Fig. 1: Ferroelectricity in a bilayer graphene moiré superlattice.
From: Giant ferroelectric polarization in a bilayer graphene heterostructure
a Schematic of a van der Waals heterostructure and the device measurement set-up, in which the graphene is roughly twisted by 0° and 30° with two hBN flakes, respectively. A moiré superlattice is thus formed at one interface and a close-quasicrystal at the other. Vt: the top gate voltage; Vb: the back gate voltage. b The transfer curves have no hysteresis between the forward and backward scanning of Vb. The second Dirac peak indicates the moiré superlattice is of 11.5 nm, corresponding to an angle of 0.69° between BLG and hBN. c A ferroelectric hysteresis is observed by sweeping Vt. d A complete phase diagram of resistance is constructed by sweeping Vt forth (left) and back (right) while increasing Vb in a step-by-step fashion. Anomalous screening at both CNP and FFP could be identified by horizontal lines (red and white in color, respectively). e Difference in resistance between the two panels in d. Multiple hysteresis loops are formed by three pairs of blue and red peak lines at CNP and FFP. Note that the loops for electron and hole FFP (highlighted by dashed lines) are only half of a closed loop.
