Imaging moiré deformation and dynamics in twisted bilayer graphene

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Magic angle twisted bilayer graphene (TBG) exhibits flat bands, leading to correlated insulator behavior and superconductivity.
• The spatial variation of the moiré structure in TBG significantly impacts device conductance properties and observed phase diagrams.

Purpose of the Study:

• To investigate the spatial and temporal variations of the moiré pattern in TBG.
• To understand the influence of local moiré variations on electronic properties.
• To explore the role of thermal fluctuations and defects in TBG.

Main Methods:

• Utilized aberration-corrected Low Energy Electron Microscopy (AC-LEEM) to probe TBG.
• Analyzed spatial variations in moiré patterns.
• Observed thermal fluctuations and atomic displacements.
• Investigated structural integrity at elevated temperatures (up to 600°C).

Main Results:

• Observed smaller spatial moiré variations than previously reported.
• Detected thermal fluctuations with collective atomic displacements of ~70 pm on a second timescale.
• Confirmed no untwisting of TBG up to 600°C.
• Identified edge dislocations in the underlying atomic lattice, magnified by the moiré structure.

Conclusions:

• Thermal annealing can effectively reduce local disorder in TBG.
• Edge dislocations, acting as topological defects, are expected to possess unique local electronic properties.
• Understanding local moiré variations is crucial for controlling TBG's correlated electronic states.