  Ferroelectricity (Valasek, J. Phys. Rev. 1921, 17, 475) - a spontaneous
formation of electric polarisation - 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 polarisation, 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 polarisation 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 polarisation.
