▎ 摘　　要

Graphene has high-quality transport properties, but currents in graphene ribbons cannot be switched OFF, because of the absence of a bandgap. This is the most important obstacle for the use of graphene in the fabrication of integrated logic circuits. Here, we study current switching in zigzag graphene quantum point contacts using tight-binding Hamiltonians and the nonequilibrium Green function method. The current in these quantum point contacts is controlled by a back-gate and a top-gate potential. Our results show that the current can be effectively switched OFF for a potential range of 0.6 V. We explain this effect by computing the energy-band structure corresponding to the various regions of the quantum point contact. We show that these regions do not have a common conducting channel in a sufficiently large energy range and this results in zero conductance for energies in this range.