ARPES Signatures of Few-Layer Twistronic Graphenes

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanoscience

Background:

• Twisted graphene multilayers exhibit diverse correlated electron phenomena.
• Electronic structure predictions are abundant, but experimental validation is limited.
• Momentum-resolved electronic structure measurements are crucial for testing theoretical models.

Purpose of the Study:

• To experimentally investigate the twist-dependent electronic band structure of twisted graphene systems.
• To compare angle-resolved photoemission spectroscopy (ARPES) data with theoretical predictions.
• To validate theoretical models and explore emergent phenomena like field-induced gaps.

Main Methods:

• Angle-resolved photoemission spectroscopy (ARPES) was employed.
• The study focused on twisted-bilayer graphene, monolayer-on-bilayer graphene, and twisted double-bilayer graphene (tDBG).
• A hybrid k·p model was used for theoretical calculations of interlayer coupling.

Main Results:

• Quantitative agreement was achieved between ARPES measurements and theoretical models across various twist angles, stacking geometries, and back-gate voltages.
• Field-induced gaps were observed in twisted graphene systems.
• Near the magic angle (θ ≈ 1.3°), tDBG exhibited a flat band with a measured bandwidth of 31 ± 5 meV.
• A significant deviation was found between the experimental gap (46 ± 5 meV) and theoretical predictions (5 meV) for the valence band in tDBG.

Conclusions:

• The hybrid k·p model accurately describes the electronic structure of twisted graphene systems.
• The observed discrepancies near the magic angle indicate the importance of lattice relaxation effects.
• ARPES measurements provide critical validation for theoretical models in twisted graphene research.