Electron-Hole Asymmetric Integer and Fractional Quantum Hall Effect in Bilayer Graphene

The nature of fractional quantum Hall (FQH) states is determined by the interplay between the Coulomb interaction and the symmetries of the system. The unique combination of spin, valley, and orbital degeneracies in bilayer graphene is predicted to produce novel and tunable FQH ground states. Here we present local electronic compressibility measurements of the FQH effect in the lowest Landau level of bilayer graphene. We observe incompressible FQH states at filling factors v = 2p + 2/3 with hints of additional states appearing at v = 2p + 3/5, where p = -2,-1, 0, and 1. This sequence of states breaks particle-hole symmetry and instead obeys a v --> v + 2 symmetry, which highlights the importance of the orbital degeneracy for many-body states in bilayer graphene.