Anomalous Hall effect and superconductivity in BN-aligned magic-angle twisted bilayer graphene

Magic-angle twisted bilayer graphene (MATBG) hosts many exotic electronic states due to its combination of strong electron-electron correlations and band topology. Results published in 2019 reveal that MATBG, when tuned to a charge carrier density of 3 electrons per moire cell (ν=+3), exhibits a quantum anomalous Hall effect, but not the canonical superconducting state typically observed near ν=+2 [1,2]. These results are likely explained by the added moire potential of an aligned BN which breaks inversion symmetry, gapping the otherwise protected Dirac cones of MATBG [3,4].

Using atomic force microscopy based techniques, we verify BN alignment in a MATBG heterostructure prior to device fabrication. Subsequent transport measurements of a fabricated device reveal an anomalous Hall effect when filling 1 electron or hole per moire cell (ν=±1). The anomalous Hall signal is comparable in both fillings, in contrast to earlier studies showing a strong particle-hole asymmetry. Additionally, we find hints of superconductivity near ν=2 despite the BN-induced inversion symmetry breaking, suggesting superconductivity and the quantum anomalous Hall effect might coexist in the same device.

[1] A. L. Sharpe et al, Science 365, 605 (2019)

[2] M. Serlin et al, Science 367, 900 (2020)

[3] D. Mao and T. Senthil, Phys. Rev. B 103, 115110 (2021)

[4] J. Shi, J. Zhu, and A. H. MacDonald, Phys. Rev. B 103, 075122 (2021)