Broken symmetry quantum Hall states, layer hybridization and screening effects in twisted bilayer graphene at intermediate angles

Twisted bilayer graphene (TBLG) at intermediate twist angles ( 3^o ≤ 8^o), forms a bilayer two-dimensional electron/hole gas system with sub-nm layer separation, in which the momentum mismatch between the Dirac cones of individual layers leads to a breakdown of interlayer coherence. This removes the layer degree of freedom from the spin and valley degrees of freedom of individual layers resulting in eight-fold degeneracy in the Landau levels (LL). Here, we discuss the role of charge imbalance, layer hybridization and broken symmetries in the Quantum Hall (QH) states of twisted bilayer graphene with intermediate twist angle. The longitudinal magnetoresistance (R_xx) minima and the corresponding QH plateaus were observed at total filling factors, ν_tot, similar to Bernal-stacked BLG, but with magnetic field, B-dependent LL crossings at large ν_tot, where the QH sequence changes. This is attributed to the charge carrier imbalance between the top and bottom layers arising from partial screening of the gate field (V_G) where the filling of LLs of each layer is determined by the compressibility of the bottom layer and the charging energy of the top layer. At low filling factors the broken symmetry QH states were observed where the spin, valley and layer degeneracies are broken, with a QH insulator state emerging at ν_tot = 0. In addition to these, a notable B-dependent hysteresis emerged in the R_xx - V_G sweeps which can be understood as charge localization in individual layers manifesting in asymmetric charge distribution between the layers. These results provide a comprehensive understanding of layer hybridization, screening and charge localization in the QH states of twisted bilayer graphene at intermediate twist angles.