▎ 摘　　要

The threshold voltages at the onset of conduction for electron and hole branches can provide information on band gap values or interface states in a gap. We measured conductivity of bilayer graphene encapsulated by hexagonal boron nitride as a function of back and top gates, where another bilayer graphene is used as a top gate. From the measured conductivity the transport gap values were extracted assuming zero interface trap states, and they are close to the theoretically expected gap values. From a little discrepancy an average density of interface states per energy within a band gap (D-it) is also estimated. The data clearly show that D-it decreases as a bilayer graphene band gap increases rather than being constant. Despite the decreasing trend of D-it interestingly the total interface states within a gap increases linearly as a band gap increases. This is because of similar to 2x10(10) cm(-2) interface states localized at band edges even without a band gap, and other gap states are equally spread over the gap.