Symmetry Breaking and Anomalous Conductivity in a Double-Moiré Superlattice.

In a two-dimensional moiré superlattice, the atomic reconstruction of constituent layers could introduce significant modifications to the lattice symmetry and electronic structure at small twist angles. Here, we employ conductive atomic force microscopy to investigate a twisted trilayer graphene double-moiré superlattice. Two sets of moiré superlattices are observed. At neighboring domains of the large moiré, the current exhibits either 2- or 6-fold rotational symmetry, indicating delicate symmetry breaking beyond the rigid model. Moreover, an anomalous current appears at the "A-A" stacking site of the larger moiré, contradictory to previous observations on twisted bilayer graphene. Both behaviors can be understood by atomic reconstruction, and we also show that the measured current is dominated by the tip-graphene contact resistance that maps the local work function qualitatively. Our results reveal new insights of atomic reconstruction in novel moiré superlattices and opportunities for manipulating exotic quantum states on the basis of twisted van der Waals heterostructures.