Reversible Switching of the Environment-Protected Quantum Spin Hall Insulator Bismuthene at the Graphene/SiC Interface

TL;DR

This study demonstrates reversible switching of a bismuthene-based quantum spin Hall insulator at the graphene/SiC interface through hydrogenation, enabling control over its electronic state and protection from environmental effects.

Contribution

It introduces a method to reversibly switch a bismuthene layer between inactive and QSHI states via hydrogenation, enhancing device stability and control.

Findings

Reversible switching achieved by hydrogenation and dehydrogenation.

Bismuthene state exhibits predicted topological band structure.

Protected QSHI system demonstrated beyond graphene.

Abstract

Quantum Spin Hall Insulators (QSHI) have been extensively studied both theoretically and experimentally because they exhibit robust helical edge states driven by spin-orbit coupling and offer the potential for applications in spintronics through dissipationless spin transport. However, to realize devices, it is indispensable to gain control over the interaction of the active layer with the substrate, and to protect it from environmental influences. Here we show that a single layer of elemental Bi, formed by intercalation of an epitaxial graphene buffer layer on SiC(0001), is a promising candidate for a QSHI. This layer can be reversibly switched between an electronically inactive precursor state and a ``bismuthene state'', the latter exhibiting the predicted band structure of a true two-dimensional bismuthene layer. Switching is accomplished by hydrogenation (dehydrogenation) of the sample, i.e., a partial passivation (activation) of dangling bonds of the SiC substrate, causing a lateral shift of Bi atoms involving a change of the adsorption site. In the bismuthene state, the Bi honeycomb layer is a prospective QSHI, inherently protected by the graphene sheet above and the H-passivated substrate below. Thus, our results represent an important step towards protected QSHI systems beyond graphene.