Broken Symmetry States in Twisted Bilayer Graphene

Graphene bilayer with multiple degeneracy provides an access to rich quantum Hall states (QHS) with broken symmetry, arising from electron-electron interactions and Zeeman splitting. Here, we present quantum Hall effect in high-quality twisted bilayer graphene. At high density regime, we found several QH plateaus are suppressed or emerged with magnetic fields, indicating transitions between different QH states. We ascribe this to imperfect screening of twisted bilayer, which results in different Landau levels formation on each layer and their mixings. As low density regime, odd integer QHS are observed, suggesting an important role of the interlayer charge transfer for stabilizing broken symmetry QHS