Visualization of moiré superlattices.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Moiré superlattices in van der Waals heterostructures exhibit emergent electronic phenomena like superconductivity and magnetism.
• Characterizing the local structure of these moiré superlattices has been a significant challenge, hindering research progress.

Purpose of the Study:

• To develop a straightforward, room-temperature method for visualizing real-space moiré superlattices.
• To enable detailed structural characterization of various twisted van der Waals heterostructures.

Main Methods:

• Utilized piezoresponse force microscopy (PFM), an atomic force microscopy technique measuring electromechanical surface deformation.
• Applied the method to diverse heterostructures including graphene, boron nitride, and transition metal dichalcogenides.

Main Results:

• Successfully visualized moiré superlattices with sub-5-nm spatial resolution under ambient conditions.
• Demonstrated that all moiré superlattices exhibit a mechanical response to electric fields, linked to flexoelectricity.
• Showed that moiré superlattices manifest as polarized domain walls within a non-polar matrix.

Conclusions:

• The developed PFM method provides a simple and effective way to characterize moiré superlattices.
• This visualization technique is crucial for understanding the structure-property relationships driving emergent phenomena in these systems.
• Flexoelectricity plays a key role in the electromechanical response of moiré superlattices.