The Landau levels of a two-dimensional electron system support a plethora of fascinating many-body ground states and collective low-energy excitations, thanks to enhanced electron-electron interactions and the characteristics of the LL wave functions. The n=1 LL is particularly fascinating as it hosts even-denominator fractional quantum Hall states and other exotic topological orders that are potentially useful in topological quantum computation. In this talk, I will describe a few recent experiments of ours in Bernal-stacked bilayer graphene, which is a remarkably tunable platform for exploring emergent phenomena. I will show our observations of a new even-denominator fractional quantum Hall state at filling factor 5/2 and its spontaneous valley isospin polarization and discuss the particle-hole symmetry breaking of a family of even-denominator fractional quantum Hall states in bilayer graphene. In the second half of the talk, I will describe an experiment probing the momentum dispersion of gapless spin wave excitations of a quantum Hall easy-plane canted-antiferrormagnet using transport techniques and a Fabry-Perot resonant cavity. This strongly correlated magnetic state forms at the charge neutrality point of bilayer graphene purely through Coulomb interactions and may support spin superfluidity.
1. K. Huang, H. Fu, Danielle Reifsnyder Hickey, Nasim Alem, Xi Lin, K. Watanabe, T. Taniguchi, J. Zhu, "Valley Isospin Controlled Fractional Quantum Hall States in Bilayer Graphene", Physical Review X 12, 031019 (2022).
2. H. Fu, K. Huang, K. Watanabe, T. Taniguchi, and J. Zhu, “Gapless Spin Wave Transport through a Quantum Canted Antiferromagnet”, Physical Review X 11, 021012 (2021)