Imaging quantum oscillations and millitesla pseudomagnetic fields in graphene.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Atomically thin quantum materials exhibit emergent phenomena due to tunable electronic energy bands.
• Current methods lack versatility for mapping local band structure in complex, multi-layered 2D material devices.

Purpose of the Study:

• To develop a versatile method for mapping local band structure and strain in advanced 2D materials.
• To precisely characterize tunable band engineering in van der Waals devices.

Main Methods:

• Utilized a scanning superconducting quantum interference device (SQUID) to image de Haas-van Alphen quantum oscillations.
• Reconstructed band structure by resolving thermodynamic quantum oscillations across numerous Landau levels.
• Employed Landau-level interferometry to detect and map shear-strain-induced pseudomagnetic fields.

Main Results:

• Successfully mapped the local band structure and its evolution with displacement field in Bernal-stacked trilayer graphene with nanoscale resolution.
• Detected naturally occurring pseudomagnetic fields as low as 1 mT, corresponding to 1 millidegree graphene twist.
• Demonstrated the ability to resolve strain at the nanoscale, significantly lower than typical angle disorder in twisted bilayer graphene.

Conclusions:

• The developed scanning SQUID technique provides unprecedented precision and spatial resolution for band structure mapping.
• This method enables detailed characterization of strain-induced phenomena and band engineering in practical van der Waals heterostructures.
• Facilitates the advancement of novel electronic devices based on tunable quantum materials.