Engineering Quantum Spin Hall Effect in Graphene Nanoribbons via Edge Functionalization

TL;DR

This paper proposes a method to induce strong spin-orbit coupling in graphene nanoribbons through edge functionalization with heavy elements, enabling the realization of quantum spin Hall states.

Contribution

It introduces a novel approach of covalent edge functionalization with heavy elements to control spin-orbit interactions in graphene nanoribbons, facilitating topological phases.

Findings

Strong spin-orbit coupling can be induced in graphene nanoribbons.

Quantum spin Hall states can be realized over broad energy ranges.

Electronic bands with Rashba splitting are achievable in functionalized nanoribbons.

Abstract

Kane and Mele predicted that in presence of spin-orbit interaction graphene realizes the quantum spin Hall state. However, exceptionally weak intrinsic spin-orbit splitting in graphene ($\approx 10^{-5}$ eV) inhibits experimental observation of this topological insulating phase. To circumvent this problem, we propose a novel approach towards controlling spin-orbit interactions in graphene by means of covalent functionalization of graphene edges with functional groups containing heavy elements. Proof-of-concept first-principles calculations show that very strong spin-orbit coupling can be induced in realistic models of narrow graphene nanoribbons with tellurium-terminated edges. We demonstrate that electronic bands with strong Rashba splitting as well as the quantum spin Hall state spanning broad energy ranges can be realized in such systems. Our work thus opens up new horizons towards engineering topological electronic phases in nanostructures based on graphene and other materials by means of locally introduced spin-orbit interactions.