Twelve-fold degenerate quantum Hall state in near 30°-twisted bilayer graphene

Twisted bilayer graphene (tBLG) has attracted tremendous interest but so far has mostly focused on the use of small twist angles. One of the major reasons is that the interlayer coupling between the incommensurate layers, which is normally the case of a large-angle-tBLG, was generally negligible and hence exotic quantum phases of matter are rarely expected. However, when the twist angle is rotated to near 30°, it becomes a very different story. The tBLG forms into dodecagonal quasicrystal with electronic properties distinct from the conventional periodic tBLG [1, 2]. It remains a challenge to explore these quasicrystalline tBLG states through the electrical transport measurements. Here, we use dry transfer methods to fabricate near 30°-tBLG devices and observe an anomalous anti-symmetry of quantum Hall plateaus. Moreover, a robust 12-fold degeneracy is observed in the quantum Hall regime up to ~60 K in both electron and hole transport.

[1] Ahn, S. J. et al. Dirac electrons in a dodecagonal graphene quasicrystal. Science 361, 782–786 (2018).

[2] Yao, W. et al. Quasicrystalline 30° twisted bilayer graphene as an incommensurate superlattice with strong interlayer coupling. Proc. Natl. Acad. Sci. USA 115, 6928–6933 (2018).