  Graphene nanoribbons with perfect edges are predicted to exhibit interesting
electronic and spintronic properties, notably quantum-confined bandgaps and
magnetic edge states. However, graphene nanoribbons produced by lithography
have, to date, exhibited rough edges and low-temperature transport
characteristics dominated by defects, mainly variable range hopping between
localized states in a transport gap near the Dirac point. Here, we report that
one- and two-layer nanoribbons quantum dots made by unzipping carbon
nanotubes10 exhibit well-defined quantum transport phenomena, including Coulomb
blockade, Kondo effect, clear excited states up to ~20meV, and inelastic
co-tunnelling. Along with 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.
