Spin splitting of Dirac fermions in graphene on Ni intercalated with alloy of Bi and Au

By angle- and spin-resolved photoemission we have studied electronic structure and spin-orbit splitting in graphene/Ni(111) intercalated with alloy of high spin-orbit materials Bi and Au. Results are compared to ultimate cases of (i) graphene/Ni intercalated only with Au which shows giant Rashba splitting (similar to 100 meV) and (ii) graphene/Ni intercalated only with Bi for which spin splitting of the Dirac cone is nearly zero (<= 10 meV). Our results demonstrate that partial substitution of intercalated Au with Bi reduces spin splitting of the Dirac cone in graphene and even allows for its systematic adjustment through concentration of Bi. Observed effects are ascribed to peculiar electronic structure of Bi which has in the valence band no d electronic states responsible for the onset of giant Rashba effect through electronic hybridization with pi band of graphene. We also report in details electronic properties of graphene/Ni(111) intercalated only with Bi in various concentrations. Such graphene reveals undistorted band structure characteristic to quasifreestanding graphene with small n-doping and a minor band gap at the Dirac point (similar to 200 meV) which depends weakly on the concentration of Bi. It has been shown that this gap is related to the symmetry breaking rather than to the topological phase formation. (C) 2015 Elsevier Ltd. All rights reserved.