▎ 摘　　要

We perform transport measurements in high quality bilayer graphene pnp junctions with suspended top gates At a magnetic held B = 0, we demonstrate band gap opening by an applied perpendicular electric field with an On/Off ratio up to 20 000 at 260 mK Within the band gap, the conductance decreases exponentially by 3 orders of magnitude with increasing electric field and can be accounted for by variable range hopping with a gate-tunable density of states, effective mass, and localization length At large B, we observe quantum Hall conductance with fractional values, which arise from equilibration of edge states between differentially doped regions, and the presence of an insulating state at filling factor v = 0 Our work underscores the importance of bilayer graphene for both fundamental interest and technological applications