Graphene intercalation of the large gap quantum spin Hall insulator bismuthene

TL;DR

This paper demonstrates that intercalating bismuthene with graphene preserves its topological properties and protects it from oxidation, enabling practical applications outside ultra-high vacuum environments.

Contribution

The study introduces a novel graphene intercalation method that maintains bismuthene's topological integrity and prevents oxidation, advancing its potential for real-world device integration.

Findings

Graphene intercalation preserves bismuthene's topological gap.

Intercalation protects bismuthene from air oxidation.

Hydrogen is essential for effective intercalation.

Abstract

The quantum spin Hall insulator bismuthene, a two-third monolayer of bismuth on SiC(0001), is distinguished by helical metallic edge states that are protected by a groundbreaking 800 meV topological gap, making it ideal for room temperature applications. This massive gap inversion arises from a unique synergy between flat honeycomb structure, strong spin orbit coupling, and an orbital filtering effect that is mediated by the substrate. However, the rapid oxidation of bismuthene in air has severely hindered the development of applications, so far confining experiments to ultra-high vacuum conditions. Here, we successfully overcome this barrier, intercalating bismuthene between SiC and a protective sheet of graphene. As we demonstrate through scanning tunneling microscopy and photoemission spectroscopy, graphene intercalation preserves the structural and topological integrity of bismuthene, while effectively shielding it from oxidation in air. We identify hydrogen as the critical component that was missing in previous bismuth intercalation attempts. Our findings facilitate ex-situ experiments and pave the way for the development of bismuthene based devices, signaling a significant step forward in the development of next-generation technologies.