Graphene nanoribbons with smooth edges behave as quantum wires

Graphene nanoribbons with perfect edges are predicted to exhibit interesting electronic and spintronic properties(1-4), notably quantum-confined bandgaps and magnetic edge states. However, so far, graphene nanoribbons produced by lithography have had rough edges, as well as low-temperature transport characteristics dominated by defects (mainly variable range hopping between localized states in a transport gap near the Dirac point(5-9)). Here, we report that one-and two-layer nanoribbon quantum dots made by unzipping carbon nanotubes(10) exhibit well-defined quantum transport phenomena, including Coulomb blockade, the Kondo effect, clear excited states up to similar to 20 meV, and inelastic co-tunnelling. Together with the signatures of intrinsic quantum-confined bandgaps and high conductivities, our data indicate that the nanoribbons behave as clean quantum wires at low temperatures, and are not dominated by defects.