Transport measurements on ultra-clean dual-gated suspended bilayer graphene

Abstract

We fabricate ultra clean contactless dual-gated devices comprised of suspended bilayer graphene (BLG) and investigate their low temperature electron transport properties as functions of charge density n, magnetic field B and electric field E⊥ We find that for devices with moderate mobility, conductance remains finite at the charge neutrality point and decreases monotonically with increasing |E⊥|, as expected in the picture of single particle behavior. In contrast, devices with highest mobility display an insulating state at B=E⊥=n=0, and conductance’s dependence on E⊥ is non-monotonic. This surprising behavior arises from electronic interactions. In finite B, we observe quantum Hall plateaus with the 8-fold degeneracy of the lowest Landau level completely broken, as well as a fractional state.