Enhanced Phonon-Assisted Tunneling in Metal-Twisted Bilayer Graphene Junctions

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Twisted bilayer graphene exhibits unique electronic properties due to moiré superlattices.
• Electron-phonon coupling is crucial for understanding transport phenomena in 2D materials.
• Planar tunneling spectroscopy is a powerful probe for electronic states and interactions.

Purpose of the Study:

• To investigate electron-phonon coupling in metal-WSe2-twisted bilayer graphene heterostructures.
• To compare phonon-assisted tunneling in twisted bilayer graphene (TBG) versus Bernal bilayer graphene (BBG).
• To elucidate the role of moiré bands and momentum matching in tunneling processes.

Main Methods:

• Planar tunneling spectroscopy measurements across a wide range of gate and bias voltages.
• Theoretical calculations of phonon dispersions for both TBG and BBG.
• Analysis of experimental features attributed to phonon-assisted tunneling and density of states.

Main Results:

• Observed experimental features linked to phonon-assisted tunneling and high density of states in moiré bands.
• Significantly enhanced phonon-assisted tunneling in TBG compared to BBG.
• Identification of low-energy phonon modes in both graphene stacking configurations.

Conclusions:

• The enhanced tunneling in TBG stems from a relaxed in-plane momentum matching criterion.
• Planar tunneling spectroscopy is established as a versatile tool for studying electron-phonon coupling.
• The findings provide insights into the fundamental mechanisms governing tunneling in twisted van der Waals heterostructures.