Designer quantum spin Hall phase transition in molecular graphene

Graphene was the first material predicted to be a time-reversal-invariant topological insulator [C. L. Kane and E. J. Mele, Phys. Rev. Lett. 95, 226801 (2005)]; however, the insulating gap is immeasurably small owing to the weakness of spin-orbit interactions in graphene. A recent experiment [K. K. Gomes, W. Mar, W. Ko, F. Guinea, and H. C. Manoharan, Nature (London) 483, 306 (2012)] demonstrated that designer honeycomb lattices with graphenelike "Dirac" band structures can be engineered by depositing a regular array of carbon monoxide atoms on a metallic substrate. Here, we argue that by growing such designer lattices on metals or semiconductors with strong spin-orbit interactions, one can realize an analog of graphene with strong intrinsic spin-orbit coupling, and hence a highly controllable two-dimensional topological insulator. We estimate the range of substrate parameters for which the topological phase is achievable, and consider the experimental feasibility of some candidate substrates.