Imaging moire deformation and dynamics in twisted bilayer graphene

In `magic angle' twisted bilayer graphene (TBG) a flat band forms, yielding correlated insulator behavior and superconductivity. In general, the moire structure in TBG varies spatially, influencing the overall conductance properties of devices. Hence, to understand the wide variety of phase diagrams observed, a detailed understanding of local variations is needed. Here, we study spatial and temporal variations of the moire pattern in TBG using aberrationcorrected Low Energy Electron Microscopy (AC-LEEM). We find a smaller spatial variation than reported previously. Furthermore, we observe thermal fluctuations corresponding to collective atomic displacements over 70 pm on a timescale of seconds. Remarkably, no untwisting is found up to 600 degrees C. We conclude that thermal annealing can be used to decrease local disorder. Finally, we observe edge dislocations in the underlying atomic lattice, the moire structure acting as a magnifying glass. These topological defects are anticipated to exhibit unique local electronic properties.

Automated summary

In twisted bilayer graphene, the moire pattern shows smaller spatial variation than previously reported. Thermal fluctuations and edge dislocations are observed, providing insights into the properties of twisted bilayer graphene.