Proximity Effect Induced Electronic Properties of Graphene on Bi2Te2Se

We report that the ye-electrons of graphene can be spin-polarized to create a phase with a significant spin orbit gap at the Dirac point (DP) using a graphene-interfaced topological insulator hybrid material. We have grown epitaxial Bi2Te2Se (BTS) films on a chemical vapor deposition (CVD) graphene. We observe two linear surface bands from both the CVD graphene notably flattened and BTS coexisting with their DPs separated by 0.53 eV in the photoemission data measured with synchrotron photons. We further demonstrate that the separation between the two DPs, Delta(D-D), can be artificially fine-tuned by adjusting the amount of Cs atoms adsorbed on the graphene to a value as small as Delta(D-D) = 0.12 eV to find any proximity effect induced by the DPs. Our density functional theory calculation shows the opening of a spin orbit gap of similar to 20 meV in the pi-band, enhanced by 3 orders of magnitude from that of a pristine graphene, and a concomitant phase transition from a semimetallic to a quantum spin Hall phase when Delta(D-D) <= 0.20 eV. We thus present a practical means of spin-polarizing the pi-band of graphene, which can be pivotal to advance graphene-based spintronics.