Session 5-4

Abstract

Twisted bilayer graphene (TBG) at the magic angle of 1.1 degrees exhibits many intriguing electronic phases. In particular, the quantum anomalous Hall effect (QAHE), in which the Hall conductivity is quantized in units of the conductance quantum at zero magnetic field, has been observed in only a single TBG device [1,2]. Although the QAHE in TBG could be key to elucidating the relationship between strong electron-electron correlations and band topology, its underlying mechanism remains inconclusive. Theoretical models predict that the percolation of domains with the same Chern number across a TBG channel could induce the QAHE. This condition could be satisfied when the isolated narrow energy band of TBG interacts with the moiré potential of a commensurately aligned hexagonal boron nitride (hBN), which breaks inversion symmetry and opens a gap in the otherwise protected Dirac cones of TBG [3].

In this study, we establish a fabrication process for TBG/hBN superlattice devices in which the TBG moiré pattern and the moiré pattern between one of the graphene layers and hBN have the same periodicity, i.e., a commensurate structure. Using atomic force microscopy-based techniques, we verify the alignment of hBN within the TBG stack prior to device fabrication. Subsequent transport measurements of the fabricated device revealed a pronounced anomalous Hall effect at a carrier density corresponding to one hole per moiré unit cell. Furthermore, we observed hysteresis loop reversal depending on the channel location, indicating the presence of multiple Chern domains.