Ferroelectricity
(ValasekJ.Phys. Rev.1921,17,475),
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.