  Metallic graphene nanoribbons (GNRs) represent a critical component in the
toolbox of low-dimensional functional materials technolo-gy serving as 1D
interconnects capable of both electronic and quantum information transport. The
structural constraints imposed by on-surface bottom-up GNR synthesis protocols
along with the limited control over orientation and sequence of asymmetric
monomer building blocks during the radical step-growth polymerization has
plagued the design and assembly of metallic GNRs. Here we report the
regioregular synthesis of GNRs hosting robust metallic states by embedding a
symmetric zero-mode superlattice along the backbone of a GNR. Tight-binding
electronic structure models predict a strong nearest-neighbor electron hopping
interaction between adjacent zero-mode states resulting in a dispersive
metallic band. First principles DFT-LDA calculations confirm this prediction
and the robust, metallic zero-mode band of olympicene GNRs (oGNRs) is
experimentally corroborated by scanning tunneling spectroscopy.
