Moir\'e Imaging in Twisted Bilayer Graphene Aligned on Hexagonal Boron Nitride

TL;DR

This paper employs advanced microscopy techniques to directly image and analyze moiré superlattices in twisted bilayer graphene on hBN, revealing complex interactions and symmetry-breaking effects in multilayer van der Waals structures.

Contribution

It provides the first direct imaging of dual moiré patterns in trilayer stacks and demonstrates how hBN modifies the moiré structure of twisted bilayer graphene.

Findings

Two sets of moiré superlattices with different periodicities observed.

The smaller moiré breaks rotational symmetry and shows boundary discontinuities.

hBN layer significantly alters the moiré pattern of twisted bilayer graphene.

Abstract

Moir\'e superlattices (MSL) formed in angle-aligned bilayers of 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 with each other. In this work, we directly image the moir\'e patterns in both monolayer graphene aligned on hBN and twisted bilayer graphene aligned on 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-moir\'e system.