Fermi velocity engineering in graphene by substrate modification

The Fermi velocity, v(F), is one of the key concepts in the study of a material, as it bears information on a variety of fundamental properties. Upon increasing demand on the device applications, graphene is viewed as a prototypical system for engineering v(F). Indeed, several efforts have succeeded in modifying v(F) by varying charge carrier concentration, n. Here we present a powerful but simple new way to engineer v(F) while holding n constant. We find that when the environment embedding graphene is modified, the v(F) of graphene is (i) inversely proportional to its dielectric constant, reaching v(F) similar to 2.5 x 10(6) m/s, the highest value for graphene on any substrate studied so far and (ii) clearly distinguished from an ordinary Fermi liquid. The method demonstrated here provides a new route toward Fermi velocity engineering in a variety of two-dimensional electron systems including topological insulators.