Electronic Compressibility of Magic-Angle Graphene Superlattices

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• Magic-angle twisted bilayer graphene exhibits unique electronic properties due to strong electron-electron interactions.
• Previous studies using transport and tunneling methods have limitations in probing the interaction-driven ground state.

Purpose of the Study:

• To perform the first electronic compressibility measurements on magic-angle twisted bilayer graphene.
• To investigate the ground state properties and energy gaps at fractional fillings.
• To compare experimental findings with theoretical predictions and transport measurements.

Main Methods:

• Utilizing capacitance measurements to determine electronic compressibility.
• Measuring chemical potential as a function of carrier density.
• Exploring field dependence up to the quantum Hall regime.

Main Results:

• Observed unexpectedly large energy gaps at quarter- and half-filling in the electron-doped regime.
• Identified strong electron-hole asymmetry in compressibility.
• Measured a minibandwidth of approximately 35 meV, significantly wider than theoretical estimates.
• Found discrepancies between compressibility and transport measurements in the quantum Hall regime.

Conclusions:

• Electronic compressibility provides new insights into the interaction-driven ground state of twisted bilayer graphene.
• The observed large gaps and wide minibandwidth challenge existing theoretical models.
• Further investigation is needed to reconcile compressibility and transport data, particularly in high magnetic fields.