Ultrafast charge separation induced by a uniform field in graphene nanoribbons

When heteronuclear molecules are illuminated by light of spatially uniform intensity, electronic excitations may, nevertheless, be restricted to parts of the system, depending on the absorption properties of its constituents. Here, we show that this effect is observed also in homogeneous carbon-based systems, such as graphene nanoribbons (GNRs): A spatially uniform laser pulse can create strongly localized carrier excitations, including excitons, on the subnanometer scale within a few femtoseconds. The origin of this effect is the unusual topological-based electronic structure of the GNRs. This opens exciting avenues for nanoelectronics and brings petahertz switching within reach. Using nonequilibrium Green’s function simulations, we demonstrate this effect by exciting small GNR heterostructures of suitable geometry with a laser pulse with carefully chosen photon energy, polarization, and carrier-envelope phase.