirac cone in both real space and momentum space, as the top surface layer transitions from quintuple Se-Bi-Se-Bi-Se to bilayer-Bi. Additionally, charge transfer among different surface layers is identified. Our study provides a precise method to manipulate surface configurations, allowing for the fine-tuning of the topological surface states in Bi$_2$Se$_3$, which represents a significant advancement towards nano-engineering of topological states.