Induced spin–orbit splitting in graphene: the role of atomic number of the intercalated metal and π–d hybridization

This paper reports spin-dependent valence-band dispersions of graphene synthesized on Ni(111) and subsequently intercalated with monolayers of Au, Cu and Bi. We have previously shown that after intercalation of graphene with Au the dispersion of the π band remains linear in the region of the K-bar point of the surface Brillouin zone even though the system exhibits a noticeable hybridization between π states of graphene and d states of Au. We have also demonstrated a giant spin–orbit splitting of π states in Au-intercalated graphene which can reach up to ∼100 meV. In this paper we probe in detail dispersions of graphene π–Au d hybridized bands. We show that intercalation of Cu does not produce a noticeable spin–orbit splitting in graphene although this system, similarly to Au-intercalated graphene, also reveals hybridization between graphene states and d states of Cu. To clarify the role of intercalated Au, the electronic and spin structures of Au monolayers on Ni(111) are comparatively studied with and without graphene on top and the importance of the spin splitting of the d states of the intercalated material is established. These Au d states in graphene/Au/Ni(111) are further studied in detail by spin- and angle-resolved photoemission, and spin-dependent hybridization between graphene and Au bands is revealed. In contrast, intercalation of the sp metal Bi, despite its high atomic number, does not lead to any measurable spin–orbit splitting of the π states of graphene. This means that for the creation of large spin–orbit splitting in graphene, neither hybridization with d states (as with Cu) nor the high atomic number of the intercalated material alone (as with Bi) is sufficient, and a combination of them is required (as with Au). (paper)