Electron interactions and gap opening in graphene superlattices

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanoscience

Background:

• Graphene superlattices exhibit tunable properties based on periodicity.
• Controlling the electronic band gap at the Dirac point is crucial for graphene applications.
• Recent experiments show large, tunable Dirac point gaps in graphene on hexagonal boron nitride (G/h-BN) heterostructures.

Purpose of the Study:

• To develop a theoretical framework for understanding interaction effects in graphene superlattices.
• To explain the origin of large Dirac point gaps in G/h-BN heterostructures.
• To elucidate the tunability of these gaps by superlattice parameters, particularly the twist angle.

Main Methods:

• Development of a many-body theory for interaction effects in graphene superlattices.
• Application of the theory to the specific case of graphene on hexagonal boron nitride (G/h-BN).
• Analysis of the interplay between moiré superlattice periodicity and electronic band structure.

Main Results:

• The theory predicts substantial many-body enhancement of the Dirac point gap in G/h-BN.
• Tunable superlattice periodicity allows for orders of magnitude enhancement of the Dirac point gap.
• The Dirac point gap enhancement significantly exceeds that of minigaps from Bragg scattering.

Conclusions:

• The developed theory successfully explains the observed large Dirac point gaps in G/h-BN.
• Many-body interactions, modulated by superlattice periodicity, are key to gap enhancement.
• The tunability of the Dirac point gap by the G/h-BN twist angle is a direct consequence of the theory.