ARPES Signatures of Few-Layer Twistronic Graphenes

Abstract

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 <b>k</b>·<b>p</b> 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 <i>E</i>_w = 31 ± 5 meV. An analysis of the gap between the flat band and the next valence band shows deviations between experiment (Δ_h = 46 ± 5 meV) and theory (Δ_h = 5 meV), indicative of lattice relaxation in this regime.