Electrostatic confinement of electrons in graphene nanoribbons

Coulomb blockade is observed in a graphene nanoribbon device with a top gate. When two $pn$ junctions are formed via the back gate and the local top gate, electrons are confined between the $pn$ junctions which act as the barriers. When no $pn$ junctions are induced by the gate voltages, electrons are still confined, as a result of strong disorder, but in a larger area. Measurements on five other devices with different dimensions yield consistent results.