Graphene nanoribbons with smooth edges behave as quantum wires

Graphene nanoribbons with perfect edges are predicted to exhibit interesting electronic and spintronic properties^1,2,3,4, 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^5,6,7,8,9). Here, we report that one- and two-layer nanoribbon quantum dots made by unzipping carbon nanotubes¹⁰ exhibit well-defined quantum transport phenomena, including Coulomb blockade, the Kondo effect, clear excited states up 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.