Novel interlayer quantum Hall states in double bilayer graphene

Bilayer graphene hosts exotic even-denominator fractional quantum Hall states due to the special form of Coulomb interaction in its N=1 Landau level. On the other hand, when we bring two two-dimensional electron systems close to each other, the introduction of interlayer Coulomb interaction gives rise to a set of new interlayer correlated states. Previous experiments [1,2] on the double-layer structure of bilayer graphene revealed exciton condensation phases, or equivalently interlayer quantum Hall states with integer total filling factors, when both bilayer graphene layers are in the N=0 Landau level. Now with improved quality in devices of such a system, here we report our observation of interlayer quantum Hall states with fractional total fillings when both layers are in the N=0 Landau level. More interestingly, we also observe integer interlayer states when both layers are in the N=1 Landau level, which show different signatures compared to their N=0 counterparts.

[1] Liu, X. et al. Nature Phys 13, 746–750 (2017)

[2] Li, J. et al. Nature Phys 13, 751–755 (2017)