Lattice Relaxation in Magic Angle Twisted Trilayer Graphene*

Magic angle twisted trilayer graphene (MATTG) has recently emerged as a new platform to study strong correlations in flat band systems. Composed of graphene layers with an alternating twist angle of roughly 1.56 degrees, initial transport studies in these systems suggested some role for structural relaxation that may act to align the top and bottom layers reducing the twist angle disorder. However, a complete understanding of how the lattices relax in trilayer systems requires direct imaging of the lattice. Using scanning tunnelling microscopy (STM) and Piezoresponse force microscopy (PFM), we report on evidence of moiré lattice relaxation that leads to the formation of large regions of highly uniform local twist angle at the magic angle, which are bounded by regions of higher local twist angle.