ARPES Signatures of Few-Layer Twistronic Graphenes

• Published in: Nano letters Vol. 23; no. 11; pp. 5201 - 5208
• Main Authors: Nunn, James E., McEllistrim, Andrew, Weston, Astrid, Garcia-Ruiz, Aitor, Watson, Matthew D., Mucha-Kruczynski, Marcin, Cacho, Cephise, Gorbachev, Roman V., Fal’ko, Vladimir I., Wilson, Neil R.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 14-06-2023
• Subjects: Letter; twistronics, moiré; graphene; flat band; angle-resolved photoemission spectroscopy; twistronics, moiré
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.3c01173

Diverse emergent correlated electron phenomena have been observed in twisted-graphene layers. Many electronic structure predictions have been reported exploring this new field, but with few momentum-resolved electronic structure measurements to test them. We use angle-resolved photoemission spectroscopy to study the twist-dependent (1° < θ < 8°) band structure of twisted-bilayer, monolayer-on-bilayer, and double-bilayer graphene (tDBG). Direct comparison is made between experiment and theory, using a hybrid k·p model for interlayer coupling. Quantitative agreement is found across twist angles, stacking geometries, and back-gate voltages, validating the models and revealing field-induced gaps in twisted graphenes. However, for tDBG at θ = 1.5 ± 0.2°, close to the magic angle θ = 1.3°, a flat band is found near the Fermi level with measured bandwidth E w = 31 ± 5 meV. An analysis of the gap between the flat band and the next valence band shows deviations between experiment (Δh = 46 ± 5 meV) and theory (Δh = 5 meV), indicative of lattice relaxation in this regime.