A ballistic gate-tunable contact junction in graphene

Field-effect control of carrier is very efficient in graphene and allows controlling the doping profile with a great accuracy and high spatial resolution. This is needed if one wants to implement Dirac fermion optics experiments or simply to improve the performance of graphene devices. In this work we realize graphene transistors equipped with a set of local back-gates that provide control of local electric fields in the $10^8 V/m$ range at the $10$ nanometer scale. In particular we demonstrate ballistic contact junctions using transistors with independent channel and contact back-gates. We shall discuss the possibilities offered by this technology for ballistic electronic and opto-electronic applications.