▎ 摘　　要

The elementary excitations of monolayer graphene, which behave as massless Dirac particles, make it a fascinating venue in which to study relativistic quantum phenomena. One notable example is Klein tunneling, a phenomena in which electrons convert to holes to tunnel through a potential barrier. However, the omnipresence of charged impurities in substrate-supported samples keep the overall charge distribution nonuniform, obscuring much of this "Dirac" point physics in large samples. Using local gates, one can create tunable heterojunctions in graphene, isolating the contribution of small regions of the samples to transport. In this review, we give an overview of quantum transport theory and experiment on locally gated graphene heterostructures, with an emphasis on bipolar junctions.