Enhanced spin–orbit coupling in hydrogenated and fluorinated graphene

The spin–orbit couplings (SOCs) of hydrogenated and fluorinated graphenes are calculated by the first principles method. It is found that the SOC-induced band splittings near their Fermi energies can be significantly increased to the order of 10-2eV from the order of 10-6eV in the pure graphene, which is comparable to those found in diamond and archetypal semiconductors. Two different mechanisms are proposed to explain the SOC increases in these two systems. The increases are found to come not only from the sp3 hybridization of carbon atoms, but also from the intrinsic SOC of the fluorine atom, which is larger than that of the carbon atom.