Ferromagnet-to-Topological Insulator Transition via Lithiation and Their Lateral Heterostructures within Intercalated Graphene: An ab Initio Study

On the basis of ab initio calculations, we report the quantum phase transition from ferromagnet to topological insulator via lithiation of Mo intercalated epitaxial graphene on SiC(0001). The original Mo intercalated system is characterized by spin-polarized Dirac cones with the Dirac points locating above the Fermi level. Electron donation due to the lithiation quenches the system magnetism and meanwhile raises the Fermi energy to the Dirac point. The large spin-orbit coupling of Mo d-electrons then opens a nontrivial gap up to 64 meV, leading to the quantum spin Hall state. Lateral ferromagnet/topological insulator heterostructures can be readily constructed with the interface in an atomically seamless fashion, which thus represents a promising platform for exploring exotic topological magnetoelectric effects such as the Kondo effect and other thermal and electrical quantum Hall effects.