Electronic states and magnetotransport in unipolar and bipolar graphene ribbons

We investigate the electronic and transport properties of undistorted gated polymers of the polyacene family by exploiting the tight-binding model for the system Hamiltonian and the nonequilibrium Keldysh formalism for charge transport. Our simulations reveal that, for smooth gate potentials varying only along the ribbon longitudinal axis, the electronic conductance as a function of the energy is quantized and presents crossover from conducting to insulating regimes. We interpret this behavior on the basis of the band structures entailed by the bipartite honeycomb topology of the lattice and the symmetry of the ribbons with even or odd number of chains (even-odd effect).