a spontaneous formation of electric polarization, is a solid state phenomenon, usually, associated with ionic compounds or complex materials. Here we show that, atypically for elemental solids, few-layer graphenes can host an equilibrium out-of-plane electric polarization, switchable by sliding the constituent graphene sheets. The systems hosting such effect include mixed-stacking tetralayers and thicker (5−9 layers) rhombohedral graphitic films with a twin boundary in the middle of a flake. The predicted electric polarization would also appear in marginally (small-angle) twisted few-layer flakes, where lattice reconstruction would give rise to networks of mesoscale domains with alternating value and sign of out-of-plane polarization.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.