Imaging Dual-Moire Lattices in Twisted Bilayer Graphene Aligned on Hexagonal Boron Nitride Using Microwave Impedance Microscopy

Moire superlattices (MSLs) formed in van der Waals materials have become a promising platform to realize novel two-dimensional electronic states. Angle-aligned trilayer structures can form two sets of MSLs which could potentially interfere. In this work, we directly image the moirepatterns in both monolayer and twisted bilayer graphene aligned on hexagonal boron nitride (hBN), using combined scanning microwave impedance microscopy and conductive atomic force microscopy. Correlation of the two techniques reveals the contrast mechanism for the achieved ultrahigh spatial resolution (<2 nm). We observe two sets of MSLs with different periodicities in the trilayer stack. The smaller MSL breaks the 6-fold rotational symmetry and exhibits abrupt discontinuities at the boundaries of the larger MSL. Using a rigid atomic-stacking model, we demonstrate that the hBN layer considerably modifies the MSL of twisted bilayer graphene. We further analyze its effect on the reciprocal space spectrum of the dual-moire system.

Automated summary

This research directly observes the moire patterns in monolayer and twisted bilayer graphene aligned on hexagonal boron nitride using scanning microwave impedance microscopy and conductive atomic force microscopy. Two sets of moire superlattices with different periodicities are observed in the trilayer stack, with the smaller superlattice breaking the 6-fold rotational symmetry and exhibiting abrupt discontinuities at the boundaries of the larger superlattice. The study demonstrates that the hBN layer significantly modifies the moire superlattice of twisted bilayer graphene and analyzes its effect on the reciprocal space spectrum of the dual-moire system.