Coherent Tunneling and Negative Differential Conductivity in a Graphene/h-BN/Graphene Heterostructure

We address the tunneling current in a graphene/h-BN/graphene heterostructure as a function of the twisting between the crystals. The twisting induces a modulation of the hopping amplitude between the graphene layers that provides the extra momentum necessary to satisfy momentum and energy conservation and to activate coherent tunneling between the graphene electrodes. Conservation rules limit the tunneling to states with wave vectors lying at the conic curves defined by the intersection of two Dirac cones shifted in momentum and energy. There is a critical voltage where the intersection is a straight line, and the joint density of states presents a maximum. This peak in the number of states where both the wave vectors and the energies are matched reflects in a peak in the tunneling current and in a negative differential conductivity.