  The 2007 discovery of quantized conductance in HgTe quantum wells delivered
the field of topological insulators (TIs) its first experimental confirmation.
While many three-dimensional TIs have since been identified, HgTe remains the
only known two-dimensional system in this class. Difficulty fabricating HgTe
quantum wells has, moreover, hampered their widespread use. With the goal of
breaking this logjam we provide a blueprint for stabilizing a robust TI state
in a more readily available two-dimensional material---graphene. Using symmetry
arguments, density functional theory, and tight-binding simulations, we predict
that graphene endowed with certain heavy adatoms realizes a TI with substantial
band gap. For indium and thallium, our most promising adatom candidates, a
modest 6% coverage produces an estimated gap near 80K and 240K, respectively,
which should be detectable in transport or spectroscopic measurements.
Engineering such a robust topological phase in graphene could pave the way for
a new generation of devices for spintronics, ultra-low-dissipation electronics
and quantum information processing.
