Symmetry Breaking and Anomalous Conductivity in a Double-Moire Superlattice

In a two-dimensional moire 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-moire superlattice. Two sets of moire superlattices are observed. At neighboring domains of the large moire, 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 moire, 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 moire superlattices and opportunities for manipulating exotic quantum states on the basis of twisted van der Waals heterostructures.