Protective capping of topological surface states of intrinsically insulating Bi$_2$Te$_3$

TL;DR

This study demonstrates that epitaxial Te capping preserves the topological surface states of Bi$_2$Te$_3$, enabling protected, stable, and clean surfaces for ex-situ analysis without altering the material's intrinsic properties.

Contribution

The paper introduces epitaxial Te as an effective capping layer that maintains the topological surface states of Bi$_2$Te$_3$ and can be removed to restore pristine surfaces after air exposure.

Findings

Te capping preserves surface state dispersion.

Capping layer has minimal impact on conductivity.

Te overlayer can be annealed off to recover clean Bi$_2$Te$_3$ surface.

Abstract

We have identified epitaxially grown elemental Te as a capping material that is suited to protect the topological surface states of intrinsically insulating Bi$_2$Te$_3$. By using angle-resolved photoemission, we were able to show that the Te overlayer leaves the dispersive bands of the surface states intact and that it does not alter the chemical potential of the Bi$_2$Te$_3$ thin film. From in-situ four-point contact measurements, we observed that the conductivity of the capped film is still mainly determined by the metallic surface states and that the contribution of the capping layer is minor. Moreover, the Te overlayer can be annealed away in vacuum to produce a clean Bi$_2$Te$_3$ surface in its pristine state even after the exposure of the capped film to air. Our findings will facilitate well-defined and reliable ex-situ experiments on the properties of Bi$_2$Te$_3$ surface states with nontrivial topology.