Tunable symmetries of integer and fractional quantum Hall phases in   heterostructures with multiple Dirac bands
  The co-presence of multiple Dirac bands in few-layer graphene leads to a rich phase diagram in the quantum Hall regime. Using transport measurements, we map the phase diagram of BN-encapsulated ABA-stacked trilayer graphene as a function charge density n, magnetic field B and interlayer displacement field D, and observe transitions among states with different spin, valley, orbital and parity polarizations. Such rich pattern arises from crossings between Landau levels from different subbands, which reflect the evolving symmetries that are tunable in situ. At D=0, we observe fractional quantum Hall (FQH) states at filling factors 2/3 and -11/3. Unlike those in bilayer graphene, these FQH states are destabilized by a small interlayer potential that hybridizes the different Dirac bands. 
Petr Stepanov, Yafis Barlas, Tim Espiritu, Shi Che, Kenji Watanabe,   Takashi Taniguchi, Dmitry Smirnov, Chun Ning Lau
cond-mat.mes-hall