AFM-Based Alignment of MATBG with hBN

In van der Waals heterostructures, two adjacent layers with similar lattice constants and a small angle alignment create a large length-scale moire pattern, changing periodically as the atoms modulate in and out of registry. When two moire patterns are overlaid, a larger supermoire can emerge. This supermoire pattern may be relevant in magic-angle twisted bilayer graphene (MATBG) aligned with hexagonal boron nitride (hBN), where it is possible to observe a quantum anomalous hall effect (QAHE) instead of the canonical superconducting phase [1, 2]. Recent theory papers suggest that quantization relies on the percolation of a well-defined non-zero Chern number throughout the sample, arising precisely when the two moire patterns are commensurate [3, 4]. However, crystal alignment between MATBG and hBN layers at precise angles close to zero degrees is challenging, requiring the identification of crystallographic edges as armchair- or zigzag-type cleavages. We use lateral force microscopy (LFM) techniques to determine the crystal orientation with high precision. We then use torsional force microscopy (TFM) to analyze the supermoire formed by the moire patterns. By constructing devices with well-characterized stacks, we aim to connect the supermoire length scale back to the QAHE.

[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)