Ferroelectricity in mixed stacked tetralayer graphene

Mixed stacked tetra-layer graphene (ABCB) lacks inversion symmetry, resulting in charge carriers localised in A and C layers, this leads to spontaneous out-of-plane polarisation and correlated states in moiré-less graphene. We report the electron ratchet or hysteresis effect in non-aligned hexagonal boron nitride-encapsulated ABCB stacked tetralayer graphene using low-temperature magneto-transport experiments. We found strong hysteresis on the charge neutrality point in response to an out-of-plane displacement field, which was affected by the direction and magnitude of the field. These effects persist at ambient temperature, enabling ultrafast flash memory and synaptic devices in natural graphitic materials without the requirement for moiré superlattice engineering.