Cloning the Dirac cones of bilayer graphene to the zone center by selenium adsorption

Controlled manipulation of Dirac fermions in nontrivial systems is central to the engineering of high-performance devices with unusual but versatile transport properties. Surprisingly, through angle-resolved photoemission, we demonstrate that such band tuning can even occur through van der Waals molecular adsorption of selenium (Se) vapor onto bilayer-graphene-terminated SiC surfaces maintained at sufficiently low temperatures. Although elemental Se—a component material in many topological insulators—itself should be topological in certain structural forms, pure Se structures with nontrivial order are energetically unfavorable, and elemental topological systems themselves are quite rare. Here instead, an adsorbed Se layer on bilayer graphene, which is an ordered array of large Se₈ molecules based upon our first-principles analysis, acts as a natural conduit for generating an emergent clone of graphene’s Dirac cones at the zone center. Overall, our systematic experimental and first-principles study not only reveals an underlying cloning mechanism based upon band folding but also offers a new, simple methodology for creating and/or manipulating Dirac fermions via gentle surface modification.